Deuterium and 37Chlorine Rich Fluids on the Surface of Mars: Evidence From the Enriched Basaltic Shergottite Northwest Africa 8657

摘要

Apatite, a major hydrous mineral in Martian meteorites, has the potential to reveal history of volatiles on Mars. Here we report the H and Cl isotopic systematics of apatite from the enriched basaltic shergottite Northwest Africa (NWA) 8657 to better understand the processes influencing volatiles at or near the Martian (sub)surface. The apatite in NWA 8657 has the highest reported δD value (up to 6,509‰) of any phosphates in Martian meteorites. The positive correlation between the H_2O contents (72-2,251 ppm) and δD values (3,965-6,509‰) as well as between the Cl contents (1.28-6.17wt%) and δ~(37)Cl values (-1.7-4.0‰) in NWA 8657 apatite are consistent with mixing between volatiles derived from the Martian mantle and meteoric water/fluid. The D- and ~(37)Cl-enrichment of apatite in NWA 8657 implies isotopic exchange with subsurficial fluids during postcrystallization hydrothermal event(s).