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Ancient debris key to Earth’s secrets

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An international team of researchers, led by scientists from Monash University, has uncovered new evidence about the formation of Earth.

For years experts have known that the movement of tectonic plates caused continents to collide, resulting in a massive build-up of assorted geological ‘debris’, including great mountain belts and ranges. The collisions, which occurred millions of years ago, and some which are still happening today, have resulted in some of the world’s most stunning landscapes – which contain diverse varieties of rock, baffling scientists until now.

The major new study, published today in Nature, 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. Led by Professor Louis Moresi, The Dynamics of Continental Accretion, reveals for the first time the impact of these collisions, and crucially, how evidence of these events can be preserved largely intact in the Earth’s crust for millions of years.

The results may lead to significant new insights into regions where data is incomplete. This includes 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.

According to Professor Moresi, geologists are accustomed to finding unusual material mashed up in ancient mountain belts – what wasn’t certain is how this happened.

“Classical geology focused on examining old rocks formed millions or sometimes billions of years ago, in an attempt to piece information together. Through vastly improved computer power now available, an exciting new avenue has opened up for us,” said Professor Moresi.

The team combined advanced computer models with classical geological practices to gain new insights into rock sequences in eastern Australia. The computer model gave scientists an accelerated simulation of synthetic rocks behaving in a digital Earth. This 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.

“Traditional geological studies, examines minuscule fractions of the rock record, piecing this together to get the bigger picture. Our research differs as 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 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.

Professor Moresi said the team aim to use the research to analyse sites of more recent collisions.

“We hope that the insights we have gained can be applied to younger 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, and that’s very exciting for us,” Professor Moresi said.

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