A thermo-mechanical model of horizontal subduction below an overriding plate

Abstract

Subduction of young oceanic lithosphere cannot be explained by the gravitational driving mechanisms of slab pull and ridge push. This deficiency of driving forces can be overcome by obduction of an actively overriding plate, which forces the young plate either to subduct or to collide. This mechanism leads to shallow flattening of the slab as observed today under parts of the west coast of North and South America. Here this process is examined by means of numerical modeling. The convergence velocity between oceanic and continental lithospheric plates is computed from the modeling results, and the ratio of the subduction velocity over the overriding velocity is used as a diagnostic of the efficiency of the ongoing subduction process. We have investigated several factors influencing the mechanical resistance working against the subduction process. In particular, we have studied the effect of a preexisting lithospheric fault with a depth dependent shear resistance, partly decoupling the oceanic lithosphere from the overriding continent. We also investigated the lubricating effect of a 7 km thick basaltic crustal layer on the efficiency of the subduction process and found a log^linear relation between convergence rate and viscosity prefactor characterizing the strength of the oceanic crust, for a range of parameter values including values for basaltic rocks, derived from empirical data. A strong mantle fixes the subducting slab while being overridden and prevents the slab from further subduction in a Benioff style. Viscous heating lowers the coupling strength of the crustal interface between the converging plates with about half an order of magnitude and therefore contributes significantly to the subduction process. Finally, when varying the overriding velocity from 2.5 to 10 cm yr 31 , we found a non-linear increase of the subduction velocity due to the presence of non-linear mantle rheology. These results indicate that active obduction of oceanic lithosphere by an overriding continental lithosphere is a viable mechanism for shallow flat subduction over a wide range of model parameters. ß

Interplate deformation at early‐stage oblique subduction: 3‐D thermomechanical numerical modeling

“…In the following we'll discuss some processes related to the bending of the upper plate: some authors (Buiter et al, 2001;Cattin and Lyon-Caen, 1997;Hampel and Pfiffner, 2006;Heuret et al, 2007;Van Dinther et al, 2010;Van Hunen et al, 2000) propose that shortening and therefore mountain building on the overriding plate can be allowed by increasing trench-ward motion of the upper plate that causes its over-thrusting onto the slab. Uyeda and Kanamori (1979) and Heuret et al (2007) observed in fact that trenches migrate at a rate close to the overriding plate motion and the delay between the trench and the overriding plate shift generates back-arc deformation.…”

“…Some topics, such as motion and role of the upper plate (defined also "overriding plate"), or interplate coupling by thrusting, are however still poorly understood (e.g., Van Hunen et al, 2000;Lallemand et al, 2005;Heuret et al, 2007). In active subduction zones, the upper plate is strongly stressed and, in response to the motion of the subducting slab, it undergoes both short-and long-term deformation (Hoffman-Rothe et al, 2006).…”

“…Lallemand et al, 2005;Schellart et al, 2010) or by numerical, analogue, semi-analytic modelling (e.g. Boutelier and Oncken, 2010;de Franco et al, 2006;Gerya and Meilick, 2011;Jadamec et al, 2013;Regard et al, 2008;Royden and Husson, 2006;Sharples et al, 2014;Van Dinther et al 2010;Van Hunen et al, 2000;Yamato et al, 2009).…”

Future directions in subduction modeling

“…Several numerical studies have been performed to address the influence of overriding plate dynamics on subduction process (e.g., Van Hunen et al, 2000Sobolev and Babeyko, 2005;Clark et al, 2008;Gerya and Meilick, 2011). An early prominent study (Van Hunen et al, 2000 demonstrated that active horizontal movement of the overriding plate toward the subducting slab (i.e., obduction) notably flattens the subducting slab angle (Fig.…”

Implications of post-perovskite transport properties for core–mantle dynamics

“…We have solved the equations of the mass, momentum and energy conservation (for the details see e.g. van Hunen et al, 2000) using the finite element package SEPRAN (Segal and Praagman, 2005). …”