西藏中仓蛇绿混杂岩中辉长岩锆石U-Pb定年及其地质意义

Zircon U-Pb Dating of Gabbro from Zhongcang Ophiolitic Mélange in Tibet and Its Geological Implications

作为大洋演化的残余,蛇绿混杂岩的形成时代是确定缝合带构造演化的重要依据.中仓蛇绿混杂岩位于狮泉河-永珠-嘉黎蛇绿混杂岩带西段,是达查沟地区区域地质调查过程中新发现的,主要由变质橄榄岩、堆晶辉长岩和辉长岩墙组成.本文应用LA-ICP-MS锆石U-Pb技术,对中仓蛇绿混杂岩中堆晶辉长岩和辉长岩墙进行了测年,分别获得(116.1±1.8)Ma和(113.4±1.7)Ma,该年龄代表了中仓蛇绿混杂岩的形成时代.结合前人的研究成果,初步认为狮泉河-永珠-嘉黎蛇绿混杂岩带在早白垩世仍处于弧后盆地的演化阶段.

As relicts of oceanic evolution,the formational age of ophiolitic mélange is an important evidence for pinning down the tectonic evolution of suture.Located in the western part of Shiquanhe-Yongzhu-Jiali ophiolitic mélange belt,Zhongcang ophiolitic mélange was newly discovered during regional geological surveying in Dachagou area.Zhongcang ophiolitic mélange mainly consists of metamorphic peridotite,cumulate gabbro,and gabbro dike.LA-ICP-MS technique is applied to U-Pb zircon dating of the gabbro from Zhongcang ophiolitic mélange.and the ages of cumulate gabbro and gabbro dike as(116.1±1.8)Ma and(113.4±1.7)Ma respectively are obtained.The ages stand for the formation time of Zhongcang ophiolitic mélange.Combined with previous studies,this research tentatively proposes that Shiquanhe-YongzhuJiali ophiolitic mélange belt was probably still in back-arc basin′s evolutional stage in Early Cretaceous.