用Mg-Ca同位素制约HIMU地幔组分的属性

洋岛玄武岩同位素组成上的变化说明下地幔是高度不均一的，包含HIMU、EM1、EM2和FOZO端元组分，揭示这些地幔端元的属性是解密地幔的化学结构以及硅酸盐地球的分异演化历史等问题的“钥匙”。HIMU地幔组分因具有异常高的放射成因铅同位素组成而备受关注，然而对其属性的认识仍然存在较大的分歧。本项目拟选择来自南大西洋St.Helena岛和南太平洋Cook-Austral群岛的经典HIMU型洋岛玄武岩为研究对象，对新鲜的全岩样品和斑晶进行高精度的镁和钙稳定同位素分析，以查明HIMU型洋岛玄武岩的镁-钙同位素组成及其变化规律，并结合全岩的放射成因同位素组成和元素地球化学特征来约束HIMU地幔组分的属性，以揭示HIMU地幔组分的形成机制及其与再循环碳酸盐组分之间的潜在成因联系。

The wide isotopic variations in ocean island basalts (OIBs) reflect that the lower mantle is highly heterogeneous and is composed of several mantle components including HIMU, EM1, EM2 and FOZO. To unveil the nature of these mantle components is the “key” to decode the chemical structure of the mantle and the differentiation and evolution history of the bulk silicate Earth. The HIMU component is famous for its exceptionally high radiogenic Pb isotopic compositions, however, opinions on the nature of this mantle component go their separate ways. This project will conduct high-precision Mg and Ca isotopic analysis of typical HIMU OIBs and their phenocrysts, which were sampled from St. Helena Island in the South Atlantic Ocean and Cook-Austral volcanic chain in the South Pacific Ocean. The Mg and Ca isotope data, combining with published whole-rock geochemical and radiogenic isotope data, will be used to constrain the nature of the HIMU component. The ultimate goal of this project is to uncover the specific formation mechanism of the HIMU component and its potential genetic relationship with recycled carbonate-bearing materials.