Volatiles in the martian crust and mantle: Clues from the NWA 6162 shergottite

Martian meteorites of various petrogeneses retain a record of volatiles on Mars: from the hydrosphere, crustal water to the mantle. Sputtering of the martian atmosphere by solar wind after the loss of Mars' magnetic field enriched it in deuterium, which exchanged with martian crustal water. Recent studies show that the hydrogen isotopic composition of the martian crustal water reservoir varies from 3000 to 7000 parts per thousand but requires better constraints. Melt inclusion glasses, maskelynite and fusion crust from the depleted olivine-phyric shergotite NWA 6162 were analyzed using NanoSIMS, providing a unique insight into the hydrogen isotopic and volatile elemental content of both the martian crustal water reservoir and the mantle source. The H2O, S, and CI contents of the melt inclusion glasses are similar to 0-3137, 14-239, and 16-967 ppm, respectively. delta D values vary from -560 to 6137 parts per thousand. The water content positively correlates with the delta D values in both the melt inclusion glasses and maskelynite in a two end-member mixing trend. One end-member is the magmatic water with a delta D value of similar to 0 parts per thousand, and the other end member is the martian crustal water with delta D ranging from 5000 to 6000 parts per thousand. NWA 6162, a depleted olivine-phyric shergottite, originated from a different mantle source to the enriched lherzolitic shergottites. However, both types of shergottites exchanged with martian crustal water with the same delta D values, indicating a homogeneous martian crustal water hydrogen isotopic composition (5000-6000 parts per thousand). Most melt inclusion glasses from NWA 6162 have low water content (0-234 ppm) except for two enriched locations as micron-sized bands and dendrites. The low water content in most melt inclusion glasses, the dendritic shaped water enriched areas in melt inclusions, and the martian crustal water diffusion profile recorded in maskelynite collectively suggest short-lived water-rock interactions in the NWA 6162 parent rock that was probably induced by impact. Furthermore, a great contribution (up to 98%) of surface Cl accompanying D-enriched water was recorded in the melt inclusions supported by the positive correlation between CI and H2O. The presence of sulfide and S-rich hot spots and low delta D end-member of the magmatic water indicate that the degassing during post-entrapment crystallization and ascent of the melt inclusion is negligible. H2O, S, and CI contents of the martian mantle reservoir are estimated to be 0.1-3, 0.5-15, and 0.5-4 ppm respectively, after the correction of fractional crystallization of the melt inclusions and contribution from the martian surface reservoir. The martian mantle reservoir estimated from NWA 6162 was water-, S-, and Cl-poorer than the Earth's interior. (C) 2019 Elsevier B.V. All rights reserved.