RELATIONSHIP OF SUBDUCTION RATE AND SLAB-PULL IN THE CIRCUM-PACIFIC REALM SINCE 80MA

There is a long-standing consensus in geodynamics that slab-pull is the dominant force driving plate motions. The circum-Pacific realm is the only region where the relationship between estimates of slab-pull and plate motion-derived estimates of subduction zone length-weighted mean subduction rate can be analyzed as a function of age and subducting plate with any confidence. As a starting point it is assumed that the paleo-agegrids and plate kinematic model of Müller et al (2008 Science, 319 1357, www.earthbyte.org/Resources/palaeoagegrid2008.html) and corresponding paleo-plate polygons of Gurnis et al. (2012 Comp. & Geosci. 38 35–42) provide a reasonable representation of the evolution of the circum-Pacific realm from 80Ma to the Present. We combine these datasets to compute the length-weighted mean subduction rate, mean age of oceanic lithosphere along the subduction zone boundary, and subduction zone length to examine the relationship between subduction rate and (mean age * subduction zone length), as a proxy for the negative buoyancy of subducting slabs as a function of age for Pacific, Farallon, Nazca, Cocos, and Juan de Fuca/Vancouver plates. We focus on these plates because their paleoage reconstructions are derived from constrained extrapolation, while noting that the W and SW flanks of the Pacific Plate reflect unconstrained extrapolations (Rowley, 2008, J. Geol. 116 587-598). The results show that for the Pacific Plate there is little correlation (~0.335) between its subduction rate and (mean age*length) of subducting oceanic lithosphere. Correlations increase between these for the Farallon (0.522), Juan de Fuca/Vancouver (0.578), Cocos (0.683), and Nazca (0.895). These results imply variable contributions of slab-pull to plate motions, and implying that additional sources of buoyancy contribute to driving plates.