EVOLUTION AND BIOGEOGRAPHY OF THE INDIAN PLATE SINCE THE CRETACEOUS

The evolution of the Indian plate after its breakup from Gondwana and its subsequent collision with Asia is one of the most profound, violent, and complex events in plate tectonics and geodynamics, marked by volcanism, impact and mountain building. A new model for the tectonic evolution of the Indian plate recognized a missing landmass, called Greater Somalia that occupied a position between eastern Arabia and northwestern India. Throughout most of the Cretaceous, India was separated from the rest of Gondwana, but in the latest Cretaceous it reestablished contact with Africa through Greater Somalia, allowing immigration of dinosaurs and other vertebrates from Africa and Europe. The Somalia connection solves the riddle of Indian biogeography—the lack of endemism among Indian Maastrichtian dinosaurs and other vertebrates. During its tumultuous journey for the last 145 million years, India rifted from Gondwana below the equator and traveled some 5,000 km northward across the Tethys to collide with Asia. Along its journey, it was punctured by the Rajmahal and the Deccan hotspots on its eastern and western margins during the Early and Late Cretaceous respectively, creating spectacular continental flood basalt provinces, while leaving hotspot trails on its two sides along the Indian Ocean. Between these two thermal events, the Marion hotspot initiated sea-floor spreading in the Mascarene basin around 88 Ma, resulting in the separation of Madagascar and India. About 65 million years ago, the Indian plate was severely battered by a giant asteroid on its passive western margin, creating the enormous Shiva Crater on the Mumbai Offshore Basin. The submerged Shiva crater, buried by 5 km of post-impact Tertiary sediments, is about 600 km long and 400 km wide, and is considerably larger than the Chicxulub. At the impact, the Carlsberg Ridge jumped 500 km north from the Mascarene Basin to separate the Seychelles from India. At the same time, the impact triggerered the main pulse of the of the Deccan volcanism. The interaction of impact with the Carlsberg Ridge may have generated spreading asymmetry associated with India’s sudden northward acceleration at rates more than 16 cm/year. The velocity of the Indian plate motion dropped considerably to 8 cm/year during the Eocene (50 Ma), marking the initial collision with Asia.