Major Tectonic Collisions in Tropics Trigger Earth's Ice Ages

Over last 540 million years, Earth has weathered 3 major ice ages; during that period global temperatures plunged and produced extensive ice sheets and glaciers that stretched beyond the polar caps.

Scientists at MIT, University of California at Santa Barbara, and the University of California at Berkeley have identified the likely trigger for these ice ages.

In this study, the team reports that each of the last 3 major ice ages was preceded by a tropical "arc-continent collisions", tectonic pileups that occurred near the equator, in which the oceanic plates rode up over the continental plates, exposing tens of thousands of kilometers of oceanic rock to a tropical environment.

The scientists said that the heat and humidity of the tropics triggered a chemical reaction between the rocks and the atmosphere. This weathering process, occurring over millions of sq km, can pull enough carbon dioxide out of the atmosphere to cool temperatures globally and ultimately set off an ice age.

A Tropical Trigger

In 2016, Jagoutz an associate professor in MIT and his colleagues retraced the movements of two sutures that today make up the Himalayas and they found that both sutures stemmed from the same tectonic migration. 80 million years ago, the supercontinent moved north and part of the landmass was crushed against Eurasia that exposed a long line of oceanic rock and created the 1st suture; 50 million years ago, collision between the supercontinents created a 2nd  suture.

The team found that both collisions occurred in tropical zones and both preceded global atmospheric cooling events. The researchers concluded that, both sutures might have indeed secluded enough carbon dioxide to cool the atmosphere and trigger both the ice ages.

Exposing Earth's sutures

The researchers performed an extensive search to compile the locations of all suture zones, and used a computer simulation of plate tectonics to reconstruct the movement. In this way, they were able to pinpoint approx where and when each suture originally formed, and how long it stretched.

They identified 3 periods over the last 540 million years in which major sutures, of about 10,000 kilometers in length, were formed in the tropics. Each period coincided with each major 3 ice ages, in the Late Ordovician, the Permo-Carboniferous, and the Cenozoic. They found there were no ice ages or glaciations events during periods when major suture zones formed outside of the tropics.

Jagoutz notes that a major suture zone, about 10,000 kilometers, is still active today in Indonesia, and is possibly responsible for the Earth's current glacial period.

By: Aishwarya Sharma

Content: https://www.sciencedaily.com/releases/2019/03/190314151645.htm