Diamond- and coesite-bearing chromitites from the Luobusa ophiolite, Tibet
- Jing-Sui Yang*1,
- Larissa Dobrzhinetskaya2,
- Wen-Ji Bai3,
- Qing-Song Fang3,
- Paul T. Robinson*†4,
- Junfeng Zhang5 and
- Harry W. Green II5
- 1Key Laboratory for Continental Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
- 2Department of Earth Sciences and Institute of Geophysics and Planetary Physics, University of California–Riverside, Riverside, California 92521, USA
- 3Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
- 4GeoForschungsZentrum, Telegrafenberg, D-14473 Potsdam, Germany
- 5Department of Earth Sciences and Institute of Geophysics and Planetary Physics, University of California–Riverside, Riverside, California 92521, USA
Abstract
Diamonds and other ultrahigh pressure (UHP) minerals have been reported previously from the Luobusa ophiolite of Tibet, but these minerals have thus far been found only as individual grains. Here we report the occurrence of diamond as an inclusion in OsIr alloy and coesite as part of a silicate assemblage rimming a grain of FeTi alloy, both of which were recovered from chromitite. These occurrences confirm the presence of UHP minerals in the Luobusa chromitite requiring minimum pressures of ∼2.8–4 GPa. Individual coesite “crystals” have external form similar to that of stishovite and are polycrystalline, suggesting pseudo morphic replacement and implying a pressure >9 GPa. We propose that the UHP minerals were incorporated into the chromitites in the deep upper mantle or that they have an impact origin; the preponderance of evidence favors the former.
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- Accepted 13 May 2007.
- Received 2 February 2007.
- Revision received 8 May 2007.
- The Geological Society of America, Inc.
