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Ahrensite, γ-Fe_2SiO_4, a new shock-metamorphic mineral from the Tissint meteorite: Implications for the Tissint shock event on Mars

Ma, Chi and Tschauner, Oliver and Beckett, John R. and Liu, Yang and Rossman, George R. and Sinogeikin, Stanislav V. and Smith, Jesse S. and Taylor, Lawrence A. (2016) Ahrensite, γ-Fe_2SiO_4, a new shock-metamorphic mineral from the Tissint meteorite: Implications for the Tissint shock event on Mars. Geochimica et Cosmochimica Acta, 184 . pp. 240-256. ISSN 0016-7037. doi:10.1016/j.gca.2016.04.042.

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Ahrensite (IMA 2013-028), γ-Fe_2SiO_4, is the natural Fe-analog of the silicate-spinel ringwoodite (γ-Mg_2SiO_4). It occurs in the Tissint Martian meteorite, where it forms through the transformation of the fayalite-rich rims of olivine megacrysts or Fe-rich microphenocrysts in contact with shock melt pockets. The typical sequence of phase assemblages traversing across a Tissint melt pocket into olivine is: quenched melt or fayalite-pigeonite intergrowth ⇒ bridgmanite + wüstite ⇒ ahrensite and/or ringwoodite ⇒ highly-deformed olivine + nanocrystalline ringwoodite ⇒ deformed olivine. We report the first comprehensive set of crystallographic, spectroscopic, and quantitative chemical analysis of type ahrensite, and show that concentrations of ferric iron and inversion in the type material of this newly approved mineral are negligible. We also report the occurrence of nanocrystalline ringwoodite in strained olivine and establish correlations between grain size and distance from melt pockets. The ahrensite and ringwoodite crystals show no preferred orientation, consistent with random nucleation and incoherent growth within a highly strained matrix of olivine. Grain sizes of ahrensite immediately adjacent to melt pockets are consistent with growth during a shock of moderate duration (1–10 ms).

Item Type:Article
Related URLs:
URLURL TypeDescription
Ma, Chi0000-0002-1828-7033
Tschauner, Oliver0000-0003-3364-8906
Liu, Yang0000-0002-8155-9134
Rossman, George R.0000-0002-4571-6884
Additional Information:© 2016 Elsevier Ltd. Received 11 July 2014; accepted in revised form 21 April 2016; Available online 27 April 2016. Associate editor: Wolf Uwe Reimold. SEM, EBSD and EPMA analyses were carried out at the Caltech GPS Division Analytical Facility, which is supported, in part, by NSF Grants EAR-0318518 and DMR-0080065. Synchrotron micro-diffraction was carried out at the 16-IDB beamline of the Advanced Photon Source. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. OT was sponsored in part by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Cooperative Agreement #DE-NA0001982. LAT and JRB acknowledge the support from NASA Cosmochemistry grants NNX11AG58G and NNX12AH63G, respectively. GRR acknowledges the support from NSF grant EAR-1322082. YL acknowledges the support of JPL, which is managed by California Institute of Technology under a contract with NASA. We thank Tom Sharp, Makoto Kimura and an anonymous reviewer for their constructive reviews.
Funding AgencyGrant Number
Department of Energy (DOE)DEAC02-06CH11357
Department of Energy (DOE)DE-NA0001982
Subject Keywords:Ahrensite; γ-Fe_2SiO_4; New high-pressure mineral; Shock metamorphism; Nanomineral; Ringwoodite group; Tissint meteorite; Martian shergottite; Synchrotron diffraction
Record Number:CaltechAUTHORS:20160510-133623803
Persistent URL:
Official Citation:Chi Ma, Oliver Tschauner, John R. Beckett, Yang Liu, George R. Rossman, Stanislav V. Sinogeikin, Jesse S. Smith, Lawrence A. Taylor, Ahrensite, γ-Fe2SiO4, a new shock-metamorphic mineral from the Tissint meteorite: Implications for the Tissint shock event on Mars, Geochimica et Cosmochimica Acta, Volume 184, 1 July 2016, Pages 240-256, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:66913
Deposited By: Ruth Sustaita
Deposited On:11 May 2016 00:24
Last Modified:11 Nov 2021 00:24

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