西藏双湖地区蓝闪片岩原岩Sm-Nd同位素定年

Sm-Nd dating of the protolith of blueschist in the Shuanghu area,Tibet

西藏双湖纳若地区蓝片岩中青铝闪石40Ar/39Ar定年为222.5Ma,其原岩时代争论颇大,以往多数研究者认为早于泥盆纪,甚至为中新元古代,称阿木岗群。在1∶10万填图和实测剖面的基础上,系统采集了相关样品,获得了蓝片岩原岩Sm-Nd法等时线年龄分别为272±7Ma,268±5.6Ma和252±4.6Ma,结合区域地质条件和双湖地区蓝片岩的产状,认为双湖地区的蓝片岩原岩时代为二叠纪,将双湖地区原定为前泥盆纪或中新元古代阿木岗群时代重新划定为二叠纪,恰格勒拉蛇绿杂岩时代确定为早二叠世晚期,为龙木错—双湖古特提斯洋的演化提供了重要年代依据。

The 40 Ar / 39 Ar age of crossite in blueschist in the Shuanghu area,Tibet,but the age of the pro-tolith of the blueschist is highly controversial.Previously most researchers think that the protolith is earlier than Devonian in age and some researchers even think it to be Meso-and Neoproterozoic in age and call it the Amugang Group.On the basis of 1∶100000mapping and measurements of the section,the authors collected relevant samples and obtained the Sm-Nd isoch ron ages of 272±7Ma,268±5.6Ma and252±4.6Ma for the protoli th of the blueschist.On that basis,combined with the regional geological con ditions and occurrence of blueschist in the Shuanghu area,it is believed that the age of the protolith of the blueschist is Permian,and the age of the Am ugang Group is assigned to Permian and the age of the Qiagelela ophio-lite is determined to be late Early Permian.The age dating provides important evidence for the evidence of the Paleo-Tethys in Lungmu Co-Shuanghu.