Slab behavior, overriding plate deformation and topography at subduction zones and the India-Eurasia collision zone: Insights from four-dimensional, buoyancy-driven, analog models

Abstract

On earth, two types of convergent plate boundaries exist, namely subduction zones and collision zones. Subduction zones are the main driver of plate tectonics through sinking of negatively buoyant oceanic lithospheric slabs in the mantle and the subduction-induced large-scale mantle flow. Collision zones form when two positively buoyant continental plates meet and collide, following a phase of subduction. Both subduction zones and collision zones cause frequent and tremendous geological activities, which cause overriding plate deformation and form large-scale topography. However, the processes of subduction and collision and the mechanisms driving the associated overriding plate deformation and topography still remain unclear. Since subduction and collision operate at large spatial and temporal scales, a useful and effective way to investigate the processes of subduction and collision is by using analog or numerical modeling. Therefore, in this PhD project, I implement four-dimensional subduction and collision experiments to investigate different subduction/collision styles and mechanisms for deforming the overriding plate and forming topography during subduction/collision. This project comprises two equally weighted parts: (1) The first part investigates the two end-member styles of subduction, namely slab rollback and slab rollover, and their effect on overriding plate deformation and topography, because little research has been conducted on the rollover subduction style, and it remains unclear how and why these different subduction styles emerge. Therefore, Chapters 2 and 3 focus on subduction styles and how the two contrasting subduction styles affect mantle flow, overriding plate deformation and topography in subduction zones. This part of the thesis demonstrates how plate length can control the subduction style, and how the subduction style affects the overriding plate differently. (2) The second part investigates the India-Eurasia collision zone, which is in places characterized by a rollover slab geometry. For this collision zone, the origin of the continuous and long-term convergence, the northward Indian indentation, the slab geometry, and the amount of continental subduction are a matter of considerable debate. Thus, Chapters 4 and 5 focus on continental collision at the India-Eurasia collision zone and how such collision affects the kinematics, the slab geometry, and the overriding plate deformation and topography. This part of the thesis demonstrates the importance of the role of surrounding convergent plate boundaries, as well as that of the lower-upper mantle viscosity ratio in driving convergence, northward indentation and continental subduction.