The sources of water in Martian meteorites: Clues from hydrogen isotopes

H isotope measurements of carbonate, phosphate, feldspathic and mafic glasses, and post-stishovite silica phase in the shergottites Zagami, Shergotty, SaU 005, DaG 476, ALHA 77005 and EETA 79001, as well as in Chassigny and ALH 84001, show that all these phases contain deuterium-enriched water of extraterrestrial origin. The minerals and glasses analyzed may contain an initial primary hydrogen component, but their isotopic composition was modified to varying degrees by three different processes: interaction with a fractionated exchangeable water reservoir on Mars, hydrogen devolatilization by impact melting, and terrestrial contamination. Positive correlations between deltaD and water abundance in feldspathic glass and post-stishovite silica in Zagami, Shergotty, and SaU 005 is indicative of mixing of a high deltaD component (3000-4000parts per thousand) and a less abundant, low deltaD component (similar to0parts per thousand). The high deltaD component is primarily derived from the Martian exchangable reservoir, but may also have been influenced by isotopic fractionation associated with shock-induced hydrogen loss. The low deltaD component is either a terrestrial contaminant or a primary "magmatic" component. The negative correlation between deltaD and water abundances in mafic and feldspathic glasses in ALH 84001, ALHA 77005, and EETA 79001 is consistent with the addition of a low deltaD terrestrial contaminant to a less abundant high-deuterium Martian component. The low deltaD of magmatic glass in melt inclusions suggests that the deltaD of Martian parent magma was low and that the initial H isotope signature of Mars may be similar to that of Earth. Copyright (C) 2003 Elsevier Ltd.