喜马拉雅淡色花岗岩结晶分异机制概述

近年来，喜马拉雅淡色花岗岩的高分异成因得到了学术界的高度关注。另外，有调研工作发现，喜马拉雅淡色花岗岩具有良好的稀有金属成矿潜力，是未来矿产勘探的重点靶区。稀有金属元素的富集过程应与岩浆的结晶分异作用密切相关。但是，目前我们对喜马拉雅淡色花岗岩的岩浆分异演化过程缺乏深入的了解，因而也难以对其成矿效应进行有效评估。针对该问题，本文选择喜马拉雅带中两个颇具代表性的、明显发生稀有金属矿化现象的岩体（特提斯喜马拉雅带中的然巴淡色花岗岩和高喜马拉雅带中的告乌淡色花岗岩）开展系统野外地质、岩相学、矿物学、岩石学和地球化学调查研究，就喜马拉雅淡色花岗岩的结晶分异机制进行初步探讨。综合近年来有关花岗岩结晶分异作用的研究进展，我们认为喜马拉雅淡色花岗岩的结晶分异过程可以划分为原地结晶分异和岩浆侵位运移过程中流动分异两种主要机制，大部分的喜马拉雅淡色花岗岩应是两种机制共同作用的产物。

The mechanisms of fractional crystallization for the Himalayan leucogranites

Recently, the petrogenesis of highly fractionated Himalayan leucogranites has been paid great attention. Moreover, a preliminary study has showed that the Himalayan leucogranites is commonly related to the rare-metal mineralization and warrants future investigation. It is well known that the enrichment of rare-metal elements should be closely related to the magmatic differentiation, which is mainly derived by fractional crystallization. However, relatively little work has focused on the mechanisms and processes of fractional crystallization of the Himalayan leucogranites. In this study, we investigated two typical Himalayan leucogranite plutons, i.e., the Ramba leucogranites within the Tethyan Himalayan belt and the Gaowu leucogranites within the Higher Himalayan belt, which are both characterized by the often presence of rare-metal bearing minerals. According to the comprehensive study on the two plutons including petrography, mineralogy, petrology and whole-rock geochemical composition, we suggest that the fractional crystallization processes of Himalayan leucogranites can be ascribed to two main mechanisms, which are in-situ differentiation and flowage differentiation, respectively. It is noteworthy that most of the Himalayan leucogranites have experienced both of the two processes at different stages during its migration and emplacement.