冈底斯带桑巴区早白垩世后碰撞花岗岩类的确定及构造意义  

The determination of early Cretaceous post-collision granitoids in Sangba area of Gangdese tectonic belt and its tectonic significance

作　　者：和钟铧[1] 杨德明[1] 王天武[1] 

机构地区：[1]吉林大学地球科学学院,吉林长春130026

出　　处：《岩石矿物学杂志》2006年第3期185-193,共9页Acta Petrologica et Mineralogica

基　　金：国土资源部地质调查项目(H46002002);吉林大学"985"工程资助项目

摘　　要：桑巴区花岗岩体位于冈底斯带嘉黎断裂之北,呈近东西向分布于桑巴、建多等地。岩石类型主要有巨斑黑云母花岗岩、黑云母花岗岩及斑状花岗闪长岩。其中斑状花岗闪长岩(TW1530)的SHRIMP锆石U-Pb年龄为117.2±1.6Ma,黑云母花岗岩(TW1637)年龄为121.2±1.7Ma,表明桑巴区花岗岩体形成于早白垩世。桑巴区花岗岩类为高钾钙碱性岩,根据地球化学特征和微量元素构造判别图解,确定该时代的花岗岩具后碰撞花岗岩特征,形成于从挤压体制向拉张体制转变的构造环境。早白垩世后碰撞花岗岩的出现预示着班公湖怒江缝合带主造山作用的结束,冈底斯火山岩浆弧带至此进入造山后伸展构造环境,并一直持续至晚白垩世竟柱山组沉积之前。Sangba granitoids are exposed near Sangba and Jianduo areas to the north of Jiali fault in Gangdese tectonic belt. The main rock types include granitite, porphyritic granitite and porphyritic granodiorite. The SHRIMP U-Pb dating results of zircons from porphyritic granodiorite （TW1530） and granitite （TW1637） are 117.2 ±1.6 Ma and 121.2 ±1.7 Ma, respectively, suggesting that Sangba granitoids were formed in early Cretaceous. Sangba granitoids belong to high K and calc-alkalic rocks. According to geochemistry and the trace element discrimination diagrams for tectonic interpretation, the early Cretaceous granitoids are considered to be of the post-collision type formed in a transitional tectonic setting from the compressional system to the tensional system. The appearance of the early Cretaceous Sangba granitoids marked the end of the main orogenic event in Bangonghu-Nujiang suture. From early Cretaceous, Gangdese tectonic belt entered the tensional stage until the deposition of Jingzhushan Formation in late Cretaceous.

关 键 词：SHRIMP测年 地球化学 构造意义 花岗岩类 桑巴区 西藏 

分 类 号：P588.121[天文地球—岩石学] P542[天文地球—地质学]