地幔的Ba同位素地球化学

Ba isotope geochemistry of the mantle

钡(Ba)是大离子亲石碱土金属元素,也是流体活动元素。Ba在地幔熔融过程中高度不相容,因此在地壳中含量远高于地幔。Ba同位素在低温环境和流体作用下可发生显著的分馏,而在高温基性和中性岩浆过程中分馏有限。因此,近年来Ba同位素得到了越来越多的关注,成为示踪地壳物质俯冲再循环的新工具,特别有助于鉴别流体和沉积物对地幔的影响。准确获取上地幔Ba同位素组成是开展应用研究的前提,目前关于地幔Ba同位素组成的研究很少,还存在很大的争议。本文对Ba同位素分析方法、分馏机理和重要地质储库的组成进行了总结。本文重点讨论了幔源岩浆岩的Ba同位素变化,以及岩浆岩和变质岩中的Ba同位素分馏行为及潜在应用,并对当前存在的问题及未来的研究方向进行了展望。

Barium is a large ion lithophile alkaline-earth element and it is also fluid-mobile.Since Ba is highly incompatible during mantle melting,Ba content in the crust is much higher than that in mantle.Ba isotopes can be significantly fractionated in low-temperature conditions or during fluid processes,but Ba isotope fractionation in mafic-intermediate magmatism is negligible.Therefore,Ba isotopes have been recently used as a novel tool to study recycling of subducted materials,especially in tracing the effect of fluid and sediment on the composition of the mantle.It is a prerequisite to estimate the average Ba isotope compositions before applying Ba isotopes to high temperature geochemistry studies.Ba isotope data for the mantle are still rare and controversial.This study summarizes Ba isotope analytical method,fractionation mechanism,and composition of important reservoirs.We focus on Ba isotope variation on basaltic rocks,behavior of Ba isotopes during magmatism and metamorphism,and potential applications.We believe that the future of Ba isotopes will be quite promising.