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High- and low-Cr chromitite and dunite in a Tibetan ophiolite: evolution from mature subduction system to incipient forearc in the Neo-Tethyan Ocean.
- Source :
- Contributions to Mineralogy & Petrology; Jun2017, Vol. 172 Issue 6, p1-22, 22p
- Publication Year :
- 2017
-
Abstract
- The microstructures, major- and trace-element compositions of minerals and electron backscattered diffraction (EBSD) maps of high- and low-Cr# [spinel Cr# = Cr/(Cr + Al)] chromitites and dunites from the Zedang ophiolite in the Yarlung Zangbo Suture (South Tibet) have been used to reveal their genesis and the related geodynamic processes in the Neo-Tethyan Ocean. The high-Cr# (0.77-0.80) chromitites (with or without diopside exsolution) have chromite compositions consistent with initial crystallization by interaction between boninitic magmas, harzburgite and reaction-produced magmas in a shallow, mature mantle wedge. Some high-Cr# chromitites show crystal-plastic deformation and grain growth on previous chromite relics that have exsolved needles of diopside. These features are similar to those of the Luobusa high-Cr# chromitites, possibly recycled from the deep upper mantle in a mature subduction system. In contrast, mineralogical, chemical and EBSD features of the Zedang low-Cr# (0.49-0.67) chromitites and dunites and the silicate inclusions in chromite indicate that they formed by rapid interaction between forearc basaltic magmas (MORB-like but with rare subduction input) and the Zedang harzburgites in a dynamically extended, incipient forearc lithosphere. The evidence implies that the high-Cr# chromitites were produced or emplaced in an earlier mature arc (possibly Jurassic), while the low-Cr# associations formed in an incipient forearc during the initiation of a new episode of Neo-Tethyan subduction at ~130-120 Ma. This two-episode subduction model can provide a new explanation for the coexistence of high- and low-Cr# chromitites in the same volume of ophiolitic mantle. [ABSTRACT FROM AUTHOR]
- Subjects :
- DUNITE
OPHIOLITES
SUBDUCTION
LITHOSPHERE
GEODYNAMICS
Subjects
Details
- Language :
- English
- ISSN :
- 00107999
- Volume :
- 172
- Issue :
- 6
- Database :
- Complementary Index
- Journal :
- Contributions to Mineralogy & Petrology
- Publication Type :
- Academic Journal
- Accession number :
- 123992456
- Full Text :
- https://doi.org/10.1007/s00410-017-1364-y