SHRIMP zircon U-Pb dating of Neoproterozoic Chencai Complex in Jiangshan-Shaoxing fault zone and its implications

A series of parametamorphic rocks, as the oldest metamorphosed basement in the Jiangshan-Shaoxing fault zone, consist of gneiss, schist and marble of medium-deep metamorphism and are in fault contact with the Shuangxiwu Group in Chencai area, Zhuji County, Zhejiang Province. Because the Chencai Group which suffered deep metamorphism and deformation is developed in the southern part of the Jiangshan-Shaoxing fault zone, most Chinese geologists assign the group to the small patch of the Cathysia Plate and make correlation with Paleoproterozoic Mayuan Group in Fujian Province or the Badu Group in Zhejiang Province and the Mesoproterozoic Tieshajie Foramtion in Jiangxi Province. Lots of zircons were collected from garnet sillimanite biotite plagiogneiss and sillimanite garnet biotite gneiss in the Xiawuzhai Formation of the Chencai Group. The zircons have a typical core, mantle and edge structure, the age of the core is usually in the range of 848~845Ma and the age of the late accretion edge is Caledonian (431Ma). According to the zircon dating of the plagioclase gneiss of the Chencai Group, the authors consider that the Chencai Group can not only be correlated with the Paleoproterozoic Mayuan Group of Fujian Province, but also with Mesoproterozoic Tieshajie Formation of Jiangxi Province. The protolith age of the Chencai Group suggests Neoproterozoic (848~845Ma), which is younger than that of the Shuangxiwu Group (905~877Ma) in the stratigraphic column and the stratigraphic division, and the age belongs to the domain of the Jiangnan Orogenic Belt. However, this age has an important significance in the correlation of metamorphosed provinces in the JiangShan-ShaoXing fault zone and the study of its tectonic evolution.