桂北四堡群火山岩锆石SHRIMP年龄及其地层学意义

摘要

The Sibao Group, outcropped in the north part of Guangxi and southeast part of Guizhou, is composed of over 5000 m thick succession of strongly-deformed, low-grade metamorphic volcanic rocks and terrigenous clastic rock, overlain unconformity by the Danzhou Group (Xiajiang Group). It is divided into three Formations: Jiuxiao Formation, Wentong Formation and Yuxi Formation. Sample A20140731-3 is lava, collected from the upper part of the Wentong Formation, and over 600 grains of zircon were sorted out from it. Fifteen of the zircons were analyzed with SHRIMP, and a weighed-mean U-Pb age of(860 ± 13)Ma was obtained, which indicates that the volcanic rocks of the Sibao Group belong to Neoproterozoic. Based on this new zircon SHRIMP U-Pb age combined with the other high-quality ages obtained recently in the Jiangnan Orogen, the authors investigated the stratigraphic correlation between Sibao Group and the other main strata, such as Lengjiaxi Group, Shuangqiaoshan Group, and Fanjingshan Group.%提四堡群为一套出露于桂北黔东南地区、变形强烈的浅变质、陆源碎屑岩火山岩、系，厚度大于5000 m，其下未见底，上被丹洲群（下江群相当地层）所覆盖。桂北四堡群自下而上划分为九小组、文通组和鱼西组3组。样品A20140731-3采自于文通组，岩性为灰绿色熔结火山岩，首次分选出600余粒岩浆型锆石，完成SHRIMP U-Pb定年测点15个，获得加权平均年龄（860±13）Ma。这表明四堡群主体属于新元古界，进而分析、讨论了江南造山带主要地层对比关系。