桂北地区新元古代地层凝灰岩锆石U-Pb年龄及地质意义  

Zircon U-Pb dating of Neoproterozoic tuff in South Gaungxi and its implications for stratigraphic correlation

作　　者：高林志[1] 陆济璞[2] 丁孝忠[1] 王汉荣[2] 刘燕学[1] 李江[2] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]广西区域地质调查研究院,广西桂林541003

出　　处：《中国地质》2013年第5期1443-1452,共10页Geology in China

基　　金：科技基础性工作专项"中国地质志;图及欧亚大陆大地构造图编制"(2011FY120100);中国地质调查局地调项目"中国及邻区泛非期构造;新元古代地层和泥盆-三叠古地理研究"(12120113013900);全国地层委员会专项"中国青白口系标准剖面及内部划分"共同资助

摘　　要：桂西北变质基底四堡群及上覆地层丹洲群之间存在着角度不整合,而丹洲群与南华纪地层之间为平行不整合,说明它们是隶属三个构造域的产物。其地层时代的定位影响着整个江南古陆变质基底地层的对比,也制约着华南地区沉积盖层的地质关系。根据丹洲群合桐组凝灰岩锆石U-Pb年龄(801±3)Ma、拱洞组锆石U-Pb年龄(786±6)Ma、南华系长安组的底界年龄(778±5)Ma和大塘坡组年龄(661±7)Ma,结合从桂北地区四堡群顶部沉积地层中凝灰砂岩获得的锆石U-Pb年龄(842±13)Ma和侵入四堡群火成岩锆石U-Pb年龄(834±4)Ma,将四堡群变质砂板岩明确定为形成于820 Ma之下的地层。该年龄对南华纪地层的区域对比和构造演化都有着重要意义。In the zircon study of bentonite from the Danzhou Group and overlying strata of the Nanhua System, the authors accurately determined the age of （801＋3） Ma for zircon from the Hedong Formation and （778＋6） Ma for zircon from the Gongdong Formation. （778＋5） Ma is the age of zircon from the Chang＇an Formation, which is the bottom of the Nanhuan System, and （661 ＋7） Ma is the age of zircon from Datangpo Formation of the intraglacial period. Some zircon ages of tuff bedding were reported for the first time from the Sibao and Xiajia Groups in Guangxi and Guizhou. In combination of the SHRIMP U-Pb age of the granite （834＋4 Ma） which intruded into the Sibao Group （842＋13 Ma） and the SHRIMP U-Pb age of （837＋7） Ma of Bendong granite, the authors hold that the Sibao Group is Late Neoproterozoic strata below the strata of 820 Ma. These isotopic data are very important for us to redefine the age of the Sibao Group and to conduct regional correlation of strata of the corresponding period as web as to study tectonic evolution. There is an angle unconformity between the Sibao Group and overlying Danzhou Group and a nonconformity between the Danzhou Group and the Nanhuan System, suggesting the existence of three levels of tectonic whole metamorphosed basement in the Jiangnan Orogen and in South China. factor. The revised age column will influence the the constraints on the relationship of the cover strata

关 键 词：桂北地区 四堡群 丹洲群 凝灰岩 锆石SHRIMP定年 

分 类 号：P597.3[天文地球—地球化学]