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Open AccessFeature PaperArticle

Hydrothermal Chromitites from the Oman Ophiolite: The Role of Water in Chromitite Genesis

1
Department of Earth Sciences, Kanazawa University, Kanazawa 920-1192, Japan
2
Identification Department, GIA Tokyo Godo Kaisha, Yamaguchi Building 7, 4-19-9 Taito, Taito-ku, Tokyo 110-0016, Japan
3
Department of Ocean Floor Geoscience, Atmosphere an Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan
4
Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8550, Japan
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(3), 217; https://doi.org/10.3390/min10030217
Received: 10 February 2020 / Revised: 26 February 2020 / Accepted: 26 February 2020 / Published: 28 February 2020
(This article belongs to the Special Issue Feature Papers in Mineral Geochemistry and Geochronology 2019)
The role of water-rich solutions in the formation of chromitites has been the matter of controversy. We found small chromite concentrations (chromitites) in diopsidites, precipitated from high-temperature hydrothermal fluids, in the mantle to the crust of the Oman ophiolite. Here, we present petrologic characteristics of the hydrothermal chromitites to understand their genesis. In the chromitites, the chromite is associated with uvarovite in the crust and diopside + grossular in the mantle. They are discriminated from the magmatic podiform chromitite by dominance of the Ca-Al silicates in the matrix. The fluids responsible for chromite precipitation are possibly saline, being derived from the seawater circulated into the mantle through the crust. The saline fluids precipitate chromite to form chromite upon decompression and cooling, and transport platinum-group elements (especially Pt and Pd). The fluids obtain Ca and Al from the crustal rocks and Cr from the mantle rocks during circulation. Saline fluids are also supplied from the slab to the mantle wedge, and can metasomatically precipitate chromite and pyroxenes within peridotites. They re-distribute Cr and chromite in peridotites along with circulation of saline fluids in the mantle wedge. View Full-Text
Keywords: hydrothermal chromitites; Ca-Al silicates; seawater; Oman ophiolite; slab-derived fluids; platinum-group elements hydrothermal chromitites; Ca-Al silicates; seawater; Oman ophiolite; slab-derived fluids; platinum-group elements
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Arai, S.; Miura, M.; Tamura, A.; Akizawa, N.; Ishikawa, A. Hydrothermal Chromitites from the Oman Ophiolite: The Role of Water in Chromitite Genesis. Minerals 2020, 10, 217.

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