四川盆地威远地区基底花岗岩锆石SHRIMP U-Pb定年及其地质意义

四川盆地内仅有5口井钻穿沉积盖层进入基底，而对基底形成时代与发育构造环境的研究较为薄弱。四川盆地威远地区威117井基底取心资料说明基底由花岗岩类组成，花岗岩锆石SHRIMP U-Pb精确定年结果表明其结晶年龄为794±11 Ma，属于新元古代，该年龄与盆地周缘的花岗岩体结晶年龄具有一致性。结合地球化学特征与岩浆成因类型分析，表明该花岗岩体形成于由挤压向伸展环境的转化阶段，即板块俯冲造山运动结束后向陆内大陆裂谷转化阶段的产物，属于Rodinia超级大陆初始裂解阶段。综合分析认为800 Ma左右是四川盆地具有意义的重要地质时期，是盆地基底形成、构造运动性质发生重要转变的主要时期，越过该时期四川盆地处于大陆裂谷伸展构造环境。

Zircon SHRIMP U-Pb dating of basal granite and its geological significance in Weiyuan area of Sichuan Basin

There are only 5 wells drilling through sedimentary cover and into the basement in Sichuan Basin, and the study for the forming age and tectonic environment is relatively weak. The core material of the Wei117 illustrates the basement is composed of granitoid in Weiyuan area of Sichuan Basin. The results of Zircon SHRIMP U-Pb dating of basal granites show that the crystallization age is 794±11 Ma, Neoproterozoic, which is consistent with the crystallization age of the granites in basin edges. Combining with the geochemical characteristics and genetic types of magma, the granite was formed in the transformation from compression to stretch environment. It was the product of the transformation stage from plate subduction orogeny to continental intracontinental rifting, and it belonged to the initial breakup stage of Rodinia supercontinent. It is thought by synthetical analysis that 800 Ma is an important geological period in Sichuan Basin. It is the main period of formation of the basement, and important change of the nature of the tectonic movement. Over this period, Sichuan Basin was in stretch environment of the continental rift.