T. Tomkinson
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.; Franchi, I.A.
Authors
M.R. Lee
D.F. Mark
K.J. Dobson
I.A. Franchi
Abstract
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.
Citation
Tomkinson, T., Lee, M., Mark, D., Dobson, K., & Franchi, I. (2015). The Northwest Africa (NWA) 5790 meteorite: A mesostasis-rich nakhlite with little or no Martian aqueous alteration. Meteoritics & Planetary Science, 50(2), 287-304. https://doi.org/10.1111/maps.12424
Journal Article Type | Article |
---|---|
Acceptance Date | Dec 6, 2014 |
Online Publication Date | Feb 16, 2015 |
Publication Date | Feb 16, 2015 |
Deposit Date | May 5, 2016 |
Publicly Available Date | May 9, 2016 |
Journal | Meteoritics and Planetary Science |
Print ISSN | 1086-9379 |
Electronic ISSN | 1945-5100 |
Publisher | Wiley |
Peer Reviewed | Peer Reviewed |
Volume | 50 |
Issue | 2 |
Pages | 287-304 |
DOI | https://doi.org/10.1111/maps.12424 |
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Copyright Statement
© 2015 The Authors. Meteoritics & Planetary Science published by Wiley Periodicals, Inc. on behalf of The Meteoritical Society. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
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