俯冲带中石墨质碳的研究进展

自然界中,石墨质碳可以稳定存在于沉积岩、岩浆岩和变质岩中,由有机质或无机碳酸盐转变而来。随着对俯冲带碳循环研究的不断深入,通常作为副矿物产出在变质岩中的石墨质碳也引起了广泛的关注。相比于碳酸盐矿物和含碳流体,石墨质碳因其低溶解性、低移动性常作为碳汇稳定存在于俯冲带中。然而,在一些特殊的地质条件下(例如流体出现的开放体系中),石墨质碳不再稳定,它会变得活跃并发生迁移。因此,石墨质碳也是俯冲带碳循环研究中的关键载体。本文在综述前人研究成果的基础上,总结了俯冲带中石墨质碳的性质、来源、形成和分解过程,并重点介绍了俯冲带中非生物成因石墨的形成机制、石墨质碳的稳定性以及石墨质碳的释放,全面探讨了石墨质碳在俯冲带碳循环中的重要意义。俯冲带中石墨质碳的成因机制主要有3种:生物有机质石墨化、饱和含碳流体沉淀、碳酸盐矿物的还原反应。俯冲带中石墨质碳可通过分解脱气和溶解的方式释放。俯冲作用和风化侵蚀是石墨质碳全球循环的两个主要过程,其中俯冲作用对石墨质碳的地球内部循环影响较大。

Progress of research on graphitic carbon in subduction zones

Graphitic carbon is mainly transformed from organic compounds or carbonate minerals in nature, and can exist stablly in sedimentary rocks, magmatic rocks and metamorphic rocks. With the development of research on the carbon cycle in subduction zones, graphitic carbon, which usually occurs as accessory mineral in metamorphic rocks, has increasingly attracted attention. Graphitic carbon can be stable in subduction zones as carbon sinks due to its low solubility with respect to carbonate and the low mobility with respect to carbonic fluids. However, graphitic carbon can be reactive under some special geological conditions (e.g., with the presence of aqueous fluids in open systems), and becomes active and migrates. Therefore, graphitic carbon is one of the key subjects to trace carbon cycle in subduction zones. Based on previous studies, this paper provides an overview of the properties, formation, and decomposition of graphitic carbon in subduction zones, and comprehensively discusses the abiotic genesis, the stability and the release of them, which can be a key participant in the carbon cycle in subduction zones. There are three main genetics mechanisms of graphitic carbon in subduction zones: graphitization of biological organic matter, precipitation of saturated carbonic fluid, and reduction of carbonate minerals. Graphitic carbon in subduction zones can be released through degassing and fluid-mediated dissolution. Subduction and weathering erosion are the two main processes in the global cycle of graphitic carbon, with subduction having a greater impact on the internal circulation of graphitic carbon.