Geodynamics of Long‐Term Indian Continental Subduction and Indentation at the India‐Eurasia Collision Zone

Abstract The India‐Eurasia convergence is a long‐term, ongoing process despite the continental collision and associated velocity reduction from ∼15 to 20 cm/yr in the Late Cretaceous‐earliest Eocene to ∼4–5 cm/yr (since ∼40 Ma). Previous studies that impose Indian plate motion imply an external force driving long‐term convergence, continental subduction and Indian indentation, and the onset of India‐Eurasia collision as the trigger for the abrupt deceleration. In this study, we investigate the mechanism(s) of this deceleration, continued convergence, long‐term continental subduction and long‐term Indian indentation using buoyancy‐driven geodynamic models. We conduct three large‐scale analog experiments to simulate the subduction and collision processes at the convergent boundary with different boundary conditions at the 660‐km discontinuity, including a lower‐upper mantle viscosity ratio ( η LM /η UM ) that is infinitely high, no viscosity step ( η LM /η UM = 1) and an intermediate viscosity step ( η LM /η UM = ∼8.6). The experiment with infinite η LM /η UM shows deceleration when the slab tip reaches the 660‐km discontinuity, while the other two experiments show a deceleration at the onset of continental subduction. Our experiments show that a higher η LM /η UM favors a lower velocity drop at the onset of continental subduction, lower convergence velocities, reduced continental subduction and a higher indentation amount. Furthermore, our models suggest that the negative buoyancy force of both upper and lower mantle slab segments is the main driver of long‐term convergence and continental subduction, while the combination of rollback‐induced mantle flow of the Sunda slab and slab negative and positive buoyancy forces of the Sunda and India slabs, respectively, drives northward Indian indentation.