东秦岭镇平地区花岗岩岩石地球化学特征及地质意义

Lithogeochemical characteristics and geological significance of granitoids in Zhenping area, Eastern Qinling Mountains

石门岩体和五垛山岩体位于北秦岭构造带的东段,侵入于下古生界二郎坪群。通过LA-ICP-MS锆石U-Pb同位素定年,获得石门岩体的年龄为428.3±2.1 Ma,五垛山岩体的年龄为414.5±2.3 Ma。两个岩体岩性均为黑云母二长花岗岩。岩石地球化学研究表明,石门岩体和五垛山岩体均显示出I型花岗岩类的地球化学属性,两个岩体的稀土元素配分模式具有弱的Eu负异常,岩石地球化学特征显示其源岩物质均以地壳为主,并可能有幔源物质参与。根据岩体的地球化学特征和年代学特征,结合区域地质构造分析,认为这两个岩体的形成与早古生代扬子板块向华北板块之下的俯冲碰撞作用有关,石门岩体形成于碰撞抬升阶段,五垛山岩体形成于碰撞晚期阶段。

Shimen and Wuduoshan granitoid are located in Zhenping area,east segment of North Qinling orogenicbelt, intruding into the Erlangping Group.The ages of the Shimen granitoid obtained by LA-ICP-MS zircon U-Pbdating is 428.3±2.1Ma, the age of Wuduoshan granitoid is 414.5±2.3 Ma.The two granitoid are all biotite gran-ite. Geochemical properties show that both Shimen and Wuduoshan granitoid belong to I type,and both of the oneshave weak Eu negative anomaly. Lithogeochemical characteristics suggest that material sources of the two grani-toid may be both from crust, possibly participated by small amounts of mantle material. Based on chronology char-acteristics and regional geological analyses, the authours consider that the granitoid of Shimen and Wuduoshanare ralated to the subduction of North China block to Yangtze block in early Paleozoic. The Shimen granitoidformed during the ulifting period of the collision, while the Wuduoshan granitoid formed during the late of theplate collision.