南海北缘琼南缝合带的锆石U-Pb年龄制约

ZIRCON U-PB AGE CONSTRAINTS TO QIONGNAN SUTURE ZONE ON THE NORTHERN MARGIN OF SOUTH CHINA SEA

为了获得南海北缘琼南缝合带南北两侧地块的碰撞时间,对九所陵水东段采集的中高级变质石榴石石英片岩和花岗质片麻岩进行了LA-ICP-MS锆石U-Pb定年。实验结果发现:原岩为沉积岩的石榴石石英片岩形成于晚泥盆纪;3个锆石变质壳谐和/近谐和年龄表明碰撞事件发生在(233±4)Ma左右;花岗质片麻岩原岩为同构造侵位的花岗岩,其8个锆石增生年龄显示的是深熔作用的时间,为(206±3)Ma。这些研究成果对重建南海北缘琼南缝合带在研究区内的演变历史具有重要意义。

In order to obtain the collision time of the Qiongnan block and the Qiongzhong block,or the forming time of the Qiongnan Suture Zone in the northern South China Sea,the authors collected the samples of garnet quartz schist and granitic gneiss for LA-ICP-MS zircon U-Pb dating.The results show that the protolith of garnet quartz schist is a kind of sedimentary rock formed after late Devonian;three concordant/near concordant data from the shells of metamorphic zircons indicate the collision time of about（233±4）Ma;and the protolith of the granitic gneiss is granite that formed when tectonic emplacement happened about（242±5）Ma,and the dating results of（206±3）Ma of eight zircon shells suggest the time of anatexis of granitic gneiss.All these results provide meaningful clues for the construction of Qiongnan Suture Zone in the research area.