| In-situ Moissanite in Dunite: Deep Mantle Origin of Mantle Peridotite in Luobusa Ophiolite, Tibet |
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| 作者姓名： | LIANG Fenghu XU Zhiqin and ZHAO Jianan |
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| 作者单位： | 1 State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
2 School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China |
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| 基金项目： | This research is granted by the National Natural Science Foundation of China (Grant No. 41002076 and No. 40921001), the China Geological Survey (Grant No. 1212011121275), and the SinoProbe-05-07 of the Ministry of Science and Technology of China (Grant No. 05-07). |
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| 摘 要： | We report the discovery of an in-situ natural moissanite as an inclusion in the Cr-spinel from the dunite envelope of a chromitite deposit in Luobusa ophiolite, Tibet. The moissanite occurs as a twin crystal interpenetrated by two quadrilateral signal crystals with sizes of 17 μm× 10 μm and 20 μm× 7 μm, respectively. The moissanite is green with parallel extinction. The absorption peaks in its Raman spectra are at 967-971 cm-1, 787-788 cm-1, and 766 cm-1. The absorption peaks in the infrared spectra are at 696 cm-1, 767 cm-1, 1450 cm-1, and 1551 cm-1, which are distinctly different from the peaks for synthetic silicon carbide. Moissanites have been documented to form in ultra-high pressure, high temperature, and extremely low fO2 environments and their 13C-depleted compositions indicate a lower mantle origin. Combined with previous studies about other ultra-high pressure and highly reduced minerals in Luobusa ophiolite, the in-situ natural moissanite we found indicates a deep mantle origin of some materials in the mantle sequence of Luobusa ophiolite. Further, we proposed a transformation model to explain the transfer process of UHP materials from the deep mantle to ophiolite sequence and then to the supra-subduction zone environment. Interactions between the crown of the mantle plume and mid-ocean ridge are suggested to be the dominant mechanism.
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| 关 键 词： | 罗布莎蛇绿岩 地幔橄榄岩 深部地幔 原位 西藏 纯橄岩 桑 铬铁矿矿床 |
| 收稿时间： | 2013/11/12 0:00:00 |
| 修稿时间： | 2014/2/14 0:00:00 |
In-situ Moissanite in Dunite： Deep Mantle Origin of Mantle Peridotite in Luobusa Ophiolite,Tibet |
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| Authors: | LIANG Fenghua XU Zhiqin ZHAO Jianan |
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| Institution: | [1]State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 10003 7, China [2]School of Earth Sciences andResources, China University ofGeosciences, Beijing 100083, China |
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| Abstract: | We report the discovery of an in‐situ natural moissanite as an inclusion in the Cr‐spinel from the dunite envelope of a chromitite deposit in Luobusa ophiolite, Tibet. The moissanite occurs as a twin crystal interpenetrated by two quadrilateral signal crystals with sizes of 17 μm × 10 μm and 20 μm × 7 μm, respectively. The moissanite is green with parallel extinction. The absorption peaks in its Raman spectra are at 967–971 cm–1, 787–788 cm–1, and 766 cm–1. The absorption peaks in the infrared spectra are at 696 cm–1, 767 cm–1, 1450 cm–1, and 1551 cm–1, which are distinctly different from the peaks for synthetic silicon carbide. Moissanites have been documented to form in ultra‐high pressure, high temperature, and extremely low fO2 environments and their 13C‐depleted compositions indicate a lower mantle origin. Combined with previous studies about other ultra‐high pressure and highly reduced minerals in Luobusa ophiolite, the in‐situ natural moissanite we found indicates a deep mantle origin of some materials in the mantle sequence of Luobusa ophiolite. Further, we proposed a transformation model to explain the transfer process of UHP materials from the deep mantle to ophiolite sequence and then to the supra‐subduction zone environment. Interactions between the crown of the mantle plume and mid‐ocean ridge are suggested to be the dominant mechanism. |
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| Keywords: | moissanite deep mantle origin mantle peridotite Luobusa ophiolite Tibet |
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