Eocene high grade metamorphism and crustal anatexis in the North Himalaya Gneiss Domes,Southern Tibet  

作　　者：GAO LiE ZENG LingSen XIE KeJia 

机构地区：[1]Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China [2]Non-Ferrous Mineral Exploration Engineering Research Center of Henan Province,Zhengzhou 450016,China

出　　处：《Chinese Science Bulletin》2012年第6期639-650,共12页

基　　金：supported by the National Natural Science Foundation of China (41073024 and 40921001);the National Basic Research Program of China (2011CB403102);the Outlay Research Fund of Institute of Geology (J1004)

摘　　要：Determination of the timing and geochemical nature of early metamorphic and anatectic events in the Himalayan orogen may provide key insights into the physical and chemical behavior of lower crustal materials during the early stage of tectonic evolution in large-scale collisional belts.The Yardoi gneiss dome is the easternmost dome of the North Himalayan Gneiss Domes(NHGD),and contains three types of amphibolites with distinct mineral assemblage,elemental and radiogenic isotope geochemistry,as well as various types of gneisses.SHRIMP zircon U/Pb analyses on the garnet amphibolite and garnet-bearing biotite granitic gneiss yield ages of nearly peak metamorphism at 45.0±1.0 Ma and 47.6±1.8 Ma,respectively,which are 2 to 4 Ma older than the age for partial melting in migmatitic garnet amphibolite(43.5±1.3 Ma).Available data have demonstrated that ultra-high pressure metamorphism in the Tethyan Himalaya occurred at ～55 Ma,and high amphibolite facies to granulite facies metamorphism at 45 to 47 Ma.In addition,partial melting at thickened crustal conditions occurred at 43.5±1.3 Ma,which led to the formation of high Sr/Y ratios two-mica granites.The high-grade metamorphic rocks in the NHGD may represent the subducted front of the Indian continental lithosphere.In large collisional belts,fertile components in crustal materials could melt and form granitic melts with relatively high Na/K and Sr/Y ratios under thickened crustal conditions,significantly different from those formed by decompressional melting during rapid exhumation.Determination of the timing and geochemical nature of early metamorphic and anatectic events in the Himalayan orogen may provide key insights into the physical and chemical behavior of lower crustal materials during the early stage of tectonic evolution in large-scale collisional belts. The Yardoi gneiss dome is the easternmost dome of the North Himalayan Gneiss Domes （NHGD）, and contains three types of amphibolites with distinct mineral assemblage, elemental and radiogenic isotope geochemistry, as well as various types of gneisses. SHRIMP zircon U/Pb analyses on the garnet amphibolite and garnet-bearing biotite granitic gneiss yield ages of nearly peak metamorphism at 45.0±1.0 Ma and 47.6±1.8 Ma, respectively, which are 2 to 4 Ma older than the age for partial melting in migmatitic garnet amphibolite （43.5±1.3 Ma）. Available data have demonstrated that ultra-high pressure metamorphism in the Tethyan Himalaya occurred at -55 Ma, and high amphibolite facies to granulite facies metamorphism at 45 to 47 Ma. In addition, partial melting at thickened crustal conditions occurred at 43.5±1.3 Ma, which led to the formation of high Sr/Y ratios two-mica granites. The high-grade metamorphic rocks in the NHGD may represent the subducted front of the Indian continental lithosphere. In large collisional belts, fertile components in crustal materials could melt and form granitic melts with relatively high Na/K and Sr/Y ratios under thickened crustal conditions, significantly different from those formed by decompres- sional melting during rapid exhumation.

关 键 词：花岗片麻岩 地壳物质 变质年龄 北喜马拉雅 深熔作用 西藏南部 元素和同位素地球化学 地球化学性质 

分 类 号：P588.345[天文地球—岩石学] P315.2[天文地球—地质学]