中文摘要：

根据黔东地区梵净山群回香坪组第6段凝灰岩SHRIMP锆石U-Pb年龄（840Ma±5Ma）,结合下江群芙蓉坝组碎屑锆石年龄谱系及下江群新寨组（板溪群马底驿组）凝灰岩SHRIMP锆石U-Pb年龄（813.5Ma±9.6Ma）,将其与广西四堡群和丹州群凝灰岩年龄进行对比。梵净山群回香坪组年龄与四堡群鱼西组凝灰岩年龄一致,2个地区均发育早期基性岩和枕状熔岩、晚期浅色花岗岩。该事件的精确定年对江南造山带西南端构造演化将有重要的地质意义。依据江南古陆新元古代低变质绿片岩的最新锆石U-Pb年龄,梵净山群（贵州）、四堡群（广西）、冷家溪群（湖南）、双桥山群（江西）与仓溪岩群（湖南）、宜丰岩群（江西）、张村群（江西）,甚至与双溪坞群（浙西）在沉积年代上有一定的时间差,而上覆贵州下江群甲路组（814Ma）、广西丹州群合桐组（802Ma）、湖南板溪群张家湾组（802Ma）、江西登山群邓家组（766Ma）和浙江河上镇群骆家门组（791Ma）沉积起点的时间也不一致,但是两者之间均为角度不整合接触,反映出明显的造山事件。研究认为,不断地获得精确的地层年代数据将影响整个江南古陆变质基底的地层对比,并制约江南造山带的地质背景和成矿条件。

英文摘要：

Zircon dating（840Ma±5Ma） of tuff bedding is reported for the first time for the sixth member of the Huixiangping Formation in the Fanjingshan Group. The SHRIMP U-Pb dating of detrital zircon of the Furongba Formation is combined with tuff zircon dating（813.5Ma±9.6Ma） of the Xinzhai Formation in Xiajia Groups in Guizhou and Hunan Provinces, and also with the dating of the Sibao and Danzhou Groups in Guangxi. The tuff zircon age of the Huixiangping Formation in Fanjingshan Group is the same as the age of the Yuxi Formation of the Sibao Group, which intruded into early basic dykes and lava pillow in both groups, and developed late granite. It is very important to conduct the accurate dating of the events for the tectonic evolution in the southwest part of the Jiangnan orogenic belt. According to zircon U-Pb dating of lower metamorphosed rocks in the Jiangnan orogenic belt, there exist certain time differences for sedimentation between Fangjingshan Group, Sibao Group, Lengjiaxi Group, Shuangqiaoshan Group,Cangxi Rock Group, Yifeng Rock Group, Zhangcun Group and Shuangxiwu Group. Even the overlying strata have different ages,such as the Jialu Formation（814Ma） of the Xiajiang Group in Guizhou, the Hetong Formation（802Ma） of the Danzhou Group in Guahgxi, the Zhagnjiawan Formation（802Ma） of the Benxi Group in Hunan, the Dengjia Formation（766Ma） of the Dengshan Group in Jiangxi, and the Luojiamen Formation（791Ma） of the Heshangzheng Group in Zhejiang; there exists an angler unconformity between them, suggesting the existence of obvious orogenic event between the two tectonic horizons. The authors thus consider that the obtaining of more qualified chronostratigraphic U-Pb data will considerably influence the stratigraphic subdivision and correlation of the metamorphosed rocks in whole Jiangnan continent and restrict the geological background and metallogenic conditions of the Jiangnan orogen.