Multiple hydrothermal events at martian surface revealed by H and Cl isotope systematics of melt inclusions and hydrous minerals from chassignite NWA 2737

Abstract

The chassignites and nakhlites could have co-magmatic origin but display distinct hydrogen and chlorine isotopic compositions, indicating that they may have experienced distinct hydrothermal activities on Mars. However, the details are not yet fully understood. Here, we performed H and Cl isotopic investigations on hydrous minerals (kaersutite and apatite) and glass-bearing melt inclusions from chassignite NWA 2737 to unravel the details of the hydrothermal events experienced by chassignites on Mars. Our results demonstrate that at least two hydrothermal events on Mars have been recorded in NWA 2737. A D- and ³⁷Cl-rich martian crustal/underground fluid was added to the parent magma of NWA 2737 prior to the entrapment of melt inclusions and later interaction of the parent rock with a D-poor fluid, probably deriving from magma degassing. The notable high-δD values (up to 6239‰) of kaersutite in NWA 2737 are comparable with those recorded in younger shergottites, suggesting that the martian exchangeable water reservoir has retained a nearly constant δD value over the past 1.3 Ga.