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Assessment of shock effects on amphibole water contents and hydrogen isotope compositions: 2. Kaersutitic amphibole experiments

Minitti, Michelle E. and Leshin, L. A. and Dyar, M. Darby and Ahrens, Thomas J. and Guan, Yunbin and Luo, Sheng-Nian (2008) Assessment of shock effects on amphibole water contents and hydrogen isotope compositions: 2. Kaersutitic amphibole experiments. Earth and Planetary Science Letters, 266 (3-4). pp. 288-302. ISSN 0012-821X. doi:10.1016/j.epsl.2007.11.012. https://resolver.caltech.edu/CaltechAUTHORS:20141022-114335915

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Abstract

To constrain the influence of impact shock on water and hydrogen isotope signatures of Martian meteorite kaersutites, we conducted shock recovery experiments on three terrestrial kaersutite crystals. Homogeneous impact shock to 32 GPa, commensurate with shock levels experienced by Martian meteorite kaersutites, led to increases in kaersutite water contents (ΔH_2O = 0.25–0.89 wt.%), decreases in Fe^3+/ΣFe (4–20%), and enrichments in hydrogen isotope composition (ΔD = + 66 to + 87‰) relative to pre-shock values. The latter values represent the largest shock-induced hydrogen isotope fractionations measured to date. These observations are explained most completely by a two-step shock process. First, shock-induced devolatilization led to hydrogen isotope enrichment through preferential loss of H relative to D. Second, reaction of the kaersutite with the ambient atmosphere led to increased water contents and reduced Fe. Fe reduction and water addition via the reaction Fe^2+ + OH^− ↔ Fe^3+ + O_2− + ½H_2 explain the Fe^3+/ΣFe data and some of the water data. Further water addition mechanisms (irreversible adsorption, shock implantation) are necessary to fully explain the increased water contents. Addition of water from the terrestrial atmosphere, which is isotopically light relative to the experimental kaersutite compositions, means the measured hydrogen isotope enrichments are likely minima. The measured (minimum) levels of hydrogen isotope enrichment are relevant to the hydrogen isotope variability within and among Martian kaersutites, but are minor relative to their absolute δD values. Alternatively, addition of water from the enriched Martian atmosphere could explain both Martian kaersutite hydrogen isotope variability and absolute δD values. However, the low Martian kaersutite water contents leave little room for significant water addition. The importance of the ambient atmosphere to the outcome of the shock experiments makes it difficult to translate our results to Mars given the unknown influence of its more tenuous atmosphere on the processes observed in the experiments. Our results suggest that shock is a feasible mechanism for influencing Martian kaersutite water contents and hydrogen isotope compositions but that its complex signature precludes precise determination of that influence.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.epsl.2007.11.012DOIArticle
http://www.sciencedirect.com/science/article/pii/S0012821X07007303PublisherArticle
ORCID:
AuthorORCID
Minitti, Michelle E.0000-0003-4715-4544
Dyar, M. Darby0000-0003-4272-793X
Guan, Yunbin0000-0002-7636-3735
Additional Information:© 2007 Elsevier B. V. Received 10 April 2007; received in revised form 25 October 2007; accepted 4 November 2007; available online 17 November 2007; Editor: G.D. Price. MEM and MDD appreciate the contributions of Elizabeth Sklute in producing the Mössbauer data. This work was supported by a National Research Council/ NASA Astrobiology Institute Postdoctoral Fellowship. The comments of an anonymous reviewer clarified the paper.
Funders:
Funding AgencyGrant Number
National Research CouncilUNSPECIFIED
NASA Postdoctoral ProgramUNSPECIFIED
Subject Keywords:Mars; Martian meteorites; amphibole; impact shock; hydrogen isotopes
Issue or Number:3-4
DOI:10.1016/j.epsl.2007.11.012
Record Number:CaltechAUTHORS:20141022-114335915
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20141022-114335915
Official Citation:Minitti, M. E., Leshin, L. A., Dyar, M. D., Ahrens, T. J., Guan, Y., & Luo, S.-N. (2008). Assessment of shock effects on amphibole water contents and hydrogen isotope compositions: 2. Kaersutitic amphibole experiments. Earth and Planetary Science Letters, 266(3–4), 288-302. doi: http://dx.doi.org/10.1016/j.epsl.2007.11.012
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50683
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:22 Oct 2014 23:59
Last Modified:10 Nov 2021 18:59

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