Halfway to the center of the Earth, at the boundary between the core and the mantle, lies a massive folded slab of rock that once formed the ocean floor and sank beneath North America some 50 million years ago. A team of seismologists led by scientists at the University of California, Santa Cruz, detected the slab by analyzing seismic waves reflected from the deepest layer of the mantle beneath an area off the west coast of Central America.
"If you imagine cold honey pouring onto a plate, you would see ripples and folds as it piles up and spreads out, and thats what we think we are seeing at the base of the mantle," said Alex Hutko, a graduate student in Earth sciences at UCSC and first author of a paper describing the new findings in the May 18 issue of the journal Nature.
The discovery sheds new light on the processes that drive the movement of Earths tectonic plates. The planets outermost layer, or lithosphere, is broken into large, rigid plates composed of the crust and the outer layer of the mantle. New plate material is created at mid-oceanic ridges, where the ocean floor spreads apart, and old plate material is consumed in subduction zones, where one plate dives beneath another. But the fate of subducted lithosphere has been uncertain.
Tim Stephens | EurekAlert!
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