西藏冈底斯东段墨竹工卡地区洞中拉辉绿玢岩锆石SHRIMP U-Pb定年及意义

Zircon SHRIMP U-Pb age and its geological significance in Dongzhongla allgovite,Mozhugongka area,eastern segment of Gangdise,Tibet,China

洞中拉地区的辉绿玢岩出露于冈底斯弧背断隆带东段,地质研究程度很低,过去一直认为形成于古生代二叠纪。为精确地限制洞中拉辉绿玢岩的形成时代,对冈底斯东段墨竹工卡县洞中拉地区的辉绿玢岩进行锆石SHRIMP U-Pb定年,结果显示洞中拉辉绿玢岩的年龄为117.1Ma±1.0Ma,为早白垩世中期。与冈底斯带中北部地区带状岩浆大爆发的年龄(大约110Ma)时限和冈底斯弧后裂谷拉张作用的时限(120～95Ma)相一致。洞中拉辉绿玢岩可能是冈底斯弧背断隆东段早白垩世弧间裂谷阶段岩浆侵位的产物,与班公湖-怒江特提斯洋壳向南、新特提斯洋壳向北的双向俯冲有关。

Allgovite in Dongzhongla area outcrops in the east segment of Gangdese retroarc uplift belt,and the degree of research geology in this area is low.In the past,it was believed that the Dongzhongla allgovite were formed in the Permian of Paleozoic.In order to define accurate forming time of the allgovite in Dongzhongla,firstly we used Zircon SHRIMP U-Pb isotope dating technology and obtained the age of 117.1±1Ma,which is middle of the Early Cretaceous.The age is consistent with both the zonal magmatic flare-up with strong input of mantle derived materials（110 Ma） in the northern parts of the Gangdese and the Gangdese back-arc rift age（120～95Ma）.Dongzhongla allgovite is probably the result of the invasion activities during the intra-arc rift stage in the east Gangdese retroarc uplift in the Early Cretaceous,and is related to southward subduction of Bangong Co-Nujiang oceanic crust and northward subdution of Neo-Teths oceanic crust.