中喜马拉雅（中国-尼泊尔-不丹）榴辉岩带的岩石学特征、PTt轨迹及其大地构造意义

A huge eclogite-facies metamorphic belt with more than 200 km long has been recently recognized in central Himalaya: i.e., it expends from the westernmost Thongmön area in Tingri county, through Ama Drime Massif in Dinggye county in China and Arun valley in the northeast of Nepal to Yadong in China and connects to the northwestern part of Bhutan. These eclogites with 13-14 Ma ages were overprinted by granulite-facies retrograde metamorphism extensively, which should be the youngest eclogites in Himalayan orogenic belt. In this study, we plan to do the metamorphic geological study on eclogites in central Himalaya such as the field occurrences, petrological characteristics, metamorphic PT conditions and dating of eclogites. The aim of this project is to obtain the metamorphic evolution of eclogites and their tectonic implication in central Himalaya. This study should be very significance for understanding the tectonic evolution of Himalayan orogenic belt and dynamic process during continental convergence in Tethys tectonic system.

在喜马拉雅造山带中段高喜马拉雅结晶岩系中出露了一条东西长约200多公里榴辉岩带，它西起我国境内的定日通门一带，经定结的Ama Drime地区，到尼泊尔东北部的Arun 山谷地带, 再到我国亚东地区，向东延伸到不丹西北部与我国接壤地带。该带榴辉岩普遍遭受了强烈的麻粒岩相退变质作用的叠加，是目前喜马拉雅造山带中发现的最年轻的榴辉岩（13-38Ma）。该项申请拟对这条榴辉岩带开展深入的变质地质学研究，确立它们的野外分布、岩石学特征、温压条件和形成时代，建立喜马拉雅造山带中段榴辉岩带变质演化和形成机制。该项研究对于探讨喜马拉雅造山带的形成与演化、揭示特提斯构造域大陆汇聚动力学过程都具有重要意义。

在喜马拉雅中段确定了一条以退变麻粒岩相叠加为特征的榴辉岩带，它西起定日县的通门，经定结的日屋（尼泊尔的Arun山谷）到东部的亚东地区（印度锡金），全长约200千米的中喜马拉雅榴辉岩带。根据详细的岩石学研究，确立了它们经历了5期变质演化阶段：进变质角闪榴辉岩相阶段（温压条件为640–660 °C 和19–20 kbar）；峰期榴辉岩相阶段（变质条件为>750°C和>21 kbar）；退变高压麻粒岩相阶段（790–820 °C和13–14 kbar）；退变二辉麻粒岩相（变质条件为830–870°C和8.5–10.0 kbar）；最后退变角闪岩相（600–650 °C和6–7 kbar）。亚东地区略有不同的是具有超高温变质作用的叠加，其超高温温压条件可以达到900–950 ℃ at ~0.8 GPa。峰期榴辉岩相变质时代为~17Ma左右，而麻粒岩相退变的时代为~15.6Ma。中喜马拉雅榴辉岩的原岩是侵入于片麻岩中的基性岩脉，可能是形成于印度板块北部的元古代大陆溢流玄武岩。我们认为，喜马拉雅中段的榴辉岩带是印度板块持续向欧亚板块之下俯冲碰撞发生高压变质作用形成的。