Zircon U-Pb age and metamorphic age of biotite monzogneiss from the Jitang Group, eastern Tibet

The attribution of the metamorphic basement age of the Jitang Group in eastern Tibet has been controversial. Here we report the results of detrital zircon U-Pb dating for the Duoqionggou biotite monzogneiss in the Jitang Group from the Jitang area, Chaya County, eastern Tibet, and compared with the northwest Jitang Group in the Leiwuqi area. LA-ICP-MS zircon U-Pb dating results indicate that the maximum depositional time of biotite monzogneiss in the Jitang Group is no earlier than 566±9.5 Ma and is of the Late Neoproterozoic. The protolith of biotite monzogneiss is paragneiss, and the detrital materials are probably derived from the Archean to Neoproterozoic granitic rocks and felsic volcanic rocks. By comparison, the Jitang Group in the Jitang area is similar to the Jitang Group in the Leiwuqi area in material composition. The orthogneiss unit of the latter belongs to a product of magmatism of the Variscan-Indosinian period, and instead of being part of the crystalline basement of the Jitang Group.Combined with existing data, we propose that the protoliths of the Jitang Group underwent five periods of tectono-thermal events after diagenesis, with peak metamorphic ages of ca. 427 Ma, ca. 377~359 Ma, ca. 308~273 Ma, ca. 255~252 Ma, and ca. 226~203 Ma, respectively, of which the magmatic activity at ca. 226~203 Ma may have resulted in the remelting of the Jitang Group.