Net Characteristics and Driving Forces of Plate Tectonics
Channel: Paul Wessel
Date: 2020-02-05

Dr. Clinton P. Conrad (CEED, University of Oslo, Norway) gave a guest lecture via Skype in Spring 2012 for a graduate class on Advanced Plate Tectonics in SOEST, University of Hawaii at Manoa.  The students recorded the lecture and produced video podcasts of the event.  This is one of 8 such lectures from the course which was taught by Prof. Paul Wessel.

ABSTRACT:

"Since it was first proposed in its modern form half a century ago, plate tectonics has successfully explained a wide variety of geological and geophysical data and now provides a basic framework that underpins entire subfields of the Earth and Planetary sciences. Yet, although it is clear that convection in the Earth’s mantle provides the energy to drive plate tectonics, the specific driving force that links mantle convection to surface plate motions is still debated. One reason for this continued uncertainty is that the proposed “driving forces”, which include slab pull, ridge push, and shear tractions on the base of plates, all tend to drive individual plates in the same direction, which makes constraining their relative importance difficult. However, the different driving forces do produce unique patterns of plate motions when multiple plates are considered simultaneously. To utilize this constraint, we estimated the slab pull forces and basal tractions for every plate, and used a force balance approach to predict plate motions globally. By comparing predicted to observed plate motions, we demonstrate that both basal tractions and slab pull drive the plates, a finding that places new constraints on both slab strength and asthenospheric viscosity. This intimate link between surface plate motions and mantle flow patterns is also evident in a comparison of the longest-wavelength “net characteristics” of plate motions to those of the slab pull and basal traction driving forces. This consistency that we observe for the present-day can also be extrapolated into the deep past: we can infer large-scale patterns of past mantle flow by examining the “net characteristics” of plate motions that have been reconstructed for the Cenozoic and Mesozoic. A first attempt at performing this type of “mantle flow reconstruction” reveals remarkable stability of two major upwelling regions beneath present-day Africa and the South Pacific, a finding that has also been inferred from other independent observations. This analysis demonstrates how plate tectonics continues to provide insight into the dynamics of the Earth system, particularly now that the driving link between surface tectonics and mantle convection is better understood."