俯冲带典型碳酸盐矿物在流体中溶解度和碳种型的实验研究

碳是组成地表生物圈和影响地球宜居性的关键元素之一。俯冲带是地球表层和深部发生碳循环，影响地表碳储库的最重要界面。碳酸盐矿物是俯冲板片中碳存在的主要形式，在俯冲带发生迁移，部分通过岛弧火山作用返回地表。对全球俯冲带的研究表明，俯冲板片脱出的富水流体是碳迁移的主要载体，但目前对碳酸盐矿物在俯冲带流体，特别是弧下深度流体中的溶解度和碳赋存形式的研究非常缺乏，严重阻碍了对俯冲带碳循环的准确定量约束。本项目设计通过高温高压实验方法，在俯冲带条件下(0.5-3 GPa，400-900 ℃)，对典型碳酸盐矿物方解石/文石和菱镁矿在纯水和不同浓度NaCl溶液中的溶解度进行原位和非原位的准确测定，同时对高温高压流体中的碳种型及含量进行原位光谱学分析，查明温度、压力和盐度对碳酸盐溶解度和流体中碳种型及分布的影响，定量解析板片流体迁移碳的能力和机制，深化对俯冲带碳循环的认识。

Carbon is one of the key constituent elements of the biosphere and influence the habitability of the Earth. Subduction zone is the most important interface of carbon cycle between the surface and the deep Earth，and significantly affects the surficial carbon reservoir. Carbon was mainly presented as carbonates in the subducted slab, and was partly became entrained and migrated in the slab fluids and eventually degassed through arc volcanoes. It has been demonstrated that aqueous fluid derived from the subducted slab is the main carrier of carbon according to the research of the global subduction zones. However, the solubility of carbonates and the speciation of carbon in the aqueous fluid under subduction zone conditions are poorly constrained, especially at subarc depth, which deeply hinders the accurately quantitative constraint of the carbon cycle in the subduction zone. This project is designed to investigate the solubility of typical subducting carbonates, calcite/aragonite and magnesite, in water and NaCl solution with different salinity by both in-situ and ex-situ experimental methods under subduction zone condition (0.5-3 GPa, 400-900 ℃), and to determine the speciation and distribution of carbon in high temperature and high pressure fluids by in-situ spectroscopy analyses at meantime. The results will help us to clarify the effects of temperature, pressure and salinity on carbonate solubility and carbon speciation of slab fluid, to model the carrying capacity and mechanism of slab fluid in the carbon migration, and to deepen our understanding of subduction zone carbon cycle.