Overriding plate controls on subduction evolution

Abstract

Geologic and geophysical observations indicate that the thickness, density, and strength of the lithosphere vary on the Earth. However, the role of the overriding plate lithosphere properties on the evolution and morphology of subduction is not well understood. This paper presents time-dependent numerical models of subduction that vary the overriding plate thickness, strength, and density and allow for a plate interface that evolves with time via an anisotropic brittle failure rheology. We examine the effect of these parameters on subduction evolution, in particular, the emergence of (a) asymmetric versus symmetric subduction, (b) trench retreat versus advance, (c) subduction zone geometry, (d) slab stagnation versus penetration into the lower mantle, and (e) flat slab subduction. Almost all of the models presented result in sustained asymmetric subduction from initiation. Trench advance occurs in models with a thick and or strong overriding plate. Slab dip, measured at a depth below the plate boundary interface, has a negative correlation with an increase in overriding plate thickness. Overriding plate thickness exerts a first-order control over slab penetration into the lower mantle, with penetration most commonly occurring in models with a thick overriding plate. Periods of flat slab subduction occur with thick, strong overriding plates producing strong plate boundary interface coupling. The results provide insight into how the overriding plate plays a role in establishing advancing and retreating subduction as well as providing an explanation for the variation of slab geometry across subduction zones on Earth, where similar patterns of evolution are observed. Show more