喜马拉雅造山带地壳物质部分熔融中放射性同位素行为的研究

在地壳深熔作用研究中，存在两个困惑地球科学家的课题：（1）重要副矿物（如锆石、石榴子石等）的溶解作用如何调制熔体的元素和放射性同位素地球化学特征？（2）地壳物质部分熔融是否存在明显的放射性同位素（如Sr、Nd、Hf和Pb）不平衡？喜马拉雅淡色花岗岩是地壳深熔作用的典型产物，具有元素和Sr-Nd-Hf同位素组成高度不均一的特征，是探讨上述问题的理想对象。本项目拟以马拉山-吉隆、雅拉香波-错那和珠峰地区淡色花岗岩和变质岩为主要研究对象，确定淡色花岗岩和变质围岩的元素和放射性同位素地球化学特征，了解副矿物（石榴子石、锆石、独居石、磷灰石等）在地壳深熔作用中的地球化学效应。结合实验岩石学成果，构建地壳物质深熔作用过程中副矿物控制熔体元素和同位素特征的理论模型。预期成果将有助于深入了解中下地壳岩石部分熔融过程中元素和同位素的分配过程，提高对地壳深熔作用中放射性同位素不平衡的形成机理的认识。

Geologists have long been puzzled by two intriguing questions on crustal anatexis: (1) how do important accessory minerals (such as zircon, garnet) affect the geochemical natures of crustally derived melts? (2) whether are there radiogenic isotope (such as Sr, Nd, Hf and Pb) disequilibrium during crustal anatexis? The Himalayan Cenozoic leucogranites are the typical product of crustal anatexis and are characterized by large magnitude of heterogeneities in element as well as radiogenic isotope compositions. These young leucogranites provide an important chance to answer the above questions. In this project, we will focus on the Miocene granites and metamorphic wall-rocks from Malashan-Gyirong, Yardoi-Cona and Everest area, and systematically determine their element and radiogenic isotope (especially Pb and Hf) compositions. These new data will used to investigate the geochemical effects of differential dissolution of garnet, zircon, monazite, and apatite on the element and isotope compositions of melts and the magnitude of radiogenic isotope disequilibrium in the Himalayan leucogranites. Further, combined with experiment data, we will provide theoretical models that combining melting reactions with dissolution of accessory minerals to constrain how dissolution of accessory phases affect the element as well as radiogenic isotope nature of anatectic melts. New results and knowledge achieved from this project will promote our understanding on the distribution process of element and isotope during partial melting of middle-lower crustal materials in orogenic belts, and on the mechanism for the development of radiogenic isotope disequilibrium during crustal anatexis.