Computer models help solve geologic riddle from millions of years

An international team of scientists that included USC's Meghan Miller used computer modeling to reveal, for the first time, how giant swirls form during the collision of tectonic plates.

The team's 3D models suggest a likely answer to a question that has long plagued geologists: why do long, curving mountain chains form along some subduction zones - where two tectonic plates collide, pushing one down into the mantle?

Based on the models, the researchers found that parts of the slab that is being subducted sweep around behind the collision, pushing continental material into the mountain belt.

With predictions confirmed by field observations, the 3D models show a characteristic pattern of intense localized heating, volcanic activity and fresh sediments that remained enigmatic until now.

"The new model explains why we see curved mountains near colliding plates, where material that has been scraped off of one plate and accreted on another is dragged into a curved path on the continent," Miller said.

Their research specifically looked at the ancient geologic record of Eastern Australia, but is also applicable to the Pacific Northwest of the United States, the Mediterranean, and southeast Asia. Coastal mountain ranges from Northern California up to Alaska were formed by the scraping off of fragment of the ancient Farallon plate as it subducted beneath the North American continent.

The geology of the Western Cordillera (wide mountain belts that extend along all of North America) fits the predictions of the computer model.

The research is published online in the journal Nature.