印度大陆俯冲过程中的高压变质与深熔作用:东喜马拉雅构造结南迦巴瓦杂岩的相平衡模拟研究

High-pressure metamorphism and anatexis during the subduction of Indian continent: Phase equilibria modeling of the Namche Barwa complex,Eastern Himalayan Syntaxis

位于东喜马拉雅构造结的南迦巴瓦杂岩是高喜马拉雅结晶岩系的一部分，是印度大陆深俯冲到欧亚板块之下经历了高压变质作用的产物。基于岩相学和矿物化学研究，本文对南迦巴瓦杂岩中的泥质变质岩进行了相平衡模拟研究。结果表明，泥质岩石经历了高压麻粒岩相变质作用，峰期矿物组成是石榴石＋蓝晶石＋黑云母＋斜长石＋钾长石＋石英＋金红石，峰期变质条件是～820℃，13．0～13．5kb，表明印度大陆至少俯冲到了约45km深度，构成了青藏高原的加厚下地壳。高压泥质变质岩在进变质和峰期变质过程中经历了白云母和黑云母脱水反应引起的部分深熔，熔融程度可达27v01％，形成了花岗质成分的熔体，构成了喜马拉雅造山带淡色花岗岩的源区。因此，青藏高原具有一个深熔融的中下地壳，为其侧向流动提供了有利的流变学环境。

The Namche Barwa complex （NBC） in Eastern Himalayan Syntaxis, is generally interpreted as a part of the Higher Himalayan Crystalline Series. The Namche Barwa complex experienced high pressure （HP） metamorphism during the deep subduction of the Indian continent beneath Eurasian continent. In this paper, based on petrology and mineral chemistry, phase equilibria modeling was carried out for high-pressure pelitie rocks of NBC. This results show that the pelitic rocks have suffered HP granulite facie metamorphism, with a peak-metamorphic assemblage of garnet ＋ kyanite ＋ biotite ＋ plagioclase ＋ k-feldspar ＋ quartz ＋ rutile, and a peak-metamorphic condition of - 820℃ and 13.0 - 13.5kb. This indicates the Indian continent subducted to more than 45km depth and formed the thickened lower ernst of the Tibetan Plateau. This research also indicates the HP pelitie rocks have undergone dehydration melting of muscovite and biotite under HP granulite facies conditions, and may produce up to 27vo1% granitic melt, which may be the source of leucogranites in Himalayan orogeny. Thus, Qinghai-Tibet Plateau has a partly melted thickened lower crust, and provides advantageous rheologieal conditions for lateral flow.