Utilizing Euler poles for the evaluation of plate rigidity in numerical mantle convection models

Abstract

We implement an innovative method of plate identification for the purpose of evaluating plate motion in numerical mantle convection models. Our method utilizes an existing tool,  Automatic Detection Of Plate Tectonics (ADOPT), which applies a tolerance (threshold) algorithm to elevation maps, to detect candidate plate boundaries at the surface of 3-D spherical mantle convection models. The logarithm of the strain-rate field yields a well-defined elevation map where local maxima lineations indicate spreading centres, zones of convergence, transform faults or diffuse deformation zones. For the plates found by ADOPT’s analysis, we determined rotation (Euler) poles implied by the velocities  within  the plate interiors. Subsequently, we examined the velocity field of each model plate for its agreement with rigid motion about the Euler poles.  We apply our method to snapshots taken from three previously published mantle convection calculations that appear to generate plate-like surface behaviour. Self-consistently generated model plates were obtained by combining a highly temperature-dependent viscosity with a yield stress that adds a strain-rate dependence to the viscosity, thus allowing for both intra-plate low strain-rate and weakening along tightly focussed plate boundaries. We generally identify more (and smaller) rigid plates for low yield stress or low threshold. Strong agreement of the surface velocities with rigid-body rotation around Euler poles is found for many of the plates identified; however, some plates also exhibit internal deformation. Regions that show a departure from rigidity can be decomposed into subsets of rigidly moving plates. Thus, the identification of a mantle convection model's maximally rigid plate surface may require plate boundary detection at both low and high thresholds. We suggest that as global mantle convection models superficially converge on the generation of plate boundary network similar to those observed with plate tectonics (including transform fault generation), testing for plate rigidity through the determination of Euler poles can serve as a quantitative measure of plate-like surface motion.