Investigating the geodynamics of the Indian plate using time-dependent mantle convection models

Abstract

The northward migration of the Indian plate after breaking apart from Pangaea in Mesozoic followed by its collision with Eurasia during Cenozoic is a remarkable example of continental drift. Associated with this tectonic drift, there are several outstanding geodynamic problems. I investigated some of those in this thesis viz, the sudden acceleration and deceleration of the Indian plate 65 Myr ago, which coincided with the timing of the Deccan flood basalt eruption, and the formation of the Indian Ocean Geoid Low (IOGL), the Earth’s lowest geoid anomaly. These anomalous geophysical phenomena are a result of convective circulation of the Earth’s mantle. In order to investigate these geodynamic problems, one needs optimized time-dependent mantle convection models. While we have knowledge of the present-day mantle structure from seismic tomography models, the mantle structure in the past is unknown. However, the Earth’s past surface tectonics (plate motions and locations) can be reconstructed using paleo-magnetic data, which can be used to drive mantle convection in the past. I used these plate reconstruction models to simulate mantle convection initiating at some time in the past and run forward in time till the present-day. At first, I explored a wide model parameter space to constrain certain physical properties of the Earth’s mantle using present-day geophysical observations of mantle structure and long-wavelength geoid. Then, I investigated the origin and evolution of the IOGL. I found that the closure of the Tethys Ocean generated an immense volume of slabs in the Indian Ocean mantle domain, which perturbed the African Large Low-Velocity province at the base of the mantle and generated plumes. These plumes eventually spread beneath the lithosphere under the Indian Ocean region, giving rise to the IOGL. The sudden velocity change of the Indian plate around 65 Myr ago was investigated using these forward mantle convection models. The results suggest that the plume push force generated by the Reunion plume accelerated the Indian plate. The timing of this acceleration could match the observed timing of peak Deccan eruption. Finally, I also investigated the consistency of different published plate reconstructions as these models become more uncertain as we go back in time due to sparse geological rock records. Using different plate reconstructions as surface velocity boundary condition, I used forward mantle convection models to predict present-day slab structures, long wavelength geoid and dynamic topography, which were then compared with observations.