铁同位素的分馏机制研究：以南太平洋深海橄榄岩、罗布莎蛇绿岩套橄榄岩和大庙钒钛磁铁矿为例

One of the major advances in marine geology research is the birth and development of the plate tectonics theory, in which oceanic plate is a necessary constituent. The geological society gradually pays attention to the iron isotope variation and its possible geological implications in the ocean lithosphere rocks. However, compared with the frequently-used Sr-Nd-Pb isotopic system, the mechanism of iron isotope fractionation remains in dispute due to the deficiency of data accumulation. Only when the fractionation mechanism is well studied can iron isotope be used for tracing geological processes. This proposal focuses on systematic determination of iron isotope composition of abyssal peridotite from south Pacific, chromite-bearing peridotite from Luobusha ophiolite and vanadium-titanium magnetite from Damiao using MC-ICPMS method, to (1) reveal the influence of valence change and redox reaction to iron isotope fractionation and (2) obtain the iron isotope fractionation profile in high-temperature diffusion process. This project will enhance the theory of iron isotope for better application and provide new method and perspective on the core issues of solid earth science such as evolution of ocean lithosphere and mantle differentiation.

板块构造学说的诞生和发展是海洋地质研究最主要的进展之一。大洋板块是板块构造的必要组成部分，其中不同类型岩石Fe同位素分馏的发现及其可能的地质意义引起学者们的广泛关注。但相对于常用的Sr-Nd-Pb同位素示踪体系，Fe同位素的研究目前仍处于数据积累阶段，其分馏机制依然存在争议。只有明确分馏机制，才可用Fe同位素示踪地质过程。本项目拟使用MC-ICPMS方法，对采自南太平洋深海橄榄岩、罗布莎蛇绿岩套中含铬铁矿橄榄岩和大庙钒钛磁铁矿开展系统的Fe同位素研究，从而（1）揭示Fe同位素分馏与铁赋存价态、与氧化还原反应的关系；（2）获取Fe同位素在高温扩散过程的分馏情况。该研究结果将为Fe同位素的应用提供基础理论支持，并为大洋岩石圈的演化和地幔分异等固体地球科学领域的重要问题提供新的研究思路和方法。