Xenon Isotopes in Shergottites Rbt 04262, Dag 489, Shergotty and Eet

Introduction: Previous research on noble gases within Martian meteorites has identified numerous distinct trapped Xe components that have characteristic isotopic signatures. Three distinct reservoirs are needed to explain these components. One reservoir is the Martian atmosphere, containing an elevated 129 Xe/ 132 Xe of 2.4 [1], which has clearly contributed to the Xe budget in the Martian meteorites. Two distinct reservoirs in the Martian interior contribute to the Xe components. One reservoir, identified with the Martian mantle is indistinguishable from solar Xe with 129 Xe/ 132 Xe of 1.03 [2], whilst the second reservoir contains a solar xenon composition that has been modified by fission of 244 Pu. The sources and trapping mechanisms of the components are controversial and poorly understood, and three mechanisms of incorporation have been proposed: dissolution in primary magma, aqueous alteration and shock incorporation. These three mechanisms would yield elevated noble gas concentrations in primary melt inclusions, alteration products and shock glasses (and, perhaps, close to grain boundaries where shock pressures are elevated) respectively. To constrain the location and trapping mechanisms of noble gases, and help characterize parent reservoris of meteorites, we have analysed mineral separates of shergottites olivine-phyric RBT 04262, basaltic EET 79001 lithology B, basaltic Shergotty and olivine-orthopyroxene DaG 489. Comparison of shergottite type and the analysis of crystallization histories by investigation of melt inclusions may improve the understanding of meteorite formation and their relationship with each other, and increase understanding of the interior and atmospheric evolution processes on Mars. Our results will be compared to previous results by [3] on mineral separates of Shergotty. Methodology: Following crushing in a clean laboratory , hand-picked mineral separates including ali-quots of olivine, pyroxene, olivine/pyroxene, whole rock, iddingsite, maskelynite and opaques from the four meteorites were analysed on the RELAX instrument (Refrigerator Enhanced Laser Analyser for Xe-non) using laser step-heating experiments to determine xenon isotopic ratios and concentrations [4-5]. It was impossible to distinguish between olivine and pyroxene in the crushed RBT 04262 fragments due to their similarity in colour, and small sample size. The aliquots were heated under vacuum until melting using an infra-red Nd:YAG laser (λ = 1064 nm), and the gas emitted