Computer models reveal the impact of continental collisions

An international research project has uncovered new evidence about the formation of Earth. The study is the result of more than 10 years’ work by scientists from Monash University, The University of Melbourne, the University of Southern California and the Geological Survey of Victoria, and has been published in the journal Nature.

For years, experts have known that the movement of tectonic plates caused continents to collide. Subduction zones, where one plate dives under another, become clogged when they try to swallow crust that is thicker and less dense than normal oceanic crust. The arrival of such ‘exotic terranes’ at subduction zones, and their accretion onto the overriding plate, is one of the main mechanisms of lateral continental growth. The remnants of this process - great mountain belts known as accretionary orogens - have been identified from all stages of Earth history.

The collisions have resulted in some of the world’s most stunning landscapes, whose diverse varieties of rock have baffled scientists. There has also been little detailed understanding of how accretionary margins recover their stability after the incorporation of an exotic terrane. The study reveals the impact of these collisions and how evidence of the events can be preserved largely intact in the Earth’s crust for millions of years.

Professor Louis Moresi, leader of the study, said the team used three-dimensional computer models of the arrival of a slice of buoyant crust at a subduction zone to show how the geometry of the system evolves to accommodate the incorporation of new crustal material and re-establish a stable plate boundary. The model provided an accelerated simulation of synthetic rocks behaving in a digital Earth. It indicated that rocks caught in collisions were swept in a huge arcing path, where they were stretched, rotated and dragged hundreds of kilometres from their original location - a process called subduction roll back.

The computer modelling matched over 20 years of geological mapping and geophysical data interpretation in eastern Australia gathered by a team of experts from the Geological Survey of Victoria. The region surveyed had embedded blocks of older continental crust, suggesting a collision took place in Australia between 380 and 450 million years ago.

“Not only did we have a substantial volume of geological data, but we also had access to comprehensive geophysical datasets and the sweeping vision of the computer models, which undoubtedly helped us to gain greater insights into the creation of some of Australia’s distinctive geology,” Professor Moresi said. 

The results of the study may lead to significant new insights into regions where data is incomplete, such as ancient, deeply buried geological material beneath the Antarctic and Africa, and in regions such as the Himalayas, North America, Australia and South-East Asia, where vast volumes of new crust has accumulated over the last 500 million years. Professor Moresi said the team also aims to analyse sites of more recent collisions, such as Alaska.

“We know there’s a block of rock in this region that’s being pulled into the subduction zone right now,” he said, “and that’s very exciting for us.”