SHRIMP zircon U-Pb age of Yutian Group basalts in Longnan area of southern Jiangxi Province and its geological significance

The bimodal volcanic rocks of Yutian Group are located in Longnan, Baimianshi and Changpu basins along the EW-trending Sannan-Xunwu fault belt in southern Jiangxi Province. The zircon U-Pb dating yields the following results: the age of the basalt at the bottom of Yutian Group in Dongkeng basin is 194.4Ma±2.0Ma, whereas the age of the basalt at the top of Yutian Group in Changpu basin is 191.9Ma±2.2Ma. These dating results not only indicate that the age of Yutian Group belongs to the early Early Jurassic but also show that the basalt and the rhyolite have the same age, coincident with the stratigraphic sequence of the section and belonging to typical bimodal volcanic rocks. Age determinations of the bimodal volcanic rocks in Yutian Group provide the age evidence for the extension tectonic environment during the early Early Jurassic in southern Jiangxi Province. Meanwhile, the residual zircon (2571-2225Ma) exists in the basalt of Changpu basin, which also supplies the collateral evidence to the existence of the late Neo-Archean to Palaeo-Proterozoic basement in southern Jiangxi.