Rift-Induced Repositioning of Mantle Plumes Beneath the Indian Lithosphere: Implications for Deccan Volcanism

Indian craton comprises a number of old rifts, e.g., the Narmada, the Mahanadi and the Godavari rifts, which reactivated in multiple stages during the supercontinent breakup events. The latest reactivation of the Indian rift system occurred at the Cretaceous-Tertiary boundary when the Réunion plume interacted with the Indian plate, leading to the massive Deccan volcanism at 66 Ma. Although the plume-driven rift tectonics has been a subject of lively research over past decades, how a pre-existing rift system can modulate the plume dynamics, particularly in continental settings, remains inadequately explored. This study addresses this problem in the context of the Réunion plume encountering the Indian lithosphere. We develop 2D thermomechanical models to simulate plume-rift interactions, systematically investigating the modes of interactions as a function of plate velocity (Vp) and plume–rift (δ) distance. Our numerical experiments reveal that small δ (< 250 km) or high Vp (> 1cm/year) conditions redirect a large portion of the plume material towards the pre-existing rift, resulting in significant underplating and subsequent melting beneath the rift undergoing reactivation. Increasing δ or lowering of Vp weakens the plume-rift interaction, leaving the pre-existing rift zone almost passive, where the underplated plume materials stagnate beneath the lithosphere with little melting. The model results suggest that the Narmada rift, which was closer to the Réunion plume, caused significant deflection of the plume and its melting with Moho upwraping. In contrast, the Godavari rift, located at a larger distance from the plume, behaved passively, allowing underplating of the plume at the lithospheric base with no significant melting and Moho downwraping, as supported by geophysical observations. Finally, this study provides a new insight into the differential responses of the Indian rift system during the Reunion plume event.