Geodynamics of long-term Indian continental subduction and indentation at the India-Eurasia collision zone

The ongoing convergence between India and Eurasia has been a long-term process marked by a significant reduction in convergence velocity, from about 15-20 cm/year to 4–5 cm/year about 50 million years ago. Previous studies attribute the continued convergence to external forces such as ridge push, and the slowdown to the onset of continental collision that formed the Himalaya. This study examines the reasons behind the convergence and slowdown through laboratory experiments that simulate subduction and collision at the India-Eurasia-Sunda collision-subduction zone under various conditions for the mantle viscosity. Three experiments were conducted, each with a different viscosity change at Earth's upper-lower mantle boundary. The results indicate that a very high lower mantle viscosity leads to a deceleration of the sinking slab when it reaches 660 kilometers depth. In contrast, reduced lower mantle viscosity conditions result in deceleration during the start of continental (India) subduction. Findings suggest that a higher lower mantle viscosity increases the deceleration, reduces convergence rates, and increases Asian deformation. Ultimately, the study concludes that the downward forces from the negative buoyancy of the subducting slab segments and the mantle flow triggered by the movement of the subducting slab significantly contribute to the long-term convergence and deformation.