Using open sidewalls for modelling self-consistent lithosphere subduction dynamics

Abstract

Abstract. Subduction modelling in regional model domains, in 2-D or 3-D, is commonly performed using closed (impermeable) vertical boundaries. Here we investigate the merits of using open boundaries for 2-D modelling of lithosphere subduction. Our experiments are focused on using open and closed (free slip) sidewalls while comparing results for two model aspect ratios of 3:1 and 6:1. Slab buoyancy driven subduction with open boundaries and free plates immediately develops into strong rollback with high trench retreat velocities and predominantly laminar asthenospheric flow. In contrast, free-slip sidewalls prove highly restrictive on subduction rollback evolution, unless the lithosphere plates are allowed to move away from the sidewalls. This initiates return flows pushing both plates toward the subduction zone speeding up subduction. Increasing the aspect ratio to 6:1 does not change the overall flow pattern when using open sidewalls but only the flow magnitude. In contrast, for freeslip boundaries, the slab evolution does change with respect to the 3:1 aspect ratio model and slab evolution does not resemble the evolution obtained with open boundaries using 6:1 aspect ratio. For models with open side boundaries, we could develop a flow-speed scaling based on energy dissipation arguments to convert between flow fields of different model aspect ratios. We have also investigated incorporating the effect of far-field generated lithosphere stress in our open boundary models. By applying realistic normal stress conditions to the strong part of the overriding plate at the sidewalls, we can transfer intraplate stress to influence subduction dynamics varying from slab roll-back, stationary subduction, to advancing subduction. The relative independence of the flow field on model aspect ratio allows for a smaller modelling domain. Open boundaries allow for subduction to evolve freely and avoid the adverse effects (e.g. forced return flows) of free-slip boundaries. We conclude that open boundaries in combination with intraplate stress conditions are to be preferred for modelling subduction evolution (rollback, stationary or advancing) using regional model domains.

Slab detachment in laterally varying subduction zones: 3-D numerical modeling

“…Due to the confined boundaries, continued convergence after detachment [Capitanio and Replumaz, 2013] is limited and dynamic effects such as plate eduction [Duretz et al, 2012b] are minimized. Further studies would benefit from the implementation of dynamic boundary conditions [e.g., Chertova et al, 2012] to circumvent that aspect.…”

Underpinning tectonic reconstructions of the western Mediterranean region with dynamic slab evolution from 3‐D numerical modeling

“…The top boundary is free slip and the bottom is no slip. To allow for slab decoupling from the top surface, a weak crustal layer is emplaced on top of the oceanic lithosphere following Chertova et al [2012]. The side boundaries are open for lateral inflow and outflow [Chertova et al, 2012], except for the top 150 km of the southern and northern parts of the domain at which kinematic boundary conditions of plate motion will be implemented.…”

Absolute plate motions and regional subduction evolution

“…The equations of mass, momentum and energy conservation and the transport equation for advection of nondiffusive material properties are solved in the extended Boussinesq approximation [Christensen and Yuen, 1984; van Hunen, 2001;Chert14]. Our models include two major phase transitions at 410 km and at 660 km in the unperturbed mantle [Cizkova et al, 2007;Chertova et al, 2012;Garel et al, 2014]. For the detailed description of these equations, we refer to Christensen and Yuen [1984].…”