Multiple stages of India-Eurasia collision

A volcanic island chain existed in the Neotethys Ocean before the continental collision between India and Eurasia. Constraining the tectonic motion of this volcanic arc is important to understand the sequence of tectonic events that proceeded the formation of the Himalaya. It is also important for understanding the forces driving the rapid motion of India in the Cretaceous and the mechanisms controlling global climate changes in the Cenozoic.

To answer these questions, we measured the magnetic records preserved in the Khardung volcanics, a suite of rhyolitic volcanic rocks in Ladakh, NW India. We also used the radioactive decay of uranium to lead inside zircon crystals to precisely measure the age of the eruptions. Our paleomagnetic results show that the volcanics were erupted at a latitude close to the equator, a long way south of the Eurasian margin, between 61.6 and 66.1 million years ago.

The equatorial position of the Khardung volcanics suggests that there was a second subduction zone between India and Eurasia in the lead-up to the continental collision. The combined slab-pull force of the two subcuction zones caused India to move northward rapidly in the Cretaceous. The two stages of collision between India, the Kohistan-Ladakh arc, and Eurasia uplifted mafic rocks to the surface, where they were then exposed to chemical weathering. This chemical process drew CO2 out of the atmosphere and into the ocean sediments and caused a cooling trend in global climate.

Paleomagnetic data from Khardung Volcanics rhyolite flows.

The paleolatitude of the Kohistan-Ladakh arc suggests that the India-Eurasia collision was a multi-stage process involving at least two subduction systems.