Reconstructing Early Cenozoic Paleodrainage and Tectonic Evolution in the Southeastern Tibetan Plateau: Evidence From Detrital Zircon and Tourmaline Provenance

The Paleogene sedimentary basins of southeastern Tibet record sediment dispersal patterns associated with crustal deformation during the early stages of the India–Asia collision. We present detrital zircon U–Pb geochronology, tourmaline geochemistry, and petrographic data from the Gonjo and Mangkang basins that suggest a reginal interconnected paleodrainage during the Paleocene–Eocene. Sediments were likely sourced from the distal Songpan–Ganzi and proximal northern Qiangtang terranes. Stratigraphic relationships and paleoelevation estimates support the interpretation of a paleodrainage system that may have extended toward the Lanping–Simao region and northern Vietnam. This system appears to have been disrupted in the late Eocene, possibly due to sinistral shearing along the Ailao Shan–Red River fault zone. These findings offer new insights into sediment routing and landscape evolution along the southeastern margin of the Tibetan Plateau during the early Cenozoic.