蚀变洋壳的金属稳定同位素研究进展

The research progress of metal stable isotope systematics for altered oceanic crust

蚀变洋壳在形成过程中会经历热液蚀变和低温风化,是高温和低温地质系统耦合的产物。通过研究蚀变洋壳的化学组成,可以反演热液对洋壳的改造。结合海水及地幔衍生岩浆岩的研究,可以制约地球内部岩石圈与外部水圈间的化学循环。随着质谱分析技术的发展,诸多金属稳定同位素体系开始应用于蚀变洋壳的研究。金属稳定同位素的分馏受到地质过程中物理和化学条件的控制,因此金属同位素可以反演水岩相互作用的历史。前人已对蚀变洋壳的Li、Mg、Ca、Cu、Zn、K、Fe、V和Si的同位素特征进行了初步研究。目前取得的认识有:流体活动性强的元素(如Li、Mg、Ca、Si和K)的同位素组成受到温度和水岩比的控制;变价的过渡族金属元素(如Cu、Fe和V)的同位素分馏效应受到氧逸度的控制。随着研究的深入,金属同位素的应用将为探讨蚀变洋壳的形成与演化、洋壳–海洋–地幔相互作用过程提供更多重要的信息。

Altered oceanic crust(AOC)underwent hydrothermal alteration and low-temperature weathering and is a typical production of the geochemistry process that couples high-and low-temperature geological systems.By investigating the chemical composition of the AOC,we can constrain the extent of the alteration process that modifies the oceanic crust and the chemical recycling between the lithosphere and the hydrosphere.Integrated investigations of seawater and mantle-derived igneous rocks can offer insights into material recycling between the earth’s surface and interior.With the development of mass spectrometry analysis,an increasing number of metal stable isotope systems are serving as tools to study the alteration history of AOC because of their ubiquitous nature.Previous studies have investigated the Li,Mg,Ca,Cu,K,Fe,V,and Si isotope systematics of AOC.Fluid-mobile elements(such as Li,Mg,Ca and K)and their isotope compositions are affected by temperature and water-rock ratio.For elements with multiple valence states(such as Cu,Fe and V),their isotope compositions are governed by oxygen fugacity.With the deepening of metal stable isotope studies on AOC,more valuable information about the alteration history of the oceanic crust will be revealed.