Late Cenozoic tectonic evolution of the Tengchong and Baoshan blocks, southeastern Tibetan Plateau: Insights from low-temperature thermochronology

Abstract

The southeastern Tibetan Plateau has been a key area for Cenozoic deformation and orogenic expansion during India-Asia convergence. Yet, its tectonic and exhumation histories remain inadequately understood. In addition, significant debate has focused on whether lateral growth of the plateau was controlled by continental-scale, discrete faulting and/or lower crustal flow. To address these questions for the southeastern Tibetan Plateau, we performed field mapping and low-temperature thermochronology across the Tengchong and Baoshan blocks and along the Gaoligong and Chongshan shear zones. Cooling ages and thermal history models indicate that the region experienced at least four distinct cooling phases since the Miocene: ca. 18–10 Ma, ca. 7–5 Ma, and ca. 5–2 Ma. The Early to Middle Miocene (ca. 18–10 Ma) phase is characterized by greater and more rapid cooling and thus, dominated the exhumation history of the southeastern Tibetan Plateau margin. Ca. 18–10 Ma cooling is interpreted to be associated with oblique slip along the Gaoligong shear zone. Regional cooling from ca. 15–10 Ma was likely driven by lower crustal flow. Late Miocene (ca. 7–5 Ma) cooling was restricted to areas featuring deep river incision, suggesting influences from topography and enhanced erosion. Pliocene–early Pleistocene (ca. 5–2 Ma) cooling is linked to fault activity and volcanism associated with Indian slab dynamics beneath the Myanmar subduction zone. Our results also suggest that the lateral expansion of the southeastern Tibetan Plateau was driven by both continental-scale shear and lower-crustal flow rather than a singular dynamic mechanism.