India-Asia collision and the Cenozoic slowdown of the Indian plate: Implications for the forces drivingplate motions

摘要

The plate motion of India changed dramatically between 50 and 35 Ma, with the rateof convergence between India and Asia dropping from ~15 to~4cm/yr. This changeis coincident with the onset of the India-Asia collision, and with a rearrangement of plate boundaries in the Indian Ocean. On the basis of a simple model for the forces exertedupon the edges of the plate and the fractions on the base of the plate, we performforce balance calculations for the precollision and postcollision configurations. We showthat the observed Euler poles for the Indian plate are well explained in terms of theirlocations and magnitudes if (1) the resistive force induced by mountain building in theHimalaya-Tibet area is ~5-6 x 10~(12)N/m, (2) the net force exerted upon the Indian plateby subduction zones is similar in magnitude to the ridge-push force (~2.5 x 10~(12)N/m),and (3) basal tractions exert a resisting force that is linearly proportional to the platevelocity in the hot spot reference frame. The third point implies an asthenosphericviscosity of ~2-5 x 10~(19)Pa s, assuming a thickness of 100-150 km. Synthetic Eulerpoles show that crustal thickening in the Tibetan Plateau was the dominant cause ofthe Cenozoic slowdown of the Indian plate.