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Geochronology and geochemistry of granites in the Gaoligong tectonic belt,western Yunnan:Tectonic implications.

YANG QiJun XU YiGang HUANG XiaoLong LUO ZhenYu Key Laboratory of Isotope Geochronology and Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China  
The origin and evolution of the Gaoligong tectonic belt,which is located on the east of eastern Himalaya syntaxis,is pivotal to understanding the genesis of the Gandese Block.For this purpose,studies have been carried out on the granitoids in the Gaoligong area with focus on the field relationship,crystallized ages,mineralogical and geochemical characteristics and their tectonic significance.The Gaoligong pluton complex,bounded by the Nujiang Fault in east and Sagain Fault in west,form an elongated ductile deformation zone.The granites are intensively deformed along the peripheries of the faults but show little deformation in the center. They are mainly composed of biotite monzogranite,biotite granite,two-mica granites.Geochemical analyses suggest that these peraluminous to strongly peraluminous granites were formed by anatexis of precambrian continental crust in a arc to post-collisional setting.The source rocks lie in the middle crust and are heterogeneous including both meta-sediments and meta-basalts.The SHRIMP U-Pb zircon dating indicates that they were emplaced during the early Cretaceous(118 to 126 Ma).The Gaoligong granites share geochemical and chronological similarities with the Gandese granites,suggesting that they represent eastern extension of the Gandese belt.It is proposed that the Gaoligong granites resulted from crustal melting during the southward subduction of the Meso-Tethys oceanic lithosphere undemeath the Gandese Block.
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