Natural occurrence of Fe2SiO4-spinel in the shocked Umbarger L6 chondrite

Zhidong Xie, Naotaka Tomioka, Thomas Sharp

Research output: Contribution to journalArticle

22 Scopus citations

Abstract

Here we report the first natural occurrence of Fe2SiO4-spinel in a shock-induced melt pocket of the Umbarger L6 chondrite. Optical microscopy, scanning electron microscopy, electron microprobe analysis, and analytical transmission electron microscopy were used to examine the sample. Fe2SiO4-spinel was identified by TEM using selected-area electron diffraction and energy-dispersive X-ray spectroscopy. The symmetry of the diffraction patterns, the ratios of d-spacings, and interplanar angles are consistent with the spinel structure. However, the cell parameter of Fe2SiO4-spinel (8.52 Å), calculated from d-spacing data, is 3.5% larger than that of synthetic Fe2SiO4-spinel (8.235 Å). Chemical analysis of the spinel show olivine stoichiometry with Fe/(Fe + Mg) ratios ranging from 0.62 to 0.99. Fe2SiO4-spinel and stishovite occur within FeO-SiO2-rich zones in the melt pocket, surrounded by SiO2-rich glass and Fe-rich phyllosilicates. Fe2SiO4-spinel plus stishovite also occur with other high-pressure minerals in the melt pocket: ringwoodite, akimotoite, augite, and hollandite- structured plagioclase. We infer that the Fe2SiO4-spinel crystallized from a zone of FeO-SiO2-rich melt within the shock-induced melt pocket. Two models for FeO-SiO2-rich melt are discussed: it was either a residual melt after crystallization of MgO-rich silicates in a chondritic melt pocket, or it was produced by shock melting of FeO-SiO2-rich material.

Original languageEnglish (US)
Pages (from-to)1257-1260
Number of pages4
JournalAmerican Mineralogist
Volume87
Issue number8-9
DOIs
StatePublished - Jan 1 2002

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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