A new high-resolution model for India–Capricorn motion since 20 Ma: Implications for the chrono- logy and magnitude of distributed crustal deformation in the Central Indian Basin

We use more than 5000 crossings of magnetic anomalies and fracture zones along the Carlsberg and Central Indian ridges to examine whether the onset of widespread reverse faulting at ~ 8 Ma in the Central Indian Basin was accompanied by a significant change in India–Capricorn motion, whether the onset of this faulting represented the initiation of motion between these two plates, and whether the predicted shortening since 8 Ma agrees within uncertainties with fault-related shortening estimated from marine seismic profiles. The new high-resolution plate kinematic model, which specifies India–Capricorn finite and stage rotations at 20 distinct ages since 20 Ma, predicts that motion across the equatorial Indian Ocean was extremely slow from 17.4 Ma to 8 Ma, averaging less than 1 mm yr everywhere along the plate boundary. A significant acceleration in the rate of angular rotation at 8 Ma ended the period of slow or possibly no motion and constitutes the first evidence for a significant change in India–Capricorn plate motion at this time. The change in motion at ~ 8 Ma coincided remarkably well with the onset of widespread reverse faulting in the Central Indian Basin, suggesting a cause–effect relationship. Despite evidence for the period of nearly negligible motion from 17.4 Ma to 8 Ma, motion of ~ 1–2 mm yr from 20.1 Ma to 17.4 Ma (chrons 6no-5D) is highly significant, thereby implying that the onset of faulting at ~ 8 Ma did not mark the time that India–Capricorn motion began. The total north-to-south shortening predicted by the 7.9 Ma finite rotation agrees within uncertainties with shortening estimated from faults imaged along marine seismic profiles, thereby indicating that most or all shortening of the upper crust since 8 Ma has been accommodated by faulting.