PhD defence : Towards reconciling geodynamic models with kinematic reconstructions of slab sinking and plate motion

The Earth's crust deforms and experiences earthquakes, volcanoes, and the formation of geo-resources due to processes in its interior.

Geodynamical models help us understand these interactions between the deep Earth and its surface, which operate over millions to billions of years. This thesis focuses on how the Earth's mantle interacts with tectonic plate movements using new kinematic observations from plate-tectonic reconstructions based on geological data. One key observation is the sinking rates of slabs in the mantle, which show slabs slowing down from upper mantle plate speeds to lower mantle sinking rates. Our models indicate that with slab sinking rates of 10-15 mm/a, mantle motion is minimal, preserving distinct zones even after 1000 million years. We are able to compare these models by reintroducing a measure to that quantifies mixing. High-resolution reconstructions of the Indian Plate reveal rapid plate motion changes, our models show that bending of such a slab, before sinking into the lower mantle, may cause these oscillations. Plates without a slab don't stay stationary in the mantl, we show that an oceanic plate may be affected by neighboring plate motions and can trail behind faster-moving plates.

This thesis demonstrates that by aligning geodynamic models with specific plate motion observations, we can better understand the processes shaping tectonic plates and mantle motion, improving our overall understanding of the Earth's solid interior.