大洋俯冲带蛇纹岩变质脱水过程中的Mg-Fe同位素分馏行为

大洋蛇纹岩在板块俯冲过程中的变质脱水作用对地球内部挥发分含量和组成、元素再循环和岛弧岩浆作用都具有重要意义。然而，目前对俯冲带蛇纹岩在不同变质脱水阶段Mg-Fe及氧化还原敏感元素（主要为C和S）的活动性和Mg-Fe同位素分馏行为的认识极为有限。针对这些问题，本项目拟主要选取阿尔卑斯造山带和Betic Cordillera造山带中出露的一套包括不同变质程度蛇纹岩的独特样品（低压蛇纹岩->叶蛇纹岩->绿泥石橄榄岩->石榴橄榄岩）进行系统的岩石学和地球化学研究。紧密结合岩石学和地球化学分析，制约大洋蛇纹岩在不同变质阶段脱水过程中Mg、Fe在流体中的赋存形式和迁移行为。在此基础上，系统查明高压蛇纹岩全岩和矿物的Mg-Fe同位素组成，明确揭示不同变质脱水阶段控制Mg-Fe同位素分馏的主要因素，为深入理解俯冲带深部流体性质、地幔楔和岛弧岩浆岩Mg-Fe同位素组成变化的过程和机制提供关键依据。

The metamorphic dehydration of serpentinites during their subduction in oceanic subduction zones has great bearing on the contents and composition of volatiles in the Earth’s interior, the elemental recycling and arc magmatism in subduction zones. However, currently little is known about the mobility of Mg, Fe and related redox sensitive elements (mainly C and S) as well as the Mg-Fe isotope fractionation behavior during metamorphic dehydration of the serpentinites in different stages. Focusing on these questions, this project chooses a suite of excellent samples that include serpentinites metamorphosed at different P-T conditions in the Alpine and Betic Cordillera orogens, i.e., low-pressure serpentinite, antigorite serpentinite, chlorite peridotite and garnet peridotite. Combined with the petrological and geochemical studies, we aim to constrain the species and mobility behavior of Mg and Fe in subduction zone fluids. On this basis, we will systematically determine the Mg and Fe isotope compositions of whole-rock and minerals in the serpentinites, elucidate the main controlling factors for Mg and Fe isotope fractionations during different stages of serpentinite dehydration. These results will provide key constraints on fluid property in deep subduction zones as well as the process and mechanism for the Mg-Fe isotope variations in both mantle wedges and island arc magmas.