Absolute plate motions and regional subduction evolution

Abstract

We investigate the influence of absolute plate motion on regional 3-D evolution of subduction using numerical thermomechanical modeling. Building on our previous work, we explore the potential impact of four different absolute plate motion frames on subduction evolution in the western Mediterranean region during the last 35 My. One frame is data-based and derived from the global moving hotspot reference frame (GMHRF) of Doubrovine et al. (2012) and three are invented frames: a motion frame in which the African plate motion is twice that in the GMHRF, and two frames in which either the African plate or the Iberian continent is assumed fixed to the mantle. The relative Africa-Iberia convergence is the same in all frames. All motion frames result in distinctly different 3-D subduction evolution showing a critical dependence of slab morphology evolution on absolute plate motion. We attribute this to slab dragging through the mantle forced by the absolute motion of the subducting plate, which causes additional viscous resistance affecting subduction evolution. We observed a strong correlation between increase in northward Africa motion and decrease in the speed of westward slab rollback along the African margin. We relate this to increased mantle resistance against slab dragging providing new insight into propagation and dynamics of subduction transform edge propagator (STEP) faults. Our results demonstrate a large sensitivity of 3-D slab evolution to the absolute motion of the subducting plate, which inversely suggests that detailed modeling of natural subduction may provide novel constraints on absolute plate motions.