Plate bending at subduction zones: Consequences for the direction of plate motions Bruce A. Buffett ⁎ , David B. Rowley Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637 USA Received 27 November 2005; received in revised form 26 February 2006; accepted 6 March 2006 Available online 19 April 2006 Editor: S. King Abstract Bending of lithospheric plates at subduction zones is thought to be an important source of dissipation for convection in the Earth's mantle. However, the influence of bending on plate motion is uncertain. Here we use a variational description of mantle convection to show that bending strongly affects the direction of plate motion. Subduction of slabs and subsidence of oceanic lithosphere with age provide the primary driving forces. Dissipation is partitioned between plate bending and various sources of friction at plate boundaries and in the interior of the mantle due to viscous flow. We determine the poles of rotation for the Pacific and Nazca plates by requiring the net work to be stationary with respect to small changes in the direction of motion. The best fit to the observed rotation poles is obtained with an effective lithospheric viscosity of 6 × 10 22 Pa s. Bending of the Pacific plate dissipates roughly 40% of the energy released by subduction through the upper mantle. © 2006 Elsevier B.V. All rights reserved. Keywords: plate motions; mantle convection; rheology of lithosphere 1. Introduction Cold lithospheric plates impose a kinematic con- straint on the motion of the Earth's surface. The plates organize the large-scale flow in the interior [1,2], but it is unclear whether the rheology of the plates affects the dynamics of mantle convection. Recent theoretical [3,4] and experimental [5,6] studies suggest that the work required to bend the lithosphere at subduction zones constitutes a major source of dissipation for convection. Geophysical constraints on plate rheology [7,8] support this contention, but there is little direct evidence for a significant influence of bending on mantle convection. Present-day plate motions provide a clue to the role of plate bending. Cooling of the lithosphere supplies the primary source of buoyancy for convection in the mantle [9]. However, the cost of bending the lithosphere penalizes subduction of cold, thick plates because bending has a strong dependence on plate thickness. The interplay between subduction and bending influ- ences the direction of motion toward the trench, especially when the downgoing plate has a distribution of ages [10], and hence thicknesses. We search for evidence of the effect of plate bending by examining the direction of motion into subduction zones. Earth and Planetary Science Letters 245 (2006) 359 – 364 www.elsevier.com/locate/epsl ⁎ Corresponding author. Tel.: +1 773 702 8107; fax: +1 773 702 9505. E-mail address: buffett@geosci.uchicago.edu (B.A. Buffett). 0012-821X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2006.03.011