Tectonics - erosion - sedimentation interactions during structural inversion: insights from fully coupled 3D numerical models

The evolution of orogens and sedimentary basins, together with associated vertical motions and thermal fields, is controlled by crustal and lithospheric thickness variations, linked to plate kinematics and rheological properties. All these factors are tightly coupled to surface processes such as erosion and sedimentation, and they are linked to climatic variations. However, understanding the distinct effects and complex interplay between tectonic and surface processes requires new, coupled approaches.

Here we present results from three-dimensional numerical models based on the thermo-mechanical code I3ELVIS, which uses finite differences and marker-in-cell methods and incorporates elasto-visco-plastic rheologies of compressible and thermally expanding/contracting rocks and parametrized partial melting, coupled to a newly developed erosion–sedimentation module. Mass is conserved between eroded and deposited material at each time step. Surface evolution is governed by advection, onshore hillslope diffusion, fluvial incision following a stream-power law, sediment diffusion from river mouths into the sea and pelagic sedimentation, and is described by

∂h/∂t + u_H ∇_H h = u_V + ∇_H(κ ∇_H h) - K Q^m Sⁿ + D

where h is the elevation, t is time, u is the velocity, H and V denotes horizontal and vertical quantities or operators, respectively, κ is diffusivity, K, m and n are stream power parameters, Q is water discharge, S is the local slope and D is a pelagic sediment source term. A node-based drainage network is built by steepest-descent flow routing, with discharge accumulated from laterally variable rainfall. Sediment delivered at river mouths is transported into the marine domain by a two-stage diffusive process, using a low diffusivity in proximal shelf environments and a higher diffusivity offshore to represent more efficient gravity-driven and pelagic redistribution.

Using this fully coupled framework, we investigate the effects of climate variability and mantle potential temperature during rifting and subsequent tectonic inversion. The models allow us to analyze strain localization, fault longevity, degrees of partial melting, and the spatial and temporal distribution of syn-tectonic sedimentary successions.