Episodic crustal anatexis and the formation of Paiku composite leucogranitic pluton in the Malashan Gneiss Dome, Southern Tibet  

作　　者：GAO LiE ZENG LingSen HOU KeJun GUO ChunLi TANG SuoHan XIE KeJia HU GuYue WANG Li 

机构地区：[1]State Key Laboratory of Continental Tectonics and Dynamics,Institute of Geology,Chinese Academy of Geological Sciences [2]Institute of Mineral Resources,Chinese Academy of Geological Sciences [3]Non-Ferrous Mineral Exploration Engineering Research Center of Henan Province

出　　处：《Chinese Science Bulletin》2013年第28期3546-3563,共18页

基　　金：supported by the National Basic Research Program of China(2011CB403102);the National Natural Science Foundation of China(41073024 and 41273034)

摘　　要：The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite,two-mica granite and garnet-bearing leucogranite.Zircon U-Pb dating yields that(1)tourmaline leucogranite formed at28.2±0.5 Ma and its source rock experienced simultaneous metamorphism and anatexis at 33.6±0.6 Ma;(2)two-mica granite formed at 19.8±0.5 Ma;(3)both types of leucogranite contain inherited zircon grains with an age peak at^480 Ma.These leucogranites show distinct geochemistry in major and trace elements as well as in Sr-Nd-Hf isotope compositions.As compared to the two-mica granites,the tourmaline ones have higher initial Sr and zircon Hf isotope compositions,indicating that they were derived from different source rocks combined with different melting reactions.Combined with available literature data,it is suggested that anatexis at^35 Ma along the Himalayan orogenic belt might have triggered the initial movement of the Southern Tibetan Detachment System(STDS),and led to the tectonic transition from compressive shortening to extension.Such a tectonic transition could be a dominant factor that initiates large scale decompressional melting of fertile high-grade metapelites along the Himalayan orogenic belt.Crustal anatexis at^28 Ma and^20 Ma represent large-scale melting reactions associated with the movement of the STDS.The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite, two-mica granite and garnet-bearing leucogranite. Zircon U-Pb dating yields that （1） tourmaline leucogranite formed at 28.2±0.5 Ma and its source rock experienced simultaneous metamorphism and anatexis at 33.6±0.6 Ma; （2） two-mica granite formed at 19.8±0.5 Ma; （3） both types of leucogranite contain inherited zircon grains with an age peak at -480 Ma. These leucogranites show distinct geochemistry in major and trace elements as well as in Sr-Nd-Hf isotope compositions. As compared to the two-mica granites, the tourmaline ones have higher initial Sr and zircon Hf isotope compositions, indicating that they were derived from different source rocks combined with different melting reactions. Combined with available literature data, it is suggested that anatexis at -35 Ma along the Himalayan orogenic belt might have triggered the initial movement of the Southern Tibetan Detachment System （STDS）, and led to the tectonic transition from compressive shortening to extension. Such a tectonic transition could be a dominant factor that initiates large scale decompressional melting of fertile high-grade metapelites along the Himalayan orogenic belt. Crustal anatexis at -28 Ma and -20 Ma represent large-scale melting reactions associated with the movement of the STDS.

关 键 词：淡色花岗岩 熔融反应 西藏南部 穹隆 地壳 岩体 复合 锆石U-PB定年 

分 类 号：P542[天文地球—构造地质学]