黔东南—桂北地区四堡群凝灰岩锆石SHRIMP U-Pb年龄及其地层学意义

Zircon SHRIMP UPb dating of tuff bed of the Sibao Group in southeastern Guizhou-northern Guangxi area,China and its stratigraphic implication

首次获得黔桂地区晚前寒武纪四堡群凝灰岩(斑脱岩)锆石SHRIMP U-Pb年龄,结合新获得的侵位于四堡群的花岗岩锆石SHRIMP U-Pb年龄,将四堡群明确定位于新元古界。"江南造山带"普遍发育的新元古代四堡群(梵净山群、冷家溪群、双桥山群)和上覆的丹州群(下江群、板溪群、河上镇群)均为低变质绿片岩系,构成了江南古陆的变质基底。多年来四堡群一直划归中元古界,并且构成"四堡运动"的主体,其时代的定位一直影响着整个江南古陆变质基底的地层划分和对比,也制约着中国地质学家对江南造山带的地质背景和成矿条件解疑。通过对四堡群及其上覆地层中斑脱岩锆石的研究,精确地测定并获得了四堡群斑脱岩锆石的年龄841.7Ma±5.9Ma和黔东南摩天岭地区侵入四堡群的花岗岩锆石的年龄826.8Ma±5.9Ma。

Zircon dating age of tuff bedding from the Sibao Group in Guangxi and Guizhou provinces is firstly reported in this paper.Integrating the zircon SHRIMP U-Pb dating of the granite which intruded into the Sibao Group,the group is thus determined to be Neoproterozoic.The Sibao Group（same as the Fanjingshan,Lengjiaxi and Shuangqiaoshan groups） and the Danzhou Group（same as the Xiajiang,Banxi and Heshangzhen groups）,which are slightly metamorphosed rocks are well developed in the Jiangnan Orogen,formed a metamorphosed basement of the Jiangnan old land.Many years ago,the Sibao Group was categorized into Mesoproterozoic,and it was main part of the Sibao Movement.The age of Sibao Group is still influencing the strata subdivision and correlation for the metamorphosed rocks in whole Jiangnan old land and has restricted the Chinese geologists to resolve the geological background and mineralization condition of the Jiangnan Orogen.In zircon study from bentonite in the Sibao Group,we＇ve accurately determined the zircon dating of 841.7 Ma±5.9 Ma in the group and intruded granite zircon dating of 826.8 Ma ± 5.9 Ma from the Mt.Motianling.