南祁连扎子沟埃达克岩年代学、地球化学特征及地质意义

扎子沟岩体位于南祁连西段党河南山,由石英闪长岩和花岗闪长岩组成.利用LA-ICPMS锆石U-Pb法测得花岗闪长岩年龄(450±12)Ma(MSWD=0.23,n=24),侵位时代为晚奥陶世.岩石主量元素显示,SiO2介于58.46％～69.14％,Al2O3介于13.70％～16.6％,MgO介于1.43％～4.31％...

Geochronological and Geochemical Characteristics of the Zhazigou Adakite in South Qilian and the Geological Significance

Zhazigou batholith,which is composed of quartz diorite and granodiorite,is located in Danghenanshan of South Qilian.The LA-ICP-MS and zircon U-Pb age of the granodiorite is(450±12)Ma(MSWD=0.23,n=24),and the emplacement age is late Ordovician.The major elements show that SiO2 is 58.46%~69.14%,Al2O3 is 13.70%~16.6%,and MgO is 1.43%~4.31%,belonging to High-K calc-alkaline quasi-aluminous granite.Trace elements are rich in light rare earth and large ion lithophile elements such as Rb,Ba,Th,U,Sr,and depleted in heavy rare earth and high field strength elements such as Nb,Ta,Ti,P.The content of Sr is 130.0×10^-6~460.0×10^-6 with an average content of 310.93×10^-6;the content of Yb is 0.7×10^-6~1.81×10^-6 with an average content of 1.26×10^-6.The content of Y is 6.44×10^-6~17.68×10^-6 with an average content of 12.96×10^-6,weak to positive Eu anomaly(δEu=0.77~1.55)and higher Sr/Y ratio(20.2~37.1),having adakite characteristics geochemically.Combined with the regional geological background,it is believed that Zhazigou batholith formed in the continental collision environment,which was related to the close of south Qilian ocean in the Late Ordovician.The collision of the Oulongbuluke block and the middle Qilian block caused the thickening of the crust and the delamination.Then the hot mantle material upwelled leading to the partial melting of the lower crust.