Reconciling plate kinematic and seismic estimates of lithospheric convergence in the central Indian Ocean

Abstract

The far-field signature of the India-Asia collision and history of uplift in Tibet are recorded by sediment input into the Indian Ocean and the strain accumulation history across the diffuse plate boundary between the Indian and Capricorn plates. We describe the history of India-Capricorn convergence from updated estimates of India-Somalia-Capricorn plate rotations and observations derived from seismic reflection data. New India-Capricorn plate rotations for the past 20 m.y. are consistent with slow north-south convergence from 18 Ma about a stationary or nearly stationary pole near the eastern edge of the Chagos-Laccadive ridge, simpler than predicted by previous models based on many fewer data. The new rotations suggest that convergence began between 18 and 14 Ma, consistent with marine seismic evidence for an onset of deformation at 15.4–13.9 Ma. They further show that convergence rates doubled at 8 Ma, in agreement with a sharp increase in fault activity at 8–7.5 Ma seen on seismic reflection profiles. A discrepancy between the total strain estimated from kinematic and seismic reflection data can be reconciled if pervasive reverse faulting within the diffuse plate boundary is accompanied by block rotations of 1°–3°.