The role of the Zagros orogeny in slowing down Arabia-Eurasia convergence since ～5 Ma

摘要

Large topographic belts along convergent margins have been recognized with the ability to slowdown the kinematics of subduction over geologically short time periods (i.e., few Myr), because their associated gravitational spreading provides significant resistive force within the framework of plate tectonics. The record of past and present-day plate kinematics provides important constraints on the dynamics of the lithosphere, because plate-motion changes must reflect temporal changes in the balance of driving and resisting forces. Here we focus on the convergence between the Arabian and Eurasian plates, across the Zagros mountain belt. Relative motion across this plate boundary is reconstructed since 13 Ma from published paleomagnetic and geodetic data, and features a slowdown of ～30% from ～5 Ma to the present day. We employ global dynamic models of the mantle/lithosphere system to test whether the most recent uplift across the Arabia-Eurasia collision zone, including the Zagros orogeny, may induce the observed slowdown since 5 Ma. Specifically, we use constraints from the geologic record to infer past topography and quantify its influence on the convergence rate between Arabia and Eurasia. We test the sensitivity of our models to assumptions made in estimating the paleoelevation by perturbing the orogeny parameterization within reasonable ranges. Finally, we speculate on the potential effects of Tethys slab break-off, changes of the deformation style within the collision zone, and the Afar plume on the dynamics of convergence. Our results indicate that orogenic uplift across the Arabia-Eurasia collision zone played a key role in slowing down convergence since ～5 Ma.