The Global Range of Temperatures on Convergent Plate Interfaces

Abstract

AbstractWe present accurate analytical expressions for temperatures on the upper parts of convergent plate boundaries where there are rigid plates both above and below the subduction interface. We expand on earlier formulations, which considered planar interfaces of small dip, to give expressions suitable for use on all present plate interfaces, which have both curved cross sections and maximum dips of up to 30°. We also explain the errors in studies that have asserted the inapplicability of such analytical approximations to temperatures near curved plate boundaries, or where young oceanic lithosphere is subducted. We show, by comparing these expressions with numerical solutions to the full equations, that the approximations agree with the numerical calculations to within a few percent—appreciably smaller than the uncertainties associated with the physical parameters of actual plate interfaces. The common equating of “warm” subduction interfaces with the subduction of young lithosphere, and “cold” with old lithosphere, is not valid. In the absence of dissipation, thermal gradients on the plate interface vary inversely with the product of age of the subduction ocean plate and its descent speed. Where shear stresses during slip on the plate interface exceed a ~10 MPa, the temperature gradients along the interface vary with the product of full convergence rate and shear stress during slip on the interface.