Planforms of self‐consistently generated plates in 3D spherical geometry

Abstract

In the past decade, several studies have documented the effectiveness of plastic yielding in causing a basic approximation of plate tectonic behavior in mantle convection models with strongly temperature dependent viscosity, strong enough to form a rigid lid in the absence of yielding. The vast majority of such research to date has been in either two‐dimensional, or three‐dimensional cartesian geometry. In the present study, mantle convection calculations are performed to investigate the planform of self‐consistent tectonic plates in three‐dimensional spherical geometry. The results are compared to those of similar calculations where a three dimensional cartesian geometry is used. We found that when yield stress of the lithosphere is low (∼20 MPa) a “great circle”‐subduction zone forms. At low‐intermediate yield stresses (∼100 MPa) plates, spreading centers and subduction zones formed and were destroyed over time. At high‐intermediate yield stresses (∼200 MPa) two plates form, separated by a great circle boundary that is a spreading centre on one side and a subduction zone on the other side. At high yield stresses (∼400 MPa) a rigid lid was observed. The great circle subduction zone and the rigid lid are stable over time while at intermediate yield stresses some episodic behavior is observed. The spherical cases showed a higher, more Earth‐like, toroidal‐poloidal ratio of the surface velocity field than the cartesian cases.