Factors controlling topography at ocean-continent convergent margins using 2D numerical models

Ocean-continent subduction zones are convergent margins where the negative buoyancy of oceanic lithosphere drives its descent into the mantle, under an adjacent continental lithosphere. The process induces a variety of geologic phenomena such as mega-thrust earthquakes, volcanoes, and in some locations, the formation of mountainous topography. These mountains form due to strong coupling at the interface of the plates which induces a sufficient transfer of stress to the overriding continental plate. However, the exact mechanisms that produce this coupling are not well understood 2gmail-p1">To systematically investigate what physical features of ocean-continent subduction produce strong coupling, we use geodynamic models that account for a sediment layer coating the oceanic crust; the sediment layer is modeled as a thin layer of low viscosity material. The characteristics of the sediment layer, primarily its thickness and viscosity, influence the erosive or accretionary nature of the subduction zone and the plate interface coupling. We use the code LaMEM (Lithosphere and Mantle Evolution Model) to analyze 36 2D simulations. The model represents a 6000 by 1560 km profile of a subduction zone, and we use the "sticky-air" approach to allow for the development of topography 2gmail-p1">In order to affect changes in the degree of plate coupling, the varied physical parameters are the i) sediment thickness and viscosity, ii) continental crust viscosity and density, iii) presence of a driving velocity on the subducting plate, iv) and presence of highly viscous "strong blocks" in the continental crust to represent cratonic blocks, concentrating stress in weaker parts of the lithosphere. Preliminary results show that high amplitudes of continental topography are obtained by introducing the forcing velocity on the subducting plate and by including strong blocks. Additionally, we obtain initial evidence of distinctive topographic features depending on the sediment layers' thickness and viscosity.