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Doctoral Thesis
Physical properties of plagioclase- and bubble bearing magmas
Author(s): Tripoli, Barbara Andrea
Publication Date: 2016
Permanent Link: https://doi.org/10.3929/ethz-a-010691444
Rights / License: In Copyright - Non-Commercial Use Permitted
This page was generated automatically upon download from the ETH Zurich Research Collection. For moreinformation please consult the Terms of use.
ETH Library
DISS. ETH NO. 22938
PHYSICAL PROPERTIES OF
PLAGIOCLASE- AND BUBBLE-
BEARING MAGMAS
A thesis submitted to attain the degree of
DOCTOR OF SCIENCES of ETH ZURICH
(Dr. sc. ETH Zurich)
Presented by
BARBARA ANDREA TRIPOLI
Master in Earth Sciences, ETH Zürich, Switzerland
born on January 22, 1983
citizen of Valais, Switzerland
Accepted on the recommendation of
Prof. Dr. Peter Ulmer ETH Zürich Examiner
Prof. Dr. Jean-Pierre Burg ETH Zürich Co-Examiner
Dr. Alison Rust University of Bristol Co-Examiner
2016
ii
iii
" Dans la vie, rien n’est à craindre, tout est à comprendre. "
Marie Curie
A ma famille, A celle qu’on m’a donnée,
A celle que je construis.
Abstract
IV
Abstract
V
ABSTRACT
Seismic tomography of potentially hazardous volcanoes is a prime tool to assess the dimensions of magmatic
reservoirs and the possible modes and pathways of magma ascent. Magma rheology and volcanic eruptive style
are to a first order controlled by processes occurring within the conduit or in the magma chamber, such as
crystallization and bubble exsolution. Seismic velocities are strongly affected by these processes, but the
limited number of constrained measurements does not allow yet establishing a firm link between seismic
tomography and the textural and hence rheologic state of a particular volcanic system. Elastic parameters of
vapor-saturated, partially molten systems are thus providing fundamental information for the identification of
such reservoirs under active and seemingly dormant volcanoes.
In this PhD thesis, we investigated a chemically simplified melt analogous to andesite and trachyte, in the
system CaO-Na2O-Al2O3-SiO2-H2O-CO2, which undergoes plagioclase crystallization and bubble exsolution. A
Paterson-type internally-heated gas pressure apparatus was employed to measure the ultrasonic velocities at a
constant pressure of 250 MPa and at a frequency of 0.1 MHz. Samples were first heated at 850 °C for 30
minutes. Subsequently, the temperature was decreased at a rate of 0.5 or 0.1 °C/min to 700 °C and velocities
were recorded every 45 minutes. In order to characterize the microstructure evolution, series of cold-seal
experiments at identical pressure conditions but with rapid-quenching at each of the recorded temperatures
have been conducted in addition.
Magmatic processes such as crystallization, bubble nucleation and coalescence have been recognized
throughout the measurements of seismic velocities in the laboratory. Compression and shear wave velocities
increase non-linearly during crystallization. At crystal fractions exceeding 45 vol%, the formation of a crystal
network favors the propagation of seismic waves through magmatic liquids. However, bubble nucleation
induced by crystallization leads to an increase of magma compressibility resulting in a reduction of the wave
propagation velocities. These two processes occurring simultaneously have thus competing effects on the
seismic properties of magmas. In addition, when the bubble fraction is less than 10 vol%, the decrease in
seismic velocities is more pronounced than for higher bubble fractions. The effect of bubble coalescence on
elastic properties is thus lower than the effect of bubble nucleation.
In this study, the effect of increasing the amount of water dissolved in the melt is not taken into account in the
variation of seismic velocities, as no data at high pressure and high temperature are available in the current
literature. Consequently, velocities have been measured at high pressure and high temperature conditions in
hydrous phonolites from the Teide volcano, Canary Islands (Spain). At temperatures lower than the glass
transition, temperature derivatives of seismic velocities are independent of the dissolved water content. Upon
crossing the glass transition, temperature derivatives of both compression and shear wave velocities
significantly increase. This increase is accentuated by the addition of water following a trend previously
Abstract
VI
observed for melt viscosity. Indeed, the increase in temperature derivatives of seismic velocities is higher at
low water content. Glass transition temperatures estimated from the measured seismic velocities and
calculated relaxation times suggest that measurements in the liquid-like state have predominantly been
performed on relaxed samples.
Consequently, by continuously monitoring small seismic velocity perturbations in volcanic areas and by
combining these data with laboratory measurements of seismic velocities, evolution of the physical state of
magmatic reservoir could be assessed more precisely. In addition, a more accurate interpretation of available
seismic tomography images is possible and may permit a better assessment of potential volcanic hazards.
Another important aspect in volcanic hazards assessment is linked to the efficiency of the crystal-bearing melt
to release or withhold the volatile phase. We thus implemented the Paterson apparatus with a pore-fluid
system in order to explore the effect of crystallization on the extent of outgassing of bubble-bearing
haplotonalite melt.
The presence of crystals may favor or inhibit the outgassing. On one hand, the crystallization of anhydrous
minerals increases the water content dissolved in the melt. The induced decrease in viscosity leads to a higher
ascent velocity of bubbles, hence more extensive outgassing. In addition, a forced migration of bubbles due to
the growing plagioclase contributes to sustain the presence of large bubbles by coalescence and additionally
increases the outgassing rate. However, considering the same melt viscosity, the presence of crystals lowers
the outgassing rate by adding obstacles to the ascent path of bubbles. Crystallization of hydrous magma is thus
regulating the outgassing rate by (1) increasing the fraction and size of bubbles by exsolution and decreasing
the melt viscosity and (2) lowering their ascent velocity by increasing pathways length.
Consequently, the outgassing potential of a crystallizing magma chamber is high. In our experiments,
crystallization of more than 50 vol% of plagioclase in a melt containing initially 4.2 vol% of bubbles induced
outgassing of 4.6 to 6.6 vol% of bubbles over a rather limited time. Crystallization is thus only partially trapping
the magmatic volatiles into the system. Large bubbles produced in a hydrous melt are, thus, relatively free to
rise through a magmatic mush. These bubbles may ultimately rise to the surface through permeable networks
of fractures in the surrounding volcanic edifice or accumulate at the top of the magmatic reservoir and trigger
explosive eruptions.
Résumé
VII
RÉSUMÉ
La tomographie sismique effectuée sur des volcans potentiellement dangereux est un outil essentiel pour
l’identification et l’évaluation de la taille des chambres magmatiques. La rhéologie des magmas et le style
d’éruption volcanique sont principalement contrôlés par des processus se produisant dans le conduit ou dans la
chambre magmatique, tels que la cristallisation ou l’exsolution des phases gazeuses. Les vitesses sismiques
sont fortement affectées par ces processus, mais le nombre limité de mesures ne permet pas encore d’établir
un lien solide entre la tomographie sismique et l’état texturale et donc rhéologique d’un système volcanique.
Les paramètres élastiques des systèmes saturés en gaz et partiellement fondus peuvent donc fournir des
informations fondamentales dans l’identification des réservoirs magmatique de volcans actifs ou endormis.
Durant ce projet de thèse doctorale, nous avons étudié un liquide silicaté, chimiquement simplifié et analogue
aux andésites et trachytes, composé de CaO-Na2O-Al2O3-SiO2-H2O-CO2, qui cristallise des plagioclases tout en
formant des bulles. Une presse de type Paterson a été utilisée pour mesurer les vitesses ultrasoniques à haute
température, à une pression constante de 250 MPa et à une fréquence de vibration de 0.1 MHz. Les
échantillons ont d’abord été chauffés à 850°C pour une durée de 30 minutes. Par la suite, la température a été
descendue à un taux de 0.5 ou 0.1°C/min jusqu’à 700°C tout en mesurant les vitesses sismiques à intervalle de
45 minutes. Afin de caractériser l’évolution des microstructures, une série d’expériences dans une autoclave à
joint froid (Cold-Seal Vessel) a été réalisée à des pressions identiques mais en refroidissant rapidement
l’échantillon sur chaque palier de températures correspondant à la prise de mesures sismiques.
Les processus magmatiques, tels que la cristallisation, la nucléation et la coalescence des bulles ont été
reconnus au travers des mesures de vitesses sismiques en laboratoire. Les vitesses d’onde de compression et
de cisaillement augmentent de manière non-linéaire pendant la cristallisation. Lorsque le contenu en cristaux
est supérieur à 45% du volume, les cristaux forment un réseau continu ce qui favorise la propagation des ondes
sismiques dans les liquides magmatiques. Cependant, la nucléation des bulles induites par la cristallisation
produit une augmentation de la compressibilité ce qui réduit les vitesses de propagation des ondes. Ces deux
processus simultanés ont donc des effets contraires sur les propriétés sismiques des magmas. De plus, lorsque
le contenu en bulles est inférieur à 10% du volume, la diminution des vitesses sismiques est plus prononcée
que lorsque le contenu dépasse cette valeur. Il s’impose donc que la nucléation des bulles a un effet plus
important sur les vitesses sismiques que la coalescence des bulles.
Dans cette étude, l’augmentation du contenu en eau dissoute dans le liquide résiduel n’est pas prise en compte
dans les variations des vitesses sismiques, car aucune donnée à haute pression et haute température n’est
disponible dans la littérature. Par conséquent, les vitesses ont été mesurées à haute pression et à haute
température dans des phonolites hydratées du volcan Teide, situé à Tenerife (Espagne). A des températures
plus basses que la transition vitreuse, les dérivées des vitesses sismiques en fonction de la température sont
Résumé
VIII
indépendantes du contenu en eau dissoute. Lorsque la température dépasse celle de la transition vitreuse, les
dérivées des vitesses d’onde de compression et de cisaillement augmentent de manière significative en
fonction de la température. Cette augmentation est accentuée par l’ajout d’eau et suit une tendance
précédemment observée dans les études de la viscosité des liquides silicatés hydratés. En effet, l’augmentation
des dérivées des vitesses sismiques selon la température est plus importante pour des contenus en eau
inférieur à 1% pds. Les mesures de température de transitions vitreuses estimées par les vitesses sismiques et
les calculs de temps de relaxation suggèrent que les mesures dans l’état liquide ont été faites sur des
échantillons relaxés.
Par conséquent, en surveillant les petites perturbations des vitesses sismiques dans les zones volcaniques et en
combinant ces données aux mesures faites en laboratoire, l’évolution d’un réservoir magmatique peut être
estimée plus précisément. De plus, une interprétation plus précise des images de tomographie sismique est
possible et peut permettre une meilleure évaluation des risques potentiels liés aux volcans.
Un autre aspect important pour l’évaluation des risques volcaniques est lié à la capacité des liquides silicatés
contenant des cristaux à relâcher ou retenir la phase gazeuse. Nous avons donc implémenté dans la presse
Paterson un système mesurant la pression de pores, afin d’explorer l’effet de la cristallisation sur le dégazage
dans les liquides haplotonalitiques contenant des cristaux.
La présence des cristaux peut favoriser ou inhiber le dégazage. D’un côté, la cristallisation de minéraux
anhydres augmente le contenu en eau dissoute dans le liquide silicaté. La diminution de la viscosité induite par
ce processus produit une augmentation de la vitesse d’ascension des bulles, ce qui augmente le dégazage. De
plus, une migration forcée due à la croissance des plagioclases contribue à maintenir la présence de larges
bulles par coalescence et augmente encore plus le taux de dégazage. Cependant, en considérant une viscosité
identique du liquide silicaté, la présence de cristaux diminue le taux de dégazage en ajoutant des obstacles au
trajet ascensionnel des bulles. La cristallisation de magma aqueux a donc pour effet de réguler le taux de
dégazage par (1) l’augmentation de la fraction et de la taille des bulles par exsolution et la diminution de la
viscosité du liquide résiduelle et (2) la diminution de la vitesse d’ascension en augmentant la longueur du
parcours effectué par les bulles.
Par conséquent, le potentiel de dégazage d’une chambre magmatique cristallisant des minéraux est grand. Lors
de nos expériences, la cristallisation de plus de 50% du volume de plagioclase contenant initialement 4.2% du
volume de bulles induit un dégazage de 4.6 à 6.6% du volume de bulles dans un temps relativement limité. La
cristallisation piège donc seulement partiellement la phase volatile dans le système. Les grandes bulles
produites dans les liquides silicatés aqueux sont donc relativement libres de traverser une chambre
magmatique partiellement cristallisée. Ces bulles peuvent finalement atteindre la surface en passant par un
réseau de fractures dans l’édifice volcanique ou s’accumuler dans la partie supérieure d’une chambre
magmatique ce qui peut entraîner une éruption de type explosif.
Table of Content
IX
TABLE OF CONTENTS Abstract .................................................................................................................................................................... v Résumé................................................................................................................................................................... vii 1 Introduction .................................................................................................................................................... 1
1.1 General Introduction ............................................................................................................................. 1 1.1.1 Seismic properties of magmas .......................................................................................................... 2 1.1.2 Outgassing of volatile phases ............................................................................................................ 3
1.2 Structure of the thesis ........................................................................................................................... 4 1.3 References ............................................................................................................................................. 5
2 Experimental and analytical techniques ........................................................................................................ 8 2.1 Starting Materials .................................................................................................................................. 8
2.1.1 Phase equilibria calculation ............................................................................................................... 9 2.1.2 Glass Synthesis ................................................................................................................................ 10
2.2 Seismic velocities measurements ........................................................................................................ 12 2.2.1 Sample preparation ......................................................................................................................... 12 2.2.2 Paterson apparatus ......................................................................................................................... 12 2.2.3 Up-date of the assembly ................................................................................................................. 14 2.2.4 Calibration of the assembly ............................................................................................................. 15 2.2.5 Measurements strategy .................................................................................................................. 15
2.3 Rapid quench experiments .................................................................................................................. 16 2.4 Degassing Measurements.................................................................................................................... 16
2.4.1 Sample preparation ......................................................................................................................... 16 2.4.2 Paterson apparatus ......................................................................................................................... 16 2.4.3 Measurements strategy .................................................................................................................. 17
2.5 Analytical techniques ........................................................................................................................... 18 2.5.1 Microstructure analysis (2D) ........................................................................................................... 18 2.5.2 Chemical composition ..................................................................................................................... 20 2.5.3 Density............................................................................................................................................. 20
2.6 References ........................................................................................................................................... 21 3 Effects of crystallization and bubble nucleation on the seismic properties of magmas ............................ 22
3.1 Abstract ............................................................................................................................................... 22 3.2 Introduction ......................................................................................................................................... 22 3.3 Methodology ....................................................................................................................................... 24 3.4 Experimental and analytical results ..................................................................................................... 27
3.4.1 Microstructure: Cooling rate of 0.5 °C/min ..................................................................................... 27 3.4.2 Microstructure: Cooling rate of 0.1 °C/min ..................................................................................... 27 3.4.3 Microstructure: Interpretation........................................................................................................ 30
3.5 Discussion ............................................................................................................................................ 31 3.5.1 Effect of crystallization .................................................................................................................... 31 3.5.2 Effect of bubble nucleation ............................................................................................................. 32 3.5.3 Effect of bubble coalescence ........................................................................................................... 34 3.5.4 Effect of outgassing ......................................................................................................................... 34
3.6 Summary and application to natural system ....................................................................................... 36 3.7 Tables ................................................................................................................................................... 38 3.8 References ........................................................................................................................................... 40
4 Laboratory measurements of seismic velocities at HT-HP conditions in hydrous phonolite from Teide volcano, Tenerife, Canary Islands ........................................................................................................................ 42
4.1 Abstract ............................................................................................................................................... 42 4.2 Introduction ......................................................................................................................................... 42
4.2.1 Phonolite at Teide volcano .............................................................................................................. 43 4.3 Methods .............................................................................................................................................. 44
4.3.1 Glass synthesis ................................................................................................................................ 44 4.3.2 Seismic velocity measurements ...................................................................................................... 45
4.4 Results ................................................................................................................................................. 46
Table of Content
X
4.4.1 Glass synthesis ................................................................................................................................ 46 4.4.2 Effect of temperature on seismic velocities .................................................................................... 47 4.4.3 Effect of water content on temperature derivatives ...................................................................... 47 4.4.4 Effect of pressure on seismic velocities .......................................................................................... 49
4.5 Discussion ............................................................................................................................................ 49 4.5.1 Glass transition ................................................................................................................................ 49 4.5.2 Density............................................................................................................................................. 51 4.5.3 Elastic properties ............................................................................................................................. 52 4.5.4 Application to the magmatic chamber of teide volcano ................................................................. 53
4.6 Conclusion ........................................................................................................................................... 56 4.7 Tables ................................................................................................................................................... 57 4.8 References ........................................................................................................................................... 61
5 Outgassing induced by crystallization: An experimental study .................................................................. 64 5.1 Abstract ............................................................................................................................................... 64 5.2 Introduction ......................................................................................................................................... 64 5.3 Methods .............................................................................................................................................. 66
5.3.1 Sample synthesis ............................................................................................................................. 66 5.3.2 Outgassing experiments .................................................................................................................. 67 5.3.3 Evaluation of the microstructural variations ................................................................................... 68
5.4 Experimental and analytical results ..................................................................................................... 68 5.4.1 Involved magmatic processes ......................................................................................................... 69 5.4.2 Composition of the melt pockets .................................................................................................... 70 5.4.3 Microstructures of the samples recovered from the outgassing experiments ............................... 71 5.4.4 Outgassing measurements .............................................................................................................. 72
5.5 Discussion ............................................................................................................................................ 73 5.5.1 Cooling rate of 0.1°C/min ................................................................................................................ 75 5.5.2 Cooling rate of 0.5°C/min ................................................................................................................ 77
5.6 Conclusion ........................................................................................................................................... 78 5.7 Tables ................................................................................................................................................... 79 5.8 References ........................................................................................................................................... 81
6 Conclusion..................................................................................................................................................... 83 6.1 Seismic properties ............................................................................................................................... 83 6.2 Outgassing properties.......................................................................................................................... 84 6.3 Suggestions for future research .......................................................................................................... 84
Acknowledgements ............................................................................................................................................... 86 Curriculum Vitae ................................................................................................................................................... 88 Appendix A List of synthetized samples ......................................................................................................... 90 Appendix B Lists of experiments .................................................................................................................... 92
B.1 Paterson apparatus 9 ........................................................................................................................... 92 B.2 MHC cold-sealed pressure vessel ........................................................................................................ 93 B.3 Paterson apparatus 6 ........................................................................................................................... 93
Appendix C List of measured densities .......................................................................................................... 94 Appendix D Lists of chemical analyses ........................................................................................................... 95
D.1 Karl Fisher Titration measurements .................................................................................................... 95 D.2 Electron Microprobe measurements ................................................................................................... 97
D.2.1 Haplotonalite ................................................................................................................................... 97 D.2.2 Lavas Negras .................................................................................................................................. 108
Chapter 1 Introduction
1
1 INTRODUCTION
1.1 GENERAL INTRODUCTION
Volcanoes characterized by intermediate composition span a wide range of eruptive style, from relatively
benign effusive flows to devastating explosive Plinian eruptions. This dynamic variety of volcanic activities is a
direct consequence of both the underground driving forces (Takeuchi, 2004; Allan et al., 2012) and the magma
rheological properties. Magma rheology is strongly dependent on the intrinsic parameters of the involved
magma, i.e. melt composition, volatile content and bubble and crystal fractions (Giordano et al, 2008; Pistone
et al., 2012; Champallier et al, 2008) and on extrinsic parameters, such as temperature and strain rate (Webb
and Dingwell, 1990; Carricchi et al., 2007).
However, the internal structure of magmatic reservoirs is continuously evolving through various processes,
including cooling, heating or decompression. Once emplaced in the crust, magma crystallizes due to cooling
induced by conductive heat loss to the wall of the magma chamber (Brandeis and Jaupart, 1986; Sparks et al.,
1993). As a consequence, the melt becomes oversaturated in water and bubbles exsolve. Potentially, magma
mingling/mixing induces thermal and chemical instabilities and may trigger eruptions (Sparks and Sigurdsson,
1977). Petrologic data, such as chemical zonation or reaction patterns, suggest local temperature increases
prior to eruption and are attributed either to a direct injection of mafic magma into a felsic body (Murphy et
al., 2000) or to the conductive heat transfer from an underlying mafic magma body (Couch et al., 2001).
In addition, degassing-induced crystallization (e.g. Cashman and Blundy, 2000) results in close interdependence
of melt composition, crystal and bubble contents. As magma undergoes decompression during ascent,
exsolution of volatile components must occur. This phenomenon increases the melt liquidus temperature, and
ultimately leads to microlite crystallization. As a consequence, the crystal fraction increases, leading to a melt
with a continuously decreasing volatile content, and a shift towards silica-rich compositions (Hammer et al.,
1999; D'Oriano et al., 2005; Platz et al., 2007; Blundy et al., 2006). These processes operating in subvolcanic
magma reservoirs and within the volcanic conduit result in increasing the magma viscosity by orders of
magnitude.
Seismic velocities are strongly affected by processes such as crystallization or degassing. However, the limited
number of constrained measurements does not allow yet establishing a firm link between seismic tomography
and the textural and hence rheologic state of a particular volcanic system. Elastic parameters of vapor-
saturated, partially molten systems are thus providing fundamental information for the identification of such
reservoirs under active and seemingly dormant volcanoes. This PhD thesis is, therefore, dedicated to the
measurements of seismic properties and outgassing efficiency of crystal- and bubble-bearing magmas.
Chapter 1 Introduction
2
1.1.1 SEISMIC PROPERTIES OF MAGMAS
Seismic tomography of potentially hazardous volcanoes is a prime tool to identify and determine the size and
location of subvolcanic magma reservoirs (e.g. Ohlendorf et al., 2014; Chouet, 2003). Estimated through the
inversion of first-arrival times from local earthquakes, volcanic plumbing systems are recognized at depth by
their lower seismic velocity. Attempts to determine the physical state of magma reservoirs, i.e. melt
proportion, are more and more often conducted by combining seismic tomography with available laboratory
data and numerical simulation (Lin et al., 2014; Paulatto et al., 2012; Annen et al., 2014). Indeed, these low-
velocity zones may correspond to eruptible magma or non-eruptible mush depending on their phase fractions.
In situ laboratory measurements of compression and shear wave propagation velocities of magmas are thus
providing fundamental information for the identification of such reservoirs.
Laboratory measurements of elastic parameters have been performed on melts and glasses of various
compositions (Askarpour et al., 1993; Schilling et al., 2003; Webb and Courtial, 1996). Seismic velocities
decrease continuously with increasing temperature until reaching the glass transition temperature. This
temperature range corresponds to a transition in the physical properties of the melt from a solid-like (low
temperature) to a liquid-like behavior (high temperature). By crossing this region, a marked increase of the
temperature derivative of the compressional wave propagation velocity is observed. This break is less
pronounced for shear waves.
Although both mafic and silicic magmas can contain up to at least 6 wt% of dissolved water at depth (e.g.
Sisson and Layne, 1993; Hervig et al., 1989), studies on the effect of water on the seismic properties of magmas
are scarce. Experiments using Brillouin scattering spectroscopy have been performed on glasses with variable
composition and dissolved water content at room temperature (Richet and Polian, 1998; Malfait et al., 2011;
Whittington et al., 2012). Compression and shear wave velocities decrease linearly with the addition of water
for rhyolitic and andesitic glasses but remain constant for basaltic glasses (Malfait et al., 2011). With increasing
alkalinity of the investigated glasses, the addition of water results in increasing seismic velocities (Whittington
et al., 2012). These studies have been performed at room conditions and data collected at temperature
ensuring the liquid-like behavior of silicate are lacking to date.
The variation in elastic properties at the glass transition temperature has also been reported for crystal-bearing
melt (Caricchi et al., 2008). However, the amplitude of this variation decreases with increasing crystal content.
Microstructure, such as crystal or bubble content, is as well a fundamental parameter in determining the elastic
properties (e.g. Mueller et al., 2003; Hier-Majumder, 2008; Schmeling, 1985; Mavko, 1980). The non-linear
increase of seismic wave velocities by increasing the crystal fraction is a direct result of the formation of a
continuous crystal network (Caricchi et al., 2008). In addition, the orientation of elongated melt pockets
influences the seismic anisotropy of partially molten rocks and may result in erroneous estimation of the melt
fraction from seismic velocities (e.g. Mainprice, 1997)
Chapter 1 Introduction
3
Experimental studies on the effect of bubbles are scarce (Caricchi et al., 2008; Bagdassarov et al., 1994) and
their role on the elastic properties of magmas is not well-defined. However, some insight is given by studies
involving bubbly water. The addition of gas bubble critically decreases the seismic properties of the mixtures in
a logarithmic fashion, i.e. over the first percent of bubble, 90% of the total decrease of the sound speed is
achieved (Gibson, 1970; Kieffer, 1977). The density variation is not sufficient to account for this large variation
in the sound speed and it is, thus, attributed to the large increase in compressibility (Temkin, 2005). In their
numerical model involving bubble-bearing basaltic melt, Marchetti et al. (2004) applied equations of seismic
velocities derived for low- viscosity liquids, i.e. bubbly water, in order to better estimate variations in physical
properties of magmas. However, increasing the confining pressure and increasing the melt viscosity (compared
to measurements made on water at 1 atm) prevent a strong decrease in seismic velocities (Kieffer, 1977;
Ichihara et al., 2004; Ichihara and Kameda, 2004).
1.1.2 OUTGASSING OF VOLATILE PHASES
Another important aspect in volcanic hazards assessment is linked to the efficiency of the crystal-bearing melt
to release or not the volatile phase. Indeed, when the ascent velocity of large bubbles in a volcanic conduit is
faster than the ascent rate of the surrounding magma, the volcanic activity is characterized by passive
outgassing potentially accompanied by lava flows (e.g. Slezin, 2003, Melnik et al., 2005). However, more
explosive eruptions occur when the gas phase cannot separate from the rapidly ascending magma (e.g. Melnik
et al., 2005; Jaupart and Allègre, 1993). In addition, when outgassing is inhibited, the volatile phase may
accumulate in the magma chamber leading to a decrease in the bulk density (e.g. Blake, 1984). The increased
magma buoyancy may thus generate an overpressure higher than the strength of the country rocks, i.e.
overpressure higher than 10-40 MPa (Jellinek and DePaolo, 2003), leading to highly explosive eruptions (Malfait
et al., 2014; Bachman and Bergantz, 2008; Caricchi et al., 2014). The efficiency of outgassing is thus an
important parameter in determining the eruption style.
Various studies focused on mechanisms favoring or impeding outgassing in volcanoes. Bubbles may rise
buoyantly into the magma chamber or the volcanic conduit or volcanic gas can escape through interconnected
bubbles (e.g. Gonnermann and Manga, 2007). Eichelberger et al. (1986) observed that vesicular obsidian
becomes permeable at a porosity higher than 60 % whereas Klug and Cashman (1996) measured permeability
between 10-14 and 10-12 m-2 at a porosity as low as 30 %. In addition, when vesicular magmas are subject to
shearing, the bubbles are elongated and their connectivity is promoted (e.g. Saar and Manga, 1999). Gas can
thus escape in magmas with a porosity lower than 30 % depending on bubble shape. The crystalline phase
contributes as well to the extent of degassing: Bubbles are restricted to the melt phase and a large amount of
crystals would thus contribute to increase the connectivity in the residual melt although the porosity remains
low (Sparks, 2003). On the other hand, the crystalline phase may reduce the extent of degassing by inhibiting
the ascent of small bubbles (Belien et al., 2010).
Chapter 1 Introduction
4
Magmas at depth become saturated with volatile by two processes. The “first boiling” occurs when hydrous
melts are ascending towards the surface. Due to decompression, the solubility of water decreases and bubbles
exsolve (e.g. Cashman and Blundy, 2000). The second process that causes the volatile exsolution from the
silicate melt is linked to crystallization at constant pressure. Known as “second boiling”, this process is activated
by a cooling magma chamber which leads to crystallization. As a consequence, the melt becomes oversaturated
in water and bubbles exsolve. In both cases, the produced gas phase could escape from the magma chamber
along fracture networks developed within the magma and the conduit walls (Jaupart, 1998; Rust et al., 2004).
The “first boiling” has been studied experimentally (e.g. Mangan and Sisson, 2000; Mourtada-Bonnefoi and
Laporte, 2004) and numerically (e.g. Lensky et al., 2003; Proussevitch and Sahagian, 1998). Recently, some
studies investigated the influence of decompression on the permeability of magma (Okomura et al., 2012,
Namiki and Manga, 2008). However, no studies on the potentiality of degassing by “second boiling” have been
performed.
The studies presented in this PhD thesis are aimed at a better understanding of the seismic properties and
outgassing efficiency of magmas during crystallization. Simplified hydrous tonalite in the ternary system quartz-
albite-anorthite (Qtz-Ab-An; e.g. Johannes and Holtz, 1996; Johannes, 1989) is prone to crystallize plagioclase
at temperature and pressure conditions obtainable in the internally-heated gas pressure Paterson rig of the
Rock Deformation Laboratory (ETHZ). In addition, the crystallization of an anhydrous phase infers an increase in
water content in the melt which ultimately results in additional bubble nucleation.
1.2 STRUCTURE OF THE THESIS
The chapters of this PhD thesis are written in the form of paper for future submission to international journals.
The structure is as follow:
Chapter 2 is dedicated to the methodology followed during this thesis. A detailed description of the glass
synthesis and of the experimental techniques used for the measurements of physical properties during
crystallization are provided. In addition, analytical techniques used for the compositional and microstructural
characterization of the samples are described.
Chapter 3 reports the results of in-situ measurements of seismic properties of crystallizing magmas. Through
the continuous measurements of compression and shear wave velocities, magmatic processes, such as
crystallization, bubble nucleation and coalescence, as well as outgassing have been recognized and quantified.
This study has been accepted for publication in Geochemistry, Geophysics, Geosystems in February 2016.
Chapter 4 provides information on the effect of water content on the elastic properties of a natural melt from
the Teide volcano, Tenerife Island, Spain. The obtained data are directly applied to available seismic
tomography of the Teide volcano to infer the structure of the magmatic plumbing system.
Chapter 1 Introduction
5
Chapter 5 is dedicated to a study investigating the outgassing induced by crystallization. In-situ measurements
of the volume of gas lost from the sample with or without crystallization give some insight into gas migration in
magmatic chamber.
A series of Appendices are located at the end of this thesis. Tables containing all synthetized samples, all
performed experiments and all analytical measurements are available in this section.
1.3 REFERENCES
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Askarpour, V., Manghnani, M. H., & Richet, P. (1993). Elastic properties of diopside, anorthite, and grossular glasses and liquids: a Brillouin scattering study up to 1400 K. Journal of Geophysical Research: Solid Earth (1978–2012), 98(B10), 17683-17689.
Bachmann, O., & Bergantz, G. (2008). The magma reservoirs that feed supereruptions. Elements, 4(1), 17-21. Bagdassarov, N., Dingwell, D. B., & Webb, S. L. (1994). Viscoelasticity of crystal-and bubble-bearing rhyolite
melts. Physics of the earth and planetary interiors, 83(2), 83-99. Belien, I. B., Cashman, K. V., & Rempel, A. W. (2010). Gas accumulation in particle-rich suspensions and
implications for bubble populations in crystal-rich magma. Earth and Planetary Science Letters, 297(1), 133-140.
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Blundy, J., Cashman, K., & Humphreys, M. (2006). Magma heating by decompression-driven crystallization beneath andesite volcanoes. Nature, 443(7107), 76-80.
Brandeis, G., & Jaupart, C. (1986). On the interaction between convection and crystallization in cooling magma chambers. Earth and Planetary Science Letters, 77(3), 345-361.
Caricchi, L., Annen, C., Blundy, J., Simpson, G., & Pinel, V. (2014). Frequency and magnitude of volcanic eruptions controlled by magma injection and buoyancy. Nature Geoscience, 7(2), 126-130.
Caricchi, L., Burlini, L., & Ulmer, P. (2008). Propagation of P and S-waves in magmas with different crystal contents: Insights into the crystallinity of magmatic reservoirs. Journal of volcanology and geothermal research, 178(4), 740-750.
Caricchi, L., Burlini, L., Ulmer, P., Gerya, T., Vassalli, M., & Papale, P. (2007). Non-Newtonian rheology of crystal-bearing magmas and implications for magma ascent dynamics. Earth and Planetary Science Letters, 264(3–4), 402-419. doi: http://dx.doi.org/10.1016/j.epsl.2007.09.032
Cashman, K., & Blundy, J. (2000). Degassing and crystallization of ascending andesite and dacite. Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences, 358(1770), 1487-1513.
Champallier, R., Bystricky, M., & Arbaret, L. (2008). Experimental investigation of magma rheology at 300 MPa: From pure hydrous melt to 76 vol.% of crystals. Earth and Planetary Science Letters, 267(3), 571-583.
Chouet, B. (2003). Volcano seismology. Pure and Applied Geophysics, 160(3-4), 739-788. Couch, S., Sparks, R., & Carroll, M. (2001). Mineral disequilibrium in lavas explained by convective self-mixing in
open magma chambers. Nature, 411(6841), 1037-1039. D’Oriano, C., Poggianti, E., Bertagnini, A., Cioni, R., Landi, P., Polacci, M., & Rosi, M. (2005). Changes in eruptive
style during the AD 1538 Monte Nuovo eruption (Phlegrean Fields, Italy): the role of syn-eruptive crystallization. Bulletin of Volcanology, 67(7), 601-621.
Eichelberger, J., Carrigan, C., Westrich, H., & Price, R. (1986). Non-explosive silicic volcanism. Nature, 323(6089), 598-602.
Gibson, F. W. (1970). Measurement of the effect of air bubbles on the speed of sound in water. The Journal of the Acoustical Society of America, 48(5B), 1195-1197.
Giordano, D., Russell, J. K., & Dingwell, D. B. (2008). Viscosity of magmatic liquids: a model. Earth and Planetary Science Letters, 271(1), 123-134.
Gonnermann, H. M., & Manga, M. (2007). The fluid mechanics inside a volcano. Annu. Rev. Fluid Mech., 39,
Chapter 1 Introduction
6
321-356. Hammer, J., Cashman, K., Hoblitt, R., & Newman, S. (1999). Degassing and microlite crystallization during pre-
climactic events of the 1991 eruption of Mt. Pinatubo, Philippines. Bulletin of Volcanology, 60(5), 355-380.
Hervig, R. L., Dunbar, N., Westrich, H. R., & Kyle, P. R. (1989). Pre-eruptive water content of rhyolitic magmas as determined by ion microprobe analyses of melt inclusions in phenocrysts. Journal of volcanology and geothermal research, 36(4), 293-302.
Hier‐Majumder, S. (2008). Influence of contiguity on seismic velocities of partially molten aggregates. Journal of Geophysical Research: Solid Earth (1978–2012), 113(B12).
Ichihara, M., & Kameda, M. (2004). Propagation of acoustic waves in a visco-elastic two-phase system: influences of the liquid viscosity and the internal diffusion. Journal of volcanology and geothermal research, 137(1), 73-91.
Ichihara, M., Ohkunitani, H., Ida, Y., & Kameda, M. (2004). Dynamics of bubble oscillation and wave propagation in viscoelastic liquids. Journal of volcanology and geothermal research, 129(1), 37-60.
Jaupart, C. (1998). Gas loss from magmas through conduit walls during eruption. Geological Society, London, Special Publications, 145(1), 73-90.
Jaupart, C., & Allègre, C. J. (1991). Gas content, eruption rate and instabilities of eruption regime in silicic volcanoes. Earth and Planetary Science Letters, 102(3), 413-429.
Jellinek, A. M., & DePaolo, D. J. (2003). A model for the origin of large silicic magma chambers: precursors of caldera-forming eruptions. Bulletin of Volcanology, 65(5), 363-381.
Johannes, W. (1989). Melting of plagioclase-quartz assemblages at 2 kbar water pressure. Contributions to Mineralogy and Petrology, 103(3), 270-276.
Johannes, W., & Holtz, F. (1996). Petrogenesis and experimental petrology of granitic rocks (Vol. 335): Springer Berlin.
Kieffer, S. W. (1977). Sound speed in liquid‐gas mixtures: Water‐air and water‐steam. Journal of Geophysical research, 82(20), 2895-2904.
Klug, C., & Cashman, K. V. (1996). Permeability development in vesiculating magmas: implications for fragmentation. Bulletin of Volcanology, 58(2-3), 87-100.
Lensky, N., Navon, O., & Lyakhovsky, V. (2004). Bubble growth during decompression of magma: experimental and theoretical investigation. Journal of volcanology and geothermal research, 129(1), 7-22.
Lin, G., Amelung, F., Lavallée, Y., & Okubo, P. G. (2014). Seismic evidence for a crustal magma reservoir beneath the upper east rift zone of Kilauea volcano, Hawaii. Geology, 42(3), 187-190.
Mainprice, D. (1997). Modelling the anisotropic seismic properties of partially molten rocks found at mid-ocean ridges. Tectonophysics, 279(1), 161-179.
Malfait, W. J., Sanchez-Valle, C., Ardia, P., Médard, E., & Lerch, P. (2011). Amorphous Materials: Properties, Structure, and Durability Compositional dependent compressibility of dissolved water in silicate glasses. American Mineralogist, 96(8-9), 1402-1409.
Malfait, W. J., Seifert, R., Petitgirard, S., Perrillat, J.-P., Mezouar, M., Ota, T., . . . Sanchez-Valle, C. (2014). Supervolcano eruptions driven by melt buoyancy in large silicic magma chambers. Nature Geoscience, 7(2), 122-125.
Mangan, M., & Sisson, T. (2000). Delayed, disequilibrium degassing in rhyolite magma: decompression experiments and implications for explosive volcanism. Earth and Planetary Science Letters, 183(3), 441-455.
Marchetti, E., Ichihara, M., & Ripepe, M. (2004). Propagation of acoustic waves in a viscoelastic two-phase system: influence of gas bubble concentration. Journal of volcanology and geothermal research, 137(1), 93-108.
Mavko, G. M. (1980). Velocity and attenuation in partially molten rocks. Journal of Geophysical Research: Solid Earth (1978–2012), 85(B10), 5173-5189.
Melnik, O., Barmin, A., & Sparks, R. (2005). Dynamics of magma flow inside volcanic conduits with bubble overpressure buildup and gas loss through permeable magma. Journal of volcanology and geothermal research, 143(1), 53-68.
Mourtada-Bonnefoi, C. C., & Laporte, D. (2004). Kinetics of bubble nucleation in a rhyolitic melt: an experimental study of the effect of ascent rate. Earth and Planetary Science Letters, 218(3), 521-537.
Müller, K., Bagdassarov, N., James, M., Schmeling, H., & Deubener, J. (2003). Internal friction spectroscopy in Li2O–2SiO2 partially crystallised glasses. Journal of non-crystalline solids, 319(1), 44-56.
Chapter 1 Introduction
7
Murphy, M., Sparks, R., Barclay, J., Carroll, M., & Brewer, T. (2000). Remobilization of andesite magma by intrusion of mafic magma at the Soufriere Hills Volcano, Montserrat, West Indies. Journal of petrology, 41(1), 21-42.
Namiki, A., & Manga, M. (2008). Transition between fragmentation and permeable outgassing of low viscosity magmas. Journal of volcanology and geothermal research, 169(1), 48-60.
Ohlendorf, S. J., Thurber, C. H., Pesicek, J. D., & Prejean, S. G. (2014). Seismicity and seismic structure at Okmok Volcano, Alaska. Journal of volcanology and geothermal research, 278, 103-119.
Okumura, S., Nakamura, M., Nakano, T., Uesugi, K., & Tsuchiyama, A. (2012). Experimental constraints on permeable gas transport in crystalline silicic magmas. Contributions to Mineralogy and Petrology, 164(3), 493-504.
Paulatto, M., Annen, C., Henstock, T. J., Kiddle, E., Minshull, T. A., Sparks, R., & Voight, B. (2012). Magma chamber properties from integrated seismic tomography and thermal modeling at Montserrat. Geochemistry, Geophysics, Geosystems, 13(1).
Pistone, M., Caricchi, L., Ulmer, P., Burlini, L., Ardia, P., Reusser, E., . . . Arbaret, L. (2012). Deformation experiments of bubble‐and crystal‐bearing magmas: Rheological and microstructural analysis. Journal of Geophysical Research: Solid Earth (1978–2012), 117(B5).
Platz, T., Cronin, S. J., Cashman, K. V., Stewart, R. B., & Smith, I. E. (2007). Transition from effusive to explosive phases in andesite eruptions—A case-study from the AD1655 eruption of Mt. Taranaki, New Zealand. Journal of volcanology and geothermal research, 161(1), 15-34.
Proussevitch, A., & Sahagian, D. (1998). Dynamics and energetics of bubble growth in magmas: analytical formulation and numerical modeling. Journal of Geophysical Research: Solid Earth (1978–2012), 103(B8), 18223-18251.
Richet, P., & Polian, A. (1998). Water as a dense icelike component in silicate glasses. Science, 281(5375), 396-398.
Rust, A., Cashman, K., & Wallace, P. (2004). Magma degassing buffered by vapor flow through brecciated conduit margins. Geology, 32(4), 349-352.
Saar, M. O., & Manga, M. (1999). Permeability‐porosity relationship in vesicular basalts. Geophysical Research Letters, 26(1), 111-114.
Schilling, F. R., Sinogeikin, S. V., Hauser, M., & Bass, J. D. (2003). Elastic properties of model basaltic melt compositions at high temperatures. Journal of Geophysical Research: Solid Earth (1978–2012), 108(B6).
Sisson, T., & Layne, G. (1993). H 2 O in basalt and basaltic andesite glass inclusions from four subduction-related volcanoes. Earth and Planetary Science Letters, 117(3), 619-635.
Slezin, Y. B. (2003). The mechanism of volcanic eruptions (a steady state approach). Journal of volcanology and geothermal research, 122(1), 7-50.
Sparks, R. (2003). Dynamics of magma degassing. Geological Society, London, Special Publications, 213(1), 5-22. Sparks, R. S., Huppert, H. E., Koyaguchi, T., & Hallworth, M. A. (1993). Origin of modal and rhythmic igneous
layering by sedimentation in a convecting magma chamber. Nature, 361(6409), 246-249. Sparks, S. R., & Sigurdsson, H. (1977). Magma mixing: a mechanism for triggering acid explosive eruptions.
Nature, 267, 315-318. Takeuchi, S. (2004). Precursory dike propagation control of viscous magma eruptions. Geology, 32(11), 1001-
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1004. Temkin, S. (2005). Suspension acoustics: An introduction to the physics of suspensions: Cambridge University
Press. Webb, S., & Courtial, P. (1996). Compressibility of melts in the CaO-Al2O3-SiO2 system. Geochimica et
cosmochimica acta, 60(1), 75-86. Webb, S. L., & Dingwell, D. B. (1990). The onset of non-Newtonian rheology of silicate melts. Physics and
Chemistry of Minerals, 17(2), 125-132. Whittington, A. G., Richet, P., & Polian, A. (2012). Water and the compressibility of silicate glasses: A Brillouin
spectroscopic study. American Mineralogist, 97(2-3), 455-467.
Chapter 2 Experimental and Analytical Techniques
8
2 EXPERIMENTAL AND ANALYTICAL TECHNIQUES
2.1 STARTING MATERIALS
Studying the seismic and/or degassing properties of magmas requires a composition that crystallizes phases
relevant for volcanology in the P-T range achievable with the available apparatus. The simplified hydrous
tonalite system has been intensively studied in the ternary system quartz-albite-anorthite (Qtz-Ab-An; e.g.
Johannes and Holtz, 1996; Johannes, 1989) and has the advantage to either crystallize quartz and plagioclase or
a cotectic mixture of the two at low temperature and high pressure conditions (Figure 2.1).
Figure 2.1: (a) Ternary diagram of the simplified tonalite system quartz-albite-anorthite displaying variation in the cotectic line separating the plagioclase and quartz primary phase field as a function of pressure. (b) Liquidus surfaces from (a) at 5 kbar as cross-sections drawn from the Qz apex to the albite-anorthite join (Johannes and Holtz, 1996).
However, for this study, the crystallization of a single phase (plagioclase) was chosen in order to facilitate the
interpretation of the acquired physical properties data. We have chosen the same composition as Picard et al.
(2011) used for studying rheological properties of plagioclase-bearing melt (see Table 2.1). Their starting
material has been obtained by crystallization of plagioclase from a tonalite melt at 300 MPa and 800°C for a
duration of 7 days. This method has the advantage to produce a suspension of anisotropic, chemically (nearly)
homogeneous, euhedral and regularly distributed crystals.
Chapter 2 Experimental and Analytical Techniques
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Table 2.1: Compositions of the starting material containing 2.8 wt% H2O measured by electron microprobe in wt%. The nominal composition corresponds to the composition of the powder before the HIP. Water and CO2 contents have been measured by KFT and by coulometry respectively. The CO2 contained in the starting mix is contained in the coexisting bubbles in the synthetic glass (“measured composition”).
Sample SiO2 Al2O3 CaO Na2O H2O CO2 Total
Nominal Composition 65.69 18.56 3.33 7.61 2.80 2.00 100
Measured Composition 65.26 18.81 3.49 7.51 2.75* 0.03 97.82
2.1.1 PHASE EQUILIBRIA CALCULATION
In this study we investigated a chemically simplified melt analogous to andesite and trachyte in the system
CaO-Na2O-Al2O3-SiO2-H2O-CO2 (Picard et al, 2011). This composition has the advantage of containing the
element naturally present in plagioclase and is thus prone to crystallize this phase. The addition of water to this
system lowered the liquidus temperature as well as the temperature of phase stability; the addition of carbon
dioxide insured the presence of bubble at the investigated pressure as the CO2 solubility in this silica-saturated
composition at the conditions of synthesis and the subsequent crystallization experiments is very low. We
computed the phase equilibria of the considered system (Figure 2.2) for various pressure, temperature and
water contents using Perple_X (Connolly and Kerrick, 2002; Connolly, 2009). The water content dissolved in the
melt influences the position of various boundary curves: a) at 200 MPa, the liquidus temperature is 1171 °C for
2.8 wt% H2O, 1201 °C for 2 wt% H2O and 1255 °C for 1 wt% H2O; b) at temperature higher than the solidus,
water exsolution is shifted to higher pressure with increasing water content; and c) the stability of quartz
increases at the expense of plagioclase with decreasing water content (the plagioclase liquidus is suppressed
more effectively than the quartz liquidus).
Figure 2.2: P-T-Phase diagram of a simplified tonalite containing various amount of water.
Chapter 2 Experimental and Analytical Techniques
10
Based on these (computed) phase diagrams, we decided to synthetize bubble-bearing glasses with various
water contents (Figure 2.2) at the highest pressure and temperature achievable with the Hot Isostatic Press, i.e.
1200 °C (1473 K) and 200 MPa (2000 bars).
2.1.2 GLASS SYNTHESIS
2.1.2.1 BUBBLE-BEARING GLASS
In order to produce large quantities of chemically homogeneous, hydrated glasses, oxide, hydroxide and
carbonate powders were mixed to obtain the desired compositions. These mixtures were subsequently cold
pressed into stainless steel canisters with a uniaxial pressure of 200 MPa. Molybdenum foils lining the border
of the canister avoided contamination from the container wall. Subsequently, these mechanical mixtures have
been thermally equilibrated in a Hot Isostatic Press (HIP) at 1200 °C and 200 MPa for 24 hours (see Figure 2.3).
The vessel was then rapidly cooled to 550 °C in order to quench the samples. This temperature corresponds to
the glass transition temperature of the least hydrated sample, i.e. containing 1 Wt% H2O, calculated using the
model of Giordano et al. (2008) and assuming a viscosity of 1012 Pa*s. From 550°C to room temperature, a
cooling rate of 0.6°C/min was applied to allow for thermal relaxation of the glass.
Figure 2.3: Pressure and temperature path applied in the Hot Isostatic Press (HIP) during the synthesis of glasses. The dark grey line represents the pressure and the light grey line the temperature. After technical upgrade of the HIP, the pressure could be maintained to 200 MPa (± 10 MPa) during the fast cooling (dashed line).
Samples containing less than 2 wt% H2O crystallized large and euhedral plagioclase rich in anorthite. A minor
amount of spherulitic albite (less than 1 vol%) crystallized in the sample containing more than 2 wt% H2O.
However, the resulting hydrated glasses are chemically homogeneous and their compositions correspond to
the nominal values within 1 % (Table 2.1). CO2-rich bubbles (4.2 vol%) have a number density of 167 [1/mm2]
and their sizes have a narrow distribution located around 6 µm (see Figure 2.4). The sample containing 2.8 wt%
H2O was finally selected for the experiments.
Chapter 2 Experimental and Analytical Techniques
11
Figure 2.4: SEM image (A) of the bubble-bearing glass synthetized in the HIP and its bubble-size distribution (B).
As the sample containing less than 2 wt% H2O crystallized more than 20 vol% of anorthite, we decided to use
natural phonolite glass to study the effect of dissolved water on the seismic properties of melt.
2.1.2.2 PHONOLITE GLASS
For the synthesis of hydrated phonolite glass, we used the same P-T path in the HIP. However, the hydration of
a natural sample needs to be done through the addition of distilled water. The samples collected in the Lavas
Negras (Teide volcano, Spain) were first melted in air at 1600 °C. The resulting glass was crushed and mixed
with various amount of distilled water, i.e. 0.1, 0.5, 1.0, 2.0 and 3.0 wt% H20. The procedure for cold-pressing
these mixtures into stainless steel canisters was identical with the procedure used for the bubble-bearing glass.
Table 2.2: Composition in [wt%] of the hydrous phonolite from Lavas Negras (Tenerife, Spain) measured by electron microprobe. *The water content was measured by Karl Fisher Titration.
LN5 LN4 LN3 LN2 LN1
SiO2 60.16 60.23 60.65 60.24 60.39
Al2O3 18.33 18.52 18.66 18.56 18.58
FeO (tot) 3.04 3.36 3.37 3.40 3.44
TiO2 0.63 0.67 0.68 0.67 0.68
MnO 0.19 0.19 0.20 0.20 0.21
MgO 0.32 0.35 0.37 0.37 0.36
CaO 0.73 0.72 0.71 0.72 0.72
Na2O 8.74 9.05 9.19 9.33 9.24
K2O 4.72 4.75 4.84 4.85 4.85
H2O* 1.87 1.37 0.56 0.32 0.36
Nominal H2O 3.00 2.00 1.00 0.50 0.10
Total 98.74 99.21 99.23 98.66 98.84
After synthesis in the HIP, the water content of the glasses were measured by Karl Fisher Titration (KFT). The
sample containing nominally 0.1 wt% H20, i.e. LN1, has a water content higher than expected whereas samples
Chapter 2 Experimental and Analytical Techniques
12
containing nominally more than 0.5 wt% H20 lost some water. All glasses are chemically homogeneous except
for LN4 and LN5 that contain 1.4 and 3.5 vol% of iron oxides, respectively. In order to quantify the influence of
these microlites on the seismic properties, we calculated the Voigt-Reuss-Hill average VVRH by using these
equations:
𝑉𝑉𝑅𝐻 = 𝑉𝑉 + 𝑉𝑅
2
𝑉𝑉 = ∑ 𝛷𝑖 ∗ 𝑉𝑖
𝑁
𝑖=1
1
𝑉𝑅
= ∑𝛷𝑖
𝑉𝑖
𝑁
𝑖=1
where VV is the Voigt upper bound, VR is the Reuss lower bound, Φi is the fraction of the ith component and Vi
is the seismic velocity (shear or compression waves) of the ith component (Mavko et al., 2009). Assuming a
compression wave velocity Vp of 6.04 km/s for the phonolite glass (Seifert et al., 2013) and 7.35 km/s for the
iron oxides (data for a magnetite crystal taken from Ji et al., 2002), the Voigt-Reuss-Hill average is 6.06 and 6.08
km/s for a crystal content of 1.4 and 3.5 vol%, respectively. Concerning the shear wave velocity Vs, we assumed
a velocity of 3.59 km/s for the phonolite glass (Seifert et al., 2013) and 4.2 km/s (Ji et al., 2002) for magnetite.
The calculated velocities are 3.60 and 3.61 km/s for a crystal content of 1.4 and 3.5 vol%, respectively.
Based on these calculations, we decided to measure the seismic properties of all phonolite glasses synthetized
in the HIP. The error induced by the presence of Fe-oxide microlite is effectively within the error of the
measurements, i.e. 0.1 km/s for Vp and 0.4 km/s for Vs.
2.2 SEISMIC VELOCITIES MEASUREMENTS
2.2.1 SAMPLE PREPARATION
Glasses synthetized in the HIP were drilled into cores of 22 mm diameter for the measurements of pressure
and temperature derivatives and 15 diameter mm for determination of the effect of crystallization on the
seismic and degassing properties of magmas. The cores were cut to a length of 30 mm and double polished to
obtain parallel faces. Bubble-free samples were dried at 110 °C for 24 hours prior to measurements whereas
bubble-bearing samples were dried at 40 °C for 24 hours. Higher temperature provoked the fracture of the
cored glasses due to the expansion of gas in the bubbles.
2.2.2 PATERSON APPARATUS
Absolute velocities as well as changes in seismic properties of crystallizing magmas have been measured in a
Paterson-type internally-heated gas pressure apparatus (Paterson and Olgaard, 2000). Piezoelectric
transducers placed at both extremities of the assembly (see Figure 2.5A) permit the in-situ measurement of
Chapter 2 Experimental and Analytical Techniques
13
compression wave velocities using the pulse transmission technique (Birch, 1960). Electric waves with known
frequency, pulse width and repetition rate are generated using a pulser (PC-plug-in thoneburst card controlled
by the software Matec). The generated pulses (see Figure 2.5B) are sent to a piezoelectric transducer, which
converts them into elastic ultrasound waves, i.e. when an electric field is applied, the transducers expand and
produce compressional waves. The vibrational frequency applied to the transducers ranges from 0.1 to 3 MHz.
After traveling through the sample, the signals are converted back into electric waves by a second transducer
placed on the opposite side of the assembly and they are finally displayed on an oscilloscope (see Figure 2.5C).
The time required for the wave to travel through the sample can be deduced from the oscilloscope
measurement. Knowing the length of the core, the velocity can finally be calculated. For each measurements,
we recorded waveforms averaged over 1000 received signal. The picking of the first arrival was done after the
experiments through a code written in Matlab.
Figure 2.5: (A) Schematic drawing of the HP-HT Paterson apparatus implemented with the setup to measure seismic velocities. (B) Electronic signal emitted by the pulser. The frequency is 1 MHz, the pulse width is 2 µs and the repetition rate is 5 ms. (C) Electronic signal received by the oscilloscope. This waveform has been recorded while the assembly was at 310 MPa and ambient temperature.
As the piezoelectric transducers are inefficient at high temperature, alumina rods placed between the
transducers and the sample are used to obtain pulse generation and recording at considerably lower
temperature (less than 100°C). However, considering the length of the sample, i.e. 30 mm, we had to insure
that the furnace was producing a constant temperature all along the sample. The furnace was thus calibrated
using an assembly made of alumina rods having a 2 mm diameter hole. This hole permits the insertion of an R-
Chapter 2 Experimental and Analytical Techniques
14
type thermocouple. In order to constrain the temperature during the experiments, two thermocouples are
inserted in the assembly, i.e. one at the bottom and one at the top of the sample. The temperature difference
between these two thermocouples never exceeded 5 °C.
In order to have hydrostatic condition, the system uses argon gas as confining medium. The assembly is
isolated from the argon by an iron jacket of 0.2 mm wall thickness.
2.2.3 UP-DATE OF THE ASSEMBLY
In order to obtain the elastic properties of a crystallizing melt, both compressional and shear wave velocities
need to be measured simultaneously. The assemblies for high temperature measurements previously
employed in the Rock Deformation laboratory are suitable for samples that do not significantly change their
physical state as they contain only one piezoelectric transducer. This is not the case for our synthetic samples
as crystal and bubble contents change during the experiment.
Based on the work of the previous head of the laboratory, PD Dr. Luigi Burlini, two different types of
piezoelectric transducers, producing vertical or horizontal motions, have been introduced in the high
temperature assembly (see Figure 2.6). In order to avoid the simultaneous excitation of the transducers, a disk
of pyrophillite is separating them. This assembly is placed at the end of the alumina spacers in order to avoid
the high temperature plateau in the center of the sample assembly.
Figure 2.6: Drawing of the Vp/Vs transducers assembly designed for high temperature measurements.
In order to calibrate this new transducers assembly, an isotropic standard was used instead of the commonly
employed anisotropic sapphire used for compression wave velocities measurements. This new standard had to
fulfill several specific conditions: high melting temperature, isotropic physical properties, low compressibility
and low thermal expansion. In addition, the pressure and temperature derivatives of at least two elastic
constants should be known. The most suitable standard resulted to be fused quartz glass.
Chapter 2 Experimental and Analytical Techniques
15
2.2.4 CALIBRATION OF THE ASSEMBLY
The time delay caused by the stack of alumina rods have been measured at various pressures and
temperatures using a sapphire crystal cut parallel to [0001] for compression wave velocity. The formula used to
determine the travel time through the standard is:
𝑉𝑝,𝑠𝑡𝑟𝑑 = 11.356 + 5.4 ∗ 10−5 ∗ 𝑃 − 3.986 ∗ 10−4 ∗ 𝑇
where P is the confining pressure in MPa and T is the temperature in K. For the calibration of the time delay
when shear waves are travelling through the assembly, we used a glass of fused quartz manufactured by
Goodfellow. The formula for calculating the travel time is an average of data collected in various studies
(Peselnick et al., 1967; Manghnani, 1974; Gerlich and Kennedy, 1978; Polian et al., 2002; Spinner, 1956; Gieske
and Frost, 1991; Bucaro and Dardy, 1974):
𝑉𝑠,𝑠𝑡𝑟𝑑 = 3.7251 + 2.0641 ∗ 10−4 ∗ 𝑇
where T is the temperature in °C and P is set constant at 250 MPa.
The error on the measurements is mainly linked to the picking of the first arrival and reaches 0.1 km/s for
compression wave velocity and 0.2 km/s for shear wave velocity.
2.2.5 MEASUREMENTS STRATEGY
2.2.5.1 PRESSURE AND TEMPERATURE DERIVATIVES
The arrival times were recorded first at room temperature and various pressures in order to determine the
pressure derivative of shear and compression waves. Then, the pressure was maintained at 250 MPa and the
temperature was increased to the maximum temperature planned for the experiment. Ultrasonic velocities has
been recorded each 20 to 50 °C while decreasing the temperature at a rate of 10 °C/min. In order to allow the
sample and the assembly to equilibrate to the new thermal condition, constant temperature was maintained
during a minimum of 20 minutes.
2.2.5.2 CRYSTALLIZATION AND BUBBLE NUCLEATION
We performed the experiments at a constant pressure of 250 MPa. Samples were first heated at a rate of
30°C/min to 850°C. This temperature was maintained constant for 30 minutes. Subsequently, the temperature
was decreased to 700°C at a cooling rate of 0.5 or 0.1°C/min. Seismic velocities were recorded every 45
minutes. At 700°C, the temperature was decrease to room temperature at a rate of 30°C/min.
Chapter 2 Experimental and Analytical Techniques
16
2.3 RAPID QUENCH EXPERIMENTS
In order to determine the evolution of the microstructure during the seismic property measurement
experiments, the P-T conditions applied in the Paterson apparatus were reproduced in a rapid-quench
molybdenum-hafnium-carbide (MHC) cold-seal pressure vessel. Placed on a rotary table, this externally heated
pressure vessel permits dropping the sample into the cold steel extremity linked to the MHC part by a water-
cooled nut. This setup allows rapid quench of the sample at a rate of about 100°C/s, which allows preserving
the microstructure formed at run pressure and temperature. The temperature gradient in the hot MHC
extremity never exceeded 5°C over the sample length. Cores of 4 mm in length and in diameter drilled from the
starting glass were contained in Au capsules that were welded shut using a W-electrode arc-welder. Runs were
quenched under pressure at identical time steps, and thus identical temperatures, as the seismic velocities
measurements were performed.
Figure 2.7: Schematic drawing of the Molybdenum-Hafnium-Carbide (MHC) cold-seal vessel.
2.4 DEGASSING MEASUREMENTS
2.4.1 SAMPLE PREPARATION
The bubble-bearing glasses were prepared with the same method as for the seismic velocity measurements,
except for their length. We double polished the samples to a length of approximatively 10 mm.
2.4.2 PATERSON APPARATUS
The extent of degassing during plagioclase crystallization was determined using a Paterson apparatus
implemented with a volumometer and upstream and downstream pore-fluid connections (see Figure 2.8). The
volumometer has a confined diameter of 7 mm and a length of 50 mm, which permits to achieve an accuracy of
the pore pressure (argon gas) of 0.1 MPa. Pressure sensors are placed in the upstream and downstream pore-
fluid connections. A Schaevitz LVDT placed on the axis of the actuator measures the displacement of the
volumometer piston with a resolution of 0.01 mm.
Chapter 2 Experimental and Analytical Techniques
17
Figure 2.8: Schematic drawing of the Paterson apparatus implemented with a pore-fluid system (Violay et al., 2015).
The assembly is composed of zirconia and alumina rods with a 2 mm hole drilled in the center for the insertion
of the pore-fluid and the thermocouple. The sample is isolated from the pore fluid pressure at the bottom by
an alumina disc. Bubbles can thus escape from the sample only through the porous top mullite disc.
2.4.3 MEASUREMENTS STRATEGY
The temperature paths were identical to the seismic experiments, i.e. maintained during 30 minutes at 850 °C
and then cooled down to 700 °C at a rate of 0.5 and 0.1 °C/min respectively. The confining pressure was kept
constant at 250 MPa. As the precision of the volumometer is better at higher pressure, the pore-fluid pressure
was initially set to 5 MPa. A gradient of 5 MPa was therefore present within the sample; The alumina discs
placed at the bottom of the sample was at a pressure equal to the confining pressure (Pc) and the porous
mullite disc placed at the top of the sample was subjected to a pressure that is equal to Pc – Pf, i.e. the top part
of the sample was at 245 MPa.
During the experiments, the position of the volumometer piston was kept constant. The number of mole
degassed from the sample was calculated from the variation of pore pressure assuming ideal gas behavior:
𝑃 ∗ 𝑉 = 𝑛 ∗ 𝑅 ∗ 𝑇
where P is the variation of pressure measured in the volumometer in Pa, V is the volume of the pore fluid
system (assembly, pipes and volumometer) in m3, n is the number of moles degassed from the sample in mol, R
is the gas constant (8.3144621 J/(mol*K)) and T is the temperature in the volumometer in K. Although the
sample is degassing a mixture of H2O and CO2, we used the ideal gas law as more than 90 % of the gas in the
system at the end of the experiments is argon.
Chapter 2 Experimental and Analytical Techniques
18
As the temperature was decreased during the experiments, the pore-fluid pressure was additionally corrected
for the variation of temperature:
𝑃 = 𝑃𝑚𝑒𝑎𝑠 −𝑑𝑃
𝑑𝑇∗ 𝑇
where Pmeas is the pore-fluid pressure measured during the experiments in MPa, T is the temperature of the
sample in °C and dP/dT is the calibrated variation of pressure as function of temperature changes. The
calibration has been done prior to the experiments using an alumina rod instead of the sample in the assembly.
2.5 ANALYTICAL TECHNIQUES
2.5.1 MICROSTRUCTURE ANALYSIS (2D)
Microstructures (phase fraction, bubble number density, bubble size distribution, spherulite number density
and spherulite diameter) have been determined by evaluation of BSE (back-scattered electron) images of the
starting material (synthetized in the HIP), the final sample (crystallized in the Paterson apparatus) and the
rapidly quenched samples (crystallized in the MHC cold-sealed vessel). Images were taken at a magnification of
200x over 1 cm2 for the starting and final samples and over the entire capsules (16 mm2) for the quenched
samples.
The phase fractions were determined by grayscale dissociation using the software ImageJ. The images were
first hand-corrected for bubbles that didn’t appear in black (see Figure 2.9A and B) and for the cracks that
appeared during the fast quench in the cold-sealed apparatus. We manually adjusted the threshold of each
image to separate individual phases (see Figure 2.9C, E and F). ImageJ was then used to calculate the total area
occupied by melt, crystals and bubbles respectively.
Chapter 2 Experimental and Analytical Techniques
19
Figure 2.9: Example of the image processing using ImageJ. (A) Original BSE (back-scattered electron) image taken by SEM. (B) Image with enhanced contrast and corrected for bubbles and cracks. The scale bar has been removed. (C) Binary image of the bubble fraction. (D) Outlines of the bubbles from image (C). (E) Binary image of the melt fraction. (F) Binary image of the crystal fraction.
Another function in ImageJ permits to count and measure the size of each particles (see Figure 2.9D). The SEM
images were thus assembled and bubble number density and bubble size distribution were calculated for the
entire area covered by the image. Bubbles smaller than 3 pixel units, i.e. with a diameter smaller than 1.5 µm,
have been excluded from the bubble characterization. The diameters of irregular bubbles in the crystallized
samples were calculated assuming a spherical shape.
Chapter 2 Experimental and Analytical Techniques
20
Spherulite number density and spherulite diameters were determined by manually drawing the limits of each
spherulite aggregate. The resulting drawing was then used in ImageJ for the spherulite characterization.
2.5.2 CHEMICAL COMPOSITION
2.5.2.1 MAJOR ELEMENTS
Melt compositions were measured with a JEOL JXA-8200 electron probe micro-analyzer (EPMA) employing a 20
µm beam diameter, 10 kV acceleration voltage and 20 nA beam current. The beam diameter was set to 3 µm
for the measurements of plagioclase composition. In order to minimize alkali loss, the counting time was set to
20 s for each elements and 10 s for the background. The standardization for the measurements of the tonalite
glass was done on a natural albite crystal (internal standard name: H021) for Na and Si and on a natural
anorthite (H103) for Al and Ca. The standardization for the measurements of the composition of the hydrous
phonolite was done on a natural wollastonite (H055) for Si and Ca, on a natural albite (H021) for Na, on an
natural orthoclase (H011) for K, on a synthetic corundum (D006) for Al, on a synthetic periclase (D044) for Mg,
on a synthetic rutile (D015) for Ti, on a natural hematite (D014) for Fe and on a synthetic pyrolusite (D023) for
Mn. The compositions given in this thesis are the average of more than 20 measurements.
2.5.2.2 WATER CONTENT
Water content in the samples before and after the experiments were measured by Karl Fisher Titration (KFT).
The samples were first crushed and dried for 24 hours at 110°C prior to analysis. 20 to 30 mg of sample were
placed in a platinum crucible and transferred to the heating chamber. Exsolution of water from the sample was
promoted by heating the chamber to 1250°C, i.e. above the liquidus temperature of the respective
compositions. Pure argon gas (Ar 6.0, PanGas AG) flowing through the chamber transported the water
molecules an oxidation furnace. A network of quartz and CuO was heated to 450°C which promoted oxidation
of hydrogen or hydrocarbons. Finally, the water was further transported to the titration cell, where it was
quantified by a CA-100 Moisture meter (Mitsubishi Chemical Corporation).
As the samples are crushed and well mixed, this method gives only the bulk water content of the samples. The
maximum uncertainty of this method is ± 0.15 wt% (Behrens et al., 1996).
2.5.3 DENSITY
Density was measured on the cored samples before and after the experiments performed in the Paterson
apparatus with a Micromeritics Accupyc pycnometer. A gas displacement pycnometer measures the density of
a sample using gas pressure changes. It utilizes helium gas that is first inserted in the cell chamber, which holds
the sample, and then in the expansion chamber, which has been previously calibrated. Using Boyle’s law, which
relates gas pressure to volume, this laboratory device automatically calculates the volume of the sample with a
precision of 0.0001 cm3. The weight was measured with a precision of 0.001 g.
Chapter 2 Experimental and Analytical Techniques
21
2.6 REFERENCES
Behrens, H., Romano, C., Nowak, M., Holtz, F., & Dingwell, D. B. (1996). Near-infrared spectroscopic determination
of water species in glasses of the system MAlSi 3 O 8 (M= Li, Na, K): an interlaboratory study. Chemical
geology, 128(1), 41-63.
Bucaro, J., & Dardy, H. (1974). High‐temperature Brillouin scattering in fused quartz. Journal of Applied Physics,
45(12), 5324-5329.
Connolly, J. (2009). The geodynamic equation of state: what and how. Geochemistry, Geophysics, Geosystems,
10(10).
Connolly, J., & Kerrick, D. (2002). Metamorphic controls on seismic velocity of subducted oceanic crust at 100–250
km depth. Earth and Planetary Science Letters, 204(1), 61-74.
Gerlich, D., & Kennedy, G. C. (1978). Second pressure derivatives of the elastic moduli of fused quartz. Journal of
Physics and Chemistry of Solids, 39(11), 1189-1191.
Gieske, J. H., & Frost III, H. M. (1991). Technique for measuring ultrasonic velocity and attenuation changes in
attenuative materials at temperature such as during sintering processes. Review of scientific instruments,
62(12), 3056-3060.
Giordano, D., Russell, J. K., & Dingwell, D. B. (2008). Viscosity of magmatic liquids: a model. Earth and Planetary
Science Letters, 271(1), 123-134.
Ji, S., Wang, Q., & Xia, B. (2002). Handbook of seismic properties of minerals, rocks and ores: Presses inter
Polytechnique.
Johannes, W. (1989). Melting of plagioclase-quartz assemblages at 2 kbar water pressure. Contributions to
Mineralogy and Petrology, 103(3), 270-276.
Johannes, W., & Holtz, F. (1996). Petrogenesis and experimental petrology of granitic rocks (Vol. 335): Springer
Berlin.
Manghnani, M. H. (1974). Pressure and Temperature Studies of Glass Properties Related to Vibrational Spectra:
DTIC Document.
Mavko, G., Mukerji, T., & Dvorkin, J. (2009). The rock physics handbook: Tools for seismic analysis of porous media:
Cambridge university press.
Paterson, M., & Olgaard, D. (2000). Rock deformation tests to large shear strains in torsion. Journal of Structural
Geology, 22(9), 1341-1358.
Peselnick, L., Meister, R., & Wilson, W. H. (1967). Pressure derivatives of elastic moduli of fused quartz to 10 kb.
Journal of Physics and Chemistry of Solids, 28(4), 635-639.
Picard, D., Arbaret, L., Pichavant, M., Champallier, R., & Launeau, P. (2011). Rheology and microstructure of
experimentally deformed plagioclase suspensions. Geology, 39(8), 747-750.
Polian, A., Vo-Thanh, D., & Richet, P. (2002). Elastic properties of a-SiO2 up to 2300 K from Brillouin scattering
measurements. EPL (Europhysics Letters), 57(3), 375.
Seifert, R., Malfait, W. J., Lerch, P., & Sanchez-Valle, C. (2013). Partial molar volume and compressibility of dissolved
CO 2 in glasses with magmatic compositions. Chemical geology, 358, 119-130.
Spinner, S. (1956). Elastic moduli of glasses at elevated temperatures by a dynamic method. Journal of the
American Ceramic Society, 39(3), 113-118.
Chapter 3 Seismic Properties of Crystallizing Magmas
22
3 EFFECTS OF CRYSTALLIZATION AND BUBBLE NUCLEATION ON THE SEISMIC
PROPERTIES OF MAGMAS
Accepted for publication in Geochemistry, Geophysics, Geosystems in February 2016.
Tripoli Barbara1, Cordonnier Benoit2, Zappone Alba3, Ulmer Peter1
1 Institute of Geochemistry and Petrology, Earth Sciences Department, ETH Zurich
2 No Affiliation
3 Geological Institute, Earth Sciences Department, ETH Zurich
3.1 ABSTRACT
Seismic tomography of potentially hazardous volcanoes is a prime tool to assess the location and dimensions of
magmatic reservoirs. Seismic velocities are strongly affected by processes occurring within the conduit or in the
magma chamber, such as crystallization and bubble exsolution. However, the limited number of constrained
measurements does not allow yet to link seismic tomography and the textural state of a particular volcanic
system. In this study, we investigated a chemically simplified melt in the system CaO-Na2O-Al2O3-SiO2-H2O-CO2,
which undergoes plagioclase crystallization and bubble exsolution. A Paterson-type internally-heated gas
pressure apparatus was employed to measure ultrasonic velocities at a constant pressure of 250 MPa and at
temperature from 850 to 700 °C. Magmatic processes such as crystallization, bubble nucleation and
coalescence have been recognized throughout the measurements of seismic velocities in the laboratory.
Compression and shear wave velocities increase non-linearly during crystallization. At a crystal fraction
exceeding 0.45, the formation of a crystal network favors the propagation of seismic waves through magmatic
liquids. However, bubble nucleation induced by crystallization leads to an increase of magma compressibility
resulting in a lowering of the wave propagation velocities. These two processes occur simultaneously and have
a competing influence on the seismic properties of magmas. In addition, as already observed by previous
authors, when the bubble fraction is less than 0.10, the decrease in seismic velocities is more pronounced than
for higher bubble fractions. The effect of bubble coalescence on elastic properties is thus lower than the effect
of bubble nucleation.
3.2 INTRODUCTION
Seismic tomography of potentially hazardous volcanoes is a prime tool to identify and determine the size and
location of subvolcanic magma reservoirs (e.g. Ohlendorf et al., 2014, Chouet, 2003). Recent progresses in data
acquisition and processing led to higher precision and resolution (e.g. Nagaoka et al., 2012). In addition,
Chapter 3 Seismic Properties of Crystallizing Magmas
23
attempts to determine the physical state of magma reservoirs, e.g. melt proportion, are more and more often
conducted by combining tomographic data with available laboratory data and numerical simulation (e.g. Lin et
al., 2014; Paulatto et al., 2012).
Laboratory measurements of elastic parameters have been performed on melts of various compositions at a
large range of temperatures (e.g. Rivers and Carmichael, 1987; Askarpour et al., 1993; Schilling et al., 2003;
Webb and Courtial, 1996). Due to the temperature-dependence of the elastic moduli, seismic velocities
decrease continuously with increasing temperature until the glass transition temperature is reached (e.g.
Schilling et al., 2003). This temperature range corresponds to a transition in the physical properties of the melt
from a solid-like (below the glass transition temperature) to a liquid-like behavior (above the glass transition
temperature) (e.g. Webb and Dingwell, 1990). By crossing this region, a marked increase of the temperature
derivative of the compressional wave propagation velocity is observed (e.g. Askarpour et al., 1993). This break
is less pronounced for shear waves (e.g. Caricchi et al., 2008). This variation in elastic properties at the glass
transition temperature has also been reported for crystal-bearing melt (Caricchi et al., 2008). However, the
amplitude of this variation decreases with increasing crystal content. Microstructure is as well a fundamental
parameter in determining the elastic properties (e.g. Mueller et al., 2003; Hier-Majumder, 2008; Schmeling,
1985; Mavko, 1980). The non-linear increase of seismic wave velocities by increasing the crystal fraction is a
direct result of the formation of a continuous crystal network (Caricchi et al., 2008).
Figure 3.1 : Phase diagram of an haplotonalite containing 2.8 wt% of water calculated with Perple_X (Connolly, 2009). The blue polygon corresponds to the P-T conditions used for the glass synthesis. The starting condition for the crystal and bubble growth experiments is shown by the yellow star.
The internal structure of magmatic reservoirs and conduits is continuously evolving through various processes.
Degassing-induced crystallization (e.g. Cashman and Blundy, 2000) reveals the close interdependence of melt
composition, crystal and bubble contents. Caricchi et al. (2008) and Bagdassarov et al. (1994) shows that the
Chapter 3 Seismic Properties of Crystallizing Magmas
24
presence of bubbles in crystal-bearing magmas tends to decrease their elastic properties. However, the effect
of bubbles on seismic velocities is not well defined. In addition, processes occurring within the conduit or in the
magma chamber, such as crystallization and bubble exsolution, control the magma rheology, hence the style of
volcanic eruption (Cordonnier et al., 2009; Gonnerman and Manga, 2013; Pistone et al., 2013). Here we present
a new set of compression and shear wave velocity laboratory data at high pressure and temperature on a
chemically simplified melt analogous to andesite and trachyte, in the system CaO-Na2O-Al2O3-SiO2-H2O-CO2.
This melt composition undergoes plagioclase crystallization and bubble exsolution closely simulating the
evolution of natural magmas crystallizing and decompressing in magma reservoirs and within volcanic conduits.
3.3 METHODOLOGY
In order to study the effect of crystallization and bubble nucleation on the seismic properties of magmas we
synthetized a chemically simplified tonalite melt (Table 3.1), which is prone to crystallize plagioclase (Picard et
al., 2011). First, oxide and hydroxide powders were mixed to obtain the desired compositions (Table 3.1). The
mixtures have been cold pressed into stainless steel canisters with a uniaxial pressure of 200 MPa.
Molybdenum foils lining the border of the canister avoid contamination from the wall. Subsequently, the
mixtures have been thermally equilibrated in a Hot Isostatic Press (HIP) at 1200 °C and 200 MPa for 24 hours. In
the phase diagram calculated using Perple_X (Connolly, 2009), this P-T condition corresponds to superliquidus
conditions (Figure 3.1). The resulting hydrated glasses are chemically homogeneous and their compositions
correspond to the nominal values within 1% (Table 3.1). The hydrated glass contains a bubble fraction of 0.04.
These CO2-rich bubbles have a number density of 167 mm-2 and their sizes exhibit a narrow distribution
situated around 6 µm (Figure 3.2A and Figure 3.5E and 3.5F). In addition to bubbles, the glass contains less than
0.01 fraction of spherulitic plagioclase, with a mean size of 150 µm (Figure 3.5). This bubble-bearing glass has
been drilled into cores of 30 mm length and 15 mm diameter to perform seismic velocities measurements.
Figure 3.2: SEM images of (A) the bubble-bearing glass synthetized in the HIP apparatus (starting material) and (B) the plagioclase- and bubble-bearing glass crystallized in the Paterson apparatus (experiment cooled at 0.1 °C/min). Lath shaped crystals are plagioclase (spherulites), darker grey interstitial patches is glass (quenched melt), black holes correspond to former bubbles.
Chapter 3 Seismic Properties of Crystallizing Magmas
25
Changes in seismic properties of crystallizing magmas have been measured in a Paterson-type internally-heated
gas pressure apparatus (Paterson and Olgaard, 2000). Piezoelectric transducers placed at both extremities of
the assembly (Figure 3.3) permit direct measurement at high pressure and high temperature of compression
wave velocities using the pulse transmission technique (Birch, 1960). The vibration frequency applied to the
transducers was 0.1 MHz and the input voltage was 300 V peak to peak. The alumina rods in the assembly have
a 2 mm diameter hole that permits the insertion of thermocouples at the bottom and at the top of the sample.
The temperature difference over the entire length of the sample never exceeded 5 °C. The temperature was
controlled by a Eurotherm controller connected to the thermocouple placed at the bottom of the sample. In
situ pressure conditions are simulated by hydrostatically confining the assembly in the pressure vessel with
argon. The assembly is isolated from the gas pressure medium by an iron jacket of 0.2 mm wall thickness.
Figure 3.3: Drawing of the HP-HT Paterson apparatus implemented with the setup to measure seismic velocities.
The stack of alumina rods in the assembly produces a time delay in the measurements of the P- and S-waves
arrival time. This delay has been determined at various pressure and temperature using a well-known sapphire
crystal cut parallel to (0001) for calibration of the compression wave velocity (see Burlini et al. (2005), Ferri et
al. (2007) Caricchi et al. (2008) for additional details on the experimental procedure) and a glass rod of fused
quartz for calibration of the shear wave velocity. Experiments were performed at a constant confining pressure
of 250 MPa. This pressure has been selected for the higher quality of the received seismic signal. Samples were
first heated to 850°C at a rate of 30°C/min. This temperature was maintained constant for 30 minutes.
Subsequently, the temperature was continuously decreased to 700°C at a cooling rate of 0.5 or 0.1°C/min.
Chapter 3 Seismic Properties of Crystallizing Magmas
26
Seismic velocities were recorded every 45 minutes. The error on the measurements is mainly linked to picking
of the first arrival (for additional details on data processing, see Caricchi et al. (2008)) and reaches 0.1 km/s for
compression wave velocity and 0.2 km/s for shear wave velocity.
In order to determine the evolution of the microstructure during the experiments, the P-T conditions applied in
the Paterson apparatus have been reproduced in a rapid-quench molybdenum-hafnium-carbide (MHC) cold-
sealed pressure vessel. Placed on a rotary system, this externally heated pressure vessel permits dropping the
sample into the cold steel extremity linked to the MHC part by a water-cooled nut. This setup results in a rapid
quench of the sample at a rate exceeding 100°C/s, which allows preservation of the microstructure formed at
high temperature. The temperature gradient in the hot MHC extremity never exceeded 5 °C over the length of
the sample. Cores of 4 mm in length and in diameter, previously drilled from the starting glass and placed into
Au capsules that were welded shut, have been quenched under pressure at identical time steps as the seismic
velocities measurements were obtained.
Microstructures (phase fraction, bubble number density, bubble size distribution, spherulite number density
and spherulite diameter) have been determined by evaluation of SEM images of the starting material
(synthetized in the HIP), the final sample (crystallized in the Paterson apparatus) and the quenched samples
(crystallized in the MHC cold-sealed vessel). Images were taken at a magnification of 200x over 1 cm2 for the
starting and final samples and over the entire capsules (16 mm2) for the quenched samples. The phase
fractions have been determined by grayscale dissociation using the open source software ImageJ (Schneider et
al., 2012). Bubbles smaller than 3 pixel units, i.e. with a diameter smaller than 1.5 µm, have been excluded
from the bubble characterization. Melt and plagioclase compositions have been measured with a JEOL JXA-
8200 electron microprobe employing a 20 and 3 µm beam diameter respectively, 10 kV acceleration voltage
and 20 nA beam current.
Figure 3.4: Compression (Vp, in green) and shear (Vs, in purple) wave velocities as a function of temperature measured on the sample cooled at 0.5 °C/min (CR05, triangle symbols) and on the sample cooled at 0.1°C/min (CR01, circle symbols).
Chapter 3 Seismic Properties of Crystallizing Magmas
27
3.4 EXPERIMENTAL AND ANALYTICAL RESULTS
The evolution of seismic velocities through time is cooling rate-dependent (Figure 3.4). The sample cooled at
0.5°C/min (CR05) reveals a smooth variation of its seismic properties whereas sharp changes and an overall
larger variation of the seismic velocities are observed in the measurements conducted at lower cooling rate,
i.e. 0.1°C/min (CR01). This discrepancy highlights the transient dynamics of the observed microstructures and
thus the involved magmatic processes.
3.4.1 MICROSTRUCTURE: COOLING RATE OF 0.5 °C/MIN
By decreasing the temperature (T) from 850 to 830°C at a rate of 0.5°C/min, the compression wave velocity (Vp)
measured in the bubble-bearing tonalite melt increases from 5.01 to 5.16 km/s and the shear wave velocity (Vs)
increases from 2.88 to 2.94 km/s (Figure 3.5A and Table 3.2). Crystallization of spherulitic plagioclase is clearly
documented by the increase of the crystal fraction to 0.4 and a concomitant increase in the mean diameter of
spherulites to 350 µm (Figure 3.5B and 3.5C). As expected for closed system crystallization of plagioclase, the
Na, Ca and Al contents of the melt decrease while the Si content increases (Table 3.1). Bubble nucleation
occurs and is evidenced by a shift to smaller diameters in the bubble size distribution (Figure 3.5F) and by an
increase of the bubble number density (Figure 3.5E). After this initial increase, the bubble number density
decreases continuously in the interval between 810°C (t=120 minutes) and 790°C (t=165 minutes) (Figure 3.5E)
while the bubble fraction increases to 0.13 (Figure 3.5B). Although the crystal fraction increases in this interval
to 0.54 at 790°C (t=165 minutes), Vp reaches a plateau at 5.30 km/s and Vs only slightly increase from 2.99 to
3.00 km/s (Figure 3.5A). At 770°C (t=210 minutes), the acquired microstructure is similar to the final one at
690°C (Figure 3.5B). The interstitial rhyolite melt (Table 3.1) contains a plagioclase fraction of 0.54 and a bubble
fraction of 0.13. Vp continuously increases from 770°C to 690°C (from t=210 to t=390 min) to 5.47 km/s at a
mean rate of -2.2 (±0.2) × 10-3 km/s/°C. The relative evolution of Vs mimics the one of Vp although its absolute
change in amplitude is considerably lower (Figure 3.5A). Indeed, the difference in velocities at the beginning
and at the end of the experiment is higher for compression wave velocity (ΔVp=0.46 km/s) than for shear wave
velocity (ΔVs=0.16 km/s).
Chapter 3 Seismic Properties of Crystallizing Magmas
28
Figure 3.5: Evolution of seismic properties of the sample cooled at 0.5 °C/min and its associated microstructure. (A) Compression (green circle) and shear (purple circle) wave velocities measured during the crystallization of the bubble-bearing haplotonalite melt. The trends have been divided into three intervals: (CR05a) crystallization and bubble nucleation; (CR05b) crystallization and bubble coalescence; (CR05c) temperature derivative of the bubble- and crystal-bearing melt. (B) Temporal evolution of the crystal (square), melt (cross) and bubble (triangle) fractions. (C) Temporal evolution of the spherulite number density. (D) Temporal evolution of the spherulite diameter. The orange stars correspond to the average value for one specific time. (E) Temporal evolution of the bubble number density. (F) Evolution of the bubble size distribution (normalized bubble fraction as a function of bubble diameter) for various time steps. Each curve has been normalized to the highest number of bubbles measured for a specific time.
Chapter 3 Seismic Properties of Crystallizing Magmas
29
Figure 3.6: Evolution of seismic properties of the sample cooled at 0.1 °C/min and its associated microstructure. (A) Compression (green circle) and shear (purple circle) wave velocities measured during the crystallization of the bubble-bearing haplotonalite melt. The trends have been divided into four intervals: (CR01a) temperature derivative of the bubble-bearing melt and outgassing; (CR01b) crystallization and bubble nucleation; (CR01c) bubble coalescence; (CR01b) temperature derivative of the bubble- and crystal-bearing melt and textural maturation. (B) Temporal evolution of the crystal (square), melt (cross) and bubble (triangle) fractions. (C) Temporal Evolution of the spherulite number density. (D) Temporal evolution of the spherulite diameter. The orange stars correspond to the average value for one specific time. (E) Temporal evolution of the bubble number density. (F) Evolution of the bubble size distribution (normalized bubble fraction as a function of bubble diameter) for various time steps. Each curve has been normalized to the highest number of bubbles measured for a specific time.
Chapter 3 Seismic Properties of Crystallizing Magmas
30
3.4.2 MICROSTRUCTURE: COOLING RATE OF 0.1 °C/MIN
From 850°C to 795°C, i.e. during the first 525 minutes of the experiment cooled at a rate of 0.1 °C/min,
compression and shear wave velocities slowly increase with a mean rate of -4.0 (±0.1) × 10-3 and -1.8 (±0.2)
×10-3 km/s/°C , respectively (Figure 3.6A and Table 3.3). The bubble size distribution (dominant peak around 6
µm) and the bubble fraction, i.e. 0.04 (±0.02), remain constant during this interval and are basically identical to
the initial conditions (Figure 3.6F and 3.6B, respectively). Substantial crystallization of plagioclase initiates 570
minutes after the beginning of the experiment at T= 790 °C (Figure 3.6B). From 790°C down to 770°C (between
t=570 and t=750 minutes), seismic velocities increase from 5.20 to 5.71 km/s for Vp and from 2.98 to 3.08 km/s
for Vs (Figure 3.6A). During this interval, the crystal and bubble fractions increase up to 0.58 and 0.09,
respectively (Figure 3.6B). The bubble number density first increases from 142 to 1510 mm-2 between 790 and
785°C (between t=570 and t=615 minutes) and subsequently slowly decreases to 905 mm-2 at T=770°C and
t=750 minutes (Figure 3.6E). By decreasing the temperature from 770°C to 750°C (t=750 and 930 minutes), we
observe a decrease in the compression wave velocities down to 5.66 km/s (Figure 3.6A), although the crystal
and bubble contents remain nearly constant (Figure 3.6B). The spherulite number density amounts to 1.71 mm-
2 and the bubble number density is 1010 mm-2 at 755°C (t=885 minutes) (Figure 3.6C and 3.6E). From 750°C
(t=930 minutes) to the end of the experiment (at t=1335 minutes and T=700°C), Vp and Vs are increasing
linearly at a mean rate of -6.9 (±0.3) × 10-3 and -1.82 (±0.07) × 10-3 km/s/°C, respectively (Figure 3.6A). The only
microstructural parameter changing during this period is the spherulite number density, which increases to 5
mm-2 (Figure 3.6C).
3.4.3 MICROSTRUCTURE: INTERPRETATION
The seismic velocity trends measured for the sample cooled at 0.5 °C/min can be divided into three intervals.
The first interval (interval CR05a in Figure 3.5A) lasts 120 minutes, i.e. down to 810°C, and is dominated by
crystallization and bubble nucleation of tonalitic melt. The compression wave velocity increases by 5 % at a
mean rate of -6.5 (±0.8) × 10-3 km/s/°C during this first interval. The second interval between 810°C and 770°C
(interval CR05b in Figure 3.5A)) is characterized by a constant Vp value of 5.30 km/s that most likely results
from bubble coalescence which attenuates the increase due to crystallization and temperature decrease. The
final increase in compression wave velocity cannot be directly linked to any major changes in the
microstructure and is, thus, attributed to the temperature decrease. This third interval, i.e. interval CR05c in
Figure 3.5A, is characterized by a temperature derivative of the compression wave velocity of the final bubble-
and plagioclase-bearing rhyolite melt of -2.2 (±0.2) × 10-3 km/s/°C.
Upon cooling of the bubble-bearing tonalite melt at a rate of 0.1 °C/min, the measured Vp and Vs significantly
change. We divided the measured seismic velocity trend into four intervals. From 850 to 790°C, (interval CR01a
in Figure 3.6A), no crystallization occurs. However, inspection of the microstructures reveals that the largest
bubbles could have outgassed during this first interval. The second interval (from 790 to 770°C) is dominated by
the crystallization of ~60 vol% of spherulitic plagioclase generating an increase of 9 % in the compression wave
Chapter 3 Seismic Properties of Crystallizing Magmas
31
velocities at a mean rate of -2.4 (±0.3) × 10-2 km/s/°C. We attributed this continuous increase in Vp to be due to
a continuous increase of crystal content. However, the sample quenched at t=615 minutes (T=785°C) is
characterized by a large crystal and bubble fractions, as well as a large spherulite and bubble number densities.
This microstructure could be generated during the quench process due to a large degree of super-saturation.
During the second interval (interval CR01b in Figure 3.6A), the bubble number density increase suggests bubble
nucleation induced by crystallization. Coalescence of these newly formed bubbles characterizes the third
interval (interval CR01c in Figure 3.6A) and induces a decrease of Vp of 0.7 % at a mean rate of 2.5 (±0.2) × 10-3
km/s/°C. The last interval, i.e. interval CR01d in Figure 3.6A, is characterized by a textural maturation of the
plagioclase spherulites, which tends to decrease their sizes. This phenomenon may favor additional outgassing
of the sample thereby contributing to the recorded velocity increase at a rate of -6.9 (±0.3) × 10-3 km/s/°C.
3.5 DISCUSSION
The observed microstructures demonstrate the occurrence of crystallization, bubble nucleation and
coalescence and correlate with the seismic velocity measurements. In order to better understand the relation
between each of these processes and the seismic properties of magmas, we first estimated the seismic
velocities characterizing them as a suspension of solid grains in a fluid using the Reuss lower bound equation
(e.g. Mavko et al., 2009). We then compare the results with the measured seismic velocities and separated the
effect of bubble nucleation and coalescence from crystallization.
The calculation of the Reuss lower bound VReuss involves the weighted mean of the seismic wave velocities of
each of the involved phases as follow:
1
Re( )plag plag
uss
plag melt
VV V
(1)
where Φplag is the crystal fraction comprised between 0 and 1, Vplag and Vmelt are the seismic velocities in km/s
of the crystal phase and the melt phase respectively. This approach requires an estimation of the seismic
velocities of each phase for every temperature. For the melt phase, we measured the temperature derivatives
of compression and shear waves velocities of the starting material (tonalitic melt + 0.04 bubble fraction).
Temperature was kept below 650 °C to avoid any crystallization but higher than 440 °C, above the glass
transition temperature, to ensure liquid-like behavior of the sample. The equations derived from the measured
Vp and Vs are:
3
( ) 1.75( 0.05) 10 6.43( 0.07)p meltV T (2)
3
( ) 1.31( 0.04) 10 3.92( 0.02)s meltV T (3)
Chapter 3 Seismic Properties of Crystallizing Magmas
32
where T is the temperature in °C and Vp(melt) and Vs(melt) are the compression and shear wave velocities in km/s.
For the crystalline phase, data on the seismic properties of albite aggregates at high pressure and high
temperature are not available. In order to estimate the contribution of plagioclase, we thus used the pressure
derivative of its sodic end-member, an albitite from Sylmar (USA) measured by Simmons (1964) and the
temperature derivative of its calcic end-member, an anorthosite from Tanaelv Belt (Norway/Finland) measured
by Kern et al. (1993). These two samples are aggregates of randomly oriented plagioclase and do not have any
significant seismic anisotropy. Combining the two provides a first order estimate of the bulk seismic velocities
of the crystalline phase in the form of:
4
(plag) 1.84( 0.06) 10 6.65( 0.01)pV T (4)
5
s(plag) 9.99( 0.04) 10 3.61( 0.01)V T (5)
Figure 3.7: Compression (green diamonds) and shear (purple circles) wave velocities as a function of the crystal fraction. Dark colored symbols represent measured values; light colored symbols represent values calculated using the Reuss lower bound equation. The dashed lines have been drawn for visual purposes only.
3.5.1 EFFECT OF CRYSTALLIZATION
By comparing the variation of the crystal content and the seismic velocities as a function of time (representing
decreasing temperature), we observe that the crystal content is the principal parameter influencing the seismic
properties of the investigated magmas. Crystallization is thus inducing an increase in both measured and
calculated compression and shear waves velocities. Caricchi et al. (2008) demonstrated that this increase is
non-linear. Indeed, the formation of a crystal network at crystal fractions higher than 0.5 produces a non-linear
increase of both Vp and Vs. This characteristic is observed in our experiments as well (Figure 3.7). At crystal
fractions lower than 0.45, the maximum increase observed for a total difference in crystal fraction of 0.41 is 4
% for Vp and 2 % for Vs. In contrast, at crystal fractions higher than 0.45, Vp increases by 8 % and Vs by 5 % for a
Chapter 3 Seismic Properties of Crystallizing Magmas
33
much smaller difference in crystal fraction of only 0.14. Crystallization has, therefore, the strongest influence
on the seismic properties of magma above a critical crystal fraction.
The Reuss lower bound is a good estimation of the seismic velocities characterizing a suspension of solid grains
in a fluid (e.g. Mavko et al., 2009). The difference observed between the calculated values and our
measurements (Figure 3.7) are, thus, attributed to the presence of bubbles in addition to crystals.
3.5.2 EFFECT OF BUBBLE NUCLEATION
In our experiments, bubble nucleation occurs by water exsolution induced by crystallization of anhydrous
phases (plagioclase). Its effect on the seismic velocities is thus best appreciated in the first time interval of the
experiment cooled at a rate of 0.5 °C/min (interval CR05a in Figure 3.5A) and in the second interval of the
experiment cooled at a rate of 0.1 °C/min (interval CR01b in Figure 3.6A). These intervals are characterized by
simultaneous crystallization and bubble nucleation. Therefore, the effect of crystallization has to be considered
and subtracted in a first step.
Figure 3.8: Seismic velocities of the sample cooled at 0.5 °C/min as a function of temperature. Dark colored diamonds represent measured values; light colored diamonds are calculated values using the Reuss lower bounds (equation 1). The red and blue lines are the temperature derivatives of the bubble-bearing melt (measured) and the plagioclase aggregates (from equations 4 and 5), respectively. (A) Compression wave velocities. (B) Shear wave velocities.
For a cooling rate of 0.5 °C/min, Vp increases by 5 % (from 5.01 to 5.27 km/s) and Vs by 3 % (from 2.88 to 2.97
km/s) between 850 and 810°C (Figure 3.8). Comparatively and for the same variation of crystal fraction (i.e. 13
to 47%), the theoretical Reuss lower bound would increase by 9 % (from 5.11 to 5.62 km/s) for Vp and by 8 %
(from 2.88 to 3.14 km/s) for Vs. If this calculated effect of crystallization is subtracted from our measurements,
bubble nucleation results in a decrease of 4 % in Vp and 5 % in Vs.
For a cooling rate of 0.1 °C/min, Vp increases by 10 % (from 5.15 to 5.71 km/s) and Vs by 4 % (from 2.96 to 3.08
km/s) between 795 and 770°C (Figure 3.9). For the same amount of crystallization, i.e. for a crystal fraction of
0.58, the Reuss lower bound increases by 13 % (from 5.04 to 5.82 km/s) for Vp and by 9 % (from 2.87 to 3.15
Chapter 3 Seismic Properties of Crystallizing Magmas
34
km/s) for Vs. Subtracting the effect of crystallization from our experimental results, we obtain a decrease
induced by bubble nucleation of 3 % in compression and 5 % in shear wave velocities respectively.
Figure 3.9: Seismic velocities of the sample cooled at 0.1 °C/min as a function of temperature. Dark colored diamonds represent measured values; light colored diamonds are calculated values using the Reuss lower bounds (equation 1). The red and blue lines are the temperature derivatives of the bubble-bearing melt (measured) and the plagioclase aggregates (calculated from equation 4 and 5), respectively. (A) Compression wave velocities. (B) Shear wave velocities.
Although the bubble fraction increases only by 0.01, the appearance of a large amount of small bubbles
produces a significant decrease in measured seismic velocities. Similar behavior, but with a larger magnitude,
has been observed in previous studies involving bubbly water. The addition of gas bubbles critically decreases
the seismic properties of the mixtures in a logarithmic fashion, i.e. over the first percent of bubbles, the sound
speed decreases by 90%, from ~1500 m/s for pure water to ~150 m/s for water containing 0.8 % of bubbles
(Gibson, 1970; Kieffer, 1977). The density variation is not sufficient to account for this large variation in the
sound speed and it is, thus, attributed to the large increase in compressibility (Temkin, 2005). In their numerical
model involving bubble-bearing basaltic melt, Marchetti et al. (2004) applied equations of seismic velocities
derived for low-viscosity liquids, i.e. bubbly water, in order to better estimate variations in physical properties
of magmas (Figure 3.10). In our experiments, we observed that the decrease in seismic velocities due to bubble
nucleation could be similarly linked to an increase of the compressibility in a bubble-bearing melt. However,
increasing the confining pressure and increasing the melt viscosity (compared to measurements made on water
at 1 atm) prevent a strong decrease in seismic velocities (Kieffer, 1977; Ichihara et al., 2004; Ichihara and
Kameda, 2004). Consequently, the addition of a large amount of small bubbles in melts at high pressure and
high temperature decreases the seismic wave velocities only up to 5 %.
3.5.3 EFFECT OF BUBBLE COALESCENCE
Bubble coalescence is observed in interval CR05b (Figure 3.5A) and in interval CR01c (Figure 3.6A). Interval
CR05b is characterized by a constant Vp value of 5.30 km/s and a slight increase of Vs from 2.99 to 3.00 km/s.
Interval CR01c displays a decrease of Vp of less than 1 % (from 5.71 to 5.66 km/s) and an increase of Vs of less
than 1 % (from 3.08 to 3.10 km/s).
Chapter 3 Seismic Properties of Crystallizing Magmas
35
Bubble coalescence is thus producing less significant variations in seismic velocities than bubble nucleation.
This phenomenon is additionally linked to the variation of compressibility as function of bubble fraction.
Compressibility calculated by Marchetti et al. (2004) is strongly increasing for low bubble fraction but this
increase is much less pronounced when the bubble fraction exceeds 0.1 (Figure 3.10). In our experiments, the
bubble fraction is significantly increasing prior to or during bubble coalescence. Following equations derived for
low viscosity bubble-bearing liquids (Gibson, 1970; Kieffer, 1977), the compressibility of our sample containing
0.12 bubble fraction would not increase enough to affect the measured wave propagation velocities.
Consequently, the increase in compressibility at relatively low density contrast leads to large decrease in
seismic properties during bubble nucleation and less or no variation during bubble coalescence.
Figure 3.10: Variation of (A) density, (B) compressibility and (C) longitudinal wave propagation velocity in function of the void fraction calculated for basaltic melts nucleating bubbles by decompression (modified from Marchetti et al. (2004)). The shaded area represents the variation of properties with the addition of a bubble fraction of 0.1.
3.5.4 EFFECT OF OUTGASSING
Depending on the cooling rate, post-mortem evaluation of samples from the experiments conducted with the
Paterson apparatus reveals that the samples contain different amounts of bubbles. The bubble fraction
amounts to 0.12 in the experiment cooled at 0.5 °C/min and to 0.04 in the experiment cooled at 0.1 °C/min.
This difference strongly suggests the occurrence of outgassing during the lower cooling rate experiments most
likely caused by the 3.5 times longer duration of the experiments. As the samples are sealed into Au capsules,
the setup of the MHC experiments prevents outgassing of the samples during run time as well as during rapid-
quench. Consequently, microstructure observations of these latter experiments corresponding to various time
steps in the Paterson apparatus did not support any outgassing evidence.
Additionally, by comparing the calculated and the measured seismic velocities of interval CR01a (Figure 3.9),
we observed that the temperature derivatives of Vp (-4.0 (±0.1) × 10-3 km/s/°C) and Vs (-1.8 (±0.2) ×10-3
Chapter 3 Seismic Properties of Crystallizing Magmas
36
km/s/°C) are slightly higher than the temperature derivatives of the starting material (-1.75 (±0.05) × 10-3
km/s/°C for Vp and -1.31 (±0.04) × 10-3 km/s/°C for Vs) measured at lower temperature. This shift is interpreted
to be due to the outgassing of large bubbles.
3.6 SUMMARY AND APPLICATION TO NATURAL SYSTEM
Magmatic processes occurring in (sub)volcanic environments have been recognized and identified through the
measurement of seismic velocities in the laboratory. Compression and shear wave velocities increase non-
linearly during crystallization. At crystal fractions higher than 0.45, the formation of a crystal network favors
the propagation of seismic waves through magmas. However, bubble nucleation induced by crystallization
produces an increase in magma compressibility thereby lowering the wave propagation velocities. These two
processes occurring simultaneously have thus competing effects on the seismic properties of magmas. In
addition, when the bubble fraction is less than 0.1, the decrease in seismic velocities is more pronounced than
for larger bubble fractions. The effect of bubble coalescence on elastic properties is distinctly lower than the
effect of bubble nucleation.
Processes linked to the formation and growth of bubbles are, thus, lowering the increase of seismic velocities
induced by crystallization. In our experiments, the difference in compression wave velocities between melts
containing crystal fraction from 0 to 0.51 is as low as 0.5 km/s due to the presence of bubbles. The detection of
these small variations in velocities could be possible but difficult for conventional methods used to determine
the location and size of magmatic chambers. For example, tomographic data inferred from the inversion of
first-arrival times from local earthquakes are highly dependent on the spatial sampling (Chouet, 2003). Thus, a
large number of earthquakes with a high magnitude and a random spatial distribution should be collected by a
dense seismometers network in order to achieve high resolution and precision. This configuration is highly
improbable over a long period of time. Small variation of seismic properties induced by crystallization and
bubble nucleation in magmatic chambers can hardly be estimated with these methods.
However, improvement in tomographic techniques involving ambient seismic noise can achieve a
measurements resolution on the order of 0.05 % with a minimum of only two seismic receivers (Duputel et al.,
2008). Brenguier et al. (2008) monitored the ambient seismic noise at Piton de la Fournaise (Reunion Island,
France) over a period of 18 months. Each eruption is preceded by a decrease in relative seismic velocities
changes of 0.05 to 0.1 %, which is interpreted as an inflation of the volcanic edifice due to the pressurization of
the magma chamber. Indeed, when the pressure in a magma chamber is high enough, the wall rocks may crack
due to the applied stress (e.g. Jellinek and DePaolo, 2003) and these newly formed cracks induce a decrease in
elastic moduli (e.g. Heap et al., 2010). In view of our results, the variation in velocity observed by Brenguier et
al. (2008) could be similarly linked to (1) an increase in the melt fraction or (2) to bubble nucleation induced by
crystallization. However, a more precise interpretation could be assessed only through laboratory
measurements at pressure and temperature conditions similar to the basaltic magma chambers of Piton de la
Fournaise. In addition, as seismic velocities in magmas are strongly frequency-dependent, these measurements
Chapter 3 Seismic Properties of Crystallizing Magmas
37
should be adequately scaled for frequency, as discussed previously by Caricchi et al. (2008). Consequently, by
continuously monitoring small seismic velocity perturbations and by combining these data with laboratory
measurements of seismic velocities, evolution of the physical state of magmatic reservoir could be assessed
more precisely.
3.7 ACKNOWLEDGMENTS
This research was supported by Swiss National Foundation (grant 200020_140578 and 200020_132878). We
wish to thank: Robert Hoffmann for his precious technical support and Marie Violay for her scientific support at
the Rock Deformation Laboratory of ETH Zurich. In addition, we would like to thank Mike Heap, an anonymous
reviewer and the editor Ulrich Faul for their detailed and constructive comments that helped improving this
paper. We note that there no data sharing issues since all of the numerical information is provided in the
figures produced by solving the equations in the paper. The raw data are stored in the Rock Deformation
Laboratory at ETH, Zurich, and are available upon request ([email protected]).
Chapter 3 Seismic Properties of Crystallizing Magmas
38
3.8 TABLES
Table 3.1 : Compositions in wt% of the starting material, the interstitial glass and the plagioclase measured by electron microprobe. *The nominal composition corresponds to the composition of the powder before the HIP. **Water and CO2 contents have been measured by KFT and by coulometry respectively.
Sample SiO2 Al2O3 CaO Na2O H2O CO2
Total
HIP: Nominal Composition* 65.69 18.56 3.33 7.61 2.80 2.00
100
HIP: Measured Composition 64.96 18.78 3.49 7.46 2.78** 0.03**
97.47
Exp. 0.5°C/min: t=75 min (melt) 65.35 16.96 2.47 7.05 - -
91.83
Exp. 0.5°C/min: t=120 min (melt) 70.83 12.95 1.34 5.68 - -
90.08
Exp. 0.5°C/min: t=165 min (melt) 72.66 12.09 1.06 5.78 - -
91.59
Exp. 0.5°C/min: t=390 min (melt) 74.19 9.82 0.72 4.75 - -
89.48
Exp. 0.5°C/min: t=75 min (plag.) 61.86 23.74 5.38 8.08 - -
99.05
Exp. 0.5°C/min: t=120 min (plag.) 61.50 23.37 5.37 7.96 - -
98.20
Exp. 0.5°C/min: t=165 min (plag.) 62.95 23.28 5.53 8.04 - -
99.80
Exp. 0.5°C/min: t=390 min (plag.) 62.02 23.55 5.06 8.51 - -
99.14
Exp. 0.1°C/min: t=603 min (melt) 71.83 12.06 1.09 4.41 - -
89.40
Exp. 0.1°C/min: t=701 min (melt) 73.63 10.60 0.87 4.08 - -
89.18
Exp. 0.1°C/min: t=861 min (melt) 77.19 10.97 1.01 4.93 - -
94.10
Exp. 0.1°C/min: t=925 min (melt) 73.85 10.93 1.35 3.98 - -
90.10
Exp. 0.1°C/min: t=1335 min (melt) 75.47 10.03 1.28 3.87 - -
90.65
Exp. 0.1°C/min: t=603 min (plag) 61.20 24.32 5.57 8.09 - -
99.18
Exp. 0.1°C/min: t=701 min (plag) 62.65 23.14 4.78 8.48 - -
99.05
Exp. 0.1°C/min: t=861 min (plag) 62.90 23.69 5.18 8.14 - -
99.91
Exp. 0.1°C/min: t=925 min (plag) 62.96 23.43 5.23 8.08 - -
99.70
Exp. 0.1°C/min: t=1335 min (plag) 63.13 23.55 5.08 8.34 - -
100.09
Chapter 3 Seismic Properties of Crystallizing Magmas
39
Table 3.2: Summary of measured seismic velocities and microstructures at a cooling rate of 0.5 °C/min.
T [°C] t [min] Vp [km/s] Vs [km/s] Φcrystal [n.u.]
Φmelt [n.u.]
Φbubble [n.u.]]
SND [1/mm2]
BND [1/mm2]
850 30 5.01 2.88 0.13 0.79 0.06 0.60 157
830 75 5.16 2.94 0.40 0.52 0.06 2.50 985
810 120 5.27 2.97 0.42 0.42 0.05 2.50 880
790 165 5.29 2.99 0.52 0.33 0.11 2.18 725
770 210 5.30 3.00 0.54 0.36 0.10 1.92 823
750 255 5.34 3.04
730 300 5.39 3.05
710 345 5.44 3.06
690 390 5.47 3.04 0.51 0.33 0.12 1.52 917
Table 3.3: Summary of measured seismic velocities and microstructures at a cooling rate of 0.1 °C/min.
T [°C] t [min] Vp [km/s] Vs [km/s] Φcrystal [vol%]
Φmelt [vol%]
Φbubble [vol%]
SND [1/mm2]
BND [1/mm2]
850 30 4.94 2.86
845 75 4.95 2.87 0.0 0.95 0.05 0.00 136
840 120 4.96 2.88
835 165 5.00 2.91
830 210 5.01 2.91
825 255 5.03 2.92
820 300 5.06 2.93
815 345 5.07 2.94 0.00 0.97 0.03 0.00 177
810 390 5.09 2.95
805 435 5.12 2.95 0.00 0.95 0.05 0.00 149
800 480 5.14 2.94
795 525 5.15 2.96 0.00 0.97 0.03 0.00 142
790 570 5.20 2.98
785 615 5.30 3.00 0.54 0.34 0.10 2.17 1506
780 660 5.39 3.06
775 705 5.47 3.07 0.50 0.40 0.10 1.65 1284
770 750 5.71 3.08 0.58 0.31 0.09 1.94 905
765 795 5.70 3.08
760 840 5.68 3.08 0.57 0.30 0.10 1.71 1014
755 885 5.67 3.09
750 930 5.66 3.10 0.59 0.30 0.09 4.95 908
745 975 5.69 3.10
740 1020 5.71 3.11
735 1065 5.76 3.12 0.61 0.27 0.09 5.90 2219
730 1110 5.79 3.13
725 1155 5.81 3.15
720 1200 5.85 3.15
715 1245 5.87 3.16
710 1290 5.94 3.17
700 1335 6.01 3.18 0.60 0.34 0.04 4.47 918
Chapter 3 Seismic Properties of Crystallizing Magmas
40
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Chapter 4 Seismic Properties of Hydrous Phonolite
42
4 LABORATORY MEASUREMENTS OF SEISMIC VELOCITIES AT HT-HP
CONDITIONS IN HYDROUS PHONOLITE FROM TEIDE VOLCANO, TENERIFE, CANARY ISLANDS
Tripoli Barbara1, Giordano Daniele2, Cordonnier Benoit3, Ulmer Peter1
1 Institute of Geochemistry and Petrology, Earth Sciences Department, ETH Zurich
2 Earth Sciences Department, Università degli Studi di Torino
3 No Affiliation
4.1 ABSTRACT
Seismic tomography performed under active volcanoes usually reveal low velocity zones interpreted as magma
chambers feeding volcanic eruptions. However, some volcanoes, such as Teide in Tenerife, Canary Islands, lack
evidences of a large magmatic reservoir. Measurements of seismic velocities at high pressure and high
temperature performed on hydrous melt are fundamental for a better understanding of seismic tomography
images. In order to better constrain the magmatic system at Teide volcano, new laboratory measurements of
seismic velocities of natural hydrous phonolite have been performed at pressure from 150 to 300 MPa and
temperature from 100 to 550°C. The temperature derivatives of seismic velocities are constant at temperature
lower than the glass transition. In the region characterized by liquid-like behavior, compression and shear wave
velocities vary significantly in function of the dissolved water content. The increase in temperature derivatives
of phonolite liquid is higher at water content lower than 1 wt%.
The data recorded in the region characterized by liquid-like behavior have been extrapolated to magmatic
temperatures (850 to 950°C) and combined to calculated seismic properties of prominent phenocrysts in the
investigated phonolite. The resulting seismic velocities vary between 4.4 and 5.0 km/s for a magma chamber
containing 30 to 40 vol% crystals. Various hypotheses concerning the magmatic plumbing system of Teide may
be related to the higher velocities observed in the currently available seismic tomography images (García-
Yeguas et al., 2012). These hypotheses include (1) the absence of a large eruptible magmatic reservoir, (2) a
magma chamber smaller than 3 km thickness, (3) a network of sills and dykes producing small magma pockets,
or (4) a cooling magma chamber containing more than 60 vol% crystals.
4.2 INTRODUCTION
Knowledge on the physical properties of magmas at high pressure and high temperature is prerequisite for a
better and more fundamental understanding of the magmatic plumbing system ultimately feeding volcanic
edifices. Indeed, parameters such as seismic velocities are fundamental for an accurate interpretation of
Chapter 4 Seismic Properties of Hydrous Phonolite
43
seismic tomography performed in volcanic environments. Laboratory measurements of elastic parameters
have been performed on melt of various compositions (Askarpour et al., 1993; Schilling et al., 2003; Webb and
Courtial, 1996). Seismic velocities decrease continuously with increasing temperature until the glass transition
temperature is attained. This temperature range corresponds to a transition in the physical properties of the
melt from a solid-like (low temperature) to a liquid-like behavior (high temperature). By crossing this region, a
marked increase of the temperature derivative of the compressional wave propagation velocity is observed.
This discontinuity is distinctly less pronounced for shear waves.
Although both mafic and silicic magmas can contain up to at least 6 wt% of dissolved water at depth (e.g.
Sisson and Layne, 1993; Hervig et al., 1989), studies on the effect of water on the seismic properties of magmas
are scarce. Experiments using Brillouin scattering spectroscopy have been performed on glasses with variable
composition and dissolved water content at room temperature (Richet and Polian, 1998; Malfait et al., 2011;
Whittington et al., 2012). Compression and shear wave velocities decrease linearly with the addition of water
for rhyolitic and andesitic glasses but remain relatively constant for depolymerized basaltic glasses (Malfait et
al., 2011). With increasing alkalinity of the investigated glasses, the addition of water results in increasing
seismic velocities (Whittington et al., 2012).
The studies mentioned above investigated the effect of water on the seismic properties of glasses at room
conditions. Data collected at temperature ensuring the liquid-like behavior of silicate are lacking to date. In this
study, compression and shear wave velocities have been measured at high pressure and high temperature on
hydrated phonolite collected in Tenerife, Canary Islands.
4.2.1 PHONOLITE AT TEIDE VOLCANO
The volcanic activity in Tenerife, Canary Islands, can be divided into three main phases: (1) a mafic alkaline
shield that forms about 90% of the island (e.g. Ancochea et al., 1990); (2) a Central complex subdivided into a
Lower Group dominated by mafic to intermediate compositions, and an Upper Group dominated by felsic
compositions. This volcanic cycle is characterized by explosive eruptions and triggered three caldera collapses
(e.g. Martí and Gudmundsson, 2000); (3) the active Teide and Pico Viejo stratovolcanoes which erupted a
significant volume of phonolitic magmas, and the volumetrically smaller basaltic rifts (e.g. Ablay and Martí,
2000).
Phonolites produced during the third volcanic cycle contain variable amount of crystals. The Roques Blancos
eruption (1714 BP) is characterized by a crystal content of approximatively 14 vol%, being mainly anorthoclase
(13.7 vol%) and to a lower extent biotite, magnetite, diopside and ilmenite. In order to determine the storage
conditions prior to the eruption, Andújar et al. (2013) compared the mineral compositions and fractions in
natural samples and in hydrous samples synthetized at various pressure and temperatures in the laboratory.
They concluded that the Roques Blancos phonolite was stored at 900 ± 15 °C, 50 ± 15 MPa, with about 2.2 wt%
H2O dissolved in the melt. In contrast, prior Teide phonolites as the products of the Montañas Blancas eruption
(2020 BP) are nearly aphyric and contain 1 to 4 vol% of crystals of anorthoclase, biotite, clinopyroxene,
Chapter 4 Seismic Properties of Hydrous Phonolite
44
magnetite/ilmenite and apatite (Andújar and Scaillet, 2012). Phase equilibrium experiments suggests that the
magma chamber was at 850 ± 15 °C, 50 ± 20 MPa with melt containing 2.5 ± 0·5 wt% H2O. Higher temperature
and pressure conditions have been inferred from the same type of experiments for the storage conditions of
the most recent Lavas Negras (1150 BP), i.e. 900 ± 20 °C, 150 ± 50 MPa, with 3 ± 0.5 wt% dissolved H2O in the
melt (Andújar et al., 2010). The product of this eruption contains up to 37 vol% phenocrysts (anorthoclase: 32
vol%, clinopyroxene: 2 vol%, magnetite: 3 vol%).
Although the crystal content varies considerably, these phonolites are chemically similar (Andújar and Scaillet,
2012). Interestingly, phonolitic eruptions at Teide are characterized by a wide range of eruptions styles, ranging
from effusion of thick lava flows to sustained explosive eruptions generating thick and widespread fallout
deposits (e.g. García et al., 2012). Phase equilibrium experiments revealed the importance of pre-eruptive
conditions, such as pressure and water content dissolved in the melt, on the dynamics and on the location, i.e.
summital (e.g. Lavas Negras) versus flank vents (e.g. Montañas Blancas; Roques Blancos), of the eruptions
(Andújar and Scaillet, 2012; Andújar et al., 2013). The identification of subvolcanic magma reservoirs at Teide
volcano would thus help to assess future volcanic activity. However, recent seismic tomography images lack
evidences of a low velocity zone common marker of magmatic chambers (García-Yeguas et al., 2012; Barros et
al., 2012).
In order to better constrain the magmatic system at Teide volcano, new laboratory measurements of seismic
velocities of natural hydrous phonolite have been performed at pressure from 150 to 300 MPa and
temperature from 100 to 550°C. We first emphasize the effect of water on the elastic properties of phonolite at
HP-HT. Extrapolation of these results to magmatic conditions are combined with seismic properties of mineral
assemblage characteristic of these phonolite.
4.3 METHODS
4.3.1 GLASS SYNTHESIS
Natural samples from the Lavas Negras lava flows (Teide, Tenerife) were melted in air at 1600°C for 24 hours
and quenched. The recovered glass was crushed and subsequently mixed with the desired amount of distilled
water in order to obtain several hydrous phonolitic glasses, i.e. 0.1, 1.0, 2.0 and 3.0 wt% H20. The mixtures
were cold pressed into stainless steel canisters with a uniaxial pressure of 200 MPa. Molybdenum foils lining
the border of the canister avoided contamination from the wall. Glass synthesis was performed in a Hot
Isostatic Press (HIP) at 1200 °C and 200 MPa for 24 hours. In order to obtain crystal-free samples, the glass-
bearing canisters were first cooled at a rate of 60°C/min to 650°C. This temperature corresponds to a
temperature higher than the glass transition temperature of 613°C of the sample containing nominally 0.1 wt%
H2O (Giordano et al., 2008). The temperature was ultimately decreased to room temperature at a rate of
0.6°C/min to prevent thermally induced cracks. Drill cores of 30 mm length and 22 mm diameter were
extracted from the glasses to perform elastic property measurements.
Chapter 4 Seismic Properties of Hydrous Phonolite
45
Karl Fisher Titration has been used on all glasses before and after experiments to assess the bulk water content
(Table 4.1). The data presented represent averages of at least 3 individual analyses. We determined the major
element composition of the recovered experimental samples with a JEOL JXA-8200 electron microprobe
employing a 20 µm beam diameter, 10 kV acceleration voltage and 20 nA beam current. The homogeneity of
the samples was assessed by measuring the composition at various locations (Table 4.1). The data presented
are the average of at least 10 analyses.
Figure 4.1: Schematic drawing of the HP-HT Paterson apparatus implemented with the setup to measure seismic velocities.
4.3.2 SEISMIC VELOCITY MEASUREMENTS
Seismic velocities of the hydrous phonolites were measured in a Paterson-type internally-heated gas pressure
apparatus (Paterson and Olgaard, 2000). Piezoelectric transducers placed at both extremities of the assembly
permit the in-situ measurement of compression and shear wave velocities using the pulse transmission
technique (Birch, 1960). The vibration frequency applied to the transducers was 1 MHz. The alumina rods in the
assembly have a 2 mm diameter hole allowing insertion of thermocouples at the bottom and top of the sample
(Figure 4.1). The temperature difference between these two thermocouples never exceeded 5°C. The assembly
is isolated from the gas pressure medium (argon) by an iron jacket of 0.2 mm wall thickness. The time delay
caused by the stack of alumina rods was determined at various pressure and temperature conditions
employing a fused silica glass rod. Most seismic property measurement experiments were performed at a
constant pressure of 250 MPa. Some additional measurements were obtained at 150, 200 and 300 MPa on the
more hydrated samples to assess the effect of pressure. Samples were first heated at a rate of 10°C/min to the
highest temperature (between 500 and 550°C depending on the water content). Ultrasonic velocities were
Chapter 4 Seismic Properties of Hydrous Phonolite
46
recorded every 20 to 50 °C while decreasing the temperature at a rate of 10 °C/min. In order to allow the
sample and the assembly to equilibrate at the new thermal condition, constant temperature was maintained
during a minimum of 20 minutes prior to recording the arrival times and waveforms. The error on the
measurements is dominated by the picking of the first arrival (for additional details on data processing, see
Caricchi et al., 2008) and reaches 0.1 km/s for compression wave velocity and 0.2 km/s for shear wave velocity.
After the termination of the experiments, the density of the core samples was determined by measuring their
volume with a helium pycnometer and by weighing them with a high precision balance. The error on the
measured density amounts to 0.001 kg/cm3.
4.4 RESULTS
4.4.1 GLASS SYNTHESIS
After synthesis in the HIP, the water content of the glass was determined by Karl Fisher Titration (KFT). The
sample containing nominally 0.1 wt% H20, i.e. LN1, resulted in water contents higher than expected, whereas
samples containing nominally more than 1 wt% H20 lost some water (Table 4.1). All glasses are compositionally
homogeneous and do not contain any crystals except for LN4 and LN5 that contain 1.4 and 3.5 vol% of iron
oxides, respectively. In order to quantify the influence of these microlites on the seismic properties, we
calculated the Voigt-Reuss-Hill average VVRH using the following equations:
𝑉𝑉𝑅𝐻 = 𝑉𝑉𝑜𝑖𝑔𝑡+𝑉𝑅𝑒𝑢𝑠𝑠
2 (1)
𝑉𝑉𝑜𝑖𝑔𝑡 = ∑ 𝛷𝑖 ∗ 𝑉𝑖𝑁𝑖=1 (2)
1
𝑉𝑅𝑒𝑢𝑠𝑠= ∑
𝛷𝑖
𝑉𝑖
𝑁𝑖=1 (3)
where VVoigt is the Voigt upper bound, VReuss is the Reuss lower bound, Φi is the fraction of the ith component
and Vi is the seismic velocity (of shear or compression waves) of the ith component (e.g. Mavko et al., 2009).
Assuming a compression wave velocity Vp of 6.04 km/s for the phonolite glass (Seifert et al., 2013) and 7.35
km/s for the iron oxides (data for a magnetite crystal taken from Ji et al., 2002), the Voigt-Reuss-Hill average is
6.06 and 6.08 km/s for a crystal content of 1.4 and 3.5 vol%, respectively. Concerning the shear wave velocity
Vs, we adopted a velocity of 3.59 km/s for the phonolite glass (Seifert et al., 2013) and 4.2 km/s (Ji et al., 2002)
for the magnetite. The calculated velocities are 3.60 and 3.61 km/s for a crystal content of 1.4 and 3.5 vol%,
respectively. The error induced by the presence of microlites is within the error of the measurements, i.e. 0.1
km/s for Vp and 0.2 km/s for Vs.
Chapter 4 Seismic Properties of Hydrous Phonolite
47
4.4.2 EFFECT OF TEMPERATURE ON SEISMIC VELOCITIES
While increasing temperature, the seismic velocities of the phonolite samples display the behavior previously
observed for silicate melts (Askarpour et al., 1993; Schilling et al., 2003; Webb and Courtial, 1996).
Compression and shear wave velocities continuously decrease with increasing temperature until a critical
temperature Tc (Figure 4.2). This temperature corresponds to a transition in the physical properties from a
solid-like (low temperature) to a liquid-like behavior (high temperature). Above this temperature, the
temperature derivative of wave propagation velocity becomes significantly steeper.
Figure 4.2: Compression (A) and shear (B) wave velocities measured in phonolite containing different amount of H2O. The glass transition temperature has been determined for each sample as the intersection between linear regressions obtained for the liquid-like (dashed lines) and the solid-like behavior (full lines).
4.4.3 EFFECT OF WATER CONTENT ON TEMPERATURE DERIVATIVES
Although the seismic velocities generally decrease with the addition of dissolved water (Figure 4.2), the four
hydrous phonolite display identical temperature derivatives of the compression wave velocities dVp/dT of -5.10
(±0.02) *10-4 km/s/°C at temperatures less than Tc (Figure 4.3). The temperature derivative of shear wave
velocities dVs/dT in the region characterized by solid-like behavior are slightly increasing with decreasing water
content. Above Tc, variable water content result in much larger variations in the temperature derivatives
(Figure 4.3). The LN5 (1.87 Wt.% H2O) super-cooled liquid displays a dVp/dT of -3.03*10-3 km/s/°C whereas LN1
(0.36 Wt.% H2O) results a dVp/dT of -1.71*10-3 km/s/°C for LN1. This difference in temperature derivatives is
lower for shear wave velocities ranging from -2.02*10-3 km/s/°C for LN5 to -1.27*10-3 km/s/°C for LN1.
Chapter 4 Seismic Properties of Hydrous Phonolite
48
Figure 4.3: Variation of the temperature derivatives of compression (dark symbols) and shear (light symbols) wave velocities as a function of the water content above (green squares) and below (purple circles) the glass transition temperature.
The critical temperature Tc is as well dependent on the water content. Calculated as the intersection between
the linear regressions of the solid-like and the liquid-like seismic velocities, Tc differs slightly for regressions
done for Vs and Vp measurements (Table 4.2). The difference does not exceed 8 °C for samples containing more
than 0.5 wt% H2O, i.e. LN5, LN4 and LN3, but reaches 13 °C for LN1. However, Tc derived from both Vp and Vs
varies non-linearly with the addition of dissolved water (Figure 4.4).
Figure 4.4: Glass transition temperatures Tg as a function of water concentration dissolved in the melt. The seismic Tg (crosses) were obtained from the intersections of the temperature dependence of compression wave velocities of solid-like and liquid-like behavior (Figure 4.2). Solid lines represent Tg at various cooling rates calculated with equations 4 and 5.
Chapter 4 Seismic Properties of Hydrous Phonolite
49
4.4.4 EFFECT OF PRESSURE ON SEISMIC VELOCITIES
Temperature derivatives of sample LN5 (1.87 Wt.% H2O) have been determined at 150, 200, 250 and 300 MPa.
Below Tc, compression wave velocities Vp are slightly higher at lower pressure but converge to the same values
above Tc (Figure 4.5A). Shear wave velocities displays the inverse pattern, i.e. Vs collected at lower pressure are
slightly lower at temperature above Tc (Figure 4.5B). Although some variations in the seismic velocities can be
observed, the data collected at various pressures are within the error of the measurements. We thus assumed
that Vp and Vs are not pressure-dependent over the range of investigated pressures.
Figure 4.5: Compression (A) and shear (B) wave velocities of samples containing 1.87 wt% H2O at various pressures. The variation of velocities at pressures from 150 to 300 MPa are within the error of the measurements.
4.5 DISCUSSION
4.5.1 GLASS TRANSITION
The critical temperatures Tc defined in this paper as the intersection between temperature derivatives of
seismic velocities at low and high temperature have previously been attributed to the glass transition
temperature Tg (e.g. Schilling and Sinogeikin, 2003; Askarpour et al., 1993). The glass transition is associated
with the theory of visco-elasticity and the structural relaxation timescale of silicate melt (e.g. Dingwell and
Webb, 1989). When a stress is applied to a melt, two possible reactions are expected, either, (1) liquid-like and
entirely viscous (Newtonian) behavior revealing the relaxed state of the material; or (2) solid-like and entirely
elastic behavior at small strains but brittle under large strains (Dingwell, 1997). These two states are separated
by a viscoelastic region where non-Newtonian rheology can be observed (Webb and Dingwell, 1990). This
particular behavior describes the inability of the melt to relax on the timescale of the experiment (Dingwell,
1997). Being dependent on the kinetics, the glass transition temperature of silicate melts is thus a temperature
range rather than a single temperature. However, this transition is often observed through marked variations
Chapter 4 Seismic Properties of Hydrous Phonolite
50
in the temperature derivatives of physical properties, such as thermal expansion (e.g. Knoche et al., 1995),
seismic velocities (e.g. Askarpour et al., 1993) or specific heat capacity (e.g. Moynihan et al., 1974).
Giordano et al. (2005) estimated Tg of hydrous phonolite through the measurement of specific heat capacity by
Differential Scanning Calorimetry (DSC) at cooling rates varying from 5 to 20 °C/min. Their glass transition
temperatures are significantly higher than the values obtained in this study, i.e. approximatively 80 °C for a
cooling rate of 10°C/min (Table 4.2). There is, however, a significant difference between a cooling experiment
conducted in DSC and the seismic velocity measurements as conducted in this study. During our experiments,
the temperature was maintained constant for 20 minutes prior to measuring the seismic velocities. This dwell
time was required to allow for thermal equilibration of the entire assembly in order to obtain accurate velocity
measurement. The bulk cooling rate in our experiments, therefore, resulted to be 1.3°C/min, considerably
lower than 10°C/min on the temperature cooling segments alone.
In order to extrapolate the data of Giordano et al. (2005) to lower cooling rate, viscosity η of hydrous phonolite
was calculated for each Tg measured by DSC using an empirical Vogel-Fulcher-Tammann (VFT) equation
(Giordano et al., 2009):
𝑙𝑜𝑔10𝜂 = −4.55 + (10261 − 26.21(𝐻2𝑂))/(𝑇𝑔 − 263.8 + 257.8𝑙𝑜𝑔10(1 + (𝐻2𝑂))) (4)
where Tg is the glass transition temperature in K and H2O is the water content in wt%. As viscosity is linearly
proportional to cooling rate (Scherer, 1984; Gottsman et al., 2002; Stevenson et al., 1995), extrapolation to
lower cooling rates is obtained through a regression in the form of:
𝑙𝑜𝑔10(𝜂) = 𝑘 − 𝑙𝑜𝑔10(𝑞) (5)
where q is the cooling rate in °C/min and k is a composition dependent shift factor (Gottsman et al., 2002).
Linear regressions between the calculated viscosity at Tg and the cooling rate provided by Giordano et al.
(2005) have a slope lower than 1 ( Figure 4.6 and Table 4.3). For the precision of our calculation, we have thus
introduced a parameter A as the slope of the regressions. A and k are estimated for each water content (Table
4.3). Calculated Tg using equations 4 and 5 are plotted in Figure 4.4 as a function of water content for various
cooling rates. Glass transition temperatures derived from the temperature derivatives of compression and
shear wave velocities, i.e. elastic Tg, correspond to a cooling rate of 10-4 °C/min, except for LN3 which lies
outside the calculated trends. This cooling rate is much lower than the bulk cooling rate applied during our
experiments, i.e. approximatively 1.3 °C/min.
This discrepancy could be linked to the relaxation time τ of the sample, which is calculated using the simplified
Maxwell relationship:
𝜏 =𝜂
𝐺∞ (6)
Chapter 4 Seismic Properties of Hydrous Phonolite
51
where η is the viscosity in Pas and G∞ is the shear modulus at infinite frequency approximated to a constant
value of 10 GPa (Dingwell and Webb, 1990). ). The calculated relaxation time of the samples is less than 20
minutes at temperature above the seismic Tg (Table 4.4). These calculations reveal that the structure of the
super-cooled liquid had sufficient time to relax during the 20 minutes dwell time and appeared as thermally
stable before the seismic velocity measurements were taken. The shift between the Tg measured by Giordano
et al. (2005) and our seismic Tg can thus be explained by the difference in the structural relaxation state of the
investigated samples. Indeed, at constant cooling, magmas store the stress generated from the thermal
contraction and are in a visco-elastic unrelaxed condition. If enough time is given to release this stress, the
sample returns to a relaxed liquid state.
Figure 4.6: Linear dependence of the viscosity at the glass transition temperature as a function of the cooling rate applied to hydrous samples (data from Giordano et al., 2005).
4.5.2 DENSITY
Density has been measured on the post-experiment samples at room conditions using a gas displacement
pycnometer (Table 4.2). In order to assess the variation of density during our experiments, the volumes of
silicate liquids are calculated as a function of composition, pressure and temperature (Carroll and Holloway,
1994) using an equation in the form of:
𝑉𝑙𝑖𝑞 = ∑ 𝑋𝑖 [�̅�𝑖,𝑇𝑟𝑒𝑓,𝑃𝑟𝑒𝑓+
𝑑𝑉𝑖
𝑑𝑇∗ (𝑇 − 𝑇𝑟𝑒𝑓) +
𝑑𝑉𝑖
𝑑𝑃∗ (𝑃 − 𝑃𝑟𝑒𝑓)] (7)
where Xi is the mole fraction of the ith oxide component, T is the temperature, P is the pressure, V̅i is the
partial molar volume of the ith oxide component, dV̅i/dT is the temperature derivative of V̅i and dV̅i/dP is the
pressure derivative of V̅i (parameters are given in Table 4.5). Density of silicate melt ρliq is calculated using the
following relationship:
Chapter 4 Seismic Properties of Hydrous Phonolite
52
𝜌𝑙𝑖𝑞 =∑ 𝑋𝑖∗(𝑀.𝑊.)𝑖
𝑉𝑙𝑖𝑞 (8)
where (M.W.)i is the molecular weight of the ith oxide component. Figure 4.7 provides the results of the
density calculations as a function of water content for all samples investigated at a pressure of 250 MPa and a
temperature corresponding to the glass transition temperature estimated from the seismic velocities
measurements. Although the density measured by pycnometry is always somewhat lower than the calculated
density, the calculated and measured values are within the errors identical. The density variation induced by
the decrease of temperature and pressure in the solid-like state, i.e. glassy state, is thus lower than the errors.
This feature has been observed by Malfait et al. (2014) on glasses of various compositions quenched and
decompressed from HT-HP. By comparing their measurements of glasses and calculated properties of melts
using their equations of state, they observed that glasses preserve the configuration induced by pressure and
temperature at Tg. For the calculation of the elastic properties, we are thus assuming that the density at
temperature lower than Tg remains constant.
Figure 4.7: Density as a function of the dissolved water in the melt. Densities were determined on recovered experimental charges by He pycnometry and calculated using equations 7 and 8 at the P-T conditions corresponding to the seismic Tg.
4.5.3 ELASTIC PROPERTIES
Shear (G) and bulk (K) moduli (Table 4.4) have been calculated at various temperatures from the measured
seismic velocities (Vp, Vs) and from the calculated density (ρ) using the following relationships:
𝐺 = 𝑉𝑠2 ∗ 𝜌 (9)
𝐾 = 𝜌 ∗ (𝑉𝑝2 −
4
3∗ 𝑉𝑠
2) (10)
Chapter 4 Seismic Properties of Hydrous Phonolite
53
Elastic moduli of phonolitic glasses have previously been determined at room temperature by Whittington et
al. (2012). As observed by Malfait et al. (2014) for density, the measured elastic properties of their phonolite
reflect the properties frozen at the glass transition temperature. Their measurements of bulk and shear
modulus are compared to our measurements at the glass transition temperature in Figure 4.8. Although their
synthesis pressure was 300 MPa and their phonolite has a different composition, our measurements give
similar results and follow the same trend within error. Yet the addition of water in glasses slightly decreases the
elastic moduli.
Figure 4.8: Variation of bulk (green diamonds) and shear (purple circles) modulus as a function of water content. Our data (dark symbols) are calculated at the seismic Tg using equations 9 and 10. The data from Whittington et al. (2012) (light symbols) are plotted for comparison.
However, the temperature dependency of the elastic properties above Tg depends significantly on the
dissolved water content (Figure 4.9). For the same temperature difference, the bulk and shear moduli of the
sample containing more water decrease steeper than for the sample with the lowest water content. This
feature could be linked to the efficiency of water to depolymerize silicate melt. At constant temperature, the
addition of less than 1 wt% H2O in melts decreases the viscosity by orders of magnitudes (e.g. Dingwell et al.,
1996; Richet et al., 1996). This effect levels out when the water content is further increased (Ardia et al, 2008).
Temperature derivatives of elastic moduli, and thus seismic velocities, are similarly affected by water content
above Tg.
4.5.4 APPLICATION TO THE MAGMATIC CHAMBER OF TEIDE VOLCANO
The measured compression wave velocity of hydrous phonolite has been employed to evaluate the seismic
properties of a potential magma chamber under the Teide volcano. First, our results were fitted from a
regression analysis into:
Chapter 4 Seismic Properties of Hydrous Phonolite
54
𝑉𝑝(𝑚𝑒𝑙𝑡) = 7.00 − 𝑙𝑜𝑔10(1 + 𝐻2𝑂) ∗ 1.28 − 𝑇 ∗ 2.47 ∗ 10−3 (11)
where Vp(melt) is the compression wave velocity of the melt in Km/s, H2O is the water content in wt% and T is the
temperature in °C. This regression has been used to extrapolate the experimental data set to magmatic
temperature conditions. As the recorded seismic velocities in the liquid-like state were performed on fully
relaxed samples, we are confident about the temperature extrapolation up to 1000 °C. Pressure has not been
included into the calculation as we infer only insignificant changes in seismic velocities due to pressure
variation over the range 100-300 MPa.
Figure 4.9: Contour map of compression wave velocity in function of water content and temperature, calculated using equation 11.
The Teide phonolites contain up to 40 vol% crystals. Therefore the effect of crystals has to be considered and
was taken into account in our calculation by using the Voigt upper bound and the Reuss lower bound, which
are the best estimations of the highest and lowest expected seismic velocities of a suspension of solid grains in
a fluid (e.g. Mavko et al., 2009). The Voigt upper bound VVoigt and the Reuss lower bound VReuss were calculated
using equation 2 and 3, respectively. The seismic velocities of the crystals corresponding to the phenocrysts
contained in the Lavas Negras, i.e. anorthoclase, clinopyroxene and magnetite, have been calculated using
Perple_X (Connolly, 2009). This thermodynamic model permits computation of elastic properties of minerals
depending on their compositions. We thus selected mineral compositions similar to the Lavas Negras
phenocrysts (Table 4.6) and computed the seismic velocity of each crystal phase following an equation in the
form of:
𝑉𝑝(min) = 𝑉0(𝑚𝑖𝑛) +𝑑𝑉𝑝(𝑚𝑖𝑛)
𝑑𝑇∗ 𝑇 +
𝑑𝑉𝑝(𝑚𝑖𝑛)
𝑑𝑃∗ 𝑃 (12)
where P is the pressure in bar and V0(min), dVp(min)/dT and dVp(min)/dP are constants listed in Table 4.6. We
calculated the Voigt and Reuss bounds at conditions relevant for the Lavas Negras prior to eruption (Andújar et
Chapter 4 Seismic Properties of Hydrous Phonolite
55
al., 2010), i.e. at a pressure of 150 MPa for a melt containing initially 2 wt% water. The water content in the
melt is increasing as function of the crystal content in order to simulate the effect of close system
crystallization. The anorthoclase fraction increases from 0 to 35 vol%, the clinopyroxene fraction from 0 to 2
vol% and the magnetite fraction from 0 to 3 vol%.
The seismic velocity of the magma chamber containing the phonolitic Lavas Negras varies between 5 km/s
(Voigt upper bound in Figure 4.10A) and 4.4 km/s (Reuss lower bound in Figure 4.10B) depending on the
temperature and the total crystal content. In case a large magmatic chamber is currently present under the
Teide volcano, it should be observable in the seismic tomography images provided by García-Yeguas et al.
(2012). These images reveal close to the surface, i.e. in the first 2-3 km, zones having a velocity comprised
between 3.5 and 5 km/s and interpreted as volcaniclastic sediments and hydrothermal deposits. At higher
depth, compression wave velocities are increasing from ~5.5 km/s at 4 km depth to more than 7.0 km/s at 8 km
depth. Low velocity zones are not observed.
Figure 4.10: Contour maps of the Voigt upper bound (A) and Reuss lower bound (B) in km/s as a function of the total crystal content and temperature. The shaded area represents the inferred condition of the magma chamber feeding the Lavas Negras eruption (Andújar et al., 2010).
Consequently, four hypotheses are possible. The first involves the total absence of a magmatic chamber under
Teide volcano. However, this hypothesis is in contradiction with the seismic activity in 2004 suggesting
magmatic intrusion (Cerdeña et al., 2011; Almendros et al., 2007). The second hypothesis involves a magma
chamber too small to be detected by seismic tomography. Considering that one of the largest volume phonolite
eruption at Teide was about 1 km3 (Roques Blancos; Andújar et al., 2013), it is possible that the magma
chamber is smaller than the resolution of the tomography image provided by García-Yeguas et al. (2012), i.e. 3
km. It is as well possible that the magmatic system under Teide is not characterized by a unique magma
chamber but by a network of more isolated and thin dykes and sills leading to a value which tends towards the
country rock one. This third hypothesis has been previously raised by Barros et al. (2012) who identified
scattering structures probably related to a complex network of dykes and sills. Petrologic evidences actually
Chapter 4 Seismic Properties of Hydrous Phonolite
56
support a complex structure producing multiple small magmatic reservoirs (Andújar et al., 2013). Finally, the
crystal content could be much higher at depth than the erupted product. Indeed, the phonolite erupted at
Teide volcano may have been extracted from a ‘mushy’ zone and would thus reflect mainly the residual melt
(Dávila-Harris et al., 2013; Sliwinski et al., in review).
4.6 CONCLUSION
Seismic velocities have been measured at high pressure and high temperature conditions in hydrous phonolites
from the Teide volcano. At temperature lower than the glass transition, compression wave velocities vary
between 5.7 and 5.9 km/s and shear wave velocities vary between 3.3 and 3.6 km/s. Their temperature
derivatives are independent of the dissolved water content. Upon crossing the glass transition, temperature
derivatives of both, compression and shear wave velocities, significantly increase. This increase is accentuated
by the addition of water following a trend previously observed for melt viscosity. Indeed, the increase in
temperature derivatives of seismic velocities is higher at low water content. Measured seismic glass transition
temperatures and calculated relaxation times suggest that measurements in the liquid-like state have
predominantly been performed on relaxed samples.
Combining the experimental results of this study with calculated seismic properties of relevant mineral phases
forming prominent phenocrysts in the investigated phonolite provides insights into the magmatic system
potentially present beneath the Teide volcano. The resulting seismic velocities vary between 4.4 and 5.0 km/s
for a magma chamber at 850 to 950 °C and containing 30 to 40 vol% crystals. In the currently available seismic
tomography images of the area (García-Yeguas et al., 2012), higher velocities are observed, i.e. from ~5.5 km/s
at 4 km depth to more than 7.0 km/s at 8 km depth. The absence of a low velocity zone leads to hypotheses
involving (1) the absence of a large eruptible magmatic reservoir, (2) a magma chamber smaller than 3 km
thickness, (3) a network of sills and dykes producing small magma pockets, or (4) a cooling magma chamber
containing more than 60 vol% crystals.
Chapter 4 Seismic Properties of Hydrous Phonolite
57
4.7 TABLES
Table 4.1: Compositions of hydrous phonolite from Lavas Negras (Tenerife, Spain) in wt.%. Major elements are determined by electron microprobe. The water content was measured by Karl Fisher Titration. Td_ph - composition of phonolite from Montañas Blancas (Tenerife, Spain) used in the study of Giordano et al. (2005).
LN5 LN4 LN3 LN1 Td_ph
SiO2 60.16 60.23 60.65 60.39 60.46
Al2O3 18.33 18.52 18.66 18.58 18.81
FeO (tot) 3.04 3.36 3.37 3.44 3.31
TiO2 0.63 0.67 0.68 0.68 0.56
MnO 0.19 0.19 0.20 0.21 0.20
MgO 0.32 0.35 0.37 0.36 0.36
CaO 0.73 0.72 0.71 0.72 0.67
Na2O 8.74 9.05 9.19 9.24 9.76
K2O 4.72 4.75 4.84 4.85 5.45
P2O2 ---- ---- ---- ---- 0.06
H2O 1.87 1.37 0.56 0.36 ----
Nominal H2O 3.00 2.00 1.00 0.10 ----
Total 98.74 99.21 99.23 98.84 99.64
Table 4.2: Comparison of measured properties between sample containing different water contents. The calorimetric Tg are calculated from data of Giordano et al. (2005) and corresponds to the onset of Tg, i.e. the temperature where the specific heat capacity starts to deviate, at a cooling rate of 10 °C/min.
LN5 LN4 LN3 LN1
H2O [wt%]
1.87 1.37 0.56 0.36
Density [g/cm3]
2.459 2.475 2.487 2.500
Seismic Tg [°C] Vp 320 336 382 459
Vs 329 335 380 473
Calorimetric Tg [°C]
408 426 455 542
T. deriv. below Tg dVp/dT -5.12 -5.12 -5.10 -5.14 [10-4 km/s/°C]
dVs/dT -4.93 -3.81 -3.92 -3.24
T. deriv. above Tg dVp/dT -3.03 -2.67 -2.21 -1.71 [10-3 km/s/°C] dVs/dT -2.02 -1.89 -1.46 -1.27
Chapter 4 Seismic Properties of Hydrous Phonolite
58
Table 4.3: Glass transition temperatures of hydrous phonolite measured by DSC (Giordano et al., 2005) used to derive viscosity at Tg for various cooling rate using equation 4. Parameters A and B are calculated using equation 5.
Cooling rate [°C/min]
H2O content [wt%]
0.03 0.85 0.95 2.10 3.75
Tg [°C] 20 670 522 505 456 403 15 665 516 500 451 398 10 656 509 492 446 392 5 648 501 482 434 382 1
621
log10η [Pas] 20 10.31 10.46 10.65 10.33 10.52 15 10.41 10.59 10.76 10.44 10.63 10 10.61 10.75 10.94 10.55 10.76 5 10.79 10.93 11.18 10.82 10.99 1
11.44
Parameter A 0.860 0.773 0.887 0.790 0.766 Parameter K 11.432 11.493 11.809 11.359 11.524
Table 4.4: Summary of measured seismic velocities and calculated physical properties.
Sample T [°C] Vp [km/s] Vs [km/s] ρ [g/cm3] G [Gpa] K [GPa] log10η
[Pas]
τ [min]
LN5 500 5.14 2.97 2.441 21.57 35.81 9.59 0.001
480 5.19 3.01 2.445 22.14 36.45 9.99 0.02
460 5.25 3.04 2.448 22.62 37.33 10.41 0.04
440 5.31 3.08 2.452 23.23 38.22 10.85 0.12
420 5.37 3.12 2.455 23.90 39.07 11.31 0.34
400 5.44 3.16 2.459 24.60 40.08 11.81 1.08
380 5.51 3.21 2.463 25.41 40.76 12.34 3.66
350 5.59 3.27 2.468 26.43 41.81 13.20 26.62
300 5.68 3.32 2.474 27.27 43.35
250 5.72 3.35 2.474 27.73 44.03
200 5.76 3.37 2.474 28.15 44.53
150 5.77 3.41 2.474 28.73 43.96
100 5.78 3.41 2.474 28.82 44.28
LN4 560 5.14 2.94 2.455 21.19 36.57 8.96 0.002
530 5.22 2.98 2.460 21.85 38.00 9.51 0.01
500 5.30 3.04 2.465 22.76 38.88 10.11 0.02
450 5.45 3.13 2.474 24.25 41.06 11.22 0.28
420 5.52 3.20 2.479 25.32 41.79 11.97 1.57
390 5.59 3.25 2.484 26.23 42.68 12.80 10.53
Chapter 4 Seismic Properties of Hydrous Phonolite
59
Table 4.4: Continued
Sample T [°C] Vp [km/s] Vs [km/s] ρ [g/cm3] G [Gpa] K [GPa] log10η
[Pas]
τ [min]
LN4 360 5.67 3.31 2.489 27.27 43.67
330 5.75 3.35 2.493 27.91 45.09
300 5.76 3.37 2.493 28.36 44.89
250 5.78 3.38 2.493 28.43 45.28
200 5.82 3.43 2.493 29.32 45.27
150 5.83 3.43 2.493 29.39 45.59
100 5.87 3.43 2.493 29.36 46.71
LN3 550 5.37 3.17 2.487 24.98 38.52 10.51 0.05
520 5.44 3.21 2.491 25.69 39.41 11.20 0.26
490 5.50 3.25 2.495 26.39 40.36 11.95 1.49
460 5.57 3.30 2.500 27.24 41.32 12.78 10.10
430 5.63 3.35 2.504 28.08 41.88
400 5.68 3.38 2.509 28.67 42.59
350 5.74 3.43 2.511 29.61 43.35
300 5.79 3.45 2.511 29.98 44.27
250 5.82 3.50 2.511 30.82 44.04
200 5.84 3.50 2.511 30.71 44.58
150 5.87 3.51 2.511 31.00 45.25
100 5.87 3.50 2.511 30.70 45.61
LN1 550 5.57 3.31 2.496 27.37 40.87 11.17 0.25
510 5.64 3.37 2.501 28.33 41.87 12.20 2.62
480 5.69 3.40 2.506 28.97 42.40 13.05 18.91
440 5.74 3.42 2.509 29.33 43.57
390 5.76 3.44 2.509 29.65 43.62
340 5.81 3.46 2.509 29.96 44.63
300 5.83 3.48 2.509 30.36 44.74
250 5.84 3.49 2.509 30.55 44.76
200 5.85 3.50 2.509 30.73 44.75
150 5.89 3.51 2.509 30.94 45.69
100 5.89 3.52 2.509 31.16 45.64
Chapter 4 Seismic Properties of Hydrous Phonolite
60
Table 4.5: Partial molar volumes and their pressure and temperature derivatives used for the calculation of density at experimental conditions (equations 7). References are given in parenthesis: (a) Lange, 1997; (b) Lange and Carmichael, 1987; (c) Ochs and Lange, 1999; (c) Kress and Carmichael, 1991.
V(i,1673K,1bar) [10-5 m3/mol] dV/dT [10-9 m3/mol*K] dV/dP [10-6 m3/mol*Gpa]
Si02 2.69 (a) 0.00 (a) -1.89 (d)
TiO2 2.32 (b) 7.24 (b) -2.31 (d)
Al2O3 3.74 (a) 0.00 (a) -2.26 (d)
FeO 1.37 (b) 2.92 (b) -0.45 (d)
MgO 1.17 (a) 3.27 (a) 0.27 (d)
CaO 1.65 (a) 3.74 (a) 0.34 (d)
Na2O 2.89 (a) 7.68 (a) -2.4 (d)
K2O 4.61 (a) 12.1 (a) -6.75 (d)
H2O 2.67 (c) 9.55 (c) -3.2 (c)
Table 4.6: Compositions in [wt%] and fit parameters (equation 12) of minerals included in the calculation of the magma chamber seismic properties.
Feldspar Clinopyroxene Magnetite
SiO2 66.20 53.82 0.00
TiO2 0.00 0.00 19.17
Al2O3 20.07 1.58 0.00
FeO (tot) 0.00 7.72 79.11
MgO 0.00 12.50 1.72
CaO 1.11 23.45 0.00
Na2O 7.79 0.93 0.00
K2O 4.84 0.00 0.00
V0 [km/s] 6.39 8.27 8.07
dVp/dT [km/s/°C] -4.63E-04 -5.93E-04 -2.67E-04
dVp/dP [km/s/bar] 2.63E-05 1.21E-05 5.15E-06
Chapter 4 Seismic Properties of Hydrous Phonolite
61
4.8 REFERENCES
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Mavko, G., Mukerji, T., & Dvorkin, J. (2009). The rock physics handbook: Tools for seismic analysis of porous media: Cambridge university press.
Moynihan, C. T., Easteal, A. J., Wilder, J., & Tucker, J. (1974). Dependence of the glass transition temperature on heating and cooling rate. The Journal of Physical Chemistry, 78(26), 2673-2677.
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Chapter 4 Seismic Properties of Hydrous Phonolite
63
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Chapter 5 Outgassing Induced by Crystallization
64
5 OUTGASSING INDUCED BY CRYSTALLIZATION: AN EXPERIMENTAL STUDY
Tripoli Barbara1, Marie Violay2, Cordonnier Benoit3, Ulmer Peter1
1 Institute of Geochemistry and Petrology, Earth Sciences Department, ETH Zurich
2 Laboratoire de Mécanique des Roches, ENAC, EPF Lausanne
3 No Affiliation
5.1 ABSTRACT
Volcanic eruptions style is to a first order controlled by the ability of the gas phase to separate from the
crystallizing melt. Determining the outgassing potential of a crystallizing magma chamber is thus fundamental
to understand a wide range of volcanic phenomena, from quiescent emissions of gas at the surface to explosive
plinian eruptions. In this study, we explore the effect of crystallization on the extent of outgassing of a
synthetic bubble-bearing haplotonalite melt at high pressure and high temperature. A Paterson-type internally-
heated gas pressure apparatus implemented with a pore-fluid system was employed to measure in situ the
volume of outgassed volatile during plagioclase crystallization and bubble exsolution. Samples were first
heated at 850 °C for 30 minutes. Subsequently, the temperature was decreased at a rate of 0.5 or 0.1 °C/min to
700 °C. In order to characterize the microstructure evolution, series of cold-seal experiments at identical
pressure conditions but with rapid-quenching have been conducted in addition.
The rate and extent of outgassing is directly related to the evolution of the microstructures. If no crystallization
occurs, the measured outgassing rate is fully explained by the ascent of bubbles calculated using Stoke’s law.
The presence of crystals may favor or inhibit the outgassing by (1) increasing the fraction and size of bubbles by
exsolution and decreasing the melt viscosity and (2) lowering their ascent velocity by increasing pathways
length or by acting as barriers. In our experiments, crystallization of more than 50 vol% of plagioclase in a melt
containing initially 4.2 vol% of bubbles induced outgassing of 4.6 to 6.6 vol% of bubbles over a rather limited
time. Consequently, the outgassing potential of a crystallizing magma chamber is high.
5.2 INTRODUCTION
A better understanding of the transport of gas in volcanic environment is fundamental to constrain a wide
range of volcanic phenomena, from quiescent emissions of gas at the surface to explosive plinian eruptions.
Indeed, when the rise speed of large bubbles in a volcanic conduit is faster than the ascent rate of the
surrounding basaltic magma, the volcanic activity is characterized by passive outgassing potentially
accompanied by lava flows (e.g. Slezin, 2003, Melnik et al., 2005). In silicic volcanoes, explosive hazards is
reduced when magmatic volatiles outgas through a permeable network of fractures (e.g. Gonnermann and
Manga, 2003; Castro et al., 2012). However, more explosive eruptions occur when the gas phase cannot
Chapter 5 Outgassing Induced by Crystallization
65
separate from the rapidly ascending magma (e.g. Melnik et al., 2005; Jaupart and Allègre, 1991). In addition,
when outgassing is inhibited, the volatile phase may accumulate in the magma chamber leading to a decrease
in the bulk density (e.g. Blake, 1984). The increased magma buoyancy may thus generate an overpressure
higher than the strength of the country rocks, i.e. overpressure higher than 10-40 MPa (Jellinek and DePaolo,
2003), leading to highly explosive eruptions (Malfait et al., 2014; Bachman and Bergantz, 2008; Caricchi et al.,
2014). The efficiency of outgassing is thus an important parameter in determining the eruption style.
Various studies focused on mechanisms favoring or impeding outgassing in volcanoes. Bubbles may rise
buoyantly into the magma chamber or the volcanic conduit or volcanic gas can escape through interconnected
bubbles (e.g. Gonnermann and Manga, 2007). Eichelberger et al. (1986) observed that vesicular obsidian
becomes permeable at porosity higher than 60 % whereas Klug and Cashman (1996) measured permeability
between 10-14 and 10-12 m-2 at porosity as low as 30 %. In addition, when vesicular magmas are subject to
deformation, the bubbles are elongated (e.g. Rust et al., 2003) and their connectivity is promoted (e.g. Saar and
Manga, 1999). Gas can thus escape in magmas with porosity lower than 30 % depending on bubble shape. The
crystalline phase contributes as well to the extent of outgassing. Indeed, bubbles are restricted to the melt
phase and a large amount of crystals would thus contribute to an increase of the connectivity in the residual
melt although the porosity remains low (Sparks, 2003). On the other hand, the crystalline phase, acting as
barriers, may reduce the extent of outgassing by inhibiting the ascent of bubbles (Belien et al., 2010).
The exsolution of volatiles from magmas at depth is achieved through two processes. The “first boiling” occurs
when hydrous melts are ascending towards the surface. Due to the decompression, the solubility of water
decreases and bubbles exsolve (e.g. Cashman and Blundy, 2000). The second process that causes the volatile
exsolution from the silicate melt is due to crystallization at constant pressure. Known as “second boiling”, this
process is activated by a cooling magma chamber which leads to crystallization. As a consequence, the melt
becomes oversaturated in water and bubbles exsolve. In both cases, the produced gas phase could escape from
the magma chamber along fracture networks developed in the magma and in the conduit walls (Jaupart, 1998;
Rust et al., 2004).
The “first boiling” has been studied experimentally (e.g. Mangan and Sisson, 2000; Mourtada-Bonnefoi and
Laporte, 2004) and numerically (e.g. Lensky et al., 2004; Proussevitch and Sahagian, 1998). Recently, some
studies investigated the influence of decompression on the permeability of magma (Okomura et al., 2012,
Namiki and Manga, 2008). However, until now, no studies investigated the outgassing potential from “second
boiling”. Indeed, technical challenges related to pore fluid confinement impeded reproducing the pressure and
temperature conditions typical of volcanoes. We surpassed this limitation thanks to the technical
improvements of the Paterson apparatus at the Rock deformation laboratory of ETHZ, equipped with a
purpose-built pore pressure system (Violay et al., 2015). This allowed us to explore the effect of crystallization
on the extent of outgassing of a synthetic haplotonalite magma at high pressure and high temperature by
measuring in situ the volume of outgassed volatile.
Chapter 5 Outgassing Induced by Crystallization
66
5.3 METHODS
5.3.1 SAMPLE SYNTHESIS
In order to study the effect of crystallization on the extent of outgassing of magmas, we synthetized a
chemically simplified tonalite melt (Table 5.1), which is prone to crystallize plagioclase (Picard et al., 2011).
First, oxide and hydroxide powders were mixed to obtain the desired compositions (Table 5.1). The mixtures
have been cold pressed into stainless steel canisters with a uniaxial pressure of 200 MPa. Molybdenum foils
lining the inside of the canister avoid contamination of the melt by reaction with the wall. Subsequently, the
mixtures have been thermally equilibrated in a Hot Isostatic Press (HIP), installed in the Rock Deformation
Laboratory of ETHZ, at 1200 °C and 200 MPa for 24 hours. The vessel was then rapidly cooled at a rate of 60
°C/min to 550 °C in order to quench the samples. Subsequently, a cooling rate of 0.6°C/min was applied to
allow for thermal relaxation of the glass. The resulting hydrated glasses are chemically homogeneous and their
compositions correspond to the nominal values within 1% (Table 5.1). CO2-rich bubbles (4.2 vol%) have a
number density of 167 [1/mm2] and their sizes exhibit a narrow distribution situated around 6 µm (Figure 5.1).
The largest bubble measured is 643 µm. The glass contains less than 1 vol% of spherulitic plagioclase, with a
mean size of 150 µm. This bubble-bearing glass has been drilled into two cores of 10 mm length and 15 mm
diameter to perform measurements.
Figure 5.1: SEM image (a) of the bubble-bearing glass synthetized in the HIP and its bubble-size distribution (b).
The extent of outgassing during plagioclase crystallization was determined using a Paterson-type internally-
heated gas pressure apparatus (Paterson and Olgaard, 2000) implemented with a volumometer and upstream
and downstream pore-fluid connections. The volumometer piston has a diameter of 7 mm and a length of 50
mm, which permits to achieve an accuracy of the pore pressure (argon gas) of 0.1 MPa. Pressure sensors are
placed in the upstream and downstream pore-fluid connections. A Schaevitz LVDT placed on the axis of the
actuator measures the displacement of the volumometer piston with a resolution of 0.01 mm. The sample
assembly is composed of zirconia and alumina rods with a 2 mm hole drilled in the center for the insertion of
the pore-fluid and the thermocouple (Figure 5.2). The sample is isolated from the pore fluid pressure at the
bottom by an alumina disc. Bubbles can thus escape from the sample only through the porous top mullite disc.
This upper disc is made of Mullite C530 and has a connected porosity of 27 % and a young modulus of 60 GPa.
Chapter 5 Outgassing Induced by Crystallization
67
Figure 5.2: Schematic drawing of the assembly used in the outgassing experiments in the Paterson apparatus implemented with a pore-fluid system.
5.3.2 OUTGASSING EXPERIMENTS
We performed two different experiments. In both cases, samples were initially maintained during 30 minutes
at a constant temperature of 850 °C. Subsequently, the first sample was cooled down to 700 °C at a rate of 0.5
°C/min and the second sample down to 740 °C at a rate of 0.1 °C/min. The confining pressure was kept
constant at 250 MPa. As the precision of the volumometer is better at higher pressure, the pore-fluid pressure
Pf was initially set to 5 MPa. A gradient of 5 MPa was therefore present within the sample; The alumina discs
placed at the bottom of the sample was at a pressure equal to the confining pressure (Pc) and the porous
mullite disc placed at the top of the sample was subjected to a pressure that is equal to Pc – Pf, i.e. the top part
of the sample was at 245 MPa.
During the experiments, the position of the volumometer piston, i.e. the volume V, was kept constant. The
number of mole degassed from the sample was calculated from the variation of pore pressure assuming ideal
gas behavior:
𝑃𝑓 ∗ 𝑉 = 𝑛 ∗ 𝑅 ∗ 𝑇 (1)
where Pf is the variation of pressure measured in the volumometer in Pa, V is the volume of the pore fluid
system (assembly, pipes and volumometer) in m3, n is the number of moles degassed from the sample in mol, R
is the gas constant (8.3144621 J/(mol*K)) and T is the temperature in the volumometer in K. Although the
sample is outgassing a mixture of H2O and CO2, we used the ideal gas law as more than 90 % of the gas in the
system at the end of the experiments is argon.
Chapter 5 Outgassing Induced by Crystallization
68
As the temperature was decreased during the experiments, the pore-fluid pressure was additionally corrected
for the variation of temperature:
𝑃𝑓 = 𝑃𝑚𝑒𝑎𝑠 −𝑑𝑃𝑓
𝑑𝑇∗ 𝑇 (2)
where Pmeas is the pore-fluid pressure measured during the experiments in MPa, T is the temperature of the
sample in °C and dPf/dT is the calibrated variation of pressure as function of temperature changes. The
calibration has been done prior to the experiments using an alumina rod instead of the sample in the assembly
and resulted in a value of dPf/dT= 3.6119*104 [MPa/°C].
5.3.3 EVALUATION OF THE MICROSTRUCTURAL VARIATIONS
In order to determine the evolution of the microstructure during the experiments, the P-T conditions applied in
the Paterson apparatus have been reproduced in a rapid-quench molybdenum-hafnium-carbide (MHC) cold-
sealed pressure vessel. Placed on a rotary system, this externally heated pressure vessel permits dropping the
sample into the cold steel extremity linked to the MHC part by a water-cooled nut. This setup results in a rapid
quench of the sample at a rate exceeding 100°C/s, which allows preservation of the microstructure formed at
high temperature. The temperature gradient in the hot MHC extremity never exceeded 5 °C over the length of
the sample. Cores of 4 mm in length and in diameter, previously drilled from the starting glass and placed into
Au capsules that were welded shut, have been quenched under pressure at various time steps.
Microstructures (phase fraction, bubble number density, bubble size distribution, spherulite number density
and spherulite diameter) have been determined by evaluation of SEM images of the starting material
(synthetized in the HIP), the final samples (crystallized in the Paterson apparatus) and the quenched samples
(crystallized in the MHC cold-sealed vessel). Images were taken at a magnification of 200x over the entire
length of the final samples and over the entire capsules (16 mm2) for the quenched samples. The phase
fractions have been determined by grayscale dissociation using ImageJ. Bubbles smaller than 3 pixel units, i.e.
with a diameter smaller than 1.5 m, have been excluded from the bubble characterization. Interstitial melt
compositions have been measured with a JEOL JXA-8200 electron microprobe employing a 20 µm beam
diameter, 10 kV acceleration voltage and 20 nA beam current.
5.4 EXPERIMENTAL AND ANALYTICAL RESULTS
The evolution of the microstructure determined from the quenched samples are cooling rate dependent and
are documented in chapter 3. The magmatic processes identified through these microstructures are
summarized for both cooling rates. Additionally, we report here measurements of major elements composition
performed across large melt pockets (more than 1 mm) and on small interstitial melts (size smaller than 30
µm). Microstructures of the recovered samples from the Paterson apparatus are then characterized from the
bottom to the top of the samples. Finally, the extent and the rate of outgassing, which is as well cooling-rate
dependent, is documented as a function of time.
Chapter 5 Outgassing Induced by Crystallization
69
Figure 5.3: Volume of gas lost over time from the sample cooled at 0.5 °C/min (in green) and from the sample cooled at 0.1°C/min (in red). Figures A and B display the data corrected for the decrease in temperature (see text). The steps in the recorded data are a consequence of the resolution of the sensor. Figure C and D displays the average of each steps as well as the intervals determined from the evolution of the microstructure. Each interval correspond to specific magmatic processes.
5.4.1 INVOLVED MAGMATIC PROCESSES
The evolution of the microstructure of the sample cooled at 0.5 °C/min (CR05) can be divided into three
intervals. The first interval (interval CR05a in Figure 5.3C) lasts 120 minutes and is dominated by the
crystallization of ~40 vol% of spherulitic plagioclase which induced bubble nucleation. The second interval,
between 120 and 210 minutes (interval CR05b in Figure 5.3C), is characterized by bubble coalescence. No
major crystallization process is observed during the third interval, i.e. interval CR05c in Figure 5.3C.
Upon cooling of the bubble-bearing tonalitic melt at a rate of 0.1 °C/min (CR01), the evolution of the observed
microstructures significantly changes. We divided the trend into four intervals. During the first 570 minutes
(interval CR01a in Figure 5.3D), no crystallization occurs. The second interval (from t=570 to t=750 minutes) is
characterized by the crystallization of ~60 vol% of spherulitic plagioclase and by bubble nucleation (interval
CR01b in Figure 5.3D). Coalescence of these newly formed bubbles is observed during the third interval (from
t=750 to t=930 minutes; interval CR01c in Figure 5.3D). The last interval, i.e. interval CR01d in Figure 5.3D, is
characterized by a textural maturation of the plagioclase spherulites, which tend to decrease their sizes.
Chapter 5 Outgassing Induced by Crystallization
70
Figure 5.4: (A) SEM image of the plagioclase- and bubble-bearing glass crystallized in the Paterson apparatus (CR01). (B) Evolution of the composition of the interstitial melts of CR01 (red circles) and CR05 (green circles).
5.4.2 COMPOSITION OF THE MELT POCKETS
All recovered samples from the quenched experiments present residual melts between or within the
spherulites (Figure 5.4A) which are smaller than 30 µm. As plagioclase crystallizes, the Na, Ca and Al contents of
these melts decrease while the Si content increases (Figure 5.4B). The observed trend is linked to the
crystallization of plagioclase in a closed system, i.e. the crystals are not physically separated from the melt.
Samples cooled at 0.5 °C/min present additionally larger melt pockets, up to mm-size (Figure 5.5A). In this
section, we present the compositional data on two melt pockets observed in the sample quenched at t=75
minutes. The composition in major elements of the smaller melt pocket, i.e. 1.3 mm-thickness, is constant
through the melt pockets and corresponds within analytical error to the analyses performed on the starting
material (Figure 5.5B-D and Table 5.1)). In the larger melt pockets (~1.8 mm-thickness), the content of Al, Na
and Ca is constant through the melt pockets whereas the content of Si is varying in the 400 µm next to the
spherulite (Figure 5.5B). Indeed, Si content increases from ~75.5 mol% in the center to ~76.5 mol% close to the
crystal-melt contact. In addition, the total of measured oxides in wt% (Na2O + CaO + Al2O3 + SiO2) are
significantly decreasing from the center of the pockets, i.e total of ~97 %, to the border of the spherulites, i.e.
total of ~93 % (Figure 5.5D). This decrease of the total measured oxides is attributed to increased dissolved
water content (not measurable with the electron microprobe). The shape of the bubbles are as well different
throughout the melt pockets (Figure 5.5A). In the center, they are spherical and become more elliptic close to
the spherulite, reaching an aspect ratio of 3. In addition, these bubbles are often elongated parallel to the
crystallization front.
Chapter 5 Outgassing Induced by Crystallization
71
Figure 5.5: (A) SEM picture of large melt pockets observed in the sample cooled at 0.5 °C/min. (B) Variation of Al (red squares), Na (green circles) and Ca (blue triangles) contents measured across two melt pockets and in interstitial melt in between the spherulites (black colors). The darker colors represent the composition across a small melt pocket (from on extremity to the other) and the light colors represent the composition across a larger melt pockets (from one extremity to the center of the pocket). (C) Variation of Si concentration across the melt pockets (purple diamonds) and in interstitial melt (black diamonds). (D) Variation of the total sum of oxides, i.e. SiO2 + Na2O + Al2O3 + CaO, measured across the melt pockets (brown stars) and in interstitial melt (black stars).
5.4.3 MICROSTRUCTURES OF THE SAMPLES RECOVERED FROM THE OUTGASSING EXPERIMENTS
The final samples are divided into three parts for the description of their microstructures: the bottom part,
which is next to the alumina disc (closed from the pore pressure inlet), the central part and the top part, which
is next to the porous mullite disc (connected to the pore pressure inlet).
The sample cooled at 0.5 °C/min has a crystal fraction decreasing from 57 vol% at the bottom to 52 vol% at the
top part (Table 5.2). The melt fraction remains constant with a value of 34 vol% at the bottom and at the center
and 33 vol% at the top. Higher variation are observed for the bubble fraction. Indeed, although the bottom and
the center parts have a bubble fraction close to 10 vol%, the top part is as high as 14 vol%. The number
densities of spherulites and bubbles are constant along the samples with values of 1.8 (±0.3) mm-2 and 1290
(±80) mm-2, respectively. However, it should be noticed that the lowest value of number densities is always
Chapter 5 Outgassing Induced by Crystallization
72
situated at the top of the sample. The bubble size distribution is as well constant along the samples, with a
unique peak situated at 2-3 µm. The largest bubble diameter measured is 244 µm at the bottom, 274 µm in the
center and 527 µm in the top part.
The crystal fraction is slightly varying along the sample cooled at 0.1 °C/min (Table 5.2). At the bottom, it
reaches the highest value of 61 vol% whereas in the center and at the top, it amounts to 58 vol%. Although the
melt fraction is slightly lower at the bottom (31 vol%), we consider the melt fraction as constant along the
sample, with a value of 32 (±1) vol%. The bubble fraction is increasing from 7 vol% at the bottom to 10 vol% at
the top. Concerning the bubble number density, the bottom and the top parts have values in a narrow range,
i.e. 987 and 977 mm-2 respectively, whereas the center part has a value of 852 mm-2. The spherulite number
density at the bottom and in the center parts have similar values of 1.8 and 1.7 mm-2 respectively. However,
the top part has a higher value of 3.0 mm-2. A unique peak at 2-3 µm characterizes the bubble size distributions
measured in all three parts of the sample. The largest bubble diameter measured is 241 µm in the bottom, 329
µm in the center and 671 µm in the top part.
5.4.4 OUTGASSING MEASUREMENTS
The recorded variation of pore pressure as a function of time is characterized by a discontinuous trend, i.e. step
function (Figure 5.3A-B). The accuracy of the pore pressure sensor of 0.1 MPa leads to an accuracy of ~0.4 vol%
of gas lost by the samples. The data presented here are the average of the volume percent and the time for
each recorded “step” or “plateau” (Figure 5.3A-B).
The extent of outgassing is dependent on the cooling rate applied to the samples (Figure 5.6). The total volume
of gas lost by the sample cooled at 0.5 °C/min (CR05) is 4.6 vol% whereas it reaches 6.6 vol% for the sample
cooled at 0.1 °C/min (CR01). In addition, the rate of outgassing varies as a function of time. Sample CR05
outgassed at a rate of 1.51*10-2 vol%/min during the first 180 minutes and then the value decreased to
9.27*10-3 vol%/min. This decrease in outgassing rate occurred close to the end of interval CR05b (Figure 5.3C),
i.e. the sample already crystallized ~50 vol% of plagioclase and bubbles were coalescing.
The outgassing trend of sample CR01 follows a parabolic shape characterized by an outgassing rate of 1.10*10-2
vol%/min for the first 230 min (Figure 5.6). It then decreases down to 5.76*10-3 vol%/min during the next 360
min, until reaching a rate of 4.46*10-3 vol%/min for the last 450 min of the experiment. These shifts in
outgassing rate can generally not be attributed to any crystallization processes recognized in the evolution of
the microstructures. However, the crystallization interval CR01b coincides with the last shift in outgassing rate.
Chapter 5 Outgassing Induced by Crystallization
73
Figure 5.6: Volume of gas lost by the samples measured in experiments with a cooling rate of 0.5 °C/min (green) and 0.1 °C/min (red). Numbers indicate the outgassing rates of selected intervals along the curves.
5.5 DISCUSSION
Although the shifts in outgassing rate are not always related to crystallization processes, the rate and extent of
outgassing should be related to the evolution of the microstructure, as they are both cooling rate dependent.
Indeed, the total difference of gas lost between CR01 and CR05 (ΔVOutgassing=2.0 vol%) and the difference
between the bubble fraction averaged over both samples (ΔΦBB=2.9 vol%) are in good agreement (Table 5.2).
The increase in bubble content and in the diameter of the largest bubble of both samples supports as well a
link between outgassing and microstructure.
At a time of 390 minutes, CR01 lost 3.2 vol % of gas whereas CR05 lost 4.6 vol% (Figure 5.6). This discrepancy
could be linked to the crystallization processes as CR01 did not contain any plagioclase yet (interval CR01a in
Figure 5.3D). Along the crystallization front, the observed elongated bubbles evidence a stress field most likely
generated by the growing spherulites. This forced migration of bubbles into the residual melt favored their
connectivity and the coalescence into larger bubbles was thus enhanced. Although not observed, small
channels may have formed and would provide an efficient mechanism for gas migration.
However, no abrupt change in the outgassing rate is observed after 570 minutes, i.e. when plagioclase starts to
crystallize in CR01. The absence of an increase in the outgassing rate could be linked to an evolution of the
bubble size distribution at the onset of crystallization. Indeed, during these 390 minutes, the largest bubbles
could have had time to rise through the sample. This hypothesis is tested by estimating the ascent velocity
uascent of the largest bubbles from Stoke’s law as follow:
𝑢𝑎𝑠𝑐𝑒𝑛𝑡 = −2∗(𝜌𝐵𝐵−𝜌𝑚)∗𝑔∗𝑟2
9∗𝜂 (3)
where ρBB and ρm are the densities, in g/m3, of the bubble and the melt respectively, g is the gravitational
acceleration in m/s2, r is the bubble radius in m and η is the viscosity of the melt in Pas. Although the bubbles
Chapter 5 Outgassing Induced by Crystallization
74
contain a mixture of CO2 and H2O, we calculated the bubble density assuming that only water is present and
using equation 1. In order to assess the melt density, the volume of silicate melt is first calculated as a function
of composition, pressure and temperature (Carroll and Holloway, 1994) using an equation in the form of:
𝑉𝑚 = ∑ 𝑋𝑖 [�̅�𝑖,𝑇𝑟𝑒𝑓,𝑃𝑟𝑒𝑓+
𝑑𝑉𝑖
𝑑𝑇∗ (𝑇 − 𝑇𝑟𝑒𝑓) +
𝑑𝑉𝑖
𝑑𝑃∗ (𝑃 − 𝑃𝑟𝑒𝑓)]
(4)
where Xi is the mole fraction of the ith oxide component, T is the temperature, P is the pressure, V̅i is the
partial molar volume of the ith oxide component, dV̅i/dT is the temperature derivative of V̅i and dV̅i/dP is the
pressure derivative of V̅i (parameters are given in Table 5.3). Density of silicate melt ρm is calculated using the
following relationship:
𝜌𝑚 =∑ 𝑋𝑖∗(𝑀.𝑊.)𝑖
𝑉𝑚 (5)
where (M.W.)i is the molecular weight of the ith oxide component. Finally, the viscosity η is calculated using a
Vogel-Fulcher-Tammann equation:
log 𝜂 = 𝐴𝑉𝐹𝑇 +𝐵𝑉𝐹𝑇
𝑇−𝐶𝑉𝐹𝑇 (6)
where T is the temperature in K and AVFT, BVFT and CVFT are the pre-exponential factor, the pseudo-activation
energy and the VFT temperature respectively. BVFT and CVFT are calculated using the model of Giordano et al.
(2008). As Pistone et al. (2012) observed a difference of 2 log units between viscosities measured in the
laboratory and calculated using this model, they modified the pre-exponential factor to -6.55. Indeed, the
model of Giordano et al. (2008) does not take into account the viscosity of chemically simplified non-natural
synthetic melts. In addition, the viscosity and the density of silicate melt are strongly dependent on the water
content (e.g. Dingwell et al., 1996; Ochs and Lange, 1999) which is known only for the starting material, i.e.
2.72 wt%. We thus estimated the variation of water content in residual melt as a function of crystal content by
mass balance calculation (Table 5.4). As the water content is limited by its solubility, we calculated the highest
amount of dissolved water by using the model of Papale et al. (2006). The solubility limit of water in our melt
composition is 5.9 wt%.
By simplifying the problem to non-interacting rising bubbles in a homogeneous media (diluted approximation),
we calculated the amount of outgassing in function of time using a numerical model written in Matlab. The
bubbles were placed randomly into the sample with a size distribution based on our measurements. This
bubble size distribution measured in 2D on the starting material was fitted into a Weibull distribution. We used
Monte Carlo simulations to test the influence of bubbles initial positions and small fluctuations in their bubble
size distribution with a control function to keep their fraction between 3 and 5 vol%.
Chapter 5 Outgassing Induced by Crystallization
75
Figure 5.7: Dependence of the calculated viscosity η in Pas (A) and density ρ in kg/m3 (B) of the melt as a function of temperature and water content. The red circles represent the variation of η and ρ of the melt cooled at a rate of 0.1 °C/min and the green circles represent the variation of the melt cooled at 0.5 °C/min.
5.5.1 COOLING RATE OF 0.1°C/MIN
Following this approach, we observe that the calculated viscosity and density of the melt vary non-linearly
along the experiments cooled at 0.1 °C/min (Figure 5.7). Before the onset of crystallization, the logarithm of the
melt viscosity of CR01 increased from 3.03 at t=75 minutes to 3.56 Pas at t=525 minutes and the melt density
had a near constant value of ~2310 kg/m3. This increase in viscosity due to the cooling of the sample strongly
affects and continuously decrease the rising velocity of bubble (Figure 5.8A). The calculation of the distance
covered by bubble during this time reveals that, at t=570 min, two third of the sample volume will be depleted
in bubble larger than 600 µm and that one third is depleted in bubble larger than 400 µm. Indeed, during the
first 200 minutes, the calculated rate of outgassing using the Monte Carlo simulations is similar to our
measurements (Figure 5.9A and B). The rate of outgassing at the beginning of the experiment is thus fully
explained by the rise of large bubbles. At t>200 minutes, the calculated and the measured rates are diverging.
During their ascent to the top of the sample, bubbles may have interacted and coalesced into larger bubbles.
Such interaction is not considered in our calculations (Figure 5.9A and B). In the measurements, the larger rate
of outgassing between 200 and 600 minutes might thus be linked to bubble coalescence. Indeed, larger
bubbles, having a higher buoyancy, rise faster and are thus contributing to a larger increase in the volume of
outgassing.
At the onset of crystallization, the rate of outgassing increased due to a lower melt viscosity. An increase of 0.5
to 1 vol% of gas lost is observed in the simulations between 570 and 800 minutes (Figure 5.9A and B). In our
measurements, a larger increase between discrete data at 600 and 650 minutes is found (arrow in Figure 5.3B).
Although the difference of 0.5 vol% is close to the resolution of the method, i.e. 0.4 vol%, the similarity in time
and amount of gas lost is noteworthy. After this increase, the rate of measured outgassing was constant and
higher than the calculated rate of outgassing. This difference may be linked to bubble exsolution and
coalescence driven by crystallization.
Chapter 5 Outgassing Induced by Crystallization
76
Figure 5.8: Travel distance of bubbles during the experiment cooled at 0.1 °C/min (A) and 0.5 °C/min (B) calculated using
equation 3. Numbers indicate the different bubble radius (in µm) used in the calculations. The sample length (10 mm) is
as well displayed.
The rate of outgassing is thus mainly dependent on the viscosity and on the evolution of bubble size
distribution along the experiment cooled at 0.1 °C/min. If the bubble size distribution slightly varies in the
Monte Carlo simulation, the trends of outgassing are similar but the total amount of outgassing may vary
between 2.8 and 4.6 vol% (Figure 5.9A). On the other hand, the position of bubbles in the sample does not
affect the rate of outgassing (Figure 5.9B). This behavior is as well observable when the sample is cooled at 0.5
°C/min (Figure 5.9C and D).
Chapter 5 Outgassing Induced by Crystallization
77
Figure 5.9: Evolution of the volume of gas lost calculated using a Monte Carlo simulation (light blue to dark areas) and measured with the Paterson apparatus (points). (A) and (B) are the results for a cooling rate of 0.1 °C/min and (C) and (D) are results for a cooling rate of 0.5 °C/min. The plots on the left hand side (A and C) displays simulations considering various bubble size distributions. The simulations displayed on the right hand side (B and D) considered various bubbles positions within the sample.
5.5.2 COOLING RATE OF 0.5°C/MIN
The logarithm of the melt viscosity of CR05 decreased from 2.73 Pas to a minimum of 2.08 Pas at t=165
minutes due to the increase in water content and then increased to 2.87 Pas due to the cooling of the sample
(Figure 5.7). The variation in melt density follows a similar trend by decreasing first from 2290 to 2220 kg/m3 at
t=210 and then increasing up to 2230 kg/m3. Including the evolution of viscosity and density in equation 3, we
observe that the ascent velocity of CR05 bubbles is higher than velocity of CR01 bubbles (Figure 5.8B). Indeed,
the sample is completely depleted in bubbles larger than 600 µm after 100 minutes and, after 200 minutes, in
Chapter 5 Outgassing Induced by Crystallization
78
bubbles larger than 400 µm. This loss in large bubbles is observable in the numerical simulation (Figure 5.9C
and D). During the first 100 minutes, the calculated outgassing reaches 2 to 3.5 vol%. However, the measured
volume of outgassed bubbles was 1.8 vol% at 110 minutes. The presence of crystals is thus lowering the ascent
velocity of large bubbles. Indeed, the distance that bubbles have to travel is larger in a crystal-bearing melt as
they have to move around the crystals. The larger bubbles may have been deformed to bypass these obstacles
but the smaller bubbles were probably trapped by the crystals as already observed by Belien et al. (2010).
After 200 minutes, the increase in viscosity induces a decrease in the ascent velocity of bubbles (Figure 5.8B).
Interestingly, the shift in the measured outgassing rate occurred at a similar time, i.e. 180 minutes (Figure 5.6).
However, the measured outgassing rate is larger than in the Monte Carlo simulation (Figure 5.9C and D). This
difference may be explained by the continuous presence of large bubbles. Indeed, in the numerical model, the
sample is depleted in larger bubbles whereas crystallization sustained bubble coalescence in the experiments.
By comparing both cooling rates, the crystallization of CR05 resulted in a higher rate of outgassing by
decreasing the melt viscosity. However, considering the same viscosity, the presence of crystals lowers the
outgassing rate.
5.6 CONCLUSION
The rate and extent of outgassing varies between crystallizing samples cooled at a rate of 0.1 and 0.5 °C/min.
These variations are related to timing and extent of crystallization and thus to the evolution of the
microstructures. At the beginning of the experiment cooled at a rate of 0.1°C/min, the measured outgassing
rate is fully explained by the ascent of bubbles following Stoke’s law. The subsequent deviation from the
calculation is most likely linked to bubble coalescence. The bubble size distribution is thus a fundamental
parameter controlling the rate of outgassing.
The presence of crystals may favor or inhibit the outgassing. On one hand, the crystallization of anhydrous
minerals increases the water content dissolved in the melt. The induced decrease in viscosity leads to a higher
ascent velocity of bubbles, hence more extensive outgassing. In addition, a forced migration of bubbles due to
the growing plagioclase contributes to sustain the presence of large bubbles by coalescence and additionally
increases the outgassing rate. However, considering the same melt viscosity, the presence of crystals lowers
the outgassing rate by adding obstacles to the ascent of bubbles. Crystallization of hydrous magma is thus
regulating the outgassing rate by (1) increasing the fraction and size of bubbles by exsolution and decreasing
the melt viscosity and (2) lowering their ascent velocity by increasing pathways length.
Consequently, the outgassing potential of a crystallizing magma chamber is high. In our experiments,
crystallization of more than 50 vol% of plagioclase in a melt containing initially 4.2 vol% of bubbles induced
outgassing of 4.6 to 6.6 vol% of bubbles over a rather limited time. Crystallization is thus only partially trapping
the magmatic volatiles into the system. Large bubbles produced in a hydrous melt are, thus, relatively free to
Chapter 5 Outgassing Induced by Crystallization
79
rise through a magmatic mush. These bubbles may ultimately rise to the surface through permeable networks
of fractures in the surrounding volcanic edifice (Jaupart, 1998; Rust et al., 2004) or accumulate at the top of the
magmatic reservoir and produce explosive eruptions (Malfait et al., 2014; Bachman and Bergantz, 2008).
5.7 TABLES
Table 5.1: Compositions of the starting material determined by electron microprobe. The nominal composition corresponds to the composition of the powder before the HIP. Water and CO2 contents have been measured by Karl Fisher and by coulometric titrations respectively.
Sample SiO2 Al2O3 CaO Na2O H2O CO2 Total
HIP: Nominal Composition 65.69 18.56 3.33 7.61 2.80 2.00 100
HIP: Measured Composition 65.26 18.81 3.49 7.51 2.75* 0.03 97.82
Table 5.2: Summary of the microstructures measured in the samples recovered after the outgassing measurements. CR01 = Cooling Rate 0.1 °C/min. CR05 = Cooling Rate of 0.5 °C/min.
CR01 CR05
Bottom Center Top Average Bottom Center Top Average
Crystal fraction [vol%] 61.0 58.2 57.6 58.9 56.8 54.5 52.1 54.5
Melt fraction [vol%] 30.9 31.5 32.0 31.5 33.5 34.2 33.1 33.6
Bubble fraction [vol%] 6.5 8.4 10.3 8.4 9.6 10.3 14.1 11.3
Spherulite number density
[1/mm2]
1.85 1.66 3.01 2.17 1.98 2.06 1.59 1.88
Bubble number density
[1/mm2]
987.27 851.98 976.72 938.66 1313.73 1370.94 1211.78 1298.82
Largest bubble diameter
[µm]
244 274 527 241 329 671
Chapter 5 Outgassing Induced by Crystallization
80
Table 5.3: Partial molar volumes and their pressure and temperature derivatives used for the calculation of melt density at experimental conditions (equation 4). References are given in parenthesis: (a) Lange, 1997; (b) Kress and Carmichael, 1991; (c) Ochs and Lange, 1999.
V(i,1673K,1bar) [10-5 m3/mol] dV/dT [10-9 m3/mol*K] dV/dP [10-6 m3/mol*Gpa]
Si02 2.69 (a) 0.00 (a) -1.89 (b)
Al2O3 3.74 (a) 0.00 (a) -2.26 (b)
CaO 1.65 (a) 3.74 (a) 0.34 (b)
Na2O 2.89 (a) 7.68 (a) -2.4 (b)
H2O 2.67 (c) 9.55 (c) -3.2 (c)
Table 5.4: Summary of the parameters used for the calculation of the ascent velocity of bubbles.
Temperature
[°C]
Time
[s]
Crystal
fraction [vol%]
H2O
[wt%]
log η
[Pas]
ρ melt
[kg/m3]
Δρ
[kg/m3]
CR05 850 30 13.2 3.14 2.73 2294 1808
830 75 40.0 4.54 2.21 2248 1752
810 120 42.4 4.73 2.30 2245 1740
790 165 52.2 5.70 2.08 2218 1702
770 210 53.9 5.91 2.18 2216 1690
700 390 54.5 5.90 2.88 2230 1667
CR01 845 75 0.0 2.72 3.03 2310 1823
815 345 0.0 2.72 3.34 2314 1814
805 405 0.0 2.72 3.45 2315 1810
795 525 0.0 2.72 3.56 2317 1807
790 570 12.4 3.52 3.21 2289 1778
785 615 24.8 4.31 2.85 2264 1749
780 660 37.2 5.11 2.49 2239 1720
775 705 49.6 5.90 2.14 2215 1691
770 750 57.6 5.90 2.18 2216 1690
760 840 57.3 5.90 2.28 2218 1687
750 930 59.2 5.90 2.37 2220 1684
740 1020 59.2 5.90 2.59 2222 1688
Chapter 5 Outgassing Induced by Crystallization
81
5.8 REFERENCES
Bachmann, O., & Bergantz, G. (2008). The magma reservoirs that feed supereruptions. Elements, 4(1), 17-21. Belien, I. B., Cashman, K. V., & Rempel, A. W. (2010). Gas accumulation in particle-rich suspensions and
implications for bubble populations in crystal-rich magma. Earth and Planetary Science Letters, 297(1), 133-140.
Blake, S. (1984). Volatile oversaturation during the evolution of silicic magma chambers as an eruption trigger. Journal of Geophysical Research: Solid Earth (1978–2012), 89(B10), 8237-8244.
Caricchi, L., Annen, C., Blundy, J., Simpson, G., & Pinel, V. (2014). Frequency and magnitude of volcanic eruptions controlled by magma injection and buoyancy. Nature Geoscience, 7(2), 126-130.
Carroll, M. R., & Holloway, J. R. (1994). Volatiles in magmas (Vol. 30): Mineralogical Society of America. Cashman, K., & Blundy, J. (2000). Degassing and crystallization of ascending andesite and dacite. Philosophical
Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences, 358(1770), 1487-1513.
Castro, J. M., Cordonnier, B., Tuffen, H., Tobin, M. J., Puskar, L., Martin, M. C., & Bechtel, H. A. (2012). The role of melt-fracture degassing in defusing explosive rhyolite eruptions at volcán Chaitén. Earth and Planetary Science Letters, 333, 63-69.
Dingwell, D., Romano, C., & Hess, K.-U. (1996). The effect of water on the viscosity of a haplogranitic melt under PTX conditions relevant to silicic volcanism. Contributions to Mineralogy and Petrology, 124(1), 19-28.
Eichelberger, J., Carrigan, C., Westrich, H., & Price, R. (1986). Non-explosive silicic volcanism. Nature, 323(6089), 598-602.
Giordano, D., Russell, J. K., & Dingwell, D. B. (2008). Viscosity of magmatic liquids: a model. Earth and Planetary Science Letters, 271(1), 123-134.
Gonnermann, H. M., & Manga, M. (2003). Explosive volcanism may not be an inevitable consequence of magma fragmentation. Nature, 426(6965), 432-435.
Gonnermann, H. M., & Manga, M. (2007). The fluid mechanics inside a volcano. Annu. Rev. Fluid Mech., 39, 321-356.
Jaupart, C. (1998). Gas loss from magmas through conduit walls during eruption. Geological Society, London, Special Publications, 145(1), 73-90.
Jaupart, C., & Allègre, C. J. (1991). Gas content, eruption rate and instabilities of eruption regime in silicic volcanoes. Earth and Planetary Science Letters, 102(3), 413-429.
Jellinek, A. M., & DePaolo, D. J. (2003). A model for the origin of large silicic magma chambers: precursors of caldera-forming eruptions. Bulletin of Volcanology, 65(5), 363-381.
Klug, C., & Cashman, K. V. (1996). Permeability development in vesiculating magmas: implications for fragmentation. Bulletin of Volcanology, 58(2-3), 87-100.
Lensky, N., Navon, O., & Lyakhovsky, V. (2004). Bubble growth during decompression of magma: experimental and theoretical investigation. Journal of Volcanology and Geothermal Research, 129(1), 7-22.
Malfait, W. J., Seifert, R., Petitgirard, S., Perrillat, J.-P., Mezouar, M., Ota, T., Sanchez-Valle, C. (2014). Supervolcano eruptions driven by melt buoyancy in large silicic magma chambers. Nature Geoscience, 7(2), 122-125.
Mangan, M., & Sisson, T. (2000). Delayed, disequilibrium degassing in rhyolite magma: decompression experiments and implications for explosive volcanism. Earth and Planetary Science Letters, 183(3), 441-455.
Melnik, O., Barmin, A., & Sparks, R. (2005). Dynamics of magma flow inside volcanic conduits with bubble overpressure buildup and gas loss through permeable magma. Journal of Volcanology and Geothermal Research, 143(1), 53-68.
Mourtada-Bonnefoi, C. C., & Laporte, D. (2004). Kinetics of bubble nucleation in a rhyolitic melt: an experimental study of the effect of ascent rate. Earth and Planetary Science Letters, 218(3), 521-537.
Namiki, A., & Manga, M. (2008). Transition between fragmentation and permeable outgassing of low viscosity magmas. Journal of Volcanology and Geothermal Research, 169(1), 48-60.
Ochs, F. A., & Lange, R. A. (1999). The density of hydrous magmatic liquids. Science, 283(5406), 1314-1317. Okumura, S., Nakamura, M., Nakano, T., Uesugi, K., & Tsuchiyama, A. (2012). Experimental constraints on
permeable gas transport in crystalline silicic magmas. Contributions to Mineralogy and Petrology, 164(3), 493-504.
Chapter 5 Outgassing Induced by Crystallization
82
Papale, P. (1999). Modeling of the solubility of a two-component H2O+ CO2 fluid in silicate liquids. American Mineralogist, 84(4), 477-492.
Paterson, M., & Olgaard, D. (2000). Rock deformation tests to large shear strains in torsion. Journal of Structural Geology, 22(9), 1341-1358.
Picard, D., Arbaret, L., Pichavant, M., Champallier, R., & Launeau, P. (2011). Rheology and microstructure of experimentally deformed plagioclase suspensions. Geology, 39(8), 747-750.
Pistone, M., Caricchi, L., Ulmer, P., Burlini, L., Ardia, P., Reusser, E., Arbaret, L. (2012). Deformation experiments of bubble‐ and crystal‐bearing magmas: Rheological and microstructural analysis. Journal of Geophysical Research: Solid Earth (1978–2012), 117(B5).
Proussevitch, A., & Sahagian, D. (1998). Dynamics and energetics of bubble growth in magmas: analytical formulation and numerical modeling. Journal of Geophysical Research: Solid Earth (1978–2012), 103(B8), 18223-18251.
Rust, A., Cashman, K., & Wallace, P. (2004). Magma degassing buffered by vapor flow through brecciated conduit margins. Geology, 32(4), 349-352.
Rust, A., Manga, M., & Cashman, K. V. (2003). Determining flow type, shear rate and shear stress in magmas from bubble shapes and orientations. Journal of Volcanology and Geothermal Research, 122(1), 111-132.
Saar, M. O., & Manga, M. (1999). Permeability‐porosity relationship in vesicular basalts. Geophysical Research Letters, 26(1), 111-114.
Slezin, Y. B. (2003). The mechanism of volcanic eruptions (a steady state approach). Journal of Volcanology and Geothermal Research, 122(1), 7-50.
Sparks, R. (2003). Dynamics of magma degassing. Geological Society, London, Special Publications, 213(1), 5-22.
Chapter 6 Conclusion
83
6 CONCLUSION
The main goal of this PhD thesis was to include dynamic magmatic processes, such as crystallization and bubble
nucleation, in the characterization of physical properties of magmas. These processes are fundamental in the
evolution of magmatic liquids in various plutonic and volcanic environments, from deep magma chambers to
lava flows at the surface. Their effects on the seismic properties and on the ability of outgassing have been
highlighted along this thesis by measuring their evolution in a chemically simplified tonalite crystallizing
plagioclase. The main results are summarized below.
6.1 SEISMIC PROPERTIES
Magmatic processes occurring in volcanic environments have been recognized and identified through the
measurement of seismic velocities using an internally heated gas pressure Paterson apparatus. During
crystallization processes, compression and shear wave velocities increase non-linearly. Indeed, the formation of
a crystal network at crystal fractions higher than 45 vol% favors the propagation of seismic waves through
magmatic liquids. Crystal content is the principal parameter influencing the seismic velocities. However, bubble
nucleation induced by crystallization produces an increase in magma compressibility thereby reducing the
wave propagation velocities. These two processes occurring simultaneously have thus competing effects on the
seismic properties of magmas. In addition, when the bubble fraction is less than 10 vol%, the decrease in
seismic velocities is more pronounced than for larger bubble fractions. Consequently, the increase in
compressibility at relatively low density contrast leads to large decrease in seismic properties during bubble
nucleation and less or no variation during bubble coalescence.
In conclusion, by continuously monitoring small seismic velocity perturbations in volcanic areas and by
combining these data with laboratory measurements of seismic velocities, evolution of the physical state of
magmatic reservoir could be assessed more precisely. In addition, a more accurate interpretation of available
seismic tomography images is possible and may permit a better assessment of potential volcanic hazards.
In this study, the dissolved water content as well as the major elements composition is continuously changing
in the melt. In order to assess the effect of water content in the elastic properties, velocities have been
measured at high pressure and high temperature conditions in hydrous phonolites from the Teide volcano. At
temperature lower than the glass transition, temperature derivatives of seismic velocities are independent of
the dissolved water content. However, temperature derivatives of both, compression and shear wave
velocities, significantly increase at temperature higher than the glass transition. This increase is accentuated by
the addition of water following a trend previously observed for melt viscosity, i.e. the increase is higher at
water content lower than 1 wt%. Glass transition temperatures estimated through our seismic velocity
Chapter 6 Conclusion
84
measurements and calculated relaxation times suggest that measurements in the liquid-like state have
predominantly been performed on relaxed samples.
The seismic velocities measured on hydrous phonolite at temperature higher than the glass transition have
been extrapolated to magmatic temperature and combined to calculated seismic properties of prominent
phenocrysts in the Teide phonolite. The resulting seismic velocities vary between 4.4 and 5.0 km/s for a magma
chamber containing 30 to 40 vol% crystals. Despite these low values, the currently available seismic
tomography images lack evidences of a large magmatic reservoir. Based on these results, four hypotheses
concerning the magmatic plumbing system of Teide are possible: (1) the absence of a large eruptible magmatic
reservoir, (2) a magma chamber smaller than 3 km thickness, (3) a network of sills and dykes producing small
magma pockets, or (4) a cooling magma chamber containing more than 60 vol% crystals.
6.2 OUTGASSING PROPERTIES
During the experiments involving the crystallization of plagioclase in the Paterson apparatus, significant loss of
gas occurred. We thus implemented this apparatus with a pore-fluid system in order to explore the effect of
crystallization on the extent of outgassing of our bubble-bearing haplotonalite melt.
The presence of crystals may favor or inhibit the outgassing. On one hand, the water content dissolved in the
melt increases due to the crystallization of anhydrous minerals. The induced decrease in viscosity leads to a
higher ascent velocity of bubbles promoting a higher outgassing. In addition, a forced migration of bubbles due
to the growing plagioclase is evidenced by bubbles elongated along the crystallization front. This phenomenon
may contribute to sustain the presence of large bubbles by coalescence and additionally increase the
outgassing rate. However, considering the same melt viscosity, crystals act as barrier to the ascent of bubbles
and their presence reduces the outgassing rate. Crystallization of hydrous magma is thus regulating the
outgassing rate by (1) increasing the fraction and size of bubbles by exsolution and decreasing the melt
viscosity and (2) lowering their ascent velocity by increasing pathways length.
Consequently, the outgassing potential of a crystallizing magma chamber is high. In our experiments,
crystallization of more than 50 vol% of plagioclase in a melt containing initially 4.2 vol% of bubbles induced
outgassing of 4.6 to 6.6 vol% of bubbles over a rather limited time. Crystallization is thus only partially trapping
the magmatic volatiles into the system. Large bubbles produced in a hydrous melt are, thus, relatively free to
rise through a magmatic mush. These bubbles may ultimately rise to the surface through permeable networks
of fractures in the surrounding volcanic edifice or accumulate at the top of the magmatic reservoir and produce
explosive eruptions.
6.3 SUGGESTIONS FOR FUTURE RESEARCH
The outgassing occurring during the experiments performed in the Paterson apparatus impeded the presence
of more than 12 vol% of bubbles in the system. However, higher bubble content should be reached in order to
Chapter 6 Conclusion
85
evaluate the effect of crystal and bubble content in the seismic properties of magmas and implement them
into semi-empirical equations. Consequently, future research should be realized in an apparatus ensuring gas-
tight enclosure of the sample during the experiment. In addition, bubble size distribution is an important
parameter influencing physical properties and may easily change along an experiment. Characterization of its
evolution through in-situ 3D tomography would permit a better understanding of physical properties linked to
exsolved volatiles in magmas.
The plagioclases crystallized in our experiments are spherulite, which is the expected shape at high
undercooling temperature. Higher experimental temperature required for euhedral plagioclase can be
achieved with the Paterson apparatus. However, the subsequent accumulation of heat at the position where
the piezoelectric transducers are placed impeded us to perform this kind of experiments. It would, thus, be
interesting to evaluate the effect of texture on the seismic properties of magmas. In addition, natural magmas
crystallize several mineral phases having varying liquidus/solidus and elastic properties. The resulting evolution
of seismic velocities during their crystallization should as well be evaluated
Acknowledgements
86
ACKNOWLEDGEMENTS
First of all, I would like to thank Peter Ulmer. In addition to be an excellent supervisor, he’s a great person who
was here when I really needed. I thank him as well to have let my creativity growing as much as I wanted during
this PhD. The second person who was really helpful was Benoit Cordonnier. I loved our (crazy) scientific
discussions and I hope we will have much more occasions to share ideas and work together. I would like to
thank as well Jean-Pierre Burg for nice talks at Friday beer and to have helped me whenever he could. I spent
quite a lot of excellent “afterwork beers” at the Hot Pasta with Erik Reusser but I mainly would like to thank
him for his patience and precious help at the microprobe. Thank you as well to Jamie Connolly, always smiling,
who helped me with some obscure thermodynamics and who always repeated when I was not getting what he
was saying (in case, I refer to his wonderful jokes!!). I would like to thank Max Schmidt as well for his magic
phone call, without which I would have to pass my PhD exam much later. Thank you to Lucie Tajcmanova who
chaired my PhD defense. I hope you will continue to bring the sunshine in Science.
During the last years, I have shared quite a lot of time with people in the Rock Deformation Lab. Marie Violay
arrived in a chaotic place and managed to be a great lab leader. Thank you for having taken care of this lab as
much as you could. Without you and your magic furnaces, it would have been hard to finish this PhD. A big
thank is as well given to Robert Hoffmann, who always did an excellent and fast job. I would like as well to
thank Alba Zappone, the mama of the lab. She was always here to give a hand and to listen. Although he’s not
here anymore, I would like as well to thank the papa of the lab. He was the person who pushed me and helped
me to start the PhD. Grazie Luigi Burlini! And I send some big thanks around the world to all the people I met in
this lab and who made me feel like home: Mattia, Bjarne, Rolf, Liza, Jacques, Sebastien, Michaela, Nicola,
Richard, Claudio, Shankar, Rita, Melchior…
I had the chance to have excellent people in my office with who I laughed a lot: Francesca, Shahrzad, Jakub,
Natalia, Giuliano, Shan, Rohit and Sonja. Maybe I should as well apologize to them for having shouted loudly in
French to my computer… I spent a lot of great time with all the remaining of the group and I thank you all for
that: Mareen, Anna, Jule, Nico, Steffi, Ingrid, Monica, Daniel, Dawid, Max, Lucas, Julia… Sorry if I forget some
people!
There are as well all the people that passed by ERDW and with who I felt like being with my family: Marion L.,
Marion C., Jessica, Pinar, Janne, Ulrik, Mathieu, Teo, Pietro, Mat, Thiebault, Magali, Greg, Luca, Pierre, Paola,
Daniela, Sasha, Masha, Rita and many other people with you I danced the whole evening at Friday beers! I
hope we will have some more occasions to meet all together.
J’aimerai également remercier ma famille et plus particulièrement mes parents. Ils m’ont toujours poussé à
faire de mon mieux et à atteindre mes objectifs. Merci d’avoir toujours cru en moi et de m’avoir aidé à
accomplir cette thèse. Je vous aime fort ! Un grand merci aussi pour mes amis de Baden qui n’ont pas
Acknowledgements
87
forcement eu conscience du bien qu’ils m’ont procuré pendant ces années. Malgré le fait que j’arrivais tard au
Mojo, ils ont toujours réussi à me relaxer de ma journée en me faisant penser à d’autres choses. Merci !!!
Et finalement, mes plus grands remerciements reviennent à l’homme qui partage ma vie et qui m’as donné
tout le soutien dont j’avais besoin pendant cette thèse, et plus encore. Jérôme, merci d’être comme tu es.
Curriculum Vitae
88
CURRICULUM VITAE
PERSONAL INFORMATION Name: Barbara Andrea Tripoli Birth date: 22/01/1983 Nationality: Swiss/Italian Email address: [email protected] [email protected]
RESEARCH INTERESTS Physical processes occurring in volcanoes by investigating morphology, geochemistry and
stratigraphy of volcanic deposits.
Seismic properties of crystalline and partially molten rocks at crustal conditions linked to microstructural anisotropy.
Internal physical processes occurring in volcanoes with focus on rheology of fully or partially molten rocks at high pressure and high temperature.
Crystallization kinetics and bubble nucleation in magmatic liquids.
EDUCATION AND DEGREES April 2011-Sept 2015 ETH Zurich, Doctoral studies in Earth Sciences
PhD Thesis: Physical properties of plagioclase- and bubble-bearing magmas.
Advisors: Prof. Dr. Peter ULMER Prof. Dr. Jean-Pierre BURG Sept. 2006 – Sept. 2008 ETH Zurich, Master in Earth Sciences Major in Geology & Geochemistry
Master’s thesis: Physical Volcanology of the Lake Natron-Engaruka Monogenetic Field, Northern Tanzania.
Advisor: Dr. Hannes MATTSSON Sept. 2003 – Aug. 2006 University of Geneva, Bachelor of Science in Earth Sciences Including Erasmus exchange with the University of Granada (2005-2006) Course grades available on request.
PROFESSIONAL EXPERIENCES Oct. 2008 - March 2011 ETH Zurich, Seismic velocities measurement In-situ measurement of Vp/Vs in crystalline materials at high pressure
and high temperature for the Swiss Atlas of Physical Properties of Rocks (Saphyr). Density measurement. Microstructure analysis. Aug. - Sept. 2005 University of Geneva Mineral separation from basaltic samples (Frantz magnetic separator).
ASSISTANTSHIP Since Feb. 2007 ETH Zurich, Teaching assistant
Demonstrator for optical mineralogy practical classes. Duties also included additional explanation of course material and help with exam preparation.
Curriculum Vitae
89
Assistant on numerous field courses.
Demonstrator for rock physics practical courses (seismic velocities measurements). Duties also included assistantships for external guests.
EXPERIENCES IN EXPERIMENTAL AND ANALYTICAL TECHNIQUES
HP-HT internally heated gas-pressure Paterson rig
HP oil-pressure rig
Hot Isostatic Press
HP-HT externally heated gas-pressure cold-seal apparatus
Gas pycnometer
Electron Microprobe
Scanning Electron Microscope
X-Ray Diffraction
Karl Fisher Titration
WORKSHOPS / SHORT COURSES Aug. 2008 Recent Developments in Explosive Volcanism University of Iceland (IAVCEI short course) June 2009 Melts, Glasses and Magmas Ludwig-Maximilians-Universität München, Germany Feb. 2010 Rheology and Physical Properties of Magmas: Controls on Dynamics of
Magma Transport, Storage and Eruption ETH Zurich, Switzerland Jan. 2014 The Dynamics of Volcanic Explosive Eruptions University of Geneva, Switzerland
LANGUAGES French : Mother tongue English : Good - C1 (european standard CEFR) Italian : Good - C1 (european standard CEFR) Spanish : Good - C1 (european standard CEFR) German : Good - B2 (european standard CEFR)
PUBLICATION Mattsson, H. B. and Tripoli, B.A. (2011). Depositional characteristics and volcanic landforms in the Lake Natron – Engaruka monogenetic field, northern Tanzania. Journal of Volcanology and Geothermal Research,203, 23-34.
Appendix
90
Appendix A LIST OF SYNTHETIZED SAMPLES
HIP session HIP condition Canister name Sample name H2O [wt%]
CO2 [wt%]
Comments
Lausannne T = 1100°C 1A Haplotonalite 2 2 Cores exploded in the oven…
P = 130 MPa 3A Haplotonalite 2 0
ZH H018 T = 1100°C 2.1A Haplotonalite 2 2 Canisters were deformed due to gas escape. Solution: smaller canister and higher pressure.
P = 130 MPa 2.1B Haplotonalite 2 2
2.1C Haplotonalite 2 2
2.2() Haplotonalite 3.4 2
2.2A Haplotonalite 3.4 2
2.5A Haplotonalite 2.8 2
2.5B Haplotonalite 2.8 2
2.6A Haplotonalite 2 4
2.8A Haplotonalite 3.4 4
ZH H019 T = 1200°C 3.1() Haplotonalite 2 2 -Samples placed at the bottom of the alumina container were fully crystallized. Thus the fast cooling was not correctly applied all along the vessel. Solution: Alumina container was replaced by a tube in alumina. -Large and angular pieces of alumina in the glasses. Solution: Use of pulverisette in agate for crushing the initial powder.
P = 200 MPa 3.3(A) Haplotonalite 2 0
3.3(B) Haplotonalite 2 0
3.3(C) Haplotonalite 2 0
3.9(A) Haplotonalite 1.5 0
3.9(B) Haplotonalite 1.5 0
3.10(A) Haplotonalite 1 0
3.10(B) Haplotonalite 1 0
3.4(A) Haplotonalite 3.4 0
3.4(B) Haplotonalite 3.4 0
ZH H020 T = 1200°C 4.1(A) Haplotonalite 2 2 Samples with low water content were crystallized. Solution: use another composition for water content effect on seismic velocity.
P = 180 MPa 4.1(B) Haplotonalite 2 2
4.1(C) Haplotonalite 2 2
4.1(D) Haplotonalite 2 2
4.1(E) Haplotonalite 2 2
4.2() Haplotonalite 3.4 2
4.3(A) Haplotonalite 2 0
4.3(B) Haplotonalite 2 0
4.3(C) Haplotonalite 2 0
4.3(D) Haplotonalite 2 0
4.3(E) Haplotonalite 2 0
4.4() Haplotonalite 3.4 0
4.5(A) Haplotonalite 2.8 2
4.5(B) Haplotonalite 2.8 2
Appendix
91
4.9(A) Haplotonalite 1.5 0
List of synthetized samples: Continued
HIP session HIP condition Canister name Sample name H2O [wt%]
CO2 [wt%]
Comments
4.9(B) Haplotonalite 1.5 0
4.9(C) Haplotonalite 1.5 0
4.9(D) Haplotonalite 1.5 0
4.10(A) Haplotonalite 1 0
4.10(B) Haplotonalite 1 0
4.10(C) Haplotonalite 1 0
4.10(D) Haplotonalite 1 0
4.10(E) Haplotonalite 1 0
4.11(A) Haplotonalite 1.5 2
4.11(B) Haplotonalite 1.5 2
4.11(C) Haplotonalite 1.5 2
4.12(A) Haplotonalite 1 2
4.12(B) Haplotonalite 1 2
4.12(C) Haplotonalite 1 2
4.12(D) Haplotonalite 1 2
4.13(A) Haplotonalite 2.8 0
4.13(B) Haplotonalite 2.8 0
ZH H021 T = 1000°C P = 200 MPa
LN5 Lavas Negras Mantle furnace not working. LN5 and LN1 canisters were open. Solution: Furnace repaired. LN5 was ok but not LN1 so all the others canisters have been re-hipped.
ZH H022 T = 1200°C PAN1 Pantelleria 1 0
P = 200 MPa PAN2 Pantelleria 2 0
Glass Recrushed Haplotonalite
2 0
LN1 Lavas Negras 0.1 0
LN2 Lavas Negras 0.5 0
LN3 Lavas Negras 1 0
LN4 Lavas Negras 2 0
G01 HPG8 (0.1%) 0.1 2
G03 HPG8 (0.3%) 0.3 2
G05 HPG8 (0.5%) 0.5 2
G1 HPG8 (1%) 1 2
G3 HPG8 (3%) 3 2
Appendix
92
Appendix B LISTS OF EXPERIMENTS
B.1 PATERSON APPARATUS 9
Experiments Sample name Diameter [mm]
Length [mm]
P max [MPa]
T max [°C]
Comments
PP952 Fused Quartz 22 30.06 310 25 Calibration: P derivative
PP954 Fused Quartz 22 30.06 250 600 Calibration: T derivative at 250 MPa
PP955 4.13B 22 30.95 300 650 P-T derivative / T cycle at 250 MPa
PP956 4.5B 22 29.15 300 650 P-T derivative / T cycle at 250 MPa
PP957 4.5B 22 29.15 250 650 P-T derivative / T cycle at 70 MPa
PP958 3.4 22 30.27 300 600 P-T derivative / T cycle at 250 MPa
PP959 4.1B 22 28.85 300 650 P-T derivative / T cycle at 250 MPa
PP960 4.1B 22 28.85 350 650 P-T derivative / T cycle at 350 MPa
PP961 Sapphire 15 30.04 310 850 Calibration: P-T derivative
PP962 4.13A-3.4-4.1A
15 24.82 250 850 Crystallization exp. test / T cycle at 250 MPa / Cooling rate of 1 °C/min
PP963 4.13A 15 29.61 300 850 Crystallization exp. / T cycle at 250 MPa / Cooling rate of 0.5 °C/min
PP964 4.5A 15 28.81 300 850 Crystallization exp. / T cycle at 250 MPa / Cooling rate of 0.5 °C/min
PP965 4.5A 15 26.62 300 850 Crystallization exp. / T cycle at 250 MPa / Cooling rate of 0.1 °C/min
PP974 Fused quartz 22 30.04 310 450 Calibration: P-T derivative + frequency dependence
PP975 LN5 22 33.63 310 500 P-T derivative + frequency dependence / T cycle at 250 MPa
PP976 LN5 22 33.63 150 500 T derivative / T cycle at 150 MPa
PP977 LN3 22 32.02 310 550 P-T derivative / T cycle at 250 MPa
PP978 LN5 22 33.63 300 470 T derivative / T cycle at 300 MPa
PP979 LN5 22 33.63 200 470 T derivative / T cycle at 200 MPa
PP980 LN2 22 29.11 310 550 P-T derivative / T cycle at 250 MPa
PP989 Fused quartz 15 30.02 250 450 Calibration: P-T derivative
PP990 LN1 15 250 550 T derivative / T cycle at 250 MPa
PP991 LN0 22 30.06 290 680 Failed: Unstable temperature
PP992 LN4 22 26.45 250 550 T derivative / T cycle at 250 MPa
Appendix
93
B.2 MHC COLD-SEALED PRESSURE VESSEL
Experiments Sample name
Diameter [mm]
P max [MPa]
T max [°C]
Duration [min]
Cooling rate [°C/min]
Comments
CS1 4.5A 2 250 850 30 0.5 Failed: sample too small
CS2 4.13A 4 250 850 30 0.5 Failed: sample stuck; had to drill it out
CS3 4.13A 4 250 850 30 0.5
CS4 4.13A 4 250 850 75 0.5
CS5 4.13A 4 250 850 120 0.5 Failed: Fast decompression at HT
CS6 4.13A 4 250 850 165 0.5
CS7 4.13A 4 250 850 210 0.5
CS8 4.13A 4 250 850 120 0.5
CS9 4.13A 4 250 850 124 0.1 Failed: Leak during experiment
CS10 4.13A 4 250 850 345 0.1
CS11 4.13A 4 250 850 526 0.1 Failed: sample in hot zone from beginning
CS12 4.13A 4 250 850 546 0.1
CS13 4.13A 4 250 850 405 0.1
CS14 4.13A 4 250 850 72 0.1
CS15 4.13A 4 250 850 744 0.1
CS16 4.13A 4 250 850 861 0.1
CS17 4.13A 4 250 850 925 0.1 Failed: sample stuck, not placed in hot zone
CS18 4.13A 4 250 850 603 0.1
CS19 4.13A 4 250 850 701 0.1
CS20 4.13A 4 250 850 925 0.1
CS21 4.13A 4 250 850 1055 0.1
B.3 PATERSON APPARATUS 6
Experiments Sample name Diameter [mm]
Length [mm]
P max [MPa]
T max [°C]
Comments
P1771 Fused quartz 15 30.04 150 430 Thermal expansion of glass
P1772 LN3 15 30.02 150 430 Thermal expansion of glass
P18-- Crystallized haplotonalite
15 25 250 850 Degassing test failed: Porous alumina is causing leaks in the jacket
P1817 Mullite 15 20 100 100 Permeability
P1818 4.13A 15 8.07 250 850 Crystalization exp. / cooling rate of 0.5 °C/min
P1819 Alumina piston
15 20 200 750 Thermal expansion of pore pressure
P1820 4.13A 15 11.07 250 850 Crystalization exp. / cooling rate of 0.1 °C/min
Appendix
94
Appendix C LIST OF MEASURED DENSITIES
De
nsi
ty
[g/c
m3 ]
Bef
ore
exp
erim
ents
in P
ate
rso
n
2.4
63
2
2.4
70
0
2.4
85
3
2.4
83
1
2.4
74
7
2.4
48
4
2.3
20
8
2.3
08
4
2.3
49
0
2.3
03
8
Aft
er e
xper
imen
ts in
Pa
ters
on
2.5
19
2
2.5
00
3
2.4
89
0
2.4
87
1
2.4
74
6
2.4
58
6
2.4
83
1
2.4
84
5
Av.
Vo
lum
e
[cm
3 ]
1.6
92
1
5.0
25
8
5.8
25
8
1.4
99
2
10
.42
33
13
.67
76
4.7
21
9
3.8
68
3
2.3
90
3
4.1
09
5
7.9
61
9
4.2
86
9
11
.07
17
10
.93
19
6.2
41
7
7.4
57
1
2.3
42
6
2.0
09
7
4.7
24
2.3
9
4.1
09
4
4.2
88
9
1.5
00
2
4.7
22
3
3.8
68
9
2.3
90
3
4.1
10
5
4.2
88
7
2.3
41
4
2.0
08
7
5.8
25
4
1.4
98
9
4.7
22
7
3.8
7
2.3
89
3
4.1
10
6
4.2
88
2.3
43
4
2.0
10
7
5.8
24
6
1.4
99
4
4.7
21
3
3.8
70
7
2.3
91
5
4.1
09
3
4.2
85
6
2.3
42
8
2.0
08
4
1.6
92
1
5.0
25
2
5.8
25
2
1.5
10
.42
43
13
.67
74
4.7
20
7
3.8
67
5
2.3
91
3
4.1
09
8
4.2
85
1
11
.07
10
.93
22
6.2
41
7.4
58
2.3
43
1
2.0
10
5
1.6
91
5
5.0
25
8
5.8
26
2
1.5
00
5
10
.42
25
13
.67
73
4.7
23
2
3.8
67
2
2.3
89
5
4.1
08
7.9
62
4.2
85
4
11
.07
2
10
.93
07
6.2
43
3
7.4
55
3
2.3
42
6
2.0
08
8
1.6
92
1
5.0
26
4
5.8
27
1
1.5
00
3
10
.42
29
13
.67
79
4.7
2
3.8
67
6
2.3
89
6
4.1
09
8
7.9
61
9
4.2
86
5
11
.07
31
10
.93
18
6.2
41
7
7.4
57
2.3
42
1
2.0
11
7
1.6
91
9
5.0
26
5.8
27
1
1.4
98
1
10
.42
42
13
.67
79
4.7
22
8
3.8
67
9
2.3
9
4.1
08
1
7.9
61
4
4.2
88
11
.07
16
10
.93
18
6.2
41
5
7.4
56
3
2.3
42
2
2.0
1
Vo
lum
e
[cm
3 ]
1.6
92
9
5.0
25
7
5.8
25
1
1.4
97
8
10
.42
28
13
.67
75
4.7
20
2
3.8
66
9
2.3
91
6
4.1
10
5
7.9
62
3
4.2
86
7
11
.07
16
10
.93
28
6.2
41
1
7.4
58
8
2.3
42
9
2.0
08
7
We
igh
t
[g]
4.1
68
12
.41
4
14
.47
9
3.7
23
25
.79
5
33
.48
9
10
.95
9
8.9
3
5.6
15
9.4
68
20
.05
8
10
.71
9
27
.55
8
27
.18
9
15
.44
6
18
.33
4
5.8
17
4.9
93
Tem
pe
ratu
re
[°C
]
29
.8
29
.8
27
.9
28
29
.6
29
.4
28
28
.1
28
.4
28
.3
29
.6
27
.9
29
.5
29
.5
29
.7
29
.4
28
.1
28
.2
Sam
ple
LNO
LN1
LN2
LN3
LN4
LN5
4.1
3
3.4
4.3
b
3.3
c
LNO
LN1
LN2
LN3
LN4
LN5
PP
96
4
PP
96
5
Appendix
95
Appendix D LISTS OF CHEMICAL ANALYSES
D.1 KARL FISHER TITRATION MEASUREMENTS
Sample Weight [g]
H2O [ug]
Blank [ug]
Background [ug/s]
H2O [Wt%]
Average H2O [Wt%]
1A 0.02442 466.7 0 0.17 1.911
0.02310 407.1 0 0.28 1.762
0.02062 386.8 0 0.23 1.876
0.02116 319.2 0 0.29 1.509 1.764
3A 0.02158 404.1 0 0.34 1.873
0.02036 441.5 0 0.27 2.168
0.01931 429.1 0 0.26 2.222
0.02386 506.5 0 0.30 2.123
0.02072 405.7 0 0.27 1.958
0.02184 387.1 0 0.28 1.772
0.02043 340.6 0 0.33 1.667
0.02023 348.0 0 0.32 1.720 1.938
2.1A 0.01889 373.5 0 0.24 1.977
0.01920 379.0 0 0.24 1.974
0.01943 342.5 0 0.32 1.763 1.905
2.2A 0.02040 298.6 0 0.32 1.464
0.02213 334.5 0 0.27 1.512
0.02184 321.6 0 0.22 1.473 1.483
2.5A 0.02034 396.1 0 0.33 1.947
0.02109 479.3 0 0.26 2.273
0.01989 379.8 0 0.36 1.910 2.043
3.4 0.02283 639.1 0 0.32 2.799
0.02247 582.3 0 0.36 2.591
0.01985 566.1 0 0.28 2.852 2.748
3.3C 0.01864 326.0 0 0.37 1.749
0.01986 392.6 0 0.35 1.977
0.01967 358.7 0 0.34 1.824 1.850
3.3A 0.02006 312.3 0 0.38 1.557
0.02163 410.3 0 0.2 1.897
0.02096 366.8 0 0.32 1.750 1.735
4.13A 0.02065 547.8 0 0.1 2.653
0.02041 564.4 0 0.19 2.765
0.02342 683.5 0 0.13 2.918 2.779
LN1 (before) 0.01675 67.7 0 0.25 0.404
0.02240 63.9 0 0.27 0.285
0.02605 103.7 0 0.21 0.398 0.363
Appendix
96
Karl Fisher Titration measurements: Continued
Sample Weight [g]
H2O [ug]
Blank [ug]
Background [ug/s]
H2O [Wt%]
Average H2O [Wt%]
LN2 (before) 0.01834 59.8 0 0.24 0.326
0.02620 67.5 0 0.28 0.258
0.02151 44.9 0 0.24 0.209 0.264
LN2 (after) 0.02048 93.9 0 0.22 0.458
0.01830 39.3 0 0.23 0.215
0.02511 71.5 0 0.26 0.285 0.319
LN3 (before) 0.02158 179.4 0 0.25 0.831
0.01974 87.2 0 0.29 0.442
0.01808 95.0 0 0.27 0.525
0.01784 106.0 0 0.26 0.594 0.598
LN3 (after) 0.01987 102.9 0 0.31 0.518
0.02207 107.9 0 0.34 0.489
0.01977 112.9 0 0.2 0.571
0.02120 173.3 0 0.23 0.817
0.02288 95.8 0 0.32 0.419 0.563
LN4 (before) 0.01791 287.8 0 0.26 1.607
0.01776 251.4 0 0.3 1.416
0.01736 216.2 0 0.32 1.245
0.01758 247.9 0 0.28 1.410 1.419
LN4 (after) 0.01667 223.2 0 0.26 1.339
0.01748 255.9 0 0.24 1.464
0.01838 229.7 0 0.28 1.250
0.02473 350.6 0 0.28 1.418 1.368
LN5 (before) 0.01994 425.6 0 0.2 2.134
0.02076 496.2 0 0.17 2.390
0.02979 586.5 0 0.26 1.969
0.02006 398.8 0 0.19 1.988 2.120
LN5 (after) 0.02627 509.9 0 0.31 1.941
0.02256 422.0 0 0.28 1.871
0.01805 304.9 0 0.32 1.689
0.02071 409.2 0 0.25 1.976 1.869
Appendix
97
D.2 ELECTRON MICROPROBE MEASUREMENTS
All the data given in this section are in [wt%].
D.2.1 HAPLOTONALITE
D.2.1.1 INITIAL GLASS
Sample SiO2 Al2O3 CaO Na2O Total
4.5A 64.86 18.39 3.47 7.22 93.94
63.31 18.95 3.37 7.22 92.85
63.69 18.76 3.59 7.03 93.07
65.43 18.50 3.37 7.18 94.48
63.14 18.46 3.47 7.56 92.63
65.17 18.78 3.59 7.55 95.09
64.48 19.21 3.37 7.33 94.39
65.38 19.29 3.65 7.35 95.67
64.87 18.51 3.94 7.85 95.17
65.82 19.04 3.30 7.38 95.54
64.75 18.65 3.44 7.61 94.45
66.20 18.68 3.18 7.82 95.88
65.06 19.06 3.30 8.01 95.43
66.18 18.82 3.45 7.24 95.69
64.74 18.71 3.74 7.33 94.52
64.68 18.76 3.29 7.78 94.51
64.79 18.71 3.54 7.61 94.65
65.86 18.33 3.55 7.26 95.00
64.46 18.97 3.75 7.36 94.54
66.36 19.01 3.43 7.48 96.28
Average 64.96 18.78 3.49 7.46 94.69
StrDev 0.90 0.27 0.18 0.26 0.99
Appendix
98
D.2.1.2 INTERSTITIAL GLASS
Sample SiO2 Al2O3 CaO Na2O Total
CS4 64.03 17.31 2.87 7.04 91.25
64.30 17.79 2.76 7.29 92.14
63.65 18.01 2.99 7.36 92.01
64.72 17.83 2.74 7.12 92.41
64.99 17.40 2.59 7.19 92.17
64.95 17.53 2.57 7.25 92.30
65.42 17.00 2.39 7.15 91.96
65.67 15.97 2.01 6.86 90.51
67.30 15.68 2.02 6.51 91.51
68.50 15.03 1.75 6.72 92.00
Average 65.35 16.96 2.47 7.05 91.83
StrDev 1.50 1.03 0.42 0.27 0.58
CS6 72.20 12.23 1.01 5.97 91.41
73.83 12.39 1.28 5.92 93.42
73.69 12.04 1.08 5.54 92.35
71.14 12.26 1.11 5.28 89.79
74.49 11.68 0.92 5.77 92.86
72.02 12.17 0.97 5.93 91.09
73.22 12.31 1.20 5.59 92.32
74.61 11.53 0.98 5.83 92.95
71.00 11.96 0.99 5.99 89.94
70.44 12.36 1.11 5.99 89.90
Average 72.66 12.09 1.06 5.78 91.60
StrDev 1.51 0.29 0.11 0.24 1.38
CS8 71.56 12.44 1.26 6.25 91.51
71.14 12.53 1.16 5.16 89.99
69.59 13.47 1.16 6.27 90.49
72.33 11.91 1.18 5.65 91.07
70.50 12.12 1.05 5.88 89.55
71.55 12.82 1.19 6.05 91.61
68.29 14.78 1.91 6.53 91.51
71.07 12.63 1.25 6.29 91.24
71.59 13.41 1.75 3.67 90.42
70.64 13.37 1.44 5.01 90.46
Average 70.83 12.95 1.34 5.68 90.79
StrDev 1.16 0.84 0.28 0.86 0.71
PP964 76.38 8.74 0.51 4.82 90.45
76.35 9.57 0.62 4.82 91.36
77.52 8.89 0.43 3.67 90.51
72.08 10.06 1.04 4.83 88.01
Appendix
99
Interstitial glass: Continued
Sample SiO2 Al2O3 CaO Na2O Total
PP964 72.60 9.68 0.78 4.42 87.48
73.19 9.95 0.82 4.92 88.88
74.21 9.53 0.58 5.11 89.43
73.59 9.42 0.67 4.68 88.36
74.25 10.16 1.01 4.89 90.31
73.37 10.84 0.90 5.14 90.25
73.10 10.65 0.85 4.96 89.56
73.85 9.91 0.50 4.79 89.05
72.40 10.36 0.84 4.78 88.38
75.72 9.69 0.50 4.60 90.51
Average 74.19 9.82 0.72 4.75 89.47
StrDev 1.67 0.59 0.20 0.36 1.15
CS16 77.41 10.69 0.97 4.49 93.56
76.72 11.07 1.13 4.97 93.89
78.24 10.22 0.81 4.95 94.22
75.29 12.84 1.57 5.63 95.33
78.29 10.01 0.56 4.63 93.49
Average 77.19 10.97 1.01 4.93 94.10
StrDev 1.24 1.13 0.38 0.44 0.75
CS18 72.28 11.84 0.71 4.07 88.90
69.28 15.39 2.32 5.89 92.88
70.37 13.87 1.72 5.00 90.96
72.36 11.50 0.78 3.81 88.45
72.32 12.12 1.09 4.51 90.04
72.97 11.28 0.84 3.83 88.92
72.90 12.48 1.11 4.57 91.06
73.44 11.15 0.85 3.87 89.31
72.54 11.16 0.83 4.03 88.56
69.32 12.12 1.29 5.17 87.90
72.28 11.24 0.81 3.77 88.10
71.91 10.60 0.76 4.43 87.70
Average 71.83 12.06 1.09 4.41 89.40
StrDev 1.40 1.35 0.48 0.66 1.56
CS19 73.42 10.94 0.89 4.09 89.34
73.17 10.66 0.77 4.75 89.35
74.08 10.55 0.94 4.00 89.57
72.44 10.62 0.95 3.94 87.95
73.81 10.26 0.88 3.87 88.82
72.16 11.43 0.91 4.60 89.10
74.32 10.29 0.67 3.55 88.83
73.81 10.49 0.72 4.42 89.44
73.91 10.75 0.87 3.86 89.39
74.36 10.64 0.97 3.78 89.75
Appendix
100
Interstitial glass: Continued
Sample SiO2 Al2O3 CaO Na2O Total
CS19 74.46 9.92 0.97 4.05 89.40
Average 73.63 10.60 0.87 4.08 89.18
StrDev 0.77 0.39 0.10 0.36 0.50
CS20 74.02 10.45 1.22 3.04 88.73
75.20 9.48 1.22 3.58 89.48
73.56 11.29 1.31 4.41 90.57
73.35 11.91 1.51 4.80 91.57
73.55 11.44 1.48 4.18 90.65
75.29 9.88 1.07 2.93 89.17
73.32 11.29 1.43 4.17 90.21
72.53 11.67 1.53 4.71 90.44
Average 73.85 10.93 1.35 3.98 90.10
StrDev 0.95 0.88 0.17 0.72 0.92
PP965 75.89 9.94 1.29 3.64 90.76
75.76 10.36 1.30 4.50 91.92
73.30 11.43 1.61 4.40 90.74
74.84 10.12 1.50 3.98 90.44
75.80 9.94 0.64 3.75 90.13
76.54 9.80 0.84 3.81 90.99
75.10 9.42 1.59 3.83 89.94
76.99 9.13 1.30 3.61 91.03
74.41 10.13 1.14 3.62 89.30
75.64 9.79 1.48 3.61 90.52
75.89 10.07 1.29 3.81 91.06
75.24 9.80 1.18 4.00 90.22
75.67 10.44 1.50 3.79 91.40
Average 75.47 10.03 1.28 3.87 90.65
StrDev 0.93 0.55 0.29 0.29 0.68
D.2.1.3 PLAGIOCLASE
Sample SiO2 Al2O3 CaO Na2O Total
CS4 63.17 22.85 4.74 8.33 99.09
59.78 24.94 6.27 7.60 98.59
62.36 23.54 5.07 8.21 99.18
62.34 23.37 5.11 8.22 99.04
61.63 23.98 5.71 8.03 99.35
Average 61.86 23.74 5.38 8.08 99.05
StrDev 1.28 0.79 0.61 0.29 0.28
CS6 63.95 22.25 5.29 8.24 99.73
62.55 23.82 5.89 7.96 100.22
61.87 24.26 6.08 7.39 99.60
62.29 24.25 6.29 7.97 100.80
Appendix
101
Plagioclase: Continued
Sample SiO2 Al2O3 CaO Na2O Total
CS6 62.12 23.72 5.62 8.18 99.64
64.90 21.37 4.00 8.47 98.74
Average 62.95 23.28 5.53 8.04 91.79
StrDev 1.20 1.19 0.83 0.37 0.69
CS8 61.08 23.92 5.44 7.81 98.25
60.47 24.26 6.83 7.01 98.57
62.76 21.66 4.24 8.19 96.85
62.18 22.49 4.98 7.77 97.42
61.84 23.21 5.24 8.31 98.60
60.20 24.35 6.06 7.75 98.36
61.59 23.79 5.41 8.62 99.41
60.61 24.64 6.19 7.83 99.27
63.10 22.31 4.45 8.21 98.07
61.21 23.08 4.87 8.05 97.21
Average 61.50 23.37 5.37 7.96 98.20
StrDev 0.97 0.99 0.80 0.44 0.84
PP963 63.23 22.00 3.90 9.19 98.32
61.76 23.88 4.77 8.60 99.01
61.19 23.61 4.88 8.68 98.36
62.15 23.38 5.50 8.40 99.43
62.56 24.06 5.59 8.38 100.59
63.28 22.90 4.64 8.63 99.45
61.38 24.26 5.15 8.47 99.26
61.41 23.63 5.22 8.61 98.87
62.75 23.26 5.05 8.40 99.46
60.45 24.56 5.87 7.79 98.67
Average 62.02 23.55 5.06 8.52 99.14
StrDev 0.94 0.73 0.56 0.35 0.67
CS16 62.33 24.06 6.00 7.62 100.01
63.28 23.28 5.19 8.07 99.82
63.02 23.68 5.04 8.31 100.05
62.19 23.72 4.62 8.36 98.89
63.67 23.69 5.06 8.36 100.78
Average 62.90 23.69 5.18 8.14 99.91
StrDev 0.63 0.28 0.50 0.32 0.68
CS18 61.32 24.68 5.70 8.12 99.82
61.14 24.00 5.41 7.99 98.54
59.91 24.82 6.17 7.56 98.46
61.88 23.82 5.16 8.54 99.40
61.76 24.27 5.42 8.23 99.68
Average 61.20 24.32 5.57 8.09 99.18
StrDev 0.78 0.43 0.39 0.36 0.64
Appendix
102
Plagioclase: Continued
Sample SiO2 Al2O3 CaO Na2O Total
CS19 62.55 23.40 4.61 8.65 99.21
62.40 23.31 4.94 8.41 99.06
63.42 22.24 4.77 7.89 98.32
62.27 23.54 5.15 8.55 99.51
62.62 23.20 4.45 8.90 99.17
Average 62.65 23.14 4.78 8.48 99.05
StrDev 0.45 0.52 0.27 0.38 0.44
CS20 63.20 23.50 5.43 7.73 99.86
63.35 23.15 5.23 8.06 99.79
62.57 23.89 5.34 8.16 99.96
62.45 23.57 5.00 8.44 99.46
63.23 23.05 5.14 8.01 99.43
Average 62.96 23.43 5.23 8.08 99.70
StrDev 0.42 0.34 0.17 0.26 0.24
PP965 62.50 24.03 5.27 8.36 100.16
63.53 23.12 5.47 7.91 100.03
62.06 24.11 5.18 8.23 99.58
63.99 23.24 4.42 8.72 100.37
63.56 23.24 5.06 8.46 100.32
Average 63.13 23.55 5.08 8.34 100.09
StrDev 0.81 0.48 0.40 0.30 0.32
D.2.1.4 MELT POCKETS
Distance from spherulite border
[µm]
SiO2 Al2O3 CaO Na2O Total
Large melt pocket in CS4
20 76.34 12.33 3.36 7.97 91.33
40 76.24 12.05 4.06 7.65 92.86
60 76.61 12.06 3.51 7.81 91.73
80 76.01 12.17 3.60 8.22 92.63
100 76.17 12.19 3.68 7.96 92.36
120 76.00 12.16 3.98 7.86 93.43
140 75.86 12.15 3.99 8.01 94.03
160 76.27 12.21 3.71 7.81 92.57
180 75.78 12.32 4.13 7.77 92.35
200 75.94 12.13 3.90 8.03 92.44
220 75.80 12.43 3.96 7.80 93.16
240 75.74 12.21 3.83 8.23 93.30
260 75.25 12.42 4.08 8.24 94.06
280 76.33 12.42 3.42 7.82 93.21
300 75.80 12.33 3.90 7.97 93.27
320 75.99 12.19 3.80 8.02 92.61
Appendix
103
Melt pockets: Continued
Distance from spherulite border
[µm]
SiO2 Al2O3 CaO Na2O Total
Large melt pocket in CS4
340 75.93 12.33 3.71 8.03 93.26
360 75.52 12.28 3.77 8.43 93.45
380 75.96 12.45 3.62 7.97 93.36
400 75.38 12.90 3.89 7.82 93.58
420 75.60 12.52 4.01 7.88 94.43
440 75.74 12.26 4.12 7.88 93.67
460 75.03 12.37 4.33 8.27 94.54
480 75.68 12.49 4.12 7.71 94.12
500 75.74 12.37 3.98 7.90 95.79
520 75.60 12.23 4.18 8.00 94.59
540 75.30 12.36 4.01 8.33 95.69
560 75.10 12.49 4.05 8.35 95.36
580 75.55 12.44 4.16 7.86 96.00
600 75.43 12.52 3.97 8.07 95.84
620 75.71 12.36 4.36 7.58 96.12
640 75.72 12.54 4.14 7.60 95.68
660 74.80 12.60 4.54 8.06 96.65
680 75.39 12.59 4.21 7.81 94.86
700 75.80 12.29 4.03 7.89 95.60
720 75.76 12.46 4.21 7.58 95.49
740 75.49 12.61 3.83 8.06 95.22
760 75.21 12.47 4.35 7.96 95.89
780 75.34 12.39 4.25 8.01 96.04
800 75.75 12.32 3.99 7.94 96.22
820 75.49 12.09 4.35 8.07 96.08
840 75.55 12.36 4.33 7.76 96.26
860 75.61 12.29 4.32 7.78 94.97
880 75.69 12.31 4.05 7.96 95.38
900 75.62 12.44 3.99 7.95 95.74
920 75.43 12.45 4.10 8.02 95.45
940 75.64 12.45 3.97 7.94 95.55
960 75.33 12.58 4.33 7.75 95.57
980 76.03 12.36 4.00 7.61 96.37
1000 75.75 12.26 4.21 7.78 96.35
1020 75.69 12.47 4.03 7.81 95.40
1040 75.66 12.27 4.23 7.84 94.88
1060 75.86 12.38 4.33 7.43 95.71
1080 75.68 12.22 3.99 8.10 95.54
1100 75.35 12.59 4.17 7.88 95.49
1120 75.14 12.59 4.20 8.08 96.34
1140 76.21 12.16 3.87 7.76 94.86
1160 75.37 12.45 4.06 8.12 94.96
Appendix
104
Melt pockets: Continued
Distance from spherulite border
[µm]
SiO2 Al2O3 CaO Na2O Total
Large melt pocket in CS4
1180 75.81 12.53 3.85 7.80 95.25
1200 75.81 12.40 3.82 7.97 95.12
1220 75.41 12.36 4.09 8.13 96.05
1240 75.84 12.60 3.71 7.85 95.50
1260 75.53 12.46 4.16 7.85 95.92
1280 75.87 12.39 3.95 7.78 95.14
1300 75.54 12.69 4.13 7.64 94.52
1320 74.98 12.50 4.40 8.12 95.77
Small melt pocket in CS4
20 75.05 12.49 4.42 8.05 93.07
40 75.48 12.48 3.90 8.13 93.18
60 74.88 12.39 4.24 8.49 92.45
80 74.78 12.69 4.21 8.33 93.72
100 75.49 12.57 3.97 7.97 92.39
120 75.23 12.60 3.86 8.31 92.05
140 75.20 12.60 3.97 8.23 93.27
160 75.34 12.41 4.13 8.12 93.93
180 75.40 12.45 3.74 8.41 93.11
200 75.34 12.35 4.03 8.29 93.36
220 75.63 12.44 3.78 8.15 92.99
240 75.41 12.30 3.75 8.55 93.73
260 75.70 12.41 3.66 8.22 93.42
280 75.53 12.58 3.83 8.07 93.82
300 74.76 12.70 4.11 8.43 94.27
320 75.65 12.49 4.00 7.85 94.89
340 75.65 12.50 3.87 7.98 94.86
360 75.61 12.60 3.97 7.82 95.15
380 75.21 12.67 4.21 7.91 95.49
400 75.68 12.19 4.33 7.80 95.18
420 75.26 12.60 4.04 8.10 95.17
440 74.93 12.40 4.45 8.22 94.88
460 75.39 12.43 4.18 8.00 94.58
480 75.82 12.41 4.11 7.66 94.76
500 74.96 12.73 4.42 7.89 95.34
520 74.87 12.42 4.30 8.40 96.01
540 75.40 12.22 4.29 8.08 95.88
560 74.92 12.48 4.42 8.18 96.16
580 75.15 12.58 4.00 8.27 95.88
600 75.63 12.45 3.90 8.01 96.11
620 75.18 12.65 3.99 8.17 96.02
640 75.37 12.21 4.55 7.87 96.28
660 75.78 12.37 4.02 7.84 96.21
680 75.39 12.25 4.08 8.28 95.47
Appendix
105
Melt pockets: Continued
Distance from spherulite border
[µm]
SiO2 Al2O3 CaO Na2O Total
Small melt pocket in CS4
700 75.83 12.35 4.06 7.76 95.39
720 75.37 12.40 4.44 7.79 96.23
740 75.41 12.45 4.09 8.04 95.54
760 75.08 12.57 4.24 8.12 95.97
780 75.78 12.28 4.02 7.92 95.24
800 75.18 12.35 4.48 7.98 95.46
820 75.16 12.53 4.29 8.02 95.94
840 75.78 12.41 4.05 7.76 94.31
860 75.62 12.20 4.26 7.92 96.89
880 75.71 12.35 3.82 8.11 95.26
900 75.15 12.62 4.00 8.23 95.93
920 75.52 12.41 4.21 7.87 95.96
940 75.55 12.46 3.88 8.11 94.76
960 75.76 12.72 3.84 7.68 93.74
980 74.87 12.76 4.28 8.09 94.82
1000 75.92 12.15 3.93 8.00 92.93
1020 75.94 12.31 3.98 7.77 95.09
1040 75.35 12.47 3.86 8.33 94.80
1060 75.56 12.34 3.99 8.11 94.68
1080 75.58 12.35 3.94 8.13 94.03
1100 75.52 12.43 3.82 8.24 94.00
1120 75.41 12.19 3.97 8.44 93.98
1140 75.64 12.31 3.93 8.12 93.47
1160 75.65 12.40 3.80 8.14 93.95
1180 75.14 12.31 4.65 7.89 93.19
1200 75.52 12.30 4.21 7.97 93.31
1220 75.21 12.46 4.16 8.17 93.73
1240 74.96 12.50 4.21 8.32 93.70
1260 75.10 12.39 4.20 8.30 93.86
1280 75.51 12.32 4.03 8.15 93.26
1300 75.29 12.39 4.27 8.06 92.49
1320 76.10 12.25 3.69 7.95 92.92
Appendix
106
D.2.1.5 ELEMENTS DISTRIBUTION MAPS
Figure D.1: Elements distribution map performed on the haplotonalite used for the crystallization experiments (4.13A).
Appendix
107
Figure D.2: SEM image and elements distribution maps of the haplotonalite cooled at 0.5°C/min in the Paterson apparatus. The contour of the plagioclase crystal are highlighted in black in the elements distribution maps.
Appendix
108
D.2.2 LAVAS NEGRAS
Sample SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Total
LN1 60.50 0.67 18.52 3.44 0.19 0.36 0.72 9.43 4.86 98.69
60.14 0.68 18.44 3.44 0.20 0.37 0.74 9.36 4.83 98.19
60.18 0.69 18.47 3.43 0.23 0.36 0.72 9.29 4.92 98.28
59.88 0.69 18.43 3.44 0.19 0.38 0.72 9.29 4.85 97.87
60.88 0.66 18.65 3.42 0.23 0.35 0.70 9.19 4.88 98.95
60.35 0.69 18.48 3.42 0.19 0.35 0.74 9.25 4.85 98.33
60.17 0.69 18.44 3.45 0.23 0.37 0.73 9.34 4.83 98.26
59.90 0.67 18.37 3.47 0.19 0.36 0.70 9.10 4.84 97.60
60.70 0.66 18.70 3.47 0.20 0.37 0.74 9.30 4.82 98.97
60.29 0.66 18.50 3.46 0.20 0.37 0.74 9.24 4.86 98.31
60.17 0.70 18.43 3.46 0.20 0.39 0.75 9.29 4.83 98.22
60.11 0.69 18.43 3.48 0.20 0.35 0.74 9.26 4.84 98.10
60.09 0.68 18.38 3.43 0.20 0.37 0.72 9.24 4.82 97.93
60.00 0.69 18.42 3.43 0.21 0.35 0.70 9.26 4.84 97.90
60.14 0.67 18.47 3.44 0.22 0.36 0.71 9.23 4.86 98.10
60.24 0.69 18.45 3.39 0.19 0.36 0.73 9.25 4.85 98.15
60.40 0.67 18.62 3.43 0.21 0.37 0.71 9.21 4.86 98.48
60.40 0.69 18.66 3.39 0.22 0.38 0.72 9.02 4.81 98.29
60.57 0.67 18.55 3.45 0.21 0.38 0.73 9.18 4.84 98.58
60.43 0.68 18.64 3.49 0.21 0.37 0.72 9.23 4.86 98.64
60.44 0.69 18.48 3.47 0.20 0.35 0.71 9.35 4.84 98.52
60.16 0.66 18.50 3.44 0.20 0.37 0.72 9.15 4.87 98.07
61.35 0.67 18.73 3.41 0.17 0.38 0.75 9.21 4.82 99.49
60.93 0.68 18.85 3.36 0.20 0.38 0.74 9.30 4.90 99.34
61.00 0.67 18.67 3.42 0.22 0.38 0.71 9.22 4.84 99.12
61.06 0.68 18.86 3.44 0.21 0.35 0.71 9.23 4.87 99.42
60.76 0.68 18.63 3.45 0.20 0.37 0.74 9.11 4.79 98.73
60.48 0.66 18.65 3.41 0.20 0.35 0.73 9.24 4.83 98.54
60.54 0.70 18.65 3.51 0.21 0.37 0.73 9.32 4.85 98.88
60.54 0.66 18.62 3.43 0.21 0.36 0.72 9.23 4.84 98.61
60.53 0.68 18.61 3.50 0.21 0.34 0.71 9.27 4.84 98.69
60.44 0.67 18.68 3.40 0.20 0.39 0.73 9.18 4.82 98.51
60.59 0.67 18.79 3.48 0.21 0.36 0.73 9.28 4.82 98.93
60.32 0.68 18.75 3.49 0.21 0.35 0.72 9.30 4.81 98.63
60.32 0.68 18.78 3.44 0.18 0.37 0.71 9.32 4.85 98.66
60.16 0.69 18.70 3.49 0.20 0.34 0.73 9.21 4.91 98.43
60.34 0.67 18.56 3.43 0.23 0.36 0.71 9.21 4.89 98.40
60.13 0.70 18.47 3.41 0.21 0.36 0.72 9.17 4.91 98.08
59.78 0.70 18.49 3.41 0.17 0.36 0.72 9.28 4.89 97.80
60.61 0.68 18.75 3.36 0.22 0.36 0.72 9.25 4.86 98.82
Appendix
109
Lavas Negras: Continued
Sample SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Total
LN1 60.03 0.68 18.62 3.42 0.22 0.36 0.72 9.09 4.86 97.99
Average 60.39 0.68 18.58 3.44 0.21 0.36 0.72 9.24 4.85 98.48
StrDev 0.34 0.01 0.13 0.03 0.01 0.01 0.01 0.08 0.03 0.44
LN2 60.27 0.67 18.64 3.39 0.21 0.36 0.70 9.34 4.85 98.43
60.37 0.67 18.59 3.41 0.20 0.37 0.70 9.32 4.84 98.47
60.10 0.68 18.52 3.42 0.19 0.38 0.74 9.38 4.82 98.23
60.19 0.66 18.46 3.39 0.21 0.38 0.73 9.33 4.86 98.20
60.29 0.68 18.58 3.41 0.20 0.36 0.73 9.26 4.87 98.38
Average 60.24 0.67 18.56 3.40 0.20 0.37 0.72 9.33 4.85 98.34
StrDev 0.10 0.01 0.07 0.01 0.01 0.01 0.02 0.04 0.02 0.12
LN3 60.33 0.67 18.67 3.40 0.19 0.35 0.71 9.02 4.81 98.15
60.58 0.69 18.75 3.32 0.22 0.37 0.70 9.26 4.87 98.76
61.07 0.66 18.75 3.36 0.20 0.39 0.71 9.24 4.81 99.19
60.27 0.68 18.56 3.39 0.20 0.36 0.71 9.11 4.84 98.12
60.87 0.69 18.62 3.33 0.19 0.36 0.73 9.21 4.85 98.85
60.80 0.66 18.61 3.43 0.21 0.39 0.71 9.31 4.85 98.97
Average 60.65 0.68 18.66 3.37 0.20 0.37 0.71 9.19 4.84 98.67
StrDev 0.32 0.01 0.08 0.04 0.01 0.02 0.01 0.11 0.02 0.44
LN4 59.78 0.68 18.21 3.31 0.18 0.36 0.70 8.99 4.74 96.96
59.44 0.67 18.31 3.40 0.21 0.35 0.69 9.16 4.73 96.97
59.93 0.67 18.40 3.25 0.20 0.34 0.69 8.96 4.73 97.17
59.79 0.66 18.39 3.38 0.18 0.36 0.71 9.03 4.76 97.26
59.68 0.68 18.29 3.41 0.20 0.36 0.69 9.04 4.76 97.10
60.76 0.66 18.63 3.46 0.19 0.36 0.72 9.02 4.75 98.56
60.65 0.65 18.77 3.36 0.18 0.35 0.73 9.11 4.74 98.54
60.53 0.68 18.67 3.39 0.19 0.37 0.74 8.98 4.76 98.30
60.40 0.65 18.69 3.33 0.18 0.33 0.72 9.03 4.75 98.09
60.39 0.66 18.50 3.34 0.20 0.35 0.73 9.17 4.74 98.08
60.43 0.65 18.56 3.37 0.22 0.34 0.73 9.06 4.76 98.11
60.55 0.66 18.58 3.32 0.20 0.36 0.73 9.09 4.74 98.22
60.33 0.67 18.48 3.41 0.19 0.34 0.71 9.16 4.76 98.04
60.53 0.68 18.50 3.45 0.19 0.35 0.71 9.00 4.77 98.18
60.32 0.65 18.57 3.33 0.20 0.36 0.71 9.01 4.75 97.91
60.21 0.67 18.51 3.53 0.21 0.36 0.71 9.00 4.77 97.98
60.24 0.67 18.67 3.27 0.18 0.35 0.73 9.14 4.79 98.06
60.29 0.66 18.49 3.27 0.18 0.36 0.71 9.00 4.73 97.68
60.13 0.66 18.60 3.32 0.19 0.34 0.71 9.02 4.76 97.74
Average 60.23 0.67 18.52 3.36 0.19 0.35 0.72 9.05 4.75 97.84
StrDev 0.36 0.01 0.15 0.07 0.01 0.01 0.01 0.07 0.02 0.51
LN5 59.54 0.66 18.17 3.02 0.19 0.27 0.83 8.80 4.69 96.16
59.80 0.62 18.30 2.98 0.20 0.29 0.78 8.87 4.70 96.54
Appendix
110
Lavas Negras: Continued
Sample SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Total
LN5 59.59 0.64 18.39 3.30 0.20 0.38 0.68 8.76 4.72 96.65
58.98 0.63 18.08 3.18 0.20 0.35 0.71 8.73 4.70 95.56
58.59 0.64 18.04 3.15 0.20 0.34 0.74 8.68 4.79 95.17
59.40 0.66 18.16 3.10 0.19 0.33 0.75 8.23 4.76 95.58
59.69 0.66 18.41 3.19 0.20 0.39 0.73 8.58 4.77 96.62
60.88 0.57 18.52 2.54 0.18 0.16 0.74 8.66 4.70 96.94
60.10 0.57 18.49 3.05 0.20 0.37 0.61 8.87 4.75 97.01
59.99 0.66 18.18 2.98 0.20 0.32 0.80 8.81 4.70 96.65
59.55 0.64 18.08 3.12 0.17 0.32 0.74 8.63 4.75 96.00
60.30 0.64 18.49 3.15 0.18 0.35 0.74 8.65 4.75 97.26
60.58 0.66 18.44 3.07 0.21 0.30 0.74 8.98 4.71 97.70
60.44 0.62 18.32 2.82 0.17 0.27 0.81 8.77 4.66 96.88
60.63 0.62 18.46 2.82 0.19 0.25 0.81 8.68 4.76 97.22
60.44 0.60 18.28 2.79 0.18 0.26 0.70 8.75 4.77 96.76
61.18 0.51 18.62 2.80 0.15 0.34 0.58 8.91 4.69 97.78
60.85 0.65 18.31 2.99 0.19 0.29 0.77 8.77 4.72 97.53
60.53 0.64 18.29 2.81 0.19 0.26 0.85 8.74 4.71 97.02
60.84 0.63 18.42 2.91 0.18 0.39 0.66 8.68 4.65 97.36
60.64 0.64 18.33 3.17 0.19 0.32 0.78 8.66 4.70 97.43
60.33 0.65 18.31 2.98 0.19 0.29 0.80 8.81 4.66 97.02
60.70 0.63 18.47 2.83 0.20 0.24 0.75 8.81 4.75 97.38
60.16 0.61 18.28 3.34 0.21 0.48 0.59 8.65 4.78 97.09
60.69 0.66 18.47 3.25 0.17 0.27 0.64 8.86 4.66 97.68
59.54 0.69 18.30 3.57 0.21 0.59 0.64 8.71 4.77 97.01
60.10 0.65 18.25 3.07 0.17 0.33 0.77 8.76 4.71 96.81
59.84 0.67 18.27 3.16 0.19 0.32 0.75 8.86 4.71 96.77
60.68 0.68 18.37 2.97 0.20 0.27 0.80 8.89 4.74 97.58
Average 60.16 0.63 18.33 3.04 0.19 0.32 0.73 8.74 4.72 96.87
StrDev 0.62 0.04 0.14 0.21 0.01 0.08 0.07 0.14 0.04 0.66