西秦岭北缘花岗质岩浆作用及构造演化

西秦岭北部江里沟、阿夷山、德乌鲁、温泉和中川5个花岗质岩体岩石学、地球化学和LA-ICP-MS锆石U-Pb年代学研究结果表明,花岗岩体的岩性主体为花岗闪长岩-二长花岗岩,属高钾钙碱系列,少数为钙碱系列;形成时代为264~216Ma。江里沟、阿夷山和中川岩体属弱过铝质花岗岩(ACNK1.05),温泉岩体和德乌鲁岩体属准铝和弱过铝质花岗岩(ACNK=0.95~1.05);花岗岩具有埃达克岩(Sr400×10-6,Yb2×10-6)或喜马拉雅型花岗岩(Sr400×10-6,Yb2×10-6)的地球化学特征,或两者兼而有之。花岗岩浆起源于下地壳的部分熔融,源岩最有可能是古老的玄武质岩石。西秦岭北部存在埃达克岩和喜马拉雅型花岗岩,说明三叠纪时期存在陆陆碰撞或陆陆俯冲导致的地壳加厚,加厚的下地壳的部分熔融以及部分熔融发生深度的不同,形成本区具有埃达克或喜马拉雅型地球化学特点的花岗岩侵入体。埃达克岩和喜马拉雅型花岗岩对寻找金铜矿产具有一定的指导意义。

Granitoid magmatism and tectonic evolution in northern edge of the Western Qinling terrane, NW China

Zircon LA-ICP-MS dating indicates that Jiangligou monzonite, Ayishan granodiorite, Dewulu granodiorite, Wenquan granodiorite, and Zhongchuan monzonite in the northern margin of Western Qinling terrane formed at 264±1.4Ma, 241.6±4Ma, 233.5±1.5Ma, 216.2±1.1Ma, and 264.2±1.3Ma, respectively. Geochemical data suggest that these granitic rocks are mainly belonging to high-K calc-alkalic series and minor rocks are calc-alkalic. The Jiangligou, Ayishan and Zhongchuan intrusions are pre-aluminous granites with ACNK>1.05, however, the Wenquan and Dewulu intrusions are metalumious or prealuminous granites with ACNK value of 0.95~1.05. They also have the geochemical characters of adakite and Himalaya-type granites. The granites of adakite and Himalaly-type with low Mg^# may result from partial melting of basalts in thickened lower crust, which can provide some clues to the collision between the North China Plate and the Yangtze Plate and also direct Cu-Au prospecting.