Meteoritics & Planetary Science 38, Nr 8, 1217–1241 (2003) Abstract available online at http://meteoritics.org

Minor element zoning and trace element geochemistry of pallasites

Weibiao HSU1, 2*

1Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing 210008, China 2Division of Geological & Planetary Sciences, Mail Code 170–25, California Institute of Technology, Pasadena, California 91125, USA *Corresponding author. E-mail: [email protected] (Received 1 April 2003; revision accepted 9 July 2003)

Abstract–I report here on an ion probe study of minor element spatial distributions and trace element concentrations in six pallasites. Pallasite olivines exhibit ubiquitous minor element zoning that is independent of grain size, morphology, and adjacent phases. Ca, Cr, Ti, V, and Ni concentrations decrease from center to rim by factors of up to 10, while Mn is generally unzoned or increases slightly at the very edge of some olivine grains. The maximum concentrations of these elements at the center of olivine vary from grain to grain within the same meteorite and among the pallasites studied. These zoning profiles are consistent with thermal diffusion during rapid cooling. The inferred cooling rates at high temperature regimes are orders of magnitude faster than the low-temperature metallographic cooling rates (~0.5 to 2°C/Ma). This suggests that pallasites, like mesosiderites, have experienced rather complicated thermal histories, i.e., cooling rapidly at high temperatures and slowly at low temperatures. Pallasite olivines are essentially free of REEs. However, the phosphates display a wide range of REE abundances (0.001 to 100 × CI) with distinct patterns. REEs are generally homogeneous within a given grain but vary significantly from grain to grain by a factor of up to 100. Albin and Imilac whitlockite are highly enriched in HREEs (~50 × CI) but are relatively depleted in LREEs (~0.1 to 1 × CI). Eagle Station whitlockite has a very unusual REE pattern: flat LREEs at a 0.1 × CI level, a large positive Eu anomaly, and a sharp increase from Gd (0.1 × CI) to Lu (70 × CI). Eagle Station stanfieldite has a similar REE pattern to that of whitlockite but with much lower REEs by a factor of 10 to 100. Springwater farringtonite has relatively low REE concentrations (0.001 to 1 × CI) with a highly fractionated HREE-enriched pattern (CI-normalized Lu/La ~100). Postulating any igneous processes that could have fractionated REEs in these phosphates is difficult. Possibly, phosphates were incorporated into pallasites during mixing of olivine and IIIAB-like molten Fe. These phosphates preserve characteristics of a previous history. Pallasites have not necessarily formed at the mantle-core boundary of their parent bodies. The pallasite thermal histories suggest that pallasites may have formed at a shallow depth and were subsequently buried deep under a regolith blanket.

INTRODUCTION metal are physically and chemically dissimilar and immiscible due to their large contrast in density if they both Pallasites are highly differentiated meteorites with a very crystallized from a melt. Thus, one can legitimately expect simple mineralogy. They consist of roughly equal amounts of that olivine at the bottom of the mantle mixes with Fe-Ni olivine and Fe-Ni metal with minor phosphates, pyroxenes, metal from the core to form a layer of pallasite in a chromite, schreibersite, and troilite (Buseck 1977). Despite differentiated parent body. Urey (1956), however, posed a their simple mineralogy, various models have been proposed different view of the origin for pallasites. He noted that regarding the origin of pallasites and their physical position pallasites were too abundant to represent a single boundary in the parent bodies. A popular idea is that pallasites are layer and suggested that they came from discrete metal pools samples of the mantle-core boundary of the differentiated throughout the parent bodies, the so-called “raisin-bread parent bodies (Mason 1962, 1963; Anders 1964; Buseck and model.” A third theory is that pallasites originated near the Goldstein 1969). This is mainly because olivine and Fe-Ni surface of their parent bodies (Mittlefehldt 1980).

1217 © Meteoritical Society, 2003. Printed in USA. 1218 W. Hsu

Mittlefehldt (1980) found that mesosiderite and pallasite that this mineral has extremely low REE abundances (10−5 olivines have similar major element compositions and to 10−2 × CI) with a highly fractionated HREE-enriched suggested that pallasite olivine, like mesosiderite olivine, was pattern. While the REEs are virtually excluded from olivine, a product of external heating of a chondritic parent body. The they can be highly enriched in phosphates. Ion microprobe olivine layer produced by extensive partial melting and analyses revealed that pallasite phosphates exhibit diverse fractional crystallization near the surface was invaded by REE patterns with highly variable abundances (Davis and molten metal from the upper portion of the parent body. Olsen 1991, 1996). Most phosphates have relatively low Thermal histories of pallasites reveal information REE abundances (0.01 to 10 × CI) with an HREE-enriched essential to a deeper understanding of their physical position pattern (CI-normalized Lu/La ~100). A few of the phosphate in the parent bodies as well as their origin. Cooling rates grains in Springwater and Santa Rosalia are highly enriched estimated from kamacite-taenite diffusion profiles in in REEs (up to 300 × CI) with an LREE-enriched pattern pallasite Fe-Ni metal are in the range of 0.5–2°C/Ma from (CI-normalized La/Lu 3 to 10). A merrillite grain from 700 to 300°C (Buseck and Goldstein 1969), which indicates Giroux has an unusual REE pattern similar to the volatility- a burial depth of ~200 km (Fricker et al. 1970). Such slow controlled group II REE pattern commonly observed in cooling rates are generally compatible with pallasite CAIs of CV chondrites (Davis and Olsen 1996). formation at the mantle-core boundary in their parent bodies. Interpretations of this diversity include phosphate formation However, studies of major and minor element concentrations by sub-solidus redox reaction between olivine and metal, in pallasite olivines suggested much high cooling rates at crystallization from a trapped liquid, and the late-stage high temperatures (Scott 1977a; Reed et al. 1979; Miyamoto crystallization on pallasite parent bodies (Davis and Olsen 1997). Pallasite olivines are well-known to exhibit chemical 1991). In this study, I carried out an investigation of REE zoning of minor elements (e.g., Ca, Cr, Ti, and Ni), which concentrations in phosphates and olivines from 6 pallasites. were thought to represent diffusion during rapid cooling With the extensive data set on minor element zoning of processes under subsolidus temperatures (Leitch et al. 1979; olivine and REE abundances of phosphates, I will evaluate Reed et al. 1979; Zhou and Steele 1993; Steele 1994). previous models and seek additional constraints on the Diffusion induced chemical zoning in silicates potentially origin of pallasites. provides constraints on their thermal histories. Most analyses of minor element zoning in pallasite olivines were obtained ANALYTICAL METHODS with an electron microprobe (Zhou and Steele 1993; Steele 1994; Miyamoto 1997). As these minor element Six pallasites, Albin, Brenham, Eagle Station, Imilac, concentrations are usually very low and close to the Glorieta Mountain, and Springwater, were studied in this detection limit of an electron microprobe, high sensitivity work. Samples used are 1 inch round polished thick ion microprobe analyses are desired. The ion microprobe sections. All samples were studied with a JEOL JSM 35-CF data collected to date include analyses of 7 minor element scanning electron microscope (SEM) equipped with a concentrations in a Springwater olivine (Leitch et al. 1979), Tractor Northern energy dispersive (EDS) X-ray analysis the Ni concentration in 7 pallasite olivines (Reed et al. system. 1979), and 11 minor element concentrations in olivines of The spatial distributions of minor elements in pallasite Springwater and Mount Vernon (Floss 2002). In this study, I olivines were obtained with a Cameca 3f ion microprobe at extended the ion microprobe analyses to 6 minor element the California Institute of Technology. A mass resolving spatial distributions in olivine crystals from 6 pallasites. I power was set at ~3000. A liquid nitrogen trap was used near will compare this data with previously reported results and the secondary ion source to further depress the hydride signal. discuss their implications to pallasite thermal histories. No energy filtering was used in the measurements. A primary Trace elements, particularly the rare earth elements beam current of 1 nA was used, which resulted in a beam spot (REEs), provide much information about the crystallization, of ~5 µm. Standardization was done on San Carlos olivine, fractionation, and differentiation processes that led to the NBS-610 glass, and a synthetic Ti-pyroxene. The singly formation of igneous rocks. Pallasites are highly charged positive secondary ions were collected at masses 30Si, differentiated igneous meteorites. The REE distributions in 40Ca, 47Ti, 48Ti, 51V, 52Cr, 55Mn, and 60Ni. The minor element pallasites provide additional constraints on their origin. The concentrations were obtained by normalizing ion signal major REE sources in these meteorites are olivine (dominant intensities to the silicon content of olivine. The analysis phase) and phosphates (REE carrier). Early studies showed precisions (1σ) for Ca, Ti, V, Cr, Mn, and Ni are 3%, 5%, 5%, that pallasite olivine has a V-shaped CI-normalized REE 1%, 1%, and 20%, respectively. The precision error for Ni is pattern with abundances at 10−2 to 1 × CI (Schmitt et al. relatively large. This is a combination of counting statistics 1964; Masuda 1968). Recent analyses by Minowa and and the matrix effect on the ionization efficiency of Ni. Reed Ebihara (2002) indicated that much of the light REE (LREE) et al. (1979) reported a strong and systematic dependence of in pallasite olivines are due to terrestrial contamination and the secondary ion yield for Ni on the fayalite (Fa) content of Minor element zoning and trace element geochemistry of pallasites 1219 olivine. The Fa values of the olivines in this study range from RESULTS Fa10 in San Carlos olivine to Fa20 in Eagle Station olivine. Minor element distribution profiles were obtained from linear Minor Element Spatial Distributions in Pallasite Olivines traverses across olivine grains. REE measurements were also made with the Caltech ion I studied minor element spatial distributions in olivine microprobe using the techniques of Fahey et al. (1987). grains from 6 pallasites (Table 1 and Appendix). The size of Primary beam currents of 10 nA (~20 µm in beam size) for pallasite olivine ranges from 250 to 4300 µm. Both round and phosphates and 20 nA (~40 µm in beam size) for olivine were angular olivine grains were included in the analyses. These used to sputter positive secondary ions from the sample olivine crystals are adjacent to Fe-Ni metal, troilite, chromite, surfaces. The secondary ions were collected at low mass or phosphate (Fig. 1). I found that minor element zoning is resolution using 80 V of energy filtering, which efficiently ubiquitous among pallasite olivines (Fig. 2). It is independent suppresses complex molecular interferences (Zinner and of olivine grain sizes, morphologies, and adjacent phases. Crozaz 1986). A deconvolution calculation was carried out to However, each element behaves distinctly. eliminate the simple oxide interferences in the mass range of REEs. Synthetic Ti-pyroxene glass and Durango apatite Ca: Ca is zoned within 300–500 µm from the edge in all standards were measured periodically to account for any pallasite olivines. Its concentration decreases from the core to variation of ionization efficiencies caused by minor changes the rim by a factor of up to 3. Within a given meteorite, the of operating conditions. Reference element concentrations of maximum Ca concentration at the center of olivine varies by a pallasite olivine (SiO2) and phosphates (CaO and MgO) were factor of up to 3 (e.g., from 25 to 70 ppm in Albin) and the taken from the literature (Buseck and Goldstein 1969; Buseck minimum concentration at the rim by a factor of up to 4 (e.g., and Holdsworth 1977). from 12 to 47 ppm in Albin). Among the pallasites studied, the

Fig. 1. Reflected light microscope photographs of ion probe profile measurements in Albin olivine (Ol). The visible dots on the olivine crystals are the ion probe pits: a) olivine adjacent to Fe metal (Fe). The field of view is 2.25 mm; b) olivine adjacent to chromite (Chrm) and Fe metal (Fe). The field of view is 2.25 mm; c) olivine adjacent to troilite (FeS). The field of view is 2.25 mm; d) olivine adjacent to troilite (FeS) and chromite (Chrm). The field of view is 1.13 mm. 1220 W. Hsu Ca Ti V Cr Mn Ni tributions (ppm) in pallasite olivines. m) Adjacent phases Core Rim Core Rim Core Rim Core Rim Core Rim Core Rim µ 920625 Ni Fe, 310480 FeS500 Fe, Ni Chromite FeS FeS FeS Chromite 32 Fe, Ni FeS950530 25 26 51 60 Ni Fe, 330 Ni Fe, 12 70 4 Fe, Ni 24970 45 Chromite Fe, Ni250 Fe, Ni 47 2 18 2 Ni Fe, 280 2275 Ni Fe, 270480 14 186 Olivine 1300 92 2 5 Fe, Ni Ni Fe, 3 96 Ni Fe, 87 2 Ni Fe, 71 Fe, Ni 5 8 8 4 108 Fe, Ni 12 4 Fe, Ni 3 5 48 3 86 3 68 5 4 2 74 90 15 1 76 3 43 7 4 33 33 158 70 5 61 45 5 3 16 124 16 35 4 3 2250 25 3 30 20 36 8 1 2310 8 2345 2300 6 7 10 70 2300 16 94 1140 2400 2360 6 5 27 2465 5 20 8 2170 27 7 12 15 15 13 20 118 3 17 2360 5 10 2360 6 72 6 54 13 2370 2330 15 2290 48 80 173 1880 55 135 2540 55 42 62 65 2290 2800 68 45 36 2677 2290 28 40 2230 2400 1585 40 2445 25 2500 12 32 15 20 7 12 10 Albin 1220 Fe, Ni Fe, NiBrenham 4300Eagle Station 36 Fe, Ni1100 Fe, Ni 26Glorieta Mountain Fe, Ni 150 5 Fe, NiImilac 100 2 380 3Springwater 6 12013002250 1 5 15 Fe, Ni FeS 4 Olivine 5 100 Farringtonite 3 115 193 40 6 67 65 2240 3 90 2365 6 5 25 150 15 1 1 1535 38 10 1500 6 6 2245 15 2270 4 4 12 74 100 144 33 30 36 3450 3400 3750 3580 46 50 30 27 Size ( Table 1. Minor element spatial dis Table Minor element zoning and trace element geochemistry of pallasites 1221

Fig. 2. Ca, Ti, V, Cr, Mn, and Ni zoning profiles in Albin (open circle) and Eagle Station (filled circle) olivines. Note that the maximum concentrations at the center of the grains are significantly different among pallasite olivines. maximum Ca concentration at the center of olivine also varies Ti: Ti zoning in pallasite olivines can be very extensive. significantly, e.g., 25 ppm in Albin and 380 ppm in Eagle From the core to the rim, Ti content decreases by a factor of Station. Such large variations suggest that pallasite olivines up to 9. In Albin, the maximum Ti concentration at the center were heterogeneous with respect to the initial Ca concentration. of olivine ranges from 2 to 18 ppm and the minimum at the rim from 1 to 3 ppm. Imilac olivine (core) has much higher Ti Cr: Cr zoning in olivine is very similar to that of Ca but with concentration (16 to 25 ppm) than that of Breham (~3 ppm). a more pronounced zoning profile. Its concentration typically decreases by a factor of up to 4 from core to rim. Eagle Station V: Albin, Eagle Station, and Imilac olivines show clear V olivine exhibits the largest variations of Cr concentration. In zoning, but olivines from Brenham, Glorieta Mountain, and this pallasite, the maximum Cr concentration at the center of Springwater do not. Some pallasite olivines have essentially olivine varies from 27 to 150 ppm, and the minimum Cr homogeneous V within the grains. The variation of V concentration at the rim of olivine ranges from 13 to 38 ppm concentration (core) is generally insignificant within a given from grain to grain. Imilac olivine (core) has Cr meteorite and among the pallasites studied. The concentrations up to 170 ppm, and Eagle Station olivine concentration (~5 ppm) is roughly the same among pallasite (core) has Cr concentrations down to 27 ppm. olivines (core). 1222 W. Hsu

Mn: Mn behaves differently from other minor elements in The observed minor element zoning profiles in pallasite pallasite olivines. Most olivines have a constant Mn olivines are consistent with previously reported data. Ca and concentration across the crystal. In some cases (e.g., Albin), it Cr zoning profiles have been found in all pallasite olivines increases slightly at the very edge (within 50 µm) of the grain. studied, such as Admire, Eagle Station, Esquel, Imilac, Springwater olivine has a higher (~3500 ppm) and Brenham Pavlodar, and Springwater (Leitch et al. 1979; Zhou and olivine has a lower Mn concentration (~1500 ppm) than the Steele 1993; Steele 1994; Miyamoto 1997). Ion probe rest (~2300 ppm). analyses also revealed clear Ni zoning in olivines of Eagle Station (Reed et al. 1979) and Springwater (Leitch et al. Ni: Ni is clearly zoned in pallasite olivines with high Ni 1979). Reed et al. (1979) found that Ni in an Eagle Station concentration (~50 ppm, Eagle Station and Springwater). The olivine shows a decrease from 40 ppm at the core to 25 ppm concentration decreases from the core to the rim by a factor at the rim. Mn has been found either unzoned in Springwater of 2. However, Ni zoning is not pronounced in pallasite olivine (3175 ppm; Leitch et al. 1979) and Pavlodar olivine olivines with low Ni concentration (~20 ppm). (2700 ppm; Steele 1994) or increasing at the edge (50 µm) of Minor element zoning usually occurs within 300–500 Springwater olivine (Zhou and Steele 1993). Ion probe µm from the edge of the grain. Large olivine grains (>2 mm) analyses show that Ti (~6 ppm) is zoned but V (~10 ppm) is seem to have a flat top of minor element concentrations in the unzoned in Springwater olivine (Leitch et al. 1979). middle of the zoning profiles. Note that not all zoning profiles are as symmetric as in Fig. 2. Asymmetric zoning REE Concentrations in Pallasite Phosphates and Olivine profiles are also commonly observed. A few grains exhibit anomalous profiles that do not show a simple increase or Phosphates were found in 4 pallasites: Albin, Eagle decrease in concentration relative to grain edges. Sometimes, Station, Imilac, and Springwater. They have highly variable the zoning profile encounters exceptionally high values chemical compositions, from Ca-rich whitlockite (Ca3[PO4]2) (Fig. 2). This is due to the fact that pallasite olivines contain to Ca, Mg-bearing stanfieldite (Mg3Ca3[PO4]4) to Mg-rich tubular inclusions (<1 µm) (Buseck 1977). However, it is not farringtonite (Mg3[PO4]2). In Albin, I found 4 whitlockite clear what phases these inclusions are. When I traced back to grains ranging in size from 100 to 500 µm. They tend to occur check the spots with a SEM, the inclusions were not detected. interstitially between olivine and metal (Fig. 3a). In Eagle I presume that they were very small and were eroded by the Station, 1 whitlockite grain and 8 stanfieldite grains were ion beam. found; they are generally small (30 to 100 µm) and in irregular

Fig. 3. Back scattered electron images of phosphate occurrences in pallasites: a) whitlockite (whit) occurs interstitially between olivine (ol) and Fe metal (Fe) in Albin; b) stanfieldite (stan) is adjacent to the Eagle Station olivine with co-existing low-Ca pyroxene (pyx); c) whitlockite is highly fractured in Imilac; d) a round farringtonite (farr) grain occurs interstitially between olivine grains in Springwater. Minor element zoning and trace element geochemistry of pallasites 1223 shapes. These grains are commonly plastered onto the surfaces measurements were made in 4 whitlockite grains. No of olivines, and sometimes, low-Ca pyroxene is co-existing significant variation of REEs was found within a given grain. (Fig. 3b). Three whitlockite grains (200 to 500 µm) found in Inter-grain variation is generally small, up to a factor of 5. Imilac are extensively fractured with numerous iron oxide Four whitlockite grains have essentially the same REE pattern veins (Fig. 3c). They also occur interstitially between olivine that is highly enriched in Sm, Eu, and HREEs (~ 50 × CI) but and metal. No phosphate was found in Brenham and Glorieta relatively depleted in La to Nd (~1 × CI) (Fig. 4a). In general, Mountain. Although widespread, phosphates are usually CI-normalized REE abundances increase gradually from La present in minor amounts in pallasites. However, phosphates to Nd and from Sm to Lu. A clear cut in abundances exists are relatively abundant in Springwater. Buseck (1977) reported between Nd (~1 × CI) and Sm (~30 × CI). The Eu anomaly is 4 vol% phosphates in this meteorite. These phosphates are negligible. In Eagle Station, the whitlockite grain has a very large in size (up to 1.5 mm) and occur interstitially between unusual REE pattern. It has essentially flat LREEs with olivine grains (Fig. 3d). The round boundary of farringtonite depleted abundances (~0.1 × CI), a large positive Eu anomaly grains indicates that this mineral was present initially as molten (Eu/Eu* ~10, where Eu* is the interpolated value between CI- droplets. One farringtonite grain was found in a crack of an normalized Sm and Gd abundances), and a sharp increase olivine grain. No whitlockite and Mn-rich silico-phosphates from Gd (0.1 × CI) to Lu (70 × CI) (Fig. 4b). The other 5 (Davis and Olsen 1991; Hutcheon and Olsen 1991) were found stanfieldite grains analyzed have a similar REE pattern to that in the Springwater samples. of whitlockite but with much lower REE abundances, by a Pallasite phosphates display distinct REE abundances factor of 10–100 (Fig. 4b). Three whitlockite grains were and patterns (Table 2 and Fig. 4). In Albin, 8 REE found in Imilac. Four analyses were made in 1 grain and 1

Fig. 4. REE abundances and patterns of pallasite phosphates: a) Albin whitlockite; b) Eagle Station whitlockite and stanfieldite; c) Imilac whitlockite; d) Springwater farringtonite. Pallasite phosphates have highly variable REE abundances and patterns. In general, they all have an HREE-enriched pattern. 1224 W. Hsu

Table 2. REE concentrations (ppm) in pallasite phosphates. (The errors quoted are 1σ standard deviation from counting statistics only.) Albin Whitlockite Whitlockite Whitlockite Whitlockite Whitlockite Whitlockite Whitlockite Whitlockite La 0.123 ± 0.010 0.11 ± 5 0.01 0.109 ± 0.012 0.102 ± 0.01 0.218 ± 0.014 0.183 ± 0.013 0.163 ± 0.014 0.174 ± 0.014 Ce 0.438 ± 0.023 0.462 ± 0.023 0.357 ± 0.025 0.234 ± 0.018 0.683 ± 0.028 0.687 ± 0.028 0.58 ± 0.028 0.607 ± 0.03 Pr 0.082 ± 0.009 0.078 ± 0.009 0.06 ± 0.008 0.05 ± 0.006 0.101 ± 0.01 0.102 ± 0.009 0.075 ± 0.008 0.101 ± 0.012 Nd 0.61 ± 0.033 0.623 ± 0.035 0.535 ± 0.045 0.391 ± 0.027 0.966 ± 0.045 0.953 ± 0.044 0.863 ± 0.046 0.83 ± 0.048 Sm 3.318 ± 0.108 3.436 ± 0.11 3.301 ± 0.122 2.728 ± 0.085 6.312 ± 0.162 6.415 ± 0.158 5.607 ± 0.164 5.62 ± 0.172 Eu 1.952 ± 0.075 1.739 ± 0.072 1.506 ± 0.045 2.27 ± 0.08 1.504 ± 0.039 1.631 ± 0.039 1.785 ± 0.043 1.856 ± 0.046 Gd 9.22 ± 0.262 9.201 ± 0.268 6.519 ± 0.196 5.534 ± 0.141 14.075 ± 0.369 14.767 ± 0.349 12.7 ± 0.37 12.73 ± 0.397 Tb 1.662 ± 0.074 1.571 ± 0.072 1.461 ± 0.073 0.659 ± 0.032 2.527 ± 0.091 2.659 ± 0.088 2.33 ± 0.094 2.238 ± 0.095 Dy 9.089 ± 0.294 9.157 ± 0.299 8.172 ± 0.246 5.909 ± 0.189 14.75 ± 0.399 14.964 ± 0.379 12.204 ± 0.395 12.964 ± 0.418 Ho 1.794 ± 0.083 2.121 ± 0.089 1.141 ± 0.066 1.089 ± 0.048 2.931 ± 0.123 3.223 ± 0.122 2.585 ± 0.127 2.505 ± 0.131 Er 6.094 ± 0.303 6.46 ± 0.302 4.751 ± 0.264 3.297 ± 0.18 9.689 ± 0.382 9.557 ± 0.37 8.713 ± 0.419 8.197 ± 0.427 Tm 1.059 ± 0.100 1.118 ± 0.094 0.943 ± 0.074 0.42 ± 0.069 1.85 ± 0.082 1.725 ± 0.077 1.58 ± 0.099 1.55 ± 0.103 Yb 10.969 ± 0.259 12.399 ± 0.259 9.611 ± 0.254 7.495 ± 0.195 20.39 ± 0.402 21.116 ± 0.393 16.996 ± 0.401 15.244 ± 0.409 Lu 1.865 ± 0.113 1.955 ± 0.11 0.83 ± 0.072 1.294 ± 0.086 3.438 ± 0.107 3.449 ± 0.102 3.028 ± 0.109 2.612 ± 0.109 Eagle Station Stanfieldite Stanfieldite Whitlockite Stanfieldite Stanfieldite Stanfieldite La 0.008 ± 0.004 0.026 ± 0.007 0.027 ± 0.008 0.007 ± 0.004 0.008 ± 0.004 0.012 ± 0.004 Ce 0.009 ± 0.004 0.042 ± 0.007 0.083 ± 0.012 0.016 ± 0.004 0.022 ± 0.004 0.013 ± 0.004 Pr – <0.007 0.012 ± 0.004 0.004 ± 0.004 <0.004 <0.004 Nd 0.007 ± 0.004 0.04 ± 0.012 0.071 ± 0.014 0.01 ± 0.003 0.035 ± 0.007 0.01 ± 0.003 Sm 0.036 ± 0.033 0.005 ± 0.01 0.017 ± 0.008 0.011 ± 0.005 0.009 ± 0.006 0.011 ± 0.006 Eu – – 0.059 ± 0.007 0.002 ± 0.005 0.005 ± 0.003 0.015 ± 0.005 Gd 0.014 ± 0.007 0.022 ± 0.011 0.02 ± 0.013 0.032 ± 0.013 – 0.003 ± 0.003 Tb – <0.007 0.008 ± 0.004 0.008 ± 0.004 0.009 ± 0.004 – Dy 0.008 ± 0.004 0.019 ± 0.006 0.16 ± 0.018 0.018 ± 0.004 0.045 ± 0.008 0.007 ± 0.004 Ho – <0.006 0.051 ± 0.007 0.007 ± 0.004 0.019 ± 0.004 0.004 ± 0.004 Er 0.009 ± 0.004 0.041 ± 0.007 0.435 ± 0.028 0.036 ± 0.008 0.076 ± 0.008 0.012 ± 0.004 Tm – 0.026 ± 0.007 0.287 ± 0.019 0.022 ± 0.004 0.028 ± 0.004 0.012 ± 0.004 Yb 0.071 ± 0.01 0.366 ± 0.03 5.522 ± 0.148 0.472 ± 0.026 0.368 ± 0.023 0.201 ± 0.018 Lu 0.014 ± 0.007 0.144 ± 0.022 1.762 ± 0.065 0.14 ± 0.019 0.088 ± 0.014 0.066 ± 0.013 Imilac Whitlockite Whitlockite Whitlockite Whitlockite Whitlockite Whitlockite La 0.102 ± 0.012 0.099 ± 0.012 0.123 ± 0.015 0.094 ± 0.012 0.063 ± 0.014 0.099 ± 0.017 Ce 0.448 ± 0.028 0.325 ± 0.027 0.45 ± 0.029 0.322 ± 0.025 0.045 ± 0.015 0.054 ± 0.009 Pr 0.054 ± 0.009 0.068 ± 0.008 0.071 ± 0.01 0.061 ± 0.008 0.022 ± 0.007 0.009 ± 0.009 Nd 0.876 ± 0.052 0.895 ± 0.047 0.897 ± 0.052 0.83 ± 0.041 0.105 ± 0.025 0.036 ± 0.015 Sm 2.716 ± 0.128 3.149 ± 0.102 2.843 ± 0.138 2.543 ± 0.089 0.327 ± 0.051 0.097 ± 0.024 Eu 0.202 ± 0.021 0.245 ± 0.018 0.178 ± 0.019 0.178 ± 0.015 0.063 ± 0.018 0.037 ± 0.016 Gd 3.381 ± 0.159 3.938 ± 0.165 2.593 ± 0.18 3.311 ± 0.144 0.925 ± 0.107 0.176 ± 0.028 Tb 1.501 ± 0.087 1.559 ± 0.05 1.405 ± 0.087 1.408 ± 0.043 0.302 ± 0.031 0.091 ± 0.018 Dy 11.631 ± 0.453 12.77 ± 0.359 10.441 ± 0.459 11.78 ± 0.326 2.907 ± 0.113 0.735 ± 0.047 Ho 3.179 ± 0.203 3.267 ± 0.113 2.746 ± 0.207 2.917 ± 0.103 0.665 ± 0.053 0.194 ± 0.023 Er 9.935 ± 0.331 11.299 ± 0.275 8.658 ± 0.345 9.857 ± 0.241 3.323 ± 0.126 1.165 ± 0.061 Tm 1.536 ± 0.085 1.449 ± 0.041 1.285 ± 0.083 1.396 ± 0.039 0.524 ± 0.042 0.264 ± 0.025 Yb 10.835 ± 0.358 13.52 ± 0.25 9.151 ± 0.36 12.546 ± 0.233 3.049 ± 0.114 2.548 ± 0.097 Lu 0.648 ± 0.089 1.405 ± 0.077 – 1.235 ± 0.073 0.451 ± 0.047 0.462 ± 0.042 Springwater Farrringtonite Farringtonte Farringtonite Farringtonite Farringtonite La – 0.005 ± 0.002 0.001 ± 0.001 – 0.002 ± 0.001 Ce – 0.015 ± 0.002 – 0.001 ± 0.001 0.002 ± 0.001 Pr <0.001 0.007 ± 0.002 <0.001 – <0.001 Nd 0.005 ± 0.002 0.028 ± 0.006 0.003 ± 0.001 0.004 ± 0.002 0.002 ± 0.001 Sm 0.003 ± 0.002 0.012 ± 0.005 0.002 ± 0.002 0.004 ± 0.002 0.003 ± 0.002 Eu 0.001 ± 0.001 0.001 ± 0.001 <0.001 0.002 ± 0.001 0.001 ± 0.001 Minor element zoning and trace element geochemistry of pallasites 1225

Table 2. REE concentrations (ppm) in pallasite phosphates. (The errors quoted are 1σ standard deviation from counting statistics only.) Continued. Springwater Farrringtonite Farringtonte Farringtonite Farringtonite Farringtonite Gd 0.005 ± 0.003 0.006 ± 0.01 0.009 ± 0.005 0.006 ± 0.004 0.005 ± 0.002 Tb 0.003 ± 0.001 0.007 ± 0.002 0.001 ± 0.001 0.004 ± 0.001 0.001 ± 0.001 Dy 0.014 ± 0.003 0.06 ± 0.009 0.022 ± 0.003 0.012 ± 0.002 0.012 ± 0.002 Ho 0.003 ± 0.001 0.017 ± 0.004 0.005 ± 0.001 0.002 ± 0.001 0.002 ± 0.001 Er 0.026 ± 0.004 0.091 ± 0.01 0.017 ± 0.002 0.014 ± 0.002 0.011 ± 0.002 Tm 0.002 ± 0.001 0.016 ± 0.002 0.006 ± 0.001 0.003 ± 0.001 0.003 ± 0.001 Yb 0.043 ± 0.004 0.18 ± 0.013 0.064 ± 0.005 0.04 ± 0.004 0.038 ± 0.004 Lu 0.01 ± 0.002 0.057 ± 0.008 0.017 ± 0.004 0.013 ± 0.002 0.012 ± 0.002 each in the other 2 grains. Within the grain, REE abundances are essentially homogeneous. Large inter-grain variations (up to a factor of 30) of REEs exist among 3 Imilac whitlockite grains. The observed REE pattern is similar in shape to that of the Albin whitlockite but with a negative Eu anomaly (Fig. 4c). In general, Imilac whitlockite is enriched in HREEs (10 to 80 × CI) and relatively depleted in LREEs (0.1 to 1 × CI). Four farringtonite grains in Springwater were analyzed. Two measurements were made in 1 farringtonite grain and 1 each in the other 3 grains. Springwater farringtonite grains have relatively low REEs (0.001 to 1 × CI) with a highly fractionated HREE-enriched pattern (CI-normalized Lu/La ~100). Within the grain, REEs are essentially homogeneous. One grain has relatively higher REE abundances (0.02 to 2 × CI) than the other 3, by a factor of 10 (Fig. 4d). All phosphates analyzed in this study are enriched in HREEs relative to LREEs. Phosphates with LREE enrichments, as reported by Davis and Olsen (1991, 1996), were not observed. Although phosphates exhibit distinct REE abundances and patterns among the pallasites studied, they tend to have essentially the same REE pattern within a given meteorite. Fig. 5. Representative REE abundances and patterns of pallasite olivines. The REEs plotted here can only be taken as upper limits. REE concentrations in pallasite olivines are extremely They are close or below the ion probe detection limits in most cases. low and, thus, required a large primary beam current (20 nA) and long measurement time (4 hours). A total of 50 Leitch et al. 1979; Reed et al. 1979; Mittlefehldt 1980; Zhou measurements were made in olivines of the 6 pallasites. Most and Steele 1993; Floss 2002). Table 3 lists some of the olivines have REE concentrations below the ion microprobe previously published results. These data generally fall into 2 detection limit. Fig. 5 shows some representative REE categories: bulk analyses with spark-source mass abundances and patterns of pallasite olivines. They are well spectrometer (Mason and Graham 1970), INAA (Goles 1971; below the 0.1 × CI level with a gradual increase toward Mittlefehldt 1980) and X-ray fluorescence (Lovering 1957; HREEs (Fig. 5). Nichiporuk et al. 1967), and in situ measurements with electron probe (Buseck and Goldstein 1969; Zhou and Steele DISCUSSION 1993) and ion probe (Leitch et al. 1979; Reed et al. 1979; Floss 2002). Relatively abundant data are available for Comparison with Previously Reported Minor Element Springwater olivine. Large discrepancies are apparent among Concentrations in Pallasite Olivines the reported results. For example, the reported Ca concentration in Springwater olivine varies from 20 to Minor element concentrations in pallasite olivines were 980 ppm and Ni from 26 to 350 ppm. Several possible reasons previously analyzed with electron probe, instrumental exists to explain such large discrepancies. Pallasite olivines neutron activation analysis (INAA), spark-source mass are well-known to contain tubular inclusions (Buseck 1977; spectrometer, X-ray fluorescence, and ion probe techniques Steele 1994). Bulk analyses, therefore, have a tendency to (Lovering 1957; Nichiporuk et al. 1967; Buseck and yield high minor element concentrations. In Springwater Goldstein 1969; Mason and Graham 1970; Goles 1971; olivine, the reported Ca concentration with X-ray 1226 W. Hsu

Table 3. Comparison of ion probe minor element analyses (ppm) with previously reported data of pallasite olivines. Ca Ti V Cr Mn Ni Albin This study 12–70 1–18 2–8 16–158 1140–2465 6–20 Literature 60a 15a 150a 2000a 150a Brenham This study 100–150 1–3 3–4 25–90 1500–1530 12–15 Literature 10a 17a; 9.2b 100a; 196b 1500a 350a; <40b; 22c Eagle Station This study 92–380 1–15 1–6 13–150 1880–2370 33–74 Literature 35d 211 ± 18e 1250d 33–43c; 55d Glorieta Mountain This study 48–108 4–15 5–8 54–118 2290–2800 25–46 Literature 430 ± 10e 75–500d Imilac This study 43–90 7–25 3–8 42–173 1585–2445 7–20 Literature 28–35c Springwater This study 65–193 1–6 4–6 30–144 3400–3750 27–50 Literature 20d; 980 ± 10f; 10a; 6g; 40i; 10a; 10g; 23i;100a; 184 ± 8e; 2000a; 2300d; 350a; 28–34c; 32g; 64h; 2.2–5.8j 193 ± 16f; 185g; 3000 ± 30f; 50d; 97 ± 10f; 22–195j 140h; 270i; 3175g; 2750h; 26g; 110i 340–490j 2600i; 2630–2970j aLovering 1957. bMittlefehldt 1980. cReed et al. 1979. dBuseck and Goldstein 1969. eGoles 1971. fNichiporuk et al. 1967. gLeitch et al. 1979. hZhou and Steele 1993. iMason and Graham 1970. jFloss 2002. fluorescence is 980 ppm (Nichiporuk et al. 1967), much analyses of minor element contents in pallasite olivines are higher than in situ measurements (20, 32, 64 ppm) by Buseck broadly in line with the previously reported results. and Goldstein (1969), Leitch et al. (1979), and Zhou and Steele (1993). The same is true for Ni concentration, for Chemical Zoning in Olivine: Diffusion and Thermal which the bulk analyses (97, 110, and 350 ppm) are higher Histories of Pallasites than the probe analyses (26, 28–34, 50 ppm). On the other hand, in situ analysis, such as electron microprobe, suffers In this study, I observed widespread minor element low detection limits and X-ray fluorescence effect from zoning in pallasite olivine (Fig. 2). With the high sensitivity adjacent phases. An electron probe has the detectability limits of the ion microprobe, I am able to reveal, on a microscale, of 15, 10, and 20 ppm for Ca, Ti, and Ni, respectively, with the chemical zoning of minor elements (e.g., Ti, V) with very large precision errors from 20% to 100% (Buseck and low concentrations (~10 ppm). My results are basically Goldstein 1969). With its high sensitivity, ion microprobe consistent with the previous reports (Leitch et al. 1979; Reed overcomes these difficulties and yielded consistent results for et al. 1979; Zhou and Steele 1993; Miyamoto 1997). The pallasite olivines (Leitch et al. 1979; Reed et al. 1979). In origin of the zoning is intimately tied with the origin of the Springwater olivine, the ion probe analyses of Ni are 26 and olivine itself and the process or processes by which it was 28–34 ppm, respectively, by Leitch et al. (1979) and Reed et incorporated into the metal. Olivine is completely solid below al. (1979). My results range from 27 to 50 ppm. They are in 1600–1700°C, well above the temperature of metal excellent agreement. Small variations could be due to either solidification, which is ~1500 to ~1000°C depending on the the inter-grain concentration variations or the crystal sulfur content (Hansen and Anderko 1958). Thus, most orientation and cross section position, as pallasite olivines workers believe that pallasites formed when molten metal commonly display minor element zoning. My ion probe intruded a crystalline olivine layer, although their models Minor element zoning and trace element geochemistry of pallasites 1227 differ in detail (e.g., Scott 1977a, b; Buseck 1977; because grain boundary diffusion is known to be orders of Mittlefehldt 1980; Scott and Taylor 1990). At the time of magnitude faster than diffusion within a crystal (e.g., Freer metal intrusion, the chemical composition of the olivine 1981). Sinks would, thus, appear to be available for all of the would have reflected its previous igneous history. elements depending on where they appeared in the The observed chemical zoning is almost certainly not crystallization sequence, including in the subsolidus. The original igneous zoning. For example, the distribution outward decrease of Cr may reflect diffusion from olivine to coefficient for Ca in olivine relative to silicate melts is chromite and troilite. The depletions of Ca and Ti at olivine considerably less than unity (e.g., Jurewicz and Watson grain boundaries indicate migration to phosphates and 1988a), which implies that the melt should increase in Ca chromite/rutile, respectively. The zoning profile of V may content as it crystallizes olivine. Thus, one would expect the suggest its siderophile nature under reducing conditions Ca concentration in olivine to increase as the melt (Drake et al. 1989) or diffusion to chromite. Mn concentration crystallized, producing a profile of increasing concentration sometimes increases at the very edge of the crystals. This toward the crystal edge. I observe a decrease in Ca probably reflects the strong decrease in compatibility of Mn concentration from center to edge in all pallasite olivines in the metal phase with decreasing temperature coupled with (Fig. 2). Also, Hirschmann and Ghiorso (1994) have shown the freezing in of the Mn concentration profile at low that the distribution coefficients of Ni, Mn, and Co in olivine temperature. relative to silicate melts increase with decreasing temperature Cation diffusion in olivine was studied experimentally at constant composition and, independently, with decreasing under various physical conditions (e.g., temperature and MgO content in the liquid. Thus, concentrations of Ni, Mn, oxygen fugacity) (Morioka 1981; Jurewicz and Watson and Co would be expected to increase toward the edges of the 1988b; Hain et al. 1996). Olivine was found to be anisotropic crystals. In contrast, I observe the concentration of Ni to with respect to the diffusion of Ca, Fe, Mg, and Mn, i.e., decrease toward the edges of the crystals, while the Mn fastest along the c-axis and slowest along the a-axis. concentration remains essentially constant (e.g., Fig. 2). In Therefore, the diffusion-induced chemical zoning in olivine addition, diffusion rates for the elements in this study at in a random section should be smaller than that along the c- 1000–1500°C, which is the temperature range of molten iron, axis but larger than that along the a-axis. As expected, I are too high to preserve unmodified igneous profiles in the observed in this study that the degrees of minor element olivine grains for more than a few days to a few weeks (e.g., zoning (e.g., Ca and Cr) vary from grain to grain, from Jurewicz and Watson 1988b). Thus, the zoning profiles extensive to moderate zoning. It was found that, at a given probably developed by solid-state diffusion during cooling, as temperature in olivine, the diffusion rates decrease assumed by several previous workers (e.g., Leitch et al. 1979; significantly in the order of Fe, Mn, Co, Ni, Mg, and Ca Reed et al. 1979; Zhou and Steele 1993). (Morioka 1981). Cations (e.g., Mn) with higher diffusion A first-order test of the diffusion hypothesis is to invert rates more easily establish equilibrium between olivine and the concentration profiles through the error function. When the receptors than those with lower rates (e.g., Ca). My results inverted through the error function, profiles that were are basically consistent with this conclusion. Mn is essentially produced by diffusion should plot as linear functions of unzoned, while Ca and Cr exhibit ubiquitous zoning in distance from the crystal boundary. The current data do not pallasite olivines. Other elements such as Ni and V behave permit quantitative evaluation of diffusion hypothesis intermediately, sometimes zoned and sometimes unzoned. because measurements were made on random slices through Further, note that in a given meteorite (e.g., Albin), the the crystals, not through the centers, and because the initial maximum concentrations of Ca and Cr at the center of olivine concentrations of the elements in the crystals are unknown at vary widely but Mn concentration is essentially the same. present. I now consider whether the observed zoning profiles This indicates that Mn was fully equilibrated between olivine are consistent with diffusion during cooling after the intrusion and the receptors and that Ca and Cr were not, during sub- of molten iron into a previously crystallized olivine layer. solidus cooling periods. Most of the elements, except for Mn, have lower Previous studies (Davis 1977; Scott 1977a) of olivine concentrations at the surface of the olivine grains, consistent chemistry and Ni content in metal showed that pallasites can with loss of the elements to other phases. Ni is highly be divided into 2 sub-groups: main group (e.g., Albin, siderophile and is expected to concentrate in metal over Brenham, Glorieta Mountain, Imilac) and Eagle Station trio silicates. However, the other elements do not partition (e.g., Eagle Station). In this study, I found that Springwater preferentially into the metal. Pallasites contain several minor olivine has higher (~3500 ppm) and Brenham olivine has phases that could serve as sinks for the elements lost from the lower Mn concentrations (~1500 ppm) than those of Albin, olivine. Chromite, troilite, and phosphates are common, and Glorieta Mountain, and Imilac (~2300 ppm). This further traces of rutile and low-Ca pyroxene are also observed (e.g., suggests that Springwater and Brenham may be anomalous Buseck 1977). These phases are often not in direct contact and do not fit in the main group pallasites (Davis 1977; Scott with the measured olivines, but this may not be necessary 1977a). 1228 W. Hsu

In principle, diffusion-induced chemical zoning in suggests that these meteorites formed very early, probably silicates potentially provides constraints on their thermal within the first 10 Ma of the solar system history. The Re-Os histories. Because of the difficulties mentioned above, my chronology of pallasites (4.60 ± 0.05 AE) further supports data do not permit a quantitative estimation of cooling rates this suggestion (Shen et al. 1998). The mean life of 53Mn is for pallasites. In addition, the cooling rate calculation is very 5.3 Ma. Thus, if 53Mn were alive when the molten iron was sensitive to the initial temperature (To) and the parameters for intruded, the cooling would have been fast enough to preserve the diffusion coefficient (Do) and activation energy of the evidence in the olivines. This also implies that pallasites diffusion (E) in the Arrhenius relation: D = Doexp(−E/RT). cooled rapidly down to the Mn-Cr closure temperature shortly Inspection of the literature shows that there are serious after the pallasite formation. discrepancies between experimental studies (Morioka 1981; The inferred cooling rate at high temperatures is much Jurewicz and Watson 1988b; Hain et al. 1996). In particular, faster than the metallographic cooling rates (0.5–2.0°C/Ma) the extrapolation to low temperatures is very unreliable. obtained in pallasite Fe-Ni alloys. Such a fast cooling rate is However, the determination of (D) at individual elevated required to prevent immiscible separation of the metal phase temperatures appears to be more reliable. If one takes the from olivines due to their large contrast in density. Despite the result for Ni (4.7 × 10−13 cm2 sec−1) at 1200°C from Morioka uncertainties in calculated cooling rates, a general consensus (1981), then one estimates that the maximum time that an exists that pallasites cooled much faster at high temperatures olivine of 1 mm could remain at that temperature and not than at low temperatures, by several orders of magnitude. completely equilibrate Ni with the metal is ~170 yr. I noted in However, the nature of transition from a rapid cooling at high this study that the maximum concentrations of some minor temperatures to a very slow cooling at low temperatures is not elements at the center of olivine vary significantly from grain clear. It could be smooth or, more likely, mark a catastrophic to grain within a given meteorite and among the pallasites event. Thus, pallasites, like mesosiderites (Stewart et al. studied. For example, the maximum concentration of Ca at 1994), seem to have experienced rather complicated thermal the core of Albin olivine ranges from 25 to 70 ppm, much histories involving very rapid cooling at high temperatures lower than that (180 to 380 ppm) in Eagle Station olivine. and slow cooling at low temperatures. Such large variations require that the initial Ca concentration in pallasite olivines be highly heterogeneous and that the REE Distributions in Pallasites olivines have experienced rapid cooling after mixing with molten metal. For an olivine grain of 300 to 500 µm, Pallasite olivines probably have the lowest REE comparable to those of Albin, the homogenization time for Ca abundances among meteoritic and terrestrial olivines. A is less than 4 yr at 1300°C and less than 8 yr at 1100°C recent study indicated that pallasite olivines have extremely (Jurewicz and Watson 1988b). To preserve the Ca zoning and low REEs (10−5 to 10−2 × CI; Minowa and Ebihara 2002). Ion the large variation of maximum concentrations among the probe analyses showed that pallasite olivines have very low different grains, Albin olivine had cooled from 1300 to REEs that are below the detection limit (Davis and Olsen 1100°C within less than 4 yr, which is equivalent to a cooling 1991; this study). rate of >50°C/year. In evaluating the equilibration REE concentrations of pallasite phosphates were temperature for Ni between olivine and metal, Scott (1977a) previously determined by Davis and Olsen (1991, 1996) with and Reed et al. (1979) noted a wide range of apparent metal- an ion probe. They found that phosphates have large olivine equilibrium temperatures (800–1200°C) among variations of REE abundances (0.01 to 300 × CI) and display pallasites. If pallasites cooled very slowly at the rates distinct REE patterns, ranging from highly HREE-enriched to equivalent to the metallographic cooling rates (0.5–2.0°C/ LREE-enriched. In this study, I also observed that pallasite Ma) obtained in pallasite Fe-Ni alloys, Ni would be fully phosphates have large variations of REEs (0.001 to 100 × CI) equilibrated between olivine and metal, and a unique with different REE patterns (Fig. 4). Within a given equilibration temperature should be expected for all phosphate grain, REEs are generally homogeneous. REEs of pallasites. Scott (1977a) then suggested that Ni phosphate may vary from grain to grain within the same concentrations in the olivines may have been established meteorite by a factor of 10 to 100. Basically, the phosphates before metal-olivine mixing and preserved by rapid cooling analyzed in this study have an HREE-enriched pattern with down to ~800°C. Evidence for fast cooling at high either a negative or a positive Eu anomaly (Fig. 4). But, the temperatures was also provided by Miyamoto (1997). He phosphate with an LREE-enriched pattern, as reported by noted that the major and minor element zoning profiles in Davis and Olsen (1991, 1996), was not observed. pallasite olivines could be understood if they experienced fast The REE abundances and patterns of pallasite cooling (20 to 100°C/yr) through 1100 to 600°C. phosphates potentially shed light on the process or processes Evidence for the presence of live 53Mn (Birck and that led to the formation of pallasite. Davis and Olsen (1991) Allègre 1988; Hsu et al. 1997; Lugmair and Shukolyukov suggested that the HREE-enriched pattern in phosphates is 1998) and 107Pd (Chen and Wasserburg 1996) in pallasites compatible with formation of this mineral by subsolidus Minor element zoning and trace element geochemistry of pallasites 1229 redox reactions between Fe-metal and olivine. Phosphorus rates than Ca at a given temperature. Yet, this mineral from schreibersite and iron metal could have been oxidized by displays extensive and ubiquitous Ca zoning among all the oxygen originally dissolved in molten metal and incorporated pallasites studied. This indicates that Ca did not diffuse fast with Ca, Mg, and Fe from olivine to form whitlockite, enough in pallasite olivine to fully equilibrate with other stanfieldite, and farringtonite (Olsen and Fredriksson 1966; phases such as phosphate. It follows that REEs would not Davis and Olsen 1991). In this case, phosphates would have reached equilibrium partitioning between olivine and concentrate REEs from olivine and inherit its REE pattern. phosphates under subsolidus conditions. The diffusion of Davis and Olsen (1991, 1996) also found that stanfieldite and REEs from olivine to phosphates would be negligible. whitlockite in Springwater and Santa Rosalia are highly Phosphates produced in situ by redox reactions between enriched in REEs (10 to 300 × CI) with an LREE-enriched metal and olivine would be virtually free of REEs. However, pattern. This type of pattern is expected from REE it is possible that pre-existing phosphates could have equilibrium partitioning between phosphates and silicate participated in the redox reaction. In this case, REE melts. However, the pallasite parent body mantle probably did abundances of the phosphate would be diluted, but the not have enough phosphorus to crystallize phosphates when pattern would remain the same. Even if one assumes that cumulate olivine formed (Davis and Olsen 1991). Davis and REEs have much higher diffusion rates than Ca, so that REEs Olsen (1991) argued that the phosphates could have were well-equilibrated between olivine and phosphates under crystallized from a trapped liquid interstitial between these conditions, it is still hard to explain how pallasite cumulate olivines. The second alternative is that these phosphates can have large inter-grain variations of REE phosphates represent the late-stage products of crystallization abundances with significantly different patterns. One would from a silicate melt of high density and low viscosity on expect to see that all pallasite phosphates have the same REE pallasite parent bodies (Davis and Olsen 1991). This liquid concentrations with an identical pattern. The same arguments could percolate downward but not as deep as the core-mantle can be made for the liquidus conditions. boundary. This suggestion requires that pallasites formed I now consider whether pallasite phosphates could have much nearer the surface than the core-mantle boundary on crystallized from a trapped liquid remaining from olivine their parent bodies. formation. If olivine crystallized from a melt with chondritic In pallasites, the main REE source is olivine. If all REE abundances, the residual liquid would be rich in REEs phosphates were produced in situ by redox reactions between with a relatively flat but slightly LREE-enriched pattern. iron metal and olivine, they are expected to have relatively Phosphate grows from the liquid would be rich in REEs with low REE concentrations with an HREE-enriched pattern. The a relatively LREE-enriched pattern. This kind of phosphate calculation by Davis and Olsen (1991) seemed to match the was not observed in this study. Most pallasite phosphates REE abundances and pattern observed in Eagle Station have an HREE-enriched pattern. Davis and Olsen (1991) whitlockite. Davis and Olsen (1991) noted that REE reported that some Springwater and Santa Rosalia phosphates partitioning between 1.2 vol% whitlockite and 98.8 vol% have high REE concentrations with an LREE-enriched olivine would result in relatively low REEs (0.1 to 10 × CI) in pattern. Thus, a small amount of pallasite phosphates likely whitlockite with an HREE-enriched pattern. In their could have crystallized from a trapped liquid interstitial calculation, Davis and Olsen (1991) assumed that REE between olivine grains. But, such a mechanism is not partitioning between phosphate and olivine was fully responsible for the formation of the majority of the pallasite equilibrated under subsolidus conditions. I consider this phosphates. assumption to be fundamentally flawed, and the mechanism The metallic phase of pallasites is chemically related to proposed by Davis and Olsen (1991) to explain the REE IIIAB irons. It was even suggested that pallasites might have patterns observed in pallasite phosphates is implausible. formed through the mixing of IIIAB-like molten metal with an To see if REEs were completely equilibrated between olivine layer (Scott 1977a, b). IIIAB irons commonly contain phosphate and olivine during redox reactions, one has to small amounts of phosphates, such as sarcopside and graftonite consider the diffusion rates of REEs in olivine under ([Fe,Mn]3[PO4]2), johnsomervilleite (Na2Ca[Fe,Mn]7[PO4]6), subsolidus conditions. However, up to this date, these and galileiite (Na2[Fe,Mn]8[PO4]6) (Olsen and Fredriksson diffusion rates are largely unknown. A related study of self- 1966; Davis and Olsen 1990; Olsen et al. 1999). It is possible diffusion in haplobasaltic melts revealed that REEs have that phosphates were introduced into pallasites during mixing much lower diffusion rates than Mg and Ca over a and were subsequently involved in liquidus or subsolidus temperature range of 1350 to 1500°C (LaTourrette et al. redox reactions between olivine and phosphorus from metal to 1996). A general observation was also made that, at a given form pallasitic phosphates. In this case, pallasite phosphates temperature, a systematic, order of magnitude decrease would inherit the REE patterns of IIIAB-like phosphates. occurs in diffusion rates with both increasing ionic radius and Davis and Olsen (1990) found that 4 phosphate grains in El increasing cation charge. If this were true for olivine, one Sampal (IIIA) have low but variable REE abundances (0.1 to would expect that REEs would have much lower diffusion 2 × CI) with an LREE-enriched pattern and a large positive Eu 1230 W. Hsu anomaly (Eu/Eu* up to ~50). Most phosphates in IIIAB irons group of stony-iron meteorites consisting of roughly equal have relatively low REE concentrations (0.1 to 10 × CI) with amounts of Fe-metal and a silicate fraction rich in a flat pattern (Olsen et al. 1999). These REE patterns are orthopyroxene and plagioclase (Powell 1969, 1971). These apparently different from those of pallasite phosphates. This meteorites appear to have cooled very slowly (~0.1°C/Ma) at implies that either the analyses of IIIAB phosphates are so low temperatures (500 to 350°C), based on a metallographic limited that they are not fully sampled or the metallic phase of study (Powell 1969). However, the steep Fe-Mg diffusion pallasites is distinctly different from IIIAB irons and contains zoning profiles in mesosiderite pyroxenes suggest that they different types of phosphates. In general, the diversity of REE cooled very rapidly (≥100°C/year) at high temperatures abundances and patterns in pallasite phosphates can be well (>900°C) (Delaney et al. 1981; Jones 1983; Ganguly et al. understood in the view of a mixing model. Pallasite phosphates 1994). Stewart et al. (1994) proposed a model to account for were incorporated into pallasites from IIIAB-like molten metal the observed Sm-Nd ages and thermal histories of during mixing with an olivine layer. Once mixed, phosphate mesosiderites. A mass of molten Fe-metal impacted onto the grains remained isolated from one another during the regolith of a differentiated parent body 100 to 150 Ma after subsequent rapid cooling period. Each phosphate grain would the formation of the solar system. Mixing of molten Fe-metal have distinctive REE abundances and patterns that reflect with the regolith followed by rapid cooling produced olivine characteristics of a previous history. coronas and pyroxene overgrowths by the heat from molten Fe and the impact. The body was covered subsequently by a Pallasite Formation new layer of regolith, heated to ~700°C, and buried to a depth of ~3 km during a second impact event. The Widmanstätten Despite the simplicity of the mineralogy, the origin of structures were established during the subsequent slow pallasites has remained largely controversial (Anders 1964; cooling process. Buseck and Goldstein 1969; Scott and Taylor 1990). Pallasite formation must differ significantly from Models proposed for pallasite formation generally fall into mesosiderite formation even though both meteorites seem to the categories of igneous differentiation near the surface of have experienced similar thermal histories. Pallasite olivines chondritic parent bodies (Urey 1956; Mittlefehldt 1980) or could have formed as cumulates through fractional mixing of the mantle olivine with the core metal at or below crystallization from silicate melts or as residues by extensive the mantle-core interface (Mason 1962, 1963; Anders partial melting of chondritic material. Olivines produced this 1964). way would have been in equilibrium with silicate melts. The The mineralogy and slow metallographic cooling rates melts solidified and produced differentiated materials above support a core-mantle origin for pallasites. In a chondritic the olivine zone. Molten iron was later injected into the cooler magma, density differences will result in the separation of olivine zone, either during breakdown of the parent body by iron metal from the silicate melt to form a planetary core. An collision or during impact by a molten iron core from the olivine similar to pallasitic olivines, then, would be the first impacting body. Some of the olivines were brecciated. Rapid mineral to crystallize from the silicate melt. In this model, cooling prevented separation of the olivine from metal and pallasites would originate from a layer or interface where the formed pallasites. Upon cooling, minor element thermal core metal and the lower mantle silicate are mixed. Such a diffusion occurred and produced zoning profiles in the layer is assumed to be deep in the interior of asteroids, olivine. The system continued to cool down to the Mn-Cr allowing pallasites to cool very slowly, as indicated by the closure temperature within 10 Ma after CAI formation. The Widmanstätten structures in Fe-Ni alloys. However, pallasites were covered subsequently by a new layer of fragmented and angular olivines are not predicted by such a regolith produced during secondary impact events, slowing model. In addition, the observed Ni profiles show a clear the cooling at low temperatures and allowing the maximum in the center of olivine grains in several pallasites Widmanstätten structures observed in the pallasite metal to (e.g., Brenham, Eagle Station, Springwater; Leitch et al. develop. 1979; Reed et al. 1979; this study), precluding a long history at high temperatures. Pallasite olivines could not come from a Acknowledgments–Many thanks to the Smithsonian boundary between a Fe-Ni core and a silicate mantle, as Ni Institution for the loan of the samples used in this study. The would have fully equilibrated between olivine and metal author is grateful to C. Floss, M. Miyamoto, and I. Lyon for under such conditions. The olivines must have been produced their thorough and constructive reviews. He also by an independent mechanism and then be immersed in or acknowledges the support by the “One hundred talent intruded by a molten iron body. program” from the Chinese Academy of Sciences and by As mentioned above, pallasites probably cooled rapidly NASA grant NAGW-3297 (GJW). at high temperatures. This is inconsistent with pallasite origin at the mantle-core boundary but indicates thermal histories Editorial Handling—Dr. Ian Lyon similar to those of mesosiderites. Mesosiderites are another Minor element zoning and trace element geochemistry of pallasites 1231

REFERENCES Hsu W., Huss G. R., and Wasserburg G. J. 1997. Mn-Cr systematics of differentiated meteorites. 28th Lunar and Planetary Science Anders E. 1964. Origin, age, and composition of meteorites. Space Conference. pp. 609–610. Science Reviews 3:583–714. Hutcheon I. D. and Olsen E. 1991. Cr isotopic composition of Birck J. L. and Allègre C. J. 1988. Manganese-chromium isotope differentiated meteorites: A search for 53Mn. 22nd Lunar and systematics and the development of the early solar system. Planetary Science Conference. pp. 605–606. Nature 331:579– 584. Jones J. H. 1983. Mesosiderites: (1) Reevaluation of cooling rates and Buseck P. R. 1977. Pallasite meteorites—Mineralogy, petrology, and (2) experimental results bearing on the origin of metal. 14th geochemistry. Geochimica et Cosmochimica Acta 41:711–740. Lunar and Planetary Science Conference. pp. 351–352. Buseck P. R. and Goldstein J. I. 1969. Olivine compositions and Jurewicz A. J. G. and Watson E. B. 1988a. Cations in olivine, Part 1: cooling rates of pallasitic meteorites. Geological Society of Calcium partitioning and calcium-magnesium distribution America Bulletin 80:2141–2158. between olivines and coexisting melts, with petrologic Buseck P. R. and Holdsworth E. 1977. Phosphate minerals in pallasite applications. Contributions to Mineralogy and Petrology 99: meteorites. Mineralogical Magazine 41:91–102. 178–185. Chen J. H. and Wasserburg G. J. 1996. Live 107Pd in the early solar Jurewicz A. J. G. and Watson E. B. 1988b. Cations in olivine, Part 2: system and implications for planetary evolution. In Earth Diffusion in olivine xenocrysts, with applications to petrology processes: Reading the isotopic code, edited by Basu A. R. and and mineral physics. Contributions to Mineralogy and Petrology Hart S. R. Geophysical Monograph 95. Washington D.C.: 99:186–201. American Geophysical Union. pp. 1–20. LaTourrette T., Wasserburg G. J., and Fahey A. J. 1996. Self diffusion Delaney J. S., Nehru C. E., Prinz M., and Harlow G. E. 1981. of Mg, Ca, Ba, Nd, Yb, Ti, Zr, and U in haplobasaltic melt. Metamorphism in mesosiderites. Proceedings, 12th Lunar and Geochimica et Cosmochimica Acta 60:1329–1340. Planetary Science Conference. pp. 1315–1342. Leitch C. A., Steele I. M., Hutcheon I. D., and Smith J. V. 1979. Davis A. M. 1977. The cosmochemical history of the pallasites. Minor elements in pallasites: Zoning in Springwater olivine. 10th Ph.D. dissertation, Yale University, New Haven, Connecticut, Lunar and Planetary Science Conference. pp. 716–718. USA. 285 p. Lovering J. F. 1957. Pressure and temperatures within a typical parent Davis A. M. and Olsen E. J. 1990. Phosphates in the El Sampal IIIA meteorite body. Geochimica et Cosmochimica Acta 12:253–261. iron meteorite have excess 53Cr and primordial lead. 21st Lunar Lugmair G. W. and Shukolyukov A. 1998. Early solar system and Planetary Science Conference. pp. 258–259. timescales according to 53Mn-53Cr systematics. Geochimica et Davis A. M. and Olsen E. J. 1991. Phosphates in pallasite meteorites Cosmochimica Acta 62:2863–2886. as probes of mantle processes in small planetary bodies. Nature Mason B. 1962. Meteorites. New York: Wiley. 274 p. 353:637–640. Mason B. 1963. The pallasites. American Museum Novitates 2163. Davis A. M. and Olsen E. J. 1996. REE patterns in pallasite Mason B. and Graham A. L. 1970. Minor and trace elements in phosphates—A window on mantle differentiation in parent meteoritic minerals. Smithsonian Contributions to Earth Science bodies. Meteoritics & Planetary Science 31:A34–A35. 3:1–17. Drake M. J., Newson H. E., and Capobianco C. J. 1989. V, Cr, and Mn Masuda A. 1968. Lanthanide concentrations in the olivine phase of in the earth, Moon, EPB, and SPB and the origin of the moon: the Brenham pallasite. Earth and Planetary Science Letters 5: Experimental studies. Geochimica et Cosmochimica Acta 53: 59–62. 2101–2111. Minowa H. and Ebihara M. 2002. Rare earth elements in pallasite Fahey A., Goswami J. N., McKeegan K. D., and Zinner E. 1987. 26Al, olivines (abstract #1386). 33rd Lunar and Planetary Science 244Pu, 50Ti, REE, and trace element abundances in hibonite grains Conference. CD-ROM. from CM and CV meteorites. Geochimica et Cosmochimica Acta Mittlefehldt D. W. 1980. The composition of mesosiderite olivine 51:329–350. clasts and implications for the origin of pallasites. Earth and Floss C. 2002. Queen Alexandra Range 93148: A new type of Planetary Science Letters 51:29–40. pyroxene pallasite? Meteoritics & Planetary Science 37:1129– Miyamoto M. 1997. Chemical zoning of olivine in several pallasites. 1139. Journal of Geophysical Research 102:21613–21618. Freer R. 1981. Diffusion in silicate minerals and glasses: A data Morioka M. 1981. Cation diffusion in olivine—II. Ni-Mg, Mn-Mg, digest and guide to the literature. Contributions to Mineralogy Mg and Ca. Geochimica et Cosmochimica Acta 45:1573–1580. and Petrology 76:440–454. Nichiporuk W., Chodos A., Helin E., and Brown H. 1967. Fricker P. E., Goldstein J. I., and Summers A. L. 1970. Cooling rates Determination of iron, nickel, cobalt, calcium, chromium and and thermal histories of iron and stony-iron meteorites. manganese in stony meteorites by X-ray fluorescence. Geochimica et Cosmochimica Acta 34:475–491. Geochimica et Cosmochimica Acta 31:1911–1930. Ganguly J., Yang H., and Ghose S. 1994. Thermal history of Olsen E. and Fredriksson K. 1966. Phosphates in iron and pallasite mesosiderites: Quantitative constraints from compositional meteorites. Geochimica et Cosmochimica Acta 30:459–470. zoning and Fe-Mg ordering in orthopyroxenes. Geochimica et Olsen E., Kracher A., Davis A. M., Steele I. M., Hutcheon I. D., and Cosmochimica Acta 58:2711–2723. Bunch T. E. 1999. The phosphates of IIIAB iron meteorites. Goles G. G. 1971. In Handbook of elemental abundances in meteorites, Meteoritics & Planetary Science 34:285–300. edited by Mason B. New York: Gordon & Breach. 555 p. Powell B. N. 1969. Petrology and chemistry of mesosiderites—I. Hain A., Stahl S., Specht S., Laqua W., and Palme H. 1996. Tracer Textures and composition of nickel-iron. Geochimica et diffusion of 42Ca in olivine. Terra Abstracts 8:25–26. Cosmochimica Acta 33:789–810. Hansen M. and Anderko K. 1958. Constitution of binary alloys. New Powell B. N. 1971. Petrology and chemistry of mesosiderites—II. York: McGraw Hill. 1305 p. Silicate textures and compositions and metal-silicate Hirschmann M. M. and Ghiorso M. S. 1994. Activities of nickel, relationships. Geochimica et Cosmochimica Acta 35:5–34. cobalt, and manganese silicates in magmatic liquids and Reed S. J. B., Scott E. R. D., and Long J. V. P. 1979. Ion microprobe applications to olivine/liquid and to silicate/metal partitioning. analysis of olivine in pallasite meteorites for nickel. Earth and Geochimica et Cosmochimica Acta 58:4109–4126. Planetary Science Letters 43:5–12. 1232 W. Hsu

Schmitt R. A., Smith R. H., and Olehy D. A. 1964. Rare-earth, Steele I. M. 1994. Chemical zoning and exsolution in olivine of the yttrium, and scandium abundances in meteoritic and terrestrial Pavlodar pallasite: Comparison with Springwater olivine. 25th matter—II. Geochimica et Cosmochimica Acta 28:67–86. Lunar and Planetary Science Conference. pp. 1335–1336. Scott E. R. D. 1977a. Pallasites-metal composition, classification and Stewart B. W., Papanastassiou D. A., and Wasserburg G. J. 1994. Sm- relationships with iron meteorites. Geochimica Cosmochimica Nd chronology and petrogenesis of mesosiderites. Geochimica et Acta 41:349–360. Cosmochimica Acta 58:3487–3509. Scott E. R. D. 1977b. Geochemical relationships between some Urey H. C. 1956. Diamonds, meteorites, and the origin of the solar pallasites and iron meteorites. Mineralogical Magazine 41:265– system. The Astrophysical Journal 124:623–637. 272. Zhou Y. and Steele I. M. 1993. Chemical zoning and diffusion of Ca, Scott E. R. D. and Taylor G. J. 1990. Origins of pallasites at the core- Al, Mn, and Cr in olivine of Springwater pallasite. 24th Lunar mantle boundaries of asteroids. 21st Lunar and Planetary Science and Planetary Science Conference. pp. 1573–1574. Conference. pp. 1119–1120. Zinner E. and Crozaz G. 1986. A method for the quantitative Shen J. J., Papanastassiou D. A., and Wasserburg G. J. 1998. Re-Os measurement of rare earth elements in the ion microprobe. systematics in pallasite and mesosiderite metal. Geochimica et International Journal of Mass Spectrometry and Ion Processes Cosmochimica Acta 62:2715–2723. 69:17–38.

APPENDIX

Table A1. Minor element spatial distributions (ppm) in pallasite olivine and its adjacent phases. The errors are 1σ from counting statistics only. Distance (µm) Ca Ti V Cr Mn Ni Albin olivine #1 Metal 15 25.8 ± 0.7 2.07 ± 0.15 3.92 ± 0.25 32.9 ± 0.6 2273 ± 23 15.1 ± 1.2 60 27.1 ± 0.9 2.31 ± 0.15 4.75 ± 0.25 47.4 ± 0.9 2281 ± 11 15.7 ± 1.9 100 26.4 ± 0.9 2.01 ± 0.13 4.71 ± 0.25 48.2 ± 0.6 2261 ± 9 14.7 ± 1.4 145 28.6 ± 1.0 1.74 ± 0.16 5.35 ± 0.25 50.5 ± 0.9 2268 ± 13 13.5 ± 1.5 190 29.8 ± 0.8 1.86 ± 0.14 4.96 ± 0.25 53.4 ± 0.8 2268 ± 11 14.9 ± 1.7 235 31.0 ± 0.9 2.93 ± 0.21 4.98 ± 0.24 63.4 ± 0.9 2284 ± 8 14.1 ± 1.4 280 30.5 ± 0.7 2.04 ± 0.11 5.04 ± 0.26 62.8 ± 1.0 2268 ± 9 15.1 ± 1.7 330 31.6 ± 0.8 3.65 ± 0.21 5.08 ± 0.26 74.2 ± 1.0 2253 ± 13 17.6 ± 1.7 375 32.6 ± 0.8 3.84 ± 0.21 4.85 ± 0.24 74.3 ± 0.9 2286 ± 8 13.0 ± 1.3 420 31.7 ± 0.8 2.67 ± 0.21 5.01 ± 0.26 69.2 ± 0.8 2261 ± 9 15.8 ± 1.2 465 31.1 ± 1.0 2.33 ± 0.18 4.89 ± 0.24 62.7 ± 0.9 2204 ± 92 15.4 ± 1.3 510 30.8 ± 0.8 2.17 ± 0.17 4.76 ± 0.22 61.1 ± 0.8 2272 ± 10 14.8 ± 1.3 555 31.4 ± 0.8 2.32 ± 0.16 5.12 ± 0.28 65.5 ± 1.0 2264 ± 11 15.8 ± 1.5 600 32.0 ± 1.0 1.94 ± 0.14 4.91 ± 0.24 63.9 ± 0.9 2265 ± 12 14.6 ± 1.4 645 30.7 ± 0.8 2.14 ± 0.13 4.92 ± 0.21 67.5 ± 0.8 2260 ± 11 14.0 ± 1.1 690 30.7 ± 0.7 3.09 ± 0.22 4.89 ± 0.24 65.6 ± 0.9 2259 ± 10 12.7 ± 1.4 735 31.3 ± 0.9 4.62 ± 0.23 4.98 ± 0.23 73.1 ± 1.0 2271 ± 9 13.8 ± 1.3 780 33.5 ± 0.9 6.98 ± 0.29 5.29 ± 0.25 89.3 ± 1.1 2272 ± 10 14.2 ± 1.7 825 34.5 ± 0.8 10.51 ± 0.36 5.32 ± 0.24 97.8 ± 1.1 2296 ± 11 16.6 ± 1.5 870 27.8 ± 0.9 2.68 ± 0.17 4.93 ± 0.17 50.2 ± 0.7 2275 ± 12 13.3 ± 1.4 920 30.0 ± 0.8 7.64 ± 0.24 4.73 ± 0.27 65.0 ± 0.8 2310 ± 11 15.2 ± 1.8 Metal Albin olivine #2 Metal 15 28.9 ± 1.0 4.93 ± 0.27 5.21 ± 0.25 58.0 ± 0.7 2365 ± 7 15.9 ± 1.3 45 25.9 ± 0.8 1.93 ± 0.11 4.94 ± 0.28 42.3 ± 0.8 2268 ± 11 11.0 ± 1.1 75 31.0 ± 0.7 6.93 ± 0.26 5.86 ± 0.25 82.2 ± 1.2 2277 ± 11 11.1 ± 1.4 105 30.9 ± 0.8 7.33 ± 0.29 6.20 ± 0.25 90.7 ± 1.0 2257 ± 8 20.7 ± 1.8 135 27.2 ± 0.7 1.64 ± 0.15 4.84 ± 0.26 46.0 ± 0.6 2248 ± 9 11.6 ± 1.3 165 27.5 ± 0.8 1.62 ± 0.13 4.73 ± 0.24 50.1 ± 0.9 2239 ± 9 13.3 ± 1.2 195 28.5 ± 0.7 1.80 ± 0.14 4.87 ± 0.25 54.9 ± 0.6 2242 ± 8 12.9 ± 1.5 225 29.1 ± 0.7 1.78 ± 0.09 4.52 ± 0.21 52.6 ± 0.8 2242 ± 11 10.1 ± 1.1 255 31.3 ± 0.7 4.11 ± 0.19 5.25 ± 0.20 74.9 ± 1.1 2242 ± 8 13.3 ± 1.3 285 59.3 ± 2.7 8.51 ± 0.26 5.97 ± 0.26 110.8 ± 1.4 2257 ± 15 12.4 ± 1.3 315 37.6 ± 1.0 9.59 ± 0.27 6.36 ± 0.21 128.7 ± 1.3 2255 ± 8 13.1 ± 1.7 Minor element zoning and trace element geochemistry of pallasites 1233

Table A1. Minor element spatial distributions (ppm) in pallasite olivine and its adjacent phases. The errors are 1σ from counting statistics only. Continued. Distance (µm) Ca Ti V Cr Mn Ni 345 37.2 ± 0.7 11.37 ± 0.41 6.27 ± 0.25 131.0 ± 1.2 2224 ± 11 12.3 ± 1.2 375 39.1 ± 0.9 11.32 ± 0.32 6.21 ± 0.32 134.3 ± 1.0 2232 ± 10 13.6 ± 1.2 405 36.4 ± 0.8 10.47 ± 0.40 6.54 ± 0.24 129.4 ± 1.2 2241 ± 10 11.1 ± 0.9 435 32.4 ± 0.9 3.63 ± 0.19 5.47 ± 0.22 79.5 ± 0.9 2231 ± 10 12.9 ± 1.3 465 32.1 ± 0.8 4.08 ± 0.20 5.60 ± 0.35 85.9 ± 1.2 2223 ± 10 13.5 ± 1.1 495 32.7 ± 0.8 3.75 ± 0.20 5.31 ± 0.17 79.5 ± 0.8 2239 ± 12 13.2 ± 1.2 525 32.8 ± 0.9 2.50 ± 0.16 4.91 ± 0.26 67.7 ± 0.8 2238 ± 9 16.2 ± 1.4 555 33.7 ± 0.9 4.47 ± 0.22 5.47 ± 0.23 91.7 ± 1.0 2248 ± 12 12.7 ± 1.0 585 32.9 ± 1.0 4.78 ± 0.29 5.63 ± 0.25 89.9 ± 1.3 2241 ± 11 14.9 ± 1.6 615 33.5 ± 0.8 4.11 ± 0.17 5.14 ± 0.29 86.2 ± 0.8 2236 ± 12 15.6 ± 1.2 645 34.5 ± 0.9 6.17 ± 0.38 5.46 ± 0.29 104.0 ± 1.2 2245 ± 11 13.8 ± 1.3 675 35.1 ± 1.0 6.52 ± 0.22 5.88 ± 0.26 106.0 ± 1.3 2238 ± 12 14.6 ± 1.4 705 34.8 ± 0.8 7.01 ± 0.29 5.38 ± 0.23 105.5 ± 1.3 2240 ± 10 13.6 ± 1.1 735 34.5 ± 0.8 6.28 ± 0.28 5.56 ± 0.25 95.8 ± 1.1 2239 ± 11 11.2 ± 1.2 765 35.8 ± 0.7 7.23 ± 0.29 5.79 ± 0.25 112.4 ± 1.1 2271 ± 15 15.4 ± 1.4 795 34.7 ± 0.9 4.75 ± 0.23 5.27 ± 0.27 87.4 ± 1.0 2250 ± 10 14.7 ± 1.2 825 33.5 ± 0.8 3.35 ± 0.17 5.07 ± 0.13 71.1 ± 1.1 2239 ± 13 16.8 ± 1.5 855 34.4 ± 0.9 5.02 ± 0.29 5.65 ± 0.27 91.7 ± 0.9 2245 ± 8 14.2 ± 1.1 885 33.6 ± 0.9 4.88 ± 0.20 5.15 ± 0.16 87.7 ± 0.8 2227 ± 11 17.7 ± 1.7 915 31.8 ± 0.8 3.91 ± 0.19 5.18 ± 0.23 74.1 ± 0.9 2237 ± 9 13.2 ± 1.5 945 35.9 ± 1.4 5.35 ± 0.23 5.26 ± 0.24 88.4 ± 0.9 2203 ± 10 12.2 ± 1.4 975 35.2 ± 1.0 9.81 ± 0.30 6.06 ± 0.27 120.6 ± 1.7 2232 ± 10 14.1 ± 1.4 1005 30.5 ± 1.2 6.05 ± 0.30 5.42 ± 0.34 85.7 ± 1.2 2028 ± 22 11.5 ± 1.5 1035 17.8 ± 1.1 2.76 ± 0.16 3.16 ± 0.23 42.1 ± 1.4 1045 ± 46 7.4 ± 1.1 1065 22.9 ± 1.3 3.09 ± 0.34 4.17 ± 0.31 56.6 ± 4.2 1682 ± 135 9.3 ± 1.3 1095 28.4 ± 0.9 2.29 ± 0.21 4.95 ± 0.23 53.2 ± 0.7 2236 ± 9 11.4 ± 1.4 1125 31.3 ± 0.7 4.57 ± 0.30 4.93 ± 0.25 70.2 ± 0.9 2234 ± 11 13.7 ± 1.2 1155 31.5 ± 0.8 4.78 ± 0.28 5.24 ± 0.22 70.7 ± 1.0 2258 ± 9 14.8 ± 1.6 1185 29.9 ± 1.0 2.22 ± 0.20 4.47 ± 0.26 45.4 ± 0.6 2244 ± 7 11.8 ± 1.1 1215 28.5 ± 0.7 3.59 ± 0.18 5.06 ± 0.25 51.6 ± 0.7 2289 ± 13 12.6 ± 1.3 Metal Albin olivine #3 FeS 17.5 32.8 ± 2.0 3.94 ± 0.22 4.50 ± 0.30 44.5 ± 0.8 2401 ± 17 12.2 ± 1.1 38.5 32.8 ± 0.5 7.81 ± 0.30 5.36 ± 0.16 74.0 ± 1.2 2311 ± 9 11.9 ± 1.1 59.5 33.7 ± 0.6 9.58 ± 0.28 5.57 ± 0.25 86.9 ± 1.2 2306 ± 9 12.9 ± 1.2 80.5 33.7 ± 0.5 10.75 ± 0.32 5.90 ± 0.28 98.4 ± 0.9 2286 ± 8 10.9 ± 1.0 101.5 36.4 ± 0.7 8.94 ± 0.32 5.98 ± 0.23 88.0 ± 1.2 2296 ± 12 14.0 ± 1.5 122.5 40.2 ± 0.6 11.24 ± 0.31 6.41 ± 0.26 98.3 ± 0.8 2301 ± 12 15.1 ± 1.4 143.5 41.6 ± 0.5 12.94 ± 0.43 6.67 ± 0.26 115.5 ± 1.2 2308 ± 13 12.3 ± 1.2 164.5 44.6 ± 0.5 14.94 ± 0.40 6.93 ± 0.31 130.9 ± 1.3 2307 ± 12 11.2 ± 1.3 185.5 47.3 ± 0.6 15.96 ± 0.45 6.89 ± 0.25 140.9 ± 1.2 2307 ± 10 12.0 ± 1.5 206.5 47.9 ± 0.7 15.95 ± 0.38 7.48 ± 0.21 140.6 ± 1.3 2302 ± 10 15.1 ± 1.6 227.5 48.2 ± 0.5 17.52 ± 0.35 7.50 ± 0.33 148.2 ± 1.1 2305 ± 12 11.2 ± 1.5 248.5 50.2 ± 0.5 17.38 ± 0.49 7.67 ± 0.29 148.7 ± 1.4 2312 ± 11 14.6 ± 1.4 269.5 51.5 ± 0.5 18.62 ± 0.40 7.49 ± 0.32 157.3 ± 1.6 2323 ± 10 13.1 ± 1.2 290.5 51.6 ± 0.6 18.35 ± 0.54 7.55 ± 0.25 158.4 ± 1.4 2316 ± 11 14.8 ± 1.3 311.5 50.6 ± 0.4 17.71 ± 0.47 7.23 ± 0.26 153.5 ± 1.3 2311 ± 11 10.5 ± 0.9 332.5 50.1 ± 0.5 17.91 ± 0.32 7.27 ± 0.30 149.6 ± 1.5 2303 ± 10 13.1 ± 1.4 353.5 48.9 ± 0.6 15.90 ± 0.50 6.92 ± 0.31 139.4 ± 1.1 2302 ± 9 12.7 ± 1.5 374.5 45.0 ± 0.5 16.18 ± 0.43 7.17 ± 0.27 142.5 ± 1.7 2315 ± 11 12.8 ± 1.3 395.5 47.9 ± 0.6 16.88 ± 0.47 7.78 ± 0.27 144.4 ± 1.4 2312 ± 11 12.2 ± 1.2 413 47.8 ± 0.6 17.20 ± 0.37 7.23 ± 0.29 141.3 ± 1.2 2301 ± 9 10.3 ± 1.0 434 46.9 ± 0.6 16.09 ± 0.44 7.70 ± 0.21 140.4 ± 1.2 2288 ± 9 12.5 ± 1.1 455 46.0 ± 0.5 15.92 ± 0.47 7.16 ± 0.26 140.7 ± 1.1 2302 ± 10 14.3 ± 1.2 1234 W. Hsu

Table A1. Minor element spatial distributions (ppm) in pallasite olivine and its adjacent phases. The errors are 1σ from counting statistics only. Continued. Distance (µm) Ca Ti V Cr Mn Ni 476 43.3 ± 0.5 14.80 ± 0.46 6.85 ± 0.25 123.8 ± 0.8 2295 ± 11 11.8 ± 1.6 497 43.0 ± 0.7 14.77 ± 0.39 7.15 ± 0.30 132.2 ± 1.0 2300 ± 9 9.5 ± 1.1 518 41.1 ± 0.6 14.19 ± 0.39 6.73 ± 0.26 122.9 ± 1.1 2303 ± 11 11.0 ± 1.2 539 38.7 ± 0.6 13.46 ± 0.40 6.66 ± 0.32 113.9 ± 1.2 2316 ± 9 10.9 ± 1.2 560 34.4 ± 0.5 9.86 ± 0.32 5.93 ± 0.25 92.8 ± 1.1 2306 ± 9 12.2 ± 1.1 581 30.1 ± 0.8 3.93 ± 0.22 4.82 ± 0.24 50.5 ± 0.6 2299 ± 10 13.5 ± 1.4 602 24.6 ± 0.6 2.04 ± 0.15 4.58 ± 0.21 34.1 ± 0.6 2313 ± 11 20.0 ± 2.2 623 24.3 ± 0.6 2.09 ± 0.17 4.68 ± 0.16 35.4 ± 0.6 2402 ± 12 15.3 ± 1.3 FeS Albin olivine #4 Chromite 10.5 12.2 ± 0.4 0.69 ± 0.08 2.79 ± 0.30 16.5 ± 1.3 1140 ± 82 6.5 ± 1.0 35 22.7 ± 1.3 1.33 ± 0.15 5.36 ± 1.55 26.4 ± 0.5 2075 ± 19 13.0 ± 1.4 63 24.9 ± 0.7 1.74 ± 0.11 4.65 ± 0.22 34.1 ± 0.7 2277 ± 7 12.1 ± 1.1 91 24.7 ± 0.6 2.40 ± 0.17 4.49 ± 0.25 34.2 ± 0.6 2323 ± 9 9.5 ± 1.1 119 25.8 ± 0.8 1.97 ± 0.16 4.24 ± 0.21 33.9 ± 0.6 2352 ± 12 11.8 ± 1.2 147 24.5 ± 0.7 1.63 ± 0.14 4.10 ± 0.25 33.4 ± 0.6 2344 ± 9 10.0 ± 1.0 175 24.4 ± 0.6 1.69 ± 0.17 4.33 ± 0.20 32.6 ± 0.5 2325 ± 10 10.5 ± 1.2 199.5 23.5 ± 0.6 1.45 ± 0.14 4.41 ± 0.28 30.9 ± 0.5 2323 ± 11 12.8 ± 1.3 227.5 23.6 ± 0.7 1.39 ± 0.15 4.34 ± 0.21 33.7 ± 0.6 2345 ± 10 8.9 ± 1.0 252 24.6 ± 0.6 1.65 ± 0.09 4.81 ± 0.24 33.8 ± 0.6 2316 ± 8 11.1 ± 1.1 280 23.4 ± 0.6 1.39 ± 0.13 4.06 ± 0.21 31.7 ± 0.5 2348 ± 12 14.5 ± 1.6 308 22.5 ± 0.7 1.15 ± 0.12 4.64 ± 0.23 29.2 ± 0.6 2413 ± 9 11.8 ± 1.6 FeS Albin olivine #5 FeS 10.2 47.3 ± 2.2 3.53 ± 0.15 3.36 ± 0.18 41.0 ± 0.5 2169 ± 9 15.1 ± 1.2 51 46.2 ± 2.4 2.66 ± 0.17 3.48 ± 0.18 36.1 ± 0.6 2241 ± 8 20.3 ± 1.8 86.7 47.0 ± 2.3 2.78 ± 0.16 3.79 ± 0.16 39.9 ± 0.6 2268 ± 8 15.6 ± 1.6 117.3 48.7 ± 2.4 2.99 ± 0.16 3.57 ± 0.12 40.0 ± 0.5 2257 ± 8 14.6 ± 1.8 153 46.0 ± 2.4 2.29 ± 0.18 3.82 ± 0.19 36.7 ± 0.6 2274 ± 6 16.1 ± 1.5 183.6 51.6 ± 2.4 5.12 ± 0.18 4.05 ± 0.15 54.9 ± 0.6 2296 ± 7 16.8 ± 2.0 214.2 60.0 ± 2.3 8.74 ± 0.27 4.74 ± 0.17 88.8 ± 1.0 2303 ± 8 16.3 ± 1.5 249.9 61.2 ± 2.3 10.55 ± 0.23 4.67 ± 0.22 94.4 ± 0.9 2313 ± 8 14.3 ± 1.6 280.5 70.9 ± 2.6 11.56 ± 0.25 5.17 ± 0.21 107.0 ± 1.1 2342 ± 6 21.3 ± 2.0 311.1 67.9 ± 2.3 12.72 ± 0.33 4.89 ± 0.18 116.1 ± 0.9 2334 ± 8 13.0 ± 1.2 346.8 67.8 ± 2.3 13.96 ± 0.30 5.28 ± 0.22 120.4 ± 1.0 2328 ± 6 17.1 ± 1.7 377.4 68.2 ± 2.3 13.84 ± 0.26 5.43 ± 0.19 123.9 ± 1.0 2334 ± 8 18.6 ± 2.0 413.1 63.3 ± 2.5 12.83 ± 0.29 5.18 ± 0.14 114.2 ± 1.0 2349 ± 8 16.1 ± 1.7 443.7 47.8 ± 2.4 2.52 ± 0.17 3.59 ± 0.13 37.7 ± 0.7 2355 ± 7 17.4 ± 1.5 479.4 58.1 ± 1.3 3.70 ± 0.20 3.96 ± 0.16 42.9 ± 0.4 2359 ± 8 27.0 ± 2.0 FeS Albin olivine #6 Chromite 15 49.1 ± 2.2 3.63 ± 0.16 2.24 ± 0.11 31.5 ± 0.7 2200 ± 7 13.4 ± 1.1 38 50.0 ± 2.4 3.35 ± 0.15 3.24 ± 0.14 40.2 ± 0.7 2265 ± 6 22.0 ± 2.1 64 46.8 ± 2.2 2.63 ± 0.12 3.52 ± 0.16 41.8 ± 0.5 2280 ± 7 18.8 ± 1.4 89 47.6 ± 2.1 3.04 ± 0.14 3.37 ± 0.20 42.7 ± 0.7 2309 ± 7 17.2 ± 1.7 112 47.0 ± 2.0 2.75 ± 0.12 3.50 ± 0.16 42.1 ± 0.8 2305 ± 5 15.3 ± 1.3 140 48.1 ± 2.3 2.75 ± 0.12 3.65 ± 0.16 43.5 ± 0.7 2310 ± 7 16.4 ± 1.3 163 46.1 ± 2.0 2.38 ± 0.16 3.45 ± 0.14 43.6 ± 0.7 2318 ± 6 14.7 ± 1.5 191 46.6 ± 2.1 2.64 ± 0.17 3.34 ± 0.14 39.0 ± 0.7 2303 ± 8 17.6 ± 1.7 217 46.0 ± 1.9 3.03 ± 0.13 3.72 ± 0.20 45.9 ± 0.6 2319 ± 5 16.6 ± 1.5 240 496 ± 5.5 5.80 ± 0.23 3.62 ± 0.15 50.5 ± 0.7 2324 ± 6 17.7 ± 1.4 Minor element zoning and trace element geochemistry of pallasites 1235

Table A1. Minor element spatial distributions (ppm) in pallasite olivine and its adjacent phases. The errors are 1σ from counting statistics only. Continued. Distance (µm) Ca Ti V Cr Mn Ni 265 47.5 ± 2.1 3.04 ± 0.18 3.68 ± 0.16 45.8 ± 0.5 2320 ± 7 19.3 ± 1.8 291 45.5 ± 2.1 2.33 ± 0.12 3.51 ± 0.16 41.3 ± 0.7 2313 ± 6 17.9 ± 1.7 316 46.5 ± 2.0 2.55 ± 0.12 3.37 ± 0.15 43.1 ± 0.6 2327 ± 6 21.8 ± 2.1 342 46.4 ± 1.9 2.97 ± 0.11 3.55 ± 0.13 46.0 ± 0.5 2343 ± 8 21.0 ± 1.7 367 45.9 ± 2.2 2.55 ± 0.14 3.45 ± 0.13 43.8 ± 0.5 2336 ± 9 17.1 ± 1.3 393 47.6 ± 2.1 2.72 ± 0.12 3.32 ± 0.15 41.6 ± 0.6 2344 ± 5 17.9 ± 1.3 418 52.6 ± 2.2 3.19 ± 0.16 3.48 ± 0.15 42.2 ± 0.6 2360 ± 7 17.5 ± 1.5 444 55.8 ± 2.4 2.76 ± 0.13 3.11 ± 0.12 40.8 ± 0.7 2341 ± 9 18.1 ± 1.5 467 53.6 ± 2.5 4.00 ± 0.16 3.54 ± 0.16 48.2 ± 0.5 2358 ± 6 20.6 ± 1.8 490 62.3 ± 1.3 3.05 ± 0.14 3.12 ± 0.15 35.6 ± 0.5 2466 ± 7 69.5 ± 4.8 Metal Brenham olivine #1 Metal 3 99 ± 8 1.02 ± 0.14 3.95 ± 0.22 42.2 ± 0.6 1507 ± 9 12.3 ± 1.3 103 134 ± 11 1.69 ± 0.14 3.62 ± 0.22 50.5 ± 1.0 1500 ± 9 13.8 ± 1.4 203 154 ± 12 2.40 ± 0.14 4.29 ± 0.20 64.4 ± 1.0 1527 ± 6 13.4 ± 1.5 303 154 ± 11 2.91 ± 0.18 3.89 ± 0.21 73.9 ± 0.9 1525 ± 6 13.2 ± 1.2 403 159 ± 12 2.56 ± 0.19 3.97 ± 0.27 80.1 ± 1.1 1529 ± 8 13.7 ± 1.2 503 161 ± 13 2.57 ± 0.18 4.13 ± 0.20 78.8 ± 0.9 1501 ± 13 11.5 ± 1.1 603 147 ± 8 2.77 ± 0.11 4.42 ± 0.20 78.5 ± 1.3 1471 ± 20 12.7 ± 1.2 703 179 ± 13 2.50 ± 0.18 4.36 ± 0.21 83.8 ± 0.9 1541 ± 7 13.1 ± 1.8 803 168 ± 12 2.80 ± 0.18 4.17 ± 0.19 86.9 ± 1.1 1537 ± 7 16.9 ± 1.8 903 180 ± 13 2.44 ± 0.21 4.08 ± 0.18 88.6 ± 0.8 1530 ± 6 14.7 ± 1.5 1003 164 ± 13 2.60 ± 0.20 4.32 ± 0.20 89.2 ± 1.2 1537 ± 5 19.0 ± 1.4 1103 154 ± 11 2.42 ± 0.22 4.06 ± 0.18 84.5 ± 1.1 1533 ± 6 14.8 ± 1.3 1203 120 ± 8 1.79 ± 0.19 4.12 ± 0.20 85.1 ± 1.0 1535 ± 8 29.1 ± 2.2 1303 110 ± 8 1.48 ± 0.13 4.10 ± 0.15 86.9 ± 0.9 1527 ± 5 66.9 ± 5.7 1403 90 ± 6 1.66 ± 0.11 3.91 ± 0.15 86.8 ± 1.0 1526 ± 5 66.3 ± 4.9 1503 107 ± 8 1.63 ± 0.12 4.09 ± 0.20 87.6 ± 1.2 1514 ± 5 200 ± 6.2 1603 79 ± 6 1.31 ± 0.11 4.16 ± 0.20 82.9 ± 0.9 1510 ± 8 63.8 ± 4.7 1703 102 ± 8 1.21 ± 0.10 3.94 ± 0.28 85.6 ± 1.2 1526 ± 7 19.6 ± 1.4 1803 122 ± 9 1.97 ± 0.24 3.78 ± 0.21 86.5 ± 1.1 1513 ± 8 16.8 ± 1.2 1903 153 ± 11 2.02 ± 0.15 4.14 ± 0.20 89.7 ± 1.0 1515 ± 8 22.1 ± 1.3 2003 153 ± 12 2.05 ± 0.17 4.26 ± 0.20 88.9 ± 0.5 1514 ± 4 15.2 ± 0.9 2103 154 ± 11 2.19 ± 0.19 4.10 ± 0.21 90.2 ± 1.0 1508 ± 6 14.5 ± 1.0 2203 147 ± 10 2.39 ± 0.17 4.16 ± 0.17 89.3 ± 1.3 1516 ± 6 15.3 ± 1.5 2303 147 ± 10 1.93 ± 0.19 4.36 ± 0.20 88.5 ± 1.1 1505 ± 7 14.3 ± 1.7 2403 154 ± 11 2.09 ± 0.16 4.02 ± 0.22 86.6 ± 0.9 1506 ± 7 14.5 ± 1.2 2503 161 ± 11 2.28 ± 0.20 4.03 ± 0.17 85.8 ± 1.1 1500 ± 8 15.0 ± 1.2 2603 143 ± 10 2.00 ± 0.16 4.02 ± 0.21 86.5 ± 0.9 1506 ± 6 14.2 ± 1.2 2703 351 ± 44 3.40 ± 0.37 3.84 ± 0.20 73.6 ± 3.1 1345 ± 63 80.4 ± 6.5 2803 145 ± 10 1.32 ± 0.10 3.68 ± 0.18 77.9 ± 0.8 1491 ± 6 17.1 ± 1.7 2903 158 ± 11 1.41 ± 0.14 4.22 ± 0.18 74.2 ± 1.1 1495 ± 5 13.1 ± 1.3 3003 155 ± 11 1.81 ± 0.15 4.62 ± 0.26 81.0 ± 0.9 1506 ± 7 15.0 ± 1.4 3103 158 ± 12 1.94 ± 0.13 4.03 ± 0.23 77.3 ± 0.9 1491 ± 6 14.6 ± 1.4 3203 147 ± 12 1.50 ± 0.14 3.65 ± 0.15 66.9 ± 0.8 1416 ± 8 14.8 ± 1.6 3303 94 ± 11 1.21 ± 0.16 2.58 ± 0.18 44.6 ± 1.7 828 ± 37 9.3 ± 1.2 3403 69 ± 5 0.84 ± 0.10 1.84 ± 0.12 26.0 ± 0.5 412 ± 4 7.1 ± 1.0 3503 120 ± 5 1.92 ± 0.15 3.23 ± 0.20 61.3 ± 2.1 1190 ± 36 10.5 ± 1.1 3603 150 ± 12 2.59 ± 0.17 3.62 ± 0.23 69.9 ± 0.8 1423 ± 5 13.4 ± 1.3 3703 156 ± 12 2.43 ± 0.18 4.14 ± 0.20 69.2 ± 1.0 1437 ± 6 12.3 ± 1.2 3803 176 ± 12 2.28 ± 0.20 4.23 ± 0.22 66.1 ± 0.8 1467 ± 6 182 ± 7.0 3903 142 ± 12 2.13 ± 0.18 3.73 ± 0.20 54.5 ± 0.8 1442 ± 5 11.0 ± 1.0 4003 144 ± 13 1.31 ± 0.17 3.34 ± 0.17 31.2 ± 0.5 1509 ± 8 14.6 ± 1.5 Metal 1236 W. Hsu

Table A1. Minor element spatial distributions (ppm) in pallasite olivine and its adjacent phases. The errors are 1σ from counting statistics only. Continued. Distance (µm) Ca Ti V Cr Mn Ni Eagle Station olivine #1 Metal 5 152 ± 7 3.15 ± 0.28 3.17 ± 0.28 20.4 ± 0.5 2370 ± 10 581 ± 22 55 178 ± 6 4.65 ± 0.29 3.26 ± 0.24 40.0 ± 0.9 2338 ± 12 44.9 ± 2.6 100 211 ± 5 4.31 ± 0.25 2.80 ± 0.19 37.8 ± 0.8 2355 ± 9 42.5 ± 1.9 150 225 ± 5 3.95 ± 0.28 3.17 ± 0.22 33.9 ± 0.9 2321 ± 10 50.0 ± 3.1 200 308 ± 20 5.32 ± 0.41 3.04 ± 0.23 38.0 ± 0.9 2257 ± 43 55.2 ± 3.4 245 249 ± 5 5.11 ± 0.20 3.25 ± 0.23 40.1 ± 0.9 2343 ± 13 52.7 ± 2.9 295 256 ± 5 4.62 ± 0.25 3.59 ± 0.23 41.7 ± 0.7 2341 ± 10 48.6 ± 2.5 345 255 ± 5 4.75 ± 0.30 3.06 ± 0.19 40.6 ± 1.0 2360 ± 10 49.5 ± 2.6 395 280 ± 6 4.27 ± 0.23 3.41 ± 0.25 36.5 ± 0.7 2367 ± 9 48.3 ± 2.5 445 283 ± 7 4.88 ± 0.24 3.32 ± 0.24 38.1 ± 0.6 2343 ± 9 51.9 ± 3.2 495 256 ± 5 5.96 ± 0.33 2.90 ± 0.17 48.2 ± 0.8 2361 ± 9 47.6 ± 2.5 540 255 ± 5 7.04 ± 0.39 3.64 ± 0.22 57.9 ± 0.9 2342 ± 9 52.3 ± 3.1 590 264 ± 6 6.69 ± 0.29 3.79 ± 0.22 62.2 ± 0.8 2334 ± 9 53.0 ± 2.9 640 254 ± 5 7.45 ± 0.32 3.89 ± 0.24 66.5 ± 0.9 2343 ± 10 54.9 ± 2.3 690 249 ± 4 8.25 ± 0.31 3.50 ± 0.21 64.3 ± 1.1 2341 ± 9 48.7 ± 2.8 735 246 ± 5 7.48 ± 0.51 4.28 ± 0.25 69.5 ± 1.0 2376 ± 11 50.6 ± 2.3 785 229 ± 5 8.16 ± 0.45 3.95 ± 0.22 69.6 ± 1.1 2358 ± 10 51.2 ± 2.7 830 202 ± 5 5.72 ± 0.33 3.43 ± 0.20 48.3 ± 0.6 2332 ± 7 45.1 ± 2.8 880 158 ± 4 6.26 ± 0.25 3.65 ± 0.25 48.4 ± 0.8 2323 ± 7 38.0 ± 2.1 930 92 ± 4 3.58 ± 0.19 3.58 ± 0.20 27.0 ± 0.4 2319 ± 8 40.2 ± 2.2 Metal Eagle Station olivine #2 Metal 10 96 ± 4 3.81 ± 0.25 3.17 ± 0.28 26.8 ± 0.8 2336 ± 8 35.8 ± 2.4 41 144 ± 4 6.45 ± 0.30 3.80 ± 0.24 48.0 ± 0.7 2365 ± 10 40.0 ± 3.6 69 182 ± 4 7.94 ± 0.33 3.80 ± 0.18 58.7 ± 1.0 2347 ± 9 44.1 ± 2.6 99 207 ± 4 9.41 ± 0.44 4.43 ± 0.24 69.4 ± 1.1 2335 ± 11 42.9 ± 2.7 130 228 ± 3 9.50 ± 0.45 4.34 ± 0.22 78.5 ± 1.3 2346 ± 10 51.9 ± 2.4 161 244 ± 5 9.81 ± 0.31 4.09 ± 0.22 80.4 ± 1.2 2343 ± 11 51.3 ± 2.7 191 254 ± 4 10.39 ± 0.40 4.30 ± 0.24 80.1 ± 1.3 2368 ± 11 52.3 ± 2.9 222 333 ± 23 11.57 ± 0.43 4.42 ± 0.27 80.1 ± 1.6 2315 ± 37 55.4 ± 3.0 252 262 ± 5 11.34 ± 0.40 4.36 ± 0.22 88.5 ± 1.3 2357 ± 12 52.3 ± 3.1 283 270 ± 5 10.55 ± 0.47 4.64 ± 0.22 90.0 ± 1.1 2369 ± 11 54.2 ± 2.7 314 265 ± 4 11.19 ± 0.38 4.18 ± 0.23 91.5 ± 1.2 2340 ± 12 50.9 ± 3.1 344 257 ± 5 12.26 ± 0.46 4.64 ± 0.27 93.8 ± 1.2 2336 ± 10 44.7 ± 2.8 375 250 ± 4 10.96 ± 0.41 4.76 ± 0.32 82.3 ± 1.2 2338 ± 8 50.5 ± 2.5 405 241 ± 5 10.44 ± 0.45 4.14 ± 0.25 76.2 ± 0.8 2339 ± 12 56.3 ± 3.5 436 231 ± 3 9.23 ± 0.30 4.04 ± 0.23 70.8 ± 1.1 2303 ± 12 50.7 ± 3.1 467 195 ± 4 8.56 ± 0.34 4.18 ± 0.23 63.7 ± 1.0 2328 ± 11 46.7 ± 2.2 497 161 ± 4 6.24 ± 0.27 4.14 ± 0.29 49.3 ± 0.8 2309 ± 10 42.2 ± 1.9 528 101 ± 4 4.12 ± 0.22 3.47 ± 0.20 30.8 ± 0.6 2291 ± 10 37.0 ± 2.7 Metal Eagle Station olivine #3 Metal 14 120 ± 4 4.83 ± 0.25 3.71 ± 0.23 42.8 ± 0.8 2270 ± 9 47.1 ± 2.8 35 189 ± 5 8.60 ± 0.24 4.15 ± 0.18 80.3 ± 1.2 2243 ± 9 58.1 ± 2.9 63 242 ± 5 10.98 ± 0.42 4.91 ± 0.17 108.7 ± 1.2 2260 ± 9 61.0 ± 2.4 91 289 ± 5 12.06 ± 0.35 4.59 ± 0.22 119.5 ± 1.4 2306 ± 9 72.5 ± 3.9 115.5 303 ± 4 13.37 ± 0.39 5.17 ± 0.31 124.7 ± 1.4 2276 ± 7 65.6 ± 3.0 143.5 330 ± 5 12.99 ± 0.41 5.18 ± 0.24 131.2 ± 1.5 2262 ± 9 67.3 ± 3.5 171.5 347 ± 5 12.55 ± 0.36 5.00 ± 0.30 131.8 ± 1.7 2276 ± 10 68.2 ± 2.3 199.5 357 ± 5 10.72 ± 0.38 4.70 ± 0.22 109.2 ± 1.1 2275 ± 10 75.3 ± 3.7 224 358 ± 5 12.59 ± 0.45 5.05 ± 0.25 126.3 ± 1.3 2270 ± 11 73.9 ± 3.2 Minor element zoning and trace element geochemistry of pallasites 1237

Table A1. Minor element spatial distributions (ppm) in pallasite olivine and its adjacent phases. The errors are 1σ from counting statistics only. Continued. Distance (µm) Ca Ti V Cr Mn Ni 252 367 ± 5 13.51 ± 0.47 5.22 ± 0.32 138.6 ± 1.0 2281 ± 11 64.9 ± 3.1 280 374 ± 4 14.26 ± 0.44 5.34 ± 0.30 140.5 ± 1.0 2289 ± 8 69.7 ± 4.2 308 375 ± 5 14.17 ± 0.40 5.15 ± 0.23 142.4 ± 1.2 2292 ± 7 67.6 ± 2.6 339.5 379 ± 4 13.97 ± 0.42 5.13 ± 0.30 135.9 ± 1.7 2295 ± 11 68.0 ± 2.7 360.5 383 ± 4 14.79 ± 0.38 4.76 ± 0.21 149.0 ± 1.5 2288 ± 9 72.7 ± 3.4 388.5 382 ± 5 14.49 ± 0.50 5.79 ± 0.27 141.8 ± 1.2 2280 ± 9 69.4 ± 3.3 416.5 384 ± 6 12.30 ± 0.42 4.60 ± 0.34 117.8 ± 1.3 2281 ± 7 70.7 ± 4.2 444.5 383 ± 5 14.60 ± 0.38 5.31 ± 0.27 148.9 ± 1.0 2300 ± 12 69.2 ± 3.5 472.5 375 ± 4 15.50 ± 0.46 5.45 ± 0.29 148.0 ± 1.5 2290 ± 10 69.5 ± 4.3 497 381 ± 5 14.44 ± 0.54 5.25 ± 0.30 140.9 ± 1.6 2312 ± 11 67.7 ± 2.7 525 370 ± 6 13.97 ± 0.50 5.15 ± 0.26 138.8 ± 1.2 2260 ± 14 66.3 ± 3.2 553 350 ± 4 13.03 ± 0.40 5.31 ± 0.24 132.7 ± 1.2 2249 ± 7 70.4 ± 3.7 581 349 ± 5 13.02 ± 0.44 5.11 ± 0.18 126.9 ± 1.4 2239 ± 11 61.3 ± 2.3 609 335 ± 4 11.70 ± 0.37 5.01 ± 0.25 117.5 ± 1.3 2247 ± 10 63.2 ± 3.9 637 325 ± 5 10.10 ± 0.37 4.68 ± 0.27 104.2 ± 1.3 2242 ± 11 67.9 ± 2.4 661.5 314 ± 5 8.17 ± 0.32 3.78 ± 0.24 91.0 ± 1.2 2237 ± 11 63.7 ± 3.2 689.5 306 ± 5 6.44 ± 0.34 3.26 ± 0.19 74.5 ± 0.7 2250 ± 9 60.1 ± 2.4 717.5 303 ± 4 4.47 ± 0.20 2.97 ± 0.21 48.4 ± 0.8 2246 ± 9 62.5 ± 2.5 745.5 296 ± 5 7.51 ± 0.30 3.81 ± 0.23 78.5 ± 1.2 2246 ± 15 66.2 ± 3.2 773.5 287 ± 5 8.40 ± 0.39 3.79 ± 0.27 86.2 ± 1.0 2248 ± 9 61.3 ± 3.2 798 281 ± 5 7.53 ± 0.29 3.84 ± 0.19 81.6 ± 1.1 2263 ± 8 61.2 ± 3.3 826 301 ± 4 5.48 ± 0.18 3.20 ± 0.21 60.7 ± 0.9 2213 ± 11 58.8 ± 3.3 854 261 ± 4 4.39 ± 0.24 2.87 ± 0.23 45.7 ± 0.7 2201 ± 6 54.6 ± 2.6 882 259 ± 4 7.07 ± 0.28 3.62 ± 0.19 69.1 ± 1.1 2237 ± 7 56.7 ± 3.0 910 251 ± 5 6.46 ± 0.31 3.80 ± 0.18 64.7 ± 1.0 2243 ± 10 54.7 ± 3.5 934.5 216 ± 9 5.95 ± 0.40 3.19 ± 0.25 52.6 ± 1.4 1752 ± 69 47.0 ± 3.7 962.5 176 ± 6 5.19 ± 0.33 2.92 ± 0.27 49.1 ± 3.2 1535 ± 105 33.3 ± 3.0 990.5 217 ± 4 6.48 ± 0.31 3.73 ± 0.27 59.6 ± 0.8 2245 ± 8 49.3 ± 3.1 1015 197 ± 5 6.68 ± 0.26 3.56 ± 0.21 56.1 ± 1.0 2253 ± 11 52.2 ± 3.0 1046.5 166 ± 4 6.70 ± 0.31 3.31 ± 0.19 54.8 ± 0.7 2245 ± 8 49.4 ± 3.1 1071 115 ± 4 4.45 ± 0.21 3.57 ± 0.24 38.0 ± 0.6 2257 ± 8 38.5 ± 2.1 Metal Eagle Station olivine #4 Chromite 9.9 87 ± 4 2.93 ± 0.18 0.77 ± 0.09 29.5 ± 0.9 1881 ± 11 52.4 ± 2.7 36.9 123 ± 3 2.84 ± 0.19 0.92 ± 0.12 23.6 ± 0.8 2131 ± 8 53.7 ± 2.8 64.5 139 ± 4 3.04 ± 0.24 1.01 ± 0.13 21.7 ± 0.5 2277 ± 7 47.2 ± 2.6 93 155 ± 4 3.02 ± 0.20 2.37 ± 0.19 23.4 ± 0.5 2308 ± 9 39.7 ± 3.1 121.5 172 ± 4 3.59 ± 0.31 2.33 ± 0.18 27.2 ± 0.6 2331 ± 11 55.8 ± 3.7 150 179 ± 4 2.78 ± 0.22 2.40 ± 0.17 25.9 ± 0.7 2319 ± 6 47.6 ± 3.3 177 186 ± 4 2.75 ± 0.17 2.70 ± 0.16 22.8 ± 0.6 2334 ± 9 49.2 ± 2.7 205.5 295 ± 10 3.41 ± 0.26 15.44 ± 0.50 1096 ± 41 2335 ± 13 2874 ± 129 234 179 ± 4 2.34 ± 0.19 2.46 ± 0.16 23.4 ± 0.6 2314 ± 8 64.6 ± 3.1 261 167 ± 4 2.15 ± 0.17 2.70 ± 0.18 21.8 ± 0.5 2307 ± 11 64.7 ± 3.4 289.5 146 ± 4 2.20 ± 0.19 2.58 ± 0.19 20.8 ± 0.7 2308 ± 10 60.9 ± 3.4 325.5 100 ± 4 1.28 ± 0.14 2.34 ± 0.20 13.3 ± 0.5 2299 ± 7 59.4 ± 3.5 Metal Glorieta Mountain olivine #1 Metal 14 48.2 ± 2.0 7.7 ± 0.3 6.1 ± 0.2 54.3 ± 0.9 2647 ± 10 25.2 ± 1.6 45.5 60.5 ± 2.1 13.5 ± 0.3 6.4 ± 0.2 89.9 ± 1.1 2575 ± 10 24.7 ± 2.2 77 66.7 ± 2.3 14.4 ± 0.4 7.7 ± 0.3 98.3 ± 1.1 2599 ± 12 23.1 ± 2.0 112 67.7 ± 2.3 13.6 ± 0.4 7.1 ± 0.3 102.1 ± 1.0 2550 ± 8 25.6 ± 2.0 143.5 67.4 ± 1.8 14.7 ± 0.4 6.8 ± 0.4 105.6 ± 1.1 2543 ± 10 21.6 ± 1.7 175 70.8 ± 2.3 14.8 ± 0.4 7.3 ± 0.3 113.7 ± 1.3 2563 ± 20 25.3 ± 2.0 1238 W. Hsu

Table A1. Minor element spatial distributions (ppm) in pallasite olivine and its adjacent phases. The errors are 1σ from counting statistics only. Continued. Distance (µm) Ca Ti V Cr Mn Ni 210 70.0 ± 2.5 14.5 ± 0.4 7.3 ± 0.3 110.5 ± 1.1 2608 ± 7 28.0 ± 1.7 241.5 68.0 ± 2.3 15.1 ± 0.5 7.6 ± 0.3 115.0 ± 1.2 2604 ± 9 25.2 ± 1.8 276.5 65.6 ± 2.4 14.7 ± 0.3 7.7 ± 0.3 117.5 ± 1.0 2606 ± 10 26.3 ± 2.8 308 68.3 ± 2.5 14.5 ± 0.5 7.1 ± 0.3 117.5 ± 0.8 2602 ± 9 24.9 ± 1.7 339.5 69.4 ± 2.6 14.3 ± 0.4 7.5 ± 0.4 115.3 ± 1.1 2607 ± 10 26.7 ± 2.0 371 65.5 ± 2.4 13.3 ± 0.6 6.7 ± 0.2 109.2 ± 1.3 2601 ± 10 29.3 ± 1.7 406 65.7 ± 2.3 13.1 ± 0.3 7.1 ± 0.3 110.3 ± 1.4 2607 ± 8 23.6 ± 1.4 437.5 61.0 ± 2.3 10.5 ± 0.3 6.7 ± 0.3 94.8 ± 1.2 2623 ± 11 26.4 ± 1.8 469 57.8 ± 2.3 5.7 ± 0.3 6.1 ± 0.3 69.1 ± 0.9 2610 ± 7 24.6 ± 1.8 504 60.2 ± 2.6 9.6 ± 0.4 6.3 ± 0.3 89.4 ± 1.1 2637 ± 9 23.5 ± 2.2 539 59.5 ± 2.3 9.2 ± 0.4 6.7 ± 0.3 93.4 ± 1.4 2627 ± 8 25.6 ± 1.8 570.5 59.8 ± 2.5 7.7 ± 0.3 6.1 ± 0.3 86.2 ± 1.0 2627 ± 8 24.8 ± 2.0 602 58.4 ± 2.6 5.6 ± 0.3 5.9 ± 0.3 71.7 ± 0.8 2641 ± 8 27.3 ± 1.3 637 59.1 ± 2.5 5.7 ± 0.3 6.1 ± 0.2 72.7 ± 1.0 2649 ± 7 27.3 ± 1.7 668.5 57.4 ± 2.5 5.6 ± 0.3 6.1 ± 0.3 67.9 ± 0.8 2644 ± 8 28.5 ± 1.7 700 58.4 ± 2.5 6.7 ± 0.3 6.2 ± 0.3 77.8 ± 1.0 2629 ± 8 22.5 ± 1.6 735 61.7 ± 2.4 9.0 ± 0.3 6.6 ± 0.3 86.6 ± 0.9 2667 ± 9 25.0 ± 1.5 766.5 69.9 ± 2.8 9.7 ± 0.3 6.9 ± 0.3 92.2 ± 1.2 2651 ± 8 25.4 ± 1.7 798 64.4 ± 2.5 10.1 ± 0.3 6.7 ± 0.3 88.6 ± 1.2 2682 ± 8 24.6 ± 1.7 829.5 60.3 ± 2.4 8.2 ± 0.3 6.1 ± 0.2 75.5 ± 0.9 2675 ± 10 23.0 ± 1.9 861 60.6 ± 2.4 5.2 ± 0.3 6.2 ± 0.3 63.4 ± 0.9 2624 ± 10 25.6 ± 2.0 896 49.1 ± 1.7 4.7 ± 0.2 6.5 ± 0.3 54.3 ± 1.0 2726 ± 16 24.0 ± 2.6 927.5 70.3 ± 3.8 8.3 ± 0.3 6.6 ± 0.2 78.1 ± 1.2 2647 ± 7 24.0 ± 2.6 966 66.5 ± 4.3 6.7 ± 0.6 5.8 ± 0.4 56.2 ± 1.9 2804 ± 9 29.2 ± 2.5 Olivine Glorieta Mountain olivine #2 Metal 15 92.4 ± 5.8 4.39 ± 0.40 5.37 ± 0.25 47.6 ± 2.1 2677 ± 6 36.8 ± 2.3 37.5 84.6 ± 4.9 4.90 ± 0.30 5.92 ± 0.23 46.0 ± 0.8 2465 ± 5 31.9 ± 2.0 60 85.5 ± 4.7 5.55 ± 0.20 5.88 ± 0.25 47.3 ± 0.7 2428 ± 7 33.4 ± 2.0 82.5 86.2 ± 4.6 5.75 ± 0.20 5.69 ± 0.35 53.1 ± 0.5 2388 ± 5 35.3 ± 2.9 105 86.0 ± 4.5 6.20 ± 0.23 5.61 ± 0.21 56.2 ± 0.9 2382 ± 7 33.6 ± 2.1 127.5 86.7 ± 4.7 6.00 ± 0.22 5.85 ± 0.25 58.2 ± 0.9 2355 ± 5 30.1 ± 2.4 150 99.3 ± 6.4 7.39 ± 0.29 5.54 ± 0.18 60.7 ± 0.8 2369 ± 6 38.7 ± 3.2 172.5 86.3 ± 4.6 6.81 ± 0.26 6.07 ± 0.25 60.2 ± 0.5 2322 ± 6 36.1 ± 2.2 195 89.7 ± 4.8 7.14 ± 0.23 6.07 ± 0.25 62.9 ± 0.7 2334 ± 8 38.1 ± 2.4 217.5 91.4 ± 4.6 7.12 ± 0.28 6.11 ± 0.24 63.4 ± 0.8 2344 ± 16 35.3 ± 2.2 240 108.0 ± 9.4 7.28 ± 0.39 6.31 ± 0.21 71.8 ± 1.1 2292 ± 12 45.8 ± 2.5 Metal Imilac olivine #1 Metal 18 43.4 ± 1.7 9.03 ± 0.30 3.43 ± 0.21 42.0 ± 0.6 1585 ± 8 7.4 ± 1.1 30 48.2 ± 2.5 11.60 ± 0.29 3.70 ± 0.22 54.7 ± 0.9 1746 ± 8 8.1 ± 1.1 46.5 49.2 ± 2.5 9.20 ± 0.32 3.88 ± 0.20 51.9 ± 1.0 1848 ± 7 9.3 ± 0.9 60 51.1 ± 2.6 7.81 ± 0.35 3.70 ± 0.17 45.4 ± 0.7 1928 ± 8 9.0 ± 1.1 76.5 54.4 ± 2.9 9.99 ± 0.37 4.14 ± 0.23 60.1 ± 1.0 1995 ± 9 11.0 ± 1.0 91.5 58.7 ± 3.0 14.21 ± 0.43 4.43 ± 0.27 76.2 ± 1.1 2056 ± 11 9.7 ± 1.3 106.5 58.1 ± 2.8 13.80 ± 0.45 4.45 ± 0.22 75.7 ± 0.9 2051 ± 9 13.1 ± 1.4 123 56.9 ± 2.8 10.88 ± 0.38 4.46 ± 0.24 61.0 ± 0.9 2085 ± 11 11.1 ± 1.1 138 83.2 ± 3.5 13.06 ± 0.36 4.65 ± 0.27 69.8 ± 0.9 2143 ± 8 216 ± 5.2 153 67.9 ± 3.3 11.52 ± 0.37 4.86 ± 0.22 67.9 ± 0.8 2271 ± 8 10.4 ± 1.2 168 209 ± 48 12.22 ± 0.53 4.20 ± 0.20 66.1 ± 1.0 2334 ± 8 43.7 ± 2.3 184.5 67.6 ± 3.3 14.32 ± 0.38 4.39 ± 0.17 74.5 ± 1.2 2273 ± 7 12.2 ± 1.1 198 68.8 ± 3.6 15.60 ± 0.43 4.68 ± 0.28 80.2 ± 1.0 2287 ± 11 10.3 ± 1.0 214.5 66.0 ± 3.3 13.82 ± 0.39 4.48 ± 0.25 70.7 ± 1.0 2281 ± 7 10.9 ± 1.4 Minor element zoning and trace element geochemistry of pallasites 1239

Table A1. Minor element spatial distributions (ppm) in pallasite olivine and its adjacent phases. The errors are 1σ from counting statistics only. Continued. Distance (µm) Ca Ti V Cr Mn Ni 229.5 71.3 ± 3.6 15.16 ± 0.36 4.42 ± 0.16 71.3 ± 0.6 2276 ± 8 11.8 ± 1.4 244.5 64.7 ± 3.4 15.77 ± 0.43 4.55 ± 0.22 71.5 ± 0.9 2238 ± 6 13.3 ± 1.2 261 68.1 ± 3.6 11.79 ± 0.32 4.53 ± 0.22 54.7 ± 0.7 2234 ± 8 83.0 ± 3.8 274.5 60.9 ± 3. 10.74 ± 0.34 4.43 ± 0.19 54.7 ± 0.9 2277 ± 8 11.2 ± 0.8 Metal Imilac olivine #2 Metal 20.4 73.3 ± 4.9 6.99 ± 0.25 5.00 ± 0.22 62.1 ± 0.6 2356 ± 7 12.0 ± 1.3 45.9 72.2 ± 4.8 7.45 ± 0.26 5.39 ± 0.23 66.5 ± 0.8 2256 ± 24 13.9 ± 1.0 71.4 71.8 ± 4.5 8.47 ± 0.36 5.65 ± 0.19 75.9 ± 0.8 2276 ± 6 13.0 ± 1.2 96.9 73.9 ± 4.5 9.18 ± 0.37 5.91 ± 0.25 82.1 ± 0.8 2297 ± 8 12.0 ± 1.2 122.4 76.2 ± 4.9 9.08 ± 0.39 6.15 ± 0.25 85.9 ± 0.7 2290 ± 6 9.1 ± 0.9 147.9 77.5 ± 4.8 8.37 ± 0.26 5.86 ± 0.25 79.3 ± 0.9 2288 ± 6 14.7 ± 1.7 175.95 77.0 ± 4.8 8.60 ± 0.28 5.40 ± 0.24 80.3 ± 0.7 2281 ± 8 14.1 ± 1.3 201.45 78.6 ± 4.6 9.82 ± 0.30 6.45 ± 0.27 87.2 ± 0.8 2293 ± 7 15.2 ± 1.4 226.95 83.3 ± 6.0 10.71 ± 0.38 5.50 ± 0.24 86.6 ± 1.0 2296 ± 9 14.7 ± 1.2 255 78.9 ± 4.7 12.30 ± 0.41 5.80 ± 0.24 98.3 ± 1.1 2311 ± 8 12.1 ± 1.1 280.5 82.0 ± 4.8 15.72 ± 0.40 6.53 ± 0.27 121.4 ± 0.9 2315 ± 6 15.5 ± 1.4 308.55 83.6 ± 5.0 21.38 ± 0.43 7.40 ± 0.35 154.5 ± 1.0 2342 ± 10 15.2 ± 1.4 334.05 85.6 ± 5.3 23.68 ± 0.43 7.83 ± 0.23 169.3 ± 1.4 2310 ± 8 14.3 ± 1.3 359.55 91.7 ± 5.0 25.21 ± 0.58 7.94 ± 0.27 172.7 ± 1.5 2363 ± 7 13.1 ± 1.5 387.6 87.5 ± 4.8 24.26 ± 0.50 7.73 ± 0.32 166.6 ± 1.6 2354 ± 6 12.4 ± 1.0 413.1 120 ± 12 22.29 ± 0.47 7.46 ± 0.31 142.5 ± 1.6 2357 ± 9 15.2 ± 1.3 438.6 79.3 ± 4.8 17.39 ± 0.44 7.03 ± 0.26 117.6 ± 1.0 2371 ± 8 14.7 ± 1.1 466.65 69.5 ± 4.9 10.24 ± 0.39 5.12 ± 0.23 72.8 ± 1.0 2446 ± 6 16.7 ± 1.7 Metal Imilac olivine #3 Metal 16.5 61.6 ± 3.0 10.4 ± 0.4 6.07 ± 0.27 68 ± 3 2506 ± 7 14.3 ± 1.3 40.5 83.6 ± 4.0 16.2 ± 0.3 6.86 ± 0.24 106 ± 1 2452 ± 8 299 ± 12 67.5 74.2 ± 3.3 17.8 ± 0.5 7.56 ± 0.28 122 ± 1 2432 ± 7 13.8 ± 1.2 93 88.3 ± 3.9 20.0 ± 0.5 8.64 ± 0.38 138 ± 1 2452 ± 11 45.8 ± 2.8 117 76.0 ± 3.4 19.1 ± 0.5 6.94 ± 0.27 133 ± 1 2421 ± 11 20.4 ± 1.6 141 75.5 ± 3.0 18.3 ± 0.5 6.98 ± 0.27 135 ± 1 2404 ± 7 319 ± 4.7 168 72.3 ± 3.0 15.6 ± 0.4 6.73 ± 0.24 128 ± 1 2393 ± 9 122 ± 3.2 195 127 ± 17 15.3 ± 0.5 6.89 ± 0.27 108 ± 1 2419 ± 9 12.7 ± 1.1 219 72.0 ± 3.2 14.6 ± 0.4 7.22 ± 0.24 122 ± 1 2411 ± 6 14.4 ± 1.4 246 75.8 ± 3.3 14.7 ± 0.4 6.73 ± 0.34 119 ± 1 2429 ± 9 12.0 ± 1.2 273 73.0 ± 3.5 13.2 ± 0.3 6.24 ± 0.34 120 ± 1 2440 ± 9 11.9 ± 1.2 295.5 70.2 ± 3.4 11.3 ± 0.4 6.20 ± 0.42 108 ± 1 2428 ± 9 10.6 ± 1.2 Metal Springwater olivine #1 Metal 23.8 64.7 ± 2.6 0.95 ± 0.13 4.53 ± 0.25 36.4 ± 1.0 3470 ± 13 27.4 ± 2.3 56 63.3 ± 3.8 2.30 ± 0.24 5.18 ± 0.27 56.2 ± 1.8 3584 ± 80 34.3 ± 2.5 84 91.8 ± 5.4 3.82 ± 0.22 5.47 ± 0.21 76.2 ± 0.9 3448 ± 10 30.7 ± 2.2 119 69.4 ± 2.7 3.55 ± 0.19 5.46 ± 0.24 72.8 ± 1.0 3442 ± 10 35.7 ± 2.6 147 103.1 ± 5.1 5.31 ± 0.21 5.37 ± 0.27 90.9 ± 1.3 3483 ± 14 38.0 ± 2.2 182 85.0 ± 3.6 5.22 ± 0.28 5.50 ± 0.27 95.0 ± 1.3 3468 ± 12 32.8 ± 2.0 210 107.5 ± 5.3 5.14 ± 0.27 5.79 ± 0.24 95.5 ± 1.1 3414 ± 10 31.3 ± 1.8 245 127.0 ± 5.9 5.34 ± 0.23 5.63 ± 0.28 102.3 ± 1.3 3457 ± 12 36.6 ± 2.4 273 116.8 ± 4.2 5.31 ± 0.23 5.60 ± 0.24 103.4 ± 1.1 3483 ± 15 34.0 ± 1.7 308 93.6 ± 3.4 5.15 ± 0.21 5.81 ± 0.23 102.3 ± 1.1 3453 ± 8 33.3 ± 2.5 336 153.8 ± 8.2 5.44 ± 0.23 5.38 ± 0.19 108.0 ± 0.9 3460 ± 11 48.2 ± 3.4 1240 W. Hsu

Table A1. Minor element spatial distributions (ppm) in pallasite olivine and its adjacent phases. The errors are 1σ from counting statistics only. Continued. Distance (µm) Ca Ti V Cr Mn Ni 371 158.7 ± 7.0 4.94 ± 0.19 5.87 ± 0.26 109.0 ± 1.2 3422 ± 14 38.6 ± 2.3 399 143.5 ± 6.2 5.45 ± 0.26 5.37 ± 0.20 110.2 ± 1.3 3438 ± 15 41.5 ± 2.2 434 178.0 ± 7.9 5.11 ± 0.28 5.34 ± 0.26 115.3 ± 1.0 3477 ± 9 40.1 ± 2.5 462 123.3 ± 4.7 5.27 ± 0.29 5.48 ± 0.26 116.4 ± 1.1 3456 ± 12 37.1 ± 2.6 497 101.1 ± 3.1 4.66 ± 0.26 5.38 ± 0.20 115.0 ± 1.5 3465 ± 9 35.2 ± 1.7 525 96.7 ± 3.1 4.71 ± 0.27 5.76 ± 0.24 116.2 ± 1.4 3472 ± 7 34.0 ± 1.5 560 267 ± 28 11.47 ± 0.30 5.65 ± 0.24 113.8 ± 2.0 3521 ± 18 50.9 ± 3.0 588 147.1 ± 6.4 5.28 ± 0.25 5.53 ± 0.24 123.9 ± 1.2 3507 ± 12 42.6 ± 2.6 623 123.9 ± 4.9 5.08 ± 0.23 5.34 ± 0.28 122.1 ± 1.3 3470 ± 11 38.7 ± 2.3 651 99.2 ± 3.2 4.89 ± 0.30 5.71 ± 0.31 123.7 ± 1.4 3478 ± 11 37.6 ± 2.2 686 96.3 ± 3.4 5.34 ± 0.30 5.62 ± 0.18 127.5 ± 1.3 3441 ± 12 42.4 ± 2.4 721 116.8 ± 4.3 5.20 ± 0.27 5.86 ± 0.31 128.9 ± 1.3 3423 ± 9 41.4 ± 1.9 749 163.9 ± 7.2 5.54 ± 0.24 6.11 ± 0.21 130.9 ± 1.2 3487 ± 9 43.9 ± 2.1 777 165.2 ± 6.6 5.53 ± 0.22 5.74 ± 0.30 133.0 ± 1.5 3454 ± 10 56.9 ± 3.7 798 192.7 ± 9.4 5.41 ± 0.32 6.09 ± 0.26 135.3 ± 1.4 3476 ± 9 63.7 ± 4.2 840 151.8 ± 8.3 6.51 ± 0.49 5.14 ± 0.28 135.9 ± 1.3 3493 ± 10 46.0 ± 2.3 875 137.7 ± 5.9 5.19 ± 0.26 5.69 ± 0.24 134.0 ± 1.5 3498 ± 11 45.8 ± 2.8 910 111.6 ± 4.1 4.61 ± 0.27 5.79 ± 0.27 132.5 ± 1.2 3484 ± 9 37.9 ± 2.8 938 152.8 ± 5.7 5.40 ± 0.25 5.46 ± 0.34 139.2 ± 1.5 3495 ± 11 51.1 ± 3.5 973 159.1 ± 7.5 5.24 ± 0.34 5.43 ± 0.28 137.6 ± 1.2 3497 ± 14 47.2 ± 2.1 1001 492 ± 197 7.09 ± 0.86 5.98 ± 0.33 130.5 ± 2.2 3459 ± 49 60.6 ± 3.6 1036 137.6 ± 5.9 5.24 ± 0.21 5.88 ± 0.26 136.2 ± 1.2 3474 ± 10 53.6 ± 2.9 1064 120.3 ± 4.4 5.05 ± 0.23 5.41 ± 0.21 144.4 ± 1.4 3453 ± 9 46.0 ± 2.6 1099 118.4 ± 4.3 4.81 ± 0.24 5.63 ± 0.27 135.6 ± 1.4 3463 ± 9 42.5 ± 2.8 1127 119.9 ± 4.3 4.50 ± 0.32 6.14 ± 0.22 138.0 ± 1.4 3495 ± 11 42.8 ± 2.6 1162 161.3 ± 7.0 4.73 ± 0.20 6.08 ± 0.28 142.9 ± 1.4 3490 ± 14 197 ± 6.9 1197 160.4 ± 6.3 5.29 ± 0.31 5.35 ± 0.26 140.0 ± 1.2 3479 ± 9 48.5 ± 2.8 1225 144.9 ± 5.3 5.04 ± 0.24 5.27 ± 0.22 146.8 ± 1.6 3532 ± 12 50.9 ± 2.9 1260 149.9 ± 6.5 5.54 ± 0.30 5.33 ± 0.25 143.6 ± 1.4 3516 ± 12 50.2 ± 3.3 Olivine Springwater olivine #2 FeS 21 75.2 ± 3.3 0.97 ± 0.12 4.61 ± 0.26 30.5 ± 0.7 3756 ± 11 32.9 ± 2.4 77 67.4 ± 2.5 3.27 ± 0.15 5.24 ± 0.30 64.6 ± 1.0 3564 ± 10 32.7 ± 2.3 133 75.0 ± 2.8 5.17 ± 0.28 5.84 ± 0.35 86.1 ± 0.9 3569 ± 13 40.1 ± 2.9 189 99.1 ± 4.4 5.67 ± 0.24 5.24 ± 0.24 92.7 ± 1.3 3558 ± 12 41.7 ± 3.0 252 192.1 ± 9.2 5.71 ± 0.31 5.75 ± 0.26 93.3 ± 1.1 3548 ± 11 40.8 ± 2.9 308 84.2 ± 3.2 4.91 ± 0.26 5.83 ± 0.26 93.1 ± 1.2 3549 ± 12 38.4 ± 2.5 364 93.5 ± 4.1 4.90 ± 0.30 5.17 ± 0.22 96.6 ± 1.0 3536 ± 11 40.9 ± 2.9 420 284 ± 41 6.20 ± 0.42 5.53 ± 0.25 93.5 ± 1.5 3558 ± 28 59.1 ± 5.8 483 141.2 ± 7.7 5.15 ± 0.27 5.53 ± 0.23 95.1 ± 0.9 3520 ± 13 42.3 ± 2.7 539 210.3 ± 11.5 3.96 ± 0.26 4.96 ± 0.23 80.4 ± 1.1 3506 ± 14 56.8 ± 3.3 595 71.1 ± 3.0 4.42 ± 0.23 4.94 ± 0.31 95.5 ± 1.2 3493 ± 10 36.4 ± 2.6 651 111.6 ± 3.3 4.67 ± 0.26 5.96 ± 0.23 98.3 ± 1.2 3519 ± 10 37.0 ± 2.7 707 74.9 ± 3.3 1.30 ± 0.14 5.32 ± 0.25 66.9 ± 1.0 3464 ± 14 114 ± 4.1 763 74.9 ± 3.1 3.84 ± 0.22 5.20 ± 0.28 90.2 ± 1.1 3469 ± 12 45.4 ± 2.8 819 77.8 ± 3.3 4.51 ± 0.19 5.18 ± 0.25 98.3 ± 1.1 3459 ± 13 48.5 ± 2.4 875 71.5 ± 3.1 3.67 ± 0.17 5.40 ± 0.25 92.3 ± 1.3 3475 ± 10 43.0 ± 2.6 938 108.6 ± 4.7 4.60 ± 0.27 5.36 ± 0.29 103.1 ± 1.2 3458 ± 14 40.6 ± 2.0 994 113.9 ± 6.9 4.60 ± 0.26 5.48 ± 0.29 102.9 ± 1.0 3489 ± 12 46.3 ± 3.3 1036 101.3 ± 4.0 4.55 ± 0.23 5.56 ± 0.18 102.1 ± 1.3 3465 ± 11 42.2 ± 2.0 1106 108.6 ± 3.8 3.91 ± 0.19 5.71 ± 0.21 99.2 ± 1.3 3445 ± 15 41.4 ± 2.3 1169 117.4 ± 3.8 3.09 ± 0.21 5.68 ± 0.37 91.3 ± 1.2 3654 ± 12 255 ± 7.2 1218 93.7 ± 3.4 4.31 ± 0.27 5.73 ± 0.27 101.9 ± 1.0 3449 ± 11 41.7 ± 2.6 1281 79.4 ± 2.8 4.45 ± 0.19 5.95 ± 0.24 100.4 ± 1.1 3420 ± 11 43.6 ± 1.8 Minor element zoning and trace element geochemistry of pallasites 1241

Table A1. Minor element spatial distributions (ppm) in pallasite olivine and its adjacent phases. The errors are 1σ from counting statistics only. Continued. Distance (µm) Ca Ti V Cr Mn Ni 1337 106.6 ± 4.0 4.32 ± 0.24 5.28 ± 0.28 99.4 ± 1.4 3437 ± 13 40.7 ± 2.7 1393 98.8 ± 3.6 4.16 ± 0.19 5.17 ± 0.27 101.2 ± 1.4 3464 ± 15 56.3 ± 2.2 1449 108.9 ± 4.7 4.02 ± 0.20 5.35 ± 0.26 99.2 ± 1.4 3494 ± 17 43.6 ± 3.1 1512 1245 ± 70 44.1 ± 7.08 14.4 ± 0.75 638 ± 27 4037 ± 32 4668 ± 298 1561 96.0 ± 2.6 4.30 ± 0.24 5.26 ± 0.32 95.9 ± 1.2 3399 ± 24 38.2 ± 2.2 1617 115.6 ± 4.8 4.36 ± 0.25 5.88 ± 0.22 100 ± 1.0 3502 ± 10 42.8 ± 2.1 1680 94.3 ± 3.1 4.44 ± 0.24 5.39 ± 0.28 99.8 ± 1.2 3479 ± 13 38.8 ± 2.4 1736 124.9 ± 5.9 4.07 ± 0.21 5.48 ± 0.28 98.4 ± 1.0 3488 ± 13 46.5 ± 2.3 1792 84.8 ± 2.8 4.23 ± 0.22 5.84 ± 0.24 98.6 ± 0.9 3475 ± 13 42.1 ± 2.4 1848 84.4 ± 3.2 3.93 ± 0.21 5.74 ± 0.21 99.1 ± 1.0 3473 ± 10 39.8 ± 2.2 1911 123.0 ± 7.0 4.28 ± 0.26 6.16 ± 0.32 95.6 ± 1.5 3325 ± 33 67.1 ± 5.6 1967 68.6 ± 4.3 3.66 ± 0.31 4.19 ± 0.28 57.2 ± 2.0 1870 ± 83 25.1 ± 2.3 2023 152.3 ± 7.9 5.23 ± 0.24 5.94 ± 0.32 104.9 ± 1.4 3614 ± 22 45.9 ± 3.2 2079 158.9 ± 7.8 5.27 ± 0.31 5.88 ± 0.32 104.6 ± 1.5 3595 ± 11 45.6 ± 2.4 2135 173.9 ± 7.7 6.27 ± 0.31 6.41 ± 0.29 107.2 ± 1.1 3658 ± 16 47.8 ± 2.6 2191 105.7 ± 4.9 5.81 ± 0.30 5.28 ± 0.29 108.1 ± 1.2 3703 ± 10 39.4 ± 2.9 2247 122.7 ± 6.4 3.23 ± 0.22 5.66 ± 0.24 79.9 ± 1.1 3695 ± 16 30.8 ± 2.6 Farringtonite