Ahrensite, γ-Fe2SiO4, a new shock-metamorphic mineral from the Tissint meteorite: Implications for the Tissint shock event on Mars

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