Detrital zircon U–Pb geochronological and sedimentological study of the Simao Basin, Yunnan: Implications for the Early Cenozoic evolution of the Red River

Abstract

The paleo-Red River is suggested to have been a continental-scale drainage system connecting the Tibetan Plateau to the South China Sea. However, the evolution of the paleo-Red River is still under debate. This study presents new results from sedimentological analyses and detrital zircon U–Pb geochronologic data from fluvial sedimentary rocks of Paleocene to Oligocene age of the Simao Basin to constrain the nature of the paleo-drainage system of the Red River. The detrital zircon U–Pb results reveal multiple age groups at 190–240 Ma, 260–280 Ma, 450–540 Ma, 1700–1900 Ma and 2400–2600 Ma for the Paleocene to late Eocene Denghei Formation (Fm.), but only one conspicuous peak at 220–240 Ma for the late Eocene–Oligocene Mengla Fm. Provenance analyses illustrate that the former likely had source areas that included the Hoh-Xil, Songpan-Ganzi, northern Qiangtang, Yidun and western Yangtze Terranes, which are consistent with the catchments of the Upper and Lower Jinshajiang Segments, whereas the latter mainly transported material from a limited number of sources, such as the Lincang granitic intrusions west of the Simao Basin. Integrated with available detrital zircon U–Pb geochronologic and paleogeographic data, our study suggests the existence of a paleo-Red River during the Paleocene to late Eocene that was truncated and lost its northern sources after approximately 35 Ma, due to left-lateral strike-slip faulting of the Ailao Shan–Red River and clockwise rotation of the Lanping–Simao Terrane.