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Martian low-temperature alteration materials in shock-melt pockets in Tissint: Constraints on their preservation in shergottite meteorites

Kuchka, C. R. and Herd, C. D. K. and Walton, E. L. and Guan, Y. and Liu, Y. (2017) Martian low-temperature alteration materials in shock-melt pockets in Tissint: Constraints on their preservation in shergottite meteorites. Geochimica et Cosmochimica Acta, 210 . pp. 228-246. ISSN 0016-7037. http://resolver.caltech.edu/CaltechAUTHORS:20170509-131410385

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Abstract

We apply an array of in situ analytical techniques, including electron and Raman microscopy, electron and ion probe microanalysis, and laser ablation mass spectrometry to the Tissint martian meteorite in order to find and elucidate a geochemical signature characteristic of low-temperature alteration at or near the martian surface. Tissint contains abundant shock-produced quench-crystallized melt pockets containing water in concentrations ranging from 73 to 1730 ppm; water content is positively correlated with Cl content. The isotopic composition of hydrogen in the shock-produced glass ranges from δD = 2559 to 4422 ‰. Water is derived from two distinct hydrogen reservoirs: the martian near-surface (>500 ‰) and the martian mantle (-100 ‰). In one shock melt pocket comprising texturally homogeneous vesiculated glass, the concentration of H in the shock melt decreases while simultaneously becoming enriched in D, attributable to the preferential loss of H over D to the vesicle while the pocket was still molten. While igneous sulfides are pyrrhotite in composition (Fe_(0.88-0.90)S), the iron to sulfur ratios of spherules in shock melt pockets are elevated, up to Fe_(1.70)S, which we attribute to shock-oxidation of igneous pyrrhotite and the formation of hematite at high temperature. The D- and Cl-enrichment, and higher oxidation of the pockets (as indicated by hematite) support a scenario in which alteration products formed within fractures or void spaces within the rock; the signature of these alteration products is preserved within shock melt (now glass) which formed upon collapse of these fractures and voids during impact shock. Thermal modeling of Tissint shock melt pockets using the HEAT program demonstrates that the shock melt pockets with the greatest potential to preserve a signature of aqueous alteration are small, isolated from other regions of shock melt, vesicle-free, and glassy.


Item Type:Article
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https://doi.org/10.1016/j.gca.2017.04.037DOIArticle
http://www.sciencedirect.com/science/article/pii/S0016703717302600PublisherArticle
Additional Information:© 2017 Published by Elsevier Ltd. Received 24 June 2016, Accepted 28 April 2017, Available online 8 May 2017. This study was carried out as a Master’s Thesis study by CRK. Financial support for this project was provided by Natural Sciences and Engineering Research Council (NSERC) of Canada Discovery Grant RES00007057 awarded to ELW, NSERC Discovery Grant 261740 awarded to CDKH, and the ASTRO program of the Canadian Space Agency. We gratefully acknowledge the use of the SIMS facilities within the Caltech Microanalysis Center. We thank Andrew Locock and Martin von Dollen at the University of Alberta for expertise in electron microprobe and sample preparation, respectively, Andy DuFrane for assistance with LA-ICP-MS analysis, and Yang Chen for assistance with SIMS analysis. A small portion of this work was performed at JPL, which is managed by Caltech under a contract with NASA. Comments from Sarah Gleeson on the thesis are gratefully acknowledged. We thank Justin Filiberto, two anonymous reviewers and AE Greg Herzog for comments that significantly improved the manuscript.
Funders:
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada (NSERC)RES00007057
Natural Sciences and Engineering Research Council of Canada (NSERC)261740
Canadian Space Agency (CSA)UNSPECIFIED
Record Number:CaltechAUTHORS:20170509-131410385
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20170509-131410385
Official Citation:C.R. Kuchka, C.D.K. Herd, E.L. Walton, Y. Guan, Y. Liu, Martian low-temperature alteration materials in shock-melt pockets in Tissint: Constraints on their preservation in shergottite meteorites, Geochimica et Cosmochimica Acta, Volume 210, 1 August 2017, Pages 228-246, ISSN 0016-7037, https://doi.org/10.1016/j.gca.2017.04.037. (http://www.sciencedirect.com/science/article/pii/S0016703717302600)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77304
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:12 May 2017 22:45
Last Modified:02 Jun 2017 20:58

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