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

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 delta D value (up to 6,509 parts per thousand) of any phosphates in Martian meteorites. The positive correlation between the H2O contents (72-2,251 ppm) and delta D values (3,965-6,509 parts per thousand) as well as between the Cl contents (1.28-6.17wt%) and delta Cl-37 values (-1.7-4.0 parts per thousand) 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).