Geochemistry,Petrogenesis and Tectonic Setting of Early Yanshanian Yaogangxian Granite Pluton,Southeastern Hunan province

The Early Yanshanian Yaogangxian granite pluton in southern Hunan province is composing dominantly of biotite monzogranites.Their mean content of SiO2 is 75.83 wt%,K2O 4.78 wt%,Na2O+K2O 8.02 wt% with mean K2O/Na2O ratio 1.53 and Al2O3 12.98 wt%.Thus,the rocks belong to weakly perluminous granite of calc-alkaline series.eNd(t) value of-11.13～-9.13,t2DM of 1.70～1.86 Ga,coinciding with the ages for the granites from Hunan and Guangxi interior continental belt(1.8～2.4 Ga) and the basement formation ages of the study area(1.7～2.7 Ga).The magmas of the Yaogangxian granites are derived from the middle crustal crystalline basement,typical origin of the S-type granites.Multiple oxide-diagrams for discrimination of tectonic setting and regional tectonic evolution analysis indicate that the rocks are formed in the post-orogenic extension environment.