Aqueous alteration of the Martian meteorite Northwest Africa 817: Probing fluid–rock interaction at the nakhlite launch site

Lee, M.R. , Daly, L. , Cohen, B.E. , Hallis, L.J. , Griffin, S. , Trimby, P., Boyce, A. and Mark, D.F. (2018) Aqueous alteration of the Martian meteorite Northwest Africa 817: Probing fluid–rock interaction at the nakhlite launch site. Meteoritics and Planetary Science, 53(11), pp. 2395-2412. (doi: 10.1111/maps.13136)

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The nakhlite meteorites characteristically contain iddingsite, a hydrous iron–magnesium silicate that formed by aqueous alteration on Mars. Iddingsite is most abundant in Northwest Africa (NWA) 817, and alteration products in this meteorite also have the lowest deuterium/hydrogen ratio of any nakhlite. Taken together, these distinctive properties could be interpreted to show that NWA 817 was altered under different physico‐chemical conditions than the other nakhlites and by liquid water from a separate reservoir. Here this interpretation is tested through a petrographic, mineralogical, chemical, and isotopic study of NWA 817. We find that its iddingsite occurs as olivine‐hosted veins of nanocrystalline smectite and Fe‐oxyhydroxide. Strong similarities in the mineralogy of iddingsite between NWA 817 and other nakhlites suggest that these meteorites were altered under comparable physico‐chemical conditions, with the Fe‐rich composition of NWA 817 olivine grains rendering them especially susceptible to aqueous alteration. Analyses of NWA 817 bulk samples by stepwise pyrolysis confirm that its iddingsite has unusually low deuterium/hydrogen ratios, but owing to terrestrial weathering of this meteorite, the hydrogen isotopic data cannot be used with confidence to infer the origin of Martian aqueous solutions. NWA 817 was most probably altered along with the other nakhlites over a short time period and in a common aqueous system. One interpretation of a correlation between the eruption ages of three of the nakhlites and the chemical composition of their iddingsite is that water originated from close to the surface of Mars and flowed through the nakhlite lava pile under the influence of gravity.

Item Type:Articles
Additional Information:This work was funded by the Science and Technology Facilities Council through grants ST/N000846/1 and ST/H002960/1.
Glasgow Author(s) Enlighten ID:Mark, Professor Darren and Cohen, Dr Benjamin and Boyce, Professor Adrian and Lee, Professor Martin and Daly, Dr Luke and Griffin, Dr Sammy and Hallis, Dr Lydia
Authors: Lee, M.R., Daly, L., Cohen, B.E., Hallis, L.J., Griffin, S., Trimby, P., Boyce, A., and Mark, D.F.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Meteoritics and Planetary Science
ISSN (Online):1945-5100
Published Online:28 June 2018
Copyright Holders:Copyright © 2018 The Authors
First Published:First published in Meteoritics and Planetary Science 53:2395-2412
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
697411A journey from the solar nebula to planetary bodies: cycling of heat, water and organicsMartin LeeScience & Technology Facilities Council (STFC)ST/N000846/1SCHOOL OF GEOGRAPHICAL & EARTH SCIENCES
519741Follow the water: insights into the martian hydrosphere from nakhlitesMartin LeeScience & Technology Facilities Council (STFC)ST/H002960/1SCHOOL OF GEOGRAPHICAL & EARTH SCIENCES