马里亚纳弧前地幔楔蛇纹石化橄榄岩Fe同位素研究

蛇纹岩在地幔楔中广泛存在，对于俯冲带氧逸度起到极其重要的作用。其中的核心元素—铁，对氧逸度十分敏感。研究地幔楔蛇纹岩中Fe的迁移性及氧化还原状态，具有重要意义。马里亚纳岛弧系统弧前蛇纹岩泥海山中的蛇纹岩/蛇纹石化橄榄岩碎块是研究相关问题的理想样品。国际大洋发现计划（IODP）366航次于2016年12月-2017年2月对马里亚纳弧前3个蛇纹岩泥海山（受不同深度俯冲流体影响形成）进行了钻探研究，申请人曾参加该航次并获得了相关岩石样品。本申请拟选取该航次在3个海山钻取的蛇纹石化橄榄岩为研究对象，通过测定其流体活动元素和挥发分（F、Cl、B等）含量，来反映弧前区域不同深度俯冲流体的性质；结合蛇纹石化橄榄岩Fe3+/ΣFe比值，测定其Fe同位素组成，探索弧前区域俯冲洋壳脱水—地幔蛇纹石化过程中Fe的活动性及其氧化还原过程，揭示蛇纹石化过程对地幔氧逸度的影响，为岛弧地幔的氧逸度状态和成因提供依据。

Serpentinite is quite common in the mantle wedge, and it is very important to the oxygen fugacity of subduction zones. Iron, which is sensitive to oxygen fugacity, is one of the most important elements that is responsible to oxygen fugacity during serpentinization. There is great significance to study the Fe mobility and oxygen fugacity of mantle wedge serpentinite. Mariana forearc mantle serpentinites/ serpentinized peridotites obtained from active serpentinite mud seamounts are the ideal samples to study these issues. The Exp. 366 of International Ocean Discovery Project (IODP), have carried out drilling project on three of the Mariana serpentinite mud seamounts (affected by subduction fluids from different depths) from Dec. 2016 - Feb. 2017. We have obtained many core samples after attending this ocean drilling expedition. In this application, we are planning to choose the Mariana forearc mantle wedge serpentinized peridotites obtained in the IODP Exp.366 as our objects, by the determination of fluid mobile elements and volatiles (F, Cl and B) of the serpentinized peridotites in the three different seamounts, which are metasomatized by subduction fluids from various depths, to study the nature of dehydration fluids from different subduction depths in the forearc region. We will also analyze the Fe3+/ΣFe ratios. Based on these, we will study Fe isotopes of these serpentinized peridotite, to reveal the Fe mobility during subduction dehydration and mantle serpentinization in the forearc region. The oxygen fugacity of the forearc mantle will also be investigated, to provide a clue to the oxygen fugacity of arc mantle and the mechanism behind it.