依据精确地测得的修水组凝灰岩SHRIMP锆石U-Pb年龄(824Ma±5Ma,MSWD=1.3),将修水组明确定位于双桥山群的最上部.结合“江南造山带”锆石U-Pb年龄:东部变质基底双桥山群,西部变质基底梵净山群、似盖层下江群和中部变质基底冷家溪群、似盖层板溪群的锆石SHRIMP U-Pb年龄,将双桥山群上部修水组明确地定位于“武陵运动”之下的新元古代地层.同时,首次在上覆地层马涧桥组火山凝灰碎屑岩中获得3组锆石U-Pb年龄,其中一组继承锆石(824Ma±5Ma,MSWD=1.9),反映了修水组被隆起和剥蚀的证据；而最年轻的一组锆石反映了沉积同时代的凝灰岩年龄为( 769Ma ±8Ma,MSWD=0.55).依据该年龄数据,将马涧桥组明确定位于板溪期沉积地层.该年龄对限定区域地层对比和构造演化都有重要意义.上述锆石U-Pb年龄标示了赣西北地压同样存在820Ma界面上下的新元古代地层,为江南古陆变质地层的对比提供了新的年代学数据.%Zircon dating of tuff bed in the Xiushui Formation of the Shuangqiaoshan Group has yielded an age of 824 Ma±5 Ma, with MS WD equal to 1.3, and there are three groups of zircon U-Pb ages for the Majianqiao Formation, of which, one is identical with the age of the Xiushui Formation (824Ma±5Ma, MSWD=1.9), and the youngest age is 769Ma±8Ma (MSWD=0.55). In combination with the SHRIMP U-Pb dating of the tuff bed of the Shuangqiaoshan Group in the eastern part of the Jiangnan oregen, the data of the Fanjingshan and Xiajiang groups in the western part and some ages of the Lengjiaxi and Banxi groups, the authors hold that the Shuangqiaoshan Group should belong to Neoproterozoic strata below the Willing Movement. According to the isotopic data, the Majianqiao Formation should be assigned to the sedimentary strata of the Bans stage. These ages are very important for regional strati-graphic correlation of the corresponding period and tectonic evolution. The zircon U-Pb ages mentioned above demonstrate that Neoproterozoic strata were developed around the age of 820 Ma in northwestern Jiangxi Province. The results obtained also influence the stratigraphic subdivision and correlation of the metamorphosed rocks in whole Jiangnan old land and help geologists solve the problem of geological background and ore-forming conditions of the Jiangnan orogen.
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