Geochemistry Of The Qushui Intrusive Of Gangdese In Tibet And Its Implications For Magma Mixing

The Tibetan plateau is the highest, largest, and the youngest orogenic belt in the world. It is the key natural lab for studying the global geodynamics in the world.The paper focus on Qushui complex, referring to the conclusions and data from former researches in this area, using petrology, geochemistry and SHRIMP zircon U-Pb geochronology. The petrogenesis, tectonic environment of the rocks is discussed. The result of Qushui pluton is also applied in studying the crust-mantle material exchange and deep lithosphere processes.Qushui granite consists of complex compositions, mainly including granodiorite and monzonitic granite with medium to coarse particle structure. Additionally, the intrusion has long history. There are a mass of gabbros -dioritic mafic microgranular enclaves (MME). Our study concludes that: (1) the rocks belong to metaluminous to weakly peraluminous granitoids of medium or high-K calc-alkaline series;(2) there is obvious negative correlation between SiO₂ and TiO₂, Al₂O₃, MgO, FeO^*, GaO, MnO, and positive correlation between SiO₂ and K₂O;(3) study on rocks and MME shows that they are the mixing product of magma.SHRIMP II zircon U-Pb isotopic dating results show that the age of Qushui granite, including basic and acid end magma, and MME, are all around 50 Ma. This evidence and characters of mineralogy and geochemistry, indicates that Qushui complex is composed of the same original magma and two kinds of magma mixed. Qushui intrusive represents an important magmatism event during the India-Asia collision. It is also a mechanics for the crustal accretion in Gangdese belt.