青藏高原冈底斯北缘嘉玉桥群形成时代的确定

The determination of the age of Jiayuqiao Group in northern Gangdise of Tibetan Plateau

摘要: 提要：嘉玉桥群是冈底斯北缘的变质岩系之一，其形成时代存在较大分歧。通过高精度LA-ICP-MS（激光剥蚀等离子体质谱）锆石微区原位U-Pb同位素测年，获得西藏八宿县巴兼村一带嘉玉桥群上部大理岩中所夹含石榴子石绿片岩（原岩为玄武岩）的上交点年龄为（566±27）Ma，将八宿县巴兼村一带嘉玉桥群的原岩形成时代限定为晚震旦世。结合相关研究成果，初步认为冈底斯北缘自晚震旦世到寒武纪可能存在较大规模的陆缘裂谷。

Abstract: Abstract：The formation age of Jiaoyuqiao Group, i.e., the metamorphic rocks in the northern margin of Gangdise, is still in controversy. High resolution LA-ICP-MS in situ U-Pb analysis was conducted for the intercalation of garnet-bearing green schist in marbles of upper Jiayuqiao Group at Bajian Village, Baxoi County, Tibet, and an upper intercept age of 566±27 Ma was obtained. This result cinfines the formation age of the Jiaoyuqiao Group to late Sinian. Combined with related data, the authors hold that there existed a large continental margin rift in the northern margin of Gangdise in late Sinian-Cambrian period.