东准库布苏南岩体和包体的LA-ICP-MS锆石U-Pb测年及地质意义

LA-ICP-MS锆石U-Pb测年结果显示, 库布苏南花岗闪长岩形成时代为287±2 Ma, MSWD=0.15, 包体年龄为286±3 Ma, MSWD=0.22, 在误差范围内完全一致, 这就排除了暗色包体是来源于深部变质岩熔融残留体或浅部围岩捕虏体的可能性, 同时也排除了基性岩浆在花岗质岩浆固结后才侵入的可能, 为岩浆混合作用的存在提供最有力的证据.地球化学研究表明, 包体富集基性组分Ti、Zr、Nb、Hf等高场强元素以及稀土元素, 包体表现为与寄主岩石既相互联系又受其制约, 库布苏南花岗闪长岩体具有低87Sr/86Sr初始比值和高正ε_Nd(t)值, 表明花岗岩的来源有地幔物质参与, 包体是过冷的镁铁质岩浆混入到中酸性岩浆中经快速冷凝的结果.库布苏南花岗闪长岩形成的时代略晚于东准噶尔乌伦古河碱性花岗岩和卡拉麦里碱性花岗岩的形成时代(300 Ma左右), 均为准噶尔周边地区后碰撞伸展构造背景下岩浆活动的产物, 其形成和演化标志了准噶尔地区后碰撞幔源岩浆底侵作用导致大陆地壳垂向生长的过程. 

LA-ICP MS Zircon U-Pb Dating of Kubusunan Granodiorite and the Enclaves from Kalamaili Area in Eastern Junggar,Xinjiang,and Its Geological Implications

LA-ICP-MS zircon U-Pb dating of the Kubusunan granodiorite and its enclaves in the Kalamaili area of the eastern Junggar indicates that the isotopic age of the granodiorite is 287±2 Ma (MSWD=0.15), and that of its enclaves is 286±3 Ma (MSWD=0.22). The fact that they are the same in error range, showing that granodiorite and enclaves were formed at the same age, ruling out the possibility that the dark microgranule enclaves came from the solid metamorphic rock melt remaining in deep crust, or xenoliths from wall rock in the upper crust, at the same time, ruling out the possibility that the basic magma invaded solidified ganite magma. It presents strong evidence for the crust and mantle magma hybrid. Petrological and geochemical studies reveal the relationship between the enclaves and the host rock and it is found that they are related and restricted with each other. The enclaves are rich in basic ingredients HFSE(such as Ti, Zr, Nb and Hf) and REE, Kubusunan granodiorite characteristics of low 87Sr/86Sr initial values and high ε_Nd(t) values, indicating that granites originated partly from mantle magma. The large number of microgranular dioritic enclaves is direct evidence of crust-mantle magma hybrid. Kubusunan granodiorite was formed later than the Ulungur river and Kalamaili alkali granite (300 Ma±) resulting from post-collision magma activity surrounding eastern Junggar, whose formation and evolution stands for continental crust growth caused by post-collision magma underplating in eastern Junggar.