The Global Range of Temperatures on Convergent Plate Interfaces

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2021-08, Vol.22 (8), p.n/a
• Main Authors: England, Philip C., May, Dave A.
• Format: Article
• Language: English
• Subjects: analytical; Approximation; Boundaries; Carbon dioxide; Convergence; Earthquakes; Fluids; global; interface; Interfaces; Lithosphere; Mathematical models; Numerical models; Ocean floor; Oceans; Parameters; Plate boundaries; Seismic activity; Shear stress; Subduction; Subduction zones; Temperature gradients; temperatures
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2021GC009849

We 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. Plain Language Summary Convergent plate boundaries host most of Earth's great (magnitude 8 or larger) earthquakes, and conditions on those boundaries determine the degree to which sediments and fluids (in particular H2O and CO2) may be carried beyond the base of the plate boundary, where they can influence melting beneath volcanic arcs and may ultimately be transported to the deep mantle. The ability to calculate how temperatures on convergent plate boundaries respond to the parameters of subduction is a necessary precursor to understanding these processes. We present analytical expressions for temperatures on curved plate boundaries, such as those in most modern subduction zones, and show that recent claims of the inaccuracy of analytical solutions in such settings are erroneous. We use our expressions to demonstrate that the common practice of equating “warm” plate boundaries with subduction of young ocean floor, and conversely “cold” with old, is not valid. Temperature gradients along the plate interface depend most importantly upon the convergence rate and the