Exploring Constitutive Relationships for Plate Boundaries Using Kinematic Models as Constraints.

Given the relentless struggles of mantle convection modelers over the years to produce emergent plate-like behaviour from their computational models, it is easy to conclude that the constitutive models of the lithosphere which have been employed in the past have been overly simple. That being said, is it not rather surprising that the kinematic picture of plate tectonics is such a good description of the oceanic lithosphere ? One feature of the plate kinematic picture is that it draws an absolute distinction between the plate interiors and the plate boundaries. It also distinguishes the 3 plate boundary types and ascribes entirely different behaviour to each one. In a modeling sense, the constitutive behaviour of each of the different plate boundary types is distinct. This is no surprise since constitutive relationships describe how the nature of small scale physical processes is manifest at some significantly larger scale; mid-ocean ridges, transforms and subductions zones are themselves complex physical systems with complicated responses to the changes in the tectonic stress field. In order to improve our understanding of the constitutive behaviour of the plate boundary zones we explore some simple systems of plates / plate boundaries where the kinematic evolution is straightforward. We use such systems to examine possible constitutive rules for different plate boundary types in isolation and then in combination