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Ahrensite, γ-Fe<sub>2</sub>SiO<sub>4</sub>, a new shock-metamorphic mineral from the Tissint meteorite [electronic resource] : Implications for the Tissint shock event on Mars

Published
Washington, D.C. : United States. National Nuclear Security Administration, 2016.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy
Physical Description
pages 240-256 : digital, PDF file
Additional Creators
United States. National Nuclear Security Administration and United States. Department of Energy. Office of Scientific and Technical Information
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Summary
Ahrensite (IMA 2013-028), gamma-Fe2SiO4, is the natural Fe-analog of the silicate-spinel ringwoodite (gamma-Mg2SiO4). It occurs in the Tissint Martian meteorite, where it forms through the transformation of the fayalite-rich rims of olivine megacrysts or Ferich 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 + wustite → ahrensite and/or ringwoodite double right arrow 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. As a result, grain sizes of ahrensite immediately adjacent to melt pockets are consistent with growth during a shock of moderate duration (1-10 ms).
Report Numbers
E 1.99:1332393
Subject(s)
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Note
Published through SciTech Connect.
04/27/2016.
": S0016703716302113"
Geochimica et Cosmochimica Acta 184 C ISSN 0016-7037 AM
Chi Ma; Oliver Tschauner; John R. Beckett; Yang Liu; George R. Rossman; Stanislav V. Sinogeikin; Jesse S. Smith; Lawrence A. Taylor.
Univ. of Nevada, Las Vegas, NV (United States)
Funding Information
NA0001982
View MARC record | catkey: 23783123