镁同位素示踪碳酸盐岩沉积—成岩过程

镁（Mg）作为主要的造岩元素及生物营养元素，是连接大陆、海洋和地球内部循环的重要纽带。碳酸盐岩作为Mg的主要储库，是全球Mg循环的重要组成环节，利用Mg同位素示踪碳酸盐岩沉积—成岩过程是有效反演深时海水Mg同位素组成（δ26Mg_海水）、恢复全球Mg循环的基本前提。近二十年来，Mg同位素在示踪碳酸盐岩沉积—成岩过程研究中取得了较大进展:1）不同类型碳酸盐矿物形成过程中的Mg同位素分馏及其影响因素的研究得到完善；2）建立了Mg同位素地球化学模型，对不同白云石化过程进行半定量—定量模拟；3）初步探索了利用Mg同位素反演早期成岩流体体系的方法。以上研究进展为利用碳酸盐岩恢复δ26Mg_海水奠定了理论基础，在选择有效的碳酸盐岩载体恢复δ26Mg_海水时，需充分考虑碳酸盐岩的沉积—成岩过程及其对Mg同位素组成的影响，并适当结合地球化学模型，消除沉积—成岩因素的影响，进而恢复δ26Mg_海水。

Tracing Carbonate Deposition-diagenesis Process Using Magnesium Isotopes: Implications for reconstructing deep-time seawater magnesium isotopic composition

Magnesium （Mg） is a major rock-forming element and biological nutrient element， and is thus an important link between continents， oceans and the Earth’s interior. Marine carbonates are a major reservoir of Mg and an important component of the global Mg cycle. Using Mg isotopes to trace the deposition-diagenesis process of marine carbonate formation is the prerequisite for reconstructing the deep-time seawater Mg isotopic composition （δ26Mg_SW） and quantifying the Earth’s historical marine Mg cycle. Studies using this approach have made considerable progress in the past two decades； for example: （1） investigation of Mg isotope fractionation during the formation of different carbonate minerals has been enhanced； （2） numerical models of Mg isotopic behavior have been established， providing constraints on the dolomitization process； and （3） the use of Mg isotopes to trace the early diagenetic fluid system has been explored. These have provided a theoretical base for using marine carbonate data to reconstruct δ26Mg_SW. The deposition-diagenesis process and its effects on Mg isotopic composition should be considered when selecting information from marine carbonate archives to reconstruct the marine Mg cycle. Critical evaluation combined with geochemical models are necessary when choosing an archive for reconstructing deep-time δ26Mg_SW.