UNIVERSITY OF GOTHENBURG Department of Earth Sciences Geovetarcentrum/Earth Science Centre

ISSN 1400-3821 B742 Bachelor of Science thesis Göteborg 2013

Mailing address Address Telephone Telefax Geovetarcentrum Geovetarcentrum Geovetarcentrum 031-786 19 56 031-786 19 86 Göteborg University S 405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN

P‐TandEvolutionofHrólfsvíkxenolithsandhostlava,ReykjanesPeninsula,SWIceland

Linda Reyier

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Abstract

Xenoliths from Hrólfsvík on the Reykjanes Peninsula are hosted by lava of basaltic composition, containing 45-55% plagioclase, 33-43% clinopyroxene, 10% olivine, 2% Cr-spinel and titanomagnetite. The xenoliths consist of 75-85% plagioclase, 10-15% olivine, 5-10% clinopyroxene and minor Cr-spinel, reflecting olivine gabbroic to troctolitic composition. Cumulus textures in the xenoliths are the product of fractional crystallization, and SEM-EDS imaging and individual mineral grain analyses indicate that clinopyroxene was the first mineral to form, followed by plagioclase, olivine and a second generation of clinopyroxene. Geothermobarometric modelling based on clinopyroxene and whole-rock compositions yields depths down to 41-61 km for the crystallization of the first generation of clinopyroxenes. The second generation was initiated by a new injection of magma, i.e. the host lava, in the cumulate at a depth of 20-33 km. Since the crustal thickness in this area is approximately 20 km suggests that the cumulate might have resided in a magma chamber within the mantle lithosphere before being incorporated by the host lava and developed their present mineral composition. Keywords: xenoliths, host lava, Hrólfsvík, Reykjanes Peninsula, fractional crystallization, geothermobarometric modelling, TWEEQ, Domino-Theriak, clinopyroxene thermobarometry, olivine thermometry, SEM-EDS, LA-ICP-MS, classification diagrams, tectonic discrimination diagrams, REE diagrams, spider diagrams.

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Sammanfattning

Xenoliterna från Hrólfsvíkområdet på Reykjaneshalvön är belägna i ett lavaflöde av basaltisk sammansättning. Lavan innehåller 45-55% plagioklas, 33-43% klinopyroxen, 10% olivin, 2% Cr-spinell och titanomagnetit. Xenoliterna består av 75-85% plagioklas, 10-15% olivin, 5-10% klinopyroxen och små mängder Cr-spinell och kan således klassificeras som olivingabbro till troktolit. Kumulustexturer i xenoliterna är ett resultat av fraktionell kristallisering och analyser med SEM-EDS indikerar att klinopyroxen var det första mineralet att kristalliseras vilket följdes av plagioklas, olivin och en andra generation klinopyroxen. Geotermobarometriska modelleringar har gett djup ner till 41-61 km för kristallisationen av den första generationen klinopyroxener; den andra generationen bildades på ett djup av 20-33 km när ny magma intruderade kumulatet. Eftersom skorpan i detta område endast är 20 km tjock innebär det att kumulatet troligtvis legat i en magmakammare inom mantellitosfären innan det inkorporerades av den nya magman och xenoliterna fick sin ursprungliga mineralsammansättning. Nyckelord: xenoliter, lava, Hrólfsvík, Reykjaneshalvön, fraktionell kristallisering, geotermobarometrisk modellering, TWEEQ, Domino-Theriak, klinopyroxentermobarometri, olivintermometri, SEM-EDS, LA-ICP-MS, klassificeringsdiagram, tektoniska diskrimineringsdiagram, REE-diagram, spindeldiagram.

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Contents Abstract .................................................................................................................................................................................. 1

Sammanfattning ................................................................................................................................................................. 2

1. Introduction ................................................................................................................................................................ 5

1.1 Aims and objectives ....................................................................................................................................... 5

1.2 Geology of Iceland .......................................................................................................................................... 5

1.2.1 History and geologic setting ............................................................................................................. 5

1.2.2 Distribution of volcanic zones ......................................................................................................... 6

1.2.3 Extrusive products and their hosting volcanic systems ....................................................... 7

1.2.4 Mid-Ocean Ridge Basalt or Ocean-Island Basalt ...................................................................... 8

1.2.5 Crustal thickness and the lithosphere-asthenosphere boundary ..................................... 8

1.3 Study area .......................................................................................................................................................... 9

1.3.1 Geological setting .................................................................................................................................. 9

1.3.2 Eruptive history and its products................................................................................................... 9

1.4 Previous studies .................................................................................................................................................. 11

2. Methods ..................................................................................................................................................................... 11

2.1 Studied samples ........................................................................................................................................... 11

2.2 Sample preparation .................................................................................................................................... 11

2.2.1 Thin sections ........................................................................................................................................ 11

2.2.2 Whole rock ............................................................................................................................................ 12

2.3 Optical studies ............................................................................................................................................... 12

2.4 Scanning electron microscopy ............................................................................................................... 12

2.5 LA-ICP-MS ....................................................................................................................................................... 12

2.6 Geothermobarometric modelling ......................................................................................................... 13

2.7 Olivine thermometry& clinopyroxene thermobarometry .......................................................... 13

2.7.1 Olivine-liquid thermometry ........................................................................................................... 14

2.7.2 Clinopyroxene-liquid thermobarometry .................................................................................. 15

2.8 Classification & discrimination diagrams .......................................................................................... 16

2.9 Rare Earth Elements diagram................................................................................................................. 16

2.10 Spider diagrams ........................................................................................................................................... 17

3. Results ........................................................................................................................................................................ 17

3.1 Mineralogy & petrology ............................................................................................................................ 17

3.2 Geochemistry ................................................................................................................................................. 20

3.2.1 The xenoliths ........................................................................................................................................ 20

3.2.2 The host lava ........................................................................................................................................ 21

3.2.3 The contact zone ................................................................................................................................. 22

3.3 Whole rock...................................................................................................................................................... 24

3.3.1 The xenoliths ........................................................................................................................................ 24

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3.3.2 The host lava ........................................................................................................................................ 25

3.4 Geothermobarometric modelling ......................................................................................................... 26

3.4.1 The xenoliths ........................................................................................................................................ 26

3.4.2 The host lava ........................................................................................................................................ 28

3.4.3 The contact zone ................................................................................................................................. 29

4. Discussion ................................................................................................................................................................. 29

4.1 Mineralogy & petrology ............................................................................................................................ 29

4.2 Geochemistry ................................................................................................................................................. 31

4.3 P,T conditions ................................................................................................................................................ 33

5. Conclusions .............................................................................................................................................................. 33

6. References ................................................................................................................................................................ 35

Appendix A, Mineral compositions in the xenoliths ......................................................................................... 36

i) ........................................................................................................................................................................................ 36

ii) ....................................................................................................................................................................................... 37

iii) ...................................................................................................................................................................................... 38

iv) ...................................................................................................................................................................................... 39

v) ....................................................................................................................................................................................... 40

vi) ...................................................................................................................................................................................... 41

vii) ..................................................................................................................................................................................... 42

Appendix B. Mineral compositions in the lava .................................................................................................... 43

i) ........................................................................................................................................................................................ 43

ii) ....................................................................................................................................................................................... 44

iii) ...................................................................................................................................................................................... 45

iv) ...................................................................................................................................................................................... 46

v) ....................................................................................................................................................................................... 47

vi) ...................................................................................................................................................................................... 48

Appendix C. Mineral compositions at the contact ............................................................................................. 49

i) ........................................................................................................................................................................................ 49

ii) ....................................................................................................................................................................................... 50

iii) ...................................................................................................................................................................................... 51

iv) ...................................................................................................................................................................................... 52

v) ....................................................................................................................................................................................... 53

vi) ...................................................................................................................................................................................... 54

vii) ..................................................................................................................................................................................... 55

Appendix D. Whole rock analyses ............................................................................................................................ 56

i) ........................................................................................................................................................................................ 56

ii) ....................................................................................................................................................................................... 57

iii) ...................................................................................................................................................................................... 58

iv) ...................................................................................................................................................................................... 59

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1. Introduction

1.1 Aims and objectives The aim of this study is to obtain a fuller understanding of the petrology, geochemistry, and origin of the Hrólfsvík xenoliths as well as the host lava. By using geothermobarometric models such as TWEEQ and Domino-Theriak as well as clinopyroxene thermobarometry and olivine thermometry, the hope is to resolve the pressure and temperature conditions under which the protolith for the xenoliths crystallized. Xenoliths are alien rock fragments that have been incorporated in a body of magma. They can be of different origins, e.g. mantle or crustal. Furthermore, the incorporation can occur via different processes; (1) during the ascent of the magma to the surface, when they could be incorporated from the walls of the conduit, (2) via assimilation of the magma chamber wall where the magma is residing during a longer period of time, (3) partial melting of the mantle could have been incomplete, which would have left behind aggregates of crystals that survived as xenoliths. This study’s main objective will be determining the depth of the xenoliths using geothermobarometric modelling. Considering that this has not been attempted before on the Hrólfsvík xenoliths, it is of particular interest. Additional objectives for this study include: 1) Mineralogical, petrographic and

geochemical analyses of the xenoliths to

determine if they are fragments derived

from the crust or the mantle.

2) Mineralogical and petrographic analyses

of the contact rims between the xenolith and

the host lava to yield indications of how long

the xenoliths had been lying in the magma

prior to the eruption.

3) Attempt geothermobarometric modelling

of the contact mineral composition to

determine at what depth the xenoliths got

incorporated in the host lava.

4) Attempt geothermobarometric modelling

on the host lava to determine its depth of

origin.

5) Geochemical characterization of the

xenoliths and host lava in order to identify

the magma source; are their host magmas

derived from the hotspot or the rift?

1.2 Geology of Iceland

1.2.1 History and geologic setting The making of the NE Atlantic and the Mid-Atlantic Ridge (MAR) began ~160 Ma ago with the breakup of the supercontinent Pangea. At about ~65 Ma a mantle plume is believed to have been situated close to the former position of the west coast of Greenland. Due to the fact that mantle plumes are fixed relative to any plate movements above, the soon-to-be Icelandic plume left behind a trail of igneous rocks as the North American and Eurasian plate simultaneously drifted slowly towards NW (Harðarson, Fitton, & Hjartarson, 2008). It is assumed that the plume caused the MAR to move towards East Greenland and when the plume and MAR got close they started to interact. This caused immense volcanic activity due to the extra heat influx and their interaction is thought to be the reason for the construction of the vast Iceland basalt plateau at about 24 Ma (Thordarson & Larsen, 2007). Since then the mantle plume and MAR have been linked to each other (Harðarson, Fitton, & Hjartarson, 2008). Today, all the rocks produced by the Iceland mantle plume since ~65 Ma (including Iceland) comprise the North Atlantic Igneous Province; a ~2000 km long province stretching from Baffin Island in the west to Scotland in the east, also referred to as the Greenland-Iceland-Faeroes-Ridge (Fig. 1). Currently, the plume axis is situated under Vatnajökull (Fig. 1). Since both plates (North

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American and Eurasian) are drifting towards NW, the Reykjanes-Kolbeinsey plate boundary segments (the subaerial continuation of the MAR) are now situated 150-200 km northwest of the plume axis (Harðarson, Fitton, & Hjartarson, 2008). When the Icelandic rift segments no longer are accurately linked to the plume, a phenomenon called rift-relocation or ridge-jump occurs, the result of which is to maintain the rift segments position above the plume axis. This is a process that occurs by rift propagation and has taken place repeatedly since the formation of Iceland; at about 24, 15, 7 and 3 Ma (Trönnes, 2003). This process is the reason for many geological features represented in Iceland.

1.2.2 Distribution of volcanic zones The distribution and arrangement of the currently active rift segments, referred to as neovolcanic zones, results from the above mentioned rift-relocations. The neovolcanic zones are the hosts of the currently active volcanic zones in Iceland (Fig. 2); the Western Volcanic Zone including the Reykjanes Volcanic Belt, the Mid-Icelandic Volcanic Zone, the Northern Volcanic Zone, and the Eastern Volcanic Zone. The Western Volcanic Zone and Northern Volcanic Zone are today the subaerial continuations of the MAR and both were developed during the rift-relocation at ~7 Ma (Trönnes, 2003).

Figure 1. Iceland is situated in the middle of the Mid-Atlantic Ridge and is positioned in the centre of the NW-SE trending Greenland-Iceland-Faeroe Ridge. The North Atlantic Igneous Province is shown in black (onshore) and dark grey (offshore). The dotted white lines indicate the position of transform faults across Iceland whereas the solid white lines show the location of the subaerial parts of the MAR. The mantle plume is today situated beneath Vatnajökull and is marked with the number zero. From Harðarson, Fitton, & Hjartarson (2008).

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The Western Volcanic Zone is connected to the Reykjanes Ridge via the Reykjanes Volcanic Belt in the south and the Northern Volcanic Zone is connected to the Kolbeinsey Ridge by the Tjörnes Fracture Zone (TFZ) in the north (Fig. 2). Volcanic zones situated off-rift, also referred to as volcanic flank zones, are located where there currently are no active rifts manifested on the surface. Volcanic zones belonging to this group are the Snaefellsness Volcanic Zone (SVZ) in the west and the Öraefajökull Volcanic Zone (ÖVZ) in the east (Fig. 2). Furthermore, the volcanic systems in the southern end of the EVZ all belong to this group including Katla, Eyjafjallajökull,

Vestmannaeyjar, Tindfjallajökull and Surtsey (Thordarson & Larsen, 2007).

1.2.3 Extrusive products and their hosting volcanic systems

The rock compositions in Iceland are very variable, ranging from basalt to rhyolite (Jakobsson, Jónasson, & Sigurdsson, 2008); however, basalts are by far the most abundant. Thordarson & Larsen (2007) estimated that for the last 1100 years, the basaltic rocks account for 79% of the volcanic rock volume produced, intermediate rocks 16% and silicic rocks 5%. Furthermore, these three compositions are all subdivided depending on their alkali

Figure 2. Illustration of the relationship between the rift segments, volcanic zones and seismic zones. From Thordarson & Larsen (2007). The abbreviations are as follows: RR = Reykjanes Ridge; RVB = Reykjanes Volcanic Belt; SISZ = South Iceland Seismic Zone; WVZ = Western Volcanic Zone; MIB = Mid-Iceland Belt; EVZ = Eastern Volcanic Zone; NVZ = Northern Volcanic Zone; TFZ = Tjörnes Fracture Zone; KR = Kolbeinsey Ridge; ÖVB = Öræfi Volcanic Belt; SVB = Snæfellsnes Volcanic Belt.

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content into three igneous rock series; a tholeiitic, an alkalic, and a transitional alkalic series. These are then further subdivided depending on their MgO content (Table 1).

In Iceland today, 30 subaerial along with 11 submarine active volcanic systems have been confirmed. A volcanic system consists of either a fissure swarm (i.e., typically elongate structures aligned sub-parallel to the axis of the hosting volcanic zone) or a central volcano or both. Shallow (2-3 km) magma chambers typically are found located beneath the central volcanoes within the volcanic systems (Jakobsson, Jónasson, & Sigurdsson, 2008). Figure 3 illustrates the location of each volcanic system in Iceland; furthermore, this figure also illustrates the distribution of the different igneous rock series present. The active rift segments and its volcanic systems comprise the tholeiitic rock series whereas the alkalic and transitional alkalic series are confined to the flank zones (Jakobsson, Jónasson, & Sigurdsson, 2008).

1.2.4 Mid-Ocean Ridge Basalt or Ocean-Island Basalt

The position of Iceland above not only the MAR but also a mantle plume leads to the development of basalts that can be geochemically similar to both Mid-Ocean Ridge Basalt (MORB) and Ocean-Island Basalt (OIB) respectively. However, most of the basalts erupted on Iceland are OIB-like (Jakobsson, Jónasson, & Sigurdsson, 2008).

Furthermore, MORBs are generally tholeiitic in composition whereas OIBs are mostly alkaline (Jakobsson, Jónasson, & Sigurdsson, 2008). However, when OIBs are erupted on or near ocean-ridges they too can be tholeiitic which makes distinction between the two more complicated.

1.2.5 Crustal thickness and the lithosphere-asthenosphere boundary

The crustal thickness beneath Iceland varies from 15-20 km in the coastal areas up to about 40 km under central Iceland (Brandsdóttir & Menke, 2008; Sigmundsson & Saemundsson, 2008). This is several times greater than the regular thickness of oceanic crust (~5 km) and is due to the extensive influx of heat beneath Iceland which generates magmatic intrusions (Kumar, et al., 2005). The crust is the topmost part of every lithospheric plate and is divided into two parts, the crust and the mantle lithosphere. The lithospheric plates move on top of the convecting asthenosphere. The boundary between the two is referred to as the lithosphere-astenosphere boundary (LAB). At mid-ocean ridges, the lithospheric thickness is considered to be close to zero; however, below most of Iceland the LAB is 80 km down and this is thought to be an effect of the mantle plume underneath (Kumar, et al., 2005).

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1.3 Study area The xenoliths were sampled by Erik Sturkell together with the host lava in the area of Hrólfsvík located in a bay east of Grindavík town, on the southern shore of the Reykjanes Peninsula, SW Iceland (Fig. 4).

1.3.1 Geological setting The Reykjanes Peninsula, or the Reykjanes Volcanic Belt, is the subaerial continuation of the MAR in southern Iceland. The peninsula stretches from the SW tip to the Hengill Triple Junction where it joins with the Western Volcanic Zone and South Iceland Seismic Zone (Fig. 2) (Einarsson, 2008). The peninsula is the location for five en-echelon volcanic systems; from Reykjanes in the west via Grindavík, Krísuvík and

Brennisteinsfjöll ending with Hengill in the east. Each volcanic system comprises a fissure swarm consisting of normal faults and open fissures, oblique to the divergent plate boundary with a trend of ~35° (Einarsson, 2008).

1.3.2 Eruptive history and its products

According to Thordarson & Höskuldsson (2008), 144 postglacial eruptions (i.e. over the last 11,000 years) have taken place on the Reykjanes Peninsula. Out of these, 111 of them were effusive and 33 of them explosive. The latest active period began shortly after the settlement in 950 AD and ended in 1240 AD. During this period all the volcanic systems of the peninsula had an eruptive episode which generated several lava flows issuing from their fissure swarms. Monitoring of the peninsula has shown no

Figure 3. The volcanic zones active in Iceland and its insular shelf during Holocene and Late-Pleistocene. The number of volcanic systems active during Holocene are shown. Distinction is made between tholeiitic, transitional alkalic and alkalic volcanic systems. From Jakobsson, Jónasson, & Sigurdsson (2008). The black triangles indicate the sites of central volcanoes. The abbreviations are as follows: NRR = Northern Reykjanes Ridge; WVZ = Western Volcanic Zone; HVZ = Hofsjökull Volcanic Zone; EVZ = Eastern Volcanic Zone; NVZ = Northern Volcanic Zone; TVZ = Tjörnes Volcanic Zone; SVZ = Snæfellsnes Volcanic Zone; ÖVZ = Öræfajökull Volcanic Zone; SISZ = South Iceland Seismic Zone.

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Figure 4. Geological map of the Reykjanes Peninsula showing the en echelon volcanic systems and their fissure swarms. The location for the collected samples is indicated with the black box and arrow on the southern coast. Modified from Jakobsson, Jónsson, & Shido (1978).

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evidence of magmatic contribution during the last decades (Einarsson, 2008). The Reykjanes Peninsula belongs to the tholeiitic series and has almost exclusively produced rocks of basaltic composition. There is only one volcanic system on the peninsula that has produced rocks with intermediate and silicic composition and that is the easternmost Hengill system (Jakobsson, Jónsson, & Shido, 1978). Considering this, the focus is laid on the basaltic compositions which are divided into picrite, olivine tholeiite and tholeiite depending on the MgO content in the rock (Table 1) (Jakobsson, Jónsson, & Shido, 1978; Jakobsson, Jónasson, & Sigurdsson, 2008). Picrites are high-Mg rocks containing 12-18 weight percent (wt. %) MgO, olivine tholeiites contain 8-12 wt. % MgO, and the tholeiites have MgO content between 5-8 wt. % (Jakobsson, Jónasson, & Sigurdsson, 2008).

1.4 Previous studies Studies on the Hrólfsvík xenoliths and their host lava have been carried out in order to determine their petrology, geochemistry and origin. However, the available literature is scarce and only abstracts can be found written in English, making this research difficult. The other papers are written in Icelandic which makes the interpretation of the results difficult to resolve. Abstracts by Grandvuinet & Óskarsson (2006) and Grandvuinet, Óskarsson, & Grönvold (2006) have however facilitated a simplified summary of certain features displayed by the xenoliths found during their studies. 1) The xenoliths display rounded edges and include all kind of shapes with a size range of 3-25 cm. 2) They display both primary and secondary mineralization and in some cases contain groundmass pockets.

3) A simplified modal composition of 60-90% plagioclase, 10-30% olivine, minor clinopyroxene and accessory oxide has been found. 4) They can be classified as gabbroic to troctolitic. 5) Chromian diopside and few chromites indicate a deep crustal origin. 6) The outermost rim of the minerals is evolved as an outcome of partial melting; i.e., the rims have a different mineral composition then the core. 7) Because of the constantly low K2O content displayed by whole rock composition, they might be plutonic picrites, the most primitive composition of the peninsula.

Grandvuinet, Óskarsson, & Grönvold (2006) furthermore suggest that the host lava for the Hrólfsvík xenoliths issued from the Grindavík volcanic fissure swarm. During historical times, this swarm has erupted a suite of primitive olivine tholeiites with the earliest Holocene lavas being picrites.

2. Methods

2.1 Studied samples Two samples, about 20x15x15 cm in size, containing both xenoliths and host lava were collected by Erik Sturkell at Hrólfsvík: LR12-01 and LR12-02. All the preparation and analyses were performed at the Department of Earth Sciences, University of Gothenburg with help from Mattias Ek.

2.2 Sample preparation

2.2.1 Thin sections Due to the presence of oxides on the surface, thin sections were made with the innermost piece of each sample to avoid this occurrence. An effort was made to assure that the thin sections contained both the xenolith and the host lava for the purpose of studying the contact rim.

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Four thin sections were prepared; two of them were abraded down to a thickness of ~60 microns, polished and carbon-coated for use in the Scanning Electron Microscope (SEM), and the other two were given a thickness of ~30 micron and kept unpolished for use in optical studies. The reason for the chosen thicknesses results from the difference in hardness between the lava and the xenolith. There was a risk that by polishing the ~30 micron thin sections, parts of the sample could be abraded off.

2.2.2 Whole rock To get the best representative whole-rock analysis, about 15 grams of equal-sized slices without oxidation and with an apparent homogeneity were chosen. Three whole-rock samples were prepared; one for each xenolith, and one for the host lava. In addition, three standards were chosen for determining the accuracy of the analyses; NIM-D, a dunite; JB-1, a basalt; and JG-1, a granodiorite. The xenoliths and host lava were crushed and ground. The crushing transformed the samples to fine powders which were then further ground by hand using an agate mortar and alcohol. Molybdenum-boats were Au-coated to prevent contamination during the glass-making process. The glass-making was accomplished by flushing the sample chamber with argon gas for one minute before sending a current of 20V for 20 sec through the instrument to pre-heat the sample. Next the current was set to 65V which melted the powder and turned it into glass. The current was immediately switched off when the sample was seen to have melted. To make the epoxy puck for analysis, pieces of the glass samples were mounted on edge in grease and then cast into an epoxy disk. The disk was abraded by hand until all the glass pieces had been exposed; a finishing 3 micron diamond polish diminished scratches on the surface.

2.3 Optical studies The mineralogy of the Hrólfsvík xenoliths and the host lava was determined using transmission light microscopy. In addition, a visual estimate on the modal composition was performed on the xenoliths for the purpose of determining the rock type. The lava had too-small grains for determining the modal composition visually.

2.4 Scanning electron microscopy

X-ray microanalyses were carried out on the two polished thin sections and the whole-rock samples. Mineral chemistry and whole-rock chemistry were determined using an energy dispersive spectrometer (EDS) attached to the SEM. Back-scatter electron (BSE) imaging modes were used for quantitative point identification. Point counting was performed on the lava areas using a gridmask with 4 second dwell time. 812 and 999 points were analysed for sample LR12-01 and LR12-02 respectively. The SEM, a HITACHI 3400N-S, was operated with a high vacuum at 20.00 kV and 3.50 nA sample current. The live-time for quantitative analyses was set to 100 sec and the working distance was 9.9 mm.

2.5 LA-ICP-MS Laser Ablation Inductively Coupled Plasma Mass Spectrometry was carried out on the whole-rock samples in the epoxy puck with an Aglient 7500. In total, 34 elements were chosen to be analysed. In addition, the standards BIR-1, BCR2G, NIST610 and NIST612 were analysed and then compared with recommended values from GeoReM to determine the accuracy of the analysis. BIR-1 is an Icelandic basalt and BCR2G is a basalt glass; NIST610 and NIST612 are two silicate glasses with different trace element concentrations.

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2.6 Geothermobarometric modelling

Geothermobarometric modelling was carried out using two different programs; TWEEQ (TWQ) and Domino-Theriak. The difference between these two is that in TWQ one can choose specific minerals and mineral compositions to calculate reaction lines, whereas in Domino-Theriak one uses the whole rock data and modal composition to find the pressure and temperature (P,T) conditions. Furthermore, modelling in Domino-Theriak was executed using two different databases; HoPoMelt and JUN92. The difference between the two is that the HoPoMelt database can be used to plot liquids (melts) whereas JUN92 cannot. When applying geothermobarometry there are some important things to consider (Winter, 2010); 1) Are the minerals in the rock in equilibrium with each other (i.e. no compositional zoning can be detected)? If they are in equilibrium the modelling will work fine; if not, special care has to be taken with where a compositional analysis has been carried out. One can assume that the rims of adjacent minerals have been in equilibrium with each other. Likewise, a mineral inclusion within the core of another mineral can be assumed to be in equilibrium with its host. 2) It is also assumed that most mineral assemblages found in a rock represent peak metamorphic temperatures; or the crystallisation temperature in igneous rocks. 3) Minerals in a rock do not consist of simple major element compositions; additional components such as Mn, Ti, Cr or Ni can affect the ratios of the main components. Since most experimental models are based on experiments using simple mineral systems, the resulting pressure and temperature calculations are not very precise.

2.7 Olivine thermometry& clinopyroxene thermobarometry

Olivine-liquid thermometry was carried out on the olivine compositions of the phenocrysts in the host lava, the olivines situated in the contact zone as well as the olivines in the xenoliths. Both the cores and the rims were taken into account to see if they would yield different T estimates. The liquid is represented by a whole-rock composition. Thus the olivines within the lava and at the contact zone should be plotted against the liquid for the lava, whereas the olivines within the xenoliths should be plotted against the liquid for that xenolith. Clinopyroxene-liquid thermobarometry was carried out on cpx compositions from the xenoliths, host lava and contact zone. Both inclusions and individual crystals were taken into account. The liquid in this geothermobarometer is used in the same approach as for the ol-liq thermometer. However, the whole-rock composition, when used, is assumed to represent a true liquid. For the xenoliths this is not the case since they are derived from a cumulate, hence not a liquid, as suggested by Grandvuinet & Óskarsson (2006) and Grandvuinet, Óskarsson, & Grönvold (2006). Therefore the whole-rock composition of the lava may be more appropriate. The equations for the different thermobarometers used are taken from Putirka (2008) and are presented on the next page. Putirka (2008) has however used other numbers for the equations: Equation (1) in this report is numbered (19) in Putirka (2008), Eq. (2) as (22), Eq. (3) as Eq. (31) and Eq. (4) as (32a). Further studies of them can be done from Excel spreadsheets found on the webpage: http://www.fresnostate.edu/csm/ees/facstaff//putirka.html/Keith_Putirka.html.

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The olivine-liquid thermometer was used in conjunction with the cpx-liquid thermobarometers. Since the pressure in the cpx-liq barometer was noticed to be very sensitive to changing temperature a temperature was first obtained from the ol-liq thermometer which then was applied to the cpx-liq barometer.

2.7.1 Olivine-liquid thermometry The ol-liquid thermometers use the Mg-Fe partitioning between the two phases and a first study done by Roeder and Emslie (1970) showed that the equilibrium constant varies little with T or composition for the reaction (Putirka, 2008): MgOol + FeOliq = MgOliq + FeOol

Since the ol-liq thermometers are based on equilibrium constants, P estimates on

phases in disequilibrium with each other are not valid. Equilibrium can be tested in the Rhodes diagram (Fig. 5) within the spreadsheet and is based on Mg-Fe partition between olivine and liquid. This means that any composition in disequilibrium with the liquid can, and should, be excluded. Equilibrium in the Rhodes diagram is met when compositions plot within the dashed lines running sub-parallel to the solid line (Fig. 5). An additional utility of this diagram is that it also can explain disequilibrium; trends exhibited for olivine removal, olivine accumulation, magma mixing and differentiation can be indicated, all of which lead to disequilibrium with the liquid. However, this only works if you have whole rock data representing liquid compositions for each olivine grain since the same whole rock data for all olivine grains only would yield a straight vertical line.

(3)

(4)

(1)

(2)

15

The thermometers used in this study are the ones of Beattie (1993), Eq. (1); and Putirka et al. (2007), Eq. (2). Equation (1) is based on the Mg distribution between the olivine and liquid. is the molar concentration of

component NM in the liquid (L); NM is the sum of the cation fractions XFeO, XMnO, XMgO and XCaO.

is the molar

concentration of the SiO2 component in the liquid and NF includes the cation fractions XAl2O3 and XTiO2 in the equation NF = (7/2) ln(1 – XAlO3/2) 7 ln(1 – XTiO2) Equation (1) works best for anhydrous systems, whereas Eq. (2) provides the best estimates when water is present in the liquid (within H2O contents of 0-18.6%). Apart from the water this equation is based

on the same Mg distribution and components as Eq. (1) (Beattie, 1993). Both these equations are generally considered to be by far the most precise (Putirka, 2008).

2.7.2 Clinopyroxene-liquid thermobarometry

Due to the use of the ol-liq thermometer in conjunction with the cpx-liq thermobarometers, only equations calculating a pressure are used in this spreadsheet. The barometers used are Eq. (3) and (4); they are used for equilibrium and disequilibrium compositions respectively (Putirka, 2008). The equations use the cation fractions and proportions (based on 6 oxygens) of the components jadeite (Jd), diopside + hedenbergite (DiHd) and enstatite + ferrosilite (EnFs) in both the clinopyroxene and liquid compositions (Putirka, 2008). In the spreadsheet the components are divided into predicted and observed cpx components and plotted against each other in a diagram that test for equilibrium (Fig. 6). If the components have the same or similar values the cpx and liquid are in equilibrium with each other and the components will thus plot close to the straight line. If the components have values that differ too much and consequently plot outside of the dashed lines the cpx and liquid are in disequilibrium. If equilibrium is met Eq. (3) is used. This equation is dependent on the water content in the rock; this means that the pressure will change with changing water content. The equation is based on the partition of Na and Al between cpx and liquid as well as the amount of Ca, Na, K, Si, Fe and Mg in the liquid. It is calibrated from a global regression of cpx-saturated experiments where experiments performed at 1 atm and P> 40 kbar have been excluded. As explained by Putirka (2008): “Most new calibrations utilise “global” regressions, which use all available data to determine the minimum number of parameters that

Figure 5. Rhodes diagram showing the equilibrium range calculated by the Mg-Fe partitioning between the olivine and liquid and the four possible trends indicating disequilibrium shown by the arrows. The olivine composition is plotted against the y-axis whereas the whole-rock composition is plotted against the x-axis. Modified from the Excel spreadsheet by Putirka.

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are required to explain observed variability”. If there is disequilibrium Eq. (4) is used. This equation is based on the cpx compositions only and is not dependent on the water content. This equation is a barometer based on Nimis (1995) which has been recalibrated using experiments performed from 0.001-80 kbar (previously excluding pressures <1 atm and >40 kbar). It uses the partition of Mg, Na and Al between the cpx compositions (Putirka, 2008). Both barometers used can calculate P to a precision of ±1.5 kbar (Putirka, 2008).

2.8 Classification & discrimination diagrams

Classification diagrams were used for classifying the xenoliths and lava and thus being able to name them accurately. Tectonic discrimination diagrams were used for determining the tectonic setting of the studied samples. For this particular study, classification and discrimination diagrams for basalts and mafic rocks were chosen; in particular those that facilitated the recognition of tholeiite, MORB and OIB. The classification diagrams chosen are the AFM (K2O + Na2O–FeOtot–MgO) diagram of Irvine and Baragar (1971); the Fetot + Ti–Al-Mg classification diagram of Jensen (1976); and the total alkalis (K2O + Na2O) vs. silica (SiO2) (TAS-IUGS) classification diagram of Le Maitre et al. (1989). The discrimination diagrams chosen are those of Pearce and Cann (1973) which use the elements Ti-Zr-Y and Ti-Zr-Sr, and that by Meschede (1986) which uses Nb-Zr-Y.

2.9 Rare Earth Elements diagram

Chondrite-normalised REE diagrams were used for revealing any fractionation in the studied samples relative to chondrites. Chondrites are thought to be relatively unfractionated samples of the solar system dating from the original nucleosynthesis (Rollinson, 1993). Thus, fractionation is almost inevitable.

However, the REE diagrams comprise the elements La-Lu and Y; elements that have very similar chemical and physical properties due to their 3+ charge and similar ionic radius. When subjected to petrological processes, the small size difference caused by the small decrease in ionic radius with increasing atomic number causes the REE series to become fractionated relative to each other (Rollinson, 1993).

Figure 6. Diagram for checking equilibrium between the cpx compositions and liquid. Observed cpx components are derived from the cpx compositions in the sample, whereas the predicted cpx components are derived from the whole-rock composition. The components are composed of CaTs (calcium tschermakite), a Ca-rich cpx; EnFs (enstatite-ferrosilite) which are Mg and Fe end members respectively; and DiHd (diopside-hedenbergite) which are CaMg and CaFe end members respectively. If the components plot in between the dashed lines and close to the solid line, they are in equilibrium with the liquid. Modified from the Excel spreadsheet by Putirka.

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2.10 Spider diagrams Spider diagrams or normalised multi-element diagrams were used in conjunction with three different normalisation compositions; MORB, ocean island basalt (OIB) and primordial mantle (PM). These particular diagrams are especially useful for depicting basalt chemistry and measure deviations from a chosen, more primitive composition (Rollinson, 1993). MORB is an appropriate choice for rocks that are more evolved like basalts and crustal rocks, whereas PM reflects the composition of the mantle before the continental crust formed (Rollinson, 1993). OIBs on the other hand reflect mantle sources typically originating from deeper levels than MORBs (Winter, 2010).

3. Results Hereafter the two xenoliths will be referred to as X-01 and X-02 (representing the xenoliths from sample LR12-01 and LR12-02 respectively) and the host lava will be referred to as L-01. Due to the presence of the nearby shore, the lava formation comprising the Hrólfsvík xenoliths is relatively barren and is subject to mechanical weathering (Fig. 7a). This has resulted in brittle xenoliths with additional oxidation that is visible on both the xenolith and the lava surface as discolourations. The mechanical weathering results in newly exposed surfaces during time, meaning that some of the xenoliths seen were exposed recently whereas others have been exposed for a long time.

3.1 Mineralogy & petrology To the naked eye the xenoliths are determined to consist of ~70% light minerals with the rest being dark and green (Figs. 7b and c). The colours result from the minerals plagioclase, pyroxene, and olivine respectively. In addition, small grains of

oxides can be seen on the exposed surfaces which seem to concentrate at the contact with the host lava. The distribution of the different minerals seems to be random, i.e. no preferred orientation or layering can be seen. The average grain size of the essential minerals in the xenoliths is ~2 mm. Furthermore, within the xenoliths, melt inclusions and vesicles are visible. The melt inclusions are dark in colour and finegrained; they look similar to the host lava. The vesicles are empty and have no sign of precipitating minerals within them (Fig. 7c). The lava as mentioned is dark in colour, however weathered surfaces are lighter (Fig. 7a). The lava is aphanitic, which means

Figure 7. Photos taken by Professor Erik Sturkell from the sample location at Hrólfsvík. a) The general appearance of the lava flow is rich in cracks. Also, a colour difference can be seen where the more weathered parts at the top of the flow are lighter. See person for scale. b) A close-up of one of the xenoliths displaying rounded edges and a relatively light appearance. The host lava has a darker appearance with several various-sized vesicles. c) Large crystals of green olivine are seen within the light-coloured plagioclase in this funny-shaped xenolith. Also, this particular xenolith displays numerous vesicles.

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that it is very fine-grained and mineral grains cannot be distinguished. Also, no larger grains (phenocrysts) can be seen with the naked eye. An abundant feature in the lava is empty vesicles as can be seen in Figure 7a to c taken at the location. When viewed through a petrographic microscope it is evident that plagioclase is the main mineral constituting the xenoliths with only minor olivine and clinopyroxene (Figs. 8a and b). No amphibole or orthopyroxene are present (minerals otherwise common in mafic rocks) and the opaque minerals found are small and scarce. The modal compositions of the xenoliths are presented in Table 2. Using the ternary diagram for coarse grained olivine-bearing igneous rocks (IUGS) the xenoliths are identified as an olivine gabbro and a troctolitic1 olivine gabbro (Fig. 9). In both samples the plagioclase grains vary in size and shape. In X-01 the olivine and clinopyroxene grains have about the same size as the smallest plagioclase grains; whereas in X-02, the olivine and clinopyroxene vary in size and seem to get as big as the largest plagioclase grains. The textures in the two xenoliths display some similarities. They exhibit cumulate2 and poikilitic3 textures (Fig. 10a and b), where plagioclase seems to be the dominant cumulus phase (primary mineral) and

1A troctolite is a rock type representing a gabbro that contains olivine but lacks pyroxene. 2A cumulate igneous rock is characterized by a framework of touching or interlocking crystals. 3A poikilitic mineral is a larger mineral having inclusions of smaller ones.

Figure 8. Thin sections in crossed polars showing the abundant plagioclase grains in grey in the xenoliths and the finegrained host lava underneath. Notice the olivine phenocrysts in the lava and the grain size difference between the two samples. a) shows sample LR12-01 and b) shows sample LR12-02.

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Table 2 Modal analyses of two thin sections

containing both xenolith and host lava.

LR12-01

LR12-02

xenolith lava xenolith lava

Plag 75 55 85 45

Ol 15 10 10 10

Cpx 10 33 5 43

Oxides trace 2 trace 2 Modal proportion on the xenoliths were determined by visual estimation. Modal proportion on the lava was determined by point counting using the SEM-EDS. Abbreviations: Plag - plagioclase; Ol - olivine; Cpx - clinopyroxene. Oxides refer to chromium spinel and titanomagnetite.

Figure 9. Plagioclase-pyroxene-olivine ternary classification diagram for coarse grained olivine-bearing igneous rocks (IUGS) indicating the rock type for each xenolith.

olivine and clinopyroxene represent the intercumulus phases (secondary minerals). Furthermore, plagioclase often displays what looks like zonation4 as well as sieve-textures (Fig. 10c and d).

4Zonation in this case involves a change in mineral composition between a minerals core and rim.

The lava, when viewed through the petrographic microscope exhibits a felty5 texture with acicular plagioclase laths. The mineral grains can be referred to as microlites meaning that they are finegrained but large enough to be birefringent 6 . However, their size makes it impossible to separate between individual mineral grains and a modal composition had to be determined with the SEM-EDS. The results of point counting can be seen in Table 2. Some minerals can however be distinguished in both samples. Opaque grains are rather abundant in the lava and are easily spotted using plane polarized light (ppl). Olivine phenocrysts are scattered throughout the matrix and they are both larger and more frequent in sample LR12-02 (Fig. 8b). Alteration textures are displayed by the olivine and plagioclase; in the olivine minor alteration can be seen in cracks (Fig. 11a), whereas the plagioclase display an already mentioned sieve-texture. At the contact zone, both with melt inclusions and lava, broken minerals (mainly olivine) can be seen (Fig. 11b); however, no particular alteration textures (retrograde or prograde) are displayed. In sample LR12-01 a possible recrystallization can be seen where minerals have been growing perpendicular to the contact (Fig. 11c). This zone can however also be a secondary crystallization. Furthermore, some plagioclase grains display striking zonation in crossed polarized light and seem to have been growing towards the lava (Fig 11d). The opaque minerals become more frequent at the contact compared to the xenolith and one large cubic opaque grain was found in sample LR12-01 where it seems to be surrounded by plagioclase (Fig. 11e and f).

5A texture displaying random or non-aligned crystal orientation in a groundmass. 6Interference colours can be seen when viewed in plane polarised light.

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3.2 Geochemistry

3.2.1 The xenoliths SEM-EDS analysis of both thin sections gave similar results regarding the mineral compositions in the xenoliths. The plagioclase varies in composition with An62-An90 in X-01 and An85-An93 in X-02 (Table 3, Appendix Ai-ii). The possible zonation seen in the microscope is however not that distinct and seems to comprise only the outermost rims where the Ca content can go as low as An62. Overall, bytownite and anorthite are the most common plagioclase compositions. The olivine ranges between Fo82-Fo85 (Table 4, Appendix Aiii). No particular zoning is found within the olivine crystals. The Ca content in the olivine show no sign of variation between the core and rim and

ranges between 0.35-0.39 wt.% in the cores and between 0.33-0.42 wt.% in the rims. The clinopyroxenes vary greatly in composition (Ca, Mg and Fe) but are dominantly composed of the end-member augite (Table 5, Appendix Aiv-vi). However one pigeonite (low in Ca, high in Na) was found in X-01 (Fig. 12a). The variation is not due to zonation since all the compositions are seen scattered within the grains; meaning, there is not any particular compositional trend within the grains. Furthermore, the sieve-texture displayed in the plagioclase grains is in the SEM recognized as being due to inclusions of augite. Inclusions of chromium spinel (Cr-rich spinel) were found situated in plagioclase and olivine grains. The Cr-spinels have Cr contents of 12.45-26.93 wt.% (Table 6, Appendix Avii).

Figure 10. Photomicrographs showing textures and structures in x5 magnification and crossed polarised light (xpl). a) Olivine intercumulus surrounded by cumulus plagioclase, from X-02. b) Poikilitic plagioclase showing inclusions of several smaller minerals, from X-02. c) Plagioclase displaying zonation with a dark grey core and light-grey outermost rims, from X-01. d) Several plagioclase grains showing sieve-texture, from X-01.

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3.2.2 The host lava SEM-EDS analysis of the lava in both thin sections displays similar mineral compositions. Compared to the xenoliths, the Ca content in plagioclase is generally lower, however the range is greater and exhibit Ca contents of An54-An92 (Table 7, Appendix Bi).

The olivine grains comprise both phenocrysts and matrix-sized grains; however the phenocrysts are by far the more abundant. The phenocrysts show a change in Mg content, decreasing from core to rim; it ranges between Fo42-Fo88 with the lowest values found in the outermost rims (Fig. 13) (Table 8, Appendix Bii-iv). Compared to the olivine composition in the xenolith, the phenocryst cores show higher values with Fo87-Fo88. Comparing the Ca content there is no apparent difference

Figure 11. Photomicrographs showing textures and structures. a) Olivine grain displaying alteration in its cracks in plane polarised light (ppl) and x10 magnification, from LR12-02. b) A broken olivine grain surrounded by plagioclase laths in xpl and x10 magnification, from LR12-02. c) Perpendicular mineral growth at the contact in xpl and x5 magnification, from LR12-01. d) Large plagioclase grain displaying a striking zonation at the contact with the host lava in xpl and x5 magnification, from LR12-01. e) Large opaque mineral (black) within a plagioclase grain at the contact in xpl and x5 magnification, from LR12-01. f) The same area but under ppl where you clearly can see the opaque grain.

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and the olivine phenocrysts have Ca contents that ranges between 0.31-0.40 wt.% in their cores and 0.27-0.41 wt.% in their rims (Table 8, Appendix Bii-iv). The pyroxenes found are mainly augite, but a few pigeonite grains were found. In the lava as in the xenoliths, there are large variations in the Ca, Mg, Fe contents as seen in the cpx ternary diagram (Fig. 12b) (Table 9, Appendix Bv). The opaque minerals found in the lava are composed of Fe-Ti oxides and Cr-spinels. The Fe-Ti oxides are determined to be titanomagnetite and have Ti contents that reach up to 14.35 wt.% Ti and the Cr-spinels have Cr contents of between 22.56 and

25.21 wt.% Cr (Table 10, Appendix Bvi). These are usually found as inclusions in the core of the olivine phenocrysts.

3.2.3 The contact zone BSE images of the contact zone reveal the distinct margin between the host lava and xenolith (Fig. 14). Here the modal difference of the oxide minerals between the basalt and xenolith is clearly seen. SEM-EDS analyses of the larger grains (olivine and plagioclase) at the contact reveal internal zoning of the plagioclase. Here however, the Ca content slightly, but gradually, increases towards the rim (Fig. 15) which is the opposite in the xenoliths.

Figure 12. Ternary diagrams showing the shifting clinopyroxene compositions displayed. a) The clinopyroxenes in the xenoliths are divided into inclusions and individual mineral grains. b) and c) shows the distribution in cpx compositions displayed by the lava and the contact zone respectively. d) Diagram comparing all the cpx compositions between the xenoliths, lava and contact zone.

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However, there is a large compositional range in both cores and rims; between An76-An88 in the cores, and between An57-An91 in the rims (Table 11, Appendix Ci-ii). The effect on the olivine is variable; some grains display Mg-Fe variations whereas others do not. The change, when seen, is an increase in Fe content towards the rim (Fig. 13). The Mg content in the olivine ranges between Fo66-Fo86 (Table 12, Appendix Ciii-v). The Ca content in the contact olivines show no signs of variation compared to the xenoliths and host lava. The Ca contents ranges between 0.34-0.45 wt.% in the cores and between 0.35-0.44 wt.% in the rims (Table 12, Appendix Ciii-v). However, there are some anomalies; one rim has as much as 1.52 wt.% Ca, whereas

midway (core to rim) there are Ca contents that go as low as to 0.30 wt.%. Clinopyroxene is almost absent from the contact. The few grains found are small in comparison to the plagioclase and olivine and are almost always found in the adjacent matrix. Its composition varies as it does in both the xenolith and basalt with no obvious zonation (Fig. 12c). Augite is the dominant end-member; however several pigeonite grains were found with the SEM (Table 13, Appendix Cvi). The proportion of pigeonite found is largest in the contact zone compared to the clinopyroxenes in the xenolith and host lava (Fig. 12a-d). The opaque minerals found in the contact zone are the same as in the lava;

Figure 13. Diagrams showing the change in composition between the core and rim. a) Shows the decrease in Mg content towards the rim displayed in three olivine phenocrysts. b) Shows the different compositional changes displayed by four olivine grains found at the contact zone. The composition of these grains can be viewed in more detail in Table 8, Appendix Bii-iv and Table 12, Appendix Ciii-iv for a) and b) respectively.

24

titanomagnetite and Cr-spinel. The large oxide grain found in the microscope is by SEM determined to be a Cr-spinel. Cr contents in the Cr-spinels range between 26.4-27.4 wt.% and the Ti content in the titanomagnetite is about 13 wt.% (Table 14, Appendix Cvii).

3.3 Whole rock The results of the whole rock major and trace element analyses performed on the two xenoliths and host lava are presented in Tables 15 and 16 respectively (see Appendix Di and Dii-iv respectively). All values are within a two standard deviation error, meaning that the values are within a 95% confidence interval. For the studied samples and comparing standards the values were determined by calibrating them against a known standard (N612). No whole rock analysis was performed on the contact zone since this zone was too small to be separated from the rest of the rock.

3.3.1 The xenoliths The two xenoliths plot roughly in the calc-alkaline field on the AFM diagram of Irvine and Baragar (1971) (Fig. 16a); whereas

Figure 15. Photomicrograph showing the zonation of a plagioclase grain in contact with the host lava. The numbers indicate the position of each analyse taken on this grain. The diagram displays the Ca content at each number. There is a higher amount of Ca in the middle and rim compared to the core. The composition of this grain can be viewed in more detail in Table 11, Appendix Ci. when plotted in the Fetot + Ti–Al-Mg classification diagram of Jensen (1976) they more or less plot in the tholeiite field (Fig. 16b). The MgO content of 10.66 and 11.26 wt.% classifies the xenoliths as olivine tholeiites (Table 15, Appendix Di). Figs. 17a and b show N-MORB and OIB-normalised spider diagrams and Figs. 18a and b show PM-normalized spider diagram and chondrite-normalised rare earth elements (REE) patterns for the two xenoliths. The xenoliths show depletion relative to N-MORB and OIB (Figs. 17a and b); whereas they roughly follow the reference line for the PM in Figure 18a. In general, the xenoliths have matching patterns in all three diagrams with similar positive and negative anomalies (Figs. 17a,b+ and 18a). Similar values to N-MORB can be seen for Sr in X-02. In most instances, xenolith X-01 displays an enrichment relative to X-02.

Figure 14. Back-scatter electron (BSE) image showing the distinct margin between the lava and the xenolith at the contact zone. The boundary is clearly seen by the direct increase of brighter colours in the lava (lower part). The bright minerals are different types of oxides. The black areas are holes in the sample.

25

What is evident in these three diagrams is the apparent correlation with the xenoliths and primordial mantle (Figs. 17a,b and 18a). In the chondrite-normalised REE diagram both xenoliths display matching patterns with very low concentrations, around two times chondrite. X-01 shows enrichment relative to X-02 in all instances (Fig. 18b). A distinct positive Eu anomaly can be seen, stronger for X-02.

3.3.2 The host lava The lava sample plots in the basalt field on the TAS classification diagram of Le Maitre et al. (1989) and in the tholeiitic field on the AFM diagram of Irvine and Baragar (1971) (Figs. 16a and 19). However, when plotted in the Fetot + Ti–Al-Mg classification diagram of Jensen (1976) the sample plots in the komatiitic field (Fig. 16b). Using the 2*Nb-Zr/4-Y discrimination diagram for basalts of Meschede (1986) the lava plot in the field of N-type MORB and volcanic-arc basalts (Fig. 20). Figs. 17a,b and 18a,b show N-MORB, OIB and PM-normalised multi-element and

chondrite-normalised rare earth elements patterns for the lava sample. What is relevant is that the pattern for the lava always shows higher values compared to the xenoliths. In the N-MORB multi-element diagrams the lava shows a slightly depleted signature, whereas a 2-3 times enrichment is exhibited by the lava relative to PM (Fig. 17a,b and 18a). When compared to PM the lava exhibits an irregular pattern with significant peaks and troughs on the left-hand side of the diagram (Fig. 18a). It also shows lower values (depletion) at the most incompatible end (left-hand side of Fig. 18a). The lava in all three normalized multi-element diagrams display patterns that correlates well with the patterns displayed by the N-MORB source (Fig. 17a,b and 18a). Another feature represented in the N-MORB-normalised spider diagram is the characteristic “mantle bulge” displayed by the OIB (Fig. 17a). What is interesting though is that the xenoliths and host lava also display this feature, but to a lesser extent.

Figure 16. Two classification diagrams for determining to what rock series the xenoliths belong to. a) AFM diagram of Irvine and Baragar (1971). b) Fetot + Ti–Al-Mg diagram of Jensen (1976).

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3.4 Geothermobarometric modelling

3.4.1 The xenoliths Neither TWQ nor Domino-Theriak could produce any useful P,T results for the xenoliths. Additionally, the olivine-liquid thermometer for the xenoliths yielded results pointing to disequilibrium and so could not yield a viable temperature. However, using the whole-rock values for

the lava composition instead of the xenolith composition resulted in equilibrium for about 50% of the grains (Fig. 21). From these a temperature of 1338°C could be determined when the pressure was set to 1 GPa. This is an average temperature given by Equation (1) and (2) for the olivine compositions in equilibrium with the liquid. For the cpx thermobarometers there were two available sets to use; cpx inclusions in plagioclase and intercumulus cpx grains.

Figure 17. N-MORB-normalised (a) and OIB-normalised spider diagram (b) for the two xenoliths and host lava. In a) the solid black horizontal line is the reference line for the N-MORB composition. The blue line represent the OIB composition whereas the orange line represent the PM composition. The characteristic “mantle bulge” is displayed by the OIB in the left-hand side of the diagram. Both the xenoliths and host lava show depletion relative to the N-MORB composition, whereas the OIB show enrichment. In b) the OIB composition is the topmost solid black horizontal line. Once again the orange line represents the PM composition, whereas in this diagram the N-MORB composition is shown with the dark blue line. All compositions show depletion relative to OIB with the xenoliths displaying the strongest depletion. The order of elements and their values are for the N-MORB by Pearce (1983) and for the OIB by Sun (1980); both from Rollinson (1993).

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When applying the temperature of 1338°C to these cpx sets it gave pressures of 6.0-9.8 kbar and 8.0-8.9 kbar for the intercumulus cpx in X-01 and X-02 respectively. The cpx inclusions gave higher pressures of 16.3-19.3 kbar and 14.9-17.3 kbar for X-01 and X-02 respectively. These pressures were given when using the whole-rock compositions of each combining xenolith as a liquid.

When using the whole-rock composition for the lava as a liquid for the xenoliths the pressure for the cpx inclusions changes; however, the pressure for the intercumulus cpx is constant. For the cpx inclusions the pressure dropped to 14.1-18.4 kbar for X-01 and to 12.3-15.1 for X-02. The chosen pressure of 1 GPa in the ol-liq thermometer correlates well enough with the pressures of 6-19.3 kbar given by the

Figure 18. PM-normalised spider diagram (a) and chondrite-normalised REE diagram (b) for the two xenoliths and host lava. In a) the solid black horizontal line is the reference line for the PM composition. The blue line represent the OIB composition whereas the dark blue line represent the N-MORB composition. Both xenolithsis seen plotting more or less on the PM reference line whereas the lava show an enrichment relative to PM. In b) the chondrite composition is the lowermost solid black horizontal line. The lava display a flat REE pattern with no anomalies, whereas the xenoliths show a distinct positive anomaly for Eu. All three samples show an enrichment relative to the chondrites where the lava show the largest enrichment. The order of elements and their values are for the PM by Wood et al. (1979a) and for the chondrite by Evensen et al. (1978); both from Rollinson (1993).

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clinopyroxenes in the cpx-liq barometer. Changing the pressure to 1.5 GPa in the ol-liq thermometer changes the temperature by +20°C. A change that is more or less insignificant when used in the cpx-liq barometer. Hence, the temperatures and pressures given by the different thermometers and barometers are

determined to be useable and a constant pressure of 1 GPa is used as a input pressure in the ol-liq thermometer. Looking at the equilibrium diagrams (Fig. 22a and b) it is evident that there are a higher number of cpx compositions that are in equilibrium when using the lava as a liquid. These pressures indicate two separate depths. With the assumption that the pressure at 100 km depth is about 3 GPa, the intercumulus cpx give a depth of 20-33 km, whereas the cpx inclusions give depths of 41-61 km and 50-64 km for the two whole-rock compositions used (lava and xenoliths respectively).

3.4.2 The host lava The lava did not give useful P,T results in TWQ, whereas Domino-Theriak yielded more useable results when applying the HoPoMelt database (Figs. 23 and 24).

0

2

4

6

8

10

12

14

16

35 45 55 65 75

Na2

O+

K2

O (

wt%

)

SiO2 (wt%)

Total alkali vs. silica diagram (TAS)

Basalt

Foidite

Picro basalt

Trachy basalt

Phono tephite

Tephite

Basanite

Basaltic andesite

Andesite Dacite

Rhyolite

Tephri phonolite

Thachy andesite

Trachyte

Trachydacite

Basaltic trachyandesite

Phonolite

Figure 19. TAS diagram of Le Maitre et al. (1989) showing the position of the host lava in the basalt field.

Figure 20. Discrimination diagram for basalts of Meschede (1986). The lava plot in field D which represents N-MORB and volcanic-arc basalts.

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In the HoPoMelt phase diagram, the line indicating an olivine in reaction is indicative of when olivine started to crystallise from the melt (Fig. 23). At the constant pressure of for example 5 kbar and decreasing amounts of water in the system, this line gradually moves to higher temperatures. Starting with 100% water, “olivine in” gives a temperature of ~1050°C; removing water from the system to only 1% raises the “olivine in” temperature to ~1300°C (Fig. 24). However, the pressure cannot be determined due to the insensitivity of the olivine in reaction to pressure. And since the HoPoMelt database takes the liquid into account, knowing the modal composition of the lava will not help. The ol-liq thermometer yields similar temperatures for the phenocryst cores and

rims; 1314°C and 1313°Crespectively, with the input pressure of 1 GPa. Applying these temperatures to the cpx barometers yields pressures that differ by only 0.1 kbar; the pressure ranges given are between 7.1-11.2 kbar. These pressures indicate depths equivalent to 24-37 km.

3.4.3 The contact zone TWQ could not produce any useful P,T results from the contact zone and modelling in Domino-Theriak could not be done since whole-rock samples from this area could not be made. The ol-liq thermometers could not yield any usable temperatures due to disequilibrium between the contact olivines and liquid (lava). However, it is possible to use the temperatures of 1313°C and 1314°C given by the lava since the contact olivines started to develop when the lava came in contact with the xenolith cumulate. This yields a pressure of 5.5-8.1 kbar and an equivalent depth of 18-27 km.

4. Discussion

4.1 Mineralogy & petrology There are some features regarding the xenoliths which indicate that they were assimilated some time before the eruption took place: their rounded and re-melted edges; the apparent growth of minerals at the contact; and the more evolved rims of the plagioclase grains. Furthermore, the more evolved rims along with the existence of groundmass inclusions within the xenolith might also indicate that they lay in the magma long enough for partial melting to take place. The Ca-in-olivine geobarometer is one way to determine pressure variations; Ca is an element that in olivine increases at lower pressures.

Figure 21. Rhodes diagram showing two groups of data. The right group shows the displayed disequilibrium when using the xenolith as a liquid for the whole-rock composition. The left group shows partial equilibrium when using the lava as a liquid.

30

Thus, it seems like the olivines in the xenoliths crystallised at depths comparable to the host lava due to their similar Ca content of 0.33-0.42 and 0.27-0.41 for the xenoliths and host lava respectively. The cumulate texture and modal composition found in the xenoliths indicates that they formed by crystal fractionation. At first glance it appears that plagioclase is the main cumulus phase where olivine and cpx grew in the space in-between as intercumulus phases. However, the sieve-texture displayed by the plagioclase grains contains augite inclusions as determined by the SEM analyses. Thus, it seems that cpx was the first phase to crystallise from the magma; they formed oikocrysts when plagioclase started crystallising around them at a later stage. This then indicates that the intercumulus cpx seen actually is a second generation.

The fact that no cumulate structure or layering can be seen within the xenoliths suggests that the cumulate layers might have been thick, or that layering did not have time to develop completely. Since the xenoliths are cumulates, the remaining magma would have changed composition. And since the basalt has forsterite values higher than found in the xenolith, this indicates that the xenolith and basalt did not form from the same magma. If they would have, the crystal fractionation of the xenoliths would have extracted Mg from the magma and thus yielded olivine phenocrysts with lower Mg content. This is supported by the positive Eu anomalies in the xenoliths, not mirrored by negative anomalies in the basalt (Fig. 18b). Since they come from different magmas the lower Ca content in the plagioclase grains of the basalt can be explained by a lower amount of Ca in its parental magma, or a different pressure regime.

Figure 22. Equilibrium diagrams showing the distribution of the clinopyroxene compositions as calculated from the cpx in the xenoliths (y-axis) and from the whole-rock composition (x-axis). a) shows the cpx distribution in X-01 plotted against the xenolith whole-rock composition and b) shows the cpx distribution in X-01 plotted against the lava whole-rock composition. There are a higher number of grains in equilibrium when the lava is used as whole-rock.

31

Furthermore, the olivine phenocrysts within the lava matrix indicate that they started crystallising earlier than the rest of the matrix and thus had more time to grow larger. Cr-spinel inclusions within their cores indicate that Cr-spinel started crystallising even earlier and thus got enveloped by the later crystallising olivine.

4.2 Geochemistry The significant positive anomalies for Sr and Eu displayed by the xenoliths in the normalized multi-element diagrams and the chondrite-normalised REE diagram

respectively are due to the extensive amount of cumulate plagioclase (Figs. 17 and 18). Sr and Eu are both elements that can substitute for Ca in the crystal structure, and since the xenoliths are composed of >70% Ca-plagioclase, this is the reason for the distinct positive anomalies displayed for Sr and Eu. This confirms that these rocks developed as a plagioclase-rich cumulate. Furthermore, the fact that an Eu or Sr anomaly is not seen for the lava indicates that the lava is unlikely to be directly related to the xenoliths. The apparent matching patterns between the xenoliths and primordial mantle in Figs. 17a,b and 18a indicate that the xenoliths are

Figure 23. Domino plot using the HoPoMelt database for the basalt showing the area for “olivine in”. At 5000 bar the olivine starts crystallising at 1050°C when the system is saturated with water (100% water).

32

derived from a primordial mantle source, slightly contaminated by a plume component which gives rise to the minor mantle bulge. This shows that the xenoliths are more unfractionated and also less evolved than the lava. Thus, their mantle source might have come from a deeper source than the upper mantle. This is something that also can be seen in the REE diagram where the xenoliths plot closer to the chondrite composition than the host lava does (Fig.18b); denoting the lesser fractionation of the xenoliths compared to the lava. When looking at the patterns displayed by the host lava in the OIB and PM-normalised spider diagrams (Figs. 17b and 18a), one

can conclude that the lava is derived from an N-MORB mantle source due to their matching patterns. This is in good agreement with the discrimination diagram by Meshede (1986) where the basalt plots in the N-MORB field (Fig. 20).

The N-MORB-normalised diagram (Fig. 17a) in turn indicates that the host lava has been depleted relative to N-MORB. Thus, the basalt can be interpreted as being a strongly depleted N-MORB. The xenoliths are even more depleted; since these rocks are not peridotites, as they contain major plagioclase, they must have got their sub-MORB low spidergram concentrations by formation as cumulates.

Figure 24. Domino plot using the HoPoMelt for the basalt showing the area for “olivine in”. At 5000 bar the olivine starts crystallising at about 1300°C when the system is anhydrous (1% water).

33

These interpretations indicate that neither the xenoliths nor the lava are derived directly from the mantle plume; although, the displayed mantle bulge suggests that the rocks are all derived from mantle with a minor plume signature.

4.3 P,T conditions The mineral assemblage and the apparent disequilibrium within the samples lead to the result that TWQ could not plot any useful results. Domino-Theriak however gave a temperature of about 1300°C from the ol-in phase diagram which correlates very well with the temperatures of 1313°C and 1314°C seen for the olivine phenocrysts in the lava. Nevertheless, an addition of another mineral in the assemblage might have yielded more results due to the higher amount of possible reactions that then could take place in the different models. The two whole-rock compositions of liquid used for the xenolith minerals in the thermobarometers (lava and xenolith) gave different results. Which whole-rock composition that is the more suitable combination is debatable, but there seems to be a higher degree of equilibrium when the lava composition is used (Fig. 21 and 22); probably since the xenoliths are cumulates and thus will change the composition of the melt that is left after continuous crystallisation of new minerals. Hence, the whole-rock composition of the lava is believed to be the more reliable liquid for this study. However, there is still a question of using the lava as liquid for the inclusions in the xenoliths since these inclusions have not been in contact with the host lava at all. The temperatures of 1313°C and 1314°C for the phenocryst rims and cores respectively indicate that the phenocrysts in the lava crystallised rather quickly. Furthermore, the similar temperature of 1338°C for the xenoliths suggests that they crystallised at a similar depth as the phenocrysts.

The correlating depths of 24-37 km, 18-27 km and 20-33 km for the lava, contact and intercumulus cpx respectively indicate that the xenolith cumulate was residing at these depths when it got disrupted and incorporated by the intruding host lava. Hence, this event initiated the formation of the second generation (intercumulus) clinopyroxene in the xenoliths. Since the intercumulus is comprised of both cpx and olivine, the olivine is considered to have formed at the same time as the cpx. This is supported by the similarity in Ca content between the xenolith olivines and host lava olivines; the similar Ca content is due to formation at the same depth. Additionally, the similarity in olivine temperatures mentioned above reinforces this assumption further. Since the maximum crustal thickness in the study area is approximately 20 km, the depths of 18-37 km suggests that both the host lava and xenolith cumulate was residing within the mantle lithosphere before being brought to the surface; possibly within a magma chamber. The crystallisation of the first clinopyroxenes found in the xenoliths took place at depths of 41-61 km, still within the mantle lithosphere, but beneath the supposed magma chamber. If they crystallised within a magma body or within a deeper-situated magma chamber is unknown.

5. Conclusions The main objective of this study was to determine the depth of origin for the xenoliths. Two depths were discovered; the depth of the first mineral making up the xenoliths (i.e. the clinopyroxene inclusions) and the depth at where the xenoliths fully developed at 41-61 km and 20-33 km respectively. Referring to the other aims and objectives mentioned.

34

1) The xenoliths are the product of fractional crystallization of a magma body within the mantle lithosphere where clinopyroxene was the first mineral to crystallise.

2) The xenoliths seem to have been in the host lava for a rather long time prior to eruption as indicated by their round edges and evolved plagioclase rims; i.e. a change in their An content from core to rim.

3) The depth at which the xenoliths got incorporated by the host lava was determined by the correlating pressures of the host lava cpx, contact cpx and intercumulus cpx; a depth of between 18-37 km.

4) The depth of the lava was determined from the olivine phenocrysts which yielded a depth of 24-37 km.

5) The host lava is determined to have a strongly depleted N-MORB source; whereas the xenoliths are determined to have a primordial mantle source. Thus, they are not related to each other and none of them are derived from the mantle plume. However, they both seem to have been subjected to enrichment by the mantle plume as indicated by the observed mantle bulge pattern.

From the observed results there seem to be an indicator of the existence of magma chambers within the mantle lithosphere that are feeding the fissure zones at Reykjanes Peninsula. Further studies need to be done to determine their existence. Moreover, the research on the mantle sources for these two magmas are in this study minor and further research on them would help determine their origin and also give a clearer view on the mantle beneath Iceland. Also, further studies needs to be done on the plagioclase grains that make up more than 75% of the xenoliths; specifically geothermobarometric modelling since they envelope the higher-pressure cpx grains. At the moment there is a question of at what of the two depths the plagioclase cumulate crystallised. Furthermore, new geothermobarometers need to be tested, for example Ni in olivine

and ilmenite-magnetite, and the number of samples needs to be higher. The very small number of samples used in this study could have been a clear disadvantage in determining more precise depths. Additionally, a greater number of samples would have facilitated a larger investigation and more importantly, statistically probable results.

Acknowledgements First of all I would like to thank Professor David Cornell and Erik Sturkell for being my supervisors during this study. Special thanks for Erik Sturkell who collected the samples and contributed with photos from the location, but also to David Cornell who helped me understand the different geothermobarometric models. Secondly I would like to thank Ulf Christensson, Jennie Havel, Johanna Bäckström and Henrik Åslund for critical comments. Also, a special thanks to Carl-Anton Wahlström for being my opponent in this study. Last but not least I would like to thank David Nilsson for his help with the clinopyroxene and olivine thermobarometry.

35

6. References Beattie, P. (1993). Olivine-melt and

orthopyroxene-melt equilibria. Contributions to Mineralogy and Petrology, 115, 103-111.

Brandsdóttir, B., & Menke, W. H. (2008). The seismic structure of Iceland. JÖKULL, No. 58.

Einarsson, P. (2008). Plate boundaries, rifts and transforms in Iceland. JÖKULL, No. 58, 35-58.

Grandvuinet, T., & Óskarsson, N. (n.d.). Deep crustal xenoliths from Hrólfsvík, Reykjanes Peninsula. Reykjavik: Nordic Volcanological Center, Institute of Earth Sciences.

Grandvuinet, T., Óskarsson, N., & Grönvold, K. (2006). Troctolite/gabbro xenoliths from the Reykjanes Peninsula, South-Western Iceland: fragments of a dyke complex beneath a rift-zone. American Geophysical Union. Abstract #V23A-0597.

Harðarson, B. S., Fitton, G. J., & Hjartarson, Á. (2008). Tertiary volcanism in Iceland. JÖKULL, No. 58, 161-178.

Jakobsson, S. P., Jónasson, K., & Sigurdsson, I. A. (2008). The three igneous rock series of Iceland. JÖKULL, No. 58, 117-138.

Jakobsson, S. P., Jónsson, J., & Shido, F. (1978). Petrology of the Western Reykjanes Peninsula, Iceland. Journal of Petrology, Vol. 19(4), 669-705.

Kumar, P., Kind, R., Hanka, W., Wylegalla, K., Reigber, C., Yuan, X., et al. (2005). The lithosphere-asthenosphere boundary in the North-West Atlantic region. Earth and Planetary Science Letters(236), 249-257.

Putirka, K. D. (2008). Thermometers and Barometers for Volcanic Systems. In Reviews in Mineralogy & Geochemistry (Vol. 69, pp. 61-120).

Rollinson, H. (1993). Using geochemical data: evaluation, presentation, interpretation.

Sigmundsson, F., & Saemundsson, K. (2008). Iceland: a window on North-Atlantic divergent plate tectonics and geologic processes. JÖKULL, No. 58.

Thordarson, T., & Höskuldsson, Á. (2008). Postglacial volcanism in Iceland. JÖKULL, No. 58.

Thordarson, T., & Larsen, G. (2007). Volcanism in Iceland in historical time: Volcano types, eruption styles and eruptive history. Journal of Geodynamics, 43, 118-152.

Trönnes, R. G. (2003). Geology and geodynamics of Iceland. Reykjavik: Nordic Volcanological Institute.

Winter, J. D. (2010). Principles of Igenous and Metamorphic Petrology (2nd ed.). Pearson.

36

Appendix A, Mineral compositions in the xenoliths

i) Table 3

Compositions of plagioclase grains in the xenoliths (formulae to eight oxygen).

Sample LR12-01

Grain Pl1-1(x) Pl1-1(x) Pl1-11(x) Pl1-11(x) Pl1-14(x)

Area mid rim core lower rim upper rim

Na2O 1.31 4.39 2.08 1.39 2.31

MgO 0.32 0.32 0.44 0.25 0.40

Al2O3 33.64 28.95 32.24 33.71 32.1

SiO2 43.90 50.80 46.39 44.41 47.03

K2O 0.00 0.05 0.03 0.03 0.06

CaO 18.37 13.03 16.94 18.12 16.52

FeO 0.50 0.96 0.38 0.29 0.52

Total 98.04 98.45 98.47 98.17 98.88

Na 0.12 0.39 0.19 0.13 0.21

Mg 0.02 0.02 0.03 0.02 0.03

Al 1.88 1.58 1.78 1.87 1.76

Si 2.08 2.36 2.17 2.09 2.19

K 0.00 0.00 0.00 0.00 0.00

Ca 0.93 0.65 0.85 0.91 0.82

Fe 0.02 0.04 0.01 0.01 0.02

An* 0.89 0.75 0.89 0.93 0.87

Ab 0.11 0.25 0.11 0.07 0.12

Or 0.00 0.00 0.00 0.00 0.00

*Xi = i/(Ca + Na + K).

37

ii)

Table 3 Continued.

Sample LR12-02

Grain Pl2-1(x) Pl2-2(x) Pl2-6(x) Pl2-6(x) Pl2-6(x)

Area core core upper rim core lower rim

inclusion inclusion inclusion Na2O 1.74 0.92 1.13 1.38 1.25

MgO 0.33 0.3 0.26 0.29 0.28

Al2O3 33.27 34.36 34.8 33.86 33.98

SiO2 45.43 43.11 45.59 45.57 44.9 K2O 0.00 0.00 0,00 0.05 0.06

CaO 17.48 19.22 18.36 18.04 18.17

FeO 0.59 0.35 0.92 0.6 0.87

Total 98.84 98.26 101.06 99.74 99.45

Na 0.16 0.08 0.10 0.12 0.11

Mg 0.02 0.02 0.02 0.02 0.02

Al 1.83 1.91 1.88 1.85 1.87

Si 2.12 2.03 2.09 2.11 2.09

K 0.00 0.00 0.00 0.00 0.00

Ca 0.88 0.97 0.90 0.90 0.91

Fe 0.02 0.01 0.04 0.02 0.03

An* 0.85 0.92 0.94 0.93 0.93

Ab 0.15 0.08 0.06 0.07 0.06

Or 0.00 0.00 0.00 0.00 0.00

*Xi = i/(Ca + Na + K).

38

iii)

Table 4 Compositions of olivine grains (formulae to four oxygen). Cr below

detection limit with 100 sec live-time.

Sample LR12-01 LR12-02

Grain Ol1-1(x) Ol1-4(x) Ol1-5(x) Ol1-8(x) Ol2-1(x) Ol2-3(x)

Area core mid core core outer left core Na2O 0.18 0.19 0.18 0.17 0.22 0.15

MgO 46.13 45.80 45.78 47.10 44.02 44.31

Al2O3 0.11 0.09 0.09 0.12 0.09 0.00

SiO2 38.89 38.95 38.13 38.98 38.70 38.65

CaO 0.35 0.38 0.39 0.39 0.38 0.38

MnO 0.25 0.26 0.17 0.24 0.26 0.30

FeO 14.91 15.34 14.59 14.06 18.05 17.81

NiO - - 0.26 0.25 0.27 0.13

Total 100.82 101.01 99.59 101.31 101.99 101.73

Na 0.01 0.01 0.01 0.01 0.01 0.01

Mg 2.58 1.71 1.73 1.74 1.65 1.66

Al 0.01 0.00 0.00 0.00 0.00 0.00

Si 1.46 0.97 0.97 0.97 0.97 0.97

Ca 0.01 0.01 0.01 0.01 0.01 0.01

Mn 0.01 0.01 0.00 0.01 0.01 0.01

Fe 0.47 0.32 0.31 0.29 0.38 0.37

Ni - - 0.01 0.00 0.01 0.00

Fo* 0.85 0.84 0.85 0.86 0.81 0.82

Fa 0.15 0.16 0.15 0.14 0.19 0.18

*Xi = i/(Mg + Fe).

39

iv)

Table 5 Compositions of clinopyroxene grains in the xenoliths (formulae to six oxygen).

Sample LR12-01

Grain Px1-2(x) Px1-3(x) Px1-4(x) Px1-6(x) Px1-12(x) Px1-12(x) Px1-12(x)

Area rim mid rim mid core core rim

inclusion inclusion inclusion inclusion inclusion Na2O 0.26 0.85 0.81 0.25 1.11 1.48 0.69

MgO 18.17 14.99 15.51 17.71 14.12 12.85 15.27 Al2O3 3.02 6.15 6.27 3.11 7.14 7.80 5.84 SiO2 51.45 49.15 49.39 51.02 49.63 49.69 50.06

CaO 19.53 12.94 13.08 20.95 13.41 13.36 13.50

TiO2 0.57 0.69 0.75 0.44 0.70 0.72 0.78 Cr2O3 0.59 - - - 0.11 0.12 0.09

MnO 0.16 0.29 0.23 0.20 0.21 0.27 0.26

FeO 6.42 13.56 12.48 5.02 12.99 12.78 14.01

Total 99.58 98.62 98.52 98.70 99.31 98.95 100.41

Na 0.02 0.06 0.06 0.02 0.08 0.11 0.05

Mg 0.99 0.84 0.87 0.98 0.79 0.72 0.85

Al 0.13 0.27 0.28 0.14 0.31 0.34 0.26

Si 1.89 1.86 1.86 1.89 1.85 1.86 1.86

Ca 0.77 0.52 0.53 0.83 0.54 0.54 0.54

Ti 0.02 0.02 0.02 0.01 0.02 0.02 0.02

Cr 0.02 - - - 0.00 0.00 0.00

Mn 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Fe 0.20 0.43 0.39 0.16 0.41 0.40 0.44

Ca* 0.39 0.29 0.29 0.42 0.31 0.32 0.30

Mg 0.51 0.47 0.49 0.50 0.45 0.43 0.47

Fe 0.10 0.24 0.22 0.08 0.23 0.24 0.24

*Xi = i/(Ca + Mg + Fe).

40

v)

Table 5 Continued.

Sample LR12-01

Grain Px1-13(x) Px1-13(x) Px1-14(x) Px1-16(x) Px1-17(x) Px1-17(x)

Area core core core rim upper rim lower rim

inclusion inclusion inclusion Na2O 0.71 0.70 0.90 0.32 0.21 0.28

MgO 14.54 13.64 14.08 14.18 17.46 18.71 Al2O3 5.14 5.34 6.87 4.43 3.16 2.08

SiO2 52.49 52.53 50.04 48.29 51.13 52.30

CaO 13.40 13.25 12.45 19.96 21.38 19.67 TiO2 0.64 0.60 0.71 1.47 0.40 0.31

Cr2O3 0.12 0.00 0.12 0.12 0.78 0.32

MnO 0.19 0.25 0.33 0.21 0.13 0.15

FeO 11.37 11.98 15.62 9.97 5.00 5.92

Total 98.48 98.29 101.00 98.83 99.65 99.74

Na 0.05 0.05 0.06 0.02 0.01 0.02

Mg 0.81 0.76 0.78 0.80 0.96 1.02

Al 0.22 0.23 0.30 0.20 0.14 0.09

Si 1.95 1.76 1.85 1.83 1.88 1.92

Ca 0.53 0.53 0.49 0.81 0.84 0.77

Ti 0.02 0.02 0.02 0.04 0.01 0.01

Cr 0.00 0.00 0.00 0.00 0.02 0.01

Mn 0.01 0.01 0.01 0.01 0.00 0.00

Fe 0.35 0.37 0.48 0.32 0.15 0.18

Ca* 0.32 0.32 0.28 0.42 0.43 0.39

Mg 0.48 0.46 0.44 0.42 0.49 0.52

Fe 0.21 0.22 0.28 0.16 0.08 0.09

*Xi = i/(Ca + Mg + Fe).

41

vi)

Table 5 Continued.

Sample LR12-02

Grain Px2-1(x) Px2-2(x) Px2-3(x) Px2-7(x) Px2-13(x)

Area rim core core core rim

inclusion Na2O 0.27 0.34 0.69 0.24 0.33

MgO 17.38 18.07 16.31 17.71 17.38 Al2O3 3.27 4.97 6.27 3.38 3.03

SiO2 50.71 48.81 50.42 51.43 50.20

CaO 20.43 12.37 13.06 20.65 16.02 TiO2 0.40 0.62 0.53 0.51 1.02

Cr2O3 0.53 - 0.11 0.74 0.11

MnO 0.21 0.27 0.27 0.13 0.31

FeO 5.80 12.96 13.29 5.65 11.44

Total 99.00 98.41 100.95 100.44 99.84

Na 0.02 0.02 0.05 0.02 0.02

Mg 0.96 1.02 0.89 0.97 0.97

Al 0.14 0.22 0.27 0.15 0.13

Si 1.88 1.84 1.85 1.88 1.87

Ca 0.81 0.50 0.51 0.81 0.64

Ti 0.01 0.02 0.01 0.01 0.03

Cr 0.02 - 0.00 0.02 0.00

Mn 0.01 0.01 0.01 0.00 0.01

Fe 0.18 0.41 0.41 0.17 0.36

Ca* 0.42 0.26 0.28 0.42 0.33

Mg 0.49 0.53 0.49 0.50 0.49

Fe 0.09 0.21 0.23 0.09 0.18

*Xi = i/(Ca + Mg + Fe).

42

vii)

Table 6 Compositions of oxide grains in the xenoliths

(formulae to four oxygens).

Sample LR12-01

LR12-02

Mineral Cr-spinel Cr-spinel

chromite

Grain Ox1-1(x) Ox1-4(x)

Ox2-1(x)

Area core core

core

inclusion inclusion

inclusion Na2O 0.14 0.21

Na2O 0.13

MgO 18.62 14.51

MgO 17.58 Al2O3 44.90 25.44

Al2O3 30.52

SiO2 1.06 0.19

CaO 0.23

CaO 0.48 0.06

V2O3 0.20

TiO2 0.14 0.36

Cr2O3 35.57 Cr2O3 18.19 39.36

MnO 0.28

MnO 0.16 0.37

FeO 16.03

FeO 14.44 20.29

WO3 0.41

Total 98.13 100.79

Total 100.95

Na 0.01 0.01

Na 0.01

Mg 0.77 0.66

Mg 0.77

Al 1.47 0.91

Al 1.05

Si 0.03 0.01

Ca 0.01

Ca 0.01 0.00

V 0.00

Ti 0.00 0.01

Cr 0.82

Cr 0.40 0.94

Mn 0.01

Mn 0.00 0.01

Fe 0.39

Fe 0.34 0.52

W 0.00

Mg* 0.30 0.32

Mg* 0.66

Fe 0.13 0.25

Fe 0.34

Al 0.57 0.44

*Xi = i/(Mg + Fe)

*Xi = i/(Mg + Fe + Al).

43

Appendix B. Mineral compositions in the lava

i)

Table 7 Compositions of plagioclase grains in the lava (formulae to eight oxygen).

Sample LR12-01 LR12-02

Grain Pl1-1(l) Pl1-3(l) Pl1-7(l) Pl1-8(l) Pl2-1(l) Pl2-2(l)

Area core rim rim rim mid core

inclusion

Na2O 4.60 5.50 4.23 0.96 2.59 2.53

MgO 0.32 0.21 0.32 0.24 0.37 0.42

Al2O3 29.40 27.82 29.72 35.04 32.62 32.05 SiO2 52.08 53.82 50.41 43.63 48.57 48.04

K2O 0.00 0.11 0.07 0.00 0.00 0.00

CaO 12.73 11.54 13.89 18.83 16.87 16.74

FeO 1.11 1.45 1.06 0.67 0.85 1.21

Total 100.24 100.34 99.63 99.37 101.87 100.99

Na 0.41 0.48 0.38 0.09 0.23 0.22

Mg 0.02 0.01 0.02 0.02 0.03 0.03

Al 1.58 1.49 1.61 1.93 1.74 1.73

Si 2.37 2.44 2.32 2.04 2.20 2.20

K 0.00 0.01 0.00 0.00 0.00 0.00

Ca 0.62 0.56 0.69 0.94 0.82 0.82

Fe 0.04 0.06 0.04 0.03 0.03 0.05

An* 0.60 0.67 0.76 0.92 0.78 0.79

Ab 0.40 0.32 0.23 0.08 0.22 0.21

Or 0.00 0.01 0.00 0.00 0.00 0.00

*Xi = i/(Ca + Na + K).

44

ii)

Table 8 Compositions of olivine grains in the lava (formulae to four oxygens).

Sample LR12-01

Grain Ol1-6(l) Ol1-6(l) Ol1-6(l) Ol1-6(l) Ol1-6(l)

Area left rim left rim core right rim right rim

phenocryst phenocryst phenocryst phenocryst phenocryst Na2O 0.20 0.15 0.15 0.21 0.20

MgO 35.01 45.55 48.29 45.98 25.25 Al2O3 0.05 0.06 0.10 0.13 0.10 SiO2 36.31 38.25 38.97 38.41 33.44

CaO 0.33 0.33 0.34 0.36 0.41

MnO 0.42 0.23 0.23 0.28 0.51

FeO 27.21 15.26 12.12 15.47 39.04

NiO 0.13 0.30 0.29 0.23 0.10

Total 99.66 100.13 100.49 101.07 99.05

Na 0.01 0.01 0.01 0.01 0.01

Mg 1.40 1.72 1.79 1.72 1.09

Al 0.00 0.00 0.00 0.00 0.00

Si 0.98 0.97 0.97 0.96 0.97

Ca 0.01 0.01 0.01 0.01 0.01

Mn 0.01 0.00 0.00 0.01 0.01

Fe 0.61 0.32 0.25 0.32 0.94

Ni 0.00 0.01 0.01 0.00 0.00

Fo* 0.70 0.84 0.88 0.84 0.54

Fa 0.30 0.16 0.12 0.16 0.46

*Xi = i/(Mg + Fe).

45

iii)

Table 8 Continued.

Sample LR12-01

Grain Ol1-8(l) Ol1-8(l) Ol1-8(l) Ol1-8(l) Ol1-8(l)

Area left rim left rim core right mid right rim

phenocryst phenocryst phenocryst phenocryst phenocryst Na2O 0.26 0.15 0.15 0.18 0.17

MgO 18.65 46.64 48.13 47.82 33.10 Al2O3 0.16 0.16 0.23 0.13 0.23

SiO2 31.96 38.32 38.83 38.65 35.70

CaO 0.31 0.30 0.31 0.35 0.37

MnO 0.57 0.19 0.20 0.17 0.37

FeO 46.35 13.20 11.78 12.50 29.60

NiO 0.00 0.29 0.40 0.42 0.18

Total 98.26 99.25 100.03 100.22 99.72

Na 0.02 0.01 0.01 0.01 0.01

Mg 0.84 1.76 1.79 1.78 1.34

Al 0.01 0.00 0.01 0.00 0.01

Si 0.97 0.97 0.97 0.96 0.97

Ca 0.01 0.01 0.01 0.01 0.01

Mn 0.01 0.00 0.00 0.00 0.01

Fe 1.18 0.28 0.25 0.26 0.67

Ni 0.00 0.01 0.01 0.01 0.00

Fo* 0.42 0.86 0.88 0.87 0.67

Fa 0.58 0.14 0.12 0.13 0.33

*Xi = i/(Mg + Fe).

46

iv)

Table 8 Continued.

Sample LR12-02

Grain Ol2-4(l) Ol2-4(l) Ol2-4(l) Ol2-4(l)

Area outer left left rim core right rim

phenocryst phenocryst phenocryst phenocryst Na2O 0.22 0.12 0.17 0.15

MgO 37.31 44.20 47.41 45.62 Al2O3 0.12 0.00 0.06 0.16

SiO2 36.79 37.68 38.60 38.00

CaO 0.41 0.33 0.35 0.32

MnO 0.35 0.24 0.22 0.22

FeO 25.01 15.43 12.19 13.64

NiO 0.18 0.21 0.32 0.26

Total 100.39 98.21 99.32 98.37

Na 0.01 0.01 0.01 0.01

Mg 1.47 1.70 1.78 1.74

Al 0.00 0.00 0.00 0.00

Si 0.97 0.97 0.97 0.97

Ca 0.01 0.01 0.01 0.01

Mn 0.01 0.01 0.00 0.00

Fe 0.55 0.33 0.26 0.29

Ni 0.00 0.00 0.01 0.00

Fo* 0.73 0.84 0.87 0.86

Fa 0.27 0.16 0.13 0.14

*Xi = i/(Mg + Fe).

47

v)

Table 9 Compositions of clinopyroxene grains in the lava (formulae to six oxygen).

Sample LR12-01 LR12-02

Grain Px1-1(l) Px1-9(l) Px1-11(l) Px1-13(l) Px1-14(l) Px2-2(l)

Area rim mid? core rim? rim rim

matrix matrix matrix matrix matrix matrix Na2O 0.26 0.28 0.29 0.28 0.31 0.27

MgO 15.13 17.14 14.70 17.81 17.79 17.05 Al2O3 3.63 3.34 4.45 2.98 3.20 2.50

SiO2 49.32 51.39 48.62 49.88 50.60 50.94

CaO 16.61 17.80 16.66 13.39 14.19 17.91 TiO2 0.89 0.95 1.29 0.63 0.62 0.57

Cr2O3 - - - - - 0.07

MnO 0.31 0.29 0.29 0.00 0.32 0.28

FeO 13.86 10.62 13.96 13.40 13.22 10.32

Total 100.01 101.81 100.26 98.37 100.25 99.91

Na 0.02 0.02 0.02 0.02 0.02 0.02

Mg 0.85 0.93 0.83 1.01 0.99 0.95

Al 0.16 0.14 0.20 0.13 0.14 0.11

Si 1.86 1.88 1.83 1.89 1.88 1.90

Ca 0.67 0.70 0.67 0.54 0.57 0.71

Ti 0.03 0.03 0.04 0.02 0.02 0.02

Cr - - - - - 0.00

Mn 0.01 0.01 0.01 0.00 0.01 0.01

Fe 0.44 0.33 0.44 0.42 0.41 0.32

Ca* 0.34 0.36 0.35 0.28 0.29 0.36

Mg 0.43 0.48 0.43 0.51 0.50 0.48

Fe 0.22 0.20 0.23 0.22 0.21 0.16

*Xi = i/(Ca + Mg + Fe).

48

vi)

Table 10 Compositions of oxide grains in the lava (formulae to four oxygens).

Sample LR12-01 LR12-01 LR12-02

Mineral titanomagnetite titanomagnetite

Cr-spinel

Cr-spinel Cr-spinel

Grain Ox1-1(l) Ox1-2(l)

Ox1-7(l)

Ox2-2(l) Ox2-3(l)

Area core core

core

core core

matrix matrix phe. incl. phe. incl. phe. incl. Na2O 0.22 0.21

Na2O 0.21

0.16 0.14

MgO 0.24 0.32

MgO 14.12

16.28 16.30

Al2O3 3.52 3.44

Al2O3 28.09

29.42 29.93

SiO2 0.37 0.92

SiO2 0.23

0.19 0.26

CaO 0.22 0.37

CaO 0.06

- 0.00

TiO2 22.30 23.94

TiO2 0.49

- 0.13

MnO 0.51 -

Cr2O3 33.12

36.84 36.32

FeO 71.35 68.92

MnO 0.18

0.30 0.12

Total 98.73 98.12

FeO 22.24

17.54 17.35

Total 98.74

100.73 100.55

Na 0.02 0.02 Mg 0.01 0.02

Na 0.01

0.01 0.01

Al 0.16 0.16

Mg 0.65

0.71 0.72

Si 0.01 0.04

Al 1.02

1.02 1.04

Ca 0.01 0.02

Si 0.01

0.01 0.01

Ti 0.66 0.70

Ca 0.00

- 0.00

Mn 0.02 -

Ti 0.01

- 0.00

Fe 2.35 2.25

Cr 0.80

0.86 0.85

Mn 0.00

0.01 0.00

Fe* 0.74 0.72

Fe 0.57

0.43 0.43

Al 0.05 0.05 Ti 0.21 0.23

Mg* 0.29

0.33 0.33

*Xi = i/(Fe + Al + Ti).

Fe 0.26

0.20 0.20

Al 0.46 0.47 0.48

*Xi = i/(Mg + Fe + Al).

49

Appendix C. Mineral compositions at the contact

i)

Table 11 Compositions of plagioclase grains in the contact zone (formulae to eight oxygen).

Sample LR12-01

Grain Pl1-9(c) Pl1-9(c) Pl1-9(c) Pl1-9(c) Pl1-9(c) Pl1-10(c)

Area core mid rim rim rim upper rim

xenolith xenolith xenolith xenolith xenolith contact Na2O 2.13 0.98 1.25 1.49 1.90 1.50

MgO 0.44 0.32 0.39 0.28 0.34 0.32 Al2O3 32.00 33.81 33.24 33.22 32.60 33.11 SiO2 46.64 43.70 44.47 44.59 45.83 45.19

K2O 0.00 0.00 0.00 0.00 0.03 0.04

CaO 16.94 18.86 18.34 17.98 17.32 17.51

FeO 0.34 0.39 0.37 0.55 0.48 0.89

Total 98.49 98.06 98.06 98.11 98.47 98.52

Na 0.19 0.09 0.11 0.14 0.17 0.14

Mg 0.03 0.02 0.03 0.02 0.02 0.02

Al 1.76 1.88 1.85 1.85 1.80 1.83

Si 2.18 2.07 2.10 2.10 2.15 2.12

K 0.00 0.00 0.00 0.00 0.00 0.00

Ca 0.85 0.96 0.93 0.91 0.87 0.88

Fe 0.01 0.02 0.01 0.02 0.02 0.04

An* 0.89 0.95 0.94 0.92 0.90 0.92

Ab 0.11 0.05 0.06 0.08 0.10 0.08

Or 0.00 0.00 0.00 0.00 0.00 0.00

*Xi = i/(Ca + Na + K).

50

ii)

Table 11 Continued.

Sample LR12-02

Grain Pl2-2(c ) Pl2-9(c ) Pl2-19(c) Pl2-25(c) Pl2-26(c) Pl2-29(c)

Area rim core core? rim? core core?

xenolith contact matrix matrix matrix matrix Na2O 4.88 2.84 2.15 2.18 2.40 3.98

MgO 0.21 0.22 0.32 0.24 0.34 0.28

Al2O3 28.03 32.44 31.94 32.05 31.68 29.80

SiO2 51.98 49.17 46.90 46.51 46.89 51.28 K2O 0.00 0.00 0.04 0.03 0.00 0.03

CaO 11.90 15.89 16.48 16.33 16.00 13.63

FeO 1.23 1.09 0.84 1.04 0.71 1.06

Total 98.23 101.65 98.63 98.35 98.02 100.03

Na 0.44 0.25 0.19 0.20 0.22 0.35

Mg 0.01 0.01 0.02 0.02 0.02 0.02

Al 1.53 1.73 1.76 1.77 1.75 1.61

Si 2.41 2.23 2.19 2.18 2.20 2.34

K 0.00 0.00 0.00 0.00 0.00 0.00

Ca 0.59 0.77 0.83 0.82 0.81 0.67

Fe 0.05 0.04 0.03 0.04 0.03 0.04

An* 0.57 0.76 0.88 0.88 0.87 0.77

Ab 0.43 0.24 0.12 0.12 0.13 0.23

Or 0.00 0.00 0.00 0.00 0.00 0.00

*Xi = i/(Ca + Na + K).

51

iii)

Table 12 Compositions of olivine grains in the contact zone (formulae to four oxygens).

Sample LR12-01

Grain Ol1-6(c) Ol1-7(c) Ol1-8(c) Ol1-8(c) Ol1-8(c) Ol1-8(c) Ol1-16(c)

Area core, incl rim, incl upper rim upper mid core lower rim upper rim

xenolith xenolith xenolith xenolith xenolith xenolith matrix?

Na2O 0.17 0.21 0.09 0.18 0.16 0.17 0.19

MgO 43.98 42.83 44.08 43.29 44.01 42.79 43.09 Al2O3 0.12 0.08 0.18 0.12 0.11 0.14 0.14

SiO2 38.47 37.31 37.94 37.72 38.25 37.91 37.88

CaO 0.38 0.41 0.37 0.39 0.38 0.40 0.37

MnO 0.28 0.27 0.26 0.27 0.25 0.26 0.25

FeO 17.08 16.97 16.37 16.76 17.54 18.42 18.17

NiO 0.15 0.18 0.19 0.10 0.26 0.10 0.22

Total 100.63 98.26 99.48 98.83 100.96 100.19 100.31

Na 0.01 0.01 0.00 0.01 0.01 0.01 0.01

Mg 1.66 1.66 1.68 1.66 1.66 1.63 1.64

Al 0.00 0.00 0.01 0.00 0.00 0.00 0.00

Si 0.97 0.97 0.97 0.97 0.97 0.97 0.97

Ca 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Mn 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Fe 0.36 0.37 0.35 0.36 0.37 0.39 0.39

Ni 0.00 0.00 0.00 0.00 0.01 0.00 0.00

Fo* 0.82 0.82 0.83 0.82 0.82 0.81 0.81

Fa 0.18 0.18 0.17 0.18 0.18 0.19 0.19

*Xi = i/(Mg + Fe).

52

iv)

Table 12 Continued.

Sample LR12-02

Grain Ol2-7(c) Ol2-8(c) Ol2-8(c) Ol2-8(c)

Area left rim left rim core right rim

xenolith xenolith xenolith xenolith Na2O 0.20 0.19 0.23 0.17

MgO 32.82 44.65 45.06 44.65

Al2O3 0.13 0.14 0.12 0.10

SiO2 36.03 38.64 38.58 38.46

CaO 0.40 0.36 0.37 0.38

MnO 0.45 0.26 0.36 0.27

FeO 29.71 16.56 16.44 16.75

NiO 0.15 0.24 0.20 0.09

Total 99.89 101.04 101.36 100.87

Na 0.01 0.01 0.01 0.01

Mg 1.33 1.68 1.69 1.68

Al 0.00 0.00 0.00 0.00

Si 0.98 0.97 0.97 0.97

Ca 0.01 0.01 0.01 0.01

Mn 0.01 0.01 0.01 0.01

Fe 0.68 0.35 0.35 0.35

Ni 0.00 0.00 0.00 0.00

Fo* 0.66 0.83 0.83 0.83

Fa 0.34 0.17 0.17 0.17

*Xi = i/(Mg + Fe).

53

v)

Table 12 Continued.

Sample LR12-02

Grain Ol2-9(c) Ol2-9(c) Ol2-9(c) Ol2-10(c) Ol2-10(c) Ol2-10(c)

Area outer left core outer right left rim core right rim

xenolith xenolith xenolith xenolith xenolith xenolith Na2O 0.20 0.11 0.17 0.18 0.17 0.15

MgO 33.22 44.20 40.97 32.53 43.27 40.97

Al2O3 0.23 0.12 0.15 0.51 0.09 0.10

SiO2 36.33 38.60 37.58 40.72 38.36 38.00

CaO 0.42 0.39 0.38 1.52 0.42 0.44

MnO 0.45 0.26 0.34 0.42 0.34 0.29

FeO 29.99 17.73 20.77 25.67 18.92 21.06

NiO 0.14 0.10 0.15 0.00 0.20 0.13

Total 100.98 101.51 100.51 101.55 101.77 101.14

Na 0.01 0.01 0.01 0.01 0.01 0.01

Mg 1.33 1.66 1.58 1.26 1.63 1.57

Al 0.01 0.00 0.00 0.02 0.00 0.00

Si 0.98 0.97 0.97 1.05 0.97 0.98

Ca 0.01 0.01 0.01 0.04 0.01 0.01

Mn 0.01 0.01 0.01 0.01 0.01 0.01

Fe 0.67 0.37 0.45 0.56 0.40 0.45

Ni 0.00 0.00 0.00 0.00 0.00 0.00

Fo* 0.66 0.82 0.78 0.69 0.80 0.78

Fa 0.34 0.18 0.22 0.31 0.20 0.22

*Xi = i/(Mg + Fe).

54

vi)

Table 13 Compositions of clinopyroxene grains in the contact zone (formulae to six oxygen).

Sample LR12-02

Grain Px2-5(c ) Px2-14(c) Px2-15(c) Px2-18(c) Px2-19(c) Px2-20(c)

Area rim rim rim rim rim rim

contact matrix matrix contact contact xenolith Na2O 0.23 0.24 0.27 0.21 0.23 0.28

MgO 17.62 18.17 15.10 18.76 9.89 7.11 Al2O3 2.75 2.54 2.21 2.22 1.25 2.30

SiO2 51.19 51.70 47.94 52.84 48.11 46.40

CaO 20.46 20.33 8.71 19.31 9.07 18.15 TiO2 0.31 0.28 0.96 0.35 0.96 1.47 Cr2O3 0.68 0.81 0.00 0.20 0.00 0.00

MnO 0.17 0.16 0.63 0.22 0.68 0.51

FeO 5.92 5.32 22.65 7.53 30.93 22.77

Total 99.33 99.55 98.47 101.09 101.12 98.99

Na 0.02 0.02 0.02 0.01 0.02 0.02

Mg 0.97 1.00 0.88 1.01 0.59 0.43

Al 0.12 0.11 0.10 0.09 0.06 0.11

Si 1.90 1.90 1.88 1.91 1.91 1.87

Ca 0.81 0.80 0.37 0.75 0.39 0.78

Ti 0.01 0.01 0.03 0.01 0.03 0.04

Cr 0.02 0.02 0.00 0.01 0.00 0.00

Mn 0.01 0.00 0.02 0.01 0.02 0.02

Fe 0.18 0.16 0.74 0.23 1.03 0.77

Ca* 0.41 0.41 0.18 0.38 0.19 0.40

Mg 0.49 0.51 0.44 0.51 0.29 0.22

Fe 0.09 0.08 0.37 0.11 0.51 0.39

*Xi = i/(Ca + Mg + Fe).

55

vii)

Table 14 Compositions of oxide grains at the contact (formulae to four oxygens).

Sample LR12-01 Sample LR12-02

Mineral Cr-spinel Cr-spinel Cr-spinel

Mineral titanomagnetite

Grain Ox1-1(c) Ox1-3(c) Ox1-4(c)

Grain Ox2-3(c )

Area core core? core?

Area core

contact? contact? contact?

contact Na2O 0.14 0.18 0.12

Na2O 0.25

MgO 14.74 12.46 12.65

MgO 0.44

Al2O3 25.15 21.23 22.06

Al2O3 2.28

SiO2 0.26 0.24 0.17

SiO2 0.52

CaO 0.11 0.20 0.15

CaO 0.27

TiO2 0.25 0.69 0.56

TiO2 21.68

Cr2O3 39.35 38.52 38.56

V2O3 0.63

MnO 0.34 0.34 0.33

MnO 0.63

FeO 18.69 24.46 23.64

FeO 73.91

Total 99.03 98.32 98.24

Total 100.61

Na 0.01 0.01 0.01

Na 0.02

Mg 0.68 0.60 0.60

Mg 0.03

Al 0.91 0.80 0.83

Al 0.11

Si 0.01 0.01 0.01

Si 0.02

Ca 0.00 0.01 0.01

Ca 0.01

Ti 0.01 0.02 0.01

Ti 0.64

Cr 0.96 0.98 0.97

V 0.02

Mn 0.01 0.01 0.01

Mn 0.02

Fe 0.48 0.66 0.63

Fe 2.43

Mg* 0.33 0.29 0.29

Fe* 0.76

Fe 0.23 0.32 0.31

Al 0.03

Al 0.44 0.39 0.40

Ti 0.20

*Xi = i/(Mg + Fe + Al).

*Xi = i/(Fe + Al + Ti).

56

Appendix D. Whole rock analyses

i)

Table 15

Whole rock major element analyses for the lava, two xenoliths and two standards compared with recommended values from GeoReM (in wt.%).

L-01 X-01 X-02 JG-1 GeoReM JB-1 GeoReM

SiO2 47.51 44.58 44.22 64.31 72.3 51.96 52.37

TiO2 0.77 0.12 0.15 0.40 0.26 1.36 1.32

Al2O3 14.67 23.62 24.3 18.78 14.24 14.30 15.53

Fe2O3* 11.13 5.18 5.13 2.89 2.18 9.07 8.99

MnO 0.17 0.06 0.09 0.10 0.063 0.16 0.153

MgO 11.02 11.26 10.66 1.05 0.74 8.46 7.71

CaO 12.71 13.77 14.31 3.40 3.40 9.86 9.25

Na2O 1.76 1.28 1.07 4.74 3.39 3.03 2.77

K2O 0.08 0.02 0.02 4.07 3.98 1.34 1.43

P2O5 0.07 0.05 0.02 0.25 0.097 0.37 0.255

Cr2O3 0.1 0.06 0.03 0.00 0.00 0.09 0.00

Total 99.99 100.00 100.00 100.00 99.45 100.00 98.78

LOI 2.7 0.35 0.32 - -

*Total Fe reported as Fe2O3.

57

ii)

Table 16 Whole rock trace element analyses for the host lava, two xenoliths and four standards (in

ppm).

L-01 2 S.D. (in %) X-01 2 S.D. (in %) X-02 2 S.D. (in %)

Si 211500 3.40 189800 3.30 208000 4.80

Ca 91460 0.12 99570 0.69 102200 2.10

Sc 42.23 2.30 11.07 7.50 9.90 13.00

V 272 4.30 56.70 16.00 44.50 15.00

Cr 620 1.80 278 9.00 308 19.00

Co 55.30 3.70 37.87 1.80 42.00 9.60

Ni 222 6.00 311 6.70 335 8.50

Cu 96.80 3.50 210 91.00 71.00 41.00

Ga 12.90 9.60 9.04 5.00 11.86 4.40

Rb 1.15 19.00 0.57 13.00 0.37 49.00

Sr 77.30 3.80 63.9 6.40 130.70 2.80

Y 16.21 5.50 3.35 9.70 2.31 4.50

Zr 35.00 4.10 7.20 20.00 4.63 18.00

Nb 2.95 8.30 0.55 21.00 0.34 11.00

Mo 4100 110 160 90.00 360 170

Ba 16.59 5.40 4.34 6.80 5.24 6.50

La 2.49 3.60 0.93 7.90 0.72 22.00

Ce 6.66 3.60 2.02 8.00 1.63 21.00

Pr 0.97 6.10 0.33 25.00 0.22 27.00

Nd 5.08 2.60 1.23 6.90 0.94 27.00

Sm 1.69 4.40 0.36 31.00 0.27 27.00

Eu 0.66 12.00 0.21 19.00 0.20 18.00

Gd 2.26 0.39 0.47 10.00 0.31 16.00

Tb 0.41 0.83 0.10 8.90 0.08 110.00

Dy 3.02 6.30 0.61 25.00 0.41 12.00

Ho 0.66 7.20 0.14 6.80 0.10 25.00

Er 1.99 5.70 0.40 29.00 0.25 8.00

Tm 0.30 16.00 0.07 23.00 0.05 24.00

Yb 1.95 9.90 0.36 23.00 0.27 18.00

Lu 0.29 21.00 0.07 39.00 0.07 120.00

Ta 0.19 14.00 0.07 26.00 0.03 22.00

Pb 0.35 13.00 0.44 17.00 0.22 33.00

Th 0.17 4.10 0.09 15.00 0.05 79.00

U 0.11 36.00 0.12 47.00 0.05 88.00

58

iii)

Table 16 Continued (in ppm).

BIR-1 2 S.D. (in %) NIST610 2 S.D. (in %)

Si 194000 4.20 302000 3.90

Ca 94200 3.10 81800 2.10

Sc 48.40 2.40 507 2.00

V 320 5.00 442 4.20

Cr 358 2.00 387 6.40

Co 50.00 3.90 401 8.70

Ni 165 2.20 440 3.50

Cu 106 4.20 393 5.60

Ga 14.18 4.20 407 3.60

Rb 0.22 49.00 404 3.00

Sr 113 1.70 519 3.20

Y 15.86 5.10 502 5.20

Zr 15.40 7.40 484 6.20

Nb 0.56 5.60 493 6.50

Mo 0.13 99.00 411 4.90

Ba 7.10 19.00 449 8.10

La 0.68 4.00 456 6.70

Ce 1.98 5.80 478 18.00

Pr 0.38 6.60 510 41.00

Nd 2.53 11.00 454 5.80

Sm 1.30 12.00 501 4.00

Eu 0.55 4.10 454 4.60

Gd 1.94 14.00 474 6.40

Tb 0.39 4.60 520 37.00

Dy 2.85 7.30 479 4.00

Ho 0.64 11.00 540 34.00

Er 1.87 13.00 485 3.50

Tm 0.29 13.00 520 28.00

Yb 1.85 6.40 489 5.90

Lu 0.29 14.00 520 31.00

Ta 0.04 19.00 550 47.00

Pb 3.21 11.00 393 5.40

Th 0.04 22.00 491 3.80

U 0.03 120.00 455 4.20

59

iv)

Table 16 Continued (in ppm).

NIST612 2 S.D. (in %) BCR2G 2 S.D. (in %)

Si 342000 10.00 225000 6.20

Ca 85000 1.60 50300 4.30

Sc 41.00 3.70 35.80 6.80

V 39.00 4.00 416 5.90

Cr 36.20 5.50 14.50 8.40

Co 35.10 3.00 35.90 8.10

Ni 38.80 4.60 11.24 5.00

Cu 37.00 5.10 15.00 8.50

Ga 35.90 5.30 21.18 2.60

Rb 31.40 6.00 44.90 6.00

Sr 78.80 6.10 336 1.10

Y 38.20 5.90 35.50 6.30

Zr 38.10 5.10 191 5.80

Nb 39.90 4.00 12.19 6.10

Mo 40.30 21.00 240 6.80

Ba 39.90 6.40 682 3.90

La 36.00 4.90 25.70 4.90

Ce 38.90 4.70 53.70 6.40

Pr 37.30 3.80 6.84 5.90

Nd 35.90 5.10 29.60 4.20

Sm 38.50 5.60 7.11 4.70

Eu 35.20 5.40 1.92 6.80

Gd 37.00 6.70 6.62 7.40

Tb 36.50 6.30 1.04 6.70

Dy 36.20 6.50 6.77 7.70

Ho 38.00 5.60 1.38 12.00

Er 38.20 6.10 3.83 4.70

Tm 38.30 6.40 0.54 8.00

Yb 39.20 3.90 3.53 5.70

Lu 36.90 7.20 0.53 1.50

Ta 39.60 6.70 0.77 1.90

Pb 38.80 6.50 9.87 3.30

Th 38.10 7.30 6.25 3.90

U 37.70 6.80 1.66 9.00