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厘定喜马拉雅造山带早期变质和深熔作用的时限和性质有助于理解大型碰撞造山带早期下地壳物质的物理和化学行为.雅拉香波穹窿位于北喜马拉雅穹窿的最东端,穹窿内发育3种地质产状、矿物组成和地球化学特征不同的角闪岩和多种片麻岩.SHRIMP锆石年代学测试结果表明:石榴角闪岩和黑云母花岗质片麻岩的近峰期变质作用分别发生在45.0±1.0和47.6±1.8Ma,比石榴角闪岩部分熔融的时间(43.5±1.3Ma)早2～4Ma.结合已有的研究结果,在北喜马拉雅带内,榴辉岩相变质作用发生在大约55Ma,高角闪岩相-麻粒岩相变质作用发生在45～47Ma,与增厚地壳条件下部分熔融相关的变质作用发生在43.5±1.3Ma,同时形成具有高Sr/Y比值的二云母花岗岩.位于北喜马拉雅带的高级变质岩代表了俯冲印度大陆地壳的前锋,不同位置保存的变质历史存在明显的差异.在大型碰撞造山带内,地壳缩短增厚的过程中,易熔组分可发生部分熔融,形成高Na/K比和Sr/Y比的花岗质熔体,明显不同于快速折返-减压部分熔融作用形成的熔体.
Determining the duration and nature of the early metamorphism and diagenesis of the Himalayan orogenic belt may help to understand the physical and chemical behavior of the early lower crustal mass in the large collision orogenic belt.The Yala shampoo dome is located at the easternmost tip of the northern Himalayan dome with three species The geochronology, mineralogical and geochemical characteristics of amphibolite and gneisses are different.The results of SHRIMP zircon geochronology show that the metamorphism of amphibolites and biotite granitic gneiss are near-peak metamorphism Which occurred at 45.0 ± 1.0 and 47.6 ± 1.8Ma, respectively, which was 2 ~ 4Ma earlier than the time of partial melting of amphibolite (43.5 ± 1.3Ma) .Based on the previous research results, the eclogitic facies metamorphism in the Northern Himalayas The effect occurred at about 55 Ma. The amphibole facies-granulite facies metamorphism occurred at 45-47 Ma, and the metamorphism associated with partial melting under thickened crust occurred at 43.5 ± 1.3 Ma, with high Sr / Y ratios Of the two mica granites.High metamorphic rocks in the northern Himalayas represent the striking subducting Indian continental crust, the preservation of the metamorphic history of different locations there is a clear difference in the large collision orogenic belt, the crust shortening and thickening , The fusible component can be partially melted to form a granite melt with high Na / K ratio and Sr / Y ratio, which is obviously different from the melt formed by the rapid reentrant-depressurization partial melting.