独居石及磷灰石对淡色花岗岩岩浆演化的约束—以北喜马拉雅康巴淡色花岗岩为例

Nd and Sr extremely heterogeneity is a distinctive characterize of Himalaya leucogranite. However, the mechanism is not well known. The Sm/Nd ratios and Nd isotopic compositions of the melts depend on the amount of apatite and monazite dissolved into the melt during anatexis and fractional crystallization. In this project, we focus on the leucogranite which extruded in Kampa Dome, North Himalaya. Base on systematic field work, petrography and mineral microstructures, we determine the monazite in situ U-Th-Pb age to estimate timing of leucogranite emplacement and in further constraining the leucogranite formation age along the North Himalaya. We also investigate in situ trace element, Nd isotope of both monazite and apatite as well as Sr isotope of apatite. The results have implications for unraveling anatectic melt crystallisation process, the heterogeneity and disequilibrium chemistry of Nd and Sr isotopes and petrogenesis of leucogranite in Himalaya.

Nd、Sr同位素的极度不均一是喜马拉雅淡色花岗岩的典型特征，然而其形成机制尚需要深入研究。独居石、磷灰石作为淡色花岗岩中重要的副矿物共同影响着岩浆熔体的稀土元素组成，在地壳深熔或是分异结晶中控制着Sm/Nd比值和Nd同位素组成。本项目选取北喜马拉雅康巴穹窿出露的淡色花岗岩为研究对象，拟在详细野外调查基础上，结合室内矿物学、岩石学和地球化学研究，通过独居石U-Th-Pb 定年，确定康巴淡色花岗岩侵位时代，建立北喜马拉雅淡色花岗岩形成时代和期次的相互关系；通过独居石和磷灰石原位微区微量元素及Nd、Sr同位素分析相结合的方法，示踪淡色花岗岩岩浆形成演化过程，研究Nd、Sr同位素不均一及Nd同位素不平衡成因机制，探讨喜马拉雅淡色花岗岩成因。

本项目选取北喜马拉雅康巴穹窿出露的淡色花岗岩为研究对象，在详细野外调查基础上，结合室内矿物学、岩石学和地球化学研究，通过独居石、磷钇矿、锆石U(-Th)-Pb 定年，确定康巴淡色花岗岩侵位时代为晚渐新世，建立了北喜马拉雅淡色花岗岩形成时代和期次的相互关系；通过独居石和磷灰石原位微区微量元素及Nd、Sr同位素分析相结合的方法，示踪了淡色花岗岩岩浆形成演化过程，研究了Nd、Sr同位素不均一及Nd同位素不平衡成因机制，进一步探讨了喜马拉雅淡色花岗岩的岩石成因。