Subduction
The onset of subduction of the Carnegie Ridge beneath the South American Plate has been dated variously from about mid-Miocene (15 Ma) to about Pleistocene (2 Ma). Although there is agreement that the ridge is currently being subducted, there is little agreement on the effect that this has had on either the subducting or over-riding plates. Some models argue that the buoyancy associated with the thickened crust of the ridge has caused the downgoing Nazca Plate to tear, leaving a relatively flat section carrying the ridge, flanked by two sections with steeper dip. The presence of a flat section is not supported by a more recent study of earthquake hypocenters, which found a constant dip of about 25°–35° down to 200 km.
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