Ridge push, mantle plumes and the speed of the Indian plate

Abstract

SUMMARY The buoyancy of lithospheric slabs in subduction zones is widely thought to dominate the torques driving plate tectonics. In late Cretaceous and early Paleogene times, the Indian plate moved more rapidly over the mantle than freely subducting slabs sink within it. This signal event has been attributed to arrival of the Deccan-Rmantle plume beneath the plate, but itisunknowninwhichproportionstheplumeactedtoalterthebalanceofexistingplatedriving torques and to introduce torques of its own. Our plate kinematic analysis of the Mascarene Basin yields a detailed Indian plate motion history for the period 89-60Ma. Plate speed initially increases steadily until a pronounced acceleration in the period 68-64Ma, after which it abruptly returns to values much like those beforehand. This pattern is unlike that suggested to result from the direct introduction of driving forces by the arrival of a thermal plume at the base of the plate. A simple analysis of the gravitational force related to the Indian plate's thickening away from its boundary with the African plate suggests instead that the sudden acceleration and deceleration may be related to uplift of part of that boundary during a period when it was located over the plume head. In this instance, torques related to plate accretion and subduction may have contributed in similar proportions to drive plate motion.