Termination of an ancient intra-oceanic subduction zone against the eastern margin of Gondwana

The recently imaged Southeast Indian Slab (SEIS) anomaly, presently located beneath the southern Indian Ocean, is hypothesized to be the subducted portion of an ancient, previously unrecognized intra-oceanic subduction zone that once swept across the Tethys Ocean (Simmons et al., 2015). If the hypothesis is correct, this system migrated southwest across the Tethys until it collided with the eastern margin of Gondwana at approximately 140 Ma, thus terminating subduction. Through the use of thermo-mechanical geodynamic modeling, we investigate the mechanisms of the subsequent slab breakoff following the termination of intra-oceanic subduction against a continental margin. Of particular interest is the effect on the continental material attached to the downgoing slab, namely the degree to which it is subducted beneath the overriding oceanic plate, as well as the potential for delamination of the negatively buoyant lower continental lithosphere. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-699143