Sedimentation and viscosity controls on forearc highs

Abstract

Surface processes and rheology markedly influence the strain distribution and shape of orogenic wedges at their front but how they influence the wedge rear is still unclear. Here, we analyze the coupled control of sedimentation and viscosity on forearc high growth during advanced stages of subduction accretion. We use 2D thermo-mechanical finite element models constrained with data of the south Anatolian margin. Our simulations show that forearc highs grow as a thermally-activated viscosity drop in the lower crust induces ductile deformation and viscous flow. Initial viscosity and the amount of sediments in the forearc basin control non-linearly the occurrence and timing of the thermally-activated viscosity drop, and thus of the growth of the forearc high. High sedimentation rates result in thicker forearc basins that stabilize the subduction wedge and delay the onset of uplift in the forearc high. Low viscosities promote earlier onset of forearc high uplift and lead to larger morphological variability along the subduction margin. Increasing either sedimentation rate or viscosity may prevent forearc high formation entirely. Forearc highs grow without a backstop at a location set by slab geometry, and at an age set by wedge thermal state. Our models explain vertical motions in south Anatolia and in other accretionary margins, like the Lesser Antilles or Cascadia, during the formation of their broad forearc highs. Highlights2D FEM analysis of viscosity and sedimentation influence on forearc high growth.Forearc highs grow without backstop at an age set by accretionary flux and wedge thermal state.High sedimentation rates lead to thicker forearc basins and later onset of the forearc high uplift.Low viscosities lead to larger morphological variability and earlier onset of forearc high uplift.Increasing either sedimentation rate or viscosity may prevent forearc high formation entirely.