TY - JOUR
T1 - Natural occurrence of Fe2SiO4-spinel in the shocked Umbarger L6 chondrite
AU - Xie, Zhidong
AU - Tomioka, Naotaka
AU - Sharp, Thomas
PY - 2002
Y1 - 2002
N2 - 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.
AB - 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.
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U2 - 10.2138/am-2002-8-926
DO - 10.2138/am-2002-8-926
M3 - Article
AN - SCOPUS:0036698930
SN - 0003-004X
VL - 87
SP - 1257
EP - 1260
JO - American Mineralogist
JF - American Mineralogist
IS - 8-9
ER -