Indian continental subduction and slab break-off during Tertiary collision

P>High wavespeed seismic anomalies in the transition zone and uppermost lower mantle beneath the India-Asia collision zone, imaged by body-wave seismic tomography, have been interpreted as subducted fragments of continental material. In this study, we focus on the prominent anomaly located beneath India between depths of about 450 and 900 km. By combining the location of this anomaly with palaeogeographical positions of India, we constrain the timing of the subduction event probably related to this anomaly. We infer that a large portion of the north-western margin of India initiated subduction at 35 +/- 5 Ma along a 1500-km-long WNW-ESE striking zone and ended with a progressive slab break-off process. This break-off started most probably around 25 Ma at the western end of the slab and propagated eastwards until complete break-off around 15 Ma. This study helps to constrain better the amount of convergence between India and Asia absorbed by continental subduction.