Anomalously fast convergence of India and Eurasia caused by double subduction

Before its collision with Eurasia(1-5), the Indian Plate moved rapidly, at rates exceeding 140 mm yr(-1) for a period of 20 million years(1,3-7). This motion is 50 to 100% faster than the maximum sustained rate of convergence of the main tectonic plates today(8). The cause of such high rates of convergence is unclear and not reproduced by numerical models(9,10). Here we show that existing geological data(11,12) support the existence of two, almost parallel, northward dipping subduction zones between the Indian and Eurasian plates, during the Early Cretaceous period. We use a quantitative model to show that the combined pull of two subducting slabs can generate anomalously rapid convergence between India and Eurasia. Furthermore, in our simulations a reduction in length of the southern subduction system, from about 10,000 to 3,000 km between 90 and 80 million years ago, reduced the viscous pressure between the subducting slabs and created a threefold increase in plate convergence rate between 80 and 65 million years ago. Rapid convergence ended 50 million years ago, when the Indian Plate collided with the southern subduction system. Collision of India with Eurasia and the northern subduction system had little effect on plate convergence rates before 40 million years ago. We conclude that the number and geometry of subduction systems has a strong influence on plate migration rates.