Assessing the role of convergence rate, lithospheric thickness and surface processes in affecting subduction dynamics with 2D thermo-mechanical numerical modelling

Numerical modelling is widely used to investigate subduction dynamics, but the relative contribution of different parameters, such as convergence rates, lithosphere rheology and the surface mass redistribution by surface processes, in driving the overriding plate topographic evolution and overall strain remains elusive. We investigate the behaviour of the overriding continental plate during ocean-continent subduction by an extensive parametric study on key physical parameters using a 2D fully coupled thermo-mechanical and landscape evolution numerical model.

The examined parameters include the convergence rate, different crust, mantle and thermal lithospheric thicknesses, and erosion rates, also accounting for asymmetric orographic effects. Our modelling results show that a fast convergence velocity (>5 cm/yr) and a thick sub-continental lithospheric mantle promote compression of the overriding continental plate in the initial stages of subduction, when the slab dip angle is gentle, and back-arc extension during advanced stages. Conversely, a slow convergence velocity (1 cm/yr) and a thin sub-continental lithospheric mantle promote widespread extension since the initial stages of subduction, with wide back-arc extension. However, erosion and orographic effects can drastically change the subduction dynamics and associated overriding plate strain distribution, with particular effects on the location, size and fate of continental fragmentation due to back-arc extension and rifting. This continental fragmentation may produce microcontinents whose fate can change in response to the investigated parameters. Our extensive parametric study highlights hitherto unrecognized dynamics such as erosion-induced microcontinent subduction, with strong implications for plate kinematic reconstructions and our current understanding of tectonics-climate interactions.