Ophiolite-Hosted Diamond: A New Window for Probing Carbon Cycling in the Deep Mantle  

蛇绿岩型金刚石——探索深部碳循环的新窗口

作　　者：Dongyang Lian Jingsui Yang 

机构地区：[1]School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China [2]CARMA, Key Laboratory of Deep-Earth Dynamics of MLR, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

出　　处：《Engineering》2019年第3期406-420,共15页工程（英文）

基　　金：the National Natural Science Foundation of China (41720104009 and 41802034);Natural Science Foundation of Jiangsu province, China (BK20180349).

摘　　要：As reported in our prior work, we have recovered microdiamonds and other unusual minerals, including pseudomorph stishovite, moissanite, qingsongite, native elements, metallic alloys, and some crustal minerals (i.e., zircon, quartz, amphibole, and rutile) from ophiolitic peridotites and chromitites. These ophiolite-hosted microdiamonds display different features than kimberlitic, metamorphic, and meteoritic diamonds in terms of isotopic values and mineral inclusions. The characteristic of their light carbon isotopic composition implies that the material source of ophiolite-hosted diamonds is surface-derived organic matter. Coesite inclusions coexisting with kyanite rimming an FeTi alloy from the Luobusa ophiolite show a polycrystalline nature and a prismatic habit, indicating their origin as a replacement of stishovite. The occurrence in kyanite and coesite with inclusions of qingsongite, a cubic boron nitride mineral, and a high-pressure polymorph of rutile (TiO2 II) point to formation pressures of 10–15 GPa at temperatures^1300℃, consistent with depths greater than 380 km, near the mantle transition zone (MTZ). Minerals such as moissanite, native elements, and metallic alloys in chromite grains indicate a highly reduced environment for ophiolitic peridotites and chromitites. Widespread occurrence of diamonds in ophiolitic peridotites and chromitites suggests that the oceanic mantle may be a more significant carbon reservoir than previously thought. These ophiolite-hosted diamonds have proved that surface carbon can be subducted into the deep mantle, and have provided us with a new window for probing deep carbon cycling.As reported in our prior work, we have recovered microdiamonds and other unusual minerals, including pseudomorph stishovite, moissanite, qingsongite, native elements, metallic alloys, and some crustal minerals（i.e., zircon, quartz, amphibole, and rutile） from ophiolitic peridotites and chromitites. These ophiolite-hosted microdiamonds display different features than kimberlitic, metamorphic, and meteoritic diamonds in terms of isotopic values and mineral inclusions. The characteristic of their light carbon isotopic composition implies that the material source of ophiolite-hosted diamonds is surface-derived organic matter. Coesite inclusions coexisting with kyanite rimming an FeTi alloy from the Luobusa ophiolite show a polycrystalline nature and a prismatic habit, indicating their origin as a replacement of stishovite. The occurrence in kyanite and coesite with inclusions of qingsongite, a cubic boron nitride mineral, and a high-pressure polymorph of rutile（TiO2 Ⅱ） point to formation pressures of 10–15 GPa at temperatures ～1300 ℃, consistent with depths greater than 380 km, near the mantle transition zone（MTZ）. Minerals such as moissanite, native elements, and metallic alloys in chromite grains indicate a highly reduced environment for ophiolitic peridotites and chromitites. Widespread occurrence of diamonds in ophiolitic peridotites and chromitites suggests that the oceanic mantle may be a more significant carbon reservoir than previously thought. These ophiolite-hosted diamonds have proved that surface carbon can be subducted into the deep mantle, and have provided us with a new window for probing deep carbon cycling.

关 键 词：Ophiolite-hosted DIAMOND COESITE STISHOVITE Podiform chromitites MANTLE transition zone 

分 类 号：N[自然科学总论]