Characterization of the Ungrouped Pallasite Choteau

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CHARACTERIZATION OF THE UNGROUPED PALLASITE CHOTEAU

JULIA D. GREGORY

Bachelor of Science, 2014 Olivet Nazarene University Bourbonnais, IL.

Submitted to the Graduate Faculty of the College of Science and Engineering Texas Christian University in partial fulfillment of the requirements for the degree of

Master of Science

August 2016

Acknowledgements

First off, I would like to thank my advisor, Dr. Rhiannon Mayne, who introduced me to the marvelous world of meteorites. Never before had I touched a rock from space and now I can say that I’ve touched over 2000 different meteorites. Thank you for giving me this opportunity to learn, for all of your guidance throughout the whole of this project, and for battling through numerous rounds of edits.

Secondly, thank you to my committee members: Dr. Joseph Boesenberg, Dr. Helge Alsleben, and Dr. Michael DeAngelis, for agreeing to be part of this project and offering your valuable insights and suggestions in regards to thesis writing. Dr. Boesenberg, thank you for sharing your vast knowledge and love of pallasites. I would not have been able to complete this project without your help.

Thirdly, I wish to thank the other collaborators in this study: Dr. Tasha Dunn from Colby College for her work in generating the elemental maps of Choteau via Micro-XRF; David Mann at High Mesa Petrographics for making the gorgeous thin sections that were the focus of the study; the people at the Mineral Sciences Department of the Smithsonian Institution’s National Museum of Natural History for their work in producing the electron backscatter images of the thin sections; Dr. George Morgan at the University of Oklahoma for helping me collect the electron microprobe analyses; Dr. Richard Greenwood and Dr. Ian Franchi at the Open University for collecting Choteau’s oxygen isotope ratios as well as for their input into the study; and Dr. Munir Humayun and Adam Silver at Florida State University for performing the LA-ICP-MS analyses to obtain trace element data. I greatly appreciate all your help in making this study possible.

Lastly, I want to thank the people who are most important in my life. To my fiancé, Nate, thank you for always being supportive, willing to listen to presentations and proofread paragraphs on a subject that doesn’t involve engineering, and for always remembering that “pallasites are meteorites that are not supposed to contain plagioclase” – I wouldn’t have made it without you. To my family back in Illinois, thank you for providing the stress relief that only comes from a trip back home, and for all your help with wedding planning, I very much appreciate it. To Sam Crossley, thank you for being my “buddy” through these past two years. We’ve been in every class together, sat side- by-side in the TA office, and vented to each other about pretty much everything. Best of luck in Maryland, I know you’re going to do great things. And finally, I want to thank Miss Nona Batiste for being my cheerleader through this whole process.

Table of Contents

Acknowledgements ...... ii

List of Figures ...... v

List of Tables ...... vii

1.0 Introduction ...... 1

2.0 Background ...... 3

2.1 Pallasites ...... 5

2.1.1 Main Group Pallasites...... 7

2.1.2 Eagle Station Pallasites ...... 10

2.1.3 Pyroxene-Bearing Pallasites ...... 10

2.2 Acapulcoites/lodranites ...... 11

3.0 Methodology ...... 12

3.1 Micro-XRF Spectroscopy ...... 12

3.2 Thin Section Preparation ...... 14

3.3 SEM Back-scatter Images ...... 19

3.4 Oxygen Isotope Analyses ...... 19

3.5 Electron Microprobe Analyses...... 21

3.6 LA-ICP-MS Analyses ...... 21

4.0 Results ...... 22

4.1 Oxygen Isotopes ...... 22

4.2 Texture/Mineral Chemistry ...... 24

4.2.1 Olivine ...... 24

iii

4.2.2 High-Ca pyroxene ...... 26

4.2.3 Low-Ca pyroxene ...... 26

4.2.4 Plagioclase ...... 26

4.2.5 Chromite ...... 30

4.2.6 Merrillite ...... 30

4.2.7 Schreibersite...... 34

4.2.8 Troilite ...... 34

4.2.9 Metal ...... 34

4.3 Trace Elements ...... 36

5.0 Discussion ...... 42

5.1 Petrogenesis...... 42

5.1.1 Historic Models ...... 42

5.1.2 Near Surface Core-Mantle Boundary Model ...... 47

5.2 Relation to other meteorites ...... 51

6.0 Conclusions ...... 59

Appendix A ...... 60

Appendix B...... 67

Appendix C...... 90

References ...... 97

Vita

Abstract

List of Figures Figure 1: Different textures exhibited by pallasites ...... 6 Figure 2: Oxygen isotope plot of the PMG and PES ...... 8 Figure 3: Slice of Choteau used in this study ...... 13 Figure 4: Compilation map of the Si, P, S, Cr, and Ca elemental maps...... 15 Figure 5: Compilation map of the Fe and Ni elemental maps ...... 16 Figure 6: Compilation map of the elemental maps showing the thin section locations and their labels...... 17 Figure 7: Thin sections shown in plane polarized light, cross polarized light, and reflected light...... 18 Figure 8: Electron backscatter images of all thin sections for nonmetal and metal compositions...... 20 Figure 9: Choteau's new oxygen isotope ratios ...... 23 Figure 10: Choteau's olivine composition compared with that found in the acapulcoites/lodranites and Vermillion and Y-8451...... 25 Figure 11: Choteau's pyroxene compositions compared with ranges measured in Vermillion and Y-8451 and the acapulcoites/lodranites...... 27 Figure 12: Electron backscatter image of the low-Ca pyroxene inclusions within the high- Ca pyroxene...... 28 Figure 13: Electron backscatter image of plagioclase inclusions and veins in low-Ca pyroxene...... 29 Figure 14: NWA 10019, the only other known pallasite to contain plagioclase...... 31 Figure 15: Choteau plagioclase composition compared with NWA 10019 and the acapulcoites/lodranites...... 32 Figure 16: Electron backscatter image of chromite and merrillite against the olivine and metal...... 33 Figure 17: (a) Electron backscatter image of kamacite and the S-T taenite (b) Close-up electron backscatter image of the Fe-sulfide and Fe-phosphate within the S-T taenite.. . 37 Figure 18: REE abundances, relative to solar abundances, of Choteau's low-Ca pyroxene compared with those found in Vermillion, Y-8451, and the acapulcoites/lodranites ...... 39 Figure 19: REE abundances, relative to solar abundances, of Choteau's plagioclase compared with the acapulcoites/lodranites...... 40 Figure 20: Trace element analyses of Ga, Ge, Au, and Ir plotted against Ni for Choteau’s metal compared with those of other pallasites...... 41 Figure 21: Different models for the formation of pallasitic texture...... 45 Figure 22: This study’s model for Choteau's formation...... 50

Figure 23: Image of NWA 2714 and NWA 4529 showing the typical appearance and texture of an acapulcoite and lodranite respectively...... 56 Figure 24: Oxygen isotope compositions of NWA 468 and NWA 6704 plotted against the broad trend for acapulcoites/lodranitesand Choteau)...... 57

List of Tables Table 1: Metal compositions of PMG compared with PES...... 9 Table 2: Average troilite and schreibersite compositions of Choteau compared with those of Vermillion and Y-8451...... 35 Table 3: Compilation of the prevailing concepts and models concerning pallasite formation...... 43 Table 4: Summarizing the attributes of Choteau compared with those from Vermillion, Y-8451, and the acapulcoites/lodranites ...... 53 Table 5: Oxygen isotope comparisons between Choteau and Vermillion ...... 54

vii

1.0 Introduction

Pallasites are a type of meteorite characterized by having a mantle phase, primarily made up of olivine, intermixed with a core phase of Fe-Ni metal, along with minor amounts of chromite, troilite, phosphates, and sulfides. Pallasites are further divided into groups based on similarities in oxygen isotope ratios and in mineral chemistry, with the idea that each group represents a different parent body. The majority of pallasites fall into Main Group pallasites (PMG), and the only other official group,

Eagle Station pallasites (PES), has five members. There are seven pallasites that are currently classified as ungrouped due to their dissimilarity to the PMG and PES. One of these is Milton, which shows textural pallasite characteristics, but has olivine and metal compositions different from all other known pallasites (Jones et al. 2003). The remaining six ungrouped are distinct in that they contain a significant (>1% by volume) amount of pyroxene, not seen in either PMG or PES, where pyroxene has only been documented in fine symplectic intergrowths (Buseck 1977; Buseck & Clark 1984; Boesenberg et al.

2012). However, only two of these pyroxene-bearing pallasites have similar oxygen isotope ratios, the rest are distinctly different. Altogether, this means that, if current classification is correct, there could be at least ten different parent bodies all undergoing a similar formation process to produce the characteristic pallasitic assemblage.

There are two main prevailing formation models. The traditional view is that there is a pallasitic layer at the core-mantle boundary of small, differentiated parent bodies, where the pressure from above forces some olivine grains to mix into the molten core below (Rayleigh 1942; Mason 1962; Wood 1978). The newer idea is that the mantle

1 material mixes with the core material via impacts, where the materials are displaced from their original layers, mixed together, and then cooled before the layers can re-separate

(Hsu 2003; Scott 2007). Currently, there is not enough evidence to form a consensus as to the actual mechanism of formation, which is why any pallasite-related discoveries have the potential to provide valuable new insights.

In this study, I analyzed Choteau, one of the ungrouped pallasites referred to above. First recognized at an estate sale in Montana in 2011, Choteau was classified as an ungrouped pallasite because its oxygen isotope ratios were different from those of the preexisting pallasite groups and fell under the broad trend for another meteorite group- the acapulcoites and lodranites (classified by A. Irving and S. Kuehner, published in

Ruzicka et al. 2015). Since classification, Choteau has not been studied in depth, so I worked to thoroughly characterize all silicate and metal phases through use of micro x- ray fluorescence, petrographic analysis, scanning electron microscope (SEM), electron microprobe analysis, and laser ablation inductively coupled plasma mass spectrometry

(LA-ICP-MS). This approach will provide the following information: 1) do the silicate and metal phases show similarities with existing pallasite groups? 2) Can Choteau be linked to the acapulcoite and lodranite meteorite groups? 3) Does Choteau represent a new pallasite parent body or can its formation be explained in terms of pre-existing meteorite groupings? 4) What can the petrology and geochemistry tell us about its petrogenesis?

2.0 Background

In the simplest terms, meteorites are classified based on their structure and basic mineralogy and are divided into three broad categories: stony, iron, and stony-iron. Stony meteorites are by far the most common and are divided into chondrites and achondrites.

Chondrites are primitive Solar System material with spherical inclusions called chondrules that are thought to have undergone little to no melting since the birth of the

Solar System. Achondrites are chondrites that have been subjected to melting, and are thought to be remnant fragments of asteroidal crust, mantle, and core. Primitive achondrites are a link between chondrites and achondrites. They do not have chondritic textural characteristics, but still retain many of the chemical characteristics. They are more closely related to their primitive chondritic parent than the achondrites (Weisberg et al. 2006). These are all predominantly composed of silicate material with small amounts of metal. Iron meteorites are composed almost entirely of metal, with some having small silicate inclusions. Magmatic irons are thought to represent the core material of larger asteroids, where thermal energy in the interior of the body was insulated enough to allow for the body to fully melt and form the differentiated layers (Hevey & Sanders 2005;

Goldstein et al. 2009), whereas primitive irons have silicate inclusions that resemble the compositions found in other primitive achondrites (Weisberg et al. 2006). Lastly, the stony-iron meteorites are made up of roughly half metal and half silicate material. These are the rarest and only comprise two groups: mesosiderites and pallasites. Mesosiderites are composed of near equal amounts of crustal silicate (made up mostly of pyroxene and plagioclase) and metal, while pallasite silicates are dominated by olivine.

Further divisions of these three broad categories are made by comparing oxygen isotope ratios. In cosmochemistry, oxygen is uniquely important because 1) it is a major component in most minerals and rocks, making it abundant, 2) it is lightweight enough so that the stable isotopes are subject to large mass-dependent fractionation effects, meaning that the addition of a neutron is easier to distinguish in a lighter element than in a heavier element, and 3) it can exist simultaneously as a gas and a solid allowing it to serve as a tracer for interactions between different reservoirs (Clayton 1993). Chondritic parent bodies, which have not been subjected to large amounts of melting, homogenization, and differentiation, have oxygen isotope compositions characteristic of the solar nebula during formation; while achondritic parent bodies bear oxygen isotopic signatures that reflect the melting, homogenization, and differentiation that the body has undergone

(Clayton & Mayeda 1996). Because of these reasons, planetary bodies have their own unique oxygen isotope signature, which means that a group of meteorites that share mineralogical similarities and oxygen isotope trends are believed to come from the same parent body (Clayton et al. 1993).

Three oxygen isotopes are produced by star nucleosynthesis: 16O, 17O, and 18O.

The primary isotope is 16O and it is formed in massive (>10 solar masses) stars, only being ejected by supernova explosions (Clayton 2004). 17O and 18O are much rarer with

17O being from low to intermediate mass stars (<8 solar masses) and 18O being mainly from high mass stars (Clayton 2004 and references therein). Oxygen isotope compositions are calculated as ratios between 17O/16O and 18O/16O with respect to

SMOW (standard mean ocean water) (Clayton 2004):

(17푂⁄16푂) 푠푎푚푝푙푒 훿17푂 = [ − 1] ∗ 1000 (17푂⁄16푂) 푆푀푂푊

(18푂⁄16푂) 푠푎푚푝푙푒 훿18푂 = [ − 1] ∗ 1000 (18푂⁄16푂) 푆푀푂푊

These ratios are then plotted on a “three-isotope plot” with δ17O on the y-axis and

δ18O on the x-axis, which allows for any sample’s oxygen isotope composition to be plotted (Clayton 2004). Δ17O is how much the values differ from the terrestrial fractionation line and is defined as a constant for a single planetary body, following the equation:

∆17푂 = 훿17푂 − 0.52훿18푂

For example, all meteorites that come from Mars have Δ17O≅0.3‰, while howardites, eucrites, and diogenites from the HED parent body have Δ17O≅-0.3‰ (Clayton &

Mayeda 1983).

2.1 Pallasites

Pallasites are recognized from other meteorite classes based on their texture of crystalline olivine mixed with an Fe-Ni metal. The olivine grains are scattered throughout the metal in a seemingly random arrangement and, depending on the pallasite in question, can be rounded (e.g. Brenham) or more angular in shape (e.g. Fukang) (Figure 1a-b).

Olivine grains can range in size from micrometers to a few centimeters in length and can be found as single grains surrounded by metal, as large clumps of olivine with occasional metal veins (e.g. Seymchan) (Figure 1c), or as pockets of grains within a large metal region. 5

(a)

(b)

(c)

Figure 1: (a) Brenham pallasites showing rounded olivine grains; (b) Fukang pallasite with angular olivine grains; (c) Seymchan pallasites showing how the distribution of olivine and metal can vary within a single pallasite. All photos are courtesy of the Oscar E. Monnig Meteorite Collection at Texas Christian University.

Pallasite metal is an intergrowth of two Fe-Ni metal alloys: kamacite (low-Ni – ≤

7.5% Ni) and taenite (high-Ni – > 25% Ni). At temperatures above 700 ºC, both Fe and

Ni have face-centered lattices and behave as taenite (Mullane 2004). As the temperature lowers, kamacite nucleates, ejecting Ni into the remaining taenite, and growing from the pre-existing taenite (Owen & Burns 1939). These kamacite bands have a body centered lattice, which is not as tightly-packed as the face-centered lattice of the taenite. This is what forms the crosshatched Widmanstätten pattern, which can be seen in some iron meteorites with certain Ni contents, after a slice has been etched with nitric acid (Figure

1c). Pallasites are further divided into groups based on similar oxygen isotope ratios and mineral chemistries with the thought that all members of each group share the same parent body (Clayton & Mayeda 1996).

2.1.1 Main Group Pallasites

The majority of pallasite meteorites have been classified as PMG. PMG all plot along a single oxygen isotopic trend, with little to no variations (Figure 2). PMG olivine compositions range from 10.5-13% Fa (Scott 1977a) (olivine compositions are reported in percent endmember where fayalite (Fa) represents the Fe-rich endmember, and forsterite (Fo) represents the Mg-rich endmember), with metal compositions being higher in Ga and Au, and lower in Ge and Ni than the other pallasite groups (Table 1). While some PMG do contain minor amounts of pyroxene in fine symplectic intergrowths, these are generally very low in Ca with compositions of En55Wo0.05 (where En represents the

Mg-rich endmember, Wo represents the Ca-rich endmember, and Fe represents the Fe- rich endmember, which is unreported in this case) (Buseck 1977), while the actual pyroxene-bearing pallasites show much higher compositions of Ca. 7

0 -4 -2 0 2 4 6 8 10

Main Group Pallasites (PMG)

-2

O Eagle Station Pallasites (PES) 17

δ Vermillion Y-8451 -4 Acapulcoites Lodranites Acapulcoties/lodranites -6 Zinder NWA 1911 NWA 10019 -8 Old Choteau 18 (a) δ O

1.5

17 δ 0.5

0 2 2.5 3 3.5 4

-0.5 δ18O (b)

Figure 2: (a) Oxygen isotope plot comparing Choteau’s initial oxygen isotope ratios (Ruzicka et al. 2015) with those of the PMG (Greenwood et al. 2012), PES (Ali et al. 2014), Vermillion, (Boesenberg et al. 2000), Y-8451 (Boesenberg et al. 2000), Zinder (Bunch et al. 2005), NWA 1911 (Bunch et al. 2005), NWA 10019 (Boesenberg et al. 2016) and the acapulcoites/lodranites (Greenwood et al. 2012).(b) Close-up view shows the large spread between the two official groups and the ungrouped pyroxene-bearing pallasites, which indicates that they all derived from different parent bodies. 8

Table 1: Metal compositions of PMG compared with PES. Adapted from Scott (1977a). Group Ni (%) Ga (µg/g) Ge (µg/g) Au (µg/g) PMG 7.8-11.7 16-26 29-65 1.7-3.0 PES 14-16 4.5-6 75-120 0.8-1.0

2.1.2 Eagle Station Pallasites

Named after the type specimen, Eagle Station, the PES are texturally similar to the PMG (olivine surrounded by an Fe-Ni matrix); however, there are marked chemical differences between them. The oxygen isotope compositions of PES are lower in both

δ17O and δ18O than the PMG (Figure 2). PES olivine compositions are slightly more enriched in Fe (Fa19-20) (Scott 1977a) and PES metal contains a greater abundance of Ge and Ni, and lower abundance of Ga and Au than the PMG (Table 1). Additionally, the

Eagle Station meteorites contain abundant siderophile elements, which along with the oxygen isotope values, correlate with the carbonaceous chondrites in the CV, CO, and

CK groups, suggesting they were created by the differentiation of these chondritic bodies

(Humayun & Weiss 2001).

2.1.3 Pyroxene-Bearing Pallasites

The final subset of pallasites is the pyroxene pallasites. Pyroxene is generally not found in pallasites as anything more than a trace phase (Buseck 1977). Mason (1968) noted that pallasites were one of the very few groups of meteorites where pyroxene was absent and Buseck (1977) only observed pyroxene as micron sized grains and symplectic intergrowths along margins of olivine grains. With better analytical techniques and the discovery of new samples, we now know that pyroxene can be found as a major phase in pallasites, with an average composition that is much higher in Ca than what was found in the PMG. Two pallasites, Vermillion and Yamato-8451, form the basis of the pyroxene- pallasite grouplet as they have near identical oxygen isotope ratios. Other pyroxene- bearing pallasites include Choteau (Ruzicka et al. 2015; this study), NWA 1911 (Bunch

10 et al. 2005), Zinder (Bunch et al. 2005; van Niekerk 2005), and NWA 10019 (Agee et al.

2015; Boesenberg et al. 2016); the latter are not included as a part of the pyroxene- pallasite grouplet with Vermillion and Y-8451 because their oxygen isotope ratios are too different (Figure 2). This means that the pyroxene-bearing pallasites represent several different parent bodies.

2.2 Acapulcoites/lodranites

While Choteau appears texturally to be a pallasite, the oxygen isotope ratios reported during its classification correspond to the acapulcoites/lodranites (Figure 2)

(Ruzicka et al. 2015). Acapulcoites and lodranites are primitive achondrites, which are thought to be a transitional phase between chondrites and differentiated meteorites, as they have a typical chondritic bulk composition, but are not chondritic in terms of texture

(McCoy et al. 1992; Rubin 2007). Acapulcoites and lodranites, while distinct, are often discussed together because their oxygen isotope ratios are indistinguishable from each other and their mineral chemistries are near identical; it is generally accepted that they both originated from the same parent body. Acapulcoites show a fine-grained texture of olivine and pyroxene, with minor amounts of plagioclase, various sulfides, and Fe-Ni metal. They are thought to represent the outer, less thermally metamorphosed portion of the parent body that underwent a low (1-5%) fusion-grade metamorphism at temperatures of 950-1000ºC (Mittlefehldt et al. 1996; McCoy et al. 2000; Dobrica et al. 2008; Cecchi

2015). Lodranites display a coarser-grained texture with lower amounts of the plagioclase and sulfides suggesting that they experienced a higher metamorphic grade with temperatures of 1050-1200ºC, which subsequently led to a higher recrystallization rate

(McSween 1999). The overall lower amount of plagioclase, sulfides, and Fe-Ni alloys 11 implies that some were melted and removed from the system before complete solidification occurred (McCoy et al. 1992; Weisberg et al. 2006; Cecchi 2015).

Lodranites are thought to be residues from higher levels of partial melting and basaltic melt removal (Bild & Wasson 1976; Weisberg et al. 2006).

3.0 Methodology

3.1 Micro-XRF Spectroscopy

For our study, a 47.0-gram slice of Choteau (Figure 3) from the Oscar E. Monnig

Meteorite Collection was sent to Dr. Tasha Dunn at Colby College in Waterville, Maine for preliminary elemental distribution mapping using an M4 Tornado micro-XRF energy dispersive X-ray spectrometer.

Element maps of Ca, Al, Si, Cr, Ni, Fe, Mg, P, and S were generated for the entire slice (Appendix A). The micro-XRF generates these maps using a mosaic grid. All the individual sections of the slice are then merged together to create a cohesive map for each element. One of the main benefits of using this method is that different colors can be assigned to each element and any of the maps can be combined together to produce multi-elemental maps, which show element distribution, or phase maps that show the different minerals present throughout the slice.

The element maps for Ca, Cr, S, P, and Si were combined using Adobe

Photoshop CS6 to create a compilation map. In order to do this, the map with the most data, in this case Si, was used as the background image. The other maps were placed on

Figure 3: Slice provided by the Oscar E. Monnig Meteorite Collection at Texas Christian University for the purposes of this study. 1 cm cube for scale

top of this image in order of decreasing abundance: S, Cr, P, and ending with Ca. After each new map was added, the two images were blended together by changing the opacity to ensure that both layers could be read evenly with all important regions shown. Once all the layers were added and blended together, the result was essentially a phase map of the nonmetal species within the slice of Choteau, allowing us to distinguish between high-Ca pyroxene, merrillite, troilite, chromite, schreibersite, and the low-Ca silicate minerals

(olivine and low-Ca pyroxene) (Figure 4).

The element maps of Fe and Ni were combined, as described above, to produce a metal phase map for Choteau, allowing us to discriminate between taenite and kamacite, as well as between olivine and the low-Ca pyroxene (Figure 5). Together, these two phase maps helped us to determine which areas of the slice we wanted to make thin sections from.

3.2 Thin Section Preparation

Three 1-inch areas were selected from the phase maps (Figure 6). Section 1 was chosen due to the amount of variably-shaped olivine grains and the small Ca-rich (light blue) feature at the top, which turned out to be merrillite. Section 2 was chosen due to the abundance of chromite grains as well as the presence of the only low-Ca pyroxene grain not at the edge of the slice. Finally, section 3 was chosen because it is the only place in this slice where high-Ca pyroxene inclusions were observed within olivine grains.

The slice was sent to High Mesa Petrographics for thin section preparation. Once the polished thin sections arrived, images of each were taken in plane-polarized light, cross-polarized light, and reflected light (Figure 7).

Figure 4: Compilation map of the Si, P, S, Cr, and Ca elemental maps. This map allows us to distinguish between the sulfide, phosphate, chromite, and high-Ca pyroxene. The olivine and low-Ca pyroxene are indistinguishable on this map.

Figure 5: Compilation map of the Fe and Ni elemental maps allowing us to distinguish between the kamacite and taenite crystals in the metal. This map also shows a distinction between the olivine and low-Ca pyroxene (low-Ca pyroxene appearing darker as it has a lower Fe composition than the olivine).

Figure 6: Compilation map of the elemental maps showing the 1-inch round thin section locations and their labels.

Figure 7: 1-inch thin sections from sections 1 (top), 2 (middle), and 3 (bottom) shown in plane polarized light, cross polarized light, and reflected light.

3.3 SEM Back-scatter Images

All three thin sections were taken to the Smithsonian Institution's National

Museum of Natural History where back-scattered electron (BSE) images were produced using the FEI NovaSEM 600 scanning electron microscope (SEM) in the Department of

Mineral Sciences. These images are produced in a similar fashion to the XRF element maps. The SEM works along a grid, allowing it to take high resolution images. All of these images are then merged together to create a complete picture of each thin section so each tiny part can be examined in great detail (Figure 8). These images, along with petrographic observations, allowed us to highlight the various phases and points of interest for targeting with the electron microprobe.

3.4 Oxygen Isotope Analyses

Oxygen isotope analyses were performed by Dr. Richard Greenwood at the Open

University in Milton Keynes, UK. A small fragment of olivine from Choteau was sent for analyses by an infrared laser-assisted fluorination system following the methods described by Miller et al. (1999). The sample was heated in the presence of BrF5 to release the oxygen, which was then purified by two cryogenic nitrogen traps and a bed of heated KBr. The oxygen gas was analyzed using a Thermo MAT 253 dual inlet mass spectrometer. Slight changes to the procedures from Miller et al. (1999) have resulted in an improved precision of ±0.052‰ for δ17O, ±0.093‰ for δ18O, and ±0.017‰ forΔ17O

(Greenwood et al. 2015).

Figure 8: Backscatter images of all thin sections for nonmetal and metal compositions.

3.5 Electron Microprobe Analyses

All three thin sections were taken to the University of Oklahoma's Electron

Microprobe Lab in Norman, OK. The analyses were run on a Cameca SX100 (TCP/IP

Socket) with 5 tunable wavelength dispersive spectrometers. The operating conditions for the silicate analyses were a 40 degree take-off angle, beam energy of 20 keV, beam current of 20 nA, and beam diameter of 2 microns. The operating conditions for the metal and sulfide analyses were identical except for a beam current of 10 nA. The various phases analyzed were olivine, high-Ca pyroxene, low-Ca pyroxene, plagioclase, merrillite, chromite, troilite, schreibersite, kamacite, and taenite.

3.6 LA-ICP-MS Analyses

Section 2 which contained olivine, troilite, schreibersite, metal, plagioclase, and low-Ca pyroxene was sent to Dr. Munir Humayun at the Earth, Ocean, and Atmospheric

Science Department at Florida State University for Laser-Ablation-Inductively-Coupled

Plasma-Mass-Spectrometry (LA-ICP-MS) to determine trace element abundances. All

LA-ICP-MS analyses were performed with a ESI™ UP193FX ArF excimer laser coupled to a Thermo Element XR™ high-resolution inductively coupled plasma mass spectrometer at the Plasma Analytical Facility of the National High Magnetic Field

Laboratory. The procedures for the analysis of the elemental composition of metal followed Humayun et al. (2007) and Humayun (2012). Major element analysis of silicates followed Humayun et al. (2010) and Yang et al. (2015). All analyses were performed using spots of 50, 100 or 150 µm diameter, with a 5-second dwell time and 50

Hz laser repetition rate. Plagioclase and troilite were analyzed with the 50 µm spot sizes,

while metal was analyzed with 150 µm spot size to improve the detection limit for Re, Ir and Os. Standards used to calibrate the RSFs included the USGS glasses BCR-2g,

BHVO-2g and BIR-1g; NIST SRM 610 silicate glass; the iron meteorites Hoba (IVB) and North Chile (IIA); NIST SRM 1263a steel, and a pyrite grain for sulfur abundances.

Following Yang et al. (2015), we acquired data for about 65-70 elements simultaneously in low resolution mode. Detection limits were calculated as the 3-sigma standard deviation of the blank intensity measured on a set of blanks taken together with the measurements of the samples.

4.0 Results

4.1 Oxygen Isotopes

We collected new oxygen isotope data for Choteau because different labs have different techniques and procedures for oxygen isotope analysis. We chose to send the sample to Dr. Richard Greenwood and Dr. Ian Franchi at the Open University because their lab has experience with pallasites and this enables us to compare our sample with those pallasites previously analyzed at the same lab. The new oxygen isotope analyses yielded values of δ17O=0.211±0.091‰, δ18O=2.52±0.21‰, and Δ17O=-1.102±0.017‰, where Δ17O=δ17O-0.52δ18O. These results actually fall further within the general acapulcoite/lodranite trend than before (Figure 9).

When comparing Choteau’s oxygen ratios to other ungrouped pallasites, both the previous analyses and this study’s analyses plot close to pyroxene-bearing pallasites

1.5

0.5

17 δ

0 2 2.5 3 3.5 4 δ18O

-0.5

Main Group Pallasites Vermillion Y-8451 -1 Acapulcoites Lodranites Acapulcoties/lodranites Zinder NWA 1911 NWA 10019 Old Choteau New Choteau

Figure 9: Choteau's new oxygen isotope ratios plotted against the old Choteau values (Ruzicka et al. 2015), acapulcoites/lodranites (Greenwood et al. 2012), PMG (Wason & Choi 2003), and the ungrouped pallasites: Zinder (Bunch et al. 2005), NWA 1911 (Bunch et al. 2005), and NWA 10019 (Boesenberg et al. 2016).

Vermillion and Y-8451 (Figure 9). This could imply a possible connection between these three meteorites.

4.2 Texture/Mineral Chemistry

The slice of Choteau that was used in our study contains approximately 30 vol% of silicate material (olivine, high-Ca pyroxene, low-Ca pyroxene, and Na-rich plagioclase). Compared to other pallasites, such as the Brenham above (Figure 1), the overall distribution of olivine within the metal is highly irregular and random, with some regions being dominated by silicate material and other regions Fe-Ni metal. The metal contains both kamacite and taenite, with kamacite comprising 70% of the metal volume.

Below, each phase will be described in terms of texture and chemistry and compared directly to the two likely groupings for Choteau: the pyroxene-pallasite grouplet and the acapulcoites/lodranites, when applicable.

4.2.1 Olivine

The dominant silicate phase in Choteau is olivine. Olivines are randomly orientated throughout the slice in anhedral to subhedral shapes with lengths up to 1 cm.

All grains are heavily fractured. The analyses showed a homogenous composition of

Fa10.3±0.6 (Figure 10) with Fe/Mn=33.5±2.5 (Appendix B). This composition agrees with the previous mineral chemistry done by A. Irving and S. Kuehner of the University of

Wisconsin (Fa9.2-10.1, Fe/Mn=27-35) (Ruzicka et al. 2015).

Aca/Lod Y-8451 Vermillion Choteau

0 5 10 15 %Fa

Figure 10: Choteau's olivine composition compared with that found in the acapulcoites/lodranites (McCoy et al. 1997), and Vermillion and Y-8451 (Boesenberg et al. 2000).

4.2.2 High-Ca pyroxene

The high-Ca pyroxene was observed in thin section as two small inclusions within olivine grains; however, it is also found as a single grain within an area of sulfide (Figure

4). Both of the high-Ca pyroxene inclusions show very fine exsolution lamellae. All of the grains are subhedral and around 2 mm in size, with an average composition of

En56.4±3.9Wo38.7±4.8 (Figure 11) and an Fe/Mn ratio of 11.5±1.5 (Appendix B), again consistent with previous values (En49.1Wo44.3, Fe/Mn=12) (Ruzicka et al. 2015).

4.2.3 Low-Ca pyroxene

The low-Ca pyroxene was found as a single, large, standalone grain around 1 cm in length and as small inclusions in and around the high-Ca inclusions (Figure 12). The large discrete grain was more calcic (En86.8±0.5Wo2.4±0.3) (Figure 11), with a lower Fe/Mn ratio (16.7±0.6) (Appendix B); whereas, the low-Ca pyroxene around the margins of the high-Ca pyroxene had about 60% less CaO (En88.8±0.4Wo1.5±0.3) (Figure 11), and a higher

Fe/Mn ratio (19.4±0.3). This discrepancy could be explained by the proximity of the high-Ca pyroxene, which would take in CaO from its surroundings in an attempt to reach equilibrium, leaving little CaO for the low-Ca pyroxene to incorporate.

4.2.4 Plagioclase

Choteau is distinct in that it does contain small amounts of plagioclase found as small inclusions within the low-Ca pyroxene as well as veins filling cracks in the large low-Ca pyroxene grain (Figure 13). The plagioclase inclusions are highly anhedral and up to 1 mm in length. Five points were sampled from the two small inclusions that were found and the results showed relative uniformity with an average composition of

Figure 11: Choteau's pyroxene compositions plotted on a part of the pyroxene classification diagram, where Mg represents the Mg-rich endmember enstatite (En), Ca represents the Ca-rich member wollastonite (Wo), and the corner not shown represents the Fe-rich endmember ferrosilite (Fs). Values are compared with ranges measured in Vermillion (En86.0-88.5Wo0.5-2.5 & En52Wo44) and Y-8451 (En86-94Wo0-3.5 & En52Wo44) (Boesenberg et al. 2000) and the acapulcoites/lodranites (En86.0-92.1Wo1.8-2.5 & En49.4-50.6Wo44.9-45.0) (McCoy et al. 1997).

Figure 12: Electron backscatter image of the low-Ca pyroxene (darker) inclusions within the high-Ca pyroxene (lighter).

Figure 13: Electron backscatter image of plagioclase inclusions and veins in low-Ca pyroxene. Troilite and olivine inclusions are mixed in with the plagioclase as well.

An9.0±1.7Ab85.6±1.2Or5.4±0.8, which is nearly endmember albite (Appendix B). The only other pallasite known to contain plagioclase is NWA 10019 (Figure 14) (Agee et al.

2015; Boesenberg et al. 2016). However, as shown in Figure 2, NWA 10019 does not share an oxygen isotopic composition with Choteau; instead it is within the range for the

PMG. The plagioclase in NWA 10019 is also more calcic with an An content ranging from 50-84% (Boesenberg et al. 2016) (Figure 15).

4.2.5 Chromite

Chromite (FeCr2O4) was found as either euhedral grains along the margins of olivines or as complex irregular inclusions within the olivines (Figure 16). Four different grains were analyzed and a total of 13 data points collected. The average

Mg/(Mg+Fe)*100 ratio was 38.4±9.5, while the average Cr/(Cr+Al)*100 ratio was

86.9±4.0 (Appendix B). These values are very similar to those observed by Boesenberg et al. (2000) in Vermillion. Vermillion showed predominantly euhedral crystals within the metal material usually found close to olivine, with a Mg/(Mg+Fe)*100 ≈ 40 and a

Cr/(Cr+Al)*100 ≈94. Chromite has also been found in Y-8451 as fine-grained symplectic intergrowths with augite. These intergrowths were too small to be accurately examined by electron microprobe (Boesenberg et al. 2000).

4.2.6 Merrillite

Merrillite (Ca18Na2Mg2(PO4)14) was found as tiny (<1mm), irregular grains, most often adjacent to an olivine grain (Figure 16). Only two grains of merrillite were located and analyzed by electron microprobe, with a total of eight data points collected. The results show a more or less homogenous composition with an average FeO/MgO ratio of

Figure 14: NWA 10019, the only other known pallasite to contain plagioclase. Photo courtesy of the Oscar E. Monnig Meteorite Collection at Texas Christian University.

Figure 15: Choteau plagioclase composition plotted on the plagioclase classification diagram where An represents Ca-rich endmember anorthite, Ab represents Na-rich endmember albite, and Or represents K-rich orthoclase. Values are compared with NWA 10019 (Boesenberg et al. 2016) and the acapulcoites/lodranites (McCoy et al 1997; Patzer et al. 2004).

Metal

Figure 16: Electron backscatter image of chromite and merrillite against the olivine and metal. Chromite was observed in subhedral to euhedral grains along the margins of the olivines while merrillite was found as highly irregular shapes adjacent to olivines.

0.06±0.01 (Appendix B). This is slightly lower than that found in Vermillion (FeO/MgO

≈0.085) and significantly lower than Y-8451 (FeO/MgO≈0.92) (Boesenberg et al. 2000).

However, the Na2O content of merrillite in Choteau (Na2O =2.42±0.04) is similar to that in Y-8451 (Na2O≈2.36) (Boesenberg et al. 2000).

4.2.7 Schreibersite

Schreibersite, an Fe-Ni phosphide, was found adjacent to olivine throughout the slice in highly anhedral forms. 20 different locations were sampled with a homogenous composition throughout (Appendix B). When compared to Vermillion and Y-8451,

Choteau’s schreibersite composition was intermediate (Table 2). Vermillion’s schreibersite has a much lower Ni amount than both Choteau and Y-8451, which could be explained by the presence of cohenite [(Fe,Ni,Co)3C] in Vermillion (Boesenberg et al.

2000). Cohenite was not observed or analyzed for in Choteau so this connection cannot be confirmed.

4.2.8 Troilite

Lastly, troilite (FeS) could be found throughout the slice often bordering large olivine grains or connecting the smaller olivine grains together and as small inclusions within the silicates (Figure 13). Of the 20 locations analyzed, the composition was homogenous (Appendix B) and very similar to those found in Vermillion and Y-8451

(Table 2).

4.2.9 Metal

Both Choteau’s kamacite and taenite were analyzed. Two different types of taenite were observed: the normal, discrete taenite and a surface tension taenite (S-T 34

Table 2: Average troilite and schreibersite compositions of Choteau compared with those of Vermillion and Y-8451 (Boesenberg et al. 2000). Numbers are given in weight %. Choteau's values are averages with an error of one standard deviation.

Choteau Vermillion Yamato-8451 Schreibersite Troilite Schreibersite Troilite Schreibersite Troilite Fe 62.22±0.59 61.61±0.21 72.07 62.95 50.76 61.10 Co 0.19±0.01 b. d. 0.01 b. d. 0.12 0.05 Ni 21.95±0.59 0.12±0.06 12.50 b. d. 33.44 b. d. Mg n. a.1 b. d. 0.03 0.02 0.06 0.05 Mn b. d.2 b. d. b. d. b. d. b. d. 0.11 Cu b. d. 0.07±0.06 n. a. n. a. n. a. n. a. S 0.11±0.01 38.17±0.16 n. a. 36.23 n. a. 37.98 P 14.76±0.15 n. a. 15.23 n. a. 15.21 n. a. Cr b. d. n. a. 0.02 0.22 b. d. 0.65 Total 99.24±0.27 99.98±0.22 99.86 99.42 99.59 99.94 1 n.a. = not analyzed; 2 b.d. = below detection

taenite) (Figure 17), which represents one of the last residual non-metallic liquids. This area was completely cut-off from the metal melt resulting in the unusual texture and differing composition. The blebs are caused by a surface tension effect resulting from immiscible liquid separation during high temperature crystallization of the metal

(Boesenberg 2016 pers. comm.).

The discrete taenite had an average Fe composition of 76.7±0.6 wt% and an average Ni composition of 21.1±0.5 wt%, with trace amounts of Co, P, and S (Appendix

B). The S-T taenite was filled with pockets of Fe-sulfide and Fe-phosphide, which were too small to be analyzed. The S-T taenite composition had a higher and more varied Fe composition with an average of 85.2 wt%, and values ranging from 71.9 wt% to 89.3 wt%. The Ni composition was also highly variable with an average of 13.9 wt% and values ranging from 9.7 wt% to 27.1 wt% (Appendix B). While the S-T taenite still shows small amounts of Co, P, and S, these amounts are much smaller than what was observed in the discrete taenite. The 44 kamacite analyses showed an average Fe composition of 92.2±0.5 wt% and an average Ni content of 6.6±0.26 wt%, with minor amounts of Co and P present (Appendix B).

4.3 Trace Elements

Trace element data was collected for olivine, low-Ca pyroxene, plagioclase, troilite, schreibersite, and the metal within Choteau (Appendix C). Rare earth element

(REE) data for olivine were too low to be quantified. This could be explained by the presence of merrillite near the olivine, which would take in the REE from the olivine

(Humayun 2016, pers. comm); however, only a few grains of merrillite were found

500 µm (a)

(b)

Figure 17: (a) Electron backscatter image of kamacite and the S-T taenite with its uniform distribution of Fe- phosphate and Fe-sulfide. (b) Close-up electron backscatter image of the Fe-sulfide and Fe-phosphate within the S- T taenite. Shows the irregular shapes and uniform distribution.

throughout all three of the thin sections and nowhere near the olivines that were analyzed.

This could suggest that the REEs were also being absorbed by one of the phases that was not analyzed, such as the high-Ca pyroxene.

The large low-Ca pyroxene grain showed a strong negative Eu anomaly, as well as a slight enrichment in HREE over LREE, which is a mantle inherited pattern

(Boesenberg et al. 2000). (Figure 18). When compared with data from Vermillion, Y-

8451, and the acapulcoites/lodranites, no clear similarities or patterns emerged. All of the data from this study follow the same general trend, but the literature data for Vermillion,

Y-8451, and the acapulcoites/lodranites showed much more variability (Boesenberg et al.

2000; Floss 2000).

The plagioclase inclusion within the low-Ca pyroxene grain yielded a very strong positive Eu anomaly with slight LREE enrichment and a majority of the HREE compositions below the detection limits (Figure 19). These data correlated well with the literature data for acapulcoites/lodranites (Floss 2000).

When looking at the trace element abundances in Choteau's metal compared with other pallasites (Boesenberg et al. 2000; Wasson & Choi 2000), Choteau overlaps

Vermillion in regards to Ga and Au, and appears to fall between Vermillion and Y-8451 with respect to Ge and Ir (Figure 20). However, these three pallasites do not form any fractionation trends that show similarities to magmatic irons (IIIAB), as they should if originating from the same parent body (Wasson 1999). This suggests that they are not related.

10.00 Choteau

Vermillion

Y-8451

1.00

Normalized Abundances Normalized -

0.10 Solar

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

Figure 18: REE abundances, relative to solar abundances (Anders & Gervesse 1989), of three analyses from Choteau's low-Ca pyroxene (blue diamonds) compared with those found in Vermillion (purple squares) Y-8451 (green triangles) (Boesenberg et al. 2000), and two analyses from the acapulcoites/lodranites (orange circles) (Floss 2000).

100.00

10.00

1.00

Normalized Normalized Abundances -

Solar 0.10

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

Figure 19: REE abundances, relative to solar abundances (Anders & Gervasse 1989), of three analyses of Choteau's plagioclase (grey triangles) compared with four analyses from the acapulcoites/lodranites (green squares) (Floss 2000).

Figure 20: Trace element analyses of Ga, Ge, Au, and Ir plotted against Ni for Choteau’s metal compared with those of other pallasites. PMG data from Wasson & Choi (2003), IIIAB data from Wasson (1999), and Vermillion and Y-8451 data from Boesenberg et al. (2000).

5.0 Discussion

5.1 Petrogenesis

5.1.1 Historic Models

The pallasite formation process has been a continued subject of debate between those who believe the pallasite texture formed as a result of mixing at the core-mantle boundary (Rayleigh 1957; Wood 1978) and those who believe the texture formed as a result of impacts (Hsu 2003; Scott 2007). This disagreement results from having to explain the mixing of low density mantle material with high density metal. Over the years, different ideas have been proposed supporting either the core-mantle boundary mixing model or the impact model. A comprehensive overview of these studies was provided by Boesenberg et al. (2012) so we will only briefly summarize here (Table 3).

One of the earliest studies to understand pallasite formation involved pouring molten metal over olivine fragments (Rayleigh 1942). Rayleigh was able to show through experimentation that the heat from the molten metal would not melt the solid olivine. He suggested that the olivine was broken apart by impact, and then came into contact with the molten metal to form the pallasite texture. His experiments were fundamental in showing that olivine crystals could survive within a molten Fe-Ni matrix for an extended period of time, as they would if the core-mantle boundary mixing model were correct.

Wood (1978) proposed three different models for how the mixing at the core- mantle boundary could take place within a differentiated asteroidal body (Figure 21) and concluded that in order to get a large enough pallasitic layer between the core and mantle,

Table 3: Compilation of the prevailing concepts and models concerning pallasite formation. Adapted from Boesenberg et al. (2012).

Molten metal intrudes compact layers of olivine. Density separation of olivine and molten metal prevented Rayleigh (1942) by pressure of pre-existing overlying material. Partial crystallization occurs with crystals forming loose structure within silicate liquid. Silicate liquid is Urey (1956) subsequently displaced by molten metal in a low gravity environment. Fractional melting of chondritic material produces (1) dunite and peridotite (pallasites) below and (2) Ringwood (1961) segregated basaltic magma (eucrites) above. Parent body contains mantle which grades downwards into pallasites, mesosiderites, and irons. Pallasites form by igneous differentiation of chondritic body. Accumulations of olivine crystals are intruded Lovering (1962) by molten melt that contains considerable iron sulfide. Pallasites with large olivine-free metal zones (like Brenham) derive from metal-silicate interface and such Urey (1963, 1964) samples should be rare. Metal is dispersed in small pools throughout silicate matrix in parent body, resulting in large metal-silicate contact surface. Pallasites form by crystallization from chondritic melt. Metal and olivine crystallize in equilibrium from a Mason (1963) common source material. Pallasites represent transition zone between core and mantle. Metal channels, like those in Brenham, are Anders (1964) dendrites that intrude the silicate-metal mixture during solidification. Wasson and Collapse of mantle shell into molten upper core mixes solid olivine with molten metal. Wetherill (1968) Metal intrudes overlying olivine layer, dispersing olivine masses through metal. Gravitational separation of Scott (1977a, b, c) olivine and metal prevented by crystallization. Pallasite metal resembles that calculated following 80% fractional crystallization of a IIIAB metallic melt. Pallasites form deep in multiple parent bodies by recurrent processes. Pallasites could either be the residue Buseck (1977) of fractional fusion or cumulates produced by fractional crystallization. Metal and olivine form together. Pallasites contain close-packed olivine. Possible multiple immiscible melts present during formation. Olivine-molten metal assemblage accumulates stably with olivine in close-packed array. If only buoyancy is Wood (1978a, b, considered, only tiny fractions of olivine plus metal (pallasite) assemblages can exist in large parent bodies 1981) (>100km) for long times. At molten metal temperatures, olivine would exclude metal and form a dunite by power-law creep. Molten iron from core replaces silicate liquid between olivine grains. External heat source partially melts a portion of chondritic parent body surface. Accretion buries zone of Mittlefehldt maximum temperature. Dunites form in hot zone, while basaltic melts move toward surface. Pallasites form (1980) when dunite roof collapses onto contracting and crystallizing metal pods. A chondritic source partially melts. Silicate melt density-separates leaving behind residue of metal-sulfide Takahashi (1983) and olivine. Malvin et al. Double impact. First impact makes layered magma body composed of cumulate olivine over metal over (1985) residual olivine. Second impact mixes olivine and metal. Pallasites with large rounded olivines form when cumulate olivine is submerged into molten core by Scott and Taylor buoyant forces. Pallasites with angular olivines form by mixing of fragments of olivine mantle with molten (1990) metal during impacts. Davis and Olsen Based on the presence of phosphates, pallasites must come from locations in the parent body that are much (1991) closer to the surface than the core-mantle boundary. Pallasites form by intrusion of highly evolved (low Ir, high Ni, Au, and S) molten melt into fragmented Ulff-Moller et al. olivine. After intrusion, the degree of crystallization of molten melt varies with location. An FeS-rich liquid (1998) either escapes or forms underrepresented FeS-rich pallasites. Pallasites could not have formed at the core-mantle boundary because the olivine and metal are not Hsu (2003) equilibrated with respect to nickel. Wasson and Choi Pallasite precursors may be required to interact with a gas phase to produce Ga and Ge concentrations in (2003) metal.

Pallasites are impact-generated core-mantle mixtures formed as chains of differentiated bodies with diverse metal-silicate ratios following glancing impacts between proroplanets (Asphaug et al. 2006). Following Scott (2007) reassembly, the pallasite layer is emplaces shallowly, where fast cooling rates are recorded in angular olivine. Post-impact regolith buries layer deep, consistent with metal cooling rates. Differentiated asteroid of protoplanet with an olivine-rich mantle and a metallic core that is 80% solidified impacts larger body at a glancing angle. The differentiated body is torn apart forming the pallasite body Yang et al. (2010) from residual molten metal and fragments of olivine mantle. Solid core and remaining mantle do not accrete.

Figure 21: Different models for the formation of pallasitic texture. The first model (Column A) is the simplest and shows that the olivine crystals are denser than the remaining molten mafic material, thereby sinking to the core- mantle boundary. The unmelted rock at the top is partially supported by its own strength, minimizing the pressure the olivine crystals are exposed to. The slight weight from above pushes the olivine crystals into the liquid core beneath, just far enough that the buoyancy of the crystals keeps them suspended in the metal, forming a thin layer of what could become a pallasitic texture. The second model (Column B) depicts a more realistic system in which the olivine is under the pressure of all the above layers due to the mafic liquid of the mantle being able to intrude to the surface. This pushes the crystals further into the liquid Fe-Ni creating a thicker layer of olivine suspended in the metal. The final model (Column C) illustrates that as the pressure from above pushes the olivine crystals downward, it would also deform the crystals due to the high temperature of the liquid metal, making them more angular. Eventually, the crystals would come together resulting in the metal being squeezed back downward and the crystal mesh rising back up forming a layer of solid olivine instead of the desired pallasitic texture. Adapted from Wood (1978).

the initial parent body would have to be relatively small (less than 20 km in diameter)

(Wood 1978). After forming, this body must have combined with a much larger body before the final cooling phase occurred. This results in the secondary body having a

"raisin bread" internal makeup, where each pocket of pallasite material is not necessarily geochemically related to the other pockets present (Wood 1978). These models allow the discrepancies between pallasite groups to be explained with only one parent body.

Based on the presence of phosphates within analyzed olivines, Davis and Olsen

(1991) concluded that at least some pallasites must come from locations closer to the surface than the core-mantle boundary of their respective parent body, because phosphates are late-crystallizing phases and would not be expected in the deep mantle.

Additional trace elemental analyses support this conclusion. Hsu (2003) noted that the olivine and metal in pallasites were not fully equilibrated with respect to Ni, as they should have been if they formed at the core-mantle boundary, where the exchange of Ni would occur until chemical equilibrium was reached between the olivine and metal. Yang et al. (2010) concluded that PMG cooled at temperatures lower than ~700 ̊C, with cooling rates ranging from 2.5 to 18 ̊C/Myr. They inferred that pallasites could not have formed near the core-mantle boundary, since that should result in near identical cooling rates.

Hsu (2003) proposed a complicated formation process by combining both the core-mantle mixing model and an impact model. First, the olivines formed through either fractional crystallization from silicate melts or by partial melting of a chondritic material.

The olivines then cooled over time with the molten metal injected into them via impact or collision with a molten iron body. From this point, the mass would cool quickly, not allowing enough time for the phases to separate out by density, forming the pallasitic

texture. The phases would continue to slowly cool and eventually be enveloped by a new layer of rock as a result of episodic impacts, slowing the cooling process further allowing for the Widmanstätten pattern, commonly seen in pallasitic metal, to form (Figure 1c – pg

13).

Scott (2007) took it a step further than Hsu (2003) and suggested that the pallasitic texture may have formed solely from various impacts. If there were small bodies with a large, fractured olivine mantles and small volume molten metal cores, impacts would be enough to disrupt the general segregation and form pallasites. Due to the small volume of metal present in these bodies, Scott did not believe that there could be any relation between pallasites and normal iron meteorites, reconsidering his past arguments (Scott 1977b) that PMG and IIIAB irons came from the same parent body.

5.1.2 Near Surface Core-Mantle Boundary Model

Plagioclase in two different pallasites (Choteau and NWA 10019), which presumably come from two different parent bodies – based on their differing oxygen isotope ratios and plagioclase compositions – causes issues for both of the prevailing formation models. Concerning the core-mantle boundary formation model (Rayleigh

1942; Mason 1962; Wood 1978), on larger parent bodies, plagioclase crystallization is restricted to the crust or upper mantle because it is not stable with the pressures associated with the deep mantle (Green & Ringwood 1967). In smaller parent bodies, plagioclase could potentially exist throughout as the overall pressure would not be great enough to render it unstable. However, with the smaller body, cooling would happen much too quickly for the kamacite and taenite intergrowth to form.

In the impact model (Hsu 2003; Scott 2007), all phases should be in contact with the metal since it is all being physically jumbled together. We would expect pieces of crustal and mantle material mixed in with the metal. However, in both Choteau and NWA

10019, the plagioclase is never found touching the metal. As plagioclase mixed with metal is such a new discovery, no experiments or studies have looked at how plagioclase responds to contact with molten Fe-Ni metal. The solidus temperature for Choteau’s plagioclase is ~1120 ̊C and since taenite starts to crystallize from liquid metal at 1300-

1500 ̊C, it seems unlikely that if plagioclase were in contact with the metal, it would be melted completely away; however, there are currently no studies to support this assumption. The other problem with the impact model is that the plagioclase found in

Choteau is very minor – only two regions with the largest being ~800 micrometers across

(Figure 13). If impacts were the sole origin for Choteau’s make-up, we would expect a larger abundance of the crustal material mixed in with the mantle and core material. If formation occurred at the core-mantle boundary, we would only expect a minor amount of plagioclase to be mixed in with the mantle material.

Based on the insights from this study, I propose a new formation model for

Choteau’s petrogenesis. Due to the presence of plagioclase as well as pyroxene intermixed with olivine; we can hypothesize a parent body where plagioclase would exist in the mantle at the core-mantle margin where the pressure would be low enough to facilitate its existence (Green & Ringwood 1967). First, a few assumptions must be made: 1) the starting material was a homogenous, primitive mass; 2) this body underwent normal differentiation processes whereby a core, mantle, and crust were formed; and 3) unlike the models proposed by Wood (1978), the parent body in this model must be in

excess of 400 km in radius (Yang et al. 2010) to allow for a slow enough cooling rate to form the large olivine grains and the Widmanstätten pattern seen in Choteau.

Initially, there was a large asteroid of primitive material (Figure 22). This asteroid began to heat with time due to the decay of Al26 (Urey 1955), causing the material to melt and segregate out by weight, with the heavier elements sinking to the center and the lighter moving outwards (Figure 22). We can postulate that about 99% of the original chondritic material completely melted; with only the very outermost layer of crust remaining relatively primitive due to the exposure to cold space (Ghosh & McSween

1998; Weiss & Elkins-Tanton 2013). While this outer layer remains only slightly thermally metamorphosed, the inner, melted material in the asteroid is differentiated to create a parent body with a large core-mantle ratio (Figure 22). The large core-mantle ratio is important because towards the outermost edges of the core, the gravity would be significantly less than it would be near the center of the body, which allows for the molten core to mingle with the mantle above. Having a small mantle means that the core- mantle boundary is close to the surface where phases, like plagioclase, could withstand the pressure.

As the heat from the decay of radiogenic Al26 starts to dissipate, the body begins to cool inwards. It is at this point that Choteau’s pallasitic texture starts to form (Figure

22). Due to Choteau’s high Ir abundance, which is similar to Vermillion, it can be inferred that Choteau experienced metal-silicate mixing before the main bulk of core crystallization occurred (Boesenberg et al. 2000). Therefore, the mantle would solidify

Figure 22: This study’s model for Choteau's formation.

first, forming the solid silicate grains. Because the core is so large, the gravity at the outer core would be significantly less than it would near the center of the body, allowing for the core-mantle boundary to be a gradational change from solid mantle material to core material. Slowly, this pallasitic zone would begin to cool, solidifying the olivine grains within the metal. As the cooling front continued through the body, the Widmanstätten patterns would form in the metal.

Since the core-mantle boundary in this system is much closer to the actual surface of the body, the pressure would not be as great as it would in a more familiar system with a relatively small core-mantle ratio. This means that minor amounts of plagioclase would be present in the mantle peridotite as the receptacle of the excess Al in the system. This idea is also supported by Davis and Olsen (1991) who said that the phosphates in pallasites would not form in the deep mantle but must come from locations closer to the surface since phosphates typically inherit the olivine’s REE pattern which occurs by subsolidus reactions between metal and silicate.

5.2 Relation to other meteorites

Texturally, Choteau looks like a pallasite. Weisberg et al. (2006) define pallasite as a textural term used to describe a rock made up primarily of olivine and metal. The definition of a pallasite has no specific chemical signatures attached, as each group of pallasites is believed to come from a different parent body. With this definition in mind,

Choteau certainly fits with what a pallasite is characterized to be.

In regards to grouping Choteau with other pallasites, Choteau bears the most resemblance to Vermillion: the oxygen isotope ratios are close, the mineral chemistries

are similar, and there are trace element affinities between their metals (Table 4). While there is a slight disparity in the oxygen isotope ratios between Choteau and Vermillion, this can be explained by the parent body cooling before complete oxygen equilibrium was reached. Taking the average of the Δ17O values for both Choteau and Vermillion, we get Δ17O=-1.06 with a standard deviation of 0.17 (Table 5). Standard deviations for isotopically homogenous parent bodies range from 0.05-0.10, while isotopically heterogeneous parent bodies have larger values (Clayton & Mayeda 1996). Based on the standard deviation of 0.17, if Choteau and Vermillion were from the same parent body, it would be isotopically heterogeneous. This is similar to what we see in the spread for the

PES and also what is suggested for the spread in oxygen isotopic compositions in the IIE iron group (McDermott et al. 2015). However, the fact that Choteau does contain minor amounts of plagioclase (which is absent from Vermillion), and the trace element disparities in regards to the low-Ca pyroxene, negates any firm grouping of these meteorites until more data is gathered or new meteorites with similar attributes are discovered.

When looking at any possible relationship between Choteau and the acapulcoite/lodranite group, there are strong resemblances in terms of oxygen ratios, mineral chemistries, and trace element abundances, particularly when looking at plagioclase composition (Table 4). Despite all of this, Choteau does not resemble an acapulcoite or lodranite texturally, as acapulcoites are characterized by being very fine- grained, and lodranites are thought to have been subjected to a much higher metamorphic grade than acapulcoites, causing a higher recrystallization rate, which appears in thin section as abundant 120º triple junctions (Bild & Wasson 1976). Choteau’s texture does

Table 4: Summarizing the attributes of Choteau compared with those from Vermillion, Y-8451, and the acapulcoites/lodranites, where C=comparable, P=possibly related, N=no relation, and N/A=not available for comparison. Attributes are listed in order of importance, with texture being the most important, followed by oxygen isotope ratios, and mineral chemistries.

Table 5: Oxygen isotope comparisons between Choteau (Ruzicka et al. 2015; this study) and Vermillion (Boesenberg et al. 2000).

Meteorite δ17O δ18O Δ17O Mean Δ17O Stan. Dev.

Old Choteau 0.15 2.50 -1.17

0.07 2.35 -1.17

New Choteau 0.28 2.67 -1.123

0.15 2.38 -1.10

Vermillion 0.40 2.24 -0.76

-1.06 0.17

not show this and its general appearance does not coincide with any known acapulcoites or lodranites (Figure 23). Therefore, calling Choteau a acapulcoite/lodranite goes against the very definition of how these meteorites are believed to have formed.

While Choteau fits the textural description of a pallasite, this does not mean that it cannot be associated with other meteorite groups, especially when considering the formation model presented above, where there is primitive material at the outer edges of the parent body. It is not improbable to suggest that Choteau represents a pallasite from the deeper regions of the same parent body where acapulcoites/lodranites make up the crustal material. The very outermost primitive material would only be slightly thermally metamorphosed, while further down the crustal material would have undergone a more extensive thermal alteration. Acapulcoite material could represent the very outer edge, while lodranite material would be from shallowly buried locations (Figure 22). The chemical similarities between Choteau and the acapulcoites/lodranites are evident.

Conversely, there is precedence for other ungrouped meteorites falling within the broad trend for acapulcoites/lodranites in terms of oxygen isotope ratios. NWA 468 is an ungrouped IAB iron meteorite that also plots with the acapulcoites/lodranites, but is chemically distinct and unrelated (Grossman & Zipfel 2001; Rubin et al. 2002) (Figure

24). Another is NWA 6704, an ungrouped achondrite that again shares no chemical similarities to the acapulcoites/lodranites, but plots alongside them in terms of oxygen

(Garvie 2012) (Figure 24). Sanborn et al. (2013) were able to use chromium isotopes to distinguish NWA 6704 from the acapulcoites/lodranites and determine that they did not originate from the same parent body as the oxygen isotopes would suggest.

Figure 23: Image of NWA 2714 (top) and NWA 4529 (bottom) showing the typical appearance and texture of an acapulcoite and lodranite respectively. NWA 2714 photo courtesy of the Oscar E. Monnig Meteorite Collection at Texas Christian University, and NWA 4529 photo courtesy of the Hupe Collection. 1 cm cube for scale.

1.5

0.5

17 δ 0 2 2.5 3 3.5 4 δ18O

-0.5

-1 Acapulcoites Lodranites Acapulcoties/lodranites Old Choteau New Choteau NWA 6704 NWA 468

Figure 24: Oxygen isotope compositions of NWA 468 (Grossman & Zipfel 2001) and NWA 6704 (Garvie 2012) plotted against the broad trend for acapulcoites/lodranites (Greenwood et al. 2012) and Choteau (this study; Ruzicka et al. 2015).

Choteau is a pallasitic texture that may come from the same parent body as the acapulcoites/lodranites; however, the evidence from this study is not enough to conclusively support this statement. Future work to investigate this claim could analyze the chromium isotopes of Choteau and compare those with acapulcoites/lodranites to see if the similarities follow through.

6.0 Conclusions

 Choteau formed on a large (>400 km radius), differentiated parent body with a

large core-mantle ratio through mixing at the core-mantle boundary before

complete core solidification occurred. The proximity of the core-mantle boundary

to the surface allows for the presence of plagioclase as well as explains the

merrillite in Choteau. This body underwent almost complete differentiation from

a parent H-chondritic material, leaving only a small outermost layer of primitive

achondritic crust.

 Choteau represents a new group of pallasites. Based on its unusual chemistry and

oxygen isotope ratios, it cannot be grouped with any known pallasites. The fact

that it contains minor amounts of plagioclase with a near-albitic composition

makes it unique and its oxygen isotope ratios are unlike those recorded for the

pallasite groups and the several ungrouped samples.

 Choteau fits the traditional definition of a pallasite and should not be reclassified

as an acapulcoite/lodranite. Choteau is not fine-grained like the acapulcoites, nor

does it have abundant 120º triple junctions, which are characteristic of lodranites.

However, with further work, such as chromium isotope analyses and

comparisons, we may be able to conclude that Choteau represents a sample of the

core-mantle margin of the acapulcoite/lodranite parent body.

Appendix A Individual elemental maps from micro-XRF analyses

Appendix B Electron microprobe results for all the analyzed phases in Choteau. All values are in wt%.

Olivine Analysis # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 SiO2 41.02 40.66 41.08 40.12 40.57 40.58 40.50 40.82 40.19 40.45 40.80 40.65 40.97 40.42 40.45 TiO2 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.02 0.00 0.01 0.01 0.01 0.01 0.01 0.00 Al2O3 0.01 0.02 0.01 0.00 0.02 0.01 0.00 0.02 0.01 0.00 0.01 0.00 0.00 0.00 0.00 Cr2O3 0.04 0.07 0.07 0.06 0.07 0.06 0.08 0.06 0.06 0.05 0.06 0.05 0.05 0.08 0.05 FeO 9.91 10.18 10.10 10.34 10.30 10.31 10.39 10.52 10.29 10.45 10.61 10.63 10.53 10.40 10.18 NiO 0.00 0.02 0.02 0.00 0.00 0.01 0.00 0.01 0.00 0.00 0.02 0.00 0.02 0.04 0.00 MnO 0.29 0.29 0.29 0.29 0.29 0.31 0.30 0.29 0.30 0.31 0.30 0.29 0.28 0.29 0.30 MgO 49.41 49.04 48.77 48.70 48.63 48.84 48.86 48.53 48.56 48.95 48.88 48.76 48.80 48.85 48.65 CaO 0.04 0.05 0.08 0.06 0.07 0.06 0.05 0.06 0.06 0.08 0.07 0.05 0.06 0.06 0.03 Na2O 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 K2O 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 P2O5 0.01 0.01 -0.01 0.00 0.00 0.00 -0.01 0.01 0.01 0.01 0.00 0.01 0.00 0.00 0.00

Atoms/Formula Unit Si 0.998 0.996 1.003 0.992 0.998 0.996 0.994 1.000 0.994 0.992 0.997 0.996 1.000 0.993 0.997 Ti 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Al 0.000 0.001 0.000 0.000 0.001 0.000 0.000 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cr 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.001 Fe 0.202 0.208 0.206 0.214 0.212 0.211 0.213 0.216 0.213 0.214 0.217 0.218 0.215 0.214 0.210 Ni 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.000 Mn 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 Mg 1.793 1.790 1.776 1.794 1.782 1.787 1.789 1.773 1.790 1.790 1.780 1.781 1.776 1.789 1.788 Ca 0.001 0.001 0.002 0.002 0.002 0.002 0.001 0.002 0.001 0.002 0.002 0.001 0.002 0.002 0.001 Na 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 P 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Fo% 89.89 89.57 89.59 89.36 89.38 89.42 89.34 89.16 89.37 89.31 89.15 89.10 89.20 89.33 89.49

67 Fe/Mn 33.56 34.73 34.09 34.93 34.55 33.17 34.56 35.44 33.96 33.52 35.44 35.85 36.86 35.01 33.17

Olivine Analysis # 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 SiO2 40.73 41.09 40.64 40.61 40.46 40.55 40.59 40.97 40.74 40.42 40.68 40.42 40.75 41.01 41.27 TiO2 0.01 0.01 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.01 0.01 0.00 0.00 Al2O3 0.00 0.00 0.01 0.02 0.01 0.00 0.01 0.00 0.01 0.01 0.00 0.01 0.02 0.00 0.00 Cr2O3 0.05 0.04 0.06 0.06 0.08 0.07 0.08 0.07 0.07 0.05 0.06 0.07 0.08 0.02 0.04 FeO 9.94 10.23 10.40 10.49 10.57 10.56 10.41 10.52 10.65 10.48 10.53 10.37 10.30 9.27 9.65 NiO 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.01 0.00 0.00 0.01 0.00 0.00 0.00 MnO 0.30 0.30 0.29 0.29 0.30 0.29 0.29 0.29 0.29 0.29 0.29 0.29 0.29 0.28 0.29 MgO 48.98 48.94 48.59 48.71 48.64 48.77 48.79 48.55 48.60 48.22 48.47 48.63 48.53 49.50 49.25 CaO 0.04 0.06 0.06 0.06 0.07 0.08 0.06 0.06 0.07 0.06 0.05 0.06 0.05 0.01 0.04 Na2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 K2O 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 P2O5 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.01 0.00 0.02 0.00 0.00 0.00 0.01

Atoms/Formula Unit Si 0.999 1.002 0.998 0.997 0.995 0.995 0.996 1.002 0.998 0.999 0.999 0.995 1.001 1.001 1.004 Ti 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 1.004 Al 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cr 0.001 0.001 0.001 0.001 0.002 0.001 0.002 0.001 0.001 0.001 0.001 0.001 0.002 0.000 0.000 Fe 0.204 0.209 0.214 0.215 0.217 0.217 0.213 0.215 0.218 0.217 0.216 0.214 0.212 0.189 0.001 Ni 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.196 Mn 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.000 Mg 1.790 1.779 1.780 1.782 1.783 1.783 1.784 1.771 1.775 1.776 1.775 1.785 1.777 1.802 0.006 Ca 0.001 0.002 0.002 0.001 0.002 0.002 0.002 0.001 0.002 0.002 0.001 0.001 0.001 0.000 1.787 Na 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 P 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Fo% 89.78 89.51 89.28 89.23 89.14 89.17 89.32 89.16 89.06 89.13 89.14 89.32 89.36 90.50 90.10

Fe/Mn 32.20 33.88 34.93 35.49 35.07 35.63 34.86 35.79 35.91 35.38 35.80 35.34 34.54 32.68 32.39

Olivine Analysis # 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 SiO2 41.60 41.39 41.41 41.06 41.84 41.33 41.37 41.55 41.17 41.54 41.49 40.89 41.00 40.38 40.26 TiO2 0.01 0.00 0.01 0.00 0.01 0.01 0.00 0.01 0.01 0.01 0.00 0.01 0.01 0.00 0.00 Al2O3 0.00 0.01 0.01 0.00 0.01 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.01 0.00 Cr2O3 0.04 0.05 0.05 0.04 0.05 0.04 0.03 0.03 0.05 0.01 0.02 0.00 0.02 0.02 0.02 FeO 9.80 9.82 9.88 10.01 10.03 10.02 10.00 9.96 9.93 9.71 9.32 9.62 9.72 10.10 9.88 NiO 0.01 0.00 0.00 0.00 0.01 0.02 0.02 0.02 0.00 0.02 0.00 0.00 0.01 0.00 0.01 MnO 0.29 0.28 0.28 0.30 0.29 0.28 0.30 0.29 0.30 0.30 0.31 0.31 0.30 0.29 0.30 MgO 49.06 48.89 48.91 49.08 49.02 49.10 48.88 49.10 49.01 49.22 50.25 49.27 49.44 48.76 48.82 CaO 0.05 0.05 0.04 0.03 0.03 0.04 0.04 0.05 0.03 0.02 0.01 0.03 0.03 0.04 0.03 Na2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 K2O 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 P2O5 0.00 0.01 0.02 0.02 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00

Atoms/Formula Unit Si 1.009 1.008 1.008 1.002 1.011 1.004 1.007 1.007 1.004 1.008 1.000 1.000 0.999 0.996 0.995 Ti 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Al 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cr 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 Fe 0.199 0.200 0.201 0.204 0.203 0.204 0.204 0.202 0.202 0.197 0.188 0.197 0.198 0.208 0.204 Ni 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Mn 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 Mg 1.774 1.775 1.774 1.784 1.766 1.779 1.774 1.774 1.781 1.780 1.806 1.796 1.796 1.793 1.799 Ca 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.000 0.000 0.001 0.001 0.001 0.001 Na 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 P 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Fo% 89.92 89.88 89.82 89.73 89.70 89.73 89.71 89.78 89.80 90.04 90.57 90.13 90.07 89.59 89.81

Fe/Mn 33.74 34.30 35.24 33.08 33.86 34.78 32.71 33.61 32.47 32.14 29.38 30.62 31.60 34.27 32.97

Olivine Analysis # 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 SiO2 40.27 40.76 40.63 40.47 40.30 39.96 40.21 40.22 40.23 40.47 40.44 40.78 40.82 41.03 40.89 TiO2 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.01 0.00 0.00 0.00 0.01 0.01 0.01 0.00 Al2O3 0.01 0.01 0.02 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.02 0.01 0.01 0.00 0.01 Cr2O3 0.03 0.05 0.02 0.03 0.02 0.04 0.04 0.03 0.05 0.04 0.03 0.05 0.05 0.05 0.01 FeO 9.92 9.87 9.66 9.95 10.34 10.44 10.51 10.42 10.51 10.62 10.47 10.66 10.63 10.67 10.64 NiO 0.00 0.00 0.01 0.00 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.02 0.01 MnO 0.29 0.30 0.31 0.30 0.30 0.30 0.30 0.30 0.31 0.30 0.30 0.30 0.31 0.31 0.30 MgO 48.84 48.76 48.91 49.24 48.69 48.42 48.32 48.39 48.46 48.21 48.21 48.17 48.53 48.53 48.38 CaO 0.03 0.02 0.02 0.02 0.03 0.02 0.03 0.03 0.02 0.03 0.04 0.02 0.02 0.03 0.03 Na2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P2O5 0.00 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.00

Atoms/Formula Unit Si 0.994 1.001 0.999 0.993 0.994 0.992 0.995 0.996 0.995 0.999 1.000 1.003 1.000 1.003 1.003 Ti 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Al 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.000 0.000 0.000 Cr 0.001 0.001 0.000 0.001 0.000 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.000 Fe 0.205 0.203 0.199 0.204 0.213 0.217 0.218 0.216 0.217 0.219 0.216 0.219 0.218 0.218 0.218 Ni 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Mn 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 Mg 1.798 1.786 1.794 1.802 1.790 1.791 1.783 1.786 1.786 1.775 1.777 1.766 1.772 1.768 1.769 Ca 0.001 0.000 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Na 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 P 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Fo% 89.77 89.80 90.02 89.82 89.36 89.21 89.12 89.23 89.16 89.00 89.14 88.96 89.05 89.02 89.02

Fe/Mn 33.41 32.02 30.99 32.72 33.79 34.02 34.58 33.84 33.50 34.56 34.50 35.43 33.85 34.55 35.14

Olivine Analysis # 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 SiO2 41.00 40.38 40.26 40.27 40.76 40.63 40.47 40.30 39.96 40.21 40.22 40.23 40.47 40.44 40.78 TiO2 0.01 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.01 0.00 0.00 0.00 0.01 Al2O3 0.01 0.01 0.00 0.01 0.01 0.02 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.02 0.01 Cr2O3 0.02 0.02 0.02 0.03 0.05 0.02 0.03 0.02 0.04 0.04 0.03 0.05 0.04 0.03 0.05 FeO 9.72 10.10 9.88 9.92 9.87 9.66 9.95 10.34 10.44 10.51 10.42 10.51 10.62 10.47 10.66 NiO 0.01 0.00 0.01 0.00 -0.01 0.01 0.00 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 MnO 0.30 0.29 0.30 0.29 0.30 0.31 0.30 0.30 0.30 0.30 0.30 0.31 0.30 0.30 0.30 MgO 49.44 48.76 48.82 48.84 48.76 48.91 49.24 48.69 48.42 48.32 48.39 48.46 48.21 48.21 48.17 CaO 0.03 0.04 0.03 0.03 0.02 0.02 0.02 0.03 0.02 0.03 0.03 0.02 0.03 0.04 0.02 Na2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P2O5 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Atoms/Formula Unit Si 0.999 0.996 0.995 0.994 1.001 0.999 0.993 0.994 0.992 0.995 0.996 0.995 0.999 1.000 1.003 Ti 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Al 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.000 Cr 0.000 0.000 0.000 0.001 0.001 0.000 0.001 0.000 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Fe 0.198 0.208 0.204 0.205 0.203 0.199 0.204 0.213 0.217 0.218 0.216 0.217 0.219 0.216 0.219 Ni 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Mn 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 Mg 1.796 1.793 1.799 1.798 1.786 1.794 1.802 1.790 1.791 1.783 1.786 1.786 1.775 1.777 1.766 Ca 0.001 0.001 0.001 0.001 0.000 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Na 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 P 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Fo% 90.07 89.59 89.81 89.77 89.80 90.02 89.82 89.36 89.21 89.12 89.23 89.16 89.00 89.14 88.96

Fe/Mn 31.60 34.27 32.97 33.41 32.02 30.99 32.72 33.79 34.02 34.58 33.84 33.50 34.56 34.50 35.43

Olivine Analysis # 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 SiO2 40.82 41.03 40.89 41.03 40.85 40.95 40.94 41.05 40.95 41.10 41.18 41.13 39.49 41.28 41.60 TiO2 0.01 0.01 0.00 0.00 0.00 0.01 0.00 0.01 0.01 0.01 0.02 0.01 0.00 0.01 0.01 Al2O3 0.01 0.00 0.01 0.00 0.01 0.00 0.01 0.01 0.02 0.00 0.01 0.01 0.00 0.02 0.01 Cr2O3 0.05 0.05 0.01 0.05 0.03 0.04 0.04 0.02 0.04 0.03 0.05 0.04 0.03 0.02 0.05 FeO 10.63 10.67 10.64 10.48 10.50 10.60 10.25 9.91 10.14 10.09 9.36 9.50 12.49 9.36 9.66 NiO 0.02 0.02 0.01 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.04 0.00 0.00 MnO 0.31 0.31 0.30 0.31 0.29 0.31 0.29 0.30 0.30 0.30 0.30 0.29 0.27 0.28 0.29 MgO 48.53 48.53 48.38 48.38 48.32 48.48 48.37 48.95 48.55 48.62 49.26 49.28 48.73 49.16 49.68 CaO 0.02 0.03 0.03 0.04 0.03 0.02 0.02 0.03 0.05 0.05 0.03 0.02 0.02 0.03 0.03 Na2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.00 P2O5 0.02 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.02 0.00 0.00 0.01 0.04 0.00 0.02

Atoms/Formula Unit Si 1.000 1.003 1.003 1.005 1.004 1.003 1.005 1.003 1.004 1.006 1.004 1.003 0.972 1.007 1.004 Ti 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Al 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cr 0.001 0.001 0.000 0.001 0.001 0.001 0.001 0.000 0.001 0.001 0.001 0.001 0.001 0.000 0.001 Fe 0.218 0.218 0.218 0.215 0.216 0.217 0.211 0.203 0.208 0.206 0.191 0.194 0.257 0.191 0.195 Ni 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.000 Mn 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 Mg 1.772 1.768 1.769 1.767 1.770 1.769 1.771 1.783 1.774 1.774 1.791 1.792 1.789 1.787 1.788 Ca 0.001 0.001 0.001 0.001 0.001 0.000 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 Na 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 P 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.000

Fo% 89.05 89.02 89.02 89.17 89.13 89.07 89.37 89.80 89.51 89.57 90.37 90.24 87.43 90.35 90.17

Fe/Mn 33.85 34.55 35.14 33.72 36.19 34.25 34.45 33.12 33.85 33.53 31.26 32.48 45.48 32.95 32.46

Olivine Analysis # 91 92 93 94 95 96 97 98 99 100 SiO2 41.49 41.43 40.79 40.47 40.34 40.65 40.59 41.15 41.14 41.57 TiO2 0.00 0.00 0.01 0.00 0.00 0.01 0.02 0.00 0.00 0.01 Al2O3 0.01 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 Cr2O3 0.02 0.02 0.04 0.01 0.02 0.01 0.02 0.01 0.03 0.01 FeO 9.31 9.58 8.97 8.73 8.74 8.73 9.10 9.02 9.33 8.36 NiO 0.01 0.00 0.02 0.02 0.02 0.01 0.00 0.02 0.01 0.02 MnO 0.30 0.29 0.29 0.30 0.31 0.31 0.29 0.31 0.29 0.32 MgO 49.61 49.02 50.16 50.49 50.44 50.47 49.71 49.92 49.92 50.54 CaO 0.01 0.01 0.01 0.01 0.00 0.00 0.02 0.02 0.01 0.01 Na2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 K2O 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 P2O5 0.00 0.01 0.04 0.03 0.02 0.01 0.00 0.01 0.01 0.00

Atoms/Formula Unit Si 1.006 1.009 0.994 0.988 0.987 0.991 0.995 1.000 0.998 1.003 Ti 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Al 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cr 0.000 0.000 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Fe 0.189 0.195 0.183 0.178 0.179 0.178 0.187 0.183 0.189 0.169 Ni 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Mn 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.006 0.007 Mg 1.793 1.780 1.821 1.837 1.840 1.833 1.816 1.809 1.806 1.818 Ca 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Na 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 P 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000

Fo% 90.48 90.12 90.88 91.15 91.14 91.16 90.69 90.79 90.51 91.51

Fe/Mn 30.60 32.72 30.28 28.32 28.01 27.94 30.66 29.21 31.28 25.93

High-Ca Pyroxene Analysis # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 SiO2 55.99 55.61 54.92 54.98 55.11 55.17 55.18 55.39 55.34 54.58 53.61 55.95 55.41 55.78 54.96 TiO2 0.31 0.32 0.27 0.31 0.32 0.29 0.33 0.32 0.30 0.34 0.29 0.26 0.28 0.53 0.28 Al2O3 1.34 1.39 1.26 1.35 1.41 1.32 1.43 1.40 1.29 1.48 1.96 1.18 1.17 0.77 1.27 Cr2O3 1.12 1.37 1.20 1.18 1.24 1.08 1.20 1.15 1.06 1.16 4.63 1.10 1.31 1.64 1.30 FeO 3.09 2.57 3.57 3.00 2.66 3.14 2.72 2.92 3.31 2.51 4.44 2.57 2.43 2.54 2.46 NiO 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.01 0.01 0.00 0.00 MnO 0.27 0.25 0.26 0.27 0.25 0.27 0.26 0.25 0.26 0.24 0.30 0.25 0.24 0.24 0.26 MgO 19.93 18.77 21.16 19.54 18.53 19.75 18.53 18.97 21.09 18.21 21.67 18.78 18.14 18.14 18.20 CaO 18.07 20.77 16.56 18.72 20.59 18.41 20.25 19.35 17.57 20.99 15.26 20.13 21.14 20.25 20.82 Na2O 0.58 0.52 0.44 0.46 0.44 0.39 0.47 0.48 0.40 0.56 0.41 0.52 0.67 0.86 0.60 K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.00 P2O5 0.00 0.01 0.00 0.02 0.03 0.02 0.02 0.03 0.01 0.01 0.03 0.03 0.02 0.06 0.00

Atoms/Formula Unit Si 1.993 1.976 1.976 1.980 1.977 1.984 1.981 1.986 1.973 1.971 1.896 1.996 1.985 1.996 1.982 Ti 0.008 0.009 0.007 0.008 0.009 0.008 0.009 0.009 0.008 0.009 0.008 0.007 0.008 0.014 0.008 Al 0.056 0.058 0.054 0.057 0.060 0.056 0.060 0.059 0.054 0.063 0.082 0.049 0.050 0.032 0.054 Cr 0.032 0.038 0.034 0.034 0.035 0.031 0.034 0.033 0.030 0.033 0.129 0.031 0.037 0.047 0.037 Fe 0.092 0.076 0.107 0.090 0.080 0.095 0.082 0.088 0.099 0.076 0.131 0.077 0.073 0.076 0.074 Ni 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Mn 0.008 0.007 0.008 0.008 0.008 0.008 0.008 0.007 0.008 0.007 0.009 0.007 0.007 0.007 0.008 Mg 1.057 0.994 1.135 1.049 0.991 1.059 0.991 1.014 1.121 0.980 1.142 0.999 0.969 0.968 0.978 Ca 0.689 0.790 0.638 0.722 0.791 0.709 0.779 0.743 0.671 0.812 0.578 0.770 0.811 0.776 0.804 Na 0.040 0.036 0.030 0.032 0.030 0.027 0.033 0.033 0.028 0.039 0.028 0.036 0.046 0.060 0.042 K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 P 0.000 0.000 0.000 0.001 0.001 0.001 0.001 0.001 0.000 0.000 0.001 0.001 0.001 0.002 0.000

%Wo 37.48 42.47 33.95 38.80 42.50 38.08 42.06 40.29 35.49 43.47 31.22 41.71 43.78 42.66 43.32 %En 57.52 53.42 60.35 56.34 53.22 56.84 53.53 54.96 59.29 52.46 61.69 54.14 52.29 53.17 52.69

Fe/Mn 11.46 10.18 13.73 11.05 10.31 11.51 10.40 11.71 12.73 10.18 14.37 10.29 9.86 10.42 9.50

High-Ca Pyroxene Analysis # 16 17 18 19 20 21 SiO2 56.06 55.58 55.70 55.31 55.27 55.32 TiO2 0.23 0.25 0.22 0.26 0.22 0.28 Al2O3 1.01 1.19 1.02 1.17 1.20 0.87 Cr2O3 1.01 1.22 1.25 1.16 2.55 1.19 FeO 3.45 3.05 4.00 2.69 4.39 2.61 NiO 0.00 0.02 0.00 0.00 0.03 0.00 MnO 0.27 0.26 0.28 0.26 0.30 0.22 MgO 22.53 19.85 22.41 18.80 23.10 18.23 CaO 16.45 18.97 15.00 19.95 14.54 21.15 Na2O 0.35 0.49 0.31 0.51 0.41 0.57 K2O 0.00 0.01 0.00 0.00 0.00 0.00 P2O5 0.00 0.03 0.00 0.02 0.00 0.00

Atoms/Formula Unit Si 1.978 1.981 1.985 1.989 1.946 1.990 Ti 0.006 0.007 0.006 0.007 0.006 0.007 Al 0.042 0.050 0.043 0.050 0.050 0.037 Cr 0.028 0.034 0.035 0.033 0.071 0.034 Fe 0.102 0.091 0.119 0.081 0.129 0.078 Ni 0.000 0.001 0.000 0.000 0.001 0.000 Mn 0.008 0.008 0.009 0.008 0.009 0.007 Mg 1.185 1.055 1.191 1.008 1.213 0.978 Ca 0.622 0.724 0.573 0.769 0.549 0.815 Na 0.024 0.034 0.022 0.035 0.028 0.040 K 0.000 0.000 0.000 0.000 0.000 0.000 P 0.000 0.001 0.000 0.000 0.000 0.000

%Wo 32.58 38.73 30.42 41.38 29.02 43.56 %En 62.08 56.40 63.25 54.27 64.14 52.25

Fe/Mn 12.60 11.79 13.86 10.36 14.23 11.95

Low-Ca Pyroxene Analysis # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 SiO2 57.75 58.15 57.38 57.99 57.57 57.71 57.63 57.09 57.58 56.57 57.12 56.99 57.94 56.86 56.97 TiO2 0.14 0.12 0.13 0.10 0.15 0.17 0.13 0.24 0.15 0.12 0.07 0.07 0.07 0.06 0.10 Al2O3 0.50 0.44 0.37 0.29 0.36 0.39 0.30 0.48 0.33 0.45 0.45 0.50 0.39 0.38 0.42 Cr2O3 0.38 0.42 0.39 0.35 0.32 0.35 0.28 0.35 0.31 0.60 0.68 0.81 0.49 0.54 0.57 FeO 6.26 6.42 6.81 6.89 6.64 6.39 6.42 6.50 6.81 7.10 7.32 7.38 7.70 7.40 7.46 NiO 0.00 0.01 0.00 0.01 0.01 0.01 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.02 MnO 0.33 0.32 0.34 0.34 0.34 0.33 0.33 0.34 0.34 0.43 0.46 0.44 0.44 0.44 0.43 MgO 33.77 33.83 33.39 33.55 33.54 33.59 33.91 33.64 34.21 33.44 32.68 32.74 33.09 33.58 33.69 CaO 0.88 0.90 0.87 0.74 0.92 1.02 0.73 0.54 0.67 1.16 1.56 1.40 1.23 1.17 1.12 Na2O 0.00 0.00 0.02 0.02 0.03 0.03 -0.01 0.02 0.00 0.03 0.06 0.06 0.02 0.04 0.04 K2O 0.01 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.00 0.00 P2O5 0.01 0.00 0.02 0.00 0.01 0.02 0.01 0.01 0.00 0.01 0.01 0.00 0.00 0.00 0.01

Atoms/Formula Unit Si 1.993 1.996 1.992 2.000 1.994 1.994 1.995 1.988 1.985 1.970 1.982 1.979 1.990 1.971 1.969 Ti 0.004 0.003 0.003 0.003 0.004 0.004 0.003 0.006 0.004 0.003 0.002 0.002 0.002 0.002 0.003 Al 0.020 0.018 0.015 0.012 0.015 0.016 0.012 0.020 0.014 0.019 0.018 0.020 0.016 0.016 0.017 Cr 0.010 0.011 0.011 0.010 0.009 0.010 0.008 0.010 0.008 0.016 0.019 0.022 0.013 0.015 0.015 Fe 0.181 0.184 0.198 0.199 0.192 0.185 0.186 0.189 0.196 0.207 0.213 0.214 0.221 0.215 0.216 Ni 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 Mn 0.010 0.009 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.013 0.013 0.013 0.013 0.013 0.013 Mg 1.737 1.731 1.728 1.725 1.731 1.730 1.750 1.747 1.758 1.736 1.691 1.694 1.694 1.736 1.736 Ca 0.033 0.033 0.032 0.027 0.034 0.038 0.027 0.020 0.025 0.043 0.058 0.052 0.045 0.044 0.041 Na 0.000 0.000 0.001 0.001 0.002 0.002 0.000 0.001 0.000 0.002 0.004 0.004 0.001 0.002 0.002 K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 P 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

%Wo 1.67 1.70 1.64 1.40 1.74 1.94 1.38 1.03 1.24 2.18 2.96 2.66 2.32 2.18 2.08 %En 89.06 88.85 88.25 88.41 88.44 88.61 89.16 89.30 88.84 87.41 86.20 86.42 86.41 87.05 87.11

Fe/Mn 18.83 19.58 19.60 19.72 19.49 19.19 19.38 18.92 19.67 16.32 15.86 16.51 17.42 16.78 17.20

Chromite Wt% Oxides 1 2 3 4 5 6 7 8 9 10 11 12 13 SiO2 0.03 0.00 0.02 0.00 0.01 0.00 0.05 0.03 0.02 0.01 0.00 0.01 0.02 TiO2 0.49 0.48 0.49 0.59 0.64 0.64 0.76 0.79 0.80 0.63 0.65 0.67 0.61 Al2O3 5.48 2.33 1.95 6.84 6.30 7.09 7.95 8.31 8.44 7.07 7.25 7.15 6.82 Cr2O3 63.30 62.99 62.36 62.86 62.15 62.43 61.73 61.23 60.89 62.50 61.93 62.31 62.11 FeO 21.63 21.41 21.25 20.55 20.56 20.43 19.11 19.05 19.08 20.49 20.73 20.84 20.93 NiO 0.07 0.05 0.06 0.00 0.00 0.00 0.00 0.02 0.00 0.00 0.00 0.01 0.01 MnO 1.74 1.70 1.74 1.69 1.63 1.61 1.36 1.35 1.39 1.59 1.61 1.58 1.66 MgO 6.77 2.96 2.41 8.18 7.55 8.34 9.39 9.53 9.50 8.06 8.14 8.00 7.78 CaO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 Na2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 K2O 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.00 P2O5 0.05 0.04 0.04 0.04 0.05 0.07 0.05 0.05 0.06 0.03 0.04 0.06 0.06

Atoms/Formula Unit Si 0.001 0.000 0.001 0.000 0.000 0.000 0.002 0.001 0.001 0.000 0.000 0.000 0.001 Ti 0.013 0.014 0.015 0.015 0.017 0.016 0.019 0.020 0.020 0.016 0.017 0.017 0.016 Al 0.224 0.106 0.091 0.272 0.257 0.282 0.313 0.327 0.332 0.282 0.289 0.285 0.274 Cr 1.736 1.927 1.952 1.680 1.699 1.667 1.631 1.615 1.608 1.674 1.658 1.665 1.676 Fe 0.628 0.693 0.703 0.581 0.595 0.577 0.534 0.531 0.533 0.581 0.587 0.589 0.597 Ni 0.002 0.002 0.002 0.000 0.000 0.000 0.000 0.001 0.000 0.000 0.000 0.000 0.000 Mn 0.051 0.056 0.058 0.048 0.048 0.046 0.039 0.038 0.039 0.046 0.046 0.045 0.048 Mg 0.350 0.170 0.142 0.412 0.389 0.420 0.468 0.474 0.473 0.407 0.411 0.403 0.396 Ca 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Na 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 P 0.001 0.001 0.001 0.001 0.002 0.002 0.001 0.002 0.002 0.001 0.001 0.002 0.002

Mg/(Mg+Fe)*100 35.81 19.75 16.79 41.49 39.56 42.11 46.70 47.14 47.02 41.22 41.18 40.63 39.84 Cr/(Cr+Al)*100 88.58 94.76 95.56 86.05 86.88 85.53 83.90 83.17 82.88 85.57 85.14 85.39 85.93

Merrillite Analysis # 1 2 3 4 5 6 7 8 SiO2 0.01 0.23 0.01 0.01 0.03 0.03 0.01 0.01 TiO2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Al2O3 0.00 0.03 0.01 0.00 0.00 0.00 0.00 0.00 Cr2O3 0.01 0.00 0.01 0.03 0.02 0.00 0.02 0.00 FeO 0.28 0.27 0.26 0.32 0.20 0.20 0.20 0.31 NiO 0.00 0.02 0.02 0.02 0.00 0.00 0.01 0.05 MnO 0.02 0.02 0.02 0.03 0.04 0.03 0.02 0.02 MgO 4.16 4.10 4.11 4.10 4.02 4.05 4.08 4.09 CaO 46.57 46.52 46.50 46.21 46.25 46.24 46.04 46.77 Na2O 2.40 2.37 2.49 2.40 2.41 2.45 2.40 2.43 K2O 0.04 0.05 0.04 0.04 0.04 0.04 0.04 0.04 P2O5 43.10 42.90 42.90 43.42 45.01 44.54 44.56 45.26

Atoms/Formula Unit Si 0.003 0.042 0.003 0.002 0.006 0.005 0.001 0.001 Ti 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Al 0.000 0.006 0.002 0.000 0.000 0.000 0.000 0.000 Cr 0.001 0.000 0.002 0.004 0.003 0.000 0.004 0.000 Fe 0.044 0.042 0.040 0.050 0.031 0.031 0.030 0.046 Ni 0.000 0.003 0.002 0.003 0.000 0.000 0.001 0.008 Mn 0.004 0.003 0.004 0.004 0.006 0.005 0.003 0.003 Mg 1.159 1.143 1.148 1.139 1.095 1.108 1.118 1.104 Ca 9.316 9.315 9.332 9.229 9.042 9.100 9.069 9.070 Na 0.869 0.858 0.904 0.866 0.854 0.871 0.854 0.853 K 0.009 0.013 0.009 0.010 0.009 0.010 0.010 0.010 P 6.814 6.789 6.803 6.851 6.952 6.926 6.936 6.935

FeO/MgO 0.07 0.07 0.06 0.08 0.05 0.05 0.05 0.08

Troilite Wt% Oxides 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Fe 61.42 61.27 61.47 61.80 61.68 61.77 61.60 61.35 61.59 61.48 61.81 61.79 61.85 61.45 61.12 Co 0.00 0.01 0.00 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.02 0.00 0.04 Ni 0.12 0.13 0.13 0.11 0.12 0.13 0.13 0.13 0.13 0.13 0.07 0.11 0.03 0.25 0.27 Cu 0.13 0.03 0.15 0.05 0.02 0.00 0.20 0.00 0.19 0.08 0.01 0.09 0.05 0.03 0.09 Mn 0.00 0.00 0.02 0.00 0.01 0.00 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.05 0.00 Mg 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 S 38.29 38.23 38.46 38.32 38.26 38.27 38.43 38.25 38.14 38.28 38.10 38.09 38.13 37.95 38.11

Atomic % Fe 47.85 47.86 47.75 48.02 48.01 48.05 47.81 47.90 48.00 47.90 48.19 48.16 48.19 48.06 47.80 Co 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.01 0.00 0.03 Ni 0.09 0.09 0.10 0.08 0.09 0.10 0.10 0.09 0.10 0.10 0.05 0.08 0.02 0.18 0.20 Cu 0.09 0.02 0.10 0.03 0.02 0.00 0.13 0.00 0.13 0.06 0.01 0.06 0.03 0.02 0.07 Mn 0.00 0.00 0.02 0.00 0.01 0.00 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.04 0.00 Mg 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 S 51.96 52.02 52.03 51.86 51.87 51.85 51.95 52.01 51.77 51.94 51.74 51.70 51.74 51.70 51.91

Troilite Wt% Oxides 16 17 18 19 20 Fe 61.76 61.75 61.62 61.90 61.68 Co 0.00 0.00 0.00 0.00 0.00 Ni 0.10 0.08 0.10 0.04 0.05 Cu 0.01 0.10 0.01 0.06 0.05 Mn 0.00 0.00 0.00 0.00 0.00 Mg 0.00 0.00 0.00 0.00 0.00 S 37.93 37.91 37.95 38.17 38.12

Atomic % Fe 48.28 48.26 48.21 48.18 48.12 Co 0.00 0.00 0.00 0.00 0.00 Ni 0.07 0.06 0.08 0.03 0.04 Cu 0.01 0.07 0.01 0.04 0.03 Mn 0.00 0.00 0.00 0.00 0.00 Mg 0.00 0.00 0.00 0.00 0.00 S 51.64 51.60 51.71 51.75 51.80

Schreibersite Wt% Oxides 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Si 0.01 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.02 0.01 0.00 Cr 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.00 Fe 61.96 62.32 62.03 61.92 62.62 62.50 62.34 62.45 62.40 62.32 60.65 61.21 61.32 62.09 62.26 Co 0.19 0.19 0.19 0.18 0.19 0.19 0.19 0.20 0.20 0.20 0.18 0.20 0.20 0.17 0.19 Ni 22.14 22.02 21.88 21.69 21.89 21.87 21.77 21.68 21.89 21.81 23.74 22.93 22.70 22.22 21.78 Cu 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 14.33 14.60 14.55 14.72 14.75 14.79 14.83 14.84 14.91 14.91 14.90 14.68 14.85 14.99 14.80 S 0.11 0.10 0.13 0.12 0.12 0.12 0.12 0.13 0.12 0.13 0.09 0.11 0.10 0.10 0.12

Atomic % Si 0.02 0.02 0.01 0.01 0.00 0.01 0.01 0.00 0.01 0.00 0.01 0.01 0.03 0.03 0.01 Cr 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.00 Fe 56.71 56.66 56.66 56.56 56.70 56.63 56.56 56.65 56.46 56.47 54.92 55.70 55.70 56.13 56.57 Co 0.16 0.17 0.16 0.16 0.16 0.16 0.17 0.17 0.17 0.17 0.16 0.18 0.17 0.15 0.17 Ni 19.27 19.05 19.01 18.84 18.85 18.85 18.79 18.71 18.84 18.80 20.45 19.85 19.61 19.11 18.83 Cu 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 23.65 23.93 23.96 24.24 24.09 24.17 24.27 24.27 24.33 24.36 24.33 24.09 24.32 24.44 24.24 S 0.18 0.17 0.20 0.19 0.19 0.19 0.19 0.20 0.19 0.20 0.14 0.17 0.16 0.16 0.18

Schreibersite Wt% Oxides 16 17 18 19 20 Si 0.00 0.01 0.01 0.01 0.01 Cr 0.00 0.00 0.00 0.00 0.00 Fe 62.47 62.85 62.71 62.86 63.04 Co 0.21 0.20 0.20 0.18 0.21 Ni 21.69 21.37 21.39 21.26 21.30 Cu 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 P 14.79 14.69 14.66 14.82 14.78 S 0.12 0.10 0.11 0.10 0.11

Atomic % Si 0.00 0.02 0.02 0.02 0.01 Cr 0.00 0.00 0.00 0.00 0.00 Fe 56.70 57.11 57.07 57.06 57.12 Co 0.18 0.17 0.17 0.15 0.18 Ni 18.73 18.47 18.52 18.36 18.36 Cu 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 P 24.21 24.07 24.05 24.25 24.15 S 0.18 0.17 0.17 0.16 0.18

Plagioclase Wt% Oxides 1 2 3 4 5 6 SiO2 67.00 66.94 66.00 65.56 66.16 66.34 TiO2 0.04 0.04 0.03 0.03 0.01 0.02 Al2O3 21.19 21.12 21.09 21.66 22.15 21.38 Cr2O3 0.02 -0.01 0.01 0.00 0.02 0.01 FeO 0.25 0.43 0.26 0.43 0.19 0.51 NiO 0.01 0.08 0.00 0.02 0.00 0.04 MnO 0.00 0.00 0.00 0.00 0.01 0.00 MgO 0.01 0.01 0.01 0.01 0.01 0.01 CaO 1.49 1.45 1.61 2.17 2.24 1.70 Na2O 9.27 9.37 9.19 9.04 9.36 9.58 K2O 0.90 1.02 1.00 0.87 0.69 0.85 P2O5 0.03 0.03 0.01 0.02 0.03 0.01

Atoms/Formula Unit Si 2.929 2.925 2.919 2.889 2.881 2.906 Ti 0.001 0.001 0.001 0.001 0.000 0.001 Al 1.092 1.088 1.100 1.125 1.137 1.103 Cr 0.001 0.000 0.000 0.000 0.001 0.000 Fe 0.009 0.016 0.010 0.016 0.007 0.019 Ni 0.001 0.003 0.000 0.001 0.000 0.001 Mn 0.000 0.000 0.000 0.000 0.000 0.000 Mg 0.001 0.000 0.000 0.001 0.001 0.000 Ca 0.070 0.068 0.076 0.102 0.104 0.080 Na 0.785 0.794 0.788 0.773 0.791 0.813 K 0.050 0.057 0.057 0.049 0.039 0.048 P 0.001 0.001 0.000 0.001 0.001 0.000

%Ab 86.75 86.42 85.58 83.62 84.70 86.47 %Or 5.56 6.17 6.15 5.31 4.13 5.07

Taenite Wt% Oxides 1 2 3 4 5 6 7 8 9 10 Si 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.01 0.01 0.00 Cr 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe 77.56 76.85 77.18 76.29 76.49 76.37 77.02 77.46 75.90 76.03 Co 1.29 1.24 1.27 1.27 1.29 1.29 1.27 1.31 1.37 1.36 Ni 20.29 21.35 21.10 21.52 20.55 21.14 20.87 20.71 21.80 21.86 Cu 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 0.20 0.00 0.33 0.34 0.48 0.22 0.13 0.21 0.38 0.35 S 0.03 0.03 0.03 0.03 0.02 0.03 0.04 0.04 0.02 0.03

Atomic % Si 0.02 0.01 0.02 0.03 0.02 0.02 0.04 0.02 0.02 0.01 Cr 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 Fe 78.73 78.10 77.86 77.33 77.90 77.81 78.25 78.35 76.93 76.94 Co 1.24 1.20 1.22 1.22 1.24 1.24 1.22 1.25 1.31 1.31 Ni 19.59 20.64 20.25 20.75 19.91 20.49 20.17 19.93 21.02 21.04 Cu 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 0.37 0.00 0.60 0.62 0.88 0.40 0.25 0.38 0.69 0.64 S 0.06 0.05 0.05 0.06 0.04 0.05 0.07 0.07 0.03 0.06

S-T Taenite Wt% Oxides 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Si 0.01 0.01 0.01 0.01 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.00 Cr 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe 73.90 81.18 85.39 87.82 88.36 87.75 87.55 86.39 84.79 76.01 71.88 85.71 86.97 87.90 87.92 Co 0.20 0.34 0.46 0.42 0.48 0.41 0.42 0.39 0.40 0.31 0.23 0.42 0.43 0.44 0.48 Ni 25.22 18.72 13.78 11.40 11.09 11.62 11.83 12.63 13.95 22.73 27.11 13.58 12.31 11.16 10.79 Cu 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.09 0.00 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 0.02 0.02 0.03 0.05 0.05 0.05 0.04 0.03 0.02 0.01 0.05 0.04 0.03 0.04 0.06 S 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.00 0.00 0.01 0.00 0.01

Atomic % Si 0.02 0.03 0.01 0.02 0.01 0.02 0.03 0.00 0.00 0.01 0.00 0.02 0.03 0.01 0.00 Cr 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe 75.30 81.69 86.23 88.55 88.84 88.36 88.16 87.41 86.03 77.59 73.36 86.48 87.68 88.77 89.03 Co 0.19 0.33 0.44 0.40 0.46 0.39 0.40 0.37 0.38 0.30 0.23 0.40 0.42 0.42 0.46 Ni 24.44 17.91 13.24 10.94 10.61 11.13 11.33 12.16 13.47 22.07 26.32 13.03 11.81 10.72 10.39 Cu 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.08 0.00 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 0.04 0.04 0.05 0.08 0.08 0.09 0.07 0.05 0.04 0.03 0.08 0.07 0.05 0.07 0.10 S 0.00 0.00 0.02 0.00 0.01 0.01 0.01 0.01 0.00 0.01 0.01 0.00 0.02 0.00 0.02

S-T Taenite Wt% Oxides 16 17 18 19 20 Si 0.01 0.02 0.00 0.01 0.01 Cr 0.00 0.00 0.00 0.00 0.00 Fe 88.29 88.82 89.33 89.13 89.33 Co 0.49 0.48 0.53 0.50 0.50 Ni 10.48 10.03 9.80 9.69 9.87 Cu 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 P 0.04 0.04 0.04 0.05 0.01 S 0.01 0.01 0.01 0.00 0.00

Atomic % Si 0.02 0.03 0.00 0.02 0.02 Cr 0.00 0.00 0.00 0.00 0.00 Fe 89.35 89.77 90.01 90.10 90.02 Co 0.47 0.46 0.50 0.48 0.47 Ni 10.09 9.64 9.39 9.32 9.46 Cu 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 P 0.07 0.08 0.08 0.09 0.02 S 0.01 0.02 0.01 0.00 0.00

Kamacite Wt% Oxides 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Si 0.01 0.01 0.01 0.00 0.00 0.00 0.01 0.00 0.01 0.01 0.01 0.00 0.00 0.00 0.01 Cr 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.00 0.00 Fe 91.78 91.75 91.86 91.94 92.11 92.16 92.02 91.98 92.61 92.20 92.31 92.37 91.96 91.98 92.04 Co 0.52 0.58 0.54 0.51 0.53 0.59 0.58 0.58 0.55 0.54 0.56 0.54 0.53 0.57 0.61 Ni 7.10 6.96 6.91 6.83 6.79 6.83 6.68 6.58 6.62 6.97 6.90 6.98 6.75 6.70 6.64 Cu 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.00 0.01 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 0.12 0.15 0.15 0.17 0.16 0.15 0.17 0.17 0.17 0.13 0.15 0.15 0.16 0.16 0.10 S 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.01 0.01 0.00

Atomic % Si 0.02 0.03 0.02 0.00 0.00 0.00 0.03 0.00 0.01 0.03 0.02 0.01 0.01 0.01 0.02 Cr 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.00 0.00 Fe 92.47 92.47 92.56 92.66 92.70 92.63 92.70 92.81 92.80 92.55 92.60 92.52 92.70 92.71 92.84 Co 0.49 0.56 0.51 0.49 0.51 0.57 0.55 0.55 0.53 0.52 0.53 0.52 0.51 0.54 0.58 Ni 6.80 6.67 6.62 6.55 6.50 6.53 6.40 6.32 6.31 6.65 6.58 6.65 6.47 6.43 6.37 Cu 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.00 0.01 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 0.21 0.27 0.28 0.30 0.29 0.27 0.31 0.31 0.31 0.23 0.27 0.28 0.29 0.29 0.18 S 0.00 0.01 0.01 0.00 0.01 0.00 0.00 0.01 0.01 0.01 0.00 0.00 0.02 0.02 0.00

Kamacite Wt% Oxides 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Si 0.02 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.02 0.01 0.00 0.00 0.00 0.00 Cr 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.00 Fe 92.43 92.44 92.52 91.91 92.11 91.92 91.81 92.12 91.23 92.07 90.99 92.21 92.09 91.95 91.70 Co 0.52 0.56 0.56 0.58 0.56 0.58 0.58 0.55 0.57 0.58 0.51 0.60 0.55 0.56 0.54 Ni 6.68 6.55 6.48 6.61 6.71 6.81 6.82 6.85 6.91 6.76 6.64 6.67 6.67 6.80 6.61 Cu 0.00 0.01 0.00 0.00 0.03 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 0.10 0.11 0.11 0.12 0.13 0.15 0.15 0.15 0.16 0.12 0.14 0.14 0.15 0.16 0.15 S 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.01

Atomic % Si 0.04 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.04 0.01 0.00 0.00 0.01 0.01 Cr 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.00 Fe 92.89 92.98 93.06 92.85 92.77 92.64 92.63 92.63 92.46 92.70 92.79 92.77 92.80 92.64 92.81 Co 0.50 0.54 0.53 0.56 0.53 0.55 0.55 0.53 0.55 0.55 0.49 0.58 0.53 0.54 0.52 Ni 6.39 6.26 6.20 6.36 6.43 6.53 6.55 6.55 6.66 6.48 6.44 6.39 6.39 6.52 6.36 Cu 0.00 0.01 0.00 0.00 0.03 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 0.18 0.20 0.19 0.22 0.23 0.27 0.26 0.28 0.30 0.22 0.26 0.25 0.28 0.28 0.28 S 0.01 0.00 0.01 0.01 0.00 0.00 0.01 0.00 0.02 0.01 0.00 0.01 0.00 0.00 0.02

Kamacite Wt% Oxides 31 32 33 34 35 36 37 38 39 40 41 42 43 44 Si 0.01 0.01 0.01 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Cr 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe 92.15 92.00 91.85 92.12 93.33 93.14 93.04 92.73 93.11 92.44 92.80 92.52 92.93 92.99 Co 0.59 0.55 0.57 0.56 0.59 0.55 0.57 0.56 0.56 0.55 0.57 0.58 0.59 0.58 Ni 6.74 6.57 6.75 6.62 5.89 5.98 6.18 6.35 6.30 6.34 6.36 6.32 6.29 6.36 Cu 0.00 0.00 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 0.15 0.15 0.15 0.15 0.08 0.08 0.09 0.11 0.12 0.12 0.12 0.15 0.14 0.15 S 0.00 0.00 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Atomic % Si 0.03 0.02 0.01 0.00 0.00 0.03 0.02 0.03 0.01 0.02 0.01 0.01 0.02 0.02 Cr 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe 92.68 92.87 92.65 92.83 93.68 93.57 93.36 93.16 93.24 93.16 93.14 93.11 93.15 93.09 Co 0.56 0.53 0.54 0.53 0.56 0.53 0.54 0.53 0.53 0.53 0.54 0.55 0.56 0.55 Ni 6.45 6.31 6.48 6.34 5.63 5.71 5.90 6.07 6.00 6.08 6.07 6.05 6.00 6.06 Cu 0.00 0.00 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 0.27 0.27 0.27 0.28 0.14 0.14 0.17 0.20 0.22 0.22 0.22 0.28 0.26 0.27 S 0.00 0.00 0.01 0.01 0.00 0.02 0.00 0.01 0.00 0.00 0.01 0.00 0.01 0.01

Appendix C LA-ICP-MS results for trace element analyses. All results are reported in ppm. b.d. = below detection

Spot size 150 150 150 150 150 150 150 150 150 150 50 50 150 50 150 (microns) Phase metal metal metal metal metal metal metal metal metal metal troilite troilite troilite troilite schreib. CI- 40- 41- 42- 43- 44- 45- 46- 47- 51- 53- 48- 49- 50- 24- 52- normalized Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Si b. d. b. d. b. d. b. d. 298.10 b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 753.89 b. d. P 6674.63 1749.28 3795.28 5067.27 6598.26 6104.42 3366.46 5414.08 5618.86 18273.2 391.68 425.76 123.43 326.82 600125.4 S b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 48015.0 50918.1 45603.6 50723.0 220.77 V b. d. b. d. b. d. b. d. 0.02 b. d. b. d. b. d. b. d. b. d. 1.06 1.20 1.36 1.08 b. d. Cr 0.00 0.00 b. d. 0.00 0.02 b. d. 0.01 b. d. 0.00 b. d. 0.82 0.91 0.91 2.66 0.00 Mn 26.14 23.94 26.21 40.07 158.77 b. d. 48.50 b. d. b. d. b. d. 2129.47 2790.74 2508.77 3365.77 56.66 Fe 4.88 4.47 4.88 4.86 4.82 4.86 4.56 4.88 4.91 4.88 3.70 3.60 3.74 3.35 3.28 Co 10.80 7.20 9.82 10.42 10.37 10.22 8.46 10.31 10.97 10.76 0.08 0.08 0.07 0.90 3.25 Ni 5.93 13.38 6.18 6.29 6.09 6.46 11.49 6.11 5.63 5.80 0.14 0.11 0.11 0.68 18.91 Cu 1.01 3.58 0.95 1.04 1.06 1.05 3.27 1.09 0.98 0.87 2.15 3.61 4.33 2.89 0.71 Zn b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.01 0.00 b. d. Ga 4.38 4.72 4.53 4.15 4.37 4.02 5.86 4.22 4.20 4.32 b. d. b. d. b. d. 0.04 0.32 Ge 3.33 2.62 3.29 3.13 3.32 3.03 3.40 3.33 3.34 3.19 0.02 0.02 0.02 0.03 0.04 As 6.74 2.90 6.35 6.31 6.85 6.01 5.58 6.51 6.46 6.06 b. d. b. d. 0.02 0.06 0.98 Se b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 5.94 5.93 5.51 7.20 b. d. Nb b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.07 b. d. b. d. b. d. 0.37 0.24 13.72 b. d. Mo 4.71 5.28 4.00 4.21 4.77 4.75 5.54 4.73 4.86 5.35 4.89 5.11 4.50 2.64 33.27 Ru 18.13 30.37 17.94 16.86 17.54 17.33 26.51 18.22 15.04 17.10 b. d. b. d. b. d. b. d. 21.90 Rh 11.14 16.95 11.88 10.50 11.08 11.72 14.32 10.31 10.66 11.69 0.31 0.73 0.25 0.15 8.32 Pd 6.44 13.89 7.09 6.25 6.44 6.79 12.85 6.48 6.13 5.80 b. d. b. d. b. d. b. d. 6.97 Ag 0.10 0.09 0.06 0.08 b. d. 0.07 0.06 b. d. b. d. b. d. 0.10 0.30 0.21 0.41 0.08 Sn 0.32 0.21 0.30 1.28 6.18 0.27 2.51 0.48 0.26 0.22 b. d. 0.06 0.02 6.18 0.03 Sb 1.61 1.04 1.61 1.71 1.95 1.30 1.61 1.57 1.44 1.24 0.44 0.51 0.12 0.49 0.24 Te b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.68 1.09 0.77 2.67 b. d. W 10.00 7.34 8.87 6.63 8.72 8.98 7.27 8.33 8.32 7.47 b. d. b. d. 0.05 0.08 5.13 Re 1.59 1.60 1.54 0.84 1.17 1.90 2.13 1.41 1.65 1.41 0.39 b. d. b. d. b. d. b. d. Os 0.45 0.48 0.46 0.40 0.34 0.40 0.38 0.52 0.48 0.55 0.06 b. d. b. d. b. d. b. d. Ir 1.51 1.63 1.71 1.39 1.58 1.40 1.57 1.59 1.72 1.50 b. d. b. d. b. d. b. d. 0.01 Pt 19.93 22.17 21.05 18.74 18.89 19.71 19.48 20.66 20.03 19.01 0.05 0.03 b. d. 0.02 0.08 Au 9.98 14.98 11.11 10.25 9.81 9.74 13.80 10.61 9.19 8.72 b. d. b. d. b. d. 0.17 0.05

Spot Size 100.000 100.000 100.000 100.000 100.000 100.000 100.000 100.000 100.000 100.000 100.000 150.000 150.000 100.000 150.000 (microns) Phase olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine CI- 25- 26- 27- 28- 29- 30- 31- 32- 33- 34- 35- 36- 37- 38- 39- Normalized Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Li 8.435 7.988 8.664 8.768 8.572 8.492 9.679 9.335 9.840 10.578 10.528 5.507 10.973 8.763 3.758 Be b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. B b. d. b. d. b. d. 0.328 0.309 0.356 0.321 0.343 0.484 0.342 0.431 0.417 0.248 0.373 0.299 Na2O b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.380 b. d. b. d. b. d. MgO 3.017 3.028 3.026 3.060 3.038 3.035 3.060 3.068 2.985 3.011 3.057 3.023 3.023 3.080 3.124 Al2O3 b. d. 0.023 b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.035 b. d. b. d. b. d. SiO2 1.717 1.677 1.712 1.700 1.700 1.693 1.707 1.693 1.719 1.726 1.720 1.694 1.723 1.656 1.675 P2O5 0.018 0.016 0.017 0.017 0.016 0.017 0.046 0.025 0.032 0.019 0.080 0.027 0.018 0.018 0.017 S b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.009 0.002 b. d. 0.000 Cl 1.496 1.252 0.990 0.927 0.938 0.889 0.856 0.859 0.776 0.768 0.803 0.826 0.975 1.047 0.906 K2O b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. CaO 0.066 0.305 0.099 0.059 0.062 0.061 0.059 0.063 0.070 0.096 0.057 0.107 0.059 0.063 0.066 Sc b. d. 1.087 0.824 0.707 0.704 0.708 0.678 0.745 0.774 0.701 0.777 0.745 0.652 0.671 1.000 TiO2 0.095 0.168 0.093 0.074 0.077 0.081 0.057 0.087 0.075 0.073 0.079 0.112 0.108 0.098 0.136 V 0.341 1.097 0.541 0.450 0.472 0.453 0.414 0.417 0.544 0.560 0.397 0.443 0.299 0.451 0.362 Cr2O3 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 MnO 1.378 1.316 1.276 1.288 1.290 1.308 1.259 1.283 1.317 1.263 1.280 1.313 1.368 1.315 1.267 FeOT 0.447 0.441 0.442 0.437 0.451 0.460 0.431 0.438 0.467 0.441 0.419 0.446 0.440 0.463 0.415 Co 0.011 0.013 0.011 0.008 0.007 0.007 0.006 0.007 0.010 0.011 0.014 0.047 0.011 0.015 0.011 Ni 0.001 b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.001 0.001 0.006 0.031 0.001 0.005 0.001 Cu 0.012 0.010 0.010 0.009 0.009 0.009 0.010 0.009 0.011 0.011 0.010 0.024 0.021 0.018 0.012 Zn 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.002 0.003 0.003 0.003 0.003 Ga 0.012 0.026 0.009 0.008 0.006 0.006 b. d. 0.006 0.006 0.009 0.010 0.026 0.013 0.011 0.010 Ge b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.001 b. d. b. d. b. d. As 0.046 0.036 0.030 0.049 0.035 0.034 0.026 0.036 0.026 0.029 0.023 0.049 0.026 0.038 0.026 Se b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. Rb b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. Sr b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.093 b. d. b. d. b. d. Y b. d. 0.018 b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.011 b. d. 0.015 0.003 b. d. b. d. Zr 0.014 0.754 0.087 0.019 0.009 0.011 0.010 0.012 0.029 0.110 0.110 0.046 0.027 b. d. 0.074

Spot Size 100.000 100.000 100.000 100.000 100.000 100.000 100.000 100.000 100.000 100.000 100.000 150.000 150.000 100.000 150.000 (microns) Phase olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine olivine CI- 25- 26- 27- 28- 29- 30- 31- 32- 33- 34- 35- 36- 37- 38- 39- Normalized Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Choteau Nb b. d. 0.128 b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.045 b. d. 0.016 b. d. b. d. b. d. Mo b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. Ru b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. Rh 0.019 b. d. b. d. 0.028 b. d. 0.021 b. d. b. d. 0.024 b. d. 0.022 0.058 0.027 0.025 0.024 Pd b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.048 0.019 b. d. b. d. Ag b. d. 0.018 0.019 b. d. 0.029 b. d. b. d. b. d. b. d. b. d. b. d. 0.013 0.023 0.020 0.018 Cd 0.248 0.132 0.102 b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.057 0.097 b. d. 0.233 In b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.891 0.389 0.379 0.294 Sn 0.025 0.027 0.035 0.029 0.026 0.023 0.021 0.021 0.026 0.024 0.022 8.238 0.096 0.018 0.018 Sb b. d. 0.072 0.053 0.044 b. d. 0.051 b. d. 0.039 b. d. 0.039 b. d. 0.080 0.092 0.644 0.085 Te b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. Cs b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. Ba b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.066 b. d. b. d. b. d. La 0.007 0.075 b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.026 0.016 0.037 b. d. b. d. b. d. Ce b. d. 0.078 0.007 b. d. b. d. b. d. b. d. b. d. 0.005 0.023 0.048 0.202 0.006 b. d. b. d. Pr b. d. 0.089 b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.037 b. d. 0.027 b. d. b. d. b. d. Nd b. d. 0.128 0.030 b. d. b. d. b. d. 0.044 b. d. b. d. 0.070 0.061 0.023 0.021 b. d. 0.019 Sm b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. Eu b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. Gd b. d. 0.066 b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. Tb b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.042 b. d. b. d. b. d. b. d. b. d. b. d. b. d. Dy b. d. 0.054 b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.015 b. d. b. d. b. d. b. d. b. d. Ho b. d. 0.031 b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.040 b. d. b. d. b. d. b. d. b. d. Er b. d. 0.050 b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.026 b. d. b. d. b. d. Tm b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.022 b. d. b. d. b. d. Yb b. d. b. d. b. d. b. d. b. d. 0.051 b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. Lu b. d. 0.146 0.150 0.118 b. d. 0.170 b. d. b. d. b. d. b. d. b. d. b. d. b. d. 0.108 b. d. Hf 0.044 0.686 0.065 0.037 0.034 b. d. b. d. 0.035 b. d. 0.167 0.150 0.060 0.044 b. d. 0.090 Ta b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. W b. d. b. d. b. d. 0.041 0.044 0.036 b. d. b. d. 0.027 b. d. b. d. 0.022 0.018 b. d. 0.019 Re b. d. b. d. b. d. b. d. b. d. 0.090 b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d. b. d.

Spot Size 50.000 50.000 100.000 50.000 50.000 50.000 50.000 (microns) Phase pxn pxn pxn plag plag plag troilite CI- 17- 19- 23- 20- 21- 22- 24- Normalized Choteau Choteau Choteau Choteau Choteau Choteau Choteau Li b. d. b. d. 4.010 b. d. 26.391 18.738 b. d. Be 37.769 33.752 b. d. 189.516 b. d. 286.576 b. d. B 0.359 1.219 0.925 3.235 3.685 3.746 b. d. Na2O 0.281 0.997 1.328 19.848 22.240 20.160 0.706 MgO 0.116 0.115 0.110 0.003 0.014 0.009 0.002 Al2O3 0.163 0.163 0.220 6.301 6.285 6.769 0.101 SiO2 0.109 0.109 0.112 0.111 0.124 0.123 0.005 P2O5 0.082 0.629 0.096 2.573 0.543 0.377 0.182 S b. d. 0.024 0.003 0.126 0.010 0.010 1.020 Cl 0.002 0.002 0.002 0.002 b. d. b. d. b. d. K2O b. d. 1.457 b. d. 157.918 158.921 166.022 b. d. CaO 1.264 0.885 0.975 0.930 0.973 1.324 0.038 Sc 0.532 0.402 0.528 b. d. b. d. b. d. b. d. TiO2 27.469 30.431 30.537 6.250 7.591 9.112 b. d. V 0.036 0.026 0.040 0.001 0.002 0.005 0.013 Cr2O3 0.000 0.000 0.000 0.000 0.000 0.000 0.000 MnO 7.349 6.772 7.202 0.230 0.831 0.613 1.147 FeOT 0.013 0.014 0.013 0.013 0.003 0.005 0.093 Co 0.000 0.002 0.000 0.015 0.000 0.000 0.001 Ni 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cu 0.000 0.003 0.000 0.009 0.001 0.001 0.016 Zn 0.000 0.000 0.000 0.000 b. d. b. d. 0.000 Ga 0.010 0.034 0.014 0.178 0.071 0.076 0.003 Ge 0.000 0.001 0.000 0.005 0.000 0.000 0.001 As 0.015 0.361 0.054 3.392 0.210 0.165 0.026 Se b. d. 0.002 b. d. b. d. b. d. b. d. 0.262 Rb b. d. b. d. b. d. 1.857 1.734 1.755 b. d. Sr 0.004 0.022 0.023 0.840 0.821 0.843 0.016 Y 1.019 0.436 0.771 0.081 0.044 0.250 0.010 Zr 0.355 0.234 0.342 0.089 0.080 0.222 0.011

Spot Size 50.000 50.000 100.000 50.000 50.000 50.000 50.000 (microns) Phase pxn pxn pxn plag plag plag troilite CI- 17- 19- 23- 20- 21- 22- 24- Normalized Choteau Choteau Choteau Choteau Choteau Choteau Choteau Nb 1.055 1.949 2.926 1.120 2.346 3.246 37.823 Mo 0.086 0.353 b. d. 1.331 b. d. b. d. 1.929 Ru b. d. 0.170 b. d. 1.083 b. d. b. d. b. d. Rh 0.039 0.891 0.200 4.813 1.179 b. d. 0.652 Pd 0.064 1.408 0.175 5.651 0.696 b. d. b. d. Ag 0.099 0.116 0.140 3.389 1.076 b. d. 1.382 Cd 0.050 0.035 b. d. b. d. b. d. b. d. b. d. In b. d. 32.042 16.550 36.863 72.249 48.291 7.668 Sn 0.023 17.717 9.155 16.796 20.747 14.044 2.437 Sb 0.330 4.013 0.919 22.196 2.644 1.861 2.353 Te b. d. 0.090 b. d. 1.163 b. d. b. d. 0.780 Cs b. d. b. d. b. d. 113.645 b. d. b. d. b. d. Ba 0.008 0.025 0.064 3.764 4.241 4.227 0.068 La 0.848 1.064 1.901 8.893 4.648 9.573 0.402 Ce 0.680 0.604 1.206 1.430 0.869 2.304 0.076 Pr 6.477 3.923 9.109 6.104 4.241 14.786 b. d. Nd 1.834 1.012 1.897 0.863 0.341 3.202 b. d. Sm 7.871 3.434 5.634 2.189 b. d. 5.522 b. d. Eu 0.775 0.803 1.942 81.501 99.604 94.961 b. d. Gd 8.490 4.003 5.950 0.626 b. d. 3.421 b. d. Tb 47.411 21.350 35.495 4.545 b. d. 11.802 b. d. Dy 7.480 3.603 5.030 0.685 0.552 2.935 0.194 Ho 31.150 15.325 25.657 b. d. b. d. 7.796 b. d. Er 11.757 7.311 8.804 3.884 4.213 3.517 0.318 Tm 74.738 39.343 52.235 b. d. b. d. 30.479 b. d. Yb 10.151 6.553 7.581 1.056 b. d. 1.554 b. d. Lu 82.431 55.144 67.303 b. d. b. d. b. d. b. d. Hf 15.411 11.182 15.075 1.581 4.155 11.144 0.422 Ta 5.764 31.130 35.766 52.105 65.479 96.817 b. d. W 0.241 2.379 0.820 6.450 b. d. 2.454 0.562 Re b. d. 1.120 b. d. 1.515 b. d. b. d. b. d.

Spot Size 50.000 50.000 100.000 50.000 50.000 50.000 50.000 (microns) Phase pxn pxn pxn plag plag plag troilite CI- 17- 19- 23- 20- 21- 22- 24- Normalized Choteau Choteau Choteau Choteau Choteau Choteau Choteau Os b. d. b. d. b. d. b. d. b. d. b. d. b. d. Ir b. d. b. d. 0.016 0.020 b. d. b. d. b. d. Pt b. d. 0.016 b. d. 0.104 b. d. b. d. 0.011 Au b. d. 6.670 0.562 27.919 3.539 1.883 0.825 Tl 0.008 0.034 0.044 0.286 0.894 b. d. 0.159 Pb 0.005 0.013 0.016 0.062 0.065 0.045 0.008 Bi 0.102 0.147 0.177 0.323 0.515 b. d. 0.201 Th 28.207 28.048 67.074 13.141 30.288 20.884 0.385 U 97.802 249.950 307.789 361.345 657.827 296.332 80.188

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Vita

Personal Julia Dayle Gregory Background Fort Worth, Texas Daughter of Brian Todd and Marla Adella Gregory

Education Diploma, Gregory Academy, Roscoe, Illinois, 2010 Bachelor of Science, Geology, Olivet Nazarene University, Bourbonnais, Illinois, 2014 Master of Science, Geology, Texas Christian University, Fort Worth, Texas, 2016

Experience Teaching Assistant, January 2011-May 2014, Olivet Nazarene University, Bourbonnais, Illinois Graduate Teaching Assistant, August 2014-May 2016, Texas Christian University, Fort Worth, Texas

Abstract

CHARACTERIZATION OF THE UNGROUPED PALLASITE CHOTEAU

by Julia D. Gregory, M.S., 2016 School of Geology, Energy, and the Environment Texas Christian University

Thesis Advisor: Rhiannon G. Mayne, Associate Professor of Geology

Choteau is classified as an ungrouped pallasite due to its dissimilarity to other pallasite groups and its oxygen isotopic similarity to the acapulcoites/lodranites. This study uses oxygen isotope analyses, mineral chemistry, and trace element analyses to determine Choteau’s petrogenesis and if it is related to any ungrouped pallasites or the acapulcoites/lodranites.

We found that Choteau contains plagioclase, being only the second plagioclase- bearing pallasite. This suggests that Choteau formed at the core-mantle boundary of a parent body with a large core-to-mantle ratio, which would facilitate pressures low enough for plagioclase to remain stable in the mantle.

When compared with other pallasites, Choteau is unique in mineral composition and oxygen isotope ratios, therefore representing its own group of pallasites. Choteau shows similarities to the acapulcoites/lodranites in terms of oxygen isotope ratios, mineral chemistry, and trace element abundances, but not in texture. Choteau could represent a pallasite from the acapulcoite/lodranite parent body.