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Discovery of the Fe-analogue of akimotoite in the shocked Suizhou L6 chondrite

2017; Nature Portfolio; Volume: 7; Issue: 1 Linguagem: Inglês

10.1038/srep42674

2045-2322

Luca Bindi, Ming Chen, Xiande Xie,

Geological and Geochemical Analysis

Abstract We report the first natural occurrence of the Fe-analogue of akimotoite, ilmenite-structured MgSiO 3 , a missing phase among the predicted high-pressure polymorphs of Fe-pyroxene, with the composition (Fe 2+ 0.48 Mg 0.37 Ca 0.04 Na 0.04 Mn 2+ 0.03 Al 0.03 Cr 3+ 0.01 ) Σ=1.00 Si 1.00 O 3 . The new mineral was approved by the International Mineralogical Association (IMA 2016-085) and named hemleyite in honour of Russell J. Hemley. It was discovered in an unmelted portion of the heavily shocked L6 Suizhou chondrite closely associated to olivine, clinoenstatite and Fe-bearing pyroxene with a composition nearly identical to that of hemleyite. We also report the first single-crystal X-ray diffraction study of a Si-bearing, ilmenite-structured phase. The fact that hemleyite formed in a meteorite exposed to high pressures (<20 GPa) and temperatures (<2000 °C) during impact-induced shocks indicates that it could play a crucial role at the bottom of the Earth’s mantle transition zone and within the uppermost lower mantle.