南秦岭刘岭群砂岩碎屑锆石LA-ICP-MS U-Pb年龄及其构造意义  

LA-ICP-MS U-Pb geochronology of detrital zircons from the Liuling Group in the South Qinling tectonic belt and its tectonic significance

作　　者：陈龙耀[1] 罗玉凌[2] 刘晓春[1] 曲玮[1] 胡娟[1] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]中国海洋石油总公司规划计划部,北京100010

出　　处：《地质通报》2014年第9期1363-1378,共16页Geological Bulletin of China

基　　金：国家973项目(编号:2009CB825006)

摘　　要：秦岭造山带的构造演化是理解华北与扬子陆块缝合过程的关键,位于商丹断裂带以南的刘岭群是揭示秦岭造山带晚古生代构造演化历史的重要窗口。采用LA-ICP-MS对刘岭群3个变质砂岩样品中的碎屑锆石进行了U-Th-Pb同位素测定,获得最年轻的一组年龄区间为377～395Ma,主要年龄峰值约为442Ma、780～850Ma和900～970Ma,表明刘岭群沉积时代可以持续到晚泥盆世,物质来源于北秦岭构造带。结合刘岭群北侧武关杂岩的最新研究成果可以确定,刘岭群和武关杂岩共同构成了华北陆块南缘中—晚泥盆世弧前盆地的沉积序列,暗示古秦岭洋的最终闭合发生在泥盆纪之后,而华北与扬子陆块碰撞的主缝合线应位于刘岭群的南侧。The tectonic evolution of the Qinling orogen is the key to understanding the assembly of the North China and South China blocks.The Liuling Group in the south of the Shangdan fault can provide an important window for detecting the Late Paleozoic evolutionary process of the Qinling orogen.The LA-ICP-MS U-Pb ages of detrital zircons from three metasandstone samples from the Liuling Group show a age spectrum with major populations at ca.442 Ma and in the range of 780～850Ma and 900～970Ma,with the youngest population being ca.377～395Ma.These data suggest that the deposition of the Liuling Group might have lasted to the Late Devonian,and sediments were probably derived from the North Qinling tectonic belt.In combination with the recent investigation of the Wuguan complex in the north of the Liuling Group,the authors infer that a Middle to Late Devonian turbidite sequence might have formed in a fore-arc basin on the southern margin of the North China block,and the closure of the Paleo-Qinling ocean might have occurred after Devonian.Hence,the collisional boundary of the North and South China blocks should be located in the south of the Liuling Group.

关 键 词：碎屑锆石 LA-ICP-MS U-PB年龄 物质来源 晚古生代 古秦岭洋 刘岭群 秦岭造山带 

分 类 号：P588.212.3[天文地球—岩石学] P597.3[天文地球—地质学]