The D/H ratio of the Martian Mantle: Evidence from the Lafayette Meteorite

Hydrous apatite in the nakhlite group of martian meteorites shows evidence of Cl-rich fluid incorporation into the magma prior to apatite crystallisation. Thus, nakhlite apatite D/H ratios should reflect a mixture between the parental magma and this crustally derived fluid. Here we present the volatile content and D/H ratios of apatite within the nakhlite Lafayette (δD 137 to 352‰), suggesting mixing between a crustally derived Cl-rich fluid and an intermediate D/H ratio (δD ≈ 400‰) and a magma with a low D/H ratio (δD ≈ −100‰). This martian mantle D/H ratio is similar to that of Earth’s upper mantle, but is higher than recent D/H ratios measured within a number of other inner Solar System materials. Thus, D/H ratio heterogeneity in these materials points towards multiple sources of hydrogen during the formation of rocky planetary bodies in the inner Solar System.