ON THE ROLE OF UPPER MANTLE FLOW IN THE ALPINE-HIMALAYAN COLLISION

Collisional belts are generated by the arrival of continental lithosphere into a subduction zone, leading to stacking of crustal slices during indentation. The Tethyan suture from the Bitlis to the Himalayas is a prime example where the Arabian and Indian plates collided with Eurasia during the Cenozoic, generating the highest mountain belts on Earth (Argand, 1924). While the kinematics of this process are well established, its dynamics are more uncertain. India and Arabia intriguingly keep advancing in spite of large collisional resisting forces. We present results from global mantle circulation computations that allow testing the role of deep mantle flow as a driving force for the kinematics of the Tethyan collisional belt. Using high resolution models, we can evaluate different boundary conditions, such as variations in plate boundary geometry and strength, and mantle density distributions as inferred from seismic tomography or slab models. We show that mantle flow provides an explanation for much of the observed dynamic topography and microplate motion in the Mediterranean mobile belt. These models highlight intriguing links between subduction, small-scale convection and surface tectonics, with implications for other settings such as the western United States. Our results also show that mantle drag exerted on the base of the lithosphere by a large-scale upwelling rooted underneath Africa is likely the main cause for the ongoing indentation of the Indian and Arabian plates into Eurasia.