The Northwest Africa (NWA) 5790 meteorite: a mesostasis-rich nakhlite with little or no Martian aqueous alteration

Tomkinson, T., Lee, M. R. , Mark, D. F. , Dobson, K. J. and Franchi, I. A. (2015) The Northwest Africa (NWA) 5790 meteorite: a mesostasis-rich nakhlite with little or no Martian aqueous alteration. Meteoritics and Planetary Science, 50(2), pp. 287-304. (doi: 10.1111/maps.12424)

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Northwest Africa (NWA) 5790 is the most recently discovered member of the nakhlite group. Its mineralogy differs from the other nakhlites with a high abundance mesostasis (38.1 ± 3.6 vol%) and scarcity of olivine (4.0 ± 2.2 vol%). Furthermore, zoning of augite phenocrysts, and other petrographic and chemical characteristics suggest that NWA 5790 samples the chilled margin of its parent lava flow/sill. NWA 5790 contains calcite and rare clay minerals that are evidence for its exposure to liquid water. The calcite forms a cement to coatings of dust on the outer surface of the find and extends into the interior of the meteorite within veins. The presence of microbial remains within the coating confirms that the dust and its carbonate cement are terrestrial in origin, consistent with the carbon and oxygen isotope composition of the calcite. The clay minerals are finely crystalline and comprise ~0.003 vol% of the meteorite. δD values of the clay minerals range from −212 ± 109‰ to −96 ± 132‰, and cannot be used to distinguish between a terrestrial or Martian origin. As petrographic results are also not definitive, we conclude that secondary minerals produced by Martian groundwaters are at best very rare within NWA 5790. The meteorite has therefore sampled a region of the lava flow/sill with little or no exposure to the aqueous solutions that altered other nakhlites. This isolation could relate to the scarcity of olivine in NWA 5790 because dissolution of olivine in other nakhlites by Martian groundwaters enhanced their porosity and permeability, and provided solutes for secondary minerals.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Tomkinson, Dr Tim and Dobson, Dr Katherine and Mark, Professor Darren and Lee, Professor Martin
Authors: Tomkinson, T., Lee, M. R., Mark, D. F., Dobson, K. J., and Franchi, I. A.
College/School:College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing > Dental 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
Publisher:The Meteoritical Society
ISSN (Online):1945-5100
Copyright Holders:Copyright © 2015 The Authors
First Published:First published in Meteoritics and Planetary Science 50(2):287-304
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
519741Follow the water: insights into the martian hydrosphere from nakhlitesMartin LeeScience & Technologies Facilities Council (STFC)ST/H002960/1SCHOOL OF GEOGRAPHICAL & EARTH SCIENCES