The surface response to two episodes of lithosphere underthrusting and detachment during Tibetan Plateau growth

Interactions between orogenic plateau growth and environmental change, which play a key role in shaping Earth, are most pronounced in the Tibetan Plateau, affording the opportunity to explore how tectonics is coupled to surface processes during plateau uplift. The Linzhou and Wuyu depocenters of the regional intermontane basin in the Gangdese arc record a similar paleodrainage and surface evolution at ca. 60−48 Ma and 31−0 Ma, respectively, as detected by detrital zircon and apatite provenance analysis. A switch in detrital zircon and apatite populations from old and complex (polycyclic) to predominantly post−70 Ma sources in both sections highlights a decrease in sediment supply from external sources, likely caused by high-relief topography arising from surface uplift blocking distal headwaters. Abundant syndepositional zircon and apatite document rapid exhumation at ca. 54−51 Ma and 15−8 Ma, respectively, followed by a return to old (pre−70 Ma) sources with polycyclic zircon implying reactivated distal headwaters due to subsidence. The similar surface uplift and subsidence histories of the two locations in the Gangdese arc basin can be best explained by detachment of the Neo-Tethyan oceanic slab and Indian continental lithosphere, respectively, consistent with crustal thinning documented by Eu anomalies in detrital zircon. Lithospheric foundering led to asthenospheric upwelling and removed downward slab pull beneath Lhasa, triggering magmatism and uplift followed by surface subsidence linked to ongoing underthrusting. Consequently, two similar episodes of paleoelevation variations resulted from these two phases of lithospheric detachment.