Provenance of the Carboniferous Clastic Rocks in the Eastern Tibetan Plateau: Insights Into the Palaeogeography and Tectonic Evolution of the Northern Margin of East Gondwana

ABSTRACT The terranes in the eastern Tibetan Plateau are regarded as the key position in reconstructing the evolutionary history of the Paleo‐Tethys Ocean and the break‐up of East Gondwana. However, the tectonic affinities of these terranes during the late Palaeozoic, as well as the position of Gondwana's northern margin at that time, remain contentious, owing principally to inadequate investigation of the provenance characteristics and tectonic setting of the constituent strata. The late Palaeozoic strata (especially Lower Carboniferous) exposed in the eastern Tibetan Plateau terranes provide crucial constraints for understanding their tectonic affinities and for more precisely defining Gondwana's northern margin during this time interval. This study presents a systematic provenance analysis of the Carboniferous strata from Kaqiong (Bangda Fm.), Zuogong (Kagong Fm.) and Qamdo (Machala Fm.) terranes in the eastern Tibetan Plateau, via new U–Pb dating of the detrital zircons. The detrital zircon U–Pb age data of Bangda Fm. yielded ages ranging from 336 to 2837 Ma with major age peaks at ~1000 Ma. The detrital zircon U–Pb age data of Kagong and Machala formations revealed obviously different age patterns, featured by predominant late Palaeozoic zircon ages (ca. 320 ~ 380 Ma), which were similar to the timing of synsedimentary magmatic arc activities. The U–Pb age spectra of the Bangda Formation are consistent with those of the lower Carboniferous in the southern Qiangtang, Lhasa and Himalaya blocks to the south. It indicates that the sediments of the Bangda Formation shared the same sources with these blocks. In contrast, the U–Pb age spectra of the Kagong and Machala formations indicate plentiful input of the late Palaeozoic zircons, which were probably derived from arc magmatic rocks distributed in the North Qiangtang, Qamdo terranes along the Longmucuo–Shuanghu–Lancangjiang suture zone. Furthermore, the differences in paleobiogeographic assemblages, stratigraphic sequence and tectonic setting of the lower Carboniferous from the Kaqiong and Zuogong–Qamdo terranes indicate the existence of an ancient ocean along the Longmucuo–Shuanghu suture zone. From this study, we infer that the Kaqiong terrane might have been located at the northern margin of East Gondwana, while Zuogong–Qamdo terranes were located at the southern margin of the Eurasia Blocks.