The Indian Subcontinent and the Ganges Plain

The Indian subcontinent — India, Pakistan, Bangladesh, Nepal, Bhutan, and Sri Lanka — occupies a distinct tectonic plate that broke away from the supercontinent Gondwana roughly 140 million years ago and drifted northward across the Tethys Sea before colliding with the Eurasian Plate beginning around 50 million years ago, a process first modeled in detail by geophysicists Peter Molnar and Paul Tapponnier in their influential 1975 paper on continental collision and the deformation of Asia. That collision, still ongoing today, thrust up the Himalayan wall along the subcontinent's northern edge and continues to shape the region's geology. Millions of years earlier, around 66 million years ago, a separate and unrelated episode of massive volcanic activity produced the Deccan Traps, a vast field of layered basalt covering roughly 500,000 square kilometers of west-central India, an eruptive event some scientists link to the environmental stress accompanying the end-Cretaceous mass extinction. Together, the northern collision zone and the ancient volcanic plateau to the south frame two geologically very different halves of the subcontinent.