Geochemical Features and Tectonic Setting of the Laohegou Granite and the Shaiziyan Granite in Bikou Block,in Northwest Sichuan

The Louhegou granite and the Shaiziyan granite,located in southern margin of Bikou block. The data of occurrence,petrography and geochemical are reported,the source and tectonic setting of the granite are discussed in this paper. The results show that the Louhegou granite and the Shaiziyan granite have high SiO2(69.89%～71.69%),and Al2O3 composition, A/CNK=1.04～1.12. It is a type with supersaturation of Al and Si,a typical strongly peraluminous granites. The ∑REE has the range of 33.13×10-6～150.42×10-6, REE diagram shows rightward incline and obvious Eu negative abnormity. The trace elements geochemistry was characterized by evidently negative anomaly of Ta,Nb,Ti,etc positive anomaly of Rb, Ba,Sr. The Louhegou granite and the Shaiziyan granite show post-collisional granitic characteristics. These rocks are post-orogenic granite,and are typical crust source petrogenesis. These granites mass are interpreted as a kind of syn-collisional granites resulted from the crustal thickening caused by the collision between the North China massif and Yangtze massif during the Indosinian. These rocks were transitional environment of compressional orogeny and extensional structure.