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Geochemistry and petrography of martian meteorite Northwest Africa 11115: A rare earth element-enriched olivine-phyric shergottite closely linked to Northwest Africa 1068

Melwani Daswani, M. and Greber, N. D. and Hu, Jinping and Greenwood, R. C. and Heck, P. R. (2021) Geochemistry and petrography of martian meteorite Northwest Africa 11115: A rare earth element-enriched olivine-phyric shergottite closely linked to Northwest Africa 1068. . (Unpublished)

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The shergottite family of meteorites shows a remarkable petrographic and geochemical variety, revealing information about mantle processes and basalt formation on Mars. Northwest Africa (NWA) 11115, found in Morocco in 2016, is one of the newest meteorites in this family. We report bulk-rock major and trace element abundances of NWA 11115, bulk oxygen isotope systematics, and the petrography and mineralogy of a thick section, and compare the geochemistry of this recent find to other martian rocks. NWA 11115 is an olivine-phyric shergottite with an enriched rare earth element pattern, and shares similarities with NWA 1068, another enriched olivine-phyric shergottite. The large (< 2.5 mm) olivine phenocrysts are likely to be cumulates, similar to NWA 1068. However, the abundant maskelynite (~30 vol. %) in NWA 11115 places the bulk chemistry somewhat closer to the basaltic shergottites. We suggest that NWA 11115 is genetically linked to NWA 1068, perhaps crystallizing slightly above in the same cumulate pile. NWA 11115 contains one of the lowest K/Th ratios among the martian meteorites (K/Th = 2987 ± 810), and far lower than the surface of Mars (K/Th = 5300). Finally, while NWA 11115 contains abundant (~0.4 vol. %) fracture-filling calcite (presumably from hot desert alteration during its terrestrial residence), diagnostic bulk element mass ratios were not indicative of the presence of terrestrial alteration (Th/U ≈ 4.09, Sr/Nd ≈ 12.26, K/La ≈ 526.94, Ce/Ce* ≈ 1.01).

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Melwani Daswani, M.0000-0002-4611-3209
Greber, N. D.0000-0002-2209-3784
Greenwood, R. C.0000-0002-5544-8027
Heck, P. R.0000-0002-6319-2594
Additional Information:The authors acknowledge T. Boudreaux for donating NWA 11115 to the Field Museum, J. Greer and J. Holstein for help with sample preparation, L. Kööp and B. Strack for SEM support, S. Rastegar for preliminary SEM analysis, L. Dussubieux for LA-ICP-MS support, A. I. Neander and Z.-X. Luo for µCT scanning and support, and J. Filiberto and A. Treiman for useful discussions. We thank Thomas Pettke for assistance with LA-ICP-MS analyzes of the pressed powder pellets at the University of Bern. GPS Division analytical facilities at Caltech and Chi Ma are thanked for the support on EMPA analysis. PRH acknowledges support from the Tawani Foundation. MMD’s portion of the work was done partly as a private venture and not in the author’s capacity as an employee of the Jet Propulsion Laboratory, California Institute of Technology. The authors declare no competing interests.
Funding AgencyGrant Number
Tawani FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:20211012-211830294
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111394
Deposited By: George Porter
Deposited On:12 Oct 2021 21:58
Last Modified:12 Oct 2021 21:58

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