Investigating the role of mantle convection in affecting surface deformation and topography in the Indian plate and the India-Eurasia collision zone

Abstract

The India-Eurasia collision zone has been a subject of various studies that have tried to explain the forces behind the high elevation and large scale continental deformation in this region. However, the relative contribution of mantle flow in affecting the deformation in this region is not fully understood. Some studies have focused solely on contributions from topography and crustal density variations to explain deformation characteristics of this region, while others have argued that contribution from density-driven mantle flow is required to explain the kinematics of this region. In this dissertation, I investigate how the India-Eurasia collision zone and the Indian plate are affected by convecting circulation of the mantle. I build numerical models to explain topography, geoid, deformation, stress patterns and strain rates within this region. I account for contributions from two main forces in our models, forces arising from gravitational potential energy (GPE) differences due to the thickness and density variations within the lithosphere, and those due to shear tractions arising from density-driven mantle convection acting at the base of the lithosphere. The coupled models of lithosphere and mantle dynamics are found to be better in explaining various observables, such as principal stresses obtained from the World Stress Map, strain rate tensors and plate velocities, compared to a lithosphere only model. Moreover, I find that uncertainty in crustal structure, used in the computation of GPE, may lead to significant misfits with the observational constraints. I also test the importance of mantle flow within this region by investigating the link between various geophysical observations such as topography, gravity, geoid and seismic velocity anomalies. The Himalayas, which are underlain by fast velocity anomalies, show high free-air gravity anomalies along with high values of geoid-to-topography ratio (GTR), an indicator of dynamic topography. I conclude that the high values of GTR in this region arise due to the high density Indian slab in the upper mantle, rather than dynamic support from the mantle below.