Insights into magma chamber processes from the analysis of size distribution of enclaves in lava flows: A case study from Vulcano Island (Southern Italy)

al Research 166 (2007) 193–203www.elsevier.com/locate/jvolgeores

Journal of Volcanology and Geotherm

Insights into magma chamber processes from the analysis of sizedistribution of enclaves in lava flows: A case study

from Vulcano Island (Southern Italy)

Diego Perugini a,⁎, Luca Valentini b, Giampiero Poli a

a Department of Earth Science, University of Perugia, Piazza Università, 06100, Perugia, Italyb Department of Earth and Ocean Sciences, National University of Ireland, Galway, Ireland

Received 6 February 2007; accepted 31 July 2007Available online 15 August 2007

Abstract

The size distribution of latitic enclaves dispersed in a rhyolitic lava flow is studied. Enclave size distribution is self-similar, afeature that can be explained by a fractal fragmentation process, and estimated fractal dimension of fragmentation is 2.50. Fragmentsize distribution of enclaves generated by disruption of viscous fingering structures in granitoid rocks is analyzed. It is shown thatthis distribution is fractal with a value of fractal dimension of fragmentation of 2.55, in close agreement with the value estimated forenclaves in the lava flow. It is suggested that the fragmentation process producing the size distribution of enclaves in the lava flowmay have occurred in response to the disruption of viscous fingering morphologies generated by the injection of the more maficmagma into the felsic one. Accordingly, the size distribution of enclaves dispersed in the lava flow is considered a feature inheritedfrom deep magma chamber processes and gives insights into magma chamber dynamics.© 2007 Elsevier B.V. All rights reserved.

Keywords: magmatic enclaves; lava flow; fractal fragmentation; viscous fingering; magma chamber

1. Introduction

Textural heterogeneities due to magma mixing/mingling are common features in volcanic rocks (e.g.Bacon, 1986; Calanchi et al., 1993; Perugini et al.,2003), and the processes responsible for their formationhave been discussed extensively (e.g. Eichelberger,1980; Snyder, 2000; Perugini and Poli, 2004). Suchheterogeneities include enclaves, banding, and vortex-like structures (e.g. Bacon, 1986; Perugini et al., 2003).

⁎ Corresponding author.E-mail address: [email protected] (D. Perugini).

0377-0273/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.jvolgeores.2007.07.017

Although studies on the mineralogical and geochemicalfeatures of mixed rocks are abundant (e.g. Bateman,1995; Poli et al., 1996; Gioncada et al., 2005), lessefforts have been made to quantify textural heterogene-ities in mixed igneous bodies (Wada, 1995; De Rosaet al., 1996; Ventura, 1998; Smith, 2000; Perugini et al.,2002; Perugini et al., 2003). These studies were mainlyfocused on (i) the deformation of the interface betweeninteracting magmas in laminar and turbulent flows, (ii)the effects of vesiculation on the deformation ofenclaves, and (iii) the relationships between themorphology of the mingling/mixing structures and thedegree of magma interaction. In addition, studies on thefluid-dynamics of interacting liquids (e.g. Ottino, 1989),

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194 D. Perugini et al. / Journal of Volcanology and Geothermal Research 166 (2007) 193–203

as well as analogue models on magma mixing (e.g. DeCampos et al., 2004), and analyses of natural patterns(e.g. Ventura, 2004; Gonnermann and Manga, 2005),have shown that the different morphological structurescan give useful information about the dynamics ofmixing and the styles of lava flow emplacement.

In this contribution we study the size distribution ofenclaves dispersed in an obsidian lava flow cropping outon the island of Vulcano (Aeolian Archipelago,Southern Italy). Results are interpreted in the light offractal fragmentation theory and a hypothesis isadvanced regarding the possible process that acted to

Fig. 1. Schematic geologic map of the island of Vulcano (Aeolian Islands) shoCotte lava flow studied in this paper is also indicated in the North part of th

generate the observed enclave size distribution. It issuggested that the study of the size distribution ofenclaves in lava flows may give insights into magmachamber processes and dynamics.

2. General features of the studied outcrop

The studied lava flow, known as “Pietre Cotte”, waserupted fromVulcano “La Fossa” cone in 1739 A.D. (e.g.Keller, 1980; Frazzetta et al., 1983; Fig. 1). It is anobsidian lava with rhyolitic composition in whichenclaves of latitic composition are dispersed (Fig. 2A).

wing the main volcanic units (modified from Keller, 1980). The Pietree island.

http://dx.doi.org/10.1029/2003JB002740

Fig. 2. (A) Polished slab of rock showing the banding in the host lava (light colour bandings are due to vesiculation) and the presence of enclaves(indicated by thick arrows in A); (B–C) examples of enclaves. Note the deformation of banding and the presence of vesicles around enclaves(indicated by thin arrows in B and C).

195D. Perugini et al. / Journal of Volcanology and Geothermal Research 166 (2007) 193–203

Hereafter latitic enclaves will be termed as “mafic”enclaves since their composition is less evolved relative tothe host rhyolitic mass. The rhyolitic rock is characterizedby a banded aspect given by the occurrence of alternate

glassy and pumiceous bands, whose elongation is parallelto the direction of the lava flow (Figs. 2 and 3). The hostrock is phenocryst free and a spherulitic texture due todevitrification is commonly observed. Mafic enclaves

Fig. 3. Examples of enclaves dispersed in the “Pietre Cotte” lava flow. To better visualize enclave morphology, grey scale pictures have beensegmented by image analysis and black and white images showing the enclaves are given on the right side. White arrows indicate fingers of theenclave magma propagating towards the rhyolitic host; the occurrence of cuspate terminations is also indicated.


have a glassy groundmass with phenocrysts (20–25% involume, on average) of plagioclase and clinopyroxene,and minor amounts of olivine, biotite, k-feldspar andopaque minerals.

Mafic enclaves constitute 5–7% of the wholeoutcrop. In general, they have crenulated to angularmargins and the interface between enclaves and therhyolitic host is well defined (Figs. 2 and 3). Themorphology of enclaves can be better seen in Fig. 3,where grey scale pictures have been segmented byimage analysis to produce black and white images.

Although enclaves are characterized by highly variableshapes, they all display some common features; inparticular, (i) the contact with the rhyolitic magmadisplays fingers of the mafic magma directed towardsthe host magma (Fig. 3) and (ii) in many cases enclavesdisplay cuspate terminations (Fig. 3E–H).

Enclaves are commonly surrounded by vesicles(Fig. 2B–C) and, according to Blake and Fink (2000),this feature suggests a solid state rheological behavior ofthe enclaves in the lava flow. This is also supported bythe fact that the layering in the host magma is strongly

Fig. 5. Variation of the logarithm of cumulative number of enclaveswith areas A larger than comparative area a(log[N(ANa)]) against log(a) according to Eq. (3). In the graph, the value of r2 from the linearfitting, and values of m and Df are also reported; binning of dataperformed according to Izenman (1991).


deformed around the enclaves strictly following theirmorphology (Figs. 2 and 3). This feature would bedifficult to explain if the enclaves were in a plastic state,in which case, they should have been stretched intofilament-like structures by the stress imposed by themagma flow (e.g. Perugini et al., 2003). Moreover, localfragmentation of enclaves (i.e. disruption of enclavesinto smaller pieces due to the flowing of host magma) isnot observed, indicating that they have been passivelytransported during the emplacement of lava flow, andthat such a process did not play an important role in thefragmentation of the mafic magma. This is alsosupported by the fact that enclaves are dispersed intothe host magma as “non-touching” fragments (Fig. 2A)and this feature suggests that collision among enclavesand potential fragmentation was prevented in the lavaflow.

3. Fractal fragmentation theory and size distributionof enclaves

Large samples from the lava flow have beencollected and sliced, and the boundaries of the enclaveshave been traced by image analysis, in order to studytheir size variability. In particular, grayscale imagesfrom polished slabs have been acquired by using anoptical scanner with a resolution of 500 pixels/cm.Then, grayscale pictures (Fig. 3) have been processed bythe NIH (National Institutes of Health) image analysissoftware to produce binary images in which enclavesand host rock were replaced by black and white pixels,respectively (Fig. 3). A total of 1072 enclaves have beenanalyzed and results show a large variability of size(area) ranging from ca. 3 ·10− 1 to ca. 1.7 ·101 cm2.Errors on image analysis measurements have been

Fig. 4. Frequency histogram displaying the distribution of values ofelongation for enclaves occurring in the Pietre Cotte lava flow.

estimated by using different threshold values to traceenclave contours during image analysis; results indicatethat parameters of interest can be measured with errorslower than 2–3%. A feature of the studied enclaves thatmay give insights on the processes responsible for theirformation is the “elongation”. This parameter iscalculated as the ratio of the length of the minor axisto the length of the major axis. The result is a valuebetween 0 and 1. If the elongation is 1, the object is acircle. As the ratio decreases from 1, the object becomesprogressively more elongated. Elongation has beencalculated from the binary images of the enclaves byusing the values of minor and major axes as estimatedby image analysis, and is used here as a measure ofenclave morphology. The histogram of Fig. 4 displaysthe variability of elongation and shows that itsdistribution is bell-shaped and skewed towards unitywith maximum values located at ca. 0.7–0.8. This resultindicates that most of the studied enclaves have a highsphericity and did not suffer a large amount ofdeformation.

Recent studies (e.g. Holtz et al., 2004; Ventura, 2004)indicated that the size distribution of magmatic enclavesin lava flows follows a fractal behavior. Accordingly,considering the variability of enclave sizes observed inthe studied lava flow, we have attempted to quantify thedegree of fragmentation of the enclave magma by usinga fractal statistical approach.

In the light of fractal theory, Mandelbrot (1982) hasshown that fractal fragmentation can be quantified by


measuring the fractal dimension of fragments of a givenpopulation of particles through the equation:

NðRNrÞ ¼ kr�Df ð1Þ

where Df is the fragmentation fractal dimension; N(RN r) is the total number of particles with a lineardimension R greater than a given comparative size r,and k is a proportionality constant. The value of thefractal dimension (Df) derived from Eq. (1) is not ameasure of irregularity, but rather a measure of the size–number relationship of the particle population or, inother terms, the fragmentation of the population. Takingthe logarithm of both sides of Eq. (1) yields a linearrelationship between N(RN r) and r with Df related tothe slope coefficient, m, by

Df ¼ �m ð2ÞEq. (1) is based on linear size comparisons, i.e. RN r.

If the basis for size comparison is taken as “area” (ANa),as in the case of studied mafic enclaves, Eq. (1) becomes(Mandelbrot, 1982)

NðANaÞ ¼ ka�Df =2 ð3Þ

with

Df ¼ �2m ð4Þ

Fig. 5 shows the variation of the logarithm ofcumulative number of mafic enclaves with areas Alarger than comparative area a(log[N(ANa)]) against log(a) according to Eq. (3). The graph indicates that the datapoints are disposed along a straight line, fulfilling therequirement for a fractal fragmented distribution (e.g.Turcotte, 1992). The fractal scaling range of analyzedenclaves spans over ca. 1.8 orders of magnitude; thisscaling range is typical of empirical fractals and is inagreement with fractal analyses published in theliterature (e.g. Avnir et al., 1998). Linear interpolationof data gives a slope (m) equal to − 1.25, and conse-quently, a value for fragmentation fractal dimensionDf =2.50 [Eq. (4)]. The question now arises as to whatphysical mechanism may have originated the observedfractal fragmentation of the mafic magma in the con-sidered natural system.

4. Discussion

A first configuration that may be invoked to explainthe occurrence of mafic enclaves is the detachment ofsolid fragments from a previously erupted lava flow

with latitic composition over and/or across which theobsidian lava flow passed during its eruption. In suchconditions the pre-existing latitic rock may have beendisrupted and fragments (i.e. mafic enclaves) may havebeen incorporated into the flowing rhyolitic mass.Although this hypothesis may account for the fragmen-tation and, hence, potentially, for a fractal distribution offragments, there are some points which argue against it.The first is that in the area of Pietre Cotte lava flow thereis no evidence of a previously solidified latitic lava (e.g.De Astis et al., 1997). Although one may argue that thepre-existing latitic rock has been covered by the morerecent rhyolitic lava, it seems unlikely that the lattercovered totally the previous one leaving no trace of it inthe field. The second point concerns the distribution ofmafic enclaves in the obsidian lava flow. If the rhyoliticlava flowed over/across a previously solidified latiticmass one would expect latitic fragments concentratedpreferentially at the base or peripheral zones of therhyolitic mass. On the contrary, enclaves are veryhomogeneously distributed throughout the rhyoliticrock indicating that their dispersion was very efficient,a feature which is difficult to be achieved in the shortdistance covered by the rhyolitic lava of Pietre Cotte (ca.250–300 m). Therefore, it appears that this hypothesis isnot very likely to account for the observed distributionof mafic enclaves in the rhyolitic lava flow.

A second scenario that can be hypothesized is thedisruption of a latitic rock, which may have solidified insub-volcanic conduits, by the ascending rhyoliticmagma. As in the previous case such a hypothesiscould be consistent with a fragmentation process and afractal distribution of enclave sizes. In considering thishypothesis, it is to recall that mafic enclaves display aglassy groundmass. Therefore, if the latitic magma waspresent in sub-volcanic conduits, such conduits shouldhave been shallow enough to induce a degree ofundercooling such that the magma would have solidi-fied as a glass. As for the previous hypothesis thehomogeneous distribution of enclaves in the rhyoliticlava flow is the main issue arguing against the presenthypothesis. In fact, if a latitic rock was present inshallow conduits and it was intersected by the rhyoliticmagma en route to the surface one would expect apreferential clustering of mafic enclaves in the firsterupted volumes of the Pietre Cotte lava flow (frontalpart), since the distance covered by the rhyolitic magmais short enough to inhibit a homogeneous dispersion ofenclaves. On the contrary, field evidence does notindicate any preferential clustering of enclaves in thefrontal part of the lava flow. However, one may arguethat the ascent of the magma was characterized by

Fig. 6. (A–D) Examples of viscous fingering structures occurring at Vegetation Island outcrops (Terra Nova Intrusive Complex, Antarctica; e.g.Perugini and Poli, 2005). Note the widespread presence in the felsic mass of mafic enclaves (indicated by white arrows) of variable size resulting fromthe disruption of viscous fingering patterns.


turbulent flow fields and in such dynamic conditions ahomogeneous dispersion of enclaves would have beenquickly achieved. Although this idea cannot be ruled outa priori, it has to be noted that the host magma has arhyolitic composition that implies a very high viscosity,as also clearly shown by the blocky aspect of the PietreCotte lava flow. Viscosity is the most importantparameter which tends to inhibit the development ofturbulence for a fluid flowing in a conduit (e.g. Tritton,1988), such as a magma moving towards the Earthsurface. The very high viscosity of the rhyolitic magma,therefore, is likely to have inhibited a turbulent behaviorof the magmatic system. In addition, the Pietre Cottelava flow displays sub-parallel bands extending contin-uously for several meters (up to 25–30 m) in the lavaflow indicating a laminar fluid-dynamic regime rather

than a turbulent one. Therefore, we consider also thissecond hypothesis as not suitable for explaining theoccurrence of mafic enclaves in the Pietre Cotte lavaflow.

Since fragmentation of enclaves is not likely to havebeen controlled by rising or emplacement of lava flow, thecauses for the fragmentation process may be shifted tomagma chamber processes. Several authors (e.g. Sparksand Marshall, 1986; Poli et al., 1996) indicate that animportantmechanism for fragmentation ofmaficmagma isits intrusion into a felsic magma chamber. In general,during such a process, thermal and rheological contrastsbetween magmas induce a rapid quenching of the maficmagma and, because of heat dissipated by the latter, asuper-heating of the felsic host (e.g. Sparks and Marshall,1986; Poli et al., 1996). The quenching of the mafic

Fig. 7. (A–F) Examples of mafic enclaves generated by the fragmentation of viscous fingering structures at Vegetation Island outcrops (Terra NovaIntrusive Complex, Antarctica; e.g. Perugini and Poli, 2005). White arrows indicate fingers of the mafic magma propagating towards the felsic host;the occurrence of cuspate terminations is also indicated.

Fig. 8. Frequency histogram displaying the distribution of values ofelongation for mafic enclaves generated by the disruption of viscousfingering structures.


magma moves its rheology from a liquid state towards asolid state behavior. The super-heating of the felsicmagma, on the contrary, induces its thermal expansiondriving convection dynamics in the overlying magmavolume (e.g. Snyder, 2000). Under such physical condi-tions, convection dynamics may act as a mechanism forfragmentation of the quenched mafic magma. Thedevelopment of suchdynamic conditions into sub-volcanicmagma chambers has been suggested to trigger volcaniceruptions (e.g. Sparks et al., 1977; Leonard et al., 2002).

From a qualitative point of view, disruption of amafic magma during its intrusion into a felsic oneappears as a reasonable process to explain the presenceof mafic fragments (enclaves) in the studied lava flow.This would be also consistent with geochemical andpetrological studies indicating an important role playedby magma interaction processes in the genesis of rockscropping out on the island of Vulcano (e.g. De Astiset al., 1997). However, if as a first approximation such amagma chamber scenario appears reasonable, moredetailed discussions are needed. In particular, it isimportant to test whether the above process can explain(i) the fractal distribution of fragments of mafic magma

observed in the studied lava flow, and (ii) the measuredvalue of fragmentation fractal dimension.

Recent studies (e.g. Perugini and Poli, 2005) based onquantitative analysis of structure generated by fluidmechanics experiments and structures observed on natural

Fig. 9. Variation of the logarithm of cumulative number of fragmentswith areas A larger than comparative area a(log[N(ANa)]) against log(a) for enclaves resulting from fragmentation of viscous fingeringstructures. In the graph, the value of r2 from the linear fitting, andvalues of m and Df are also reported; binning of data performedaccording to Izenman (1991).


outcrops of granitoid rocks where the initial stages of theintrusion of a mafic magma into a felsic magma chamberremained fossilized, indicate that the intrusion process isgoverned by “viscous fingering” processes. Viscousfingering induces the development of interdigitatingpatterns of the mafic magma into the felsic magma, withvariablemorphologies depending on the viscosity contrast(e.g. Perugini et al., 2005) and injection pressure (e.g.Kawaguchi et al., 1997). Examples of such interdigitatingstructures occurring at Vegetation Island outcrops (TerraNova Intrusive Complex, Antarctica; Di Vincenzo andRocchi, 1999; Perugini et al., 2005) are presented in Fig. 6.These structuresmay be stable in time, providing that afterthe injection process the system remained in staticconditions. However, as discussed above, after theinjection of the mafic magma local convection dynamicsmay be triggered into the felsic magma and this mightinduce fragmentation of these structures. In particular, thefingers are the most vulnerable segments where thefragmentation process is more likely to take place. Thiseffect of fragmentation of mafic/felsic interfaces is clearlyshown in the pictures of Fig. 6, where fragments detachedfrom “fingers” of mafic magma are incorporated in thefelsic host as mafic enclaves. In Fig. 7 detailed pictures ofenclaves detached from natural viscous fingering patternsare shown.Observation of these pictures indicates a strongmorphological similarity between enclaves occurring inthe studied lava flow (Fig. 3) and those generated by

the disruption of the viscous fingering patterns (Fig. 7).In particular, in both cases, enclaves display irregularmorphologies represented by fingers of the mafic magmapropagating towards the felsic host. In the light of theabove discussion, themorphology of enclaves in the PietreCotte lava flow could be explained by considering thedisruption of viscous fingering patterns. Additionally,comparison between enclave morphology in Figs. 3 and 7highlights the occurrence of cuspate terminations in theenclaves from both the lava flow and those generated bythe disruption of viscous fingering structures. Cuspateedges may represent the points of detachment of theenclaves from the mafic mass during the fragmentation ofthe fingers. This morphological similarity may argue infavor of the hypothesis that the occurrence of maficenclaves in the studied lava flow could be associated tomagma chamber dynamics.

In order to test quantitatively the validity of this lasthypothesis, a number of enclaves occurring at Vegeta-tion Island outcrops, and resulting from the disruption ofviscous fingering structures (e.g. Figs. 6 and 7), havebeen analyzed. These enclaves have been analyzed inthis work for the first time by utilizing the same imageanalysis techniques used to analyze enclaves from thePietre Cotte lava flow. A total of 541 enclaves have beenanalyzed and results show a large variability of size(area) ranging from ca. 4 ·10− 1 to ca. 2.7 ·101 cm2. Thisrange of values is of the same order of magnitude as theone measured for the enclaves in the lava flow, thusindicating that the disruption of fingered structures cangenerate a similar enclave size variability. In order tocompare the morphological features of enclaves fromVegetation Island outcrop with those occurring in thelava flow, the elongation of enclaves resulting fromfragmentation of viscous fingering structures has beencalculated. Results are presented in Fig. 8 as a frequencyhistogram of elongation values. As in the case ofenclaves occurring in the lava flow, the distribution isbell-shaped and skewed towards unity with maximumvalues located at ca. 0.7–0.8 (compare Figs. 4 and 8).This second result indicates another point of conver-gence between the morphological features of theenclaves from the lava flow and those resulting fromthe fragmentation of fingered patterns. The same fractalstatistical approach used for the Pietre Cotte enclaveshas been applied to the size distribution of the enclavesgenerated by the fragmentation of the viscous fingeringstructures. Fig. 9 shows the variation of the logarithm ofcumulative number of fragments with areas A largerthan comparative area a(log[(ANa)]) against log(a),according to Eq. (3). It is shown that the data points aredisposed along a straight line, as for enclaves in the lava


flow, indicating that the fragmentation process ofviscous fingering structures can produce a fractaldistribution of enclaves. In addition, linear fitting ofdata gives a value of Df =2.55, which is very close to thevalue measured for the enclaves in the lava flow(Df =2.50). The fact that fragmentation of viscousfingering structures generates a fractal distribution offragments and that the value of Df is close to thatmeasured for the enclaves in the lava flow stronglysupports the hypothesis that the disruption of fingeringpatterns due to the injection of a mafic magma into afelsic magma, in the magma chamber, may be invokedas a possible explanation to account for the featuresobserved in the studied lava flow.

5. Summary and conclusions

In this contribution we have shown that enclave sizedistribution in the Pietre Cotte lava flow can beexplained by a fractal fragmentation process thatgenerates a self-similar distribution of fragments.Estimated fractal dimension of fragmentation for theenclave magma is 2.50. According to natural evidence itis suggested that the fragmentation of mafic magma mayhave occurred after its injection into the felsic magma inresponse to disruption of viscous fingering morpholo-gies generated by the injection process. Analysis ofenclaves generated by fragmentation of viscous finger-ing structures shows a fractal size distribution offragments and a value of fractal dimension of fragmen-tation of 2.55, in close agreement with natural data.According to these results, the size distribution of maficenclaves dispersed in the studied lava flow is considereda feature inherited from magma chamber processes.

Additional studies of the size distribution of magmaticenclaves and numerical and/or analogue experimentsmay help to evaluate our hypothesis and its possibleapplicability as a tool for investigating magma chamberprocesses by analyzing textural heterogeneities involcanic rocks. Such studies may help to elucidate therelationships between volcanic and deep seated magmaticprocesses, and the role of their interplay in generatingtextural heterogeneities in both plutonic and volcanicrocks.

Acknowledgements

Constructive comments of C. De Campos and ananonymous referee are gratefully acknowledged. Thiswork was funded by MIUR (Ministero dell'Istruzione,dell'Università e della Ricerca) and Università degliStudi di Perugia grants.

References

Avnir, D., Biham, M., Lidar, D., Malcai, O., 1998. Is the geometry ofnature fractal? Science 279, 39–40.

Bacon, C., 1986. Magmatic inclusions in silicic and intermediatevolcanic rocks. Journal of Geophysical Research 91, 6091–6112.

Bateman, R., 1995. The interplay between crystallization, replenish-ment and hybridization in large felsic magma chambers. Earth-Science Reviews 39 (1–2), 91–106.

Blake, S., Fink, J., 2000. On the deformation and freezing of enclavesduring magma mixing. Journal of Volcanology and GeothermalResearch 95 (1–4), 1–8.

Calanchi, N., De Rosa, R., Mazzuoli, R., Rossi, P., Santacroce, R.,Ventura, G., 1993. Silicic magma entering a basaltic magmachamber: eruptive dynamics and magma mixing — an examplefrom Salina (Aeolian Islands, southern Tyrrhenian Sea). Bulletin ofVolcanology 55 (7), 504–522.

De Astis, G., La Volpe, L., Peccerillo, A., Civetta, L., 1997.Volcanological and petrological evolution of Vulcano island(Aeolian Arc, southern Tyrrhenian Sea). Journal of GeophysicalResearch B: Solid Earth 102 (B4), 8021–8050.

De Campos, C., Dingwell, D., K.T.F., 2004. Decoupled convectioncells from mixing experiments with alkaline melts from PhlegreanFields. Chemical Geology 213, 227–251.

De Rosa, R., Mazzuoli, R., Ventura, G., 1996. Relationships betweendeformation and mixing processes in lava flows: a case study fromSalina (Aeolian Islands, Tyrrhenian Sea). Bulletin of Volcanology58 (4), 286–297.

Di Vincenzo, G., Rocchi, S., 1999. Origin and interaction of mafic andfelsic magmas in an evolving late orogenic setting: the EarlyPaleozoic Terra Nova Intrusive Complex, Antarctica. Contribu-tions to Mineralogy and Petrology 137, 15–35.

Eichelberger, J., 1980. Vesiculation of mafic magma during replen-ishment of silicic magma reservoir. Nature 288, 446–450.

Frazzetta, G., La Volpe, L., Sheridan, M., 1983. Evolution of the Fossacone. Journal of Volcanology and Geothermal Research 17, 329–360.

Gioncada, A., Mazzuoli, R., Milton, A., 2005. Magmamixing at Lipari(Aeolian Islands, Italy): insights from textural and compositionalfeatures of phenocrysts. Journal of Volcanology and GeothermalResearch 145 (1–2), 97–118.

Gonnermann, H., Manga, M., 2005. Flow banding in obsidian: arecord of evolving textural heterogeneity during magma deforma-tion. Earth and Planetary Science Letters 236, 135–147.

Holtz, F., Lenné, S., Ventura, G., Vetere, F., Wolf, P., 2004. Non-lineardeformation and break up of enclaves in a rhyolitic magma: a casestudy from Lipari Island (Southern Italy). Geophysical ResearchLetters 31 (L24611). doi:10.1029/2004GL021590.

Izenman, A.J., 1991. Recent developments in nonparametric densityestimation. Journal of the American Statistical Association 86,205–224.

Kawaguchi, M., Makino, K., Kato, T., 1997. Viscous fingeringpatterns in polymer solutions. Physica D 109, 325–332.

Keller, J., 1980. The island of Salina. Rendiconti della Societa Italianadi Mineralogia e Petrologia 36 (1), 489–524.

Leonard, G., Cole, J., Nairn, I., Self, S., 2002. Basalt triggering ofthe c. AD 1305 Kaharoa rhyolite eruption, Tarawera VolcanicComplex, New Zealand. Journal of Volcanology and GeothermalResearch 115 (3–4), 461–486.

Mandelbrot, B., 1982. The Fractal Geometry of Nature. W.H.Freeman.

Ottino, J., 1989. The Kinematics of Mixing: Stretching, Chaos andTransport. Cambridge University Press.

http://dx.doi.org/10.1029/2004GL021590


Perugini, D., Poli, G., 2004. Analysis and numerical simulation ofchaotic advection and chemical diffusion during magma mixing:petrological implications. Lithos 78 (1–2), 43–66.

Perugini, D., Poli, G., 2005. Viscous fingering during replenishment offelsic magma chambers by continuous inputs of mafic magmas:field evidence and fluid-mechanics experiments. Geology 33 (1),5–8.

Perugini, D., Poli, G., Mazzuoli, R., 2003. Chaotic advection, fractalsand diffusion during mixing of magmas: evidence from lava flows.Journal of Volcanology and Geothermal Research 124 (3–4),255–279.

Perugini, D., Poli, G., Prosperini, N., 2002. Morphometric analysis ofmagmatic enclaves: a tool for understanding magma vesiculationand ascent. Lithos 61 (3–4), 225–235.

Perugini, D., Poli, G., Rocchi, S., 2005. Development of viscousfingering between mafic and felsic magmas: evidence from theTerra Nova Intrusive Complex (Antarctica). Mineralogy andPetrology 83 (3–4), 151–166.

Poli, G., Tommasini, S., Halliday, A., 1996. Trace element and isotopicexchange during acid–basic magma interaction processes. Trans-actions — Royal Society of Edinburgh: Earth Sciences 87 (1–2),225–232.

Smith, J., 2000. Structures on interfaces of mingled magmas, StewartIsland, New Zealand. Journal of Structural Geology 22 (1),123–133.

Snyder, D., 2000. Thermal effects of the intrusion of basaltic magmainto a more silicic magma chamber and implications for eruption

triggering. Earth and Planetary Science Letters 175 (3–4),257–273.

Sparks, R., Marshall, L., 1986. Thermal and mechanical constraints onmixing between mafic and silicic magmas (Scotland). Journal ofVolcanology and Geothermal Research 29 (1–4), 99–124.

Sparks, R., Sigurdsson, H., Wilson, L., 1977. Magma mixing: amechanism for triggering acid explosive eruptions. Nature 267,315–318.

Tritton, D., 1988. Physical Fluid Dynamics. Oxford University Press,Oxford.

Turcotte, D.L., 1992. Fractals and Chaos in Geology and Geophysics.Cambridge University Press.

Ventura, G., 1998. Kinematic significance of mingling–rollingstructures in lava flows: a case study from Porri Volcano (Salina,Southern Tyrrhenian Sea). Bulletin of Volcanology 59 (6),394–403.

Ventura, G., 2004. The strain path and kinematics of lava domes: anexample from Lipari (Aeolian Islands, Southern TyrrhenianSea, Italy). Journal of Geophysica Research: Solid Earth 109(B1). doi:10.1029/2003JB002740.

Wada, K., 1995. Fractal structure of heterogeneous ejecta from the Me-akan volcano, eastern Hokkaido, Japan: implications for mixingmechanism in a volcanic conduit. Journal of Volcanology andGeothermal Research 66 (1–4), 69–79.

Documents

Insights into magma chamber processes from the analysis of size distribution of enclaves in lava flows: A case study from Vulcano Island (Southern Italy)