Raising the Gangdese Mountains via Subduction of Indian Continental Crust, Not Slab Breakoff, During Subduction to Collision Transition

Abstract

The tectonic evolution of the Tibetan Plateau, including the timing and magnitude of crustal thickening and surface uplift, is debated during the transition from oceanic subduction to India‐Asia collision. Previous studies of the Gangdese magmatic orogen show a ∼3–3.5 km apparent discrepancy between the elevations obtained from stable‐isotope‐based paleoaltimetry and those inferred from paleo‐crustal thickness estimates during the subduction‐collision transition. Here, we use thermo‐mechanical numerical modeling to investigate how subduction of the leading Indian continental margin influences Gangdese topography. We impose slab breakoff at prescribed depths using a viscosity‐reduction “control box” to assess its topographic effects. Our results show that a ∼25 km‐thick subducted Indian continental crust can provide sufficient buoyancy to rapidly uplift the elevation of southern Tibet to ∼4 km after initial India–Asia contact. In the imposed shallow‐breakoff scenarios (80–120 km depth), slab breakoff has only transient effects on surface elevation. This study highlights how discordant results from geochemical Mohometry and paleoaltimetry proxies may be reconciled. Mohometry‐derived elevations capture only the buoyancy of the upper‐plate crust, whereas paleoaltimetry proxies reflects the total elevation supported by deeper buoyancy, including the subducted Indian crust. Our results are consistent with a synchronous India–Asia collision, the continental nature of Greater India, and a stepwise increase in Gangdese elevation during the early Paleogene.