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New study explains how continents leave their roots behind

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In some areas of the seafloor, a tectonic mystery lies buried deep underground.

The ocean floor contains some of the newest rock on Earth, but underneath these young oceanic plates are large swatches of much older continents that have been dislocated from their continental plates and overtaken by the younger, denser oceanic plate.

Researchers have been puzzled by this phenomenon for some time: how does a continental plate leave some of itself behind?

In a new study published in Geophysical Research Letters, a journal of the American Geophysical Union, researchers have linked the displaced pieces of continental plates to a weak link in the plate’s layers called a mid-lithospheric discontinuity.

The crust and the upper mantle make up the lithosphere, the rigid, outer part of the Earth. A mid-lithospheric discontinuity can occur in this layer, running horizontally through the middle of the lithosphere. It is at this place where the lower layer of a continent’s lithosphere can break away from itself and dislocate, leaving behind large pieces of the lower lithosphere, called a root, which can become embedded in the oceanic plate on the trailing side of the continental plate.

The new study finds thicker and weaker mid-lithospheric discontinuity layers are more likely to leave behind roots farther from their continental origins, while thinner layers have more strength to hold onto their roots as the continental plates move, according to the new study....more

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