Post-ridge-subduction acceleration of the Indian plate induced by slab rollback

The driving forces of plate motion, especially that of its sudden change over time, has long been debated. During the closure of an old ocean, the subduction process of the mid-ocean ridge provides valuable clues to quantitative evaluation of the driving forces of plate tectonics. Here we show that the drifting rates of the Indian plate were correlated with a Late Cretaceous adakitic event hosting abundant adakites and adakitic charnockites in the Gangdese belt, southern Tibetan Plateau. While adakites form through slab melting, the ultra-high temperatures and dry nature of charnockites indicate major disturbance of the hot asthenosphere. Temporally, the oldest adakite corresponds to the initiation of the ridge subduction, whereas the youngest adakitic charnockite marks the onset of post-ridge-subduction slab rollback (steepening). Geodynamic modeling suggests that the initiation of the ridge subduction was facilitated by the Morondova mantle plume, corresponding to the lowest drifting rate of the Indian plate. Our analyses further show that the post-ridge-subduction slab rollback pushed the asthenospheric mantle backward, meanwhile it dramatically reduced the ridge-arc interaction force, leading to the first abrupt acceleration of the Indian plate. Slab rollback contributed ∼3.5 cm/yr but lasted for only ∼5 Ma, while slab pull, ridge push together with plume contributed ∼5 cm/yr to the acceleration of the Indian plate. Our study, therefore, provides evidence for a new type of driving forces of Indian plate acceleration during the Late Cretaceous Neotethys ridge subduction.