摘要
右江盆地上二叠统-中三叠统地层中常含有多层凝灰岩,对采自广西河池九圩及田林利周罗楼组和百逢组底部的4件凝灰岩样品进行锆石原位LA-ICPMS方法U-Pb同位素定年,结果显示凝灰岩的形成年龄分别为252.8±1.8Ma、253.0±2.4Ma、247.2±1.5Ma和239.3±2.7Ma,指示晚二叠世末期到中三叠世Bithynian期华南地块西南缘存在多期火山活动,其可能与华南西南缘陆块的裂解与汇聚有关.凝灰岩中继承或捕虏锆石年龄(260～270Ma)记录了中晚二叠世峨眉山大火成岩省岩浆活动或华南西南缘岛弧火山活动事件.凝灰岩的岩相学研究表明,中三叠世特别是Bithynian期之后右江盆地由伸展型向挤压型转换,盆地进入快速坳陷期.
Upper Permian-Middle Triassic sections in Youjiang basin contain many volcanic tuff horizons.Zircon LA-ICP-MS U-Pb dating of 4 volcanic tuff samples from the bottom of the Luolou and Baifeng formations in the Jiuxu and Lizhou areas,Guangxi Province,yield the depositional ages of 252.8±1.8,253.0±2.4,247.2±1.5 and 239.3±2.7 Ma,respectively,which,together with the inherited or xenocrystal zircon ages（with peak values of 264 and 267 Ma）,indicate that episodical volcanism occurred during Middle Permian Gudalupian and Middle Triassic Bithynian in southwestern China.The appearance of the inherited zircon ages（260～270 Ma） from the volcanic tuffs around the Permian-Triassic boundary（PTB） indicate the volcanic events in South China may have caused the End-Permian extinction.The depositional age of 247.2±1.5 Ma from the volcanic tuff at the bottom of the Middle Triassic Baifeng Formation indicates it is more appropriate to place the Early to Middle Trissic boundary at 247.2 Ma.The petrographical study of the volcanic tuffs indicates the Youjiang basin expierenced the tectonic transition from extension to compression after Middle Triassic,and especially after Bithynian,which resulted in the great tectonic subsidence of the basin.
出处
《地球科学（中国地质大学学报）》
EI
CAS
CSCD
北大核心
2012年第1期125-138,共14页
Earth Science-Journal of China University of Geosciences
基金
国家自然科学基金(Nos.40972078
40921062)
高等学校学科创新引智计划(No.B08030)
贵州省地矿局2009年度重大科研项目<水城-紫云-南丹晚古生代裂陷作用及其与主要矿产的关系>
