Geochemical Evolution of Basaltic Tuyas in Iceland During the Last Deglaciation

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Master's Theses and Capstones Student Scholarship

Fall 2007

Geochemical evolution of basaltic tuyas in Iceland during the last deglaciation

Kerri C. Schorzman University of New Hampshire, Durham

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Recommended Citation Schorzman, Kerri C., "Geochemical evolution of basaltic tuyas in Iceland during the last deglaciation" (2007). Master's Theses and Capstones. 312. https://scholars.unh.edu/thesis/312

This Thesis is brought to you for free and open access by the Student Scholarship at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in Master's Theses and Capstones by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. GEOCHEMICAL EVOLUTION OF BASALTIC TUYAS IN ICELAND DURING THE

LAST DEGLACIATION

KERRI C. SCHORZMAN

B.S., University of Idaho, 2004

THESIS

Submitted to the University of New Hampshire

in Partial Fulfillment of

the Requirements for the Degree of

Master of Science

Earth Sciences: Geology

September, 2007

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Thesis Co-Director, Joseph M. Licciardi, Assistant Professor of Earth Sciences

Thesishesis Co-Director, Julia G. Bryc 2 , Assistant Professor of Geochemistry

Mark D. Kurz, c ----- Senior Scientist, Geochronology ancl Radioisotopes Woods Hole Oceanographic Institution

Date

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DEDICATION

This thesis is dedicated to my parents, who always supported me while I was a student.

iii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS

I would like to thank both of my advisors who spent many hours helping me with

this project. Thank you, Julie Bryce, for helping me improve my geochemical skills and

teaching me about the solar system. Thank you, Joe Licciardi, for taking me on many

adventures from Iceland to British Columbia and helping me improve my fieldwork

skills. I am grateful to Mark Kurz for his mentoring and insight on this project. I would

also like to thank Kate Denoncourt for provided me with unpublished data from her

thesis.

Wally Bothner was very helpful with thin section preparation here at UNH. I

would like to thank Jo Laird for additional sample preparation insight and helping me

formulate geochemistry ideas. Diane Johnson, Rick Conrey, and Charles Knaack

provided me with assistance preparing samples for analysis in the GeoAnalytical

laboratory at Washington State University.

I would like to thank the UNH Earth Sciences Department for awarding me a T.A.

scholarship for three semesters and a research grant for analytical costs. I am grateful to

Jonathan Herndon for offering a scholarship that I received.

Finally, I would like to thank my friends here at UNH for staying up late with me

to meet deadlines and understanding the life of a graduate student. I would also like to

thank my family for listening to me talk on and on about volcanoes and supporting me

during this time. Fred Pearce was instrumental in teaching me how to use the program

MATLAB and assisted me in making figures for this thesis: thank you Fred.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS

DEDICATION iii

ACKNOWLEDGEMENTS iv

LIST OF TABLES vii

LIST OF FIGURES viii

ABSTRACT xi

CHAPTER PAGE

1. INTRODUCTION 1

1.1 Proj ect overview 1

1.2 Geologic setting 3

1.3 Tuya formation 5

1.4 Duration and timing of tuya emplacement 9

1.5 Melt generation and trace elemental compositions 11

1. 6 Decompression melting models 12

1.7 Magma chamber processes 14

2. METHODS 17

2.1 Field methods and sample sites 17

2.2 Northern volcanic zone sample descriptions 18

2.3 Western volcanic zone sample descriptions 20

2.4 Analytical methods 24

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3. RESULTS 27

3.1 Overview 27

3.2 Mineral chemistry 27

3.3 Major element whole rock chemistry 30

3.4 Trace element whole rock chemistry 33

3.5 Constraints on source lithology from mineral chemistry and isotopes 34

3.5.1 Constraints from mineral chemistry 35

3.5.2 Isotopic constraints 36

3.6 Modeling 39

3.7 Northern volcanic zone trends 40

3.8 Western volcanic zone trends 45

3.9 Spatial and temporal considerations 50

4. CONCLUSIONS 54

REFERENCES 56

APPENDICES 62

APPENDIX A: PHYSICAL AND CHEMICAL SAMPLE PREPARATION 63

APPENDIX B: PETROGRAPHIC DESCRIPTIONS 67

APPENDIX C: GEOCHEMICAL DATA 70

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES

TABLE PAGE

3.1 Olivine mineral compositions 29

3.2 Plagioclase mineral compositions 29

C.l Sample site descriptions for NVZ samples 70

C.2 Sample site descriptions for WVZ samples 71

C.3 Major element concentrations for NVZ samples 72

C.4 Major element concentrations for WVZ samples 73

C.5 Trace element concentrations for NVZ samples 74

C . 6 Trace element concentrations for WVZ samples 75

C.l REE concentrations for NVZ samples 76

C . 8 REE concentrations for WVZ samples 77

C.9 Microprobe data for olivine grains from Gaesafjoll tuya, NVZ 78

C.10 Microprobe data for olivine grains from HognhofQi tuya, WVZ 79

C.l 1 Microprobe data for olivine grains from RauQafell tuya, WVZ 80

C .l2 Microprobe data for olivine grains from HloQufell tuya, WVZ 81

C.l3 Microprobe data for olivine grains from SkriSa tuya, WVZ 82

C.14 Microprobe data for plagioclase grains from Gassafjoll tuya, NVZ 83

C.l5 Microprobe data for plagioclase grains from HognhofQi tuya, WVZ 83

C. 16 Microprobe data for plagioclase grains from RauQafell tuya, WVZ 84

C.l7 Microprobe data for plagioclase grains from HloQufell tuya, WVZ 84

C. 18 Microprobe data for plagioclase grains from SkriQa tuya, WVZ 85

vii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES

FIGURE PAGE

1.1 Map of Iceland 4

1.2 Growth of a basaltic tuya 6

1.3a Basal pillow basalt sample IC06-24 from HloQufell 7

1.3b Basal pillow basalt sample IC06-24 from HloQufell 7

1.4 The contact between pillow basalt and flow-foot breccias 8

1.5 HloQufell and the subaerially erupted summit lava 9

1. 6 REE signatures from glacial and postglacial units from the NVZ 9

2.1 Topographic map of Gaesafjoll and Storaviti 18

2.2a Tumuli cleft exposing sample collection site on postglacial lava unit Storaviti 19

2.2b Close-up of collection site on postglacial lava unit Storaviti 19

2.3a Gaesafjoll as seen from the north northwest 20

2.3b Gaesafjoll pillow basalt outcrop 20

2.4 Topographic maps of HloQufell, RauQafell, HognhofQi, and SkriQa 21

2.5 HloQufell 22

2.6a RauQafell 23

2.6b HognhofQi 23

2.7 SkriQa 24

3.1a Backscatter image of olivine grain from IC06-23 30

3.1b Backscatter image of plagioclase grain from IC06-23 30

3.2a Whole rock major element MgO variation diagram (MgO vs. Si0 2 ) 31

viii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.2b Whole rock major element variation diagrams (MgO vs. CaO) 31

3.2c Whole rock major element variation diagrams (MgO vs. Ti0 2 ) 31

3.2d Whole rock major element variation diagrams (MgO vs. AI2 O3 ) 31

3.2e Whole rock major element variation diagrams (MgO vs. FeO) 31

3.2f Whole rock major element variation diagrams (MgO vs. K 2 O) 31

3.3a Total alkali-silica diagram 32

3.3b Alkalinity index by latitude 32

3.4a Whole rock trace element variation diagrams (MgO vs. V) 34

3.4b Whole rock trace element variation diagrams (MgO vs. Sr) 34

3.4c Whole rock trace element variation diagrams (MgO vs. Nb) 34

3.4d Whole rock trace element variation diagrams (MgO vs. Zr) 34

3.4e Whole rock trace element variation diagrams (MgO vs. Y) 34

3.4f Whole rock trace element variation diagrams (MgO vs. Ni) 34

3.5 Forsterite vs. NiO for tuyas in the NVZ and WVZ 36

3.6a Magmatic helium ratios vs. trace element ratios (NVZ) 38

3.6b Magmatic helium ratios vs. trace element ratios (WVZ) 38

3.7a Major element modeling for tuyas in NVZ (MgO vs. Na 2 0 ) 41

3.7b Major element modeling for tuyas in NVZ (MgO vs. AI 2 O3) 41

3.8a Sm vs. Lu trace element model results for NVZ tuya samples 43

3.8b MgO vs. La trace element model results for NVZ tuya samples 43

3.9a Primitive mantle source normalized REE plots for all NVZ samples 44

3.9b REE plot for Gassafjoll and Storaviti 44

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.10a Major element modeling for tuyas in WVZ (MgO vs. Ti 0 2 ) 47

3.1 Ob Major element modeling for tuyas in WVZ (MgO vs A I 2 O 3 ) 47

3.1 la Trace element modeling for WVZ tuyas (Sm vs. Lu) 48

3.11b Trace element modeling for WVZ tuyas (MgO vs. La) 48

3.12a REE signatures for WVZ glacial and postglacial units (Mngvallahraun) 49

3.12b REE signatures for WVZ tuyas with base-cap pairs 49 ■5 3.13a He exposure age vs. trace element ratios (NVZ) 51

3.13b He exposure age vs. trace element ratios (WVZ) 51

•2 3.14a He exposure age vs. magmatic helium ratios (NVZ) 52

3.14b He exposure age vs. magmatic helium ratios (WVZ) 52

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT

GEOCHEMICAL EVOLUTION OF BASALTIC TUYAS IN ICELAND DURING THE LAST DEGLACIATION

Kerri C. Schorzman

University of New Hampshire, September, 2007

Tuyas are subglacial volcanoes that preserve a unique history of the interplay between

glaciation and hot spot volcanism in Iceland during the last deglaciation. Geochemical

signatures in eruptive units of tuyas provide insight into the influence of deglaciation on

mantle processes. Major and trace element concentrations and helium isotopes were

measured in samples from eruptive units of thirteen tuyas in Iceland, which have recently

been determined from cosmogenic He surface exposure dating to have formed during the

last deglaciation. All tuyas display temporal variations in geochemistry between eruptive

units. Geochemical analyses of eruptive units reveal that individual tuyas are subject to

crustal-level processes and source variation during emplacement. The geochemical

signatures of eruptive units suggest that the degree of partial melting did not change

significantly during tuya formation. Helium isotopic signatures suggest that tuya eruptive

units record geochemistry that reflects local mantle heterogeneity.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER!

INTRODUCTION

1.1 Project overview

Tuyas, also known as table mountains (stapi in Icelandic), are distinctive

volcanoes with steep flanks and flat tops. They are interpreted as products of subglacial

eruptions and are preserved in Iceland (e.g., van Bemmelen and Rutten, 1955; Walker,

1965; Jones, 1969, 1970), Canada (e.g., Mathews, 1947; Moore et al., 1995), Antarctica

(Smellie et al., 1993, Smellie and Skilling, 1994), and Mars (Ghatan and Head, 2002).

Geochemical analyses of tuya eruptive units can provide insight into many geologic

processes associated with rift-related volcanism including variations in magma

composition, trends in melt production rates, and the influence of deglaciation on mantle

processes (e.g., Slater et al., 1998; Maclennan et al., 2002, 2003; Sinton et al., 2005). By

studying the physical and chemical evolution of subglacial eruptions, researchers can

learn more about mantle processes during deglaciation. While few subglacial eruptions

have been directly observed, the eruption of Gjalp beneath the Vatnajokull ice cap in

Iceland provided researchers with the rare opportunity to study the stages of a subglacial

eruption (Gudmundsson, 1997). Gjalp did not breach the ice surface, however, leaving

many aspects of tuya formation poorly understood. The submarine and eventual

subaerial eruption of the island of Surtsey off the southern coast of Iceland in 1963-1967

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. is analogous to volcano-ice interactions and was witnessed by researchers (Thorarinsson,

1967). The stages of the submarine eruption of Surtsey are similar to subglacial

eruptions of tuyas, hence the opportunity to observe the historic formation of Surtsey

provided insight into eruption stages of tuyas.

One challenge for fully understanding the evolution of tuya formation is the

difficulty in dating these landforms. Few methods can provide age constraints on

geologically young volcanic products, but one approach is cosmogenic He exposure

dating. Recent work by Licciardi et al. (2007) developed exposure ages for thirteen tuyas

in the neovolcanic zones of Iceland. The exposure ages indicate that these tuyas are all

deglacial in age and experienced their last eruptive cycle from 14.5 to 10 ka B.P.

(Licciardi et al., 2007). These ages provide a chronological framework for interpreting

the geochemical signatures determined in this work from the same tuyas studied by

Licciardi et al. (2007).

Using geochemical and physical evidence, researchers have suggested that an

increase in melt production and eruption rate immediately followed the rapid deglaciation

of Iceland during the early Holocene (i.e. Maclennan et al, 2002, 2003; Sinton et al.,

2005). These studies also documented distinctive geochemical trends in glacial and

postglacial lavas. Model simulations have used these geochemical constraints to quantify

mantle melting processes during deglaciation (Jull et al., 1996). Mantle processes which

may affect trace element concentrations include an increase in melting, changing source

material, and assimilation of new material into the melting region.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The purpose of this study is to identify spatial and temporal variations in

geochemical signatures measured in eruptive units of thirteen tuyas in the neovolcanic

zones in Iceland, with a focus on major and trace element concentrations. The scope of

this investigation differs from and expands on that of previous studies, which have

concentrated on postglacial flows (Sinton et al., 2005) or eruptive units from a single tuya

(Breddam et al., 2002). Links between deglaciation and magma evolution in Iceland are

assessed by comparing the chemistry of basalt pillow units to subaerially erupted summit

lavas of several tuyas in Iceland. No studies to date have placed such data in a

chronological framework in order to address changes in geochemistry of individual tuyas

over time. This work provides the opportunity to determine changes in mantle processes

during the formation of each unit.

1.2 Geological Setting

Iceland is located at the juxtaposition of a volcanic hotspot and the Mid-Atlantic

spreading ridge. The geodynamics of Iceland are controlled by the spreading rate (2

cm/year) of the North American and Eurasian plates and the fluid dynamics of the

Iceland hotspot (Gudmundsson, 2000). Geochemical and geophysical evidence suggests

the Icelandic hotspot is a mantle plume (Morgan, 1971; Kurz et al., 1985; Wolfe et al.;

1997 Hilton et al., 1999; Breddam et al., 2001; Breddam, 2002). The most compelling

evidence for a plume comes from helium isotope ratios of Icelandic lavas that are

consistent with an undegassed mantle source. Furthermore, many Icelandic lavas are

compositionally distinct from mid-ocean ridge basalt (Breddam, 2002).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Iceland is situated at the junction between the Kolbeinsey Ridge to the north and

the Reykjanes Ridge to the south (Figure 1.1). Lithospheric accretion occurring along

these ridge systems defines the neovolcanic zones of Iceland. The zones are subdivided

into the northern volcanic zone (NVZ), eastern volcanic zone (EVZ), and western

volcanic zone (WVZ). Most preserved tuyas are sub-parallel to the axis of spreading in

the NVZ and WVZ (Figure 1.1). Iceland provides an opportunity to study the evolution

of a coupled volcanic-tectonic system that has evolved over the last 16 m.y. and

experienced repeated glaciations (Gudmundsson, 2000).

\I\va in

I atnaiokull

24°W 22« 20° 180 16© 14©

Figure 1.1: Map of Iceland showing the neovolcanic zones in purple, modem glaciers in white stipple, and tuyas with black circles (five tuyas included in study are orange circles), postglacial samples are diamonds (green diamond: hingvallahraun): Numbers correspond to table mountains: 1- HerQubrieQ; 2-Blafjall; 3 - Burfell; 4-Gassafjoll; 5-Hafrafell; 6-Sandfell; 7-Snartarstar6arnupur; 8-Hlo6ufell; 9-Hognh6f8i; 10- SkriSa; 11-Rau5afell; 12-Hvalfell; 13-Geitafell. Adapted from Licciardi et al. (2007).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.3 Tuya formation

The volcanic history of Iceland is geodynamically linked with the glacial history.

Detailed stratigraphic studies of tuyas have identified eruptive sequences that are

associated with changing ice dynamics during their formation. The most recent global-

scale glacial cycle occurred between 130 and -12 ka B.P. Marine isotope stage (MIS) 2

(Martinson et al., 1987) culminated with a peak in global ice volume during the last

(Weichselian) glacial maximum (LGM, 21 ± 2 ka; Mix et al., 2001). Previous studies

have reconstructed the Weichselian ice cap over Iceland during the LGM using

geomorphological evidence such as glacial striae and moraines (Norddahl, 1990;

Norddahl and Petursson, 2005). The estimated thickness of the LGM ice cap was 1000-

1500 m (Hubbard et al., 2006). Following the LGM Iceland experienced several episodes

of glacial advance and retreat.

The last deglaciation in Iceland began approximately 12 ka BP, as determined by

glacial-geomorphic mapping, radiocarbon dating, and tephra dating, and was followed by

rapid ice unloading between 11.8 and 10.3 ka BP (e.g. Sigmundsson, 1991; Norddahl,

1991; Norddahl and Petursson, 2005). In accordance with these reconstructions of the

timing and duration of deglaciation, geodynamic models incorporate this rapid ice

unloading event (Maclennan et al., 2002). Icelandic lavas record an initial pulse in

magmatic activity during the first 3 ka of postglacial eruptive history beginning around

12 ka B.P. This period between 12 ka and 9 ka is the early postglacial period. This pulse

in volcanism was followed by a decrease in magma production over the last 9 ka (Sinton

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. et al., 2005). The time period from ~ 12 ka B.P. to present is generally referred to as the

postglacial period.

Figure 1.2: Growth of a basaltic tuya proposed by Jones (1969). (A) Subglacial extrusion of pillow basalts; (B) continuing eruption o f pillow basalt and hyaloclastite; (C) aprons of breccia in foreset beds capped by subaerial lavas. Modified from Jones (1969).

Volcano-ice interactions that lead to the formation of tuyas begin with volcanic

activity beneath preexisting ice caps (Kjartansson, 1943; Matthews, 1947). A typical

tuya includes several volcanic units that form in varying water and ice conditions and are

separated by unconformities (Smellie, 2000). The initial stages of tuya growth begin

with the extrusion of pillow lavas into a meltwater vault. Subaqueous eruptions result in

pillow structures containing glass, absence of cinder material, and pahoehoe lava features

(Jones, 1969). The pillows basalts are nonexplosive because the hydrostatic pressure

inhibits fragmentation of eruptive material (Figure 1.2A). The pillow lavas develop a

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. glassy carapace, insulating the pillow from fragmentation. The glassy carapace is the

effective surface area of the interaction between magma and water melted from the

glacier during emplacement. Pillow basalts exhibit pipe vesicles that radiate away from

the center as the pillow is extruded into the water. These pillow units were targeted for

sample collection because they represent the oldest eruptive unit of tuyas (Fig. 1.3).

Figure 1.3: Basal pillow basalt sample IC06-24 from Hl88ufell in the WVZ, Iceland. The pillow in (a) exhibits typical radial fracturing and concentric formation; (b) Glassy carapace formed at contact between extruding basalt and water.

As the pillow lavas build upward, hydrostatic pressure at the vent decreases,

allowing fragmentation of the lava (Smellie, 2000). Hyaloclastite, composed of glass

shards and alteration minerals, is formed by the rapid heat exchange between lava and

water. Hyaloclastite material comprises a large portion of the tuya as continuing eruption

produce more pillow basalt (Figure 1.2B). Gently dipping hyaloclastite beds emanate

from the vent of the volcano and are termed flow-foot breccias (Matthews, 1947; Jones,

1969). Flow-foot breccias consist of large (up to ~10cm) pillow clasts cemented together

by interstitial palagonite and sideromelane (Figure 1.4).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 1.4: The contact between pillow basalt and flow-foot breccias. This photo taken near the base of Gaesafjoll in the NVZ. An intact pillow is located approximately 30 meters vertically above the base of the tuya. When the volcanic activity transitions from effusive eruption o f pillow basalts to increasing fragmentation, flow-foot breccias are formed stratigraphically upsection and evidenced by this gradational contact.

Continuing magma production allows the tuya structure to rise above the surface

of the intraglacial lake. This stage is accompanied by the eruption of subaerial pahoehoe

lava (Figure 1.2, panel C). The tuya summit lavas exhibit regular columnar jointing, ropy

textures, tumuli, and cinders (Figure 1.5) (Moore and Calk, 1990).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 1.5: HlS6ufell and the subaerially erupted summit lava exhibiting ropy surface features. Samples for surface exposure dating were collected by Licciardi et al. (2007) from this uppermost flow unit.

1.4 Duration and timing of tuya emplacement

Recent geochemical and stratigraphic studies of tuyas in Iceland have sought to

improve knowledge of the duration and timing of tuya formation (Moore and Calk; 1990;

Werner et al., 1996, 1999). Two contrasting hypotheses of tuya emplacement have

emerged from these previous studies, as described below.

The study by Moore and Calk (1990) suggests that tuyas are monogenetic and

formed during a relatively short-lived burst of magmatic activity. This monogenetic

origin is inferred from systematic changes in major element variation and volatile

variations at five tuyas in the WVZ. The chemical evolution of the magmatic suite

studied by Moore and Calk (1990) can be modeled along a liquid line of descent, or the

with permission of the copyright owner. Further reproduction prohibited without permission. compositional path taken by crystallizing igneous rocks. The crystallization path

followed by the tuyas in their study suggests a single cycle of fractionation, without

source change or hiatus in formation (Moore and Calk, 1990). Their study showed a

decrease in MgO from base to cap suggesting that the magmas differentiated as the tuya

evolved.

Werner et al. (1996) proposed an alternative hypothesis that Icelandic tuyas

resulted from several eruptive events, referred to as a polygenetic formation. Based on

major and minor element studies, these researchers argued that eruptive units of the tuya

Her6 ubrei 6 evolved under varying eruptive environments and changing magma sources.

Werner et al. (1996) suggested that the evolution of these volcanoes began with an

eruptive event during the last glacial period, followed by a hiatus in activity caused by

increased pressure on the magma chamber during ice accumulation. Their study

concluded that the eruption of Her3ubrei5 involved tapping of different magma bodies

and mixing events in response to fluctuations in the ice sheet over Iceland.

Because geologically young basalts are difficult to date using traditional

radiometric techniques, such as 40Ar /39Ar and K-Ar, the ages of tuya structures are

poorly constrained. Cosmogenic He surface exposure dating of subaerially erupted

summit lavas has provided ages for the final eruptive event of Icelandic tuyas during the

last glacial period (Licciardi et al., 2007). Using calibrated He production rates specific

to Iceland, results from Licciardi et al. (2007) show that 12 of the 13 tuyas in the NVZ

and WVZ were erupted during the last deglacial period. These authors argue that the

exposure ages closely reflect the timing of eruption. Tuya exposure ages are correlated

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. with episodes of glacier retreat during the last deglaciatioii (Licciardi et al, 2007).

Temporal constraints from exposure dating of tuyas in the NVZ provide ages between

14.4 and 10.5 ka B.P and ages of tuyas in the WVZ are between 12.6 to 10.2 ka B.P.

(Licciardi et al., 2007).

1.5 Melt generation and trace elemental compositions

Geochemical properties are used in volcanic regions around the world to provide

insight into how internal and external properties influence melting processes. In mid

ocean ridges and plume settings, such as under Iceland, material rises adiabatically from

depth. The ascending melt erupts at the surface, and the final chemical composition of

that lava is a function of the primary material that produced it as well as any influential

transport and crustal-level processes (cf. McKenzie and Bickle, 1998; Asimow, 2000;

Marsh, 2000). The geochemical signature of mantle melts depends on factors such as the

source composition, pressure interval of melting, and temperature. The temperature of

the magma entering the melting zone controls the fraction of melt produced.

Since mantle processes cannot be observed directly, one way to evaluate their

impact is to study how elements behave during melting. Trace elements (i.e., those with

concentrations less than 0 . 1 weight percent) are particularly helpful in this regard.

Differences in atomic radius and charge of individual trace elements define how elements

behave chemically during mantle melting (Blundy and Wood, 2003). The affinity of a

trace element for substitution into a mineral phase is the partition coefficient (D). Each

trace element has a partition coefficient uniquely defined for a given mineral-liquid

system as a function of the size, charge, and ambient conditions. Rare earth elements

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (REE), due to their similar size and charge, are especially useful for gaining insights into

melting and magma transport and storage conditions. The presence or absence of mineral

phases in the melting region can dictate the REE signatures (Blundy and Wood, 2003).

As temperature and melting increase, magnesium (Mg) concentrations increase and

incompatible trace element concentrations decrease due to a dilution effect (Hart and

Allegre, 1980).

At mid-ocean ridge and ocean island settings, the presence of water can affect

melt production and the degree of melting. The abundance of water during melting can

affect the composition of melt, and subsequently alter the petrogenetic pathway of the

magma. Water in the source region can lower the mean extent of melting but cause an

increase in the total melt production (Asimow and Langmuir, 2003). Through

quantitative models, Asimow and Langmuir (2003) also demonstrated that trace element

signatures are also sensitive to the abundance of water in the source region.

In some circumstances REE and other trace elements sensitive to degree of

melting provide insight into changing degrees of melting across a magmatic suite.

External forces acting on the mantle such as glacier removal can affect mantle processes,

ultimately altering trace element and REE signatures. Models using elemental signatures

from lavas erupted during deglaciation can quantify changes in mantle conditions (Jull et

al., 1996).

1.6 Decompression melting models

During glacial periods, thick ice sheets isostatically depress the crust and apply

pressure on the mantle. As deglaciation proceeds, rapid ice removal from the surface

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. relieves pressure on the mantle, causing an increase in decompression melting rates (Jull

and McKenzie, 1996). Studies have shown that the volume and rate of magmatism was

significantly higher (by a factor of 20-30) immediately following deglaciation in Iceland

(Jakobsson et al., 1978; Jonsson, 1978; Sigvaldason et al., 1992).

Modeling experiments by M l and McKenzie (1996) simulated the effects of

deglaciation on melt production and predicted an increase in melt production and

eruption rate by a factor of 20-30. These models show that increased melting during

deglaciation produces melts with distinctly different trace element concentrations relative

to those in melts produced during glacial periods. The geochemical data of Maclennan et

al. (2002, 2003) show that REE signatures are distinct between glacial and postglacial

times (Figure 1.6). Enriched REE signatures during glacial periods evolve into depleted

values during postglacial times, which have been interpreted as an increase in the degree

of melting of the source region (Maclennan et al., 2002).

S3 | Storaviti .2 'S £ IGassafjoll o

o £ • • ...

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Figure 1.6: REE signatures from glacial (Gaesafjoll) and postglacial (Storaviti) units from the NVZ of Iceland (Slater et al., 1998; Maclennan et al., 2002). Samples have been normalized to MORB REE values from McKenzie and O’Nions (1991). Figure modified from Maclennan et al. (2002).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.7 Magma chamber processes

An alternative model for explaining temporal variations in geochemistry in

Iceland was proposed by Gee et al. (1998a). These authors link the temporal variations in

geochemistry with magma chamber processes related to crustal instability during ice

sheet removal. Trace elemental variations can occur from magma chamber processes

such as mixing, crystallization, and assimilation. Specifically, the sinking of crystals,

which typically have compositions that differ from the bulk composition of the parent

magma, can drive chemical changes in magmas (Marsh, 2000). Crystal removal may

occur in one of two ways. Fractional crystallization involves removal of crystal phases

from melt, and continually changes the composition of the melt. Equilibrium

crystallization occurs when removed mineral phases are in equilibrium with the source

and thus ratios of incompatible elements in the volcanic product will be similar to those

in the source (Hart and Allegre, 1980). While fractional crystallization and assimilation

can alter bulk compositions, these processes are most prevalent in more evolved magmas

(e.g., those with MgO <6 wt %) (Slater et al., 1998).

Varying degrees of fractional crystallization have been documented in volcanic

products in Iceland (e.g., Gee, 1998a, 1998b, Maclennan et al., 2002, 2003, Stracke,

2003), and several studies have linked such processes as key mechanisms for driving

compositional change in Iceland (e.g., Furman et al., 1991; Sigmarsson and

Steinthorsson, 2007). The presence of bimodal magma compositions in Iceland has been

attributed to reprocessing of old oceanic crust (e.g., Kokfelt, 2006). The result of

reprocessing is that the neovolcanic zones in Iceland reheat the crust and form

progressively propagating melting fronts (Marsh, 2000). Many studies of Icelandic lavas

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. attempt to explain compositional change. Combining studies of magma chamber

processes with crustal instability, Gee et al. (1998) provide an explanation for temporal

variability in trace elements and isotopes in the WVZ.

The study by Gee et al. (1998a) found glacier-related controls on the

geochemistry of post-glacial lavas erupted along the WVZ. The geochemical signatures

of postglacial lava flows are primitive in composition and reflect depleted chemical and

isotopic values. Gee et al. (1998a) suggest a relationship between high-MgO lavas,

resulting trace elements, and isotopic signatures during the postglacial period. These

authors argue that the distinct lava compositions in early postglacial times are a function

of reduced residence times of parental magma in shallow magma chambers during glacial

unloading. Evidence for reduced magma chamber assimilation is given by an

incompatible trace element decrease during the early postglacial period as the crust

becomes isostatically unstable. The incompatible trace element trend decreases, as the

Mg# of the lavas increase during the early postglacial period as more primitive magma

sources are tapped (Gee et al., 1998a). Reduced magma chamber residence time

decreases the likelihood of melts mixing, assimilating, and undergoing fractional

crystallization.

Sinton et al. (2005) review hypotheses regarding observed geochemical variations

between glacial and early postglacial lavas in the WVZ. These authors favor the

interpretation that crustal rebound and enhanced decompression led to increased melting

and magma supply following deglaciation, in accordance with hypotheses put forth by

Maclennan et al. (2002). Magma chamber processes play a role in the petrogenesis of

glacial and postglacial lavas (Gee et al., 1998a); however, an increase in melting suggests

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. an alternate hypothesis for the observed geochemical trends between glacial and

postglacial lavas (Maclennan et al., 2002). Comprehensive evaluation of these

hypotheses requires a thorough investigation of the melt generation process during the

deglaciation. Tuyas provide a unique window into this period, and understanding the

geochemical signatures of tuyas provide insight into whether crustal instability or

increased melting during ice removal can uniquely describe the changing conditions of

magmatism in Iceland during the deglaciation period. While it has been established that

the geochemical signature and style of magmatism between glacial and early postglacial

periods are distinct (Gee et al., 1998; Maclennan et al., 2002, 2003; Sinton et al., 2005)

the geochemical evolution of lavas erupted during the glacial period are less understood.

This study compares the geochemistry of tuya base and cap eruptive units and interprets

the geochemical signatures of these units.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 2

METHODS

2.1 Field methods and sample sites

Samples analyzed in this study include a suite of subaerial lava samples collected

previously for exposure dating purposes by Licciardi et al. (2007) from 13 tuya summits

in the WVZ and NVZ. For this project, new samples were collected from basal pillow

basalts and hyaloclastites of five of these tuyas in the summer 2006 field season, as

described in more detail below. The full suite of analyzed samples thus encompasses

eruptive units from 13 tuyas, but only five of these tuyas have paired base-cap samples

that allow direct comparison of their geochemical properties (Fig. 1.1).

The goal of the 2006 field season was to collect unaltered pillow basalt

representing the initial subaqueous eruptive phase of each tuya for geochemical analysis.

The pillow lava is stratigraphically below flow-foot breccia and the final capping summit

lava unit. Where intact pillows were not present, breccias containing large clasts of

pillow basalt were collected from the hyaloclastite apron (e.g., IC06-22, IC06-24).

Altitudes and precise locations from a GPS device were recorded for each sample site,

and photos were taken to document the original state and stratigraphic relationships of

each sample.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.2 Northern volcanic zone sample descriptions

Samples were collected from the NVZ in the Myvatn region of northeast Iceland

for investigating geochemical relationships between the postglacial flow Storaviti and the

tuya Gaesafjoll (Fig. 2.1). Gaesafjoll afforded the best opportunity for sampling a tuya

base in the NVZ due to accessibility, exposure, and its direct stratigraphic relationship

with Storaviti.

( H ru.it

ftomihoU

Figure 2.1: Map showing the relationship between Storaviti and Gassafjoll with the three samples taken for this study and the two samples from previous studies, IC02-55 and IC02-57. Contour interval is 20 meters. Geologic map from Johannesson and Sasmundsson (1998).

Two samples were collected from the Storaviti lava shield. Large tumuli are

present across the shield surface and both samples (IC06-6 and IC06-7) were collected

from lower units in exposed tumulus clefts. Sample IC06-7 was collected from a tumulus

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. approximately 4 meters high. To minimize problems with chemical and physical

weathering, samples were collected near the bottom of the outcrop (Figure 2.2). Sample

IC06-8 was collected from a tumulus similar in size to IC06-7. Both samples are from

massive vesicular basalt units that contain olivine phenocrysts.

Figure 2.2: (a) Tumulus cleft exposing sample collection site on postglacial lava unit St6raviti; (b) close-up view of sample collection site on Storaviti.

Gassafjoll is a broad tuya southwest of Storaviti (Figure 2.3). The tuya flanks are

composed of interfingering flow-foot breccia and pillow basalt. Sample IC06-9 was

taken approximately 30 meters vertically from the base of the mountain on the northwest

slope. An intact pillow was located just below the contact with hyaloclastite. This

sample was recognized as the base of the tuya structure with overlying hyaloclastite and

flow-foot breccia. The two cap lava samples representing the last eruptive event, IC02-

55 and IC02-57, are from the subaerial summit lava unit.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.3: (a) Gaesafj611 as seen from the north-northwest, (b) Gaesafjoll pillow basalt outcrop. The basal sample was collected from the north slope and all cap samples were collected from the summit. The foreground is the Storaviti volcanic shield. Photo by J. Licciardi, 2006.

2.3 Western volcanic zone

Samples from the WVZ come from tuyas in the Laugarvatn region of southwest

Iceland. The most prominent tuyas in this area were selected for base-cap comparisons

because of the spatial relationship they exhibit (see figure 2.4). The study of these four

mountains allows a geochemical comparison between successive eruptive units from

mountains that are in close proximity.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. HognhofdiHlodufell

Raudafell Skrida

I ) - j m i » I i'm*&

Figure 2.4: Topographic maps of four tuyas in the WVZ. Samples IC06-21, IC06-22, IC06-23, IC06-24 and IC06-28 were collected for this project during the 2006 summer field season. All cap samples were collected by Joe Licciardi and field assistants from 2002 to present. Topographic maps created in VISIT program from Johannesson and Sasmundsson (1998). Contour interval is 20 meters.

HloQufell is a prominent tuya in the WVZ (Figure 2.5). Two new samples

collected from this tuya include a basal pillow basalt (IC06-23) and a flow-foot breccia

up-section from the pillow sample (IC06-24). The two cap lava samples, IC02-63 and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IC02-65, were collected previously from the summit by Licciardi et al. (2007). Samples

from this mountain thus form a vertical transect that includes cap, flow-foot breccia, and

base units.

Figure 2.5: Hlo3ufell as seen from the northwest. Samples were collected from a ravine cutting the slope showing intact pillows and successive units.

Hognhofdi and RauSafell are located southeast of HloSufell and described by

Jones (1969) as a single massif consisting of a common basal platform of pillow lava on

which the two edifices were formed (Figure 2.6). A ravine cuts between HognhofQi and

Raudafell and exposes the pillow basalt base. Sample IC06-21 was taken from a pillow

on the south side of the ravine, and serves as a representative sample of the base for both

tuyas. Although the ravine exposed the pillow base, it was difficult to distinguish if the

pillow base was continuous and truly a single unit for both tuyas. As discussed further in

the results chapter, it is possible that sample (IC06-21) may represent only one tuya.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A vertical transect of samples from RauSafell was assembled by collecting a

sample of flow-foot breccia (IC06-22) up-section from the basal pillow sample (IC06-

21). Two subaerial lava samples (IC03-14, IC03-16) were collected from the summit of

Raudafell and two subaerial lava samples (IC04-6, IC04-8) come from the summit of

Hognhofbi (Licciardi et al, 2007).

Figure 2.6: (a) RauQafell; (b) Hognhofbi. A ravine bisects and exposes the base of these tuyas.

SkriQa is a large tuya southwest of HloSufell and west of HognhofSi and

RauSafell (Figure 2.7). One sample (IC06-28) was collected from flow-foot breccia

forming the steep slopes of the mountain where no intact pillows were found for

sampling. This sample is part of a pillow within the foreset breccia beds and may not

represent the pillow base unit. This sample may not represent the pillow base unit;

caution must therefore be used in interpreting the results from this sample.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.7: Picture of Skri8a taken from the northeast. The tindar in the foreground is SkriSutindar and the tuya in the background is Skri8a. Photo by J. Licciardi, 2006.

2.4 Analytical methods

Major and trace element concentrations were measured in 39 samples at the

GeoAnalytical Laboratory at Washington State University. A detailed description of

sample preparation including rock crushing, XRF, and ICP-MS methodologies is located

in Appendix A.

Aliquots of - 120 grams were ground in a Chipmunk jaw crusher. After a rough

chipping, samples were ground in a disk mill and sieved to isolate the 125-250 pm size

fraction, followed by cleaning with DI water. After repeated rinsing, sonicating and wet

sieving, samples were dried in an oven. These preliminary steps reduced the total mass

of the sample by 20 to 35%, but yielded more than enough sample for both XRF and ICP-

MS analyses (~ 30 g required) and future geochemical work.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The initial steps for both XRF and ICP-MS are similar where both use a fused

bead technique (see Knaack et al. 1994, Johnson et al. 1999). The samples are taken

from the pre-treatment stage and chipped to a smaller grain size and split to ensure a

representative sample. Grinding of the split sample in an agate planetary ball mill makes

powder that is then added to a dilithium tetraborate flux agent. This mixture of sample

and flux is fused in a muffle furnace, once for ICP-MS samples and twice for the XRF

method. After polishing fused beads for XRF and diluting the reground fused bead for

ICP-MS, the samples are ready for geochemical analysis.

Major element concentrations were determined using a ThermoARL X-ray

fluorescence (XRF) spectrometer in the Geo Analytical Laboratory at Washington State

University. The spectrometer operates by beaming x-rays toward the sample which

excites the orbiting electrons around the elements and the energy created by this emits a

secondary x-ray photon. Each element emits a characteristic x-ray photon and can be

identified by the spectral wavelength created. The intensity of the spectra can be

quantified by directing the secondary x-ray from the sample through a collimator and

onto a lithium fluoride crystal, which diffracts the x-ray at varying angles proportional to

its frequency. The detector measures frequencies and calculates concentrations. This

XRF spectrometer measures 27 major and trace elements and compares these values to

nine USGS standard samples (PCC-1, BCR-1, BIR-1, DNC-1, W-2, AGV-1, GSP-1, G-2,

and STM-1 (Johnson et al. 1999).

Trace element concentrations were determined using a HP 4500+ inductively

coupled quadrapole plasma mass spectrometer (ICP-MS) in the GeoAnalytical laboratory

at Washington State University. Samples are introduced to the plasma, ionized and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. transmitted through the quadrapole for detection. Concentrations of 26 trace and rare

earth elements were made (Knaack et al. 1994). Three in-house rock standards are used

for calibration, BCR-P, GMP-01, and MON-01.

Electron microprobe analyses were conducted at Massachusetts Institute of

Technology on a JEOL JXA-733 Superprobe. This analytical method provides

quantitative analyses of microscopic amounts of material through x-ray emission

spectrometry. Mineral and glass standards were used for calibration, and an acceleration

of lOkV and a ZAF matrix conversion procedure was applied to all minerals analyzed.

The mineral grains are bombarded by a one micron-thick condensed electron beam

running on a lOnA current. Peak counting times of 40 seconds were used for all mineral

measurements.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 3

RESULTS

3.1 Overview

This study develops four broad categories of evidence to gain insight into magma

processes that occur during tuya formation. These lines of evidence include mineral

chemistry (section 3.2); whole rock major element chemistry (section 3.3); whole rock

trace element chemistry (section 3.4), and isotopic constraints on source variation

(section 3.5). Results derived from these various approaches are presented sequentially

in this chapter, as specified above, and interpretations that follow from these data are then

discussed in context of geochemical modeling (sections 3.6-3.9).

3.2 Mineral chemistry

Petrographic analyses of thin sections reveal distinct mineralogical differences

between cap and base samples. Samples selected for petrographic and microprobe

analyses include the cap (IC02-55, IC02-63, IC03-14, IC04-6, and IC04-12) and base

(IC06-9, IC06-21, IC06-22, IC06-23, IC06-24 and IC06-28) units from the five tuyas

with base-cap sample pairs. All of the above samples are composed of a glassy matrix

with glomerocrysts of plagioclase (100 pm - 1mm) and olivine (0.5-2 mm) with minor

amounts of clinopyroxene (100 - 500 pm) and iron-oxides (<100 pm). The glassy

selvedge of base samples is largely amorphous but contains microphenocrysts of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. plagioclase, olivine, and pyroxene. Many of these crystals are elongate, which is typical

of rapidly quenching mafic magma (Donaldson, 1976). The modal percentages of

phenocrysts are similar for both base and cap samples. On average, base samples contain

50% olivine, 40% plagioclase, 5% pyroxene, and 5% iron-oxide phenocrysts whereas the

cap samples contain 45% olivine, 45% plagioclase, 5% pyroxene, and 5% iron-oxide

phenocrysts. Detailed petrographic descriptions of each thin section are provided in

Appendix B.

Base samples contain undeformed euhedral olivine phenocrysts, whereas cap

samples tend to have deformed subhedral olivine phenocrysts. The olivine grains

commonly display resorption, or overgrowth, by crystallizing plagioclase grains. The

olivine resorption and deformation may be attributed to accumulation of plagioclase in

the cap unit. The base samples show significantly less crystal resorption than the cap

samples.

Microprobe measurements taken along grain boundaries and the center of grains

were used to determine if the grains had consistent composition (Figure 3.1). The

analyses proved little to no zonation of the olivine grains and no zonation of the

plagioclase grains. The average forsterite (hereafter “Fo”) content of olivine grains is

Fogo with a range of (F0 7 0 - F0 9 0 ). Two tuya base olivine grains have lower Fo

concentrations than the cap olivines and two tuya base olivine grains have higher Fo than

the cap samples (see Table 3.1). The average anorthosite composition of plagioclase

(base samples only) is An 78 with a range of (Ari66 - Angg) (see Table 3.2). There is no

dependence on location of anorthosite composition as determined by microprobe

analysis.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IC02- IC06- IC03- IC06- IC02- IC06- IC04- Sample IC06-9 55 2 1 14 24 63 28 1 2 # analyses 14 3 16 3 16 3 17 3 Unit base cap base cap base cap base cap

Si0 2 38.62 38.6 39.16 38.92 39.07 38.45 39.38 39.97

T i0 2 0.04 0 0.01 0 0.02 0 0.02 0

A12 0 3 0.06 0.03 0.09 0.03 0.06 0.03 0.08 0.03

Cr2 0 3 0.04 0.05 0.03 0.04 0.03 0.05 0.03 0.03 FeO 17.13 17.25 14.04 17.38 15.45 19.85 13.47 13.14

MnO 0.23 0.26 0.17 0.26 0 . 2 1 0.3 0.19 0 . 2 MgO 42.03 43 44.58 43.12 43.3 40.6 44.96 45.85 CaO 0.33 0.33 0.27 0.3 0.31 0.34 0.32 0.31

NiO 0.18 0 . 2 0 . 2 2 0.19 0 . 2 1 0.13 0.17 0.24

Fo (%) 80.5 81.6 83.63 81.5 82.17 78.46 84 8 6 . 1 Mg # 80.57 81.62 84.39 81.53 82.65 78.47 84.78 86.14

Table 3.1: Average microprobe analyses for olivine grains from five table mountains, (Gaesafjoll, Raubafell, HOgnhofSi, Hlobufell, and Skriba) with base-cap pairs. Olivine analyses for cap samples from Licciardi et al., (2007).

Sample IC06-9 IC06-21 IC06-24 IC06-28 # analyses 5 5 4 3 unit base base base base

Si0 2 47.89 49.4 48.94 47.4

A12 0 3 33.72 32.76 33.61 34.6

FeO 0 . 6 0.7 0.59 0.64

MgO 0 . 2 2 0.23 0 . 2 2 0.19 CaO 16.52 15.45 16.22 17.17

Na20 1.81 2.3 2 . 1 1.39

k 2o 0 . 0 2 0.03 0 . 0 2 0 An (%) 83.49 78.78 81.06 87.18

Table 3.2: Average microprobe analyses for plagioclase grains from five table mountains (Gaesafjoll, Raubafell, Hognhofbi, Hlobufell, and Skriba ) with base cap pairs. Only base samples were analyzed for plagioclase compositions.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 3.1: Backscatter images, (a) olivine from IC06-23; (b) plagioclase from IC06-23. Scale in micrometers (pm).

3.3 Major element chemistry

Paired base-cap samples of tuyas capture a time series of eruption with the oldest

unit at the base and the youngest unit toward the summit. Large variations in major

element concentrations occur from the base to the cap, where trends in oxides relative to

MgO reflect changing mantle and magma chamber conditions as the eruption proceeds.

All cap samples tend to have higher Si 0 2 , Ti0 2 , FeO, AI2 O3 , and K 2 O at a given MgO

concentration than base samples; CaO is lower in the caps (Figure 3.2). The two samples

from the post-glacial flow Storaviti exhibit the highest values of MgO and lower Ti0 2 ,

FeO, and K 2 O relative to values from all thirteen tuyas.

Analyses show that for the five tuyas with paired base-cap samples, basal pillow

lavas are consistently more primitive (ca. MgO > 9 wt %) and less evolved than their

subaerial cap lava counterparts (ca. MgO < 9 wt %). The postglacial flow Storaviti has

the highest MgO abundance (ca. 12 wt %) of all samples from this suite. Due to possible

olivine accumulation, it is difficult to directly compare major element concentrations in

the postglacial samples from Storaviti to samples from tuyas.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 50 (b)

o o in 40 ♦ ♦ 47 6 0 10 12 0 10 12

16 14 (c) (d)

14 13 ♦ a 12 1 12 o o ■ ^ g § p ° f 9 CD CD OO o © 10 & ♦ ♦ 11 ■ q 0 10 8 . 10 12 10 12

17 O (e) 0.4 16 ■ O ° i □ m 15 O 14 ' 0 ^

13 <9. 0 10 12 M gO (wt%) M gO (wt% )

Figure 3.2: Major element variation diagrams showing whole rock oxide compositions for tuya samples: Open symbols are caps and closed symbols are bases; NVZ in red circles; WVZ samples in blue squares; postglacial flow (Storaviti) in black diamonds; postglacial flow (bingvallahraun) in green diamonds. Data for bingvallahraun from Denoncourt (2006).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A total alkali-silica diagram (Figure 3.3) shows that all cap, base, and postglacial

samples fall within the tholeiitic basalt field. Samples range in SiC >2 concentration from

47-50 wt %. Most base samples have lower SiC >2 concentrations than the cap samples. In

general, the cap samples have higher total alkali (Na2 0 + K2 O) abundances than the base

samples. The postglacial flow Storaviti exhibits the lowest total alkali abundance. Tuyas

in British Columbia, Canada transition from tholeiitic to alkalic compositions as

eruptions proceed (e.g., Moore et al., 1995). The alkalinity index (Figure 3.3b) shows no

transition between alkalic and tholeiitic for this sample suite in Iceland. The index

illustrates the small variation in alkalinity between the NVZ and WVZ.

a )

4 66 ♦ G j» o' 0 5 8 o (0 3 O' -g 65 zs + O O O 15 CM 10 2 a l i D i ]

64 o ( b )

b 48 49 50 - 2-1 0 1 S i0 2 (wt%) Alkalinity Index

Figure 3.3: Total alkali-silica diagram for all cap, base and postglacial flows from the NVZ and WVZ (a), the line separating alkalic and tholeiitic lavas and is an empirical relationship from Carmichael et al., 1974 where total alkali = S i02 x 0.37-14.43. (b) Alkalinity index by latitude. Symbols are the same as described in figure 3.2. Data for bingvallahraun from Denoncourt (2006).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.4 Trace element chemistry

Temporal variations in trace elements are present between the base and cap units

of tuyas measured in Iceland. Figure 3.4 shows trace elements (ppm) vs. MgO wt %,

where all cap samples tend to have higher V, Sr, Nb, Zr, Y, and lower Ni than base

samples. The largest trace element variations are between subglacial units and the

postglacial unit Storaviti. Cap samples show the highest concentration of incompatible

element concentrations and the widest range of values compared to base samples. Base

samples are generally more depleted in incompatible trace elements relative to the cap

samples. The postglacial flow Storaviti shows the lowest abundances of incompatible

trace elements. The interpretation of the trend in Figure 3.5 (f) between Ni and MgO is

that the base samples incorporated most of the Ni available in the melt during the

crystallization of olivine. The first melt that forms incorporates higher abundances of Ni

(base units) and as crystallization proceeds, Ni becomes less abundant in the residual melt

(cap units). Trends between trace elements Nb and Sr vs. MgO may be caused by

plagioclase and pyroxene crystallizing out between base and cap eruptions.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 450 300 (§> 400 250

8a£o ^ > 300 m 15D

250 100

200 . 10 12

20 200

15 150

■m 5

0 6 0 10 12

50 300 (f) ♦ 40 200 ■ # E Q_ §; 30 Q_ □ 100 2D

10 6 0 10 12 0 10 12 MgO (wt%) M gO (wt%)

Figure 3.4: Trace element and MgO variation diagrams showing whole rock data from base and cap units of tuyas and postglacial samples: (a) V, (b) Sr, (c) Nb, (d) Zr, (e) Y, (f) Ni vs. MgO. Symbols are the same as described in figure 3.2. Data for bingvallahraun from Denoncourt (2006).

3.5 Constraints on source lithology from mineral chemistry and isotopes

Trace element signatures are useful for discerning mantle processes such as

degree of melting and crustal-level processes such as fractional crystallization. However,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. trace element concentrations alone cannot be used to discern between mantle processes.

Other methods such as isotopic analyses are needed to determine contributions from the

source. There are several techniques that provide information about the variations in

source lithology and history of enrichment. Basaltic olivine mineral chemistry and whole

rock isotopes are two such techniques.

3.5.1 Constraints from mineral chemistry

The relationship between olivine NiO and Fo contents has been used by some

researchers to constrain source lithology (Sobolev et al., 2005, 2007). The premise

behind their model is that mantle peridiotites, because of their abundance of olivine,

produce melts with relatively restricted low nickel contents. Olivine grains crystallizing

from these melts would therefore take on relatively low NiO contents. One hypothesis

suggests that in some ocean islands, such as Hawaii, elevated nickel contents (ca. NiO wt

% > 4.5) in olivine phenocrysts are most readily explained by source regions containing

both pyroxenite and peridiotite (Sobolev et al., 2005). Alternatively, most Icelandic lavas

described in the literature (Sobolev et al., 2005 and sources therein) fall within a range of

relatively low NiO contents and have been linked with source regions dominated by

peridiotite. The average NiO vs. Fo (%) determined in this study have been compared

directly with the data compilation of Sobelev et al. (2005) to help constrain the source

composition for eruptive units of tuyas (Figure 3.5). The range of NiO contents in lavas

from Iceland are most consistent with derivation from a peridiotite source lithology, with

no apparent contributions from pyroxenite source regions, according to the hypothesis put

forth by Sobolev et al. (2005).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. nl ______i i______i______i______i______i______i______i______78 80 82 84 8 6 8 8 90 92 Fo (%)

Figure 3.5: Forsterite vs. NiO (wt %) for Tuya samples NVZ and WVZ (Sample symbols are same as described in Figure 3.2; The solid line field added to this graph shows the range in compositions from tuyas in Iceland. This field falls within the values o f peridiotite (dashed line) from Sobolev et al., 2005.

3.5.2 Isotopic constraints

Helium isotope analyses provide useful information about source heterogeneity

and degassing history of the mantle (Kurz et al., 1982; Kurz, 1985; Lupton, 1983).

Helium isotope variations are related to upper mantle, mixing and have been used to

investigate the dynamics of mantle plume-spreading ridge interactions (e.g., Graham,

2002). The median 3 He/4He (R/Ra) for mid-ocean ridge basalts (MORB) is

approximately 8 R/Ra (Morgan, 1971) and is thought to reflect a degassed shallow

mantle source (Breddam et al., 2001). Icelandic 3He/4He signatures deviate significantly

from MORB 3 He/4He signatures along the adjacent Mid-Atlantic ridge (Kurz, 1985).

Systematic variations in 3 He/4He are seen in Iceland and are related to the tectonic

structure (Kurz, 1985). The highest 3 He/4He values worldwide are found in Iceland and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reach as high as 43 R/Ra (Breddam et al., 2001). High 3 He/4He signatures are indicative

of a relatively undegassed mantle source (Kurz et al., 1982).

As with many Icelandic lavas (e.g., Kurz, 1985; Hilton, 1990, Breddam et al.,

2001), the magmatic 3He/4He signatures of the NVZ and WVZ tuyas (Licciardi et al.,

2007) are enriched relative to MORB (Figure 3.7). The occurrence of two distinct bins of

magmatic 3He/4He in the NVZ (Figure 3.7a) suggests different sources supplying magma

to this region. The strikingly higher3 He/4He (20-22 Ra) measured in the northernmost

NVZ mountains (Sandfell, Hafrafell, and Snartarstardamupur; see Fig. 1.1) implies that

the magma source region tapped by these tuyas is less degassed than the magma source

for the tuyas toward the interior of Iceland (Figure 3.6). The other four NVZ tuyas

examined here (Herdubried, Gaesafjoll, Burfell, and Blafell; see Fig. 1.1) have a more

limited range of magmatic 3He/4He values (10-13 Ra) suggesting these tuyas may share a

common magma source. The interpretation of two distinct sources of magma to the NVZ

is consistent with geography and tectonic structure playing a role in 3 He/4He signatures.

Breddam et al. (2001) found that magmatic 3 He/4He values decrease with increasing

latitude, or distance from the axis of the hotspot supplying magma to Iceland. The results

for this study suggest an opposite trend where magmatic 3 He/4He values increase with

increasing latitude.

The 3He/4He signature from the WVZ is highly variable and cannot be clearly

related to geography or exposure age. Magmatic3 He/4He signatures from the base of

three of the tuyas (Rau5afell, HognhofQi and SkriSa) are systematically lower than

magmatic 3 He/4He for the cap samples. The magmatic 3 He/4He signature from the base

of Hlobufell is higher that the cap unit. Cap units from RauQafell and HognhofQi have

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. different magmatic 3 He/4He values, suggesting the magma source may have changed in

the interim between the eruptions of the two tuyas. The magmatic 3He/4He

measurements for the base units were conducted on glass separates while measurements

for the cap units were conducted on olivine grains. The magmatic 3 He/4He values

yielded values of 15.3 (± 0.1) for IC06-21, 15.0 (± 0.1) for IC06-23, and 11.0 (± 0.1) for

IC06-28. The measurements for these glass samples are most likely minimum values,

due to possible atmospheric or crustal contamination. The magmatic 3 He/4He

measurements in the WVZ may be attributed to local mantle heterogeneity as suggested

by magmatic 3He/4He data from Bumard et al. (1994).

3 ( a ) * Snart: caplava □ Sand: caplava £ 2.5 A Haf: caplava CO < < O Gae: caplava TO ♦ Gae: base 2 - ^ O Bur: caplava ♦ # o s t> Bla: caplava <1 Her: caplava 1.5 i i i 10 15 20 3He / 4He (R/Ra)

3 □ (b) □ 0 Hlo: caplava £ 2.5 ♦ Hlo: base CO O Hog: caplava TO • Ra/Ho: base 2 □ Rau: caplava <&. ♦ * Skr: caplava ★ Skr: base 1.5 10 15 20 3He / 4He (R/Ra)

Figure 3.6: Magmatic helium ratios versus trace element ratios, (a) NVZ; (b) WVZ. Helium data from all cap units are from Licciardi et al. (2007); data from the base of Gaesafjoll are from Breddam and Kurz (2001); and helium data for tuya bases in the WVZ are from this study.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.6 Modeling

Using data from the above geochemical approaches as constraints, the

compositional evolution from base to cap of a tuya can be predicted with geochemical

models. In this study, results from the whole rock major and trace element analyses serve

as model boundary conditions to evaluate the behavior of the shallow processes that

contribute to the overall compositional differences between base and cap.

The program MIXFRAC (Nielsen, 1985) is a two-lattice melt component model

that simulates major and trace element differentiation trends in crystallizing magmas.

This program allows the input of mafic and intermediate compositions and calculates

liquid lines of descent for fractionation, magma chamber recharge, and contamination

processes (Nielsen, 1985). The main parameter investigated was fractional and

equilibrium crystallization, where the system is closed and contributions from

assimilation and magma chamber recharge are assumed negligible.

The model input consists of whole rock compositions of base pillow samples and

fractional and equilibrium crystallization of olivine, plagioclase, clinopyroxene and iron-

oxide mineral phases (assuming that Fe 2 C>3/[Fe2 0 3 +Fe0 ] = 0.15). Starting with the

highest magnesium concentrations (i.e., the basal pillow compositions), the model

calculates compositions of melts produced by varying degrees of fractional

crystallization. The mineral phases that crystallized from the melt were olivine,

clinopyroxene, plagioclase, and iron-oxides, which are typical crystallizing phases in

olivine tholeiites. The pressure specified in the model is low (one atmosphere) due to the

mid-ocean ridge origin of these mafic compositions and temperatures specified in the

model range from 1500° C to 1100° C.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.7 Northern Volcanic Zone trends

Whole rock major and trace element data from NVZ cap samples from seven

dated tuyas and one base sample are plotted with the postglacial flow Storaviti (Figure

3.8). The fractional crystallization trend that originates from the base composition of

Gassafjoll predicts increasing NaiO with decreasing MgO (Figure 3.7a). The

concentration of MgO vs Na 2 0 of Gassafjoll and Storaviti shows that the composition of

Gassafjoll cap units falls below model predictions and therefore cannot be readily

predicted by simple fractional crystallization. The three northernmost NVZ mountains

Sandfell, Hafrafell, and SnartarstarQamupur (Figure 1.1) exhibit the most evolved

eruptive units. The deviation of the major element cap data in a few samples from

predicted model values indicates that the low pressure closed-system fractional

crystallization model does not adequately explain the data. Other processes, such as

assimilation, changes in the petrogenetic pathway (e.g., different pressures of

crystallization), and changes in the source region (degree of melting and/or source

variation) play an important role in the formation of these particular cap lavas.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o «r 1.5

1 8 10 12 MgO (wt%)

17 (b) ~ 16 0 ☆ Snart: caplava ss □ Sand: caplava % 15 A Haf: caplava O 14 0 Gae: caplava CN ♦ Gae: base < 13 O Bur: caplava D> Bla: caplava 12 <3 Her: caplava 11 ♦ Sto: post 8 10 12 MgO (wt%)

Figure 3.7: (a) MgO vs. Na20; (b) MgO vs. A120 3. Lines are model predictions for compositions evolving under equilibrium crystallization (solid) and fractional crystallization (dashed).

The relationship between MgO and AI 2 O3 (Figure 3.7b) shows two populations of

values. Initially, MgO is depleted in the melt due to modeled fractionation of olivine.

Later the model predicts that Sr and AI 2 O3 become depleted in the remaining liquid due

to the removal of plagioclase (Gee, 1998b). The modeled crystallization trends predict

this behavior between MgO and AI 2 O3 (Figure 3.7b). The three northernmost tuyas

(Sandfell, Hafrafell, and SnartarstarQamupur) show a decreasing AI 2 O3 trend relative to

decreasing MgO, as the model predicts. The other four NVZ tuyas, Her6ubrie5,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Gassafjoll, Burfell, and Blafell show an increase in AI 2 O3 relative to decreasing MgO.

Model predictions suggest the cap units of these four mountains have accumulated

plagioclase as eruption proceeded from base to cap. This finding is consistent with

petrographic observations.

Crustal-level processes can also be modeled using trace element abundances. The

relatively enriched concentrations of incompatible trace elements in the cap and base of

NVZ tuyas are markedly different from the depleted trace element values of the

postglacial flow Storaviti (Figure 3.8). The modeled trace element differentiation trend

for the tuya samples originates from the composition of pillow base samples from

Gassafjoll. After correcting for shallow level fractionation, some tuya cap units from the

NVZ deviate from the trend projecting from the base composition of Gassafjoll. The four

tuyas, HerQubrieS, Gassafjoll, Burfell, and Blafell show similar Sm abundances and the

three northern most mountains have highly variable Sm concentrations which may be

controlled by geography. Without additional tuya base samples in the NVZ, trace

element crystallization trends cannot be fully evaluated for all NVZ tuyas. Trace element

modeling alone cannot predict that fractional crystallization is a dominant mechanism

causing geochemical variation due to source variation.

Trace element signatures may also be affected by the presence of water in the

source region. Specifically, Asimow and Langmuir (2003) noted that within a restricted

temperature range, the abundance of water can influence the degree of LREE enrichment,

with the most pronounced effects evident in the lower pressure ranges (15 kbar).

Additionally, the presence of water in the melt may influence the petrogenetic pathway

from the base to the cap by promoting the crystallization of plagioclase.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.6

0.5 CL 0.4

0.3

0.2

Sm (ppm)

□ 15 □ (b) A ♦ Snart: caplava □ Sand: caplava A Haf: caplava E 10 Q. Q. 0 Gae: caplava * ♦ Gae: base O Bur: caplava D> Bla: caplava <1 Her: caplava ♦ Sto: post 8 10 12 MgO (wt%)

Figure 3.8: (a) Sm vs. Lu trace element model results for NVZ tuya samples; (b) MgO vs. La trace element model results for NVZ tuya samples. Lines are model predictions for compositions evolving under equilibrium crystallization (solid) and fractional crystallization (dashed).

Measurement and modeling of REE trends provide another approach for

elucidating mantle processes. The REE trend of glacial and postglacial units show

elevated light REE (LREE) relative to primitive mantle in Iceland. The tuya samples

have been normalized to a primitive mantle source composition according to Hofmann

(1988), which is reasonable because the REE concentrations in the melt are directly

related to the mantle material from which they originated (Maclennan et al., 2003).

Differences in LREE have been previously documented between Gaesafjoll and Storaviti

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (Slater, 1998; Maclennan et al., 2002, 2003). However, these research groups did not

distinguish between the eruptive units of Gaesafjoll, which have been shown in this study

to have highly variable compositions. The small variation in LREE between the base and

cap of Gaesafjoll suggests there was negligible change in the degree of melting as

eruption proceeded.

o£Z CD a> 10 co o Q ■O a) N ai E o

10 -i— i - i i i » i tiii La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

☆ Snart: caplava □ Sand: caplava A Hat: caplava 0 Gae: caplava ♦ Gae: base O Bur: caplava t> Bla: caplava <1 Her: caplava ♦ Sto: post La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Figure 3.9: Primitive mantle source normalized REE plots for all NVZ samples (a) and REE plot for Gassafjoll and Storaviti (b). The values show whole rock compositions of REE and are normalized using the primitive mantle source from Hofmann (1988).

Combined evidence from geochemical data and modeling constrains a

petrogenesis of eruptive products from tuyas in the NVZ. The eruptive products of these

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. tuyas have undergone varying degrees of fractional crystallization. In general, all NVZ

tuya cap samples can be modeled along major and trace element differentiation trends.

However, there are clearly distinct enrichments in LREE that cannot easily be explained

by fractional crystallization. For example, Gaesafjoll has strong LREE enrichment

compared with Storaviti which may be attributed to an increase in the degree of melting,

in accordance with the hypothesis of Maclennan et al. (2002).

Some constraints on source variation between tuyas in the NVZ are provided by

variations in isotope signatures. Helium isotopic data (Figure 3.6) show two distinct

populations of magmatic helium isotope ratios, which is interpreted here as evidence for

magma source heterogeneity. This conclusion is consistent with those in previous studies

of the Theistareykir volcanic system (e.g., Slater et al., 1996; Breddam et al., 2001;

Chauvel, 2002; Maclennan et al., 2002, 2003; Stracke, 2003). Geography and magma

source migration apparently play a role in the distribution of the helium isotope

populations, given that the highest 3He/4He values are clustered in the three northernmost

mountains in the NVZ.

3.8 Western Volcanic Zone trends

The major element geochemistry of the lavas from the WVZ is distinctly different

from the major element model behavior in the NVZ. For all four tuyas studied in the

WVZ, the basal pillow units are consistently more MgO-rich than the caps (Figure 3.2).

Projecting fractional crystallization trends from the common base for RauQafell and

HognhofSi (Figure 3.10a) shows that the cap TiC>2 vs. MgO composition can be modeled

along this trend at varying degrees of crystallization. Raubafell cap samples exhibit less

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. fractional crystallization than HognhofQi cap samples, which is consistent with mineral

chemistry and petrography. HloSufell base and cap compositions can be modeled by

fractional crystallization where the cap is produced by approximately 2 0 % fractional

crystallization. SkriSa requires only 5% fractional crystallization to predict the

composition of the cap from the composition of the base (Figure 3.10a).

While fractional crystallization can adequately explain variation seen between the

base and cap of one WVZ tuya, HloSufell, it does not appear to be the dominant

mechanism responsible for variation between eruptive units of other tuyas. Behavior

between MgO and AI 2 O3 in the WVZ is similar to that found in tuyas in the NVZ. The

model predicts the melt to decrease in A I 2 O 3 as plagioclase fractionates out. However,

the cap compositions have elevated A I 2 O 3 abundances suggesting the caps have

assimilated plagioclase, which is consistent with petrographic observations.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.5

CN O h-

M gO (wt% )

17 > Gei: caplava 16 A Hva: caplava 15 □ Rau: caplava • Ra/Ho: base cn 14 ☆ Skr: caplava o CN ★ Skr: base < 13 O Hog: caplava 12 0 Hlo: caplava ♦ Hlo: base 11 7 8 10 M g O (wt% )

Figure 3.10: Major element modeling for tuyas in WVZ. (a) MgO vs. T i02 (b) MgO vs. A120 3. Symbols for the WVZ are given in the legend: Lines are model predictions for compositions evolving under equilibrium crystallization (solid) and fractional crystallization (dashed).

Trace element modeling for the WVZ displays a wide range in incompatible trace

element abundances (Figure 3.11). Each tuya base-cap pair shows a different trend. The

model predicts that Sm (ppm) and Lu (ppm) are linearly related and increase in

concentration from base to cap. The cap compositions of Raudafell and HognhofSi

deviate from the projected trend, suggesting the data do not reflect the occurrence of

fractional crystallization. HloSufell base and cap samples can be predicted along major

and trace element fractional crystallization trends. The poor fit between the WVZ

geochemical data and the trace element modeling suggests that fractional crystallization

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. is not the dominant mechanism responsible for trace element variation between eruptive

units of all tuyas in the WVZ, with the exception of HloQufell.

0.6

0.5 a . a. 0.4

0.3

0.2 1

S m (ppm )

16 14 D> Gei: caplava A Hva: caplava 12 □ Rau: caplava E CL 10 • Ra/Ho: base 3 ☆ Skr: caplava to 8 ★ Skr: base 6 O Hog: caplava 4 O Hlo: caplava ♦ Hlo: base 2 '6 7 8 9 10 M g O (wt% )

Figure 3.11: Trace element modeling for WVZ tuyas. (a) Sm vs. Lu; (b) MgO vs. La. Lines are model predictions for compositions evolving under equilibrium crystallization (solid) and fractional crystallization (dashed).

Trends in REE for tuyas in the WVZ are presented in Figure 3.12. The REE

values have been normalized to primitive mantle (Hofmann, 1988). The range of LREE

values for tuyas with base-cap pairs shows that cap samples have higher LREE than the

base samples, with the exception of SkriSa. The volcanic units of the WVZ, unlike those

in the NVZ, do not display large LREE variations between glacial and postglacial units.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The variation in geochemistry from base to cap is probably not caused by increasing the

degree of melting, but may be explained by crustal-processes However, LREE variation

may be caused by a change in the degree of melting or changing sources between

volcanic units over time. For example, the REE signature variation between Raudafell

(12.2 ka B.P.) and SkriSa (10.2 ka B.P.) in Figure 3.12 may be due to a variation in the

degree of melting of the source between over time. Crossing REE patterns for Hlodufell

and HognhofQi suggests two different magma sources for these tuyas (Figure 3.12).

C o

c u0) c o o TJ 10

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

-£-Gei: caplava -A-Hva; caplava -B-Rau: caplava -♦-Ra/Ho: base A -Skr: caplava -*-Skr: base -©-Hog: caplava -O-HIo: caplava -♦-Hlo: base 4 - Ping: post La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Figure 3.12: (a) REE signatures for WVZ glacial and postglacial unit bingvallabraun; (b) REE signatures for WVZ tuyas with base-cap pairs. Data for fringvallahraun from Denoncourt (2006).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In summary, the geochemical behavior of tuyas in the WVZ is more complex than

the behavior of tuyas in the NVZ. Each tuya in the WVZ appears to represent a unique

interplay between magma chamber and melting processes. Fractional crystallization

processes most likely play a role in the petrogenesis of tuyas in the WVZ, but it is not

uniquely responsible for all geochemical variations in the WVZ.

3.9 Spatial and temporal variations

Temporal variations in geochemistry exist between tuya eruptive units and

between subglacial and postglacial units. The largest geochemical variations are seen •2 between Gaesafjoll ( He exposure age of 14.4 ka B.P.) and Storaviti (between 10.5 and 12

ka B.P) (Saemundsson, 1991; Gronvold et al., 1995), suggesting this time period is a

plausible time needed to produce such geochemical variations. Spatial relationships

between tuyas in the NVZ show that geography plays a role in geochemical signatures.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.14 ( a ) * Snart: caplava □ Sand: caplava N 0.12 A Haf: caplava n 0 Gae: caplava z 0.1 ♦ Gae: base oA O Bur: caplava D> Bla: caplava 0.08

Figure 3.13:3He exposure age vs. trace element ratios for (a) NVZ tuyas and (b) WVZ tuyas. Exposure age is an approximation for eruption age and may be affected by factors such as snow cover.

Temporal variations in trace elements in the W V Z are not as discernible as the

differences observed in the N V Z . For example, the geochemical transition between

subglacial and postglacial units is not as marked as in the N V Z . Skri5a has an exposure

age of 10.5 ka B.P. and the postglacial flow bingvallahraun has a radiocarbon age of

~10.3 ka B.P (Sinton et al., 2005), and their geochemical signatures are similar (Figure

3.13). Figure 3.13 shows decreasing trace element (Nb/Zr) ratios over time in the WVZ,

which is similar to relationships observed in the W V Z by Gee et al. (1998). Gee et al.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (1998) interpreted this decrease over time as the transition between subglacial and

postglacial geochemical signatures caused by crustal instability.

☆ to ☆ Snart: caplava 20 □ Sand: caplava A Haf: caplava < O Bur: caplava (a) [> Bla: caplava «X 10 <3 Her: caplava 10 15 20 3He exposure age (ka B.P.) 18 (b) £ 16 0 Hlo: caplava ♦ • ♦ Hlo: base 14 <1> O Hog: caplava # D • Ra/Ho: base ^ 12 □ □ Rau: caplava x 10 * Skr: caplava <0 ★ Skr: base

8 . 8 10 12 14 He exposure age (ka B.P.)

Figure 3.14: 3He exposure age versus magmatic 3He/4He for (a) NVZ tuyas and (b) WVZ tuyas. Magmatic 3He/4He data for caps proved by Licciardi et al. (2007); and base sample data from this study.

The relationship between magmatic 3He/4He and exposure age is presented in

Figure 3.14. Tuya ages in the NVZ range between 20 ka and 10 ka B.P., whereas the

tuya age range in the WVZ is narrower, between 12.2 ka and 10 ka B.P. The three

northernmost tuyas with the highest magmatic 3He/4He range in age between 20 ka and

10.2 ka B.P., suggesting that the source supplying magma to these tuyas was relatively

stable over time. The absence of a correlation between magmatic 3He/4He and exposure

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. age suggests that source variation is not controlled by eruption age of the tuyas in the

NVZ.

Some correlation is apparent between magmatic 3He/4He in tuya cap units and

exposure age in the WVZ. The concentration of 3He/4He in the cap samples increases

over time from the eruption of RauQafell at 12.2 ka B.P. (11.1 R/Ra) to the eruption of

H6gnhof3i at 10.2 ka B.P. (17 R/Ra). Without helium isotopic analyses for additional

base samples, it is difficult to determine if the increase in magmatic helium is consistent

with all eruptive units over time.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 4

CONCLUSIONS

New geochemical data are reported for 39 samples from tuyas in the NVZ and

WVZ show differing geochemistry between the first and last eruptive units of these

features. Basal and cap units record temporal trends in major and trace element

compositions during their formation over the last deglaciation in Iceland. At a given

MgO content, basal units of tuyas typically exhibit lower Si02, Ti02, FeO, and K 2 O than

summit lavas. Fractional crystallization model simulations suggest that crustal-level

processes may largely explain observed trends in geochemical properties from base to

summit in some tuyas. These findings are consistent with the earlier conclusion of

Moore and Calk (1990), who interpreted geochemical trends in tuya eruptive units to

reflect eruptions originating from a relatively short period of magmatism within one

glacial cycle.

The geochemical signatures of tuyas presented in this study are interpreted to

record negligible changes in the degree of melting during the interval of time between the

emplacement of the basal and cap units. There is, however, a consistent shift in

LREE/HREE values between tuya and postglacial lavas that cannot be explained by

fractional crystallization. Postglacial lavas most likely reflect changing melting

processes and/or changes in source chemistry. This conclusion is consistent with

hypotheses put forth by Jull and McKenzie (1996), Slater et al. (1998), and Maclennan et

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. al. (2002, 2003). However, the application of trace elements in determining a melting

history of tuyas in Iceland must be interpreted with caution because trace element

variations also reflect any changes in source composition.

Helium isotope data from tuya eruptive units show coherent populations of

magmatic helium isotope ratios (3He/4He), which is interpreted here as evidence for

magma source heterogeneity. The geographic distribution of magmatic 3He/4He in the

NVZ suggests two distinct populations, which are not controlled by exposure age. The

magmatic 3He/4He signatures of WVZ tuyas are not correlated with exposure age,

however correlation exists between the cap units, where the magmatic 3He/4He signature

decreases over time. However, overall the magmatic 3He/4He signatures of WVZ tuya

eruptive units exhibit highly variable signatures over time. Geography and magma

source migration apparently play a role in the distribution of the helium isotope

populations in the NVZ and WVZ. Magma migration dynamics may explain the

distribution of high magmatic 3He/4He signatures in the northernmost tuyas in the NVZ.

The geochemical behavior of tuyas in the WVZ is more complex than the

behavior of tuyas in the NVZ. Despite their close proximity, each of the four WVZ tuyas

investigated in this study exhibit dissimilar geochemical behavior and show unique

evolution over time. The structural relationship of the four WVZ tuyas, coupled with

variable geochemical signatures, suggests that each tuya is subject to local stress regimes

and melt migration dynamics. It is unlikely that a single magma source was responsible

for the broad range of major, trace, and isotope signatures seen in the small geographic

area occupied by these tuyas. Additional isotope systems will elucidate the role of

different sources in the formation of tuyas in Iceland.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDICES

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX A

PHYSICAL AND CHEMICAL SAMPLE PREPARATION

1) Physical sample pre-treatment

1. Weigh out 120 grams of whole rock (approximately 120 grams of rock needed to produce 60 grams of picked chips for XRF and ICP-MS analysis).

2. Coarsely crush each sample using the Chipmunk jaw crusher with a wide ~ 1 cm gap. Pulverize the sample in a disk mill to the desired grain size. Repeat crushing until sample grain size >6.3 mm.

3. Dry sieve to collect the 2-6.3 mm size fraction with a sieve stack of 6.3 mm, 2 mm, and 1 mm. Keep the size fraction between 6.3 and 2 mm; keep the fines < 2mm in a separate container. Record the weight of the sample, commonly you will retain between 50-75% of the original mass of the sample.

4. Transfer the desired grain size fraction into a 250 mL Nalgene wide-mouth bottle and rinse. Fill each bottle -2/3 full of distilled water cap and shake vigorously. Carefully decant the water into the sink until the water rinses clean, typically three to six rinsing cycles depending on the sample.

5. Transfer wet 2-6.3 mm sample into a 60 mL glass beaker. Fill the beaker with distilled water, sonicate and decant until the water is clear, samples may need several sonications.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 . Carefully pour sample from beaker into a 1 mm sieve and wet sieve with distilled water until no further fines wash out. Carefully transfer sample from the sieve to a piece of aluminum foil which will help with the transfer of wet grains. Pour sample back into the glass beaker from the foil and decant all remaining water from beaker.

7. Place samples in oven between 60° F and 80° F. Samples may take overnight to dry. Transfer dry samples from beakers into labeled containers.

2) Chemical sample preparation for XRF and ICP-MS

Sample preparation for XRF followed the technique described by Johnson et al. (1999) and Knaack et al. (1994). The sample preparation for both XRF and ICP-MS is similar until the last step described below.

1. Following sample pre-treatment, between -60-90 grams of sample are needed to create a representative sample. Chip the samples to a smaller grain size, approximately

1 mm chips in a ‘mini-chipper’.

2. Aproximately 28 grams of sample are needed for continuing the preparation. Split the sample using a splitting machine and collect approximately 28 grams from the bulk sample.

3. After separating - 28 grams of material, grind the sample in an agate planetary ball mill. This is necessary to keep the sample from being contaminated with metal. After grinding the sample for 30 seconds, remove the sample and label for the next step.

4. For XRF analysis, weigh out 3.5 g of the powdered sample into a plastic mixing jar

with 7 g of dilithium tetraborate (Li 2 B4 0 7 ). For ICP-MS analysis, weigh out 2 grams of powdered sample into a plastic mixing jar with an equal amount of dilithium tetraborate.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5. Mix the sample and flux for ten minutes in a mixing machine assisted by a plastic ball inside the sample jar. Transfer the sample and flux onto a sheet of paper and into graphite crucibles. Place twenty-four samples on a silica tray and load into a muffle furnace.

6 . Fusion takes 5 minutes after the furnace reaches an internal temperature of 1000°C. Remove the silica tray and samples from the oven and let cool.

The following steps are divided into the remaining procedures for ICP-MS and XRF.

8 . For ICP-MS, place the fused bead into a lead shatterbox swing mill and re-grind for 30 seconds. With the resulting powder, 250 mg of powder is transferred into an open

vial and placed on a hotplate at 110°C, with 6 mL HF, 2 mL HNO3 , and 2 mL HCIO 4 .

9. The samples evaporate, followed by a second evaporation with 2 mL HCIO 4 at 165°C.

10. A final volume of 60 mL is achieved by adding 3 mL HNO 3 , 8 drops of H 2 O2 , 5 drops HF and internal standards to the sample. The combination of fusion and dilution ensures the dissolution of refractory phases and removes silica and boron. The sample is then ready to load into the ICP-MS spectrometer (Knaack et al. 1994).

The following steps are for continuing XRF sample preparation:

11. For XRF, the fused bead is re-ground in a tungsten shatterbox swing mill for 30 seconds.

12. Refuse the powder in carbon crucibles in the muffle furnace for 5 minutes at 1000°C.

13. After the second fusion, engrave the cooled beads with the sample number. Polish the flat surface of the bead on a 600 silicon carbide grit followed by a final grind on a

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. glass plate with 600 grit and alcohol. The glass bead is ready to be loaded into the XRF spectrometer.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX B

PETROGRAPHIC DESCRIPTIONS

IC02-55 Gaesafjoll - cap

Petrographic description: In thin section, interstitial material comprises a majority of the bulk rock with some glomerocrysts of phenocrysts including plagioclase, olivine and some pyroxene. Olivine phenocrysts are subhedral and have been resorped by plagioclase (growing along olivine grain boundaries). Oxides are present as inclusion in the olivine grains.

IC06-9 Gaesaljoll - base

Petrographic description: In thin section, this pillow basalt is mainly amorphous glass with some glomerocrysts of phenocrysts. Olivine phenocrysts are euhedral with little alteration. The phenocrysts include plagioclase and pyroxene (-0.5 mm) and olivine grains (-0.5-2 mm). The glassy selvedge contains broken olivine grains. The pyroxene and plagioclase are twinned. Oxides are present as inclusions in the olivine grains.

IC04-6 Hognhofdi - cap

Petrographic description: In thin section, this sample has a fine grained matrix composed of mainly plagioclase. Olivine is altered or resorped during plagioclase crystallization. Some olivine grains have plagioclase inclusions as well as oxide inclusions. Pyroxene phenocrysts are small (100-300 pm).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IC03-14 Raudafell - cap

Petrographic description: In thin section, this sample is apheric with mostly plagioclase and olivine phenocrysts. The olivine grains are altered or resorped approximately ~ 0.5- 2mm in size. The olivine grains are fractured and plagioclase is growing along the grain boundaries. The plagioclase exhibits undulatory extinction. No pyroxene phenocrysts were found in this sample.

IC06-21 Hognhofdi / Raudafell - base

Petrographic description: In thin section, the matrix is very fine grained and composed mainly of plagioclase. Euhedral olivine grains show some signs of resorption, where plagioclase is growing along the grain boundaries. The olivine grains are approximately 0.5-2 mm in size. There are very few pyroxene phenocrysts (small grains, 200 pm).

IC04-12 Skrida - cap

Petrographic description: In thin section, this sample has glomerocrysts of olivine and plagioclase intergrowing together. The olivine is mainly subhedral with some euhedral olivine approximately 0.5 mm in diameter. Pyroxene is mainly CPX but some OPX. Phenocrysts of plagioclase are asicular and approximately 0.5-1 mm in diameter. The plagioclase is overgrowing the olivine. The matrix is intergranular with microphenocrysts of plagioclase, olivine, and pyroxene. Olivine has been resorped by plagioclase.

IC06-28 Skrida-base

Petrographic description: In thin section, this sample has a glassy matrix with microphenocrysts of minerals growing intergranularly. The plagioclase is asicular and abundant as a phenocryst. The olivine grains are about 0.5-1 mm in diameter and are euhedral. Glomerocrysts of plagioclase and olivine are present, with twinned plagioclase

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and olivine grains containing inclusions of oxides. Pyroxene (CPX) is present and

twinned in small phenocrysts approximately 2 0 0 microns in size.

IC02-63 Hlodufell - cap

Petrographic description: In thin section, glomerocrysts of plagioclase and olivine are present. Interstial material is glassy with microphenocrysts of asicular plagioclase. Olivine is subhedral with plagioclase growing along grain boundaries. Olivine is deformed with inclusions of oxides. Some twinned pyroxenes are present and

approximately 1 mm across.

IC06-23 Hlodufell - base

Petrographic description: In thin section, this sample has an interstital glassy matrix. Small phenocrysts compared to matching cap thin section. The olivine phenocrysts are euhedral and approximately 2 mm in diameter. The phenocrysts of plagioclase are asicular and growing along edges of olivines. The olivines have inclusions of oxides and may have inclusions of plagioclase. Small phenocrysts of pyroxene are present

(approximately 1 0 0 - 2 0 0 microns).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX C

GEOCHEMICAL DATA

Elevation Sample Unit Name Eruptive Unit Latitude Longitude (m) IC03-29 Blafjall cap lava 65.4434 16.8587 1135 IC03-30 Blafjall cap lava 65.4551 16.8678 1080 IC03-25 Burfell bomb 65.5510 16.6429 955 IC03-26 Burfell cap lava 65.5501 16.6651 954 IC03-27 Burfell cap lava 65.5486 16.6483 948 IC06-9 Gassafjoll base pillow 65.7922 16.9113 440 IC06-9B Gaesafjoll base pillow 65.7922 16.9113 440 IC02-55 Gassafjoll cap lava 65.7838 16.8822 759 IC02-57 Gaesafjoll cap lava 65.7847 16.8839 724 IC03-22 Hafrafell cap lava 66.0500 16.3452 521 IC03-23 Hafrafell cap lava 66.0503 16.3464 521 IC02-60 HerSubreiQ cap lava 65.1782 16.3614 1479 IC04-21 Her5ubrei5 cap lava 65.1770 16.3588 1479 IC02-19 Sandfell cap lava 66.1145 16.3271 525 IC02-21 Sandfell cap lava 66.1171 16.3466 523 IC02-58 Snartarstardamupur cap lava 66.3530 16.4720 270 IC02-59 Snartarstardamupur cap lava 66.3561 16.4646 277 IC06-7 Storavlti post-glacial flow 65.8221 16.9180 447 IC06-7B Storavlti post-glacial flow 65.8221 16.9180 447 IC06-8 Storavlti post-glacial flow 65.8200 16.9316 440

Table C.l: Sample description forNVZ samples.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Elevation Sample Unit Name Eruptive Unit Latitude Longitude (m) IC03-7 Geitafell cap lava 63.9410 21.5226 510 IC03-8 Geitafell cap lava 63.9405 21.5235 510 IC06-23 Hlodufell base pillow 64.4026 20.5475 550 IC06-24 Hlodufell flow-foot breccia 64.4034 20.5487 628 IC02-63 Hlodufell 1 cap lava 64.4170 20.5380 1140 IC02-65 Hlodufell cap lava 64.4180 20.5380 1165 IC06-21 Hognhofdi base pillow 64.3427 20.5313 401 IC04-6 Hognhofdi cap lava 64.3583 20.4996 1012 IC04-8 Hognhofdi cap lava 64.3574 20.4998 1013 IC03-11 Hvalfell cap lava 64.3848 21.1945 759 IC03-13 Hvalfell cap lava 64.3886 21.2055 789 IC06-21 Raudafell base pillow 64.3427 20.5313 401 IC06-21B Raudafell base pillow 64.3427 20.5313 401 IC06-22 Raudafell flow-foot breccia 64.3400 20.5506 445 IC03-14 Raudafell cap lava 64.3234 20.5818 913 IC03-16 Raudafell cap lava 64.3248 20.5782 929 IC06-28 Skrida base pillow 64.3719 20.6826 601 IC04-10 Skrida cap lava 64.3557 20.6842 992 IC04-12 Skrida cap lava 64.3537 20.6819 998 IC04-12 Skrida cap lava 64.3537 20.6819 998

Table C.2: Sample description for WVZ samples.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 O 2 P 0.171 0.173 0.213 0.252 0.175 0.052 o 2 0.2 0.211 0.4 0.322 0.180.19 0.2 0.19 0.226 0.34 0.208 0.17 0.175 0.06 0.05 0.045 0.36 0.219 k 1.99 1.94 1.93 1.56 1.47 2.54 0.36 0.288 2.45 2.65 0.42 0.326 CaO Na20 11.38 2.04 0.25 0.172 12.02 12.46 10.77 12.06 1.96 0.18 0.202 11.94 12.07 2.4 10.26 13.17 6.3 8.74 6.21 9.12 5.61 10.1 2.57 MnO MgO 0.1940.187 7.76 7.3 12.77 12.85 2.12 0.21 0.222 0.195 8.45 11.980.198 1.95 6.23 0.241 0.191 0.176 11.08 10.78 10.68 11.84 0.208 11.5311.76 0.197 0.206 9.28 7.67 12.35 0.213 6.89 12.07 2.35 13.3113.43 0.229 0.236 6.27 10.65 2.5 0.39 11.42 Fe20 3 3 o 2 14.82 15.43 13.37 14.14 0.24 5.74 14.25 a i TiOa 1.915 3.111 2.022 15.12 2.361 16.64 11.1 2.505 15.99 11.51 2.825 13.84 S i02 48.47 47.52 2.036 15.13 11.59 0.197 48.37 2.053 15.18 48.61 49.99 1.927 14.37 12.16 0.208 6.89 11.79 2.32 0.17 49.62 49.53 49.44 2.84 14 UnitName SnartarstarSamupur SnartarstarQamupur Gassafjoll Gassaijoll Her3ubrei5 Table C.3: Major element concentrations forNVZ samples. Concentrations are in weightpercent (wt%). Zone NVZ BlafjallNVZ Blafjall 48.52 48.32 1.809 1.874 15.77 16.23 NVZ Sandfell 49.91 3.187 13.21 14.45 NVZ Hafrafell NVZ NVZ NVZ Storavlti 48.84 0.757 14.87 9.43 NVZ HerSubreid Sample IC03-29 IC03-30 IC03-25 NVZ Burfell 48.9 1.674 14.76 11.67 0.204 8.77 11.49 2.11 0.25 IC03-26 NVZIC03-27 Burfell NVZ Burfell 48.9 48.87 1.679 1.677 14.81 11.82 0.208 8.67 11.44 2.04 0.25 IC02-55 NVZ Gaesafjoll 47.9 2.225 IC03-22 IC03-23 NVZ HafrafellIC04-21 IC02-58 IC06-7 IC06-9 NVZ IC06-9B NVZ Gassafjoll 47.5 IC02-57 NVZ IC02-60 IC02-19 IC02-21 NVZIC02-59 Sandfell NVZ IC06-7B NVZIC06-8 Storavlti NVZ 49.74 Storavlti 48.9 48.64 0.751 0.748 14.83 14.13 9.4 9.55 0.175 0.175 11.14 12.37 13.14 12.82 1.56 0.06 0.051

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.03 2.16 P 2 O 5 1.449 1.899 1.466 1.772 1.738 1.168 2.055 o 2 0.1 1.111 0.32 0.320.14 2.15 0.14 0.21 0.290.22 2.183 1.615 0.170.23 1.646 0.27 1.788 0.11 k 2.01 0.23 2.342.31 0.34 2.253 2.04 0.2 1.677 11.83 2.39 12.19 12.85 12.03 12.91 1.95 9.6 11.99 2.03 7.69 12 MnO MgO CaO Na20 0.2060.192 7.23 0.222 6.49 12.07 2.18 0.2 0.192 9.68 12 2.04 0.2 1.679 0.182 9.15 11.52 0.19511.08 7.19 0.19511.01 8.97 12.81 1.93 Fe20 3 3 o 2 15.1 14.88 12.19 0.196 9.22 12.1 1.86 15.03 11.12 0.191 9.63 16.02 9.92 0.175 9.25 13.21 1.83 0.09 a i 1.03 T i02 1.899 15.51 12.61 1.6151.772 15 1.679 14.98 11.25 0.196 8.46 48 47.4 1.646 14.9748.4 11.18 0.193 10.64 11.67 1.97 Si02 48.1448.19 1.44948.64 1.466 15.2 15.4347.98 11.14 11.11 1.671 0.192 15.02 9.28 1147.94 12.05 0.191 2.02 9.78 11.96 2.04 0.2 1.671 HloQufell RauQafell RauQafell 47.38 1.788 Table C.4: Major element concentrations for WVZ samples. Concentrations are inweight percent (wt%). WVZ HloQufell WVZ HloQufellWVZ HognhofQi 48.12 2.055WVZ RauQafell 15.17 13.69 0.228 6.55 11.73 2.09 WVZ Sample Zone UnitName IC03-7 WVZ GeitafellIC06-24 IC02-63IC02-65 WVZIC06-21 HloQufell 1 48.42 2.16IC03-11 15.19IC03-13 WVZ 11.74IC06-21 Hvalfell WVZ 0.206 HvalfellIC06-22 7.36IC03-14 WVZ 11.91IC03-16 WVZ IC06-28 48.05 2.43 WVZIC04-10 RauQafell WVZ SkriQa WVZ SkriQa 47.94 1.738 48.37 14.96 1.111 11.37 15.83 0.195 10.08 9.66 0.177 11.7 9.36 12.99 1.98 1.89 IC04-6 WVZ HognhofQi 48.11 2.253 15.63 IC04-12 WVZ SkxiQa 48.47 1.168 15.69 10.28 IC03-8IC06-23 WVZ Geitafell 48.43 2.15 15.39 11.79 IC04-8 WVZ HognhofQi 48.1 2.183 15.37 11.63 0.196 IC06-21B WVZ RauQafell 47.91 1.677

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. U 0.13 0.17 0.16 0.15 0.03 0.03 0.03 1.34 0.37 0.49 0.14 0.58 0.16 0.39 0.11 0.87 0.24 0.78 0.21 1.02 1.01 1.3 0.35 1.51 0.47 0.37 0.11 0.89 0.83 0.1 0.21 0.1 1.14 0.94 1.2 0.33 0.69 0.48 0.39 0.11 0.11 0.190.09 0.19 0.1 0.1 0.74 2.5 0.59 0.64 0.6 0.17 5.25 1.25 1.03 1.30.92 0.37 0.92 4.66 4.72 1.14 2.73 16 50 2.94 0.73 0.65 84 82 5.32 1.3 64 72 92 3.03 0.82 45 2.7346 2.69 0.7 Cs Ba Hf Ta Pb Th 0.03 0.03 0.02 450.02 2.79 0.630.01 0.66 14 0.6 0.92 8.78 Nb 10.54 10.42 98 28 1.38 Y Zr 16.09 29 1.58 15.02 26.22 115 12.51 0.04 55 3.03 0.8 0.64 0.46 25.76 110 11.17 0.05 25.19 90 8.9925.49 0.06 97 23.83 102 11.1 0.08 42.23 193 18.43 0.08 25.76 111 12.16 0.09 94 Sr 224 262 Rb 6.5 7.7 204 7.1 264 0.8 88 87 3.3 200 84 94 5 175 98 1.6 172 25.8564 95 Zn 130 7.8 206 44.89 189 17.95 0.08 83 284284 97 2.6 97 209 2.7 25.94 207 353 51.1 339 101 2.2 177 28.86 96 8.82 0.03 42 2.77 0.62 0.55 0.61 45.8 425 128 98 47.8 303 59 41.3 339 60 47.7 397 119 6.7 210 39.74 171 16.13 0.07 47 140 46.6 323 163 42.7 145 46.1 318 90 4.8 173 25.25 90 8.96 0.06 63 2.51 0.6 0.63 0.59 156 42.7 140 42.7 294 97 2.8 210 25.77 99 10.66 0.03 49 2.79 0.71 215 46.8 246275 61 47.5 0.9 240 Gassafjoll Burfell 145 45.9 329 91 4.6 171 24.56 89 8.92 0.06 62 2.51 0.6 1.05 Blafjall 89 44.6 293 86 3.2 UnitName Ni Sc V HerSubreiS 56 45.1 356 87 Table C.5: Trace element concentrations forNVZ samples. Concentrations are inparts permillion (ppm). Zone NVZ NVZ Burfell NVZ NVZ Burfell NVZ Gaesafjoll NVZ Storavlti NVZ Storavlti NVZ NVZ Sandfell 44 Sample IC03-25 IC03-26 IC06-9B NVZ Gassafjoll IC02-57 NVZ IC03-27 IC06-9 IC03-23 NVZ Hafrafell 62 48IC02-59 396 120 NVZ 7.5 Snartarst.IC06-7B 207 NVZ 36.57 Storavlti 49 173 51.2 16.29 0.09 221 75 47.8 247 65 0.9 95 16.17 29 1.57 0.01 16 IC03-29 NVZIC03-30 Blafjall IC02-21 NVZ Sandfell 44 47.4 432 IC02-55 NVZ Gaesafjoll 99 47.3 312 97 2.9 209 28.06 112 11.9 0.03 49 3.09 0.8 0.76 0.43 0.12 IC03-22 NVZ Hafrafell IC06-7 IC06-8 IC02-58 NVZ Snartarst. IC02-60 IC04-21 NVZIC02-19 HerQubreiQ - i^

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. U 0.14 0.14 0.23 0.27 0.27 0.16 0.29 0.17 Th 0.48 0.13 0.98 0.58 0.17 0.61 0.64 0.20 0.81 Pb 0.92 0.94 0.47 0.39 0.11 0.87 0.58 0.77 0.71 0.63 0.37 0.280.74 0.08 0.240.65 0.07 0.270.65 0.08 0.27 0.08 0.54 0.94 0.7 Ta 1.15 1.1 0.94 0.45 0.66 0.52 0.5 0.92 0.64 0.31 1.87 1.42 3.29 2.75 2.19 50 2.5 0.63 0.65 0.51 0.14 37 1.84 0.43 0.48 0.36 0.10 29 1.4829 0.31 1.48 0.31 29 0.03 0.02 0.02 0.06 86 3.21 1.07 0.04 11.5 0.05 67 2.25 0.76 0.6 6.42 0.04 39 4.74 0.02 10.31 0.04 54 16.11 95 79 48 4.7 48 4.7 26.7 115 21.89 63 26.57 88 9.46 168 21.78 63 6.46 148 18.54 210 23.46 89 14.11 0.05 75 2.46 279 273 25.86206 111 22.18 15.53 82 0.04 12.71 83 0.04 3.14 69 1.03 0.98 2.3 0.95 0.83 0.28 4 4 1.7 148 18.54 1.5 151 18.66 47 3.4 172 27.74 3.3 199 21.37 77 9.85 0.04 53 2.17 0.65 0.51 0.48 4.2 84 83 3.3 201 21.65 78 9.95 0.04 54 2.21 0.66 0.52 0.49 0.15 75 1.7 75 72 Zn Rb Sr Y Zr Nb Cs Ba Hf V 306 301 42 53.9 401 106 45.6 295 184 44.5 302 84 2.2 140 142 45.6 294 SkriQa 153 45.1 277 Geitafell 89 43.8 336 98 5.9 227 28.1 120 17.11 0.07 86 3.29 1.13 SkriQa Geitafell 87 45 328 97 5.8 227 27.76 121 17.26 0.06 85 UnitName Ni Sc HloQufell Hvalfell 115 45.9 319 88 RauQafell 184 42.1 310 86 5 206 22.35 91 13.82 0.06 75 2.53 0.9 RauQafell 219 41.3 303 89 2.7 199 20.66 77 9.84 0.03 53 2.16 RauQafell 162 45.3 317 88 4.3 199 21.6 RauQafell 177 Table C.6: Trace element concentrations for WVZ samples. Concentrations are inparts per million (ppm). WVZ WVZ WVZ HloQufell 63 WVZ WVZ WVZ WVZ WVZ Hvalfell 134 45.7 299 87 Sample Zone IC03-7 IC03-8 IC06-23 WVZ IC03-14 IC04-10IC04-12 WVZIC04-12 SkriQa WVZ SkriQa WVZ 143 46.2 268 69 1.4 138 17.58 45 3.94 0.02 25 1.36 0.26 IC06-24 WVZ HloQufell 172 45.2 306 85 2.5 168 IC02-63IC02-65 WVZIC06-21 HloQufell 1IC04-6 WVZ 57IC04-8 HognhofQi 52 WVZIC03-11 178 377 HognhofQi WVZ 42.6IC03-13 101 HognhofQi 304 86 3.2IC06-21 43.2 109 181 86IC06-21B 42.5 WVZ 350 3.4 WVZIC06-22 359 203 94 RauQafell 21.66 95 5.4 WVZ 172IC03-16 78 42.7 IC06-28 9.88 0.04 54

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.6 0.26 0.27 0.63 0.42 0.38 0.38 0.35 0.36 0.52 0.34 0.55 1.62 0.25 1.69 2.42 2.69 2.18 0.26 0.380.38 2.36 0.37 0.36 4.3 0.6 3.6 1.78 0.26 1.68 3.14 0.44 2.62 2.76 4.55 0.64 3.88 2.82 0.4 2.47 0.38 1.01 1.06 2.79 0.38 2.36 0.36 1.18 1.06 1.62 0.64 1.82 0.62 5.2 1.06 2.76 0.38 2.33 2.9 8.62 1.72 5.27 5.75 1.16 3.07 0.42 2.53 0.39 5.72 5.14 8.4 8.91 1.84 4.83 0.67 4.03 5.03 7.45 8.05 4.97 5.2 1.05 2.74 0.38 2.36 0.36 2.24 4.324.34 4.88 4.96 1.02 2.73 0.4 2.44 4.974.58 5.29 4.81 1.05 0.98 2.78 2.58 0.39 2.39 0.37 1.68 5.09 5.36 1.08 2.83 0.39 2.35 0.36 1.51 2.42 7.97 2.23 2.07 6.77 7.38 1.5 3.97 0.56 3.43 1.4 0.59 2.09 2.71 0.61 1.69 0.25 1.52 0.67 2.22 2.86 6.44 4.55 3.66 1.38 3.72 1.43 4.67 4.22 1.66 4.98 5.26 1.05 2.76 0.39 2.31 Sm Eu Gd Dy Ho Er Tm Yb Lu 4.1 1.53 0.67 3.49 15.53 4.32 1.58 14.54 4.31 1.64 4.95 13.5911.87 4.18 12.75 16.15 4.47 1.69 14.47 24.09 6.9 20.09 5.79 4.71 19.34 19.23 22.14 24.65 7.4 18.05 12.39 3.54 1.38 4.24 4.77 0.98 1.42 4.13 1.74 La Ce Nd 11.8 30.78 7.33 19.06 14.39 4.23 1.61 4.9 9.58 23.97 16.51 7.49 7.39 6.57 16.33 14.44 35.64 Storavlti Storavlti Snartarstardarnupur Gaesafjoll Gaesafjoll Gaesafjoll Burfell Table C.7: REE concentrations forNVZ samples. Concentrations are inparts per million (ppm). NVZ NVZ BurfellNVZ 7.69 18.75 12.72 3.66 1.39 NVZ Snartarstardamupur 7.81 18.93 NVZ NVZ Gaesafjoll 8.31 21.63 15.84 4.68 1.77 5.36 Sample Zone UnitName IC03-30 NVZ Blafjall IC03-25 IC03-29 NVZ. BlafjallIC03-26 NVZIC03-27 BurfellIC06-9 8.68 7.73 18.68 IC06-9B NVZ IC02-55 IC03-22 NVZ HafrafellIC02-60 NVZIC04-21 HerQubreiS NVZIC02-19 HerQubreid NVZIC02-21 Sandfell 13.61 NVZ 33.26 Sandfell 10.41 22.53 9.53 22.65 14.83 4.08 15.8 38.48 1.56 25.85 7.38 2.46 IC02-57 NVZ IC03-23 NVZ Hafrafell IC06-8 IC06-7B NVZ IC02-58 IC02-59 NVZIC06-7 NVZ Storavlti 1.75 4.83 4.13

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Lu 0.29 0.32 0.33 0.33 0.41 0.35 0.36 1.95 0.31 2.57 0.39 2.18 0.34 2.12 2.15 2.02 0.31 2.29 2.03 Yb 0.340.36 2.1 0.32 0.34 2.05 0.31 0.31 0.35 0.45 2.76 0.43 0.33 0.38 0.33 3 0.42 2.53 0.4 3.022.38 0.42 0.34 2.33 2.43 2.32 1.15 1.15 0.89 0.87 4.2 0.85 2.25 5.46 1.16 3.05 4.734.23 0.97 2.53 4.42 0.92 3.56 0.76 2.08 0.3 1.87 0.29 3.53 0.76 2.06 0.3 1.89 0.29 4.33 0.89 4 5.44 5.62 3.86 4.79 4.43 4.01 4.23 4.52.74 0.93 3.35 2.42 0.73 0.35 1.98 2.1 0.28 0.33 1.76 0.28 1.73 1.27 1.36 1.27 1.34 4.11 1.75 2.9 Eu Gd Dy Ho Er Tm 0.91 2.95 0.91 2.9 3.56 0.76 2.08 0.3 1.87 0.85 3.36 4.91 2.86 1.14 3.64 4.17 3.65 3.31 1.27 3.48 2.22 2.22 4.71 1.69 5.14n 5.27 1.07 2.72 Sm 9.46 6.91 12.14 18.48 13.65 11.91 12.85 8.18 6.14 2.02 9.77 7.12 2.26 9.34 13.08 17.64 29.72 21.53 28.06 17.53 20.45 5.3 La Ce Nd 7.51 18.06 7.57 18.13 12.08 3.43 1.29 3.93 4.37 0.87 2.37 7.39 8.86 3.99 3.26 SkriQa 3.78 9.34 6.91 SkriQa 3.78 SkriQa Geitafell 12.47 29.23 18.45 4.93 1.75 5.33 5.61 Geitafell 12.77 SkriQa Hvalfell 9.91 23.17 14.8 4.01 1.42 RauQafell 10.29 23.68 14.4 3.88 UnitName Hvalfell 9.27 HloQufellHloQufell 1HloQufell 5.34 6.99 13.3 17.78 7.25 12.38 9.63 18.53 3.65 2.95 12.94 1.39 3.93 1.16 4.53 3.65 1.48 5.16 4.21 1.09 0.9 2.97 2.44 0.42 2.62 HognhofQiHognhofQi 7.6 12.67 29.38 18.1 18.15 12.05 4.81 3.38 1.75 1.27 5.35 3.95 4.31 5.43 0.88 1.1 2.38 2.85 0.33 0.39 2.01 2.38 0.31 Table C.8: REE concentrations for WVZ samples. Concentrations are inparts permillion (ppm). WVZ WVZ WVZ WVZ WVZ WVZ WVZ WVZ WVZ Sample Zone IC03-8 WVZ IC04-12 WVZ IC03-7 Zone IC06-23 WVZ Hlobufell IC06-24IC02-63 WVZ IC02-65 IC06-22 WVZ RauQafell IC03-13 IC06-21 WVZ RauQafell IC03-11 IC06-21B WVZ RauQafell IC04-12 IC06-28 IC06-21IC04-6 WVZ IC04-8 WVZ HognhofQi 12.11 IC03-16 IC04-10 IC03-14 WVZ RauQafell

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. without prohibited reproduction Further owner. copyright the of permission with Reproduced o < O G O O o O H c4 CO m Sample Zone Unit Name CN (N FeO MnO MgO CaO NiO 0 :0 IC06-9 NVZ C/3 C3 38.66 0.0136 0.0347 0.0459 17.51 0.2829 42.27 0.3486 0.2349 d o ■*r o ■'3" IC06-9 NVZ Gaesafjoll 38.83 o 0.027 17.86 0.2735 41.49 0.3523 0.1981 ¥ o 13 o c/3 IC06-9 NVZ aa 25.51 4.83 0.0234 14.36 0.2246 33.35 0.523 0.1289 ¥ o o SO IC06-9 NVZ aa C/3 25.51 4.83 0,0234 14.36 0.2246 33.35 0.523 0.1289 lo o ¥ o aa

IC06-9 NVZ C/3 38.69 0.0163 0.0292 17.11 0.2727 42.36 0.3486 0.1672 ¥ 61900 o SO IC06-9 NVZ sa C/3 38.53 0.0036 0.0588 17.62 0.2646 42.77 0.3384 0.1843 ¥ o d

Z t H < Cr Fe Mn Mg Ca 19000 ¥ 81660 o o^ d o o 00 o o 0 © o o o © H H U o 0's SO aa m i 1.6165 0.0096 78 NVZ 0.0003 0.3758 ¥ 13 o o o o^ C5 o o o d o o o 00 O O O r- p o o o o o d p o o 00 o IC06-9 NVZ aa C/3 0.3847 1.5928 ¥ 13 o

IC06-9 NVZ aa C/3 0.8353 0.1863 0.0006 0.3933 0.0062 1.6278 0.0183 0.0034 ¥ TO £98 o SO IC06-9 NVZ aa C/3 0.8353 0.0006 0.3933 0.0062 1.6278 0.0183 0.0034 ¥ o o ) T I o d o SO C/3 IC06-9 NVZ aa 0.9945 0.0006 0.3678 0.0059 1.6226 0.0096 0.0035 ¥ o d o o o SO IC06-9 NVZ aa C/3 0.9851 0.0018 0.0013 0.3766 0.0057 1.6298 0.0093 0.0038 o o d d o d o r-- 00 O SO

IC06-9 NVZ aa C/3 KS 0.9771 0.0017 0.0075 0.0015 1.5264 0.0149 o d o o 9S000 V? 0 SO C/3 CO

IC06-9 NVZ aa 0.9933 0.0006 0.3604 1.6321 0.0093 0.0034 6639*1 ¥ 9S000 d o o 0 d o o o SO IC06-9 NVZ aa C/3 0.982 0.0021 0.3802 0.0114 0.003 ¥ d o o 0 SO C/3 IC06-9 NVZ aa 1.0037 0.0006 0.0013 0.3753 0.0054 1.5943 0.0093 0.0036

Table C.9: Microprobe data for olivine grains from Gaesafjoll tuya, NVZ. Concentrations in (wt%). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. without prohibited reproduction Further owner. copyright the of permission with Reproduced • C/3 O H O < o u O Sample Zone Unit Name (N

IC06-21 WVZ HognhofQi 39.25 0.0181 0.0686 0.032 14.53 0.1933 44.29 890£0 0.267

IC06-21 WVZ HognhofQi 39.09 d o o 96900 0.0247 14.25 0.2166 44.6 0.2928 0.1829 IC06-21 WVZ HognhofQi 39.21 0.0338 0.0747 0.0234 15.09 0.251 41.95 0.35 0.2404 *2 a SO SO IC06-21 WVZ 00 39.27 0.0206 0.051 0.0295 14.18 0.2096 44.63 0.2644 0.2349 IC06-21 WVZ HognhofQi 39.2 0.0146 0.0785 0.005 15.33 0.2174 43.88 0.3269 0.1763 d o (N d CN 00 00 IC06-21 WVZ HognhofQi 39.37 0.0654 0.0403 14.94 0.2607 44.75 t-' 0.2277 ! 22 © 00 a (N o 00 SO IC06-21 WVZ 00 39.06 0.0003 0.0779 0.0349 13.95 0.2701 44.14 0.312

IC06-21 WVZ HognhofQi 0.9996 0.0003 0.002 0.0009 0.3092 in 1.6687 0.0082 0.0047 9000‘0

79 IC06-21 WVZ HognhofQi 0.9965 0.0003 0.0021 0.3085 0.0042 1.6758 0.0083 0.0055 o o o C'' o o o 00 IC06-21 WVZ HognhofQi 0.9936 o o o O 0.0021 0.0005 0.3029 1.6896 0.0037 o o " 00 o o as r~- n IC06-21 WVZ HognhofQi |- 0.0007 0.0023 0.0005 0.3266 0.0055 1.6182 0.005 d o o O ■'3'00 1 22 o a o o o VO o o o SO IC06-21 WVZ 60 0.9959 0.0015 0.3008 0.0045 1.687 0.0072 22 d o o o o 00 ov r~- a d IC06-21 WVZ SO 0.9958 0.0003 0.0023 0.0001 0.3257 1.6614 0.0036 o o 00 d o o d o o 00 o o

IC06-21 WVZ HognhofQi 0.9915 0.0002 0.0019 0.3147 in VO 1.6797 0.0046 d o 91891 o o o '<3- d o o 00 I 22 o o o t"- n a IC06-21 WVZ SO 0.9984 0.0023 0.2983 0.0058 IC06-21 WVZ HognhofQi 0.9923 0.0006 0.0029 0.0007 0.2978 0.0056 1.6915 0.0089 0.0052

Table C.10: Microprobe data for olivine grains from Hognhofdi tuya, WVZ. Concentrations in (wt%). 0.0058 0.0044 0.0059 0.1911 0.0049 0.31320.2719 0.218 0.2907 0.2941 0.2993 0.2839 0.0085 0.00720.0081 0.0058 0.0049 44.5 0.2995 0.241 44.93 0.2648 0.2837 1.6854 0.0074 0.0059 1.6802 0.0075 0.0045 0.1956 44.83 0.2754 0.2895 0.0042 1.6961 0.0044 1.6881 0.2068 0.0051 1.6824 0.008 0.0039 0.0052 1.6866 0.0073 13.71 13.93 0.2246 44.52 0.2758 0.2227 13.96 0.1668 14.33 0.197 45.06 0.3026 0.2959 0.0605 14.04 0.0272 0.0506 14.61 0.2371 44.64 0.00090.0008 0.2905 0.0051 0.29540.0005 1.6962 0.004 0.0081 1.6991 0.0081 0.0412 Cr203 FeO MnO MgO CaO NiO 0.0822 0.0169 0.0633 0.0421 13.9 0.1875 44.85 0.29790.0702 0.2381 0.0364 A1203 0.0004 0.0019 0.0012 0.0227 0.0718 0.0249 0.0004 0.0024 0.0003 0.2892 0.0042 Ti Al Cr Fe Mn Mg Ca Ni 39.46 0.0305 0.0777 0.043 13.79 0.2373 45.16 39.71 0.0162 0.06 0.0535 14.07 0.2451 45.05 39.02 1.0014 0.0004 0.0021 0.0008 0.2949 0.0048 1.0004 0.0002 0.0021 0.0007 0.2961 0.0036 1.6818 Si Si02 Ti02 RauQafell Unit RauQafell 39.55 RauQafell 0.9965 RauQafell RauQafell RauQafell 0.9943 0.0006RauQafell 0.0023 RauQafell 0.9897RauQafell 0.9973 0.0006RauQafell 0.0019 0.0003 1.0015 0.0018RauQafell 0.0011 0.2956 Name WVZ WVZ WVZ WVZ WVZ WVZ WVZ WVZ WVZ WVZ Table 11: C. Microprobe data for olivine grains from RauQafell tuya, WVZ. Concentrations in (wt%). Sample Zone IC06-22 IC06-22 IC06-22IC06-22 WVZ IC06-22 WVZ WVZ RauQafell RauQafell 39.71 39.54 0.019 0.0236 0.0656 IC06-22 IC06-22 WVZ RauQafellIC06-22 39.19 WVZ 0.0326IC06-22 0.0628 RauQafell WVZ 39.45 RauQafell 0.0117 0.9933 0 0.0023 0.001 0.309 IC06-22 WVZIC06-22 IC06-22 RauQafell 39.28 0 0.0769 IC06-22 IC06-22IC06-22 WVZ RauQafellIC06-22 0.9917IC06-22 0.0005 0.0019 IC06-22

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.2154 0.2223 0.0046 0.2408 0.1612 0.0043 0.0048 0.0033 0.0049 0.0044 0.0042 NiO 0.31520.4029 0.204 0.0088 41.04 MgO CaO 0.184 43.63 0.3347 0.2122 0.1859 43.71 0.1937 43.86 0.3126 0.0041 1.6481 0.0084 0.0049 0.0044 1.648 0.0087 15.75 0.1713 42.93 0.3578 0.2408 15.62 16.44 16.15 0.2099 43.19 0.3214 16.29 0.2225 43.48 0.3666 0.238 0.3444 0.0048 1.63830.3364 0.0099 0.00370.3316 1.6346 0.0098 0.004 1.6539 0.0086 0.3518 0.004 1.6568 0.0091 Fe Mn Mg Ca Ni 0.024 0.0008 0.3547 0.0051 1.5635 0.011 0.0292 15.9 0.2052 43.81 0.3216 0.0345 0.0333 0.0393 Cr Cr203 FeO MnO 3 o 2 0.0546 0.0588 0.0894 0.0674 0.0017 0.0009 a i 0 0.0015 0.0006 0.0561 0.165 0.0397 16.6 0.2353 0.0011 0.005 0.0019 0.0651 0.0133 0.0169 Ti Al T i02 39.52 39.42 40.11 1.0251 0.9966 0.0004 0.9854 Si S i02 Hlodufell Hlodufell 39.25 0.0215 0.0558 0.0428 Hlodufell 39.36 0.0087 Hlodufell 0.9997 0.0003 0.0018 0.0007 0.3433 0.0045 1.6366 Hlodufell 39.32 WVZ WVZ Hlodufell 39.25 0.0077 WVZWVZ Hlodufell Hlodufell WVZ WVZ WVZ Table C.12: Microprobe data for olivine grains from Hlodufell tuya, WVZ. Concentrations in (wt%). Sample Zone UnitName IC06-24 IC06-24 IC06-24 IC06-24 WVZIC06-24 Hlodufell WVZIC06-24 IC06-24 0.9922 HlodufellIC06-24 WVZ 0.0002 WVZIC06-24 0.0016 0.9965 HlodufellIC06-24 0.0005 0.0003 Hlodufell 0.3465 1.0026 0.002 0.0001 0.9975 0.0008 0.0027 0.0007 0 0.0019 0.0006 0.3356 IC06-24 WVZ Hlodufell IC06-24 WVZ IC06-24 WVZ Hlodufell IC06-24 WVZIC06-24 Hlodufell 38.68 0.0018 0.0491 0.0317IC06-24 16.51 WVZ Hlodufell

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.005 0.0037 0.0036 0.1927 0.0033 0.0045 NiO 0.0098 0.0039 0.0096 0.3413 0.2458 0.0082 0.0032 0.0092 0.0094 0.0037 CaO 44.8 0.3235 0.18 44.15 0.3738 0.17 45.33 0.3665 44.25 0.3725 0.1842 1.6978 MgO 0.3131 0.0046 1.6711 0.0051 0.2264 0.2506 44.44 14.42 14.16 0.2216 44.9614.14 0.3449 0.240914.48 0.1829 13.97 0.297 0.3029 0.3177 0.0048 1.6617 0.0101 0.0035 FeO MnO 0.0604 0.0347 0.0452 Cr20 3 0.0541 0.0676 14.17 0.2727 45.07 0.3492 0.1854 0.0621 0.0459 15.05 0.0655 0.0404 14.24 0.2376 45.03 0.3657 0.1885 0.0018 0.0009 0.0014 0.001 0.2997 0.0049 1.6873 0.0091 0.0394 0.0012 0.0007 0.3037 0.0067 1.661 0.0101 0.0037 0.0619 0.0555 14.48 0.2183 44.58 0.3576 0.1641 0.0016 0.0012 0.3048 0.0053 1.6674 0 0 0.0018 0.0011 0 0.0018 0.0011 0.3045 0 0 0.006 0.0687 0.0549 0.013 0.0166 0.0003 0.0091 T i0 2 A120 3 39.81 0 39.66 39.94 39.66 1.0012 0.9988 0.0002 S i02 Si Ti Al Cr Fe Mn Mg Ca Ni SkriQa 39.86 0.0069 0.0639 0.0473 SkriQa SkriQa SkriQaSkriQa 39.57SkriQaSkriQa SkriQa 0 39.81 0.0474 0.0478 0 14.25 0.0539 0.2298 45 0.336SkriQa 0.2202 SkriQa 0.9989 0.0001 0.9959 0.002 0.0002 0.0011 0.0016 0.2978 0.0013 0.0051 0.2975 1.6819 0.0058 0.0087 1.687 SkriQa 39.57 0.0047 0.0609 WVZ WVZ WVZ WVZ WVZ SkriQaTable C.13: Microprobe data for olivine grainstuya, from WVZ.SkriQa Concentrations in (wt%). 1.0057 WVZ WVZ WVZWVZ SkriQa SkriQa 0.9955 0.9892 WVZ WVZ WVZ WVZ WVZWVZ SkriQa 1.0021 Zone UnitName Sample IC06-28 IC06-28 WVZIC06-28 SkriQa WVZIC06-28 SkriQaIC06-28 39.56 IC06-28 WVZIC06-28 0.9969 SkriQa 0.0001 0.0019 0.0009 0.9963 0.2921 0.0001 0.0063 0.0018 0.0009 1.6897 0.2981 0.0047 1.6873 0.0093 IC06-28 IC06-28 WVZIC06-28 SkriQa IC06-28IC06-28 WVZIC06-28 SkriQaIC06-28 IC06-28 39.42 0.0006 0.0615 0.0557 14.43 0.2378 45.39IC06-28 0.3041IC06-28 0.1601 IC06-28 IC06-28 IC06-28 WVZ SkriQa 0.9949 0 0.0019 0.0008 0.2994 0.0051 1.688 0.0099 0.0038 IC06-28 IC06-28 WVZ SkriQa 39.56 oo to

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o 2 o 2 0.0018 0.0355 0.0312 K k 0.0014 0.0248 K k 1.7353 0.0207 0.2308 0.0021 0.2432 0.0022 0.1535 0.0012 2.7832 0.0376 Na20 0.1404 0.0004 0.1628 0.0011 14.3 2.6207 15.02 15.22 2.5405 0.7253 16.35 1.8513 0.0197 Ca Na 0.8247 0.148 0.7946 0.0172 0.7372 0.2227 0.0132 0.8108 Mg Ca Na 0.2052 16.65 1.775 0.0178 0.0142 0.0142 MgO CaO Na20 Mg 0.6026 0.1939 16.59 FeO MgO CaO 0.0253 0.0179 0.7939 0.1906 0.0016 0.0184 0.0138 0.8075 0.1558 0.001 0.6175 0.2089 16.93 1.6786 FeO Fe 33.73 A120 3 33.91 1.8087 1.8288 0.0237 0.0146 0.8083 A120 3 Al 47.74 Si Al Fe 2.2892 1.7074 0.0302 0.018 0.6959 48.15 33.91 0.6098 0.2107 S i0 2 Si 2.1978 1.7808 2.1684 1.8174 0.0235 HognhofQi Gaesafjoll 47.64GaesafjollGaesafjoll 32.75 47.74 0.6564 0.2599Gaesafjoll 34.14 0.6234Gaesafjoll 16.06 2.1844 0.2159 2.131 0.028 16.6Gaesafjoll 1.5934 0.0073 2.1838 1.8123 0.0231 Gaesafjoll 47.68 WVZ HognhofQi 2.2632 1.7181 0.0314 0.0171 WVZ HognhofQi 50.4 31.89 0.7947 0.2657 WVZ HognhofQiWVZ HognhofQi 50.03 50.22 32.31 0.6879 32.35 0.2547 0.8333 0.2547 WVZ WVZ HognhofQi 2.1779 1.8133 0.023 NVZ Gaesafjoll NVZ NVZ NVZ GaesafjollNVZ 2.1698 NVZ Gaesafjoll 48.25 33.9 0.487 NVZ NVZ NVZ NVZ Sample Zone UnitName IC06-9 IC06-9 IC06-9 IC06-9 IC06-9 IC06-9 IC06-9 IC06-9 IC06-9 IC06-9 Sample Zone UnitName Si02 IC06-21 IC06-21IC06-21 WVZIC06-21 HognhofQi 2.2623 1.7218 0.026 IC06-21 IC06-21 IC06-21 WVZ HognhofQi IC06-21 Table C.14: Microprobe measurements ofplagioclase grains for Gaesafjoll, NVZ. Concentrations in (wt%). Table C.15: Microprobe measurements ofplagioclase grains for HognhofQi, WVZ. Concentrations in (wt%).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o o 2 2 0.001 0.002 0.0304 0.0297 0.0408 0.0362 0.0057 k k 3.25 4.32 0.1004 0.2838 0.0023 0.3744 0.2495 2.1164 2.6055 13.9 15.02 11.68 0.6707 Ca Na K 0.021 0.721 0.312 14.88 2.8452 0.0343 0.0242 0.2177 15.91 2.2121 0.0159 0.7283 0.2287 0.0021 0.0198 0.7248 0.2437 0.0019 0.2955 15.01 2.7893 0.0332 MgO CaO Na20 1.0434 0.3122 0.0184 0.0146 0.7689 0.1935 0.0017 0.6461 FeO 0.5833 0.1902 16.27 2.1643 0.0169 FeO MgO CaO Na20 31.92 1.7198 0.0225 A120 3 A120 3 Al Fe Mg Ca Na K 49 33.6 50.27 32.38 0.5969 49.28 33.3 0.4869 Si Si Al Fe Mg S i0 2 2.2227 1.7701 2.2823 1.703 0.0215 Raudafell 2.3346 1.6386 0.0348 Hlodufell 2.2057 1.7827 0.022 0.0128 0.7849 0.1889 RaudafellRaudafell 50.37 51.84 30.87 0.9246 0.3607 WVZ WVZ Raudafell WVZ Raudafell 2.2651 WVZ WVZ WVZ Sample Zone UnitName Sample Zone UnitName Si02 IC06-24 WVZ Hlodufell IC06-22IC06-22 WVZ Raudafell 2.2779 1.7014 0.0244 IC06-24IC06-24 WVZIC06-24 Hlodufell WVZ Hlodufell WVZ Hlodufell 48.32 33.92 49.16 0.6512 0.2208 33.61 0.6194 16.46 0.2333 1.8876 0.0227 16.25 IC06-22 WVZ Raudafell 2.4581 1.517 0.039 0.0208 0.5586 IC06-24 IC06-22 IC06-24 WVZ Hlodufell 2.2084 1.7794 0.0233 0.0156 0.7822 0.1843 0.0017 IC06-22IC06-22 WVZ Raudafell WVZ Raudafell 50.42IC06-22 31.92 0.5676 0.235 IC06-24IC06-24 WVZ Hlodufell WVZ Hlodufell 2.1846 1.8072 0.0246 0.0149 0.7971 0.1655 0.0013 IC06-22 IC06-22 WVZIC06-22 Raudafell 55.05 28.83 Table C.17: Microprobe measurements ofplagioclase grains for Hlodufell, WVZ. Concentrations in (wt%). Table C.16: Microprobe measurements ofplagioclase grains for Raudafell, WVZ. Concentrations in (wt%).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o 2 0.0005 k 1.3812 0.0086 Na K 17.09 0.8292 0.1213 Ca 0.0137 0.8294 0.1317 0 MgO CaO Na20 Mg 0.621 0.162 0.0256 FeO 1.84 34.72 0.6348 0.2033 17.35 1.3051 0.0003 A120 3 47.48 34.43 0.6753 0.2026 17.07 1.4979 0 2.151 1.8491 0.0235 0.0109 2.1404 1.8543 0.0241 0.0137 0.8426 0.1147 0 S i0 2 Si Al Fe Skrida WVZ Skrida 47.5 34.65 WVZ Skrida 2.1527 WVZ TableC.18: Microprobe measurements ofplagioclase grains for Skrida, WVZ. Concentrations in (wt%). Sample Zone UnitName IC06-28 IC06-28IC06-28 WVZ WVZ Skrida Skrida 47.23 IC06-28 IC06-28IC06-28 WVZ Skrida 00

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.