摘要
通安组是扬子克拉通西南缘褶皱基底的组成部分,可分为5个岩性段。本文利用凝灰质粉砂岩(样品100620-1)中碎屑锆石和侵入通安组的辉长-闪长岩脉(样品100620-1-1和样品100620-2-2)中岩浆锆石的LA-ICP-MSU-Pb年龄探讨通安组的形成时代。通安组三段中凝灰质粉砂岩的碎屑锆石有两个主要的峰值年龄,分别为1.8～1.9Ga和2.28～2.38Ga,这表明通安组三段的沉积物来自不同的物源区。该凝灰质粉砂岩中最年轻的3粒锆石的207Pb/206Pb平均年龄为1806Ma。从侵入到通安组第三段的辉长-闪长岩的岩浆锆石中获得了1513±13Ma的207Pb/206Pb加权平均年龄(样品100620-2-1)和1531±18Ma的上交点年龄(样品100620-2-2)。这些新获得的年龄数据可以限定通安组的形成时限为1.8～1.5Ga。辉长-闪长岩脉1513Ma和1531Ma的年龄数据与东川群黑山组火山凝灰岩1503±7Ma的年龄结果相似,表明侵入到通安组三段中的辉长-闪长岩脉与东川群黑山组的火山凝灰岩形成于一个岩浆旋回的同一阶段。因此,通安组三段大致相当于云南东川群的黑山组。
The Tong＇an Formation is part of the folded basement in the southwestern margin of Yangtze Craton and further subdivided into five lithological units. LA-ICP-MS U-Pb dating of detrital zircons from tuffaceous siltstone （sample 100620-1） and magmatic zircons from gabbro-diorite dyke （sample 100620-2-1 and 100620-2-2） in this study was used to provide insight into the geochronology of the Tong＂ an Formation. Two major age populations of 1.8~1.9 Ga and 2.28~2.38 Ga of the detrital zircons from the third lithological unit suggest that sediments of the Tong＇an Formation are of diverse provenances. Three grains of the youngest detrital zircons from the tuffaceous siltstone yielded a mean 207pb/206Pb age of 1806 Ma. Zircon 207Pb/206Pb age of 1513±13 Ma （sample 100620-2-1） and intercept up age of 1531± 18 Ma （sample 100620-2-2） have been obtained from gabbro-diorite dyke intruding the third unit. Thus, the geochronology of the Tong＇an Formation was estimated between～1.8 Ga to 1.5 Ga based upon the newly obtained U-Pb age result. The zircon ages of 1513 Ma and 1531 Ma from gabbro diorite dyke are consistent with the previous data of 1503± 17 Ma from volcanic tuff of the Heishan Formation in the Dongchuan Group, which suggests that gabbro-diorite dyke intruding the Tong＇an Formation and volcanic tuff from Heishan Formation in the Dongchuan Group belongs to the same magmatic cycle. The third lighological unit of the Tong＇an Formation is proposed to be correlated with the Heishan Formation of the Dongchuan Group in Yunnan Province.
出处
《地质学报》
CAS
CSCD
北大核心
2012年第9期1479-1490,共12页
Acta Geologica Sinica
基金
地质大调查项目(编号1212010911047)资助的成果
