How slab age and width combine to dictate the dynamics and evolution of subduction systems: a 3-D spherical study

Abstract

Many of the factors expected to control the dynamics and evolution of Earth's subduction zones are under-explored in an Earth-like spherical geometry. Here, we simulate multi-material free-subduction of a complex rheology slab in a 3-D spherical shell domain, to investigate the effect of plate age (simulated by covarying plate thickness and density) and width on the evolution of subduction systems. We find that the first-order predictions of our spherical cases are generally consistent with existing Cartesian studies: (i) as subducting plate age increases, slabs retreat more and subduct at a shallower dip angle, due to increased bending resistance and sinking rates; and (ii) wider slabs can develop along-strike variations in trench curvature due to toroidal flow at slab edges, trending towards a 'W'-shaped trench with increasing slab width. We find, however, that these along-strike variations are restricted to older, stronger, retreating slabs:. Younger slabs that drive minimal trench motion remain relatively straight along the length of the subduction zone. We summarise our results into a regime diagram, which highlights how slab age modulates the effect of slab width, and present examples of the evolutionary history of subduction zones that are consistent with our model predictions.

The Topographic Signature of Mantle Pressure Build‐Up Beneath Subducting Plates: Insights From Spherical Subduction Models

“…Most notably, the overriding plate (OP) is neglected. This is due to resolution limitations but in line with other time‐dependent subduction models within a global domain (Chamolly & Ribe, 2021; Chen et al., 2022; Morra et al., 2009, 2012). Including an OP would reduce the rate of trench retreat relative to SP motion (Butterworth et al., 2012; Yamato et al., 2009) and shift the mantle wedge corner (and hence negative pressure associated with corner flow) to greater depth.…”

“…I use a simplified geometrical, mechanical, and rheological setup and neglect the overriding plate (cf. Chamolly & Ribe, 2021; Chen et al., 2022; Morra et al., 2012). Subduction is initiated by allowing a notch to extend to an initial depth of 150 km with a 250 km radius of curvature (Figure 1).…”

“…I therefore turn to numerical models of subduction to isolate the nature of this sub‐SP positive pressure build‐up and the resultant DT, in order to assess its global relevance to oceanic topography and hence guide future observational studies. Time‐dependent subduction models within a global domain models are relatively rare (Chamolly & Ribe, 2021; Chen et al., 2022; Morra et al., 2009, 2012; Quevedo et al., 2013), due to computational challenges, but enable us to incorporate a lower mantle, examine an Earth‐like range of plate sizes, and avoid lateral boundary effects. After characterizing the dependence of sub‐SP pressure and DT on subduction properties, I search for the modeled topography signal within Holdt et al.…”

How Slab Age and Width Combine to Dictate the Dynamics and Evolution of Subduction Systems: A 3‐D Spherical Study

“…(2021). The input files required to reproduce the simulations presented herein have also been made available at Chen (2022). Figures have been prepared using Matplotlib, Cartopy, and Paraview.…”

Comparing the Dynamics of Free Subduction in Cartesian and Spherical Domains

“…The subducting lithosphere comprises a 2,200 km‐long composite plate of constant initial thickness ( h = 70 km) with a core isoviscous layer ( h c = 30 km) embedded in upper and lower visco‐plastic layers with viscosities that follow a von Mises law, consistent with the reference plate in Chen et al. (2022). Upper and lower visco‐plastic layers approximate the strain‐rate weakening that occurs above and below the slab core in thermo‐mechanical simulations of subduction (e.g., Garel et al., 2014), following OzBench et al.…”