Plates are known to undergo rather large and sudden changes in the rates and directions of their motions. The collision of the Indian and Asian plates and the change in direction of the Pacific plate, both about 40 Ma ago, are prime examples. If these changes in plate motion are not the result of changes in the deep mantle convection pattern, but rather a consequence of plate interactions, then shear flows must develop in the asthenosphere to accomodate the relative motion between the plates and deeper mantle. Alternatively, plate interactions may prevent their immediate readjustment to changes in the deep mantle convection pattern and shear flow in the asthenosphere would again be required. This paper examines the possibility that thermal expansion, due to dissipative heating in these shear flows, could produce plateau uplifts in plate interiors. We present a simple analytical model which allows us to follow the increase of temperature in the asthenosphere with time following a change in plate velocity. The production of uplifts on the order of a kilometer within a time span of 30 Ma requires velocity changes of O (10 cm/yr), creep activation enthalpies exceeding 170 kcal/mole in the asthenosphere, and a mantle temperature lower than about 1200°C. The uplifts of the Deccan and Karnataka plateaus in the Indian plate may be explained by this mechanism.
Bibliographical noteFunding Information:
This project was supported by the NSERC of Canada and by the National Science Foundation under grant EAR-77-15198. One of us (D.A.Y.) gratefully acknowledges support from the NATO Postdoctoral Fellowship Program.