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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Samples and Experimental Procedure
  5. Results and Discussion
  6. Summary
  7. Acknowledgments
  8. References
  9. Appendix

Abstract– Xenon-isotopic ratios, step-heating release patterns, and gas concentrations of mineral separates from Martian shergottites Roberts Massif (RBT) 04262, Dar al Gani (DaG) 489, Shergotty, and Elephant Moraine (EET) 79001 lithology B are reported. Concentrations of Martian atmospheric xenon are similar in mineral separates from all meteorites, but more weathered samples contain more terrestrial atmospheric xenon. The distributions of xenon from the Martian and terrestrial atmospheres among minerals in any one sample are similar, suggesting similarities in the processes by which they were acquired. However, in opaque and maskelynite fractions, Martian atmospheric xenon is released at higher temperatures than terrestrial atmospheric xenon. It is suggested that both Martian and terrestrial atmospheric xenon were initially introduced by weathering (low temperature alteration processes). However, the Martian component was redistributed by shock, accounting for its current residence in more retentive sites. The presence or absence of detectable 129Xe from the Martian atmosphere in mafic minerals may correspond to the extent of crustal contamination of the rock’s parent melt. Variable contents of excess 129Xe contrast with previously reported consistent concentrations of excess 40Ar, suggesting distinct sources contributed these gases to the parent magma.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Samples and Experimental Procedure
  5. Results and Discussion
  6. Summary
  7. Acknowledgments
  8. References
  9. Appendix

Shergottites

The shergottite Martian meteorites consist of elongate euhedral-subhedral pyroxene intergrown with subhedral-anhedral plagioclase that has been converted to maskelynite by shock (e.g., Stolper and McSween 1979; Laul 1986). Reported shock-pressures range from 30 to 45 GPa (Melosh 1989; Nyquist et al. 2001a; Fritz et al. 2005). The shergottite subgroups—basaltic, olivine-phyric, olivine-orthopyroxene, and lherzolitic—have gradational boundaries and can be separated based on olivine content (low to high, respectively), with olivine often occurring as phenocrysts or xenocrysts (McSween and Treiman 1998; Goodrich 2002). Although the basaltic, olivine-phyric, and olivine–orthopyroxene shergottites are fine to medium grained and likely formed from surface flows or minor intrusions, the lherzolitic shergottites are coarser and may have a plutonic origin (McSween 1994). The occurrence of multiple igneous lithologies within a number of shergottites (e.g., Elephant Moraine [EET] 79001 and Roberts Massif [RBT] 04262) and the presence of phenocrysts within the olivine-phyric and olivine–orthopyroxene shergottites is indicative of multiple cooling rates or magma mixing. In particular, recent work by Symes et al. (2008) suggests that the shergottites may represent a closely related group of samples, derived from distinct vents or edifices on Mars. They use rare earth element (REE) abundances to classify the shergottites in terms of parent magma composition, with endmembers of high light rare earth element (LREE) concentrations sourced from the enriched mantle, and low LREE concentrations sourced from the depleted mantle. They conclude that magma mixing may be responsible for both the variation in LREE concentrations and the compositional differences in the shergottites. Shergottite cosmic ray exposure (CRE) ages suggest ejection events at 1, 3–4, and about 20 Ma (Nyquist et al. 2001a), and more recent work has reported evidence for earlier shock prior to meteorite ejection (Bogard and Garrison 2008; Park et al. 2008). Reported crystallization ages are relatively young (<1 Ga) compared with the nakhlites (about 1.3 Ga), with a number between 165 and 180 Ma (e.g., Shergotty; Nyquist et al. 2001a) whereas others have ages of 700–900 Ma (e.g., SaU 005; Korochantseva et al. 2009). However, Bouvier et al. (2005, 2008) propose much older crystallization ages of about 4 Ga for the shergottites, and suggest that reported younger ages have been reset. Ultimately, it is clear from the observed variation in CRE ages and reported setting/resetting ages that the shergottites likely sample multiple impact events and sites on Mars.

Martian Xenon

For this research, we compare data from analyses of mineral separates and whole rock (WR) from the olivine-phyric shergottite RBT 04262, the basaltic shergottites EET 79001 lithology B and Shergotty, and the olivine–orthopyroxene shergottite Dar al Gani 489 (DaG 489) to try to identify the location and trapping mechanisms of noble gas components in Martian meteorites. Previous studies on noble gases in Martian meteorites have identified a number of distinct trapped xenon (Xe) components with characteristic isotopic signatures. Allowing for modification by in situ processes such as spallation or ingrowth of fission products, three distinct Martian reservoirs are required to account for these components.

Xe from the Martian atmosphere, distinguished by its elevated 129Xe/132Xe ratio (2.5 + 2 − 1, Owen et al. 1977; 2.4 ± 0.02, Swindle et al. 1986), has clearly contributed to the budget in Martian meteorites (Bogard and Johnson 1983; Swindle et al. 1986; Ott 1988; Pepin 1991, 1994; Gilmour et al. 1998, 2001; Mathew and Marti 2001, 2002; Swindle 2002; Ocker and Gilmour 2004). Other components are consistent with mixing of Xe from two distinct reservoirs in the Martian interior. One of these reservoirs is indistinguishable from solar Xe and has been identified with the Martian mantle (129Xe/132Xe = 1.03 ± 0.03; Ott 1988). The second is consistent with a reservoir that has been modified by the addition of Xe from fission of 244Pu, with a possible starting composition of solar Xe (Mathew and Marti 2001, 2002).

The Martian atmosphere exhibits mass-dependent fractionation from a solar composition in its nonradiogenic isotopes, and an elevated 129Xe/132Xe ratio that testifies to a contribution from decay of extinct 129I (Swindle and Jones 1997). Its origin can be explained by the early removal of I and Xe in roughly equal proportions from the interior, followed by subsequent rapid atmospheric Xe loss before the complete decay of 129I. The isotopic composition of the “solar” interior reservoir suggests that its source region had high Xe/I and Xe/Pu ratios while the short-lived radioisotopes were extant (first ∼100 Ma, first ∼500 Ma, respectively), which prevented significant modification of the respective Xe isotope ratios. The reservoir enriched in Xe from fission of 244Pu would need to have been relatively degassed while this isotope was still live; either Xe loss occurred after decay of 129I (causing just high 134Xe, 136Xe, etc.) or both Xe and I were lost before 129I became extinct.

Xe isotopes thus exhibit evidence for an early partition between the Martian interior and the Martian atmosphere, and early separation of interior reservoirs. In particular, the fission-rich reservoir is reminiscent of a proposed KREEP-like layer formed during the solidification of a Martian magma ocean (Taylor and McLennan 2008). A number of authors have found other evidence indicative of a lack of homogenization of the Martian mantle during formation (e.g., Halliday et al. 2001), with models suggesting that there was almost no large-scale mixing of the mantle (Harder and Christensen 1996; Breuer et al. 1997). This is consistent with both the distribution of tectonic features on the Martian surface, and the two major volcanic regions Tharsis and Elysium resulting from isolated plumes (Harder and Christensen 1996; Halliday et al. 2001). Understanding how Martian meteorites came to sample Xe from these reservoirs would further advance our understanding of the reservoirs themselves. This in turn requires identification of where within the rock the Xe is trapped, and how it got there.

Xe Components in Martian Meteorites, and Research Aims

The identification of trapped Martian atmosphere in shock glass in shergottites was the key piece of evidence in identifying their parent body as the planet Mars (Bogard and Johnson 1983; Wiens et al. 1986; Wiens 1988). It was subsequently demonstrated that this component is present as distinct bubbles in shock glass (Walton et al. 2007).

Martian atmospheric Xe has also been identified in the nakhlites. It is part of a component with a lower Kr/Xe ratio than the Martian atmosphere—apparently it was incorporated by a process that produced elemental fractionation. Various mechanisms have been proposed; Drake et al. (1994) noted that the nakhlites incorporated significant amounts of aqueous alteration products, and suggested that these were the host phase of the fractionated atmosphere, where dissolution in water and formation of “iddingsite” caused the mass fractionation. This account was questioned by Gilmour et al. (1999) who, inter alia, noted that Martian atmospheric Xe concentrations did not correlate with the degree of aqueous alteration observed across the nakhlites. Also, their study of mineral separates from Nakhla demonstrated that the component is not predominantly located in alteration products. To account for the distribution among all mineral phases measured, they attributed its presence to gas fractionated by adsorption onto Martian soil that had been incorporated into the parent melt.

However, Gilmour et al. (2001) subsequently demonstrated that Martian atmospheric Xe in Nakhla is sited close to grain surfaces, as it is correlated with leachable iodine. An early report of a late I-Xe “age” for Lafayette of 53 ± 9 Ma (Podosek 1970) shows that a correlation between iodine and excess 129Xe (subsequently shown to have been trapped from the Martian atmosphere rather than produced in situ) is also present in this nakhlite. Gilmour et al. (2001) also showed that the distribution of Martian atmospheric Xe among host phases is different from that of a component consistent with Xe from the Martian interior. This interior component is well mixed with spallation Xe. Target elements for spallation production of Xe are large ion lithophiles (Ba, LREE), so the consistent mixture of interior and spallation Xe shows that the interior component is present in late-stage crystallization products or melt inclusions. This implies that the Xe present in the parent melt was Martian interior Xe, and not Martian atmospheric Xe, demonstrating that the model of Gilmour et al. (1999) was incorrect. Instead, Gilmour et al. (2001) suggested that this surface-correlated Martian atmospheric Xe represented adsorbed gas from the Martian atmosphere, which was incorporated into grain surfaces by shock in the event that removed the meteorites from the Martian surface. Xe is expected to be adsorbed more efficiently than krypton at Martian surface temperatures, although Schwenzer et al. (2008) have discussed the efficacy of shock in releasing helium from the nakhlites (and shergottites) suggesting the redistribution of adsorbed Xe by this process is not implausible.

Mohapatra et al. (2009) identified elementally fractionated air (EFA) in meteorites from hot deserts—terrestrial atmosphere that is elementally fractionated favoring Xe over Kr. Essentially, this identifies a specific environmental process that, operating on Mars, plays the role of the “adsorption” suggested by Gilmour et al. (2001).

Returning to the shergottites, Ocker and Gilmour (2004) examined the Xe component derived from the Martian atmosphere present in shergottites that is not hosted in shock glass. Highest concentrations were found in maskelynite and opaques—these samples revealed increasing 129Xe/132Xe with increasing temperature—and low concentrations in pyroxene, where 129Xe/132Xe was constant over the temperature range. They suggested that the mechanism operating was similar to that which Gilmour et al. (2001) had proposed for the nakhlites—adsorption followed by shock incorporation into surfaces. They also noted that if grain surfaces are sufficiently close to one another, the Xe implanted during a shock event should be dominated by that which had been adsorbed. As the Kr/Xe ratio of adsorbed gas is lower than that in the ambient atmosphere, they expected that this component would exhibit a lower Kr/Xe ratio than shergottite shock glass (injected into large volumes with only a minor contribution from an adsorbed component). Korochantseva et al. (2009) subsequently invoked an apparently similar mechanism of implantation from a “transient atmosphere” to account for variable trapped 40Ar/36Ar ratios in shergottites. Schwenzer et al. (2007) presented a more extensive series of analyses of mineral separates from the shergottites, confirming and extending the results of Ocker and Gilmour (2004). This work included krypton and xenon analyses, but their data do not allow the Kr/Xe ratio of the Martian atmospheric component to be inferred.

In a later study, Schwenzer et al. (2009) distinguished between fractionated Martian atmosphere incorporated by “alteration” into the nakhlites and unfractionated Martian atmosphere incorporated by “shock” into the shergottites. However, in these bulk samples, it is unclear whether the gas released from the shergottites was sourced from shock glass or other minerals.

Thus, three mechanisms have been advanced for the incorporation of noble gas components into Martian rocks: present in primary magma (as for the interior component), aqueous alteration, and shock incorporation. These three mechanisms would be expected to yield elevated concentrations in primary melt inclusions, alteration products, and regions where shock effects have been intensified (such as grain boundaries and shock glasses), respectively. Each model may play a role here, as shergottites have been heavily shocked (Nyquist et al. 2001a; Fritz et al. 2005), and contain melt inclusions (Treiman 1985; Hutchison 2004) and weathering products (Bridges et al. 2001; Taylor et al. 2002; Greenwood 2008). Differentiating mineralogically between terrestrial and Martian weathering is difficult, as the majority of shergottites are finds so may have spent a considerable time on Earth. Shergottites that were seen to fall provide better evidence of Martian surface weathering (e.g., Gibson et al. 2001).

Here, we present data from mineral separates of four shergottites to constrain trapping mechanisms of noble gases, and hence characterize parent reservoirs.

Samples and Experimental Procedure

  1. Top of page
  2. Abstract
  3. Introduction
  4. Samples and Experimental Procedure
  5. Results and Discussion
  6. Summary
  7. Acknowledgments
  8. References
  9. Appendix

Sample Descriptions

Shergotty (the only fall in this study) has larger pyroxene crystals than most other basaltic shergottites with an average grain size of 0.46 mm (Stolper and McSween 1979). Our sample was supplied by the Natural History Museum (BM1985, M172). EET 79001 lithology B (our sample: parent 432, specific 562) is texturally and mineralogically similar to Shergotty (Stolper and McSween 1979; McSween 1994), being slightly more depleted in LREEs (e.g., Symes et al. 2008). Melt inclusions are present in both Shergotty and EET 79001 (Stolper and McSween 1979; McSween and Jarosewich 1983; Treiman 1985). Numerous previous studies have investigated the noble gases within these meteorites (Bogard and Johnson 1983; Swindle et al. 1986; Ott 1988; Bogard and Garrison 1999; Ocker and Gilmour 2004; Schwenzer et al. 2007).

DaG 489 was found in the Dar al Gani region of the Libyan Sahara between 1997 and 1998, and may be paired with DaG 476 (Grossman 1999; Folco et al. 2000). Phenocrysts of olivine are set in a clinopyroxene and feldspathic (now maskelynitic) groundmass (Folco et al. 2000). Except for the additional presence of orthopyroxene, it is similar to the olivine-phyric lithology A of EET 79001 (Grossman 1999; Folco et al. 2000). This has led to suggestions of a petrogenetic link (Folco et al. 2000), where DaG 489 is formed from partial melting of a lherzolitic source material. Our sample was sourced commercially.

RBT 04262 was discovered in Antarctica in 2004, and is paired with RBT 04261 (Satterwhite and Righter 2007). Two distinct igneous lithologies (Fig. 1) have been identified within RBT 04262 (Dalton et al. 2008; Mikouchi et al. 2008). Both lithologies contain significant amounts of olivine, possibly as phenocrysts. One lithology consists of coarse-grained oikocrysts of low Ca pyroxene (pigeonite), containing small olivine crystals and the occasional olivine megacryst (Dalton et al. 2008; Mikouchi et al. 2008). The second lithology is fine-grained and dominantly composed of pyroxene (augite and pigeonite) with homogenous olivine crystals that vary in size (50 μm to 2 mm), and maskelynite (Dalton et al. 2008). There is some debate over the exact classification of RBT 04262: petrography and major and trace element analyses indicate an olivine-phyric composition (McCoy and Reynolds 2007; Dalton et al. 2008; Lapen et al. 2008); REE abundances are similar to basaltic shergottites (Anand et al. 2008); and pyroxene composition is similar to lherzolitic shergottites (Mikouchi et al. 2008). Glass-filled melt inclusions are present in both olivine and pyroxene crystals in both lithologies; they are partially re-crystallized and rich in late-stage fractionates such as K-rich feldspathic glass, phosphates, and opaque oxides (Anand et al. 2008). Chromite is found scattered throughout all phases in both lithologies (Dalton et al. 2008). Alteration products such as gypsum and jarosite are present, at the expense of pyrhottite and apatite (Greenwood 2008). Our sample (RBT 04262, 14) was supplied by the Antarctic Meteorite Working Group, and was taken from the fine-grained lithology.

image

Figure 1.  Photomicrographs of RBT 04262. A) Coarser oikocryst lithology, consisting of green low Ca pyroxene crystals (Low Ca Pyx) enclosing orange (possibly iron stained) olivine crystals (Ol). The dark minerals represent opaques (Opq). Note the almost complete lack of clear maskelynite (Mask) within this region. B) Fine-grained lithology, consisting of dark green/brown pyroxene and olivine (appear more fractured) minerals, clear maskelynite, and the dark opaques (e.g., spinel). The scale bars represent 1000 μm.

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Sample Preparation

A 100 mg interior chip of RBT 04262 was partially crushed in a clean laboratory to allow component minerals to be physically separated under a binocular microscope. The minerals were hand-picked into yellow/green/brown (olivine-pyroxene: olpx), clear (maskelynite: mask), and black (opaques: opq) separates (e.g., spinel, pyrrhotite, ilmenite). It was not possible to distinguish between olivine and pyroxene crystals, due to their similarity in color, lack of other distinguishing features, and the small sample size. Aliquots of these separates are listed in Table 1, and consisted of multiple grains except where noted. Our estimated modal proportions are 72% mafic minerals (olivine and pyroxene), 25% maskelynite phases, and 3% opaque phases, consistent with the fine-grained nonpoikilitic lithology described by Dalton et al. (2008) and Mikouchi et al. (2008). Our observations located numerous melt inclusions in both olivine and pyroxene crystals, including secondary melt inclusion trails formed by the healing of cracks. We performed scanning electron microscope (SEM) analyses of RBT 04262 and identified the presence of annealed apatite veins within the maskelynite fractions, gypsum, K-rich melt glass, exsolution lamellae structures within opaque inclusions (only observed in chromite–ulvospinel/titanium chromite, rather than pure endmember chromite), ilmenite, and zircon phases. Electron probe microanalysis (EMP; Cameca SX100) of opaque fragments revealed multiple phases, including apatite, gypsum, and ilmenite. In particular, two ∼10 μm grains of baddeleyite (ZrO2) were identified in one opaque grain. They contain diagnostic high about 2 wt% levels of hafnium oxide and other element oxides including iron (∼6 wt%), titanium (∼6 wt%), and vanadium (∼0.3 wt%). This is the first reported occurrence of baddeleyite in this meteorite.

Table 1.   Summary of Xe data showing total Xe concentrations and average 129Xe/132Xe ratios for each aliquot.
AliquotTypeComment132Xe Conca129Xexsb129Xe/132Xe
  1. Olpx = olivine–pyroxene; Mask = maskelynite; Opq = opaques; Pyx = pyroxene; WR = whole rock; Ol = olivine; Idd = iddingsite.

  2. aConcentration in 10−12 cm3 STP g−1. Systematic error, derived from uncertainty in the calibration aliquot, is ±10%. Random error due to sensitivity fluctuations is quoted.

  3. b129XeXS calculated from [132Xe] × (129Xe/132Xe − 129Xe/132XeTerrestrial Air), where 129Xe/132XeTerrestrial Air = 0.9832 (Basford et al. 1973). 129XeXS for Shergotty (Ocker and Gilmour 2004) has been recalculated. For RBT 04262, 129XeXS was calculated including only those steps where 129Xe/132Xe was significantly higher than the assumed baseline.

  4. cA final step amounting to 70% of the total 132Xe release that was dominated by terrestrial air has been neglected. The step was performed after the vacuum had been broken to replace a cover slip, exposing the sample to air after heating to high temperature.

RBT 04262
 RBT-AOlpxSingle grain121 ± 8<5.11.026 ± 0.004
 RBT-COlpxSingle grain80 ± 5<0.130.985 ± 0.005
Average100 ± 5<2.61.005 ± 0.003
 RBT-BOlpx 98 ± 4<1.10.995 ± 0.003
 RBT-DOlpx 88 ± 7<2.81.015 ± 0.003
 RBT-EOlpx 83 ± 5<3.11.020 ± 0.003
 RBT-FOlpx 91 ± 8<1.30.997 ± 0.003
Average90 ± 3<2.11.007 ± 0.002
 RBT-GMask 51 ± 2<0.971.002 ± 0.003
 RBT-HMask 56 ± 4<1.31.007 ± 0.004
Average53 ± 2<1.21.005 ± 0.002
 RBT-IOpq 170 ± 15 5.3–14.41.057 ± 0.004
Shergotty
 Sherg-APyx 1.0 ± 0.40.09–0.141.124 ± 0.012
 Sherg-BMask 0.5 ± 0.20.21–0.231.486 ± 0.025
DaG 489
 DaG-AWR 3.2 ± 0.50.24–0.391.104 ± 0.011
 DaG-BOpq 15 ± 2.30.62–1.281.072 ± 0.015
 DaG-CPyx 59 ± 13<0.760.996 ± 0.007
 DaG-DMask 4.6 ± 1.30.62–0.831.164 ± 0.029
 DaG-EIddc 10 ± 2.2<0.681.051 ± 0.012
EET 79001
 EET-AWR 2.8 ± 0.20.22–0.341.107 ± 0.008
 EET-BWR 1.1 ± 0.20.46–0.511.425 ± 0.024
Average2.0 ± 0.20.33–0.421.266 ± 0.013
 EET-CPyx 7.1 ± 0.6<0.020.986 ± 0.005
 EET-DPyx 8.2 ± 0.6<0.110.997 ± 0.004
Average7.6 ± 0.4<0.070.992 ± 0.003
 EET-EOpq 8.5 ± 0.82.60–3.001.336 ± 0.016
 EET-FMask 2.3 ± 0.20.19–0.291.111 ± 0.007
Shergotty (Ocker and Gilmour 2004)
 WRWR 2.5 ± 0.030.31–0.421.153 ± 0.011
 Pyx-01Pyx 1.7 ± 0.020.25–0.331.175 ± 0.008
 Pyx-02Pyx 1.7 ± 0.020.23–0.311.161 ± 0.009
 Pyx-03Pyx 1.4 ± 0.030.23–0.301.196 ± 0.021
 AugPyx 0.9 ± 0.030.24–0.281.290 ± 0.033
 PigPyx 1.6 ± 0.030.37–0.441.264 ± 0.022
Average1.5 ± 0.010.28–0.341.217 ± 0.009
 Msk-01Mask 4.8 ± 0.030.37–0.591.105 ± 0.007
 Msk-02Mask 2.3 ± 0.041.00–1.111.473 ± 0.021
Average3.5 ± 0.020.92–1.081.289 ± 0.011
 Msk-HClMaskAcid washed2.7 ± 0.050.40–0.531.180 ± 0.020
 OPQ-01Opq 10 ± 0.092.6–3.11.285 ± 0.010

Sample preparation for EET 79001, Shergotty, and DaG 489 was similar to the method described above (and by Ocker 2002; Ocker and Gilmour 2004). In addition, a sample of weathering products—“iddingsite”—from DaG 489 was taken. This phase was scraped from the surfaces of mafic phases following major mineral separation and likely has a terrestrial origin. Although, for this research, these meteorites were not studied using SEM or EMP analysis, detailed petrographies of these meteorites are reported by Folco et al. (2000), McSween and Treiman (1998), Meyer (2009), and Hutchison (2004). Aliquots analyzed and reported are listed in Table 1. For EET 79001 and Shergotty, the mineral separates and WR separates were taken from a thick section, following carbon-coating removal, acetone washing, and cutting as described by Ocker (2002). Some aliquots of EET 79001 and Shergotty were acid washed for 19.5 h with 1% HCl to remove phosphates before Xe-isotopic analysis (Ocker 2002; Ocker and Gilmour 2004); however, this introduced a hydrocarbon contamination that compromised Xe analyses so data from these aliquots are not discussed here.

Xe-Isotopic Analysis

Samples were loaded into the sample port of the RELAX mass spectrometer (Gilmour et al. 1994; Crowther et al. 2008). Gas was released and analyzed in each of a series of heating steps using a defocused infrared Nd:YAG laser (λ = 1064 nm) until samples melted. The beam diameter encompassed the samples during heating, which occurred for 1 min periods (occasionally 2 min if at the end of the experiment, and the blank time was adjusted accordingly). The temperature used in each step was controlled by varying the output power of the laser (up to ∼11 Watts) using the laser lamp current—actual temperature readings are not available. The size of each heating step was chosen based on the amount of gas evolved from the sample in the previous step. Occasionally during analysis, it was necessary to refocus the beam to ensure melting and thus confirm that all gas present in a sample had been released.

Gas released from the sample was gettered (SAES Getter, Zr sintered, ∼350 °C) for a further minute to remove active gases and then admitted to the mass spectrometer, whereupon data acquisition began. Data were acquired in thirty 10-second segments. Xe-isotopic ratios, and the peak height of the normalizing isotope (always 132Xe), were calculated for each segment and extrapolated back to the time of gas inlet. Sensitivity and mass-discrimination corrections were made with reference to interspersed air calibrations. Sensitivity variations introduce a random error in calculated gas concentrations, whereas an additional systematic error of 10% rises from uncertainty in the amount of Xe introduced by the calibration aliquot. Data were also corrected for procedural blanks, with blank levels between 0.66 and 1.29 × 10−16 cm3 STP 132Xe. All errors discussed in this study represent 1 standard deviation (Table 1). The results from our experiments are summarized in Table 1, and full data tables are found in the Appendix.

Some aliquots of EET 79001 and Shergotty were pretreated with acids to remove phosphates. However, subsequent Xe-isotopic analyses were compromised by hydrocarbon interferences, as was the olivine separate from DaG 489; these samples are not discussed further here. Two early releases in the analysis of EET 79001 maskelynite aliquot EET-F also appear to have been compromised by a release of hydrocarbon contamination, leading to apparently low 129Xe/132Xe ratios (Fig. 2). This conclusion is based on the occurrence during the analysis of peaks at masses that do not correspond to Xe isotopes. Also, although every effort was made to create “clean” aliquots by hand picking, due to the small grain size and mineralogical diversity of the opaque samples it is inevitable that they contained a mixture of high-temperature primary phases (e.g., spinel) and low-temperature accessory phases (products of alteration such as phosphates and oxides).

image

Figure 2.  Step release diagrams from analyses of RBT 04262, DaG 489, and EET 79001 mineral separates. A) Opaque aliquots RBT-I, DaG-B, and EET-F display 129Xe/132Xe peaking at mid–high temperatures. B) Maskelynite analyses display increasing 129Xe/132Xe with temperature. Low-temperature releases observed in both opaque and maskelynite aliquots are consistent with Martian interior 129Xe/132Xe ∼ 1.03 (Ott 1988) (dashed line) and terrestrial atmosphere 129Xe/132Xe ∼ 0.98 (Swindle 2002) (dotted line). The first two releases from maskelynite EET-F were compromised by hydrocarbons and are partially shaded in B (see text).

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Results and Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Samples and Experimental Procedure
  5. Results and Discussion
  6. Summary
  7. Acknowledgments
  8. References
  9. Appendix

Previous work by Ocker and Gilmour (2004) on mineral separates of Shergotty found that the highest concentrations of Xe were released by opaque separates (∼10−11 cm3 STP g−1), followed by maskelynite sepa-rates (∼3.5 × 10−12 cm3 STP g−1), and finally pyroxene separates (∼1.5 × 10−12 cm3 STP g−1; Table 1). Xe from maskelynite and opaque separates showed clear evidence of a contribution from the Martian atmosphere, exhibiting bulk 129Xe/132Xe ratios of 1.29 (Table 1). Release patterns from opaques and maskelynite separates trended to higher 129Xe/132Xe ratios with increasing temperature. This was interpreted as reflecting shock incorporation, the higher concentration of Xe in opaques being attributed to grain-size-dependent preconcentration by adsorption. (Smaller grains have higher specific surface area and so adsorb more gas per unit mass, subsequent shock redistributes gas into sites that retain Xe to higher temperatures during step-heating, and subsequent addition of EFA populates less retentive sites so the ratio of Martian Xe to Xe from EFA increases with release temperature in step-heating experiments.) In contrast, pyroxene samples exhibited consistent 129Xe/132Xe ratios (average 1.217 ± 0.009; Table 1) across the step-heating analysis, which was interpreted as reflecting a trapped magmatic component, with a contribution from the Martian atmosphere. Schwenzer et al. (2007) subsequently reported similar elevated Xe concentrations (∼4.5 × 10−12 cm3 STP g−1) and evolution with temperature in their maskelynite fraction of Shergotty. Like Ocker and Gilmour (2004), they attributed this to the implantation of Martian atmosphere into grain surfaces. Their pyroxene fraction had a higher 132Xe concentration (∼3.5 × 10−12 cm3 STP g−1) than that of Ocker and Gilmour (2004). It exhibited a low 129Xe/132Xe ratio at low temperatures, approaching the consistent value identified by Ocker and Gilmour (2004) only at higher temperatures. This suggests modification of the uniform pyroxene signature by the addition of a low-release temperature component such as air contamination in their analyses—their elemental ratios among the heavy noble gases also suggest air contamination. Perhaps influenced by the resulting similarity in release pattern between pyroxene and maskelynite, they associated the incorporation of Martian atmospheric Xe into pyroxene with a similar mechanism to that invoked for maskelynite. However, Ocker and Gilmour (2004) had shown that this, in contrast to the maskelynite and opaque data, represents a trapped component with a 129Xe/132Xe ratio around 1.2 rather than a mixing between Martian atmospheric Xe (129Xe/132Xe = 2.4) and a second, lower release temperature component with lower 129Xe/132Xe, as present in the maskelynite and opaque separates.

We now contrast the Xe isotope distributions among mineral aliquots for the four different meteorites in order to determine differences stemming from different terrestrial histories and similarities related to their similar histories on Mars.

Concentrations and Incorporation Mechanism of Terrestrial Atmospheric Xe

132Xe concentration ([132Xe]; Table 1) varies among the four meteorites analyzed from the most gas rich—RBT 04262 ([132Xe] ∼ 10−10 cm3 STP g−1)—through DaG 489 ([132Xe] ∼ 5 × 10−11 cm3 STP g−1) to EET 79001 and Shergotty ([132Xe] <10−11 cm3STP g−1). Shergotty concentrations are consistent with those reported by Ocker and Gilmour (2004). We attribute this variation to differing extents of terrestrial weathering, noting that the calculated residence times are: Shergotty = 0 (fall); EET 79001 = 0.13 ± 0.12 Ma (Nyquist et al. 2001a); and DaG 489 = 0.85 ± 0.5 Ma (Nishiizumi et al. 1999). Park et al. (2003) report a terrestrial residence time of 0.14 Ma for its pair DaG 476 calculated from the CRE age and an apparent 81Kr-Kr age. The details of the calculation are not presented and no uncertainty is given, so it is unclear whether this is consistent with the exposure age reported for DaG 489 or not. For these three meteorites, [132Xe] increases with residence time (using 0.85 Ma as the DaG 489 terrestrial residency), and we suggest that the high [132Xe] of RBT 04262 indicates more extensive weathering, which may imply a longer residence time. (We note that Schwenzer et al. 2009 demonstrate that contamination increases with proximity to the fusion crust for Antarctic meteorites, but that our samples are all derived from interior portions.) Differences in weathering environment may also play a role, where RBT 04262 and EET 79001 experienced cold and dry conditions (Antarctica), DaG 489 warm and dry conditions (Sahara), whereas Shergotty is a fall. Excluding DaG 489, where high concentrations are observed in the pyroxenes and iddingsite, the opaque-rich separates tend to have higher gas concentrations than the other separates (Table 1).

Concentrations and Incorporation Mechanism of Martian Atmospheric Xe

We use 129XeXS as a tracer of the Martian atmosphere, where 129XeXS = (129Xe/132XeMeasured −129Xe/132XeTerrestrial Air) × 132Xe, and 129Xe/132XeTerrestrial Air = 0.9832 (Basford et al. 1973). Terrestrial air (rather than Martian interior) is adopted as the baseline over which 129XeXS is calculated as it is clearly the dominant endmember in the more weathered meteorites, where [129XeXS] (the concentration of 129XeXS) is sensitive to the choice of baseline. [129XeXS] is relatively consistent among corresponding mineral separates from all four meteorites (Table 1), although for DaG 489 and RBT 04262 large errors are introduced by the high concentrations of terrestrial 132Xe (results for EET 79001 and Shergotty are not significantly changed if the 129Xe/132Xe ratio of the Martian interior is adopted as the baseline composition). More significantly, release patterns between corresponding mineral separates from different meteorites exhibit similar trends (Fig. 2). Opaque aliquots from EET 79001, DaG 489, and RBT 04262 display increasing 129Xe/132Xe ratios with temperature, until a large release occurs at mid–high temperatures, followed by a slight decrease in 129Xe/132Xe (Fig. 2). Although a decrease in 129Xe/132Xe is not observed by Ocker and Gilmour (2004) for their opaque phases, this may be an artifact of the respective step-heating regimes and our release patterns are broadly consistent. The maximum 129Xe/132Xe ratios achieved in EET 79001 (1.69 ± 0.06; EET-E) and DaG 489 (1.56 ± 0.05; DaG-B) are not significantly different from each other or from that of Shergotty (1.61 ± 0.02; Ocker and Gilmour 2004). In contrast, RBT 04262 reached a maximum of only 1.14 ± 0.01 (RBT-I).

All maskelynite aliquots display a clear increase in 129Xe/132Xe with temperature (Fig. 2). Differences are seen in the maximum 129Xe/132Xe achieved, with the highest seen in DaG 489 (1.86 ± 0.18), then Shergotty (1.51 ± 0.03), EET 79001 (1.35 ± 0.02), and RBT 04262 (1.04 ± 0.02). The observed trends are consistent with data previously reported by Ocker and Gilmour (2004) where two samples of Shergotty maskelynite reached 129Xe/132Xe maxima of 1.3 and 1.8 at high temperature, and thus also consistent with the data of Schwenzer et al. (2007).

The peak 129Xe/132Xe ratio reached depends on the temperature resolution of the step-heating experiment and the partitioning of releases from the various components among the temperature steps. However, it is clear that the variations among the observed maxima in 129Xe/132Xe are also in part due to the different relative concentrations of 132Xe in the different meteorites, which can be attributed to variations in terrestrial contamination.

These reproducible variations in 129Xe/132Xe with release temperature in analyses of opaque and maskelynite fractions demonstrate that the terrestrial atmosphere and Martian atmosphere are not located in similar sites/phases within the meteorites. It is expected that Martian and terrestrial weathering introduce atmospheric components in similar ways (i.e., by changing the chemistry of the surface and increasing the surface area available for adsorption). As the terrestrial atmosphere has been introduced into the samples by weathering, this indicates that weathering alone cannot be responsible for the current location of the Martian atmospheric component—a further process is required to allow it to contribute to a greater extent to mid–high temperature steps. There is a stark contrast between the similar concentrations of Martian atmospheric Xe within the meteorites and the variable concentrations of 132Xe incorporated from the terrestrial atmosphere by weathering on Earth. Although similar processes in similar Martian environments have caused the similar 129XeXS distributions within the meteorites, distinct terrestrial histories have caused dramatic differences in concentrations of terrestrial 132Xe.

In addition, the similar release patterns and consistent [129XeXS] data reflect a similar 129Xe incorporation mechanism for the opaque and maskelynite fractions of all four meteorites. They exhibit distinct shock pressures and CRE ages, implying several distinct ejection events from different locales (Nyquist et al. 2001a; Nagao and Park 2008). Moreover, the crystallization ages of the four meteorites are different, with DaG 489 the oldest at 474 ± 11 Ma (Borg et al. 2003), EET 79001 174 ± 3 Ma (Nyquist et al. 2001b), Shergotty 165 ± 11 Ma (Nyquist et al. 1979), and recent works on RBT 04262 report a range in ages from 167 ± 6 Ma (Shih et al. 2009) to 225 ± 21 Ma (Lapen et al. 2008). This, in turn, suggests that the mechanism of incorporation of Martian atmospheric Xe into its current sites is either widespread in the Martian surface environment or associated with the ejection of material in impacts.

Our observations of terrestrial air within the Martian meteorites (released at low temperatures during the experiments) show that weathering introduces Xe from an ambient atmosphere into rock samples. It is likely that weathering processes on Mars act in the same way, introducing Martian atmosphere into igneous lithologies on or close to the surface. Within any one meteorite, the distribution of [129XeXS] among phases is similar to that of [132Xe]; for instance, opaque aliquots tend to contain the highest 129XeXS and 132Xe concentrations (Table 1). This suggests that the mechanisms of incorporation of Martian atmospheric Xe and terrestrial atmospheric Xe share some common features.

However, to account for the higher release temperatures of Martian atmospheric Xe in our analyses, an additional mechanism is required. We propose that shock is the mechanism responsible, acting to reposition the Xe introduced by weathering.

We thus suggest that the elevated 129Xe/132Xe ratios released at high temperatures during the step-heating experiments for the opaque and maskelynite samples represent shock-redistribution of Martian atmosphere originally introduced by adsorption during weathering or onto weathering products. Originally, the Martian atmosphere component was present within weathering products in the meteorites, as the terrestrial atmosphere is today. This component was subsequently redistributed and bound/fixed into grain surfaces of the major minerals during ejection from Mars (or possibly by previous impacts on the planet’s surface). As Ocker and Gilmour (2004) noted, this mechanism would be expected to preferentially trap Xe, resulting in elementally fractionated Martian atmosphere. To date, analyses of mineral separates have not produced data that can define the Kr/Xe ratio of the trapped component with elevated 129Xe/132Xe ratio with sufficient precision to test this hypothesis.

The DaG 489 “iddingsite” aliquot also showed an increase of 129Xe/132Xe with temperature, reaching a maximum 129Xe/132Xe of 1.38 ± 0.10, indicative of a Martian component, whereas lower temperature heating steps displayed 129Xe/132Xe ratios similar to terrestrial atmosphere. The final step amounting to 70% of the total 132Xe release was dominated by terrestrial air, but this step was measured independently of the others, following an instrument problem that resulted in the sample being exposed to terrestrial atmosphere and then reanalyzed. Accordingly, this has been omitted from the release plot, but illustrates how readily Xe is adsorbed onto mineral surfaces exposed to an atmosphere. Our data demonstrate that some of this sample was of Martian origin, but it cannot be excluded that it represents a mixture of Martian opaques with terrestrial weathering products, or that Martian atmospheric Xe survived the terrestrial weathering process in situ. The release patterns, [132Xe] and [129XeXS], are consistent with those of the maskelynite and opaque samples of RBT 04262, EET 79001, and Shergotty (Table 1) (Ocker and Gilmour 2004).

WR Samples

In contrast to mineral separates, “whole rock” aliquots from EET-A, EET-B, and DaG-A do not show obvious trends of increasing 129Xe/132Xe with increasing laser power (temperature). Additionally, WR 132Xe concentrations are lower than those of other phases (Table 1). If these WR concentrations were representative, an abundance of about 25% mafic minerals in our nominally pyroxene separates would account for all the 132Xe in EET 79001. In DaG 489, only 5% pyroxene would be required (Table 1). In each case, the complementary components would be gas free, whereas our other separates actually have higher 132Xe concentrations. This is in conflict with the modal mineralogies: 57% pyroxene, 0% olivine in EET 79001 (Lodders 1998); 54% pyroxene, 20% olivine in DaG 489 (Folco et al. 2000).

Our WR sample of DaG 489 had a 132Xe concentration of (3.2 ± 0.5) × 10−12 cm3 STP g−1 and a 129Xe/132Xe ratio of 1.104 ± 0.011 (Table 1). This is similar to the results of our maskelynite measurement from this meteorite. Folco et al. (2000) reported a bulk [132Xe] concentration of 53 × 10−12 cm3 STP g−1, and 129Xe/132Xe of 0.99 ± 0.06, similar to our pyroxene measurements. We therefore suggest that, for DaG 489, our WR phase is not representative of the bulk meteorite because of its small sample size relative to the grain size of this meteorite, and was likely dominated by maskelynite. By comparison, the remaining mineral separate data are broadly consistent with the Folco et al. (2000) bulk measurement. Mohapatra et al. (2009) found two interior chips of DaG 476 (paired with DaG 489) had 132Xe concentrations of 5.5 and 6.3 × 10−12 cm3 STP g−1, and 129Xe/132Xe ratios up to ∼1.57. A third chip from the surface of DaG 476 had an elevated 132Xe concentration of 17.90 × 10−12 cm3 STP g−1 and a lower 129Xe/132Xe ratio of 0.99. Although the surface chip clearly indicates terrestrial contamination, it is hard to account for the data from the interior chips given the mineral separate data we present. The implied bulk concentration of Martian atmospheric Xe is higher than those found in any phase we analyzed for DaG 489, whereas the comparatively low concentrations of terrestrial atmospheric Xe suggest less weathering and perhaps a shorter residence time than its pair. This is consistent with the comparatively short residence time reported by Park et al. (2003). We note caveats regarding this research above, but suggest that the pairing of these meteorites may be worthy of re-examination.

For EET 79001, our WR 132Xe concentration—(2.0 ± 0.2) × 10−12 cm3 STP g−1—is again much lower than that of the pyroxene phases—(7.6 ± 0.4) × 10−12 cm3 STP g−1—and the WR 129Xe/132Xe ratio (1.266 ± 0.013) is again higher than that of pyroxene separates (0.992 ± 0.003) (Table 1). However, in this case, literature WR data are also not consistent with our mineral separate data and modal mineralogies. Swindle et al. (1986) reported an EET 79001 (lith B) 132Xe concentration of 5.72 × 10−12 cm3 STP g−1, and an elevated 129Xe/132Xe ratio of 2.15 ± 0.01. Garrison and Bogard (1998) analyzed a shock glass inclusion from EET 79001 lithology B, and reported a total 132Xe concentration of ∼16 × 10−12 cm3 STP g−1 with 129Xe/132Xe of Martian atmosphere (maximum ∼2.42). If we assume that the WR sample from Swindle et al. (1986) lies on a mixing line between endmembers of the shock glass from Garrison and Bogard (1998) and the remaining phases in the meteorite (assumed to have Martian interior Xe with 129Xe/132Xe 1.0292; Ott 1988), the reported WR 129Xe/132Xe ratio requires that 82% of the 132Xe originate from the shock glass. This translates to a shock glass abundance in the Swindle et al. (1986) WR sample of 29% by mass. However, if we attribute the remaining 18%132Xe contribution to our EET 79001 pyroxene (Table 1), this requires a total pyroxene abundance of only 14% by mass. The remaining 57% by mass would therefore contain no gas. Substituting our WR values of [132Xe] = 2 × 10−12 cm3 STP g−1 and 129Xe/132Xe = 1.266 in place of that of Swindle et al. (1986), 17% of the 132Xe originates from shock glass. This translates to a shock glass abundance in our WR sample of ∼2%. Again, attributing the remaining 83% to our EET 79001 pyroxene requires a total pyroxene abundance of only 22% by mass, with the remaining 76% by mass containing no gas. As these calculated abundances of pyroxene are both three to four times lower than the modal abundance of pyroxene in EET 79001, we suggest that our pyroxene separates are not representative of the [132Xe] of the mineral phase in the bulk meteorite. The high 132Xe concentrations (7.6 × 10−12 cm3 STP g−1) and low 129Xe concentration (0.07 × 10−12 cm3 STP g−1) might be explained if the pyroxene samples have acquired 132Xe during the mineral-separating process. The EET 79001 mineral separates were taken from thick sections previously used for SEM analysis. Niedermann and Eugster (1992) showed that intense mechanical treatment of lunar samples caused the irreversible incorporation of atmospheric gases into the samples. The required sample preparation (cutting and polishing) to create the EET 79001 section may thus have introduced 132Xe that was not removed by subsequent cleaning. However, the Shergotty separates were prepared using the same technique, without gaining a similar high concentration of 132Xe. Possibly, our selection of pyroxene grains may have favored smaller crystals than typical of the bulk meteorite, and these may have elevated [132Xe] due to increased susceptibility to terrestrial weathering. In addition, as shock glass is a rare phase within meteorites (a “glassy mesostasis” of 0.5–1.1% was observed in EET 79001 lithology B by McSween and Jarosewich 1983), a 29% abundance for a sample is not viable. We propose that in this respect, coincidentally, our small WR samples have Xe systematics closer to those of the bulk meteorite than the data reported by Swindle et al. (1986).

Mafic Minerals

Pyroxene and olivine/pyroxene aliquots for all meteorites show similar release patterns, where 129Xe/132Xe plateaus were between about 0.98 and ∼1.03 for EET 79001, RBT 04262, and DaG 489, whereas the Shergotty pyroxene 129Xe/132Xe averaged 1.12 ± 0.01 (Table 1). This contrasts with the temperature-dependent variation exhibited by opaque- and maskelynite-rich separates (Fig. 2). Our Shergotty results are consistent with the release patterns reported in pyroxene samples by Ocker and Gilmour (2004), and their average 129Xe/132Xe is similar to that of our Shergotty separates at 1.16–1.29 (Table 1; Fig. 3). Multiple and single-grained olivine/pyroxene aliquots of RBT 04262 were used to assess grain size and surface area effects on Xe isotopes (e.g., terrestrial atmosphere adsorption or implantation during crush disaggregation of grains). However, no consistent dependence in 132Xe or 129Xe gas concentration and grain size of these samples was observed (Table 1).

image

Figure 3.  Three isotope plot displaying the bulk compositions of mafic aliquots for meteorites RBT 04262, DaG 489, EET 79001, Shergotty, and previous Shergotty data (Ocker and Gilmour 2004). The full line represents mixing between Martian interior (Ott 1988) and atmosphere (Swindle et al. 1986), and the dashed lines represent mixing between these reservoirs and Earth’s atmosphere (Basford et al. 1973). Further Martian interior components with variable amounts of fission (Chass-S, Chass-E, and an estimated ALH 84001 interior) are also plotted (Mathew and Marti 2001). The olivine/pyroxene aliquots of RBT 04262 are all seen to cluster around Earth’s atmosphere. The pyroxene aliquots for EET 79001 (EET-C, EET-D) and DaG 489 (DaG-C) cluster in a similar area, though contain higher 136Xe/132Xe values. Our Shergotty data are consistent with those found by Ocker and Gilmour (2004) for pyroxene aliquots. The data show that RBT 04262 has experienced a high amount of terrestrial contamination.

Download figure to PowerPoint

Figure 3 displays a three-isotope plot of 129Xe/132Xe versus 136Xe/132Xe (total Xe) for the mafic aliquots from this study, alongside data from the pyroxene aliquots for Shergotty reported by Ocker and Gilmour (2004). The mafic aliquots for RBT 04262 plot near terrestrial atmosphere with a suggestion of a contribution from an evolved Martian interior component similar to Chassigny E (“Chass E”; Mathew and Marti 2001). Both our data for Shergotty and those of Ocker and Gilmour (2004) contain higher 129Xe/132Xe ratios and lie on a mixing line between Martian atmosphere and a mixture of Martian interior with fission (Fig. 3). Data from DaG 489 and one aliquot of EET 79001 (EET-C) show an addition of fission Xe to a component similar to terrestrial atmosphere/Martian interior, whereas the second aliquot of EET 79001 (EET-D) presents less evidence for a fission contribution while in other respects being indistinguishable from the first aliquot (EET-C) (Fig. 3; Table 1). The range in fission contributions observed in the Shergotty pyroxene data seems similar to that observed between the two pyroxene samples from EET 79001.

The data from mafic minerals require three components mixed in varying proportions among the meteorites. Terrestrial atmosphere dominates those samples exposed to high amounts of weathering. A fission component is present but is distributed unevenly when mafic minerals are sampled on the few milligram scale employed in our analyses. Finally, excess 129Xe is present in mafic minerals from Shergotty in concentrations higher than is observed for the maximum concentrations of our EET 79001 data: overprinting with terrestrial atmospheric Xe makes it unclear whether this component is present in RBT 04262 and DaG 489.

Our data from Shergotty pyroxene are similar to those reported by Ocker and Gilmour (2004). Based on the reproducible 129Xe/132Xe ratios observed across stepped heating experiments, and noting that Herd et al. (2002) had explained high abundances of LREEs, low εNd, and log O fugacity (log fO2) values of about −1 (relative to QFM) in Shergotty as a result of assimilation of crustal material into the parent magma, Ocker and Gilmour (2004) concluded that their observation was compatible with that model. They proposed that crustal material in contact with the Martian atmosphere would contain adsorbed Xe with a high 129Xe/132Xe ratio that would mix with Martian interior Xe already present in the melt as crustal material was incorporated.

EET 79001 contains lower abundances of LREEs, lower εNd, and log fO2 ∼ −1.8, indicative of less crustal assimilation (Herd et al. 2002). This is consistent with our observation that [129XeXS] for mafic minerals in EET 79001 is lower than that observed in Shergotty (Table 1), assuming that the process or selection effect that appears to have added terrestrial 132Xe to these separates did not lead to a loss of 129XeXS. Unfortunately, although both DaG 489 and RBT 04262 display lower 129Xe/132Xe values than Shergotty, these cannot be related to crustal incorporation to test this process further; in both cases the presence of 132Xe makes the upper limit on [129XeXS] consistent with both the EET 79001 and Shergotty data.

Bogard and Park (2008a, 2008b) observed excess 40Ar (40ArXS) within mineral separates of the shergottite Zagami, which was not produced in situ. They proposed that this excess was inherited from the parent magma, either by degassing from surrounding rock or by assimilation of potassium-rich crust into the magma. The 40ArXS amounts are similar for a number of shergottites, where a constant 40Ar concentration is achieved by 40Ar loss as pressure in the rising magma was released during crystallization (Bogard and Park 2008a, 2008b). As a number of shergottites share a common crystallization age with Zagami of 170 Ma (Nyquist et al. 2001a), Bogard and Park (2008b) suggested that they are probably derived from the same source region. More recent work by Bogard et al. (2009) report 40ArXS in a number of Martian shergottites, and concluded that although some 40Ar is implanted due to shock (e.g., shock impact glass seen to carry an Ar signature of the recent Martian atmosphere, as shown by Bogard and Garrison 1999), some 40ArXS was observed uniformly distributed throughout mineral lattices within the meteorites (possibly a result of assimilation of a K-rich crustal material before crystallization, as discussed by Bogard and Park 2008a). They concluded that the inherited trapped argon component is similar in all the shergottites, suggesting a similar magma source or generation process.

The variable concentration of 129XeXS inherited from the parent magma that we observe between Shergotty and EET 79001 implies a distinct mechanism of incorporation from 40ArXS. If excess 129Xe indeed represents a crustal contribution to the melt, 40ArXS might be seen as intrinsic to the source region of the melt. A KREEP-like layer in the Martian mantle, as proposed by Taylor and McLennan (2008), might be implicated as the source of such a contribution. The hypothesis that both 129XeXS and 40ArXS are associated with the melt from which the source rocks crystallized might be tested by the analysis of melt inclusions within the mafic minerals. Melt inclusions, such as those observed in RBT 04262, are likely sites for Martian interior noble gas components, in comparison with Martian atmospheric noble gases that may be incorporated into the meteorite by weathering products or by shock.

Summary

  1. Top of page
  2. Abstract
  3. Introduction
  4. Samples and Experimental Procedure
  5. Results and Discussion
  6. Summary
  7. Acknowledgments
  8. References
  9. Appendix

Mineral separates from Martian shergottites RBT 04262, EET 79001, Shergotty, and DaG 489 were analyzed for Xe isotopes using RELAX. All meteorites show a similar distribution of Martian components among minerals, with the highest gas concentrations observed in the opaque mineral fractions. Release patterns are similar to those reported by Ocker and Gilmour (2004), where an increase in 129Xe/132Xe is observed with temperature for both maskelynite and opaque fractions. By contrast, the mafic minerals display low 129Xe/132Xe ratios. Large differences in [132Xe] are a result of variation in overprinting by terrestrial contamination. Similar 129Xe incorporation mechanisms must be invoked to account for the little variation observed for [129Xexs] among equivalent separates from different meteorites, compared with the large [132Xe] variation that is controlled by terrestrial contamination.

We suggest that the elevated 129Xe/132Xe ratios observed in high-temperature releases from maskelynite and opaque samples result from shock redistribution of Martian atmospheric Xe previously associated with pre-existing Martian weathering or alteration products. This accounts for the Martian atmospheric component having a higher release temperature than that derived from the terrestrial atmosphere, which appears to have been introduced by weathering alone. This may also have occurred for the mafic minerals, although terrestrial contamination has overprinted the signal.

Crustal contamination/incorporation into the parent melt of the meteorites is consistent with the Xe data. In this study, the variable [129XeXS] observed for the meteorites analyzed, in particular mafic samples from Shergotty and EET 79001, reflects differences in crustal contamination of the parent melt. A second source is needed to account for 40ArXS, which appears in relatively constant concentrations among the shergottites.

Although different shergottite subgroups were analyzed in this study, the observed Xe isotope variations are ascribed to differences in weathering, rather than petrographic differences, except in the case of 129XeXS, where crustal contribution to the magma is a factor.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Samples and Experimental Procedure
  5. Results and Discussion
  6. Summary
  7. Acknowledgments
  8. References
  9. Appendix

Acknowledgments— We are grateful to ANSMET for supplying the samples of EET 79001 and RBT 04262 (RBT 04262 was supplied via M. Anand, OU), and to the NHM for the Shergotty sample. We thank D. Blagburn and B. Clementson for technical support. This work was funded by the STFC and a graduate research assistantship (for K. Ocker) at the Institute for Rare Isotope Measurements, which was funded in part by NASA grants NAGW-4774 and NAG5-3464. We thank reviewers S. Schwenzer and J. Park.

Editorial Handling— Dr. Timothy Swindle

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Samples and Experimental Procedure
  5. Results and Discussion
  6. Summary
  7. Acknowledgments
  8. References
  9. Appendix
  • Anand M., James S., Greenwood R. C., Johnson D., Franchi I. A., and Grady M. M. 2008. Mineralogy and geochemistry of shergottite RBT 04262 (abstract #2173). 39th Lunar and Planetary Science Conference. CD-ROM.
  • Basford J. R., Dragon J. C., and Pepin R. O. 1973. Krypton and xenon in lunar fines. 4th Lunar Science Conference. pp. 19151955.
  • Bogard D. and Garrison D. H. 1999. Argon-39-argon-40 “ages” and trapped argon in Martian shergottites, Chassigny, and Allan Hills 84001. Meteoritics & Planetary Science 34:451473.
  • Bogard D. D. and Garrison D. H. 2008. 39Ar-40Ar age and thermal history of Martian dunite NWA 2737. Earth and Planetary Science Letters 273:386392.
  • Bogard D. D. and Johnson P. 1983. Martian gases in an Antarctic meteorite? Science 221:651654.
  • Bogard D. D. and Park J. 2008a. 39Ar-40Ar dating of the Zagami Martian shergottite and implications for magma origin of excess 40Ar. Meteoritics & Planetary Science 43:11131126.
  • Bogard D. D. and Park J. 2008b. Excess 40Ar in Martian shergottites, K-40Ar ages of nakhlites, and implications for in situ K-Ar dating of Mars’ surface rocks (abstract #1100). 39th Lunar and Planetary Science Conference. CD-ROM.
  • Bogard D., Park J., and Garrison D. H. 2009. 39Ar-40Ar “ages” and origin of excess 40Ar in Martian shergottites. Meteoritics & Planetary Science 44:905923.
  • Borg L. E., Nyquist L. E., Wiesmann H., Shih C.-Y., and Reese Y. 2003. The age of Dar al Gani 476 and the differentiation history of the Martian meteorites inferred from their radiogenic isotopic systematics. Geochimica et Cosmochimica Acta 67:35193536.
  • Bouvier A., Blichert-Toft J., Vervoort J. D., and Albarède F. 2005. The age of SNC meteorites and the antiquity of the Martian surface. Earth and Planetary Science Letters 240:221233.
  • Bouvier A., Blichert-Toft J., Vervoort J. D., Gillet P., and Albarède F. 2008. The case for old basaltic shergottites. Earth and Planetary Science Letters 266:105124.
  • Breuer D., Yuen D. A., and Spohn T. 1997. Phase transitions in the Martian mantle: Implications for partially layered convection. Earth and Planetary Science Letters 148:457469.
  • Bridges J. C., Catling D. C., Saxton J. M., Swindle T. D., Lyon I. C., and Grady M. M. 2001. Alteration assemblages in Martian meteorites: Implications for near-surface processes. Space Science Reviews 96:365392.
  • Crowther S. A., Mohapatra R. K., Turner G., Blagburn D. J., Kehm K., and Gilmour J. D. 2008. Characteristics and applications of RELAX, an ultrasensitive resonance ionization mass spectrometer for xenon. Journal of Analytical Atomic Spectrometry 23:938947.
  • Dalton H. A., Peslier A. H., Brandon A. D., Lee C.-T. A., and Lapen T. J. 2008. Petrology and mineral chemistry of new olivine-phyric shergottite RBT 04262 (abstract #2308). 39th Lunar and Planetary Science Conference. CD-ROM.
  • Drake M. J., Swindle T. D., Owen T., and Musselwhite D. S. 1994. Fractionated Martian atmosphere in the nakhlites? Meteoritics & Planetary Science 29:854859.
  • Folco L., Franchi I. A., D’Orazio M., Rocchi S., and Schultz L. 2000. A new Martian meteorite from the Sahara: The shergottite Dar al Gani 489. Meteoritics & Planetary Science 35:827839.
  • Fritz J., Greshake A., and Stöffler D. 2005. Micro-Raman spectroscopy of plagioclase and maskelynite in Martian meteorites: Evidence of progressive shock metamorphism. Antarctic Meteorite Research 18:96116.
  • Garrison D. H. and Bogard D. D. 1998. Isotopic composition of trapped and cosmogenic noble gases in several Martian meteorites. Meteoritics & Planetary Science 33:721736.
  • Gibson E. K., McKay D. S., Thomas-Keprta K. L., Wentworth S. J., Westall F., Steele A., Romanek C. S., Bell M. S., and Toporski J. 2001. Life on Mars: Evaluation of the evidence within Martian meteorites ALH 84001, Nakhla, and Shergotty. Precambrian Research 106:1534.
  • Gilmour J. D., Lyon I. C., Johnston W. A., and Turner G. 1994. RELAX: An ultrasensitive, resonance ionization mass spectrometer for xenon. Review of Scientific Instruments 65:617625.
  • Gilmour J. D., Whitby J. A., and Turner G. 1998. Xenon isotopes in irradiated ALH 84001: Evidence for shock-induced trapping of ancient Martian atmosphere. Geochimica et Cosmochimica Acta 62:25552571.
  • Gilmour J. D., Whitby J. A., and Turner G. 1999. Martian atmospheric xenon contents of Nakhla mineral separates: Implications for the origin of elemental mass fractionation. Earth and Planetary Science Letters 166:139147.
  • Gilmour J. D., Whitby J. A., and Turner G. 2001. Disentangling xenon components in Nakhla: Martian atmosphere, spallation and Martian interior. Geochimica et Cosmochimica Acta 65:343354.
  • Goodrich C. A. 2002. Olivine-phyric Martian basalts: A new type of shergottite. Meteoritics & Planetary Science 37:B31B34.
  • Greenwood J. P. 2008. Gypsum and jarosite in Roberts Massif 04262: Antarctic(?) weathering as a proxy for Martian weathering (abstract #2011). 39th Lunar and Planetary Science Conference. CD-ROM.
  • Grossman J. 1999. The Meteoritical Bulletin, No. 83, 1999 July. Meteoritics & Planetary Science 34:169186.
  • Halliday A. N., Wänke H., Birck J.-L., and Clayton R. N. 2001. The accretion, composition and early differentiation of Mars. Space Science Reviews 96:197230.
  • Harder H. and Christensen U. R. 1996. A one-plume model of Martian mantle convection. Nature 380:507509.
  • Herd C. D. K., Borg L. E., Jones J. H., and Papike J. J. 2002. Oxygen fugacity and geochemical variations in the Martian basalts: Implications for Martian basalt petrogenesis and the oxidation state of the upper mantle of Mars. Geochimica et Cosmochimica Acta 66:20252036.
  • Hutchison R. 2004. Meteorites: A petrologic, chemical and isotopic synthesis. Cambridge, UK: Cambridge University Press.
  • Korochantseva E. V., Trieloff M., Buikin A. I., and Hopp J. 2009. Shergottites Dhofar 019, SaU 005, Shergotty, and Zagami: 40Ar–39Ar chronology and trapped Martian atmospheric and interior argon. Meteoritics & Planetary Science 44:293321.
  • Lapen T. J., Brandon A. D., Beard B. L., Peslier A. H., Lee C.-T. A., and Dalton H. A. 2008. Lu-Hf age and isotope systematics of the olivine-phyric shergottite RBT 04262 and implications for the sources of enriched shergottites (abstract #2073). 39th Lunar and Planetary Science Conference. CD-ROM.
  • Laul J. C. 1986. The Shergotty Consortium and SNC meteorites: An overview. Geochimica et Cosmochimica Acta 50:875887.
  • Lodders K. 1998. A survey of shergottite, nakhlite and Chassigny meteorites whole-rock compositions. Meteoritics & Planetary Science 33:A183A190.
  • Mathew K. J. and Marti K. 2001. Early evolution of Martian volatiles: Nitrogen and noble gas components in ALH 84001 and Chassigny. Journal of Geophysical Research 106:14011422.
  • Mathew K. J. and Marti K. 2002. Martian atmospheric and interior volatiles in the meteorite Nakhla. Earth and Planetary Science Letters 199:720.
  • McCoy T. and Reynolds V. 2007. Petrographic descriptions. Antarctic Meteorite Newsletter 30:16.
  • McSween H. Y. 1994. What we have learned about Mars from SNC meteorites. Meteoritics 29:757779.
  • McSween H. Y. and Jarosewich E. 1983. Petrogenesis of the Elephant Moraine A79001 meteorite: Multiple magma pulses on the shergottite parent body. Geochimica et Cosmochimica Acta 47:15011513.
  • McSween H. and Treiman A. H. 1998. Martian meteorites. In Planetary materials, vol. 36, edited by PapikeJ. J. Washington, D.C.: Mineralogical Society of America. pp. 6.16.53.
  • Melosh H. J. 1989. Impact cratering: A geologic process. New York & Oxford: Oxford University Press.
  • Meyer C. 2009. The Mars meteorite compendium, http://curator.jsc.nasa.gov/antmet/mmc/index.cfm .
  • Mikouchi T., Kuirhara T., and Miyamoto M. 2008. Petrology and mineralogy of RBT 04262: Implications for stratigraphy of the lherzolitic shergottite igneous block (abstract #2403). 39th Lunar and Planetary Science Conference. CD-ROM.
  • Mohapatra R. K., Schwenzer S. P., Herrmann S., Murty S. V. S., Ott U., and Gilmour J. D. 2009. Noble gases and nitrogen in Martian meteorites Dar al Gani 476, Sayh al Uhaymir 005 and Lewis Cliff 88516: EFA and extra neon. Geochimica et Cosmochimica Acta 73:15051522.
  • Nagao K. and Park J. 2008. Noble gases and cosmic-ray exposure ages of two Martian shergottites, RBT 04262 and LAR 06319, recovered in Antarctica (abstract #5200). 71st Annual Meteoritical Society Meeting, Matsue, Japan.
  • Niedermann S. and Eugster O. 1992. Noble gases in lunar anorthositic rocks 60018 and 65315: Acquisition of terrestrial krypton and xenon indicating an irreversible adsorption process. Geochimica et Cosmochimica Acta 56:493509.
  • Nishiizumi K., Masarik J., Welten K. C., Caffee M. W., Jull A. J. T., and Klandrud S. E. 1999. Exposure history of new Martian meteorite Dar al Gani 476 (abstract #1966). 30th Lunar and Planetary Science Conference. CD-ROM.
  • Nyquist L. E., Wooden J., Bansal B., Wiesmann H., McKay G. and Bogard D. D. 1979. Rb-Sr age of the Shergotty achondrite and implications for metamorphic resetting of isochron ages. Geochimica et Cosmochimica Acta 43:10571074.
  • Nyquist L. E., Bogard D. D., Shih C.-Y., Greshake A., Stöffler D., and Eugster O. 2001a. Ages and geologic histories of Martian meteorites. Space Science Reviews 96:105164.
  • Nyquist L. E., Reese Y., Wiesmann H., and Shih C.-Y. 2001b. Age of EET 79001 B and implications for shergottite origins (abstract #1407). 32nd Lunar and Planetary Science Conference. CD-ROM.
  • Ocker K. 2002. Martian xenon components in the basaltic shergottite meteorites. Ph.D. thesis, University of Tennessee, Knoxville, Tennesee, USA.
  • Ocker K. D. and Gilmour J. D. 2004. Martian xenon components in Shergotty mineral separates: Locations, sources, and trapping mechanisms. Meteoritics & Planetary Science 39:19671981.
  • Ott U. 1988. Noble gases in SNC meteorites: Shergotty, Nakhla, Chassigny. Geochimica et Cosmochimica Acta 52:19371948.
  • Owen T., Biemann K., Rushneck D. R., Biller J. E., Howarth D. W., and Lafleur A. L. 1977. The composition of the atmosphere at the surface of Mars. Journal of Geophysical Research 82:46354640.
  • Park J., Okazaki R., and Nagao K. 2003. Noble gas studies of Martian meteorites: Dar al Gani 476/489, Sayh al Uhaymir 005/060, Dhofar 019, Los Angeles 001 and Zagami (abstract #1213). 36th Lunar and Planetary Science Conference. CD-ROM.
  • Park J., Bogard D. D., Mikouchi T., and McKay G. A. 2008. Dhofar 378 Martian shergottite: Evidence of early shock melting. Journal of Geophysical Research 113:112, doi:10.1029/2007JE003035.
  • Pepin R. O. 1991. On the origin and early evolution of terrestrial planet atmospheres and meteoritic volatiles. Icarus 92:279.
  • Pepin R. O. 1994. Evolution of the Martian atmosphere. Icarus 111:289304.
  • Podosek F. A. 1970. Dating of meteorites by the high-temperature release of iodine-correlated Xe129. Geochimica et Cosmochimica Acta 34:341365.
  • Satterwhite C. and Righter K., 2007. New meteorites—Shergottites and ungrouped chondrites. Antarctic Meteorite Newsletter 30:120.
  • Schwenzer S., Herrmann S., Mohapatra R. K. and Ott U. 2007. Noble gases in mineral separates from three shergottites: Shergotty, Zagami and EETA79001. Meteoritics & Planetary Science 42:387412.
  • Schwenzer S., Fritz J., Stöffler D., Trieloff M., Amini M., Greshake A., Herrmann S., Herwig K., Jochum K. P., Mohapatra R. K., Stoll B., and Ott U. 2008. Helium loss from Martian meteorites mainly induced by shock metamorphism: Evidence from new data and a literature compilation. Meteoritics & Planetary Science 43:18411859.
  • Schwenzer S. P., Herrmann S., and Ott U. 2009. Noble gases in two shergottites and one nakhlite from Antarctica: Y000027, Y000097, and Y000593. Polar Science 3:8399.
  • Shih C.-Y., Nyquist L. E., and Reese Y. 2009. Rb-Sr and Sm-Nd studies of olivine-phyric shergottites RBT 04262 and LAR 06319: Isotopic evidence for relationship to enriched basaltic shergottites (abstract #1360). 40th Lunar and Planetary Science Conference. CD-ROM.
  • Stolper E. and McSween H. Y. 1979. Petrology and origin of the shergottite meteorites. Geochimica et Cosmochimica Acta 43:14751477, 1479-1483, 1485-1498.
  • Swindle T. D. 2002. Martian noble gases. In Noble gases in geochemistry and cosmochemistry, edited by PorcelliD., BallentineC. J. and WielerR. Volume 47: Reviews in mineralogy and geochemistry. Washington, D.C.: Mineralogical Society of America. pp. 171190.
  • Swindle T. D. and Jones J. H. 1997. The xenon isotopic composition of the primordial Martian atmosphere: Contributions from solar and fission components. Journal of Geophysical Research 102:16711678.
  • Swindle T. D., Caffee M. W., and Hohenberg C. M. 1986. Xenon and other noble gases in shergottites. Geochimica et Cosmochimica Acta 50:10011015.
  • Symes S. J. K., Borg L. E., Shearer C. K., and Irving A. J. 2008. The age of the Martian meteorite Northwest Africa 1195 and the differentiation history of the shergottites. Geochimica et Cosmochimica Acta 72:16961710.
  • Taylor S. R. and McLennan S. M. 2008. Planetary crusts: Their composition, origin and evolution. Cambridge, UK: Cambridge University Press.
  • Taylor L. A., Nazarov M. A., Shearer C. K., McSween H. Y., Cahill J., Neal C. R., Ivanova M. A., Barsukova L. D., Lentz R. C., Clayton R. N., and Mayeda T. K. 2002. Martian meteorite Dhofar 019: A new shergottite. Meteoritics & Planetary Science 37:11071128.
  • Treiman A. H. 1985. Amphibole and hercynite spinel in Shergotty and Zagami—Magmatic water, depth of crystallization, and metasomatism. Meteoritics 20:229243.
  • Walton E. L., Kelley S. P., and Spray J. G. 2007. Shock implantation of Martian atmospheric argon in four basaltic shergottites: A laser probe 40Ar/39Ar investigation. Geochimica et Cosmochimica Acta 71:497520.
  • Wiens R. C. 1988. Noble gases released by vacuum crushing of EETA79001 glass. Earth and Planetary Science Letters 91:5565.
  • Wiens R. C., Becker R. H., and Pepin R. O. 1986. The case for a Martian origin of the shergottites II: Trapped and indigenous gas components in EETA79001 glass. Earth and Planetary Science Letters 77:149158.

Appendix

  1. Top of page
  2. Abstract
  3. Introduction
  4. Samples and Experimental Procedure
  5. Results and Discussion
  6. Summary
  7. Acknowledgments
  8. References
  9. Appendix

Appendix 1. Data are given for all aliquots reported in this study.

  124Xe ± error126Xe ± error128Xe ± error129Xe ± error130Xe ± error131Xe ± error134Xe ± error136Xe ± error132Xe Conc.
  1. Xenon isotopes are normalized to 132Xe, and 132Xe concentration is in cm3 STP g−1. M = 129Xe/132Xe maxima.

RBT 04262
Olivine-pyroxene A, single fragment, 0.30 mg
11.0 A 0.361 ± 0.0670.047 ± 0.0806.135 ± 0.24697.834 ± 0.97914.825 ± 0.29478.776 ± 0.83938.293 ± 0.52632.538 ± 0.4692.04 × 10−11
12.0 AM0.460 ± 0.0350.417 ± 0.0457.418 ± 0.111104.773 ± 0.49715.173 ± 0.14279.179 ± 0.40338.822 ± 0.24932.610 ± 0.2237.12 × 10−11
13.0 A 0.381 ± 0.084−0.034 ± −0.1125.922 ± 0.337103.112 ± 1.34314.311 ± 0.37976.091 ± 1.07438.512 ± 0.69732.476 ± 0.6151.23 × 10−11
14.0 A 0.350 ± 0.072−0.099 ± −0.0904.613 ± 0.26699.015 ± 1.07414.972 ± 0.31878.281 ± 0.90438.682 ± 0.58133.030 ± 0.5171.16 × 10−11
15.0 A 0.217 ± 0.127−0.154 ± −0.1894.632 ± 0.46397.872 ± 1.58513.810 ± 0.46978.243 ± 1.34837.803 ± 0.87132.318 ± 0.7615.30 × 10−12
Total         1.21 × 10−10
Average 0.414 ± 0.0270.234 ± 0.0346.658 ± 0.093102.579 ± 0.40614.948 ± 0.11578.669 ± 0.33338.643 ± 0.20632.612 ± 0.181 
Olivine-pyroxene B, multiple fragments, 1.07 mg
11.0 A 0.369 ± 0.0610.155 ± 0.0646.348 ± 0.16197.809 ± 0.66314.676 ± 0.19978.280 ± 0.56337.848 ± 0.35131.950 ± 0.3181.06 × 10−11
11.5 AM0.442 ± 0.0310.319 ± 0.0357.469 ± 0.105101.369 ± 0.46615.763 ± 0.13680.025 ± 0.39138.560 ± 0.23933.081 ± 0.2162.51 × 10−11
12.0 A 0.382 ± 0.0450.291 ± 0.0497.068 ± 0.12699.028 ± 0.54214.939 ± 0.16178.495 ± 0.45738.316 ± 0.28632.242 ± 0.2581.46 × 10−11
12.5 A 0.386 ± 0.0370.275 ± 0.0436.716 ± 0.12499.390 ± 0.54815.011 ± 0.16078.530 ± 0.46139.103 ± 0.29032.963 ± 0.2591.03 × 10−11
13.0 A 0.392 ± 0.0430.219 ± 0.0526.802 ± 0.15498.568 ± 0.67015.188 ± 0.19778.183 ± 0.56439.270 ± 0.35732.948 ± 0.3188.67 × 10−12
13.5 A 0.433 ± 0.0420.253 ± 0.0486.926 ± 0.13599.587 ± 0.59315.078 ± 0.17478.354 ± 0.49739.160 ± 0.31632.978 ± 0.2809.69 × 10−12
14.0 A 0.375 ± 0.0500.154 ± 0.0675.906 ± 0.21998.569 ± 0.93514.841 ± 0.27577.806 ± 0.78937.900 ± 0.49333.636 ± 0.4505.77 × 10−12
15.0 A 0.342 ± 0.0460.135 ± 0.0616.684 ± 0.18498.920 ± 0.78614.993 ± 0.23378.224 ± 0.66438.468 ± 0.41732.989 ± 0.3807.83 × 10−12
16.0 A 0.370 ± 0.0580.051 ± 0.0745.410 ± 0.22698.027 ± 0.93514.480 ± 0.27777.800 ± 0.79338.342 ± 0.50332.434 ± 0.4504.55 × 10−12
19.0 A −0.067 ± −0.243−1.178 ± −0.3772.489 ± 0.93496.761 ± 2.62214.771 ± 0.79477.003 ± 2.19938.600 ± 1.46331.070 ± 1.2425.77 × 10−13
Total         9.76 × 10−11
Average 0.396 ± 0.0170.231 ± 0.0186.814 ± 0.05799.455 ± 0.26515.142 ± 0.07278.723 ± 0.22038.570 ± 0.13232.782 ± 0.113 
Olivine-pyroxene C, single fragment, 0.30 mg
11.0 A 0.223 ± 0.066−0.240 ± −0.0815.640 ± 0.26598.117 ± 1.02414.689 ± 0.30880.087 ± 0.87738.296 ± 0.55231.975 ± 0.4871.39 × 10−11
12.0 AM0.388 ± 0.0600.227 ± 0.0666.314 ± 0.15698.915 ± 0.65314.074 ± 0.19478.854 ± 0.55538.493 ± 0.34932.383 ± 0.3164.13 × 10−11
13.0 A 0.332 ± 0.092−0.118 ± −0.1134.356 ± 0.32898.803 ± 1.24314.670 ± 0.37378.496 ± 1.05237.895 ± 0.67132.462 ± 0.5969.95 × 10−12
14.0 A 0.248 ± 0.0920.046 ± 0.1505.053 ± 0.42796.584 ± 1.48615.264 ± 0.44878.120 ± 1.27837.895 ± 0.81831.920 ± 0.7077.47 × 10−12
15.0 A 0.029 ± 0.090−0.635 ± −0.1213.661 ± 0.37298.217 ± 1.34014.119 ± 0.39978.000 ± 1.13037.230 ± 0.71932.712 ± 0.6387.42 × 10−12
Total         8.00 × 10−11
Average 0.306 ± 0.0370.006 ± 0.0435.590 ± 0.11698.480 ± 0.47214.370 ± 0.13878.876 ± 0.40038.211 ± 0.25032.309 ± 0.222 
Olivine-pyroxene D, multiple fragments, 1.25 mg
11.0 A 0.859 ± 0.1271.137 ± 0.1627.496 ± 0.19697.786 ± 0.80114.203 ± 0.23278.351 ± 0.67937.282 ± 0.42030.929 ± 0.3714.60 × 10−12
11.5 A 0.372 ± 0.0440.445 ± 0.0537.736 ± 0.109100.828 ± 0.48715.868 ± 0.14279.425 ± 0.40638.749 ± 0.25132.981 ± 0.2252.43 × 10−11
12.0 A 0.454 ± 0.0840.459 ± 0.0906.701 ± 0.15599.879 ± 0.75014.877 ± 0.21179.037 ± 0.62938.091 ± 0.38132.258 ± 0.3428.52 × 10−12
13.0 AM0.406 ± 0.0570.333 ± 0.0638.156 ± 0.139104.648 ± 0.66516.635 ± 0.18880.633 ± 0.54738.058 ± 0.32132.139 ± 0.2872.51 × 10−11
13.5 A 0.771 ± 0.0700.908 ± 0.0917.538 ± 0.125101.155 ± 0.55415.281 ± 0.16179.031 ± 0.45838.355 ± 0.28432.250 ± 0.2531.06 × 10−11
14.0 A 0.886 ± 0.1331.220 ± 0.1856.608 ± 0.19499.611 ± 0.84714.102 ± 0.24079.669 ± 0.71538.100 ± 0.44232.009 ± 0.3894.27 × 10−12
15.0 A 0.496 ± 0.1520.706 ± 0.1986.403 ± 0.23599.496 ± 1.04013.956 ± 0.29978.237 ± 0.87537.630 ± 0.54230.990 ± 0.4763.31 × 10−12
16.0 A 0.534 ± 0.1520.771 ± 0.1796.044 ± 0.20398.962 ± 0.91713.806 ± 0.26377.199 ± 0.76836.739 ± 0.47531.430 ± 0.4244.67 × 10−12
17.0 A 1.723 ± 0.3600.544 ± 0.3454.842 ± 0.331100.528 ± 1.40613.166 ± 0.39678.748 ± 1.16635.678 ± 0.72129.878 ± 0.6291.55 × 10−12
19.0 A 1.197 ± 0.413−0.559 ± −0.4214.249 ± 0.42898.520 ± 1.67811.930 ± 0.46975.613 ± 1.39534.817 ± 0.86229.558 ± 0.7641.25 × 10−12
Total         8.82 × 10−11
Average 0.537 ± 0.0330.558 ± 0.0407.425 ± 0.078101.460 ± 0.31415.464 ± 0.09679.412 ± 0.25638.075 ± 0.16332.169 ± 0.144 
Olivine-pyroxene E, multiple fragments, 1.21 mg
11.0 A 0.094 ± 0.1440.199 ± 0.2864.711 ± 0.57797.349 ± 1.70914.762 ± 0.51378.016 ± 1.44437.319 ± 0.91832.081 ± 0.8231.10 × 10−12
11.5 A 0.465 ± 0.0390.291 ± 0.0436.981 ± 0.13099.796 ± 0.56715.200 ± 0.16679.058 ± 0.47938.870 ± 0.29932.699 ± 0.2659.65 × 10−12
12.0 A 0.356 ± 0.0410.344 ± 0.0527.077 ± 0.120100.363 ± 0.51814.997 ± 0.15379.031 ± 0.43539.064 ± 0.27332.461 ± 0.2431.23 × 10−11
12.5 A 0.083 ± 0.168−0.691 ± −0.2503.707 ± 0.63996.856 ± 1.92714.665 ± 0.59177.551 ± 1.61337.921 ± 1.06731.743 ± 0.9227.91 × 10−13
13.0 A 0.091 ± 0.088−0.037 ± −0.1524.743 ± 0.40698.497 ± 1.39314.411 ± 0.41979.287 ± 1.18537.550 ± 0.75131.926 ± 0.6631.71 × 10−12
14.0 AM0.424 ± 0.0380.416 ± 0.0437.768 ± 0.116104.906 ± 0.51015.813 ± 0.14980.799 ± 0.42238.295 ± 0.25732.336 ± 0.2314.00 × 10−11
14.5 A 0.418 ± 0.0430.459 ± 0.0546.935 ± 0.15299.197 ± 0.65515.197 ± 0.19578.298 ± 0.55338.944 ± 0.34833.051 ± 0.3148.57 × 10−12
15.0 A 0.334 ± 0.130−0.386 ± −0.1844.360 ± 0.47396.350 ± 1.55813.930 ± 0.46475.373 ± 1.31636.237 ± 0.82631.598 ± 0.7531.35 × 10−12
16.0 A 0.289 ± 0.067−0.126 ± −0.0885.227 ± 0.28598.354 ± 1.13314.416 ± 0.33578.686 ± 0.96137.765 ± 0.60033.284 ± 0.5473.38 × 10−12
17.0 A 0.325 ± 0.137−0.638 ± −0.1894.362 ± 0.50597.118 ± 1.65414.249 ± 0.49778.626 ± 1.39937.444 ± 0.89233.026 ± 0.8041.27 × 10−12
19.0 A 0.238 ± 0.208−0.793 ± −0.3203.661 ± 0.81298.605 ± 2.29313.490 ± 0.68272.682 ± 1.90036.899 ± 1.25031.371 ± 1.0826.55 × 10−13
19.0 Afoc0.297 ± 0.097−0.183 ± −0.1274.381 ± 0.35298.482 ± 1.26614.497 ± 0.37878.340 ± 1.06338.270 ± 0.67732.993 ± 0.6101.91 × 10−12
Total         8.26 × 10−11
Average 0.391 ± 0.0220.298 ± 0.0267.023 ± 0.072102.007 ± 0.32215.342 ± 0.09079.645 ± 0.26538.432 ± 0.15932.498 ± 0.140 
Olivine-pyroxene F, multiple fragments, 0.95 mg
11.5 A 0.404 ± 0.0500.235 ± 0.0477.361 ± 0.11099.958 ± 0.50915.458 ± 0.14679.377 ± 0.42439.078 ± 0.26332.853 ± 0.2342.66 × 10−11
12.0 A 0.237 ± 0.0630.083 ± 0.0706.555 ± 0.14399.708 ± 0.73815.131 ± 0.20479.477 ± 0.61438.618 ± 0.36933.093 ± 0.3321.69 × 10−11
12.5 AM0.331 ± 0.0660.440 ± 0.0817.185 ± 0.140101.080 ± 0.69615.532 ± 0.19379.832 ± 0.57938.600 ± 0.34532.555 ± 0.3082.00 × 10−11
13.0 A 0.632 ± 0.0890.675 ± 0.1086.373 ± 0.14698.754 ± 0.70514.541 ± 0.20279.035 ± 0.59337.916 ± 0.36432.059 ± 0.3277.38 × 10−12
14.0 A 0.630 ± 0.0700.648 ± 0.0816.792 ± 0.12498.613 ± 0.57714.849 ± 0.16777.442 ± 0.48137.445 ± 0.29732.390 ± 0.2691.08 × 10−11
15.0 A 0.296 ± 0.314−0.359 ± −0.3484.215 ± 0.41197.838 ± 1.84411.849 ± 0.50876.679 ± 1.53334.915 ± 0.94729.154 ± 0.8391.22 × 10−12
16.0 A 0.357 ± 0.1970.345 ± 0.2495.706 ± 0.27698.461 ± 1.19814.155 ± 0.34777.876 ± 1.00936.965 ± 0.62630.123 ± 0.5512.32 × 10−12
17.0 A 0.932 ± 0.1480.753 ± 0.1596.275 ± 0.20098.450 ± 0.88714.229 ± 0.25779.045 ± 0.74336.969 ± 0.45931.640 ± 0.4095.44 × 10−12
Total         9.06 × 10−11
Average 0.431 ± 0.0320.363 ± 0.0356.874 ± 0.07599.743 ± 0.32115.110 ± 0.09679.143 ± 0.26338.361 ± 0.16932.520 ± 0.149 
Maskelynite G, multiple fragments, 1.06 mg
11.0 A −0.067 ± −0.404−1.528 ± −0.599−1.577 ± −1.25696.931 ± 3.48615.365 ± 1.06876.765 ± 2.91735.869 ± 1.89930.393 ± 1.6254.51 × 10−13
11.5 A 0.335 ± 0.0470.372 ± 0.0526.875 ± 0.12798.188 ± 0.54414.698 ± 0.16177.382 ± 0.45738.691 ± 0.28932.480 ± 0.2591.36 × 10−11
12.0 A 0.460 ± 0.0530.347 ± 0.0636.487 ± 0.15398.529 ± 0.63814.596 ± 0.18980.014 ± 0.54738.667 ± 0.33932.361 ± 0.3055.96 × 10−12
12.5 A 0.429 ± 0.0440.332 ± 0.0516.933 ± 0.13899.508 ± 0.60114.833 ± 0.17677.828 ± 0.50339.017 ± 0.31832.951 ± 0.2848.65 × 10−12
13.0 A 0.561 ± 0.0390.722 ± 0.0497.789 ± 0.127100.627 ± 0.54915.467 ± 0.16179.243 ± 0.46038.970 ± 0.28532.918 ± 0.2561.12 × 10−11
13.5 A 0.685 ± 0.0660.831 ± 0.0907.697 ± 0.219102.207 ± 0.87215.481 ± 0.25680.147 ± 0.73138.554 ± 0.45632.365 ± 0.4054.57 × 10−12
14.0 A 0.678 ± 0.0791.029 ± 0.1127.312 ± 0.270105.055 ± 1.03415.773 ± 0.30179.760 ± 0.84937.285 ± 0.52832.163 ± 0.4713.45 × 10−12
15.5 AM0.464 ± 0.1950.026 ± 0.3101.680 ± 0.663105.432 ± 2.15414.347 ± 0.64078.218 ± 1.75637.369 ± 1.14431.026 ± 0.9728.44 × 10−13
17.0 A 0.781 ± 0.1120.396 ± 0.1625.345 ± 0.423105.194 ± 1.51714.963 ± 0.44678.536 ± 1.24137.057 ± 0.77831.960 ± 0.6992.15 × 10−12
Total         5.09 × 10−11
Average 0.488 ± 0.0230.504 ± 0.0296.919 ± 0.070100.222 ± 0.30515.033 ± 0.08578.644 ± 0.25338.582 ± 0.15432.547 ± 0.133 
Maskelynite H, multiple fragments, 0.75 mg
11.0 A 0.439 ± 0.376−0.439 ± −0.4263.844 ± 0.44993.838 ± 1.88011.832 ± 0.52175.388 ± 1.58032.755 ± 0.95328.757 ± 0.8551.17 × 10−12
11.5 A 0.467 ± 0.0740.536 ± 0.0826.445 ± 0.13298.117 ± 0.63714.465 ± 0.18178.062 ± 0.53538.053 ± 0.33032.564 ± 0.2971.28 × 10−11
12.0 A 0.988 ± 0.1390.600 ± 0.1426.233 ± 0.18598.851 ± 0.85913.975 ± 0.24577.726 ± 0.71637.402 ± 0.44331.623 ± 0.3957.86 × 10−12
12.5 A 0.796 ± 0.1120.858 ± 0.1266.504 ± 0.155101.770 ± 0.75713.799 ± 0.20678.424 ± 0.62237.667 ± 0.38032.329 ± 0.3409.30 × 10−12
13.0 A 0.987 ± 0.1361.330 ± 0.1736.485 ± 0.187102.278 ± 0.88714.124 ± 0.24279.115 ± 0.73137.548 ± 0.44132.070 ± 0.3978.57 × 10−12
14.0 A 1.525 ± 0.1312.511 ± 0.1977.814 ± 0.165103.738 ± 0.72515.085 ± 0.20280.216 ± 0.59637.445 ± 0.35731.468 ± 0.3189.36 × 10−12
15.0 A 1.237 ± 0.4201.621 ± 0.5587.150 ± 0.523100.464 ± 1.89611.952 ± 0.51779.331 ± 1.56235.960 ± 0.94628.204 ± 0.8261.40 × 10−12
16.0 A 1.766 ± 0.2481.926 ± 0.3246.245 ± 0.286100.798 ± 1.19613.312 ± 0.33278.566 ± 0.99236.030 ± 0.59631.155 ± 0.5433.77 × 10−12
17.0 AM1.491 ± 0.4631.926 ± 0.6386.399 ± 0.511103.962 ± 1.87713.162 ± 0.52176.160 ± 1.52236.111 ± 0.92429.389 ± 0.8101.02 × 10−12
19.0 A 1.191 ± 0.6422.835 ± 0.8815.845 ± 0.755100.995 ± 2.51512.159 ± 0.70178.397 ± 2.12132.405 ± 1.22525.856 ± 1.0758.04 × 10−13
Total         5.61 × 10−11
Average 0.985 ± 0.0591.208 ± 0.0796.600 ± 0.083100.697 ± 0.35314.085 ± 0.10278.576 ± 0.28837.304 ± 0.18331.698 ± 0.162 
Opaques I, multiple fragments, 0.17 mg
11.0 A 0.482 ± 0.2370.637 ± 0.3136.275 ± 0.35299.844 ± 1.34913.084 ± 0.37477.888 ± 1.12836.438 ± 0.69230.877 ± 0.6151.29 × 10−11
11.5 A 0.258 ± 0.0980.328 ± 0.1425.891 ± 0.20299.583 ± 0.92613.742 ± 0.25378.255 ± 0.77136.937 ± 0.46731.390 ± 0.4153.73 × 10−11
12.0 A 0.555 ± 0.0820.703 ± 0.1026.545 ± 0.147105.188 ± 0.71214.780 ± 0.19478.618 ± 0.57338.062 ± 0.34932.163 ± 0.3135.81 × 10−11
12.5 AM1.133 ± 0.1521.101 ± 0.1776.520 ± 0.204113.677 ± 0.95814.026 ± 0.24779.001 ± 0.73538.193 ± 0.45332.462 ± 0.4073.43 × 10−11
13.0 A 0.977 ± 0.2590.834 ± 0.3335.894 ± 0.365112.870 ± 1.58512.920 ± 0.40778.200 ± 1.21335.937 ± 0.74130.303 ± 0.6551.24 × 10−11
14.0 A 1.144 ± 0.4371.705 ± 0.6266.770 ± 0.612104.721 ± 2.12512.427 ± 0.57374.615 ± 1.68533.346 ± 1.02427.564 ± 0.9015.30 × 10−12
15.0 A 0.896 ± 0.6810.407 ± 0.8076.255 ± 0.852104.189 ± 2.64012.150 ± 0.74874.054 ± 2.10530.380 ± 1.25526.582 ± 1.1153.11 × 10−12
16.0 A −0.120 ± −0.520−0.227 ± −0.7005.571 ± 0.636105.910 ± 2.24212.306 ± 0.60977.840 ± 1.81731.432 ± 1.05127.824 ± 0.9713.43 × 10−12
17.0 A −0.914 ± −1.6231.826 ± 2.42310.705 ± 2.00499.197 ± 4.93312.658 ± 1.46485.976 ± 4.25634.393 ± 2.53830.352 ± 2.2639.31 × 10−13
19.0 A 1.117 ± 1.0092.318 ± 1.35310.092 ± 1.04099.871 ± 2.99211.393 ± 0.84077.838 ± 2.53235.803 ± 1.53427.013 ± 1.3421.91 × 10−12
Total         1.70 × 10−10
Average 0.641 ± 0.0630.737 ± 0.0816.373 ± 0.103105.713 ± 0.44813.913 ± 0.12378.337 ± 0.35537.094 ± 0.22231.418 ± 0.197 
EET 79001
Whole rock A, 4.222 mg
11.5 A 0.515 ± 0.1610.123 ± 0.1617.844 ± 0.34397.136 ± 1.38015.387 ± 0.47978.793 ± 1.26941.808 ± 0.78933.701 ± 0.6715.67 × 10−13
12.0 A −0.284 ± −0.6430.205 ± 0.74314.932 ± 1.41895.528 ± 3.93116.720 ± 1.36377.172 ± 3.41340.232 ± 2.23233.337 ± 2.0031.08 × 10−13
12.5 A 1.869 ± 1.230−1.470 ± −1.44315.914 ± 2.227107.106 ± 5.55217.771 ± 1.89681.394 ± 4.54546.556 ± 3.20732.223 ± 2.8024.78 × 10−14
13.0 A 0.335 ± 0.7870.588 ± 0.9071.955 ± 1.230130.417 ± 4.33314.262 ± 1.39975.861 ± 3.36337.767 ± 2.18832.683 ± 2.0647.48 × 10−14
14.0 A 0.409 ± 0.1640.436 ± 0.1887.645 ± 0.376119.212 ± 1.82614.324 ± 0.51776.757 ± 1.45440.138 ± 0.86931.800 ± 0.7715.53 × 10−13
15.0 A 0.363 ± 0.1640.767 ± 0.2086.910 ± 0.407107.307 ± 1.74015.001 ± 0.51976.592 ± 1.46536.896 ± 0.87732.597 ± 0.8134.44 × 10−13
16.0 A −0.211 ± −0.3980.567 ± 0.4736.345 ± 0.861124.464 ± 3.29015.028 ± 1.03478.550 ± 2.76738.146 ± 1.68034.430 ± 1.4961.33 × 10−13
16.5 AM0.724 ± 0.3340.977 ± 0.3839.240 ± 0.720155.521 ± 3.25613.213 ± 0.81277.739 ± 2.21341.313 ± 1.40636.034 ± 1.2892.02 × 10−13
17.0 A 1.638 ± 0.8751.960 ± 1.0708.041 ± 1.803118.151 ± 5.66114.118 ± 1.62274.195 ± 4.37441.900 ± 2.92733.777 ± 2.6135.79 × 10−14
17.5 A 0.713 ± 1.251−2.941 ± −1.6373.915 ± 2.580126.846 ± 7.58011.001 ± 2.32271.267 ± 5.95734.982 ± 3.96229.953 ± 3.6414.11 × 10−14
18.0 A 1.297 ± 0.9060.359 ± 1.0668.357 ± 1.67389.524 ± 4.59913.097 ± 1.61575.909 ± 4.09345.274 ± 2.76134.582 ± 2.4256.24 × 10−14
18.5 A −1.203 ± −1.029−1.235 ± −1.3004.781 ± 1.724103.622 ± 4.69816.474 ± 1.71475.267 ± 3.93343.451 ± 2.84633.327 ± 2.5285.44 × 10−14
19.0 A −0.037 ± −0.673−0.518 ± −0.8513.710 ± 1.285101.600 ± 3.94415.798 ± 1.42177.983 ± 3.35041.469 ± 2.26234.462 ± 2.0558.65 × 10−14
20.0 A 0.288 ± 0.2130.262 ± 0.2408.211 ± 0.47196.530 ± 1.85415.175 ± 0.61579.115 ± 1.62538.342 ± 1.01536.022 ± 0.9553.25 × 10−13
Total         2.76 × 10−12
Average 0.403 ± 0.0890.329 ± 0.1047.751 ± 0.191110.716 ± 0.76714.864 ± 0.23177.512 ± 0.62739.971 ± 0.38533.536 ± 0.346 
Whole rock B, 3.312 mg
11.5 A 3.181 ± 1.4990.837 ± 1.40018.310 ± 1.99983.315 ± 5.20222.147 ± 1.93790.037 ± 4.63343.122 ± 3.01634.710 ± 3.1771.07 × 10−13
12.0 A 1.551 ± 3.1925.336 ± 3.24624.016 ± 3.89089.092 ± 9.02620.125 ± 3.44088.070 ± 7.35433.937 ± 5.33431.660 ± 6.1334.05 × 10−14
13.0 A 0.747 ± 0.303−0.272 ± −0.2607.863 ± 0.388140.328 ± 3.14513.405 ± 0.55277.595 ± 2.10639.201 ± 1.09037.574 ± 1.0685.56 × 10−13
14.0 A 0.280 ± 1.781−2.232 ± −1.6393.623 ± 1.667121.374 ± 5.6447.640 ± 1.89663.625 ± 5.06244.375 ± 3.29545.399 ± 3.7956.10 × 10−14
15.0 A −1.097 ± −1.5010.771 ± 1.1558.130 ± 1.438143.657 ± 5.86117.505 ± 1.69892.547 ± 4.43847.036 ± 2.92744.044 ± 3.2419.69 × 10−14
16.0 AM0.285 ± 0.8091.666 ± 0.8796.553 ± 0.990189.704 ± 5.10616.947 ± 1.04586.168 ± 2.85943.952 ± 1.80044.725 ± 1.9682.47 × 10−13
19.0 A 0.367 ± 3.64717.007 ± 6.057−5.536 ± −4.559120.485 ± 7.32624.703 ± 3.18689.949 ± 6.17061.151 ± 5.03385.879 ± 6.4583.90 × 10−14
Total         1.15 × 10−12
Average 0.708 ± 0.3541.018 ± 0.4238.464 ± 0.432142.462 ± 2.40515.641 ± 0.47781.908 ± 1.54742.085 ± 0.86341.243 ± 0.908 
Pyroxene C, 4.758 mg
11.5 A 0.280 ± 0.0500.213 ± 0.0847.823 ± 0.18096.802 ± 0.77614.696 ± 0.30678.902 ± 0.75040.162 ± 0.42433.792 ± 0.3741.90 × 10−12
12.0 A 0.618 ± 0.3780.585 ± 0.4409.046 ± 0.57093.455 ± 1.85512.257 ± 0.64976.355 ± 1.69740.815 ± 1.11334.983 ± 1.0017.92 × 10−13
12.5 A 0.057 ± 0.1330.163 ± 0.1956.136 ± 0.33698.125 ± 1.46814.334 ± 0.47578.957 ± 1.31538.753 ± 0.79132.048 ± 0.7165.49 × 10−13
13.0 A 0.069 ± 0.6941.609 ± 0.9697.737 ± 1.451100.376 ± 4.25414.549 ± 1.39178.963 ± 3.82940.814 ± 2.47634.902 ± 2.2868.86 × 10−14
14.0 AM0.268 ± 0.3420.236 ± 0.4497.288 ± 0.705109.684 ± 2.69314.879 ± 0.83076.536 ± 2.17639.289 ± 1.39434.146 ± 1.2741.78 × 10−13
14.5 A 0.371 ± 0.1690.496 ± 0.2197.812 ± 0.416103.205 ± 1.69812.680 ± 0.59177.012 ± 1.52539.701 ± 0.89136.444 ± 0.8444.38 × 10−13
15.0 A 0.146 ± 0.1280.352 ± 0.1926.782 ± 0.37498.911 ± 1.53512.933 ± 0.48076.386 ± 1.37038.594 ± 0.82035.157 ± 0.7654.89 × 10−13
16.0 A 0.424 ± 0.1150.116 ± 0.1487.159 ± 0.287101.175 ± 1.26813.415 ± 0.42176.909 ± 1.11941.063 ± 0.67834.940 ± 0.6236.60 × 10−13
17.0 A 0.325 ± 0.0520.378 ± 0.0756.902 ± 0.176101.430 ± 0.92314.024 ± 0.29377.024 ± 0.99239.510 ± 0.46234.322 ± 0.4201.64 × 10−12
20.0 A −0.203 ± −0.563−0.632 ± −0.77516.630 ± 1.36990.097 ± 3.47314.420 ± 1.21775.168 ± 2.98245.531 ± 2.12435.929 ± 1.8463.31 × 10−13
Total         7.07 × 10−12
Average 0.295 ± 0.0580.286 ± 0.0757.879 ± 0.12998.610 ± 0.50913.862 ± 0.16877.474 ± 0.47140.159 ± 0.26934.402 ± 0.243 
Pyroxene D, 5.866 mg
11.5 A 0.464 ± 0.0490.537 ± 0.0548.141 ± 0.132100.896 ± 0.69515.649 ± 0.24178.200 ± 0.88539.151 ± 0.35432.503 ± 0.3031.55 × 10−12
12.0 A 0.386 ± 0.0770.191 ± 0.0797.826 ± 0.20297.110 ± 0.88814.607 ± 0.30076.758 ± 0.97140.049 ± 0.48632.576 ± 0.4179.51 × 10−13
12.5 A 0.305 ± 0.0950.073 ± 0.1046.757 ± 0.253101.664 ± 1.22713.941 ± 0.40078.602 ± 1.19239.975 ± 0.64933.066 ± 0.5816.62 × 10−13
13.0 A 0.323 ± 0.1720.533 ± 0.2148.002 ± 0.402100.546 ± 1.58414.031 ± 0.53976.936 ± 1.45638.233 ± 0.85633.070 ± 0.7822.83 × 10−13
13.5 AM0.238 ± 0.1860.374 ± 0.2298.346 ± 0.486105.043 ± 1.91014.730 ± 0.61377.635 ± 1.66640.284 ± 1.01933.435 ± 0.9273.07 × 10−13
14.0 A 0.360 ± 0.0780.420 ± 0.0957.705 ± 0.236103.310 ± 1.10314.207 ± 0.36077.562 ± 1.07138.721 ± 0.56432.164 ± 0.5157.85 × 10−13
14.5 A 0.547 ± 0.1750.040 ± 0.22110.493 ± 0.498101.737 ± 1.84412.536 ± 0.57076.807 ± 1.67039.502 ± 0.98634.360 ± 0.9023.23 × 10−13
15.0 A 0.189 ± 0.0420.391 ± 0.0657.458 ± 0.16795.966 ± 0.78214.025 ± 0.27778.287 ± 0.73539.224 ± 0.41832.801 ± 0.3781.38 × 10−12
15.5 A 0.088 ± 0.1490.716 ± 0.19510.470 ± 0.43796.730 ± 1.59813.454 ± 0.53878.304 ± 1.43439.540 ± 0.88332.677 ± 0.7984.21 × 10−13
16.0 A 0.254 ± 0.1130.145 ± 0.1609.153 ± 0.36997.067 ± 1.41714.275 ± 0.46977.768 ± 1.27140.004 ± 0.78133.798 ± 0.7105.33 × 10−13
16.5 A 0.235 ± 0.0760.200 ± 0.0967.430 ± 0.224101.061 ± 1.04113.479 ± 0.36677.295 ± 0.95739.787 ± 0.54634.263 ± 0.4968.00 × 10−13
17.0 A 0.526 ± 0.3460.335 ± 0.42011.719 ± 0.789103.686 ± 2.61510.107 ± 0.74874.218 ± 2.12241.516 ± 1.39535.315 ± 1.2741.58 × 10−13
Total         8.16 × 10−12
Average 0.321 ± 0.0260.344 ± 0.0338.116 ± 0.08399.697 ± 0.39514.238 ± 0.12177.709 ± 0.37439.502 ± 0.19233.024 ± 0.173 
Opaques E, 0.379 mg
11.5 A 0.695 ± 0.3790.802 ± 0.4439.046 ± 0.76699.381 ± 2.42614.397 ± 0.79379.739 ± 2.10638.087 ± 1.33431.944 ± 1.1972.45 × 10−12
12.0 A 0.220 ± 2.706−0.018 ± −3.02016.140 ± 4.76876.209 ± 10.8437.864 ± 4.06170.330 ± 9.31136.494 ± 6.31929.515 ± 5.7282.30 × 10−13
12.5 A 2.373 ± 1.6165.175 ± 2.091−15.692 ± −3.132128.237 ± 9.79015.727 ± 3.33197.831 ± 8.58435.800 ± 5.61135.839 ± 5.3092.17 × 10−13
13.0 A 1.886 ± 1.149−0.735 ± −1.418−0.022 ± −2.325129.951 ± 7.34514.676 ± 2.21084.482 ± 6.22836.188 ± 3.98634.513 ± 3.6054.08 × 10−13
14.0 A −0.472 ± −0.3310.099 ± 0.51412.267 ± 0.901171.787 ± 3.35312.854 ± 0.82176.253 ± 2.21738.300 ± 1.31535.312 ± 1.2382.55 × 10−12
15.0 AM−0.790 ± −0.747−0.492 ± −1.06516.611 ± 1.965169.428 ± 5.94015.434 ± 1.58785.442 ± 4.22746.974 ± 2.80434.813 ± 2.4758.75 × 10−13
16.0 A 0.376 ± 0.8022.448 ± 1.23919.549 ± 2.011131.321 ± 5.15413.550 ± 1.52676.427 ± 4.00536.337 ± 2.51733.155 ± 2.3377.28 × 10−13
17.0 A −0.084 ± −0.572−0.285 ± −0.79412.527 ± 1.436107.411 ± 4.07714.059 ± 1.29671.065 ± 3.25237.954 ± 2.18134.693 ± 1.9951.05 × 10−12
Total         8.51 × 10−12
Average 0.156 ± 0.2180.480 ± 0.29511.244 ± 0.511133.615 ± 1.63313.797 ± 0.46378.359 ± 1.22638.706 ± 0.77233.850 ± 0.707 
Maskelynite F, 5.519 mg
11.5 A 0.382 ± 0.1230.196 ± 0.1768.813 ± 0.29992.364 ± 1.08315.204 ± 0.36175.665 ± 0.94742.588 ± 0.63233.597 ± 0.5326.08 × 10−13
12.0 A 0.058 ± 0.3320.165 ± 0.49915.723 ± 0.86693.548 ± 2.19415.175 ± 0.74373.732 ± 1.72848.998 ± 1.34934.693 ± 1.0791.96 × 10−13
12.5 A 0.747 ± 0.330−0.093 ± −0.3374.538 ± 0.618102.046 ± 2.36615.294 ± 0.79380.139 ± 2.07038.493 ± 1.32832.485 ± 1.1941.64 × 10−13
13.0 A 1.597 ± 0.5921.072 ± 0.6707.684 ± 1.255109.732 ± 4.20415.462 ± 1.30380.806 ± 3.53042.226 ± 2.37133.520 ± 2.1328.00 × 10−14
14.0 A 0.323 ± 0.1140.518 ± 0.1468.126 ± 0.309111.882 ± 1.40614.489 ± 0.42576.016 ± 1.13739.022 ± 0.71133.221 ± 0.6354.60 × 10−13
16.0 A 0.279 ± 0.2150.997 ± 0.2828.552 ± 0.510124.688 ± 2.10415.175 ± 0.61879.067 ± 1.65240.446 ± 1.01234.676 ± 0.9152.52 × 10−13
17.0 AM0.354 ± 0.1591.009 ± 0.2108.633 ± 0.387135.020 ± 1.85215.157 ± 0.51078.738 ± 1.42540.158 ± 0.82734.171 ± 0.7543.61 × 10−13
20.0 A 0.496 ± 0.3030.774 ± 0.41511.913 ± 0.878134.357 ± 3.32214.227 ± 0.88676.714 ± 2.35240.795 ± 1.53031.404 ± 1.3371.68 × 10−13
Total         2.29 × 10−12
Average 0.404 ± 0.0710.527 ± 0.0959.092 ± 0.179111.053 ± 0.70814.991 ± 0.20977.006 ± 0.56241.364 ± 0.35633.582 ± 0.311 
Shergotty
Pyroxene A, 7.514 mg
12.0 A 0.698 ± 0.56110.165 ± 39.4598.697 ± 1.040109.771 ± 3.84120.205 ± 1.30789.954 ± 3.60244.280 ± 2.06034.530 ± 1.7616.78 × 10−14
19.0 AM0.579 ± 0.0586.973 ± 26.2807.752 ± 0.160112.565 ± 1.19917.239 ± 0.30185.374 ± 1.27341.014 ± 0.49134.391 ± 0.4309.09 × 10−13
Total         9.77 × 10−13
Average 0.587 ± 0.0677.194 ± 27.0487.818 ± 0.168112.371 ± 1.15317.444 ± 0.30185.692 ± 1.22041.241 ± 0.48334.401 ± 0.423 
Maskelynite B, 7.134 mg
12.0 A 3.395 ± 1.589−16.577 ± −66.0671.398 ± 2.723105.411 ± 7.94916.369 ± 2.92982.098 ± 7.39935.499 ± 4.53528.634 ± 4.3452.28 × 10−14
19.0 AM5.484 ± 0.282−58.807 ± −218.65519.989 ± 0.439150.860 ± 2.62925.488 ± 0.533103.131 ± 1.99040.276 ± 0.74333.982 ± 0.6374.41 × 10−13
Total        l4.64 × 10−13
Average 5.382 ± 0.286−56.727 ± −210.90919.073 ± 0.438148.622 ± 2.53325.039 ± 0.530102.095 ± 1.93140.041 ± 0.74333.719 ± 0.644 
DaG 489
Whole rock A, 4.966 mg
11.3 A 0.724 ± 0.485−15.379 ± −58.2541.025 ± 1.01795.269 ± 2.12314.464 ± 0.83477.412 ± 2.06241.700 ± 1.22734.091 ± 1.0981.40 × 10−13
12.0 A 0.562 ± 0.24113.393 ± 50.12710.184 ± 0.45097.221 ± 1.48713.223 ± 0.57877.336 ± 1.58639.064 ± 0.79233.268 ± 0.7205.77 × 10−13
12.5 A −7.431 ± −3.04672.237 ± 271.904−0.397 ± −4.646111.644 ± 7.86023.771 ± 3.47479.365 ± 6.62753.265 ± 5.09433.544 ± 4.3415.64 × 10−14
13.0 A 0.756 ± 0.255−0.517 ± −4.2306.939 ± 0.437111.508 ± 2.02216.473 ± 0.63781.381 ± 1.87541.495 ± 0.99036.290 ± 0.9254.70 × 10−13
15.0 AM0.566 ± 0.30015.302 ± 57.2239.062 ± 0.492132.271 ± 4.61418.801 ± 0.81492.595 ± 4.00049.553 ± 1.85841.064 ± 1.5863.06 × 10−13
16.0 A 0.387 ± 0.08513.760 ± 51.2517.835 ± 0.220112.499 ± 2.31317.673 ± 0.45581.680 ± 2.64244.503 ± 0.96138.014 ± 0.8231.09 × 10−12
17.0 A −0.394 ± −0.56119.110 ± 71.6087.806 ± 0.852102.226 ± 3.18216.384 ± 1.00478.504 ± 3.26041.264 ± 1.67637.768 ± 1.5821.59 × 10−13
18.0 A −0.407 ± −0.62814.723 ± 55.4627.661 ± 0.844110.435 ± 3.31116.387 ± 1.01281.648 ± 3.24545.958 ± 1.73539.616 ± 1.5551.29 × 10−13
19.0 A 0.282 ± 0.3303.051 ± 12.6519.710 ± 0.624116.377 ± 4.10018.773 ± 0.80691.777 ± 3.85348.686 ± 1.77443.391 ± 1.6152.66 × 10−13
Total         3.19 × 10−12
Average 0.287 ± 0.10310.907 ± 40.5357.949 ± 0.197110.443 ± 1.11816.743 ± 0.28882.350 ± 1.18943.839 ± 0.50137.444 ± 0.447 
Opaques B, 15.95 mg
11.5 A 0.383 ± 0.0360.324 ± 0.0426.345 ± 0.20698.305 ± 1.03514.801 ± 0.27178.401 ± 0.95637.142 ± 0.46031.204 ± 0.4191.07 × 10−12
11.5 A 0.176 ± 0.0910.189 ± 0.1176.228 ± 0.33091.671 ± 1.48814.449 ± 0.41574.833 ± 1.31339.168 ± 0.76532.907 ± 0.6983.67 × 10−13
11.7 A 0.332 ± 0.0360.348 ± 0.0526.419 ± 0.21395.530 ± 0.99814.633 ± 0.27475.746 ± 0.92236.592 ± 0.45730.703 ± 0.4121.20 × 10−12
12.0 A 0.381 ± 0.0320.242 ± 0.0366.581 ± 0.22098.396 ± 1.26514.739 ± 0.30078.506 ± 1.17238.906 ± 0.55632.385 ± 0.4951.22 × 10−12
12.2 A 0.396 ± 0.0260.387 ± 0.0306.560 ± 0.20599.451 ± 1.25715.191 ± 0.28378.435 ± 1.16837.630 ± 0.51832.496 ± 0.4691.37 × 10−12
12.5 A 0.347 ± 0.0290.384 ± 0.0447.014 ± 0.217100.790 ± 1.38115.660 ± 0.29878.888 ± 1.25337.935 ± 0.55131.298 ± 0.4771.04 × 10−12
12.8 A 0.461 ± 0.0460.163 ± 0.0607.204 ± 0.243103.850 ± 1.79816.493 ± 0.36982.421 ± 1.68638.355 ± 0.70632.243 ± 0.6118.84 × 10−13
13.0 A 0.100 ± 0.199−0.133 ± −0.2441.987 ± 0.403102.914 ± 1.97014.736 ± 0.44376.586 ± 1.58238.859 ± 0.82133.100 ± 0.7401.08 × 10−13
13.2 A 0.240 ± 0.1120.521 ± 0.1445.493 ± 0.313103.204 ± 2.05716.323 ± 0.50878.558 ± 1.89338.772 ± 0.94133.441 ± 0.8365.98 × 10−13
13.5 A 0.122 ± 0.1200.391 ± 0.1595.376 ± 0.297101.898 ± 1.78916.720 ± 0.47079.404 ± 1.59138.524 ± 0.81032.455 ± 0.7124.05 × 10−13
13.8 A 0.422 ± 0.1410.581 ± 0.1785.972 ± 0.337112.026 ± 2.15515.331 ± 0.49680.312 ± 1.77239.031 ± 0.90633.407 ± 0.8133.67 × 10−13
15.0 A 0.518 ± 0.2350.478 ± 0.2884.123 ± 0.421119.088 ± 2.26514.246 ± 0.50077.804 ± 1.68939.902 ± 0.93433.304 ± 0.8451.56 × 10−13
16.0 A 0.357 ± 0.0650.074 ± 0.0966.520 ± 0.237132.518 ± 2.05815.361 ± 0.33579.241 ± 1.40037.676 ± 0.63233.018 ± 0.5684.68 × 10−13
17.0 A −1.577 ± −0.920−1.182 ± −1.1256.391 ± 1.203114.951 ± 5.7407.055 ± 1.40372.941 ± 4.23440.425 ± 2.76135.917 ± 2.6193.56 × 10−12
18.0 AM0.142 ± 0.5280.883 ± 0.637−1.283 ± −1.052156.434 ± 4.95815.936 ± 1.07477.434 ± 3.11241.589 ± 1.90532.907 ± 1.7084.79 × 10−14
20.0 A 0.559 ± 0.0740.438 ± 0.0825.559 ± 0.229145.652 ± 1.83314.166 ± 0.33777.638 ± 1.15737.878 ± 0.57133.239 ± 0.5274.11 × 10−13
20.0 A 0.443 ± 0.0580.197 ± 0.0635.415 ± 0.217117.121 ± 1.56214.295 ± 0.31875.025 ± 1.15937.904 ± 0.59232.493 ± 0.5365.70 × 10−13
20.0 A 0.442 ± 0.0390.376 ± 0.0496.058 ± 0.204103.892 ± 1.67915.105 ± 0.32279.259 ± 1.45239.058 ± 0.65232.939 ± 0.5756.46 × 10−13
Total         1.45 × 10−11
Average −0.109 ± −0.226−0.044 ± −0.2766.281 ± 0.339107.163 ± 1.51013.195 ± 0.37977.014 ± 1.14938.644 ± 0.72133.124 ± 0.689 
Pyroxene C, 2.87 mg
12.0 A 0.434 ± 0.1850.283 ± 0.2192.829 ± 0.410108.811 ± 2.30614.543 ± 0.53378.890 ± 1.91739.359 ± 0.98234.397 ± 0.8956.75 × 10−13
13.0 A 0.170 ± 0.0700.174 ± 0.0825.677 ± 0.227103.602 ± 1.73814.909 ± 0.34778.738 ± 1.55339.082 ± 0.70133.644 ± 0.6202.06 × 10−12
13.5 A 0.285 ± 0.3500.082 ± 0.523−0.034 ± −0.766118.059 ± 3.41316.590 ± 0.88181.844 ± 2.64840.334 ± 1.51235.260 ± 1.4053.66 × 10−13
14.0 AM0.652 ± 0.6260.735 ± 0.711−4.752 ± −0.894130.616 ± 3.85213.270 ± 0.96477.884 ± 2.67140.357 ± 1.66732.401 ± 1.5243.02 × 10−13
17.0 A 0.279 ± 0.0710.568 ± 0.1606.523 ± 0.27498.320 ± 1.38014.475 ± 0.31077.319 ± 1.18737.426 ± 0.57332.492 ± 0.5184.10 × 10−12
18.0 A −0.141 ± −0.6281.238 ± 1.0282.374 ± 1.54583.944 ± 4.88915.718 ± 1.31578.319 ± 3.43248.908 ± 2.36338.869 ± 2.1341.97 × 10−13
20.0 A 0.096 ± 0.3620.096 ± 0.5624.138 ± 0.77893.938 ± 2.88516.639 ± 0.87074.111 ± 2.31238.779 ± 1.44331.888 ± 1.3345.40 × 10−13
20.0 A 0.383 ± 0.0150.331 ± 0.0176.385 ± 0.18799.497 ± 1.16214.663 ± 0.24377.855 ± 1.05538.797 ± 0.48232.952 ± 0.4308.41 × 10−12
20.0 A 0.342 ± 0.0140.336 ± 0.0176.883 ± 0.19797.147 ± 0.98715.512 ± 0.23979.623 ± 0.93639.294 ± 0.43033.212 ± 0.3891.51 × 10−11
20.0 A 0.360 ± 0.0110.360 ± 0.0147.108 ± 0.20997.616 ± 1.24416.386 ± 0.27783.603 ± 1.21843.365 ± 0.57237.434 ± 0.5151.44 × 10−11
20.0 A 0.390 ± 0.0170.378 ± 0.0207.282 ± 0.239103.515 ± 1.98315.879 ± 0.37882.369 ± 1.77741.098 ± 0.80835.117 ± 0.7061.24 × 10−11
Total         5.86 × 10−11
Average 0.350 ± 0.0120.361 ± 0.0196.693 ± 0.18599.625 ± 0.73515.584 ± 0.20480.679 ± 0.69940.508 ± 0.33534.610 ± 0.321 
Maskelynite D, 0.43 mg
11.0 A 0.061 ± 0.545−1.782 ± −0.7681.652 ± 1.245103.764 ± 4.22816.106 ± 1.17278.536 ± 3.29839.108 ± 2.03037.628 ± 2.0001.64 × 10−12
12.0 A −0.080 ± −0.5561.457 ± 0.7300.053 ± 1.209107.673 ± 4.47813.471 ± 1.23079.759 ± 3.60940.224 ± 2.22533.512 ± 2.0941.75 × 10−12
13.0 A 0.408 ± 0.9990.871 ± 1.160−8.168 ± −1.997135.721 ± 6.91816.005 ± 1.81078.934 ± 4.93041.576 ± 3.07840.188 ± 2.9789.19 × 10−13
15.0 AM1.760 ± 2.523−1.889 ± −3.368−51.161 ± −6.145186.191 ± 18.2699.116 ± 4.29572.612 ± 10.96734.765 ± 7.51246.448 ± 7.6052.62 × 10−13
Total         4.57 × 10−12
Average 0.174 ± 0.380−0.013 ± −0.495−3.956 ± −0.838116.401 ± 2.90914.676 ± 0.78178.746 ± 2.19539.784 ± 1.36437.069 ± 1.325 
Iddingsite E, 1.21 mg
10.5 A −1.189 ± −2.041−0.645 ± −2.933−6.220 ± −5.342104.278 ± 14.28713.694 ± 3.41279.660 ± 9.01460.203 ± 6.50160.786 ± 6.4351.22 × 10−13
11.0 A 0.072 ± 0.1960.181 ± 0.2644.755 ± 0.43997.991 ± 2.09416.032 ± 0.57177.490 ± 1.79038.639 ± 0.99632.712 ± 0.9122.24 × 10−12
11.5 A 0.643 ± 0.160−0.269 ± −0.1985.367 ± 0.347100.348 ± 1.88815.081 ± 0.47779.690 ± 1.70539.487 ± 0.87233.665 ± 0.7883.14 × 10−12
12.0 A 1.123 ± 0.399−0.418 ± −0.4744.409 ± 0.777106.110 ± 3.34413.694 ± 0.89682.974 ± 2.95041.259 ± 1.65237.386 ± 1.5611.28 × 10−12
12.5 A 0.695 ± 0.359−0.242 ± −0.4012.963 ± 0.612106.633 ± 3.03014.402 ± 0.81877.155 ± 2.52937.844 ± 1.43034.171 ± 1.3471.63 × 10−12
13.0 A 1.548 ± 0.4730.374 ± 0.5592.591 ± 0.857116.290 ± 3.62014.909 ± 0.97776.656 ± 2.83637.292 ± 1.66532.438 ± 1.5539.68 × 10−13
14.0 A 0.346 ± 0.7491.737 ± 1.039−4.411 ± −1.656126.862 ± 5.74514.269 ± 1.53076.933 ± 4.23339.267 ± 2.67133.802 ± 2.5254.22 × 10−13
16.0 AM−1.438 ± −1.933−4.115 ± −2.455−17.475 ± −3.172138.162 ± 10.2525.783 ± 2.61082.972 ± 7.49832.145 ± 4.66027.955 ± 4.4972.18 × 10−13
17.0 A 0.333 ± 0.0140.389 ± 0.0196.230 ± 0.18496.564 ± 1.18614.776 ± 0.24677.383 ± 1.11639.659 ± 0.51233.970 ± 0.4602.38 × 10−11
Total         3.38 × 10−11
Average 0.410 ± 0.0390.237 ± 0.0485.393 ± 0.17099.090 ± 0.95314.764 ± 0.22677.822 ± 0.88939.502 ± 0.42334.009 ± 0.393