A thermochronological perspective on the morphotectonic evolution of the southeastern Tibetan Plateau

Abstract

Abstract A large part of the southeastern Tibetan Plateau (TP) is characterized by low‐relief surfaces at high elevations (>3.5 km). The origin of these landscapes and their geodynamic implications with regard to evolution of the southeastern TP has been the subject of considerable debate. Focusing on this topic, this study utilizes fission track and (U‐Th)/He thermochronology to reconstruct the thermal history of the Late Triassic Daocheng granite, on which a low‐relief high‐elevation landscape has developed. Results suggest that the plateau surface experienced widespread Late Jurassic to Early Cretaceous cooling (at a rate of ~1–2°C/Ma), followed by minimal regional cooling (~0.3°C/Ma) and Early Miocene enhanced cooling (~2–3°C/Ma) along deep valleys at the southern edge of the landscape. Given the subdued Late Jurassic to Early Cretaceous crustal deformation in the study area, we relate the coeval cooling to crustal refrigeration and exhumation triggered by northward subduction of the Meso‐Tethys Ocean along the Bangong suture. Subsequent Late Cretaceous to Cenozoic minimal cooling supports arguments for the formation of a low‐elevation landform prior to uplift of the southeastern TP. The enhanced cooling commenced at the Early Miocene (~15–22 Ma) along deep valleys and heralded the onset of river incision and surface uplift of the southeastern TP. This finding does not support previous proposals claiming that high elevations of the southeastern TP were formed in Late Miocene time resulting from lower crustal flow but rather supports a model highlighting continental subduction and extrusion along the large Tanggula‐Yushu‐Batang‐Red River fault system.