Noble gases of the Yamato and Yamato lherzolitic shergottites from Mars

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1 Available online at Polar Science 2 (2008) 195e2 Noble gases of the Yamato and Yamato lherzolitic shergottites from Mars Keisuke Nagao a, *, Jisun Park b, Hoon Gong Choi a a Laboratory for Earthquake Chemistry, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo , Japan b ARES code KR, NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, USA Received 31 August 2007; revised 10 June 2008; accepted 24 June 2008 Available online 22 July 2008 Abstract We used total melting and stepwise heating methods to measure noble gases within bulk samples from Yamato and Yamato lherzolites as well as a melt-vein sample from Yamato He and Ne are dominated by cosmogenic noble gases. The obtained cosmic-ray exposure age of Ma, an average age based on cosmogenic 3 He, 21 Ne, and 38 Ar for these samples, is consistent with the ages of other lherzolitic shergottites, indicating a common impact event for the ejection of lherzolites from Mars. Heavy noble gases released from the bulk samples at low temperatures were elementally fractionated terrestrial atmosphere. Martian noble-gas isotopic signatures, 40 Ar/ 36 Ar ¼ 1900 and 129 Xe/ 132 Xe ¼ 1.3, were observed at high temperatures (>1000 C). The melt-vein sample released greater amounts of atmospheric Ar, Kr, and Xe at low temperatures than the bulk samples. Large amounts of Ar and Kr, as well as excess 40 Ar and 129 Xe, were evolved from the melt-vein sample at 00 C, and the gas shows very high 36 Ar/ 132 Xe (¼3100) and 84 Kr/ 132 Xe (¼76) values. Maximum 40 Ar/ 36 Ar and 129 Xe/ 132 Xe values of the melt sample were 1100 and 1.6, respectively, at 1600 C. Cosmogenic Kr shows an absence of 80 Kr and 82 Kr produced by neutron capture on Br, which suggests a small pre-atmospheric body. Overall noble gas compositions for Y and Y support pairing for the Yamato 00 shergottites. Ó 2008 Elsevier B.V. and NIPR. All rights reserved. Keywords: Martian meteorites; Lherzolitic shergottites; Noble gases; Yamato ; Yamato Introduction Misawa et al. (2006) reported new meteorites of Martian origin recovered from the Yamato meteorite field. The Martian meteorites Yamato (Y) (9.68 g), Y (5.34 g), and Y (24.48 g) have been classified as lherzolitic shergottites, which * Corresponding author. address: nagao@eqchem.s.u-tokyo.ac.jp (K. Nagao). are composed of low-ca pyroxene, olivine, and maskelynite plagioclase with minor oxide minerals, and show poikilitic/non-poikilitic textures (Meteorite Newsletter, 2006; Misawa et al., 2006). Because the mineralogy and petrology of the three Yamato shergottites are almost identical, they are believed to be paired (e.g., Mikouchi and Kurihara, 2007; Misawa et al., 2006). The petrographic features of these lherzolites are similar to those of the lherzolites ALH77005, LEW88516, and Y793605, suggesting a similar igneous crystallization history for the /$ - see front matter Ó 2008 Elsevier B.V. and NIPR. All rights reserved. doi: /j.polar

2 196 K. Nagao et al. / Polar Science 2 (2008) 195e2 lherzolitic shergottites on Mars (Mikouchi and Kurihara, 2007). Most shergottites show relatively short cosmic-ray exposure histories (<5 Ma) compared with other Martian meteorites (i.e., w11 Ma for nakhlites and Chassigny, w15 Ma for ALH orthopyroxenite); the only exception is Dho019, which has an exposure age of w20 Ma (e.g., Christen et al., 2005; Eugster et al., 2002; Meyer, 2003; Nyquist et al., 2001). Among the shergottites, the exposure ages of lherzolitic samples are restricted to a narrow range from 4 to 5 Ma (as summarized in Christen et al., 2005), indicating that a single impact event ejected all the known lherzolites from Mars. There exist four lherzolitic shergottites for which noble gas compositions and cosmic-ray exposure ages have been determined based on cosmogenic noble gases: ALH77005 (Bogard et al., 1984; Eugster et al., 2002; Miura et al., 1995; Swindle et al., 1986), Y (Eugster and Polnau, 1997; Garrison and Bogard, 1998; Nagao et al., 1997, 1998; Terribilini et al., 1998), NWA1950 (Christen et al., 2005), and LEW88516 (Bogard and Garrison, 1993; Eugster et al., 1997, 2002; Ott and Löhr, 1992; Treiman et al., 1994). Martian meteorites have the potential to provide evidence of the chemical and isotopic compositions of the atmosphere and interior of Mars. For example, the EETA79001 shergottite contains Martian atmospheric noble gases, especially in shock-induced melt material (Becker and Pepin, 1984; Bogard and Johnson, 1983; Pepin, 1985; Wiens and Pepin, 1988). Other volatiles in this shergottite are similar to those of the Martian atmosphere (Meyer, 2003; McSween, 1994; Ott and Begemann, 1985; Swindle et al., 1986). Melt inclusions within the Zagami shergottite contain noble gases and nitrogen from the atmosphere of Mars (Marti et al., 1995). In addition to shergottites, the noble gas compositions of Chassigny are considered to represent Mars s interior component (Bogard et al., 2001; Mathew and Marti, 2001; Ott, 1988). The isotopic composition of noble gas in Mars s interior is important in clarifying the relationship between the Martian atmosphere and interior, yet these compositions remain poorly constrained based on the noble gases in Martian meteorites. Terribilini et al. (1998) reported trapped 40 Ar/ 36 Ar values for Shergotty and Y of 1100 and 950, respectively. The authors suggested that shergottites contain a mixture of Martian mantle and atmospheric Ar. Bogard and Garrison (1999) estimated the 40 Ar/ 36 Ar value of the Martian interior to be less than 500, much lower than the value for the Martian atmospheric (1700e1900). In contrast, Schwenzer et al. (2007c) reported an 40 Ar/ 36 Ar value of about 2000 for the Martian interior, comparable with the atmospheric value. Hence, the isotopic composition of noble gas from the Martian interior remains a topic of controversy. In the present study, we analyzed the noble gases within two bulk samples from the lherzolitic shergottites Y and Y000097, and a melt-vein sample from Y to clarify their cosmic-ray exposure histories and observe noble gases of Martian origin. The melt-vein in the Yamato shergottite is expected to trap Martian atmosphere, as demonstrated in EETA79001 and the Zagami shergottites by Bogard and Johnson (1983) and Becker and Pepin (1984). Comparisons of noble gas isotopic compositions in different meteorites can yield information on pairing and/or independent falls of meteorites. 2. Experimental methods Bulk samples weighing 6.0 and 53.9 mg from Y and 19.8 and mg from Y were measured for noble gases using total melting and stepwise heating methods, respectively. A melt-vein sample (30.2 mg) from Y was also measured by stepwise heating. The heating temperature for total melting was 1800 C, and the stepwise heating employed temperatures of 400, 600, 800, 1000, 1200, 00, 1600, and 1800 C. Noble gas elemental and isotopic compositions were analyzed using a noble gas mass spectrometer (modified- VG5400/MS-II) at the Laboratory for Earthquake Chemistry, University of Tokyo, Japan. The mass spectrometer was equipped with a noble-gas extraction furnace (using a molybdenum (Mo) crucible), purification line, and standard gas system (e.g., Nagao et al., 1996). Samples were wrapped in Al-foil (10 mm thick) and loaded in the branches of a glass sample holder connected to the extraction furnace. After loading the samples, the purification line was heated to about 250 C for 1 day to attain ultra-high vacuum. During the procedure, samples in the sample holder were heated to 150 C to remove any contamination by atmospheric noble gases adsorbed onto the samples. The Mo crucible in the extraction furnace was degassed at 1900 C to lower the blank level. For noble gas analysis using the total melting method, the sample was dropped into the Mo crucible and heated at 1800 C. In the stepwise heating analysis, the sample was heated at each given temperature for 30 min, after which the extracted gases were measured. In the next temperature step, the same sample was heated again at a higher temperature for 30 min to release gases from sites within the sample with higher retention.

3 K. Nagao et al. / Polar Science 2 (2008) 195e2 197 Extracted noble gases were purified by exposing the gases to hot TieZr getters heated at about 800 C. From the mixture of five noble gases, Ar, Kr, and Xe were trapped on a charcoal trap cooled to the temperature of liquid nitrogen. He and Ne remaining in the gaseous phase were introduced into the mass spectrometer and then measured for isotopic ratios and abundances using a Daly-multiplier ion detection system or an ion counting system. Ar, Kr, and Xe were released from the charcoal trap at about 200 C, and purified again with the TieZr getters and NP10 SORB-AC getters (SAES Getters Co.). Kr and Xe were trapped on a cryogenically cooled sintered stainless-steel trap maintained at a temperature of 173 C. Ar isotopic ratios were measured using the Daly-multiplier system. Kr was measured by increasing the temperature of the cryogenic trap to 138 C. Finally, Xe was measured after release from the trap at 43 C. Kr and Xe were measured using the ion counting system. Sensitivities and mass-discrimination correction factors for noble gases were calculated by measuring a known amount of atmosphere (w cm 3 STP). Mass discrimination for 3 He/ 4 He was determined using an 3 Hee 4 He mixture with 3 He/ 4 He ¼ Typical blank levels at 1000 C for 4 He, 20 Ne, 40 Ar, 84 Kr, and 132 Xe were , , , , and cm 3 STP, respectively; those at 1800 C were , , , , and cm 3 STP, respectively. Blank corrections were applied for all noble gas data. Helium concentrations and isotopic ratios for 1600 C and 1800 C fractions could not be determined due to the small amounts of released He, which were comparable to the blank level. Experimental errors for isotopic ratios are given in terms of 1s, and the uncertainties for concentrations are estimated to be about 10%. For partitioning the measured Ne and Ar into cosmogenic 21 Ne and 38 Ar, and trapped 20 Ne and 36 Ar, we employed the following isotopic ratios: ( 20 Ne/ 22 Ne) trap ¼ 9.80, ( 21 Ne/ 22 Ne) trap ¼ , ( 20 Ne/ 22 Ne) cosm ¼ 0.85, ( 21 Ne/ 22 Ne) cosm ¼ 0.80, ( 38 Ar/ 36 Ar) trap ¼ 0.188, and ( 38 Ar/ 36 Ar) cosm ¼ Measured 3 He was assumed to be entirely cosmogenic. 3. Results and discussion The noble gas data are summarized in the Appendix (Tables A1eA3). Concentrations of cosmogenic 3 He, 21 Ne, and 38 Ar for Y bulk, Y melt-vein, and Y bulk samples obtained by total melting and stepwise heating are listed in Table 1. Table 2 lists the concentrations of 21 Ne cosm, 38 Ar cosm, 20 Ne trap, and 36 Ar trap, and values of 40 Ar/ 36 Ar trap, 36 Ar trap / 132 Xe, 84 Kr/ 132 Xe, and 129 Xe/ 132 Xe for each temperature step Release patterns obtained from stepwise heating experiments Figs. 1 and 2 show the release profiles of 4 He, 21 Ne cosm, and 3 He/ 4 He plotted against the extraction temperatures; Ne isotopic ratios are shown in Fig. 3. He and Ne are predominantly cosmogenic, although Ne in the low-temperature fractions shows terrestrial atmospheric contamination. Most of the He from the bulk samples was released at temperatures of 800 and 1000 C, while the melt-vein sample showed a maximum release at 600 C. Values of 3 He/ 4 He were largely constant at temperatures of 400e00 C, within the range for cosmogenic He (i.e., between 0.16 (Welten et al., 2003) and 0.22 (Schwenzer et al., 2006)). Although radiogenic 4 He produced in situ is usually released at about 800 C, the constant 3 He/ 4 He values observed in our study suggest the presence of negligible amounts of radiogenic 4 He (<10 8 cm 3 STP/g) in the analyzed samples. The Ne isotopic ratios are presented in Fig. 3. Our Ne data for low-temperature fractions (400 and 600 C for bulk samples and 400e800 C for melt-vein) can be explained as a mixture between terrestrial atmospheric Ne and cosmogenic Ne. Hence, we found no indication of the presence of Martian atmospheric Ne in our analysis of the Y and Y lherzolites. Fig. 3 also shows cosmogenic Ne compositions produced by solar cosmic rays (SCR) and galactic cosmic rays (GCR) (e.g., Garrison et al., 1995; Garrison and Bogard, 1998; Schwenzer et al., 2007c); however, GCRproduced cosmogenic Ne in plagioclase (Smith and Huneke, 1975) is similar to SCR-produced Ne. Lowtemperature fractions (400 and 600 C) from the bulk samples plot close to the mixing line between SCR and air, and a cosmogenic 21 Ne/ 22 Ne value of about 0.75 is calculated for the bulk samples. This 21 Ne/ 22 Ne value, in combination with an Mg/(Si þ Al) value of 0.70 (Shirai and Ebihara, personal communication), means that the data plot in the lherzolitic shergottite field in an Mg/ (Si þ Al) versus cosmogenic 21 Ne/ 22 Ne diagram (Garrison et al., 1995), suggesting the presence of SCR- Ne in the Y and Y shergottites. In contrast, the data for 400, 600, and 800 C from the melt-vein sample plot on the mixing line between GCR and terrestrial atmospheric components, suggesting the absence of SCR-Ne in the melt-vein sample. Cosmogenic Ne produced by GCR was released at higher temperatures (>1000 C) than He, with

4 198 K. Nagao et al. / Polar Science 2 (2008) 195e2 Table 1 Cosmogenic noble gases and cosmic-ray exposure ages of Y and Y shergottites, and comparison with other shergottites Meteorite Y a Y a Y b Y c Y d ALH77005 e NWA1950 f LEW88516 g Unit Bulk Meltvein Bulk Bulk Glass Bulk Bulk Bulk Bulk j TM SH SH TM SH TM SH TM SH TM TM TM TM 3 He cc/g Ne Ar P cc/gma P P T 3 Ma T T Average h h i h h h h TM: total melting; SH: stepwise heating. a This work. b Nagao et al. (1997). c Nagao et al. (1998). d Eugster and Polnau (1997). e Eugster et al. (2002). f Christen et al. (2005). g Eugster et al. (1997). h Average for T 3,T 21 and T 38. i Average for T 3 and T 21. j Average of two bulk samples. a maximum release at 00 C(Fig. 1). The melt-vein sample, however, shows two peaks in cosmogenic 21 Ne, at 1000 and 00 C, indicating the formation of an additional shock-heating-related mineral(s) or phase(s) associated with the 1000 C release. The higher abundance of cosmogenic Ne in the melt-vein sample compared with the bulk samples may reflect higher concentrations of target elements such as Mg and Al in the melt-vein. In the case that the Ne with low 21 Ne/ 22 Ne values observed in the bulk samples was not produced in sodium-rich phases by GCR (Smith and Huneke, 1975), but instead produced by low-energy particles such as SCR, the results would imply that the SCR-Ne had been lost from the melt-vein during its formation by shock, whereas the bulk material in contact with the melt-vein retained a component of SCR-Ne. If SCR-Ne had been produced in space prior to the fall of the Y00 meteorites onto Earth, SCR-Ne must also have been produced in the melt-vein portion, as the degree of separation of the two phases (i.e., bulk and melt-vein) must have been extremely small in the tiny recovered mass of Y (<10 g). Hence, SCR-Ne should have accumulated in the lherzolitic material prior to intrusion of the melt-vein in association with the impact shock that occurred on Mars. In such a case, the Y00 lherzolites would have experienced a multiple-exposure history, and the travel time to Earth as a small object would have been short, of insufficient duration to accumulate SCR-Ne in the melt-vein portion. Fig. 4 shows the release profiles of heavier noble gases obtained from stepwise heating experiments. Trapped 36 Ar was corrected for cosmogenic 36 Ar, and excess 40 Ar and 129 Xe were calculated by subtracting the terrestrial atmospheric component, assuming 40 Ar/ 36 Ar ¼ 296 and 129 Xe/ 132 Xe ¼ (Ozima and Podosek, 2002). Trapped 36 Ar and 84 Kr from the two bulk samples show similar release patterns (Fig. 4): terrestrial atmospheric Ar and Kr were released at low temperatures (800 C), and trapped Ar and Kr of Martian origin released at higher temperatures, with a maximum at 00 C. The release of 40 Ar excess and 129 Xe excess at high temperatures (>1000 C) (see Fig. 4), in combination with the high values of 40 Ar/ 36 Ar and 129 Xe/ 132 Xe observed at higher temperatures (Figs. 5, 7, and 9), confirms that the Ar, Kr, and Xe released at high temperatures were derived from Mars to some extent.

5 K. Nagao et al. / Polar Science 2 (2008) 195e2 199 Table 2 Measured cosmogenic and trapped noble gases Temp. C [ 21 Ne] cosm [ 38 Ar] cosm [ 20 Ne] trap [ 36 Ar] trap 40 Ar/ 36 Ar trap 36 Ar trap / 132 Xe 84 Kr/ 132 Xe 129 Xe/ 132 Xe 10 9 cc/g Y bulk Total TM Y melt-vein e Total Y bulk e (continued on next page)

6 200 K. Nagao et al. / Polar Science 2 (2008) 195e2 Table 2 (continued) Temp. C [ 21 Ne] cosm [ 38 Ar] cosm [ 20 Ne] trap [ 36 Ar] trap 40 Ar/ 36 Ar trap 36 Ar trap / 132 Xe 84 Kr/ 132 Xe 129 Xe/ 132 Xe 10 9 cc/g Total TM TM: total melting. Unlike the similar release profiles of 36 Ar trap and Kr obtained from the bulk samples, the melt-vein sample released large amounts of trapped Ar and Kr, with peaks at 800 and 00 C(Fig. 4). Cosmogenic 21 Ne within the melt-vein sample also showed two release peaks (at 1000 and 00 C), as noted above (Fig. 1). The Ar, Kr, and Xe released at the 800 C peak and lower temperatures have terrestrial atmospheric isotopic ratios (see Figs. 5, 6, 7, and 9), indicating 4 He (10-9 cc/g) a Y Y Melt vein Y ,000 1,200 1,400 1,600 1,800 2,000 a dominantly terrestrial atmospheric origin. This finding is also clearly evident in the release profiles of 40 Ar excess and 129 Xe excess shown in Fig. 4, in which no significant amounts of 40 Ar excess and 129 Xe excess were observed at low temperatures. Accordingly, the 800 C peaks for Ar and Kr are different from that for Ne at 1000 C(Fig. 1), although Ne, Ar, and Kr from the melt-vein all show two release peaks. In contrast to the distinct release profiles for Ne, Ar, and Kr from the bulk and melt-vein samples, the profiles of 132 Xe for Y bulk and its melt-vein samples are similar; no overabundance of 132 Xe was observed in the melt-vein sample compared with the bulk samples. These results may indicate that the meltvein sample only contains a specific trapping site(s) for Ar and Kr. The low 40 Ar/ 36 Ar trap values of 302 and Necosm (10-9 cc/g) b ,000 1,200 1,400 1,600 1,800 2,000 Temperature (ºC) Fig. 1. Release profiles of 4 He and cosmogenic 21 Ne obtained from stepwise heating experiments. 3 He/ 4 He Y Y Melt vein Y ,000 1,200 1,400 1,600 1,800 Temperature (ºC) Fig He/ 4 He values obtained at different extraction temperatures. Cosmogenic 3 He/ 4 He values of 0.16 and 0.22 are from Welten et al. (2003) and Schwenzer et al. (2006), respectively. cosmogenic

7 K. Nagao et al. / Polar Science 2 (2008) 195e Ne/ 22 Ne Martian atmosphere Air 400 Y Y Melt vein Y Dho SCR GCR Ne/ 22 Ne Fig. 3. Ne three-isotope plot. SCR and GCR represent Ne components produced by irradiation by solar cosmic rays and galactic cosmic rays, respectively (e.g., Garrison and Bogard, 1998; Garrison et al., 1995; Schwenzer et al., 2007c). The shaded area (from Schwenzer et al., 2007c) represents previously proposed values for Martian atmospheric 20 Ne/ 22 Ne; that is, (Swindle et al., 1986), (Wiens et al., 1986), z7 (Garrison and Bogard, 1998), and (Park and Nagao, 2006). The estimate of 20 Ne/ 22 Ne ¼ 7.3 reported by Park and Nagao (2006) was based on the Ne-enriched 600, 800, and 1000 C fractions on pyroxene-rich separate from the Dhofar 378 shergottite. obtained at 800 and 00 C(Table 2), respectively, in combination with the unusual enrichment in Kr observed in the melt-vein (Figs. 4 and 7), are inconsistent with the proposal that the Ar and Kr are shockimplanted Martian atmosphere. Although there exist insignificant differences in noble gas compositions among the Y and Y bulk samples, the overall elemental abundances and isotopic compositions of noble gases are similar. These results support an interpretation of pairing for these meteorites, as proposed previously based on mineralogical studies (Misawa et al., 2006) Cosmic-ray exposure ages of Y and Y000097, and comparison with other lherzolites Table 1 summarizes the cosmic-ray-produced 3 He, 21 Ne, and 38 Ar concentrations within the bulk and meltvein samples obtained by total melt and stepwise experiments, as well as production rates for these isotopes and calculated cosmic-ray exposure ages. The production rates P 3, P 21, and P 38 for Y were calculated using the formulae for diogenite (Eugster and Michel, 1995; Eugster et al., 1997) and the bulk chemical compositions of Y reported by Shirai 36 Artrap (10-9 cc/g) 40 Arexcess (10-9 cc/g) 129 Xeexcess (10-12 cc/g) 132 Xe (10-12 cc/g) 84 Kr (10-12 cc/g) ,400 1,200 1, Y bulk Y Melt vein Y bulk ,000 1,200 1,400 1,600 1,800 2, ,000 1,200 1,400 1,600 1,800 2, ,000 1,200 1,400 1,600 1,800 2, ,000 1,200 1,400 1,600 1,800 2, a b c d e ,000 1,200 1,400 1,600 1,800 2,000 Temperature (ºC) Fig. 4. Release profiles of trapped 36 Ar, 84 Kr, and 132 Xe, and of 40 Ar excess and 129 Xe excess in excess to terrestrial atmospheric ratios, 40 Ar/ 36 Ar ¼ 296 and 129 Xe/ 132 Xe ¼ (Ozima and Podosek, 2002) obtained from stepwise heating experiments.

8 202 K. Nagao et al. / Polar Science 2 (2008) 195e2 40 Ar/ 36 Ar 1,100 1, Radiogenic 40 Ar or Martan atmosphere 12 Air Y Y Melt vein Y Ar/ 36 Ar and Ebihara (personal communication). Because Y appears to be paired with Y000097, the production rates for Y were also applied to Y Production rates for the melt-vein sample were calculated using the chemical composition of the melt-vein determined by EPMA (electron probe micro analyzer) analysis (Imae and Ikeda, personal communication). Exposure ages calculated based on cosmogenic Fig. 5. Plot of 40 Ar/ 36 Ar versus 38 Ar/ 36 Ar. The isotopic ratios at 400 and 600 C are similar to those of terrestrial atmosphere, 40 Ar/ 36 Ar ¼ 296 and 38 Ar/ 36 Ar ¼ (Ozima and Podosek, 2002). Numbers indicate extraction temperatures in C(100). 82 Kr/ 84 Kr Air Kr/ 84 Kr Spallation 12 Neutron capture (30-300eV) 0.19 Y bulk Y Melt vein 0.18 Y bulk Air EET Fig. 6. Plot of 82 Kr/ 84 Kr versus 80 Kr/ 84 Kr. Data for EET79001 glass samples (Garrison and Bogard, 1998) are plotted for comparison. The spallation and neutron-capture Kr compositions are from Marti et al. (1966), Eugster and Michel (1995), Okazaki and Nagao (2004), and Park and Nagao (2005). Numbers indicate extraction temperatures in C(100). cosmogenic 3 He, 21 Ne, and 38 Ar concentrations and the above production rates range from 2.6 to 7.5 Ma, with a mean age of Ma. Table 1 also lists previously published cosmic-ray exposure ages for lherzolitic shergottites to enable comparisons with the ages calculated for Y and Y Our exposure age of Ma for Y and Y is in good agreement with the ages obtained for bulk samples from other lherzolites (w4.1e4.5 Ma). These age data strongly indicate that the six lherzolitic shergottites for which exposure ages have been reported were ejected from Mars by a single impact event at about 4.4 Ma. The age, which is slightly longer than 3.9 Ma for Y glass sample (Table 1), might reflect cosmic-ray irradiation on Mars prior to ejection of these lherzolites (Nagao et al., 1998) Ar isotopic composition Fig. 5 shows the Ar isotopic ratios obtained for different heating temperatures. The 38 Ar/ 36 Ar and 40 Ar/ 36 Ar values for the bulk samples at 400 and 600 C are similar to those of the terrestrial atmosphere; however, the values increase at higher temperatures. In contrast to the data for bulk samples, data for the melt-vein sample remain at atmospheric levels until 1000 C, degassing almost an order of magnitude more atmospheric Ar than the bulk samples (see Fig. 4). The increases in 38 Ar/ 36 Ar and 40 Ar/ 36 Ar values at higher temperatures for both the bulk and melt-vein samples reflect the degassing of both cosmogenic and in situ-produced radiogenic 40 Ar from 40 K and trapped Martian Ar. Table 2 lists the trapped 36 Ar concentrations and 40 Ar/ 36 Ar trap values corrected for cosmogenic 36 Ar, and Fig. 9 shows 40 Ar/ 36 Ar trap values. Both the Y and Y bulk samples show maximum 40 Ar/ 36 Ar trap values of about 1900 at temperatures of 1000e00 C. It is difficult to estimate the contribution to the observed 40 Ar/ 36 Ar values of Ar from Mars with high 40 Ar/ 36 Ar values (w1750 for the Mars atmosphere; Bogard and Garrison, 1999). As discussed above, Ar released at low temperatures (400 and 600 C for the bulk samples, and 400, 600, and 800 C for the melt-vein sample) is apparently terrestrial atmospheric contamination. At higher temperatures, Ar from Mars is apparent, although terrestrial Ar must be included to some extent in the released Ar. In the following calculations, Ar from the bulk samples at 800 C and from the melt-vein sample at 1000 C is assumed to be of Martian origin. About 70% and 90% of total 36 Ar and 40 Ar

9 K. Nagao et al. / Polar Science 2 (2008) 195e Xe / 132 Xe 129 Xe / 132 Xe 129 Xe / 132 Xe EFA Martian atmosphere Air Y Y Melt vein Y a b c 8 10 Shergottites EFA Chass to Mars atm. 18 TM Kr / 132 Xe to Air to Air Fig Xe/ 132 Xe plotted against 84 Kr/ 132 Xe. The low-temperature data for the bulk samples lie on a line between air and EFA (elementally fractionated air) (Mohapatra et al., 2002). The shergottite line connects Chassigny (Chass; e.g., Mathew and Marti, 2001; Ott, 1988) and Mars atmosphere (e.g., Bogard and Garrison, 1998; Garrison and Bogard, 1998; Gilmour et al., 1998, 1999, 2001; Marti et al., 1995; Mathew and Marti, 2001; Mathew et al., 1998; Swindle et al., 1986). The point for Chassigny is regarded as noble gases from Mars interior (e.g., Bogard et al., 2001; Mathew and Marti, 2001; Ott, 1988; Ott and Begemann, 1985). Although EFA plots close to Chassigny, 129 Xe/ 132 Xe values for EFA and Chassigny are clearly distinct. The observed values for the Y00 shergottites 4 from the bulk samples are of Martian origin, respectively, while 53% and 70% of total 36 Ar and 40 Ar from the melt-vein sample are from Mars. Concentrations of in situ-produced radiogenic 40 Ar from 40 K are calculated to be 178 and cm 3 STP/g for the bulk and melt-vein, respectively, based on the RbeSr age of Ma reported for Y by Misawa et al. (2007) and K concentrations of wt.% for Y (Shirai and Ebihara, personal communication) and wt.% for Y melt-vein (Imae and Ikeda, personal communication). Radiogenic 40 Ar concentrations are just 16%, 10%, and 4% of the 40 Ar concentrations of the Y bulk, Y bulk, and Y melt-vein samples, respectively. Based on the remaining 36 Ar and 40 Ar concentrations, 40 Ar/ 36 Ar values are calculated to be 1210, 1370, and 590 for Y bulk, Y bulk, and Y melt-vein, respectively. Because the formation age of the melt-vein must be the same as or younger than the RbeSr age of Y000097, the radiogenic 40 Ar concentration should be lower than the value noted above; however, calculation of 40 Ar/ 36 Ar (neglecting the accumulation of radiogenic 40 Ar) yields a slightly high value of 620 for the melt-vein sample. The 40 Ar/ 36 Ar values obtained in the present study are distinctly lower than the value of 1700e1900 estimated for the Martian atmosphere (Bogard and Garrison, 1999), although we did obtain similarly high values for bulk samples at 1000 and 1200 C(Fig. 9). Terribilini et al. (1998) reported comparable values for shergottites (i.e., 1100 for Shergotty and 950 for Y793605), which the authors explained as a mixture of Martian atmospheric and mantle Ar. Such an explanation is possibly also applicable to our results; however, the low 40 Ar/ 36 Ar values obtained in the present study are likely to reflect contamination by terrestrial Ar ( 40 Ar/ 36 Ar ¼ 296). The low value obtained for the meltvein sample, about half of those for the bulk samples, probably reflects relatively heavy contamination by terrestrial Ar (and Kr), as indicated in Fig Cosmogenic Kr: spallogenic origin rather than neutron capture The plot of 80 Kr/ 84 Kr versus 82 Kr/ 84 Kr shown in Fig. 6 reveals excess 80 Kr and 82 Kr compared with terrestrial atmospheric ratios at high temperatures. The indicate mixing between EFA and Mars atmosphere rather than between Chassigny- and Mars-atmosphere-type components (see text for details). Numbers indicate extraction temperatures in C(100).

10 204 K. Nagao et al. / Polar Science 2 (2008) 195e2 data lie along the trend for spallogenic Kr, with no isotopic evidence for 80 Kr and 82 Kr produced by neutron capture. The presence of neutron-produced 80 Kr in the Martian atmosphere has been reported previously, and 80 Kr excess might have been trapped in shock-produced glasses in Martian meteorites (e.g., Rao et al., 2002 and references therein). Although the Kr isotopic ratios for EET79001 glass (Garrison and Bogard, 1998) are also shown in the figure, most of the data show a spallogenic trend: only one sample indicates the presence of neutronproduced Kr. The melt-vein sample shows small excesses in 80 Kr and 82 Kr at 00, 1600, and 1800 C. The data point at 1600 C lies on the spallation line; however, those at 00 and 1800 C may indicate a small contribution by neutron-produced Kr, although the degree of any such contribution is likely to be within experimental error. These findings may indicate that the pre-atmospheric body for the Yamato 00 lherzolites was not large enough to produce secondary neutrons within the body. This view is consistent with the small amount of total recovered mass of about 40 g (i.e., Y000027, 9.68 g; Y000047, 5.34 g; and Y000097, g). Another possible cause for the absence of neutronproduced Kr may be low concentrations of Br, which is the target element in producing 80 Kr and 82 Kr via neutron-capture reaction; however, Br concentrations have yet to be determined for the Y00 lherzolites. Br concentrations reported previously for lherzolitic shergottites (0.05 and ppm for ALH77005 and LEW88516, respectively; Dreibus et al., 1992) are lower than those of other basaltic shergottites (e.g., 0.88 ppm for Shergotty, 0.83 ppm for Zagami, and 0.35 ppm for QUE 94201; Lodders, 1998). Excess 80 Kr produced by neutron irradiation has been reported for basaltic and olivine-phyric shergottites (LA001, QUA94201, SaU005, Shergotty, and Zagami; Eugster et al., 2002), Y (Okazaki and Nagao, 2004), and for other types of Martian meteorites (Nakhla, Chassigny, and ALH84001; Eugster et al., 2002) Xe/ 132 Xe versus 84 Kr/ 132 Xe Fig. 7 shows a correlation diagram for 129 Xe/ 132 Xe versus 84 Kr/ 132 Xe, in which we plotted the end members Chassigny ( 129 Xe/ 132 Xe ¼ and 84 Kr/ 132 Xe ¼ 1.2; Ott, 1988), Martian atmosphere ( 129 Xe/ 132 Xe ¼ 2.6 and 84 Kr/ 132 Xe ¼ 20.5; Bogard and Garrison, 1998), and Earth s atmosphere ( 129 Xe/ 132 Xe ¼ and 84 Kr/ 132 Xe ¼ 27.8; Ozima and Podosek, 2002). Noble gases trapped in Chassigny are regarded as a Martian interior component (e.g., Garrison and Bogard, 1998; Mathew and Marti, 2001; Ott, 1988; Ott and Begemann, 1985). Data for the Y and Y bulk samples follow the trend observed for some shergottites (Mohapatra et al., 2002; Nagao et al., 1997; Okazaki and Nagao, 2004): data at low temperatures (800 C) plot along a horizontal line that passes through the field for Earth s atmosphere; at higher temperatures, data plot along a shergottites line that connects the end members Chassigny and Martian atmosphere, suggesting a release of Martian component trapped in the meteorites. Noble gases characterized by low 84 Kr/ 132 Xe values and air-like 129 Xe/ 132 Xe have been reported previously for Martian meteorites from hot deserts, and are explained as elementally fractionated air (EFA) trapped in the meteorites via weathering effects in the hot desert environment (Mohapatra et al., 2002). This phenomenon has been investigated previously by Schwenzer et al. (2007a,b) using rock and/or sand samples from both hot and cold deserts. Based on stepwise heating experiments, the authors obtained 84 Kr/ 132 Xe values ranging from 1 to 15, much lower than the atmospheric value of These results highlight the fact that EFA is remarkable even in meteorites found in cold conditions such as Antarctica, giving rise to the possibility of erroneous identification as a Martian interior noble gas component because of its similarity to that of Chassigny (see Fig. 7). Nagao et al. (2006) also raised the possibility that Kr and Xe released from shergottites at low temperatures are derived from the terrestrial atmosphere rather than the Martian interior. The authors presented 136 Xe/ 132 Xe, 129 Xe/ 132 Xe, and 84 Kr/ 132 Xe values for Martian meteorites using three-dimensional plots. In this case, terrestrial atmospheric contamination is easily distinguished from Martian interior Xe trapped in Chassigny because the 136 Xe/ 132 Xe value of Chassigny ( ; Mathew and Marti, 2001) is distinctly lower than that of the terrestrial atmosphere (0.3294; Ozima and Podosek, 2002). In the case of our samples, all of the 136 Xe/ 132 Xe values listed in Appendix (Table A3) are terrestrial atmospheric, within error limits. Hence, Kr and Xe of terrestrial origin may be dominant in low-temperature fractions, and may contribute to those from Mars (from both the atmosphere and interior) to some extent, even in higher-temperature fractions. Compared with the bulk samples, the melt-vein sample from Y shows a markedly different trajectory in Fig. 7. Up to an extraction temperature of 1000 C, 129 Xe/ 132 Xe values are close to 1, indicating a release of EFA-Kr and -Xe. With increasing

11 K. Nagao et al. / Polar Science 2 (2008) 195e Artrap / 132 Xe 10,000 1, chondrites Mars inter. Earth Mars atm Y bulk Y melt vein Y bulk Kr/ 132 Xe temperature, the 129 Xe/ 132 Xe values increase to 1.6, with wide variations in 84 Kr/ 132 Xe values. These 84 Kr/ 132 Xe values are much higher than those for the bulk samples, especially at 00 C extraction temperature, where 84 Kr/ 132 Xe is as high as (Table 2) at the peak release of 84 Kr (see Fig. 4c). The relative abundances of trapped Ar, Kr, and Xe (Table 2) are shown in Fig. 8, in which 36 Ar trap / 132 Xe is plotted against 84 Kr/ 132 Xe. Also shown for comparison are values for Earth s atmosphere ( 36 Ar/ 132 Xe ¼ 1340 and 84 Kr/ 132 Xe ¼ 27.7; Ozima and Podosek, 2002), Martian atmosphere ( 36 Ar/ 132 Xe ¼ 580 and 84 Kr/ 132 Xe ¼ 20.3; Pepin, 1991; 36 Ar/ 132 Xe ¼ and 84 Kr/ 132 Xe ¼ ; Bogard and Garrison, 1998), and Martian interior ( 36 Ar/ 132 Xe ¼ 19 and 84 Kr/ 132 Xe ¼ 1.2; Ott, 1988). The dashed line passing through the above three components is the trend for Martian meteorites. Achondrites such as HEDs, Brachina, and silicate in a pallasite also follow the trend line (Nagao, 1994). All data obtained in the present study plot around the trend line, showing that Ar and Kr are fractionated together against Xe, with wide variations (more than two orders 16 EETA79001 glass Fig. 8. Plot of 36 Ar trap / 132 Xe versus 84 Kr/ 132 Xe. Data obtained in the present study plot along a trend through Earth s atmosphere, Martian atmosphere, and Martian interior (Chassigny), showing wide variation of more than two orders of magnitude. Data for the melt-vein sample in the 00 C fraction correspond to very high values of 36 Ar trap / 132 Xe ¼ and 84 Kr/ 132 Xe ¼ (Table 2). Data for EETA shock-produced glass are from Wiens (1988b). Also shown are data for Martian atmosphere ( 36 Ar/ 132 Xe ¼ 580 and 84 Kr/ 132 Xe ¼ 20.3, Pepin, 1991; 36 Ar/ 132 Xe ¼ and 84 Kr/ 132 Xe ¼ , Bogard and Garrison, 1998), Martian interior ( 36 Ar/ 132 Xe ¼ 19 and 84 Kr/ 132 Xe ¼ 1.2, Ott, 1988), and Earth s atmosphere ( 36 Ar/ 132 Xe ¼ 1340 and 84 Kr/ 132 Xe ¼ 27.7, Ozima and Podosek, 2002). Numbers indicate extraction temperatures in C(100). of magnitude). Data for the melt-vein sample plot in the top-right of the figure, showing enrichments in both Ar and Kr compared with the bulk samples. Very high 36 Ar trap / 132 Xe ( ) and 84 Kr/ 132 Xe (76 11) values obtained for the 00 C fraction of the melt-vein sample reflect the release peaks of both 36 Ar trap and 84 Kr at 00 C (as indicated in Fig. 4) rather than the low abundance of 132 Xe. The fractionation trend for the 00 C melt-vein is the opposite to that observed for most meteorites, as indicated in Fig. 8, in which the data plot in the lower left, extending from Martian atmosphere or Earth s atmosphere along the trend line (for other Martian meteorites, see Nagao, 1994; Nagao et al., 1997; Okazaki and Nagao, 2004). One possible explanation of the gas in the 00 C fraction is that the melt-vein might have sampled an unknown component on Mars at the time of the shock event. A second explanation is the occurrence of intensive fractionation that selectively concentrated Ar and Kr, leaving a near-constant concentration of Xe; however, we suspect the presence of residual terrestrial contamination that cannot be removed even at high temperatures of around 00 C, as Ar and Xe with Martian atmospheric signatures become clearer at high temperatures of 1600 and 1800 C(Fig. 9). Wiens (1988b) reported that crush-released gas from EETA79001 glass shows a similar enrichment in 84 Kr compared with Martian atmosphere as plotted in Fig. 8 ( 36 Ar trap / 132 Xe ¼ and 84 Kr/ 132 Xe ¼ ). The gas with isotopic ratios of 40 Ar/ 36 Ar ¼ 430e680 and 129 Xe/ 132 Xe ¼ 0.93e1.21 released from EETA79001 glass was explained as a noble gas component, different from SPB (shergottite parent body) and contained in relatively large vesicles (10e100 mm in diameter) in shock-produced glass (Wiens, 1988b). Isotopic ratios of 40 Ar/ 36 Ar trap ¼ and 129 Xe/ 132 Xe ¼ (Table 2) obtained for our 00 C melt-vein sample are similar to the above values, which may indicate the presence of the same noble gas component in shockproduced glasses of Martian meteorites. If such vesicles contained the gas component and were broken at 00 C, this would explain the observed release peak at 00 C; however, the mechanism of the strong enrichment in both Ar and Kr from the Mars atmospheric composition remains unsolved. The melt-vein within Y would have been subjected to complex mechanisms of trapping gases of Martian origin during the shock event. Based on the results of shock experiments (Bogard et al., 1986; Wiens, 1988a; Wiens and Pepin, 1988), Martian atmospheric noble gases shock-implanted into

12 206 K. Nagao et al. / Polar Science 2 (2008) 195e2 40 Ar/ 36 Artrap 40 Ar/ 36 Artrap 2,500 2,000 1,500 1,000 a b Mars+EFA mix Mars+Earth atm. mix Mars atmosphere Ai r 4,6,8 Y bulk Y Melt vein Y bulk Xe/ 132 Xe melt portions of Martian meteorites are considered to be free of elemental or isotopic fractionation. The relatively high 129 Xe/ 132 Xe values and 129 Xe excess abundances obtained for the melt-vein at 1600 and 1800 C compared with the bulk samples (Table 2 and Figs. 4e and 9) indicate higher concentrations of Martian atmospheric Xe in the melt-vein portion than in host rock. In Fig. 8, the data at 1600 and 1800 C for Y bulk Y Melt vein Ai r 12 Y bulk Fig. 9. Plot of 40 Ar/ 36 Ar trap versus 129 Xe/ 132 Xe. The area around Air (within the dotted rectangle) in figure (a) is enlarged in figure (b) to resolve the 129 Xe/ 132 Xe values of samples from Chassigny. The Ar and Xe isotopic compositions of the bulk samples can be explained as a mixture between EFA and the Mars atmosphere (see the caption for Fig. 7). In contrast, the melt-vein sample shows a trend that represents a mixture between non-fractionated atmosphere and Mars s atmosphere. Numbers indicate extraction temperatures in C(100). 10 Chassigny the melt-vein plot close to the composition of Martian atmosphere, possibly reflecting the trapping of Martian atmosphere without fractionation Martian atmospheric Ar and Xe 129 Xe/ 132 Xe values are compared with 40 Ar/ 36 Ar trap in Table 2 and Fig. 9a and b. The compositions of the Mars and Earth atmospheres are shown for comparison. Although the value of 40 Ar/ 36 Ar for Chassigny is poorly constrained to about 300 (from 0 to 500; Bogard, 1997), the shaded area in Fig. 9b may represent the interior composition of Mars ( 129 Xe/ 132 Xe ¼ ; Ott, 1988). At low extraction temperatures, the values are similar to those of terrestrial atmosphere (see Fig. 9b). 129 Xe/ 132 Xe values for these temperature fractions are readily distinguished from Chassignytype Xe; consequently, the gases at low temperatures must represent contamination by the terrestrial atmosphere. At 1000 and 1200 C, the analyzed bulk samples show a rapid increase in 40 Ar/ 36 Ar values up to about Elevated 129 Xe/ 132 Xe values, which appear to represent the contribution of Martian atmospheric Xe, are observed at higher temperatures (1.3 at 00 C). As noted in Section 3.3, however, it is possible that Xe was trapped with Ar during crystallization in a magma chamber on Mars, and that the high 129 Xe/ 132 Xe values represent the isotopic signature of shergottite magma. The decrease in 40 Ar/ 36 Ar values at higher temperatures (1600 C) probably reflects terrestrial atmospheric Ar released from the Mo crucible in the extraction furnace, even though blank correction was applied. The melt-vein sample shows different trends to those of the bulk samples: data plot close to the terrestrial atmosphere at low temperatures (1000 C); 129 Xe/ 132 Xe values increase at higher temperatures, reaching 1.6 at 1600 C; and 40 Ar/ 36 Ar remains low (1000). The data for bulk samples appear to follow the mixing curve between Martian atmosphere and EFA. This finding is consistent with the trend illustrated in Fig. 7, in which the low-temperature data lie on the elemental fractionation line that passes through the terrestrial atmosphere, followed by shifts to the shergottites line connecting EFA (or Chassigny) and Martian atmosphere. The isotopic ratios of the melt-vein may be explained by mixing between non-fractionated terrestrial and Martian atmospheres. Concentrations of trapped 36 Ar, 40 Ar, and 132 Xe reported for EET79001, 8A, and 8B glasses are (28e29) 10 9, (49e53) 10 6, and

13 K. Nagao et al. / Polar Science 2 (2008) 195e2 207 (28e42) cm 3 STP/g, respectively, for which 40 Ar/ 36 Ar ¼ 1760e1830 and 129 Xe/ 132 Xe ¼ 2.1e2.5 were observed (Garrison and Bogard, 1998). The concentrations of 36 Ar trap ( cm 3 STP/g) and 132 Xe ( cm 3 STP/g) in our melt-vein sample are comparable with those in EET79001 glass, but the concentration of 40 Ar ( cm 3 STP/g) is as low as about 20% of those in EET79001 glass. The low concentration of 40 Ar indicates relatively heavy contamination by terrestrial atmospheric gases and low abundances of Martian atmospheric gases in the meltvein sample from the Y lherzolitic shergottite. It is possible that the trapping efficiency of the Martian atmosphere during the impact differed among the shergottites, as well as the magnitude of shock pressure and heating. 4. Conclusions We obtained the following conclusions based on isotopic analyses of noble gas within bulk samples from Yamato and Yamato lherzolitic shergottites and a melt-vein sample from Yamato (1) He and Ne are dominated by cosmogenic gases, and we failed to detect Martian atmospheric He and Ne or in situ-produced radiogenic 4 He. (2) Stepwise heating experiments revealed distinct release profiles for Ne, Ar, and Kr between the bulk and melt-vein samples. The maximum release of cosmogenic Ne from the Y bulk and Y bulk samples was recorded at 00 C, while the melt-vein sample showed peaks at 1000 and 00 C. Peaks in Ar and Kr from the meltvein sample were observed at 800 and 00 C; the amounts of released Ar and Kr were much larger than those from the bulk samples. Ar and Kr for the peak at 800 C were derived from terrestrial atmosphere, while those at 00 C may represent a mixture between terrestrial and Martian atmospheres. The release profiles for trapped 132 Xe did not show such differences between the melt-vein and bulk samples; however, remarkable release of 129 Xe excess from the melt-vein sample at 1600 and 1800 C was observed. (3) We obtained cosmic-ray exposure ages for the analyzed meteorites of Ma, in good agreement with the ages reported previously for other lherzolites (Y793605, ALH77005, NWA1950, and LEW88516; Christen et al., 2005; Eugster and Polnau, 1997; Eugster et al., 1997, 2002; Nagao et al., 1997). This finding indicates that all of these lherzolites were ejected from Mars by a single impact event. (4) Maximum 40 Ar/ 36 Ar trap values of about 1900 were observed for the bulk samples at around 1000e 00 C. Because the calculated amount of in situproduced radiogenic 40 Ar for the reported RbeSr age of 189 Ma (Misawa et al., 2007) can only account for 10% of total 40 Ar, most of the 40 Ar is regarded to be from the Martian atmosphere or interior. (5) The absence of neutron-produced 80 Kr and 82 Kr in the measured samples indicates a small pre-atmospheric body and/or negligible amounts of Martian atmospheric Kr with excess 80 Kr and 82 Kr (e.g., Rao et al., 2002). The absence of neutron-produced Kr may also reflect low Br concentrations in lherzolites compared with those in basaltic and olivine-phyric shergottites. (6) Elementally fractionated terrestrial atmosphere (EFA) is responsible for the low 84 Kr/ 132 Xe values obtained for bulk samples at low extraction temperatures (800 C). The melt-vein sample showed an extremely high 84 Kr/ 132 Xe value of 76, which is possibly a Martian component similar to the crush-released gas from EETA79001 glass reported by Wiens (1988b). (7) Ar and Xe within the bulk samples from Y and Y are a mixture of Martian atmospheric and EFA components, while those of the melt-vein sample plot along a mixing line between Martian atmospheric and non-fractionated terrestrial atmospheric components. (8) Overall noble gas compositions for Y and Y support the pairing of the meteorites, as previously proposed based on mineralogical and petrological observations (e.g., Misawa et al., 2006; Mikouchi and Kurihara, 2007). Acknowledgments We express our thanks to NIPR for providing the important Martian meteorites for analysis, and Dr. K. Misawa for organizing the consortium study on the Yamato shergottites. We thank two anonymous reviewers for their careful reading of the manuscript and constructive comments. This work was supported by a Grant-in-Aid for Scientific Research (# awarded to K.N.), a fellowship from the NASA Postdoctoral Program (awarded to J.P.), and a Japanese Government Scholarship (awarded to H.G.C.).

14 Appendix Table A1 He, Ne, and Ar concentrations and isotopic ratios of noble gases in Yamato , Yamato melt-vein, and Yamato shergottites Temperature 3 He 4 He 3 He/ 4 He 20 Ne 21 Ne 22 Ne 20 Ne/ 22 Ne 21 Ne/ 22 Ne 36 Ar 38 Ar 40 Ar 38 Ar/ 36 Ar 40 Ar/ 36 Ar 84 Kr 132 Xe C 10 9 cc/g 10 9 cc/g 10 9 cc/g cc/g Yamato bulk: stepwise heating (53.9 mg) ND ND ND ND ND ND Total Yamato bulk: total melting (6.0 mg) Yamato melt-vein: stepwise heating (30.2 mg) ND ND ND K. Nagao et al. / Polar Science 2 (2008) 195e2

15 1800 ND ND ND Total Yamato bulk: stepwise heating (110.1 mg) ND ND ND ND ND ND Total Yamato bulk: total melting (19.8 mg) ND: could not be determined. K. Nagao et al. / Polar Science 2 (2008) 195e2 209

16 210 K. Nagao et al. / Polar Science 2 (2008) 195e2 Table A2 84 Kr concentrations and Kr isotopic ratios in Yamato , Yamato melt-vein, and Yamato shergottites Temp. ( C) 84 Kr (10 12 cc/g) 78 Kr/ 84 Kr 80 Kr/ 84 Kr 82 Kr/ 84 Kr 83 Kr/ 84 Kr 86 Kr/ 84 Kr Yamato bulk: stepwise heating (53.9 mg) Total Yamato bulk: total melting (6.0 mg) Yamato melt-vein: stepwise heating (30.2 mg) Total Yamato bulk: stepwise heating (110.1 mg)

17 K. Nagao et al. / Polar Science 2 (2008) 195e2 211 Table A2 (continued) Temp. ( C) 84 Kr (10 12 cc/g) 78 Kr/ 84 Kr 80 Kr/ 84 Kr 82 Kr/ 84 Kr 83 Kr/ 84 Kr 86 Kr/ 84 Kr Total Yamato bulk: total melting (19.8 mg) Table A3 132 Xe concentrations and Xe isotopic ratios in Yamato , Yamato melt-vein, and Yamato shergottites Temp. ( C) 132 Xe (10 12 cc/g) 124 Xe/ 132 Xe 126 Xe/ 132 Xe 128 Xe/ 132 Xe 129 Xe/ 132 Xe 130 Xe/ 132 Xe 131 Xe/ 132 Xe 134 Xe/ 132 Xe 136 Xe/ 132 Xe Yamato bulk: stepwise heating (53.9 mg) ND Total Yamato bulk: total melting (6.0 mg) Yamato melt-vein: stepwise heating (30.2 mg) (continued on next page)

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