Geophysics and Tectonics Seminar winter-2020

During the Cretaceous, the Indian plate moved towards Asia at some of the fastest speeds ever recorded. The details of this journey are preserved in the Indian Ocean seafloor, which document two distinct pulses of fast motion, separated by a noticeable slowdown. The nature of this rapid acceleration, followed by an equally rapid slowdown and then succeeded by second, and longer duration speed-up is puzzling to explain. Using an extensive dataset, we confirm these observations and use numerical models of subduction to show that the arrival of the Deccan mantle plume-head at ~67Ma started a sequence of events that can explain this history of plate motion. The forces applied by the plume causes initiation of an intraoceanic subduction zone, which eventually adds enough additional force to drive the plates at the anomalously fast speeds. Our models support a two-stage India-Eurasia collision sequence starting with the 'soft' collision at ~50 Ma between the purported intra-oceanic arc above the middle plate accreting onto the Eurasian margin, followed by the 'hard' collision between continental India and Eurasia as early as 43 Ma or as late as ~25-20 Ma. The Kohistan-Ladakh Arc terranes in NW Himalayas previously suggested to represent accretion of an intra-oceanic arc are a candidate, however, the western portion of Indus-Yarlung suture zone hosts a belt of Jurassic to Early Cretaceous ophiolites that include additional potential candidates such as the Xigaze ophiolite. Either way, our hypothesis supports recent interpretations that Greater India was not an extension of the Indian continent, but instead was a micro-continent separated from northern cratonic India by an ocean basin.