Seismic imaging revisits an old question: What drives continental drift?

Sunday 13 April 2014

Seismic imaging revisits an old question: What drives continental drift?

Science Focus

Iceland is a portion of a mid-ocean ridge, where the oceanic plates spread apart and new crust is made in between, that rises above sea level.

Howard Ignatius

Long before geologists worked out the theory of plate tectonics, there was discussion about whether Earth’s continents had moved about. The most detailed, and most famous, case was made by Alfred Wegener after the turn of the 20^th century. The best objection to his idea was that he couldn’t provide a plausible mechanism that could drive this “continental drift."

In a 1928 volume, Arthur Holmes proposed a possible answer: convection of rock in the mantle could drag the plates around. This ended up being the dominant explanation when plate tectonics was accepted. But there have since been some challengers. One alternative that could move plates is the density-driven downward sinking of oceanic plates at subduction zones, which people recognized would exert a force that pulled on the portion of the plate that was still at the surface—what’s known as “slab pull.” Once the plates are moving, they'd simply drag nearby mantle along with them.

Now, thanks to some finely detailed imaging, researchers have come up with evidence that, in at least one location, the mantle drove plate motion, rather than being swept up by it. The results will have to be confirmed at other plate boundaries, but it's a good start toward settling one of the oldest arguments in plate tectonics.

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