Plate tectonics is the current consensus theory that the Earth's lithosphere is broken into fairly rigid plates, seven major plates and many smaller plates, and that convection within the underlying less rigid "asthenosphere" causes the plates (and the associated continents and crust) to move relative to each other, the movement manifested in continental drift and sea-floor spreading. The term "hot spot" (also, hotspot) refers to a long- lasting center of surface volcanism and locally high heat flow, and about 40 locations are now so labelled. Most hot spots are in ocean basins, and at points where the lithosphere has apparently upswelled, elevating the denser mantle material and creating mass anomalies. Silver et al (3 authors at 2 installations, US) report an analysis of the relative and absolute motion histories of the African Plate and South American Plate over the last 80 million years, using fracture-zone orientations, sea-floor magnetic anomalies, and the apparent motion of the African Plate with respect to the Atlantic basin hot spots Tristan da Cunha and St. Helena. The movements of the two plates are evidently correlated with an anomalous mantle upwelling. The authors suggest this flow-coupled plate interaction causally links the Andean and Alpine-Himalayan deformations that occurred about 30 million years ago.
QY: Paul G. Silver, Carnegie Inst. of Washington, Dept. Terrestrial
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