桂北四堡群火山岩锆石SHRIMP年龄及其地层学意义

SHRIMP age of the lava from the Sibao Group in Guilin and its chronostratigraphic significance

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。

The Sibao Group, outcropped in the north part of Guangxi and southeast part of Guizhou, is composed of over 5000 mthick 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 YuxiFormation. Sample A20140731-3 is lava, collected from the upper part of the Wentong Formation, and over 600 grains of zirconwere sorted out from it. Fifteen of the zircons were analyzed with SHRIMP, and a weighed-mean U-Pb age of(860±13)Ma wasobtained, which indicates that the volcanic rocks of the Sibao Group belong to Neoproterozoic. Based on this new zircon SHRIMPU- Pb age combined with the other high- quality ages obtained recently in the Jiangnan Orogen, the authors investigated thestratigraphic correlation between Sibao Group and the other main strata, such as Lengjiaxi Group, Shuangqiaoshan Group, andFanjingshan Group.