Raising the Gangdese Mountains in southern Tibet

The surface uplift of mountain belts is in large part controlled by the effects of crustal thickening and mantle dynamic processes (e.g., lithospheric delamination or slab breakoff). Understanding the history and driving mechanism of uplift of the southern Tibetan Plateau requires accurate knowledge on crustal thickening over time. Here we determine spatial and temporal variations in crustal thickness using whole-rock La/Yb ratios of intermediate intrusive rocks from the Gangdese arc. Our results show that the crust was likely of normal thickness prior to approximately 70Ma (similar to 37km) but began to thicken locally at approximately 70-60Ma. The crust reached (58-50)10km at 55-45Ma extending over 400km along the strike of the arc. This thickening was likely due to magmatic underplating as a consequence of rollback and then breakoff of the subducting Neo-Tethyan slab. The crust attained a thickness of 6812km at approximately 20-10Ma, as a consequence of underthrusting of India and associated thrust faulting. The Gangdese Mountains in southern Tibet broadly attained an elevation of >4000m at approximately 55-45Ma as a result of isostatic surface uplift driven by crustal thickening and slab breakoff and reached their present-day elevation by 20-10Ma. Our paleoelevation estimates are consistent not only with the C-O isotope-based paleoaltimetry but also with the carbonate-clumped isotope paleothermometer, exemplifying the promise of reconstructing paleoelevation in time and space for ancient orogens through a combination of magmatic composition and Airy isostatic compensation.