Mantle convection simulations with rheologies that generate plate-like behaviour

Abstract

A long-standing problem in geodynamics is how to incorporate surface plates in numerical models of mantle convection. Plates have usually been inserted explicitly in convection models as rigidrafts^1,2,3, as a separate rheological layer⁴,⁵ or as a high-viscosity region within weak zones^{6,7,8,9,10,11}. Plates have also been generated intrinsically through the use of a more complex (non-newtonian) rheology for the entire model¹²,¹³ but with a prescribed mantle flow. However, previous attempts to generate plates intrinsically and in a self-consistent manner (without prescribed flow) have not produced surface motions that appear plate-like^14,15,16. Here we present a three-dimensional convection model that generates plates in a self-consistent manner through the use of a rheology that is temperature and strain-rate dependent, and which incorporates the concept of a yield stress. This rheology induces a stiff layer on top of a convecting fluid, and we find that this layer breaks at sufficiently high stresses. The model produces a style of convection that contains some of the important features of plate tectonics, such as the subduction of the stiff layer and plate-like motion on the surface of the fluid mantle. However, the model also produces some non-Earth-like features, such as episodic subduction followed by the slow growth of a new stiff layer, which may be more consistent with the style of convection found on Venus.