The conventional view of subduction -- in which Earth's crust is pushed down into the planet's interior in the convergence of tectonic plates -- is that it happens only once and in one direction, Daniela Rubatto at the Australian National University Research School of Earth Sciences says.

"The typical idea is that the convergence of plates creates a force that pushes rocks down from the surface of the Earth making the whole system move down like a conveyor belt," she says. "Most of the material will sink forever in the planet's mantle and only a fraction will make it back to the surface."

Rubatto and colleagues at the University of Bern and University of Torino say that's not necessarily the case, PhysOrg.com reported Monday.

"However, we have now determined that the Earth's crust is pushed down from the planet's surface to a depth of 60 to 100 km (40 to 60 miles), comes back towards the Earth's surface, is pushed down again and then finally ends up back on the surface where it becomes part of mountain belts."

Within a subduction zone, Rubatto says, "individual rock units move independently, faster and in a more complex way: they go down and up and down again and up again, like a yo-yo."

Rubatto compares the findings of subduction movement to having a flight recorder giving details of an airliner's route.

"So far we have known where the plane started, that it had a stopover, and finally landed at its destination," she says. "Now we can read the actual route of the plane, how fast it went, and how long it took -- and find out that it went to a destination twice."

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New theory of Tibet geology put forward
Pasadena, Calif. (UPI) Apr 6, 2011
U.S. researchers say they have a new theory of the geology underlying the Tibetan plateau, long thought to be floating on a hot crust moving like a liquid. "The idea that Tibet is more or less floating on a layer of partially molten crust is accepted in the research community," Jean-Philippe Avouac, professor of geology at the California Institute of Technology said. "Our research propo ... read more