Noble gases of the Yamato 000027 and Yamato 000097 lherzolitic shergottites from Mars

We used total melting and stepwise heating methods to measure noble gases within bulk samples from Yamato 000027 and Yamato 000097 lherzolites as well as a melt-vein sample from Yamato 000027. He and Ne are dominated by cosmogenic noble gases. The obtained cosmic-ray exposure age of 4.6 ± 1.5 Ma, an average age based on cosmogenic ³He, ²¹Ne, and ³⁸Ar 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, ⁴⁰Ar/³⁶Ar = 1900 and ¹²⁹Xe/¹³²Xe = 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 ⁴⁰Ar and ¹²⁹Xe, were evolved from the melt-vein sample at 1400 °C, and the gas shows very high ³⁶Ar/¹³²Xe (=3100) and ⁸⁴Kr/¹³²Xe (=76) values. Maximum ⁴⁰Ar/³⁶Ar and ¹²⁹Xe/¹³²Xe values of the melt sample were 1100 and 1.6, respectively, at 1600 °C. Cosmogenic Kr shows an absence of ⁸⁰Kr and ⁸²Kr produced by neutron capture on Br, which suggests a small pre-atmospheric body. Overall noble gas compositions for Y000027 and Y000097 support pairing for the Yamato 00 shergottites.