Thursday, March 29, 2007

Geology: The driving force of plate tectonics

London (England), 28 March: The North American plate may be driven by mantle flow and deformation at the base of the continental crust, according to a report in Nature this week. David W. Eaton and colleagues studied the surface expression of the Great Meteor hotspot track to estimate the relative motion between the surface and the underside of the plate. The results provide new insights into the driving forces of plate motion.

Hotspots — relatively-fixed locations of active volcanism deep beneath the Earth’s surface — allow scientists to track the movements of plates as they pass over them, producing lines of volcanoes. The Great Meteor hotspot is one of the longest tracks in the Atlantic and reveals the movement of the North American plate over time. The authors used seismic images, geochronology and plate-motion reconstruction to compare the location and chronology of the hotspot track at the base and top of the North American lithosphere. They found that there is a displacement between the surface and deep parts of the tracks. This misalignment increases with age along the track, and is best explained by deformation in the mantle lithosphere beneath North America. They suggest that that motion of the plate is driven, rather than impeded, by viscous traction at the base of the plate.

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