Water on Mars: Clues from Deuterium/Hydrogen and Water Contents of Hydrous Phases in SNC Meteorites
Ion microprobe studies of hydrous amphibole, biotite, and apatite in shergottite-nakhlite-chassignite (SNC) meteorites, probable igneous rocks from Mars, indicate high deuterium/hydrogen (D/H) ratios relative to terrestrial values. The amphiboles contain roughly one-tentn as much water as expected, suggesting that SNC magmas were less hydrous than previously proposed. The high but variable D/H values of these minerals are best explained by postcrystallization D enrichment of initially D-poor phases by martian crustal fluids with near atmospheric D/H (about five times the terrestrial value). These igneous phases do not directly reflect the D/H ratios of martian "magmatic" water but provide evidence for a D-enriched martian crustal water reservoir.
© 1994 American Association for the Advancement of Science. Received 14 February 1994; accepted 16 May 1994. We thank A. Kennedy, G. Huss, E. Deloule, and A. Fahey for assistance with the ion microprobe; D. Stevenson for his time and effort on our behalf; G. Wasserburg for use of the ion microprobe; M. Johnson for sharing notes on kaersutite locations; T. McCoy for bringing two of the studied samples to our attention, for photos, and for advice; P. Carpenter for scanning electron microscope and electron microprobe assistance; M. Baker, B. McInnes, and J. Beckett for help with standard glass synthesis; and J. Beckett and N. Evans for comments on the manuscript. Perceptive reviews from H. McSween Jr. and an anonymous reviewer are greatly appreciated. We also thank the following for providing samples for this study: A. Brearley, University of New Mexico (UNM 991); K. Keil, University of Hawaii (UH 106 and UH 234); G. MacPherson, Smithsonian Institution (USNM 624-1 and USNM 321-1); A. Montana, University of California, Los Angeles (terrestrial amphiboles and biotites); and L. Silver, California Institute of Technology (Pacoima Canyon apatite). Supported by National Aeronautics and Space Administration (NASA) Graduate Student Research Program grant NGT 50800, NASA grants NAG 9-105 and NAGW 3533 (E.M.S.), NAG 9-46 and NAGW 3329 (S.E.), and NAGW 3297 (G. J. Wasserburg), and contribution 5377 (852), Division of Geological and Planetary Sciences, California Institute of Technology.