湘中月山中三叠世花岗岩成因及其构造意义OA北大核心

There are a series of Triassic granites in central Hunan,whose genesis and tectonic significance are highly controversial.Taking Yueshan granite as the research object,this paper has conducted research on pe-trology,zircon chronology and geochemistry.LA-ICP-MS zircon U-Pb dating results show that the weighted av-erage age of Yueshan granite is 245±1 Ma,indicating that the emplacement age of the pluton is Middle Trias-sic.Zircon trace element compositions show significant positive Ce anomaly and negative Eu anomaly,light rare earth depletion,which is consistent with typical magmatic zircon characteristics.Zircon saturation temperature is low(avg.,728.66 ℃),the main elements are rich in silica(SiO2=76.65％-81.72％),and alkali(Na2O+K2O=6.67％-8.53％)but poor in TiO2(0.04％-0.08％),showing its characteristics of peraluminous(A/CNK=1.09-1.19),and high potassium calc-alkaline S-type granite.Large ion lithophile elements such as Rb,Th and U are enriched,while high field strength elements such as Nb and Ti are depleted,with obvious negative Eu anomaly(δEu=0.13-0.36).The geochemical characteristics indicate that it belongs to crust-de-rived granite,and the magma source area is partial melting of argillaceous rocks.Combined with the discrimina-tion of tectonic environment and regional tectonic-magmatic evolution,it is concluded that Yueshan granite is formed in the co-collision tectonic environment.