Extinct spreading on the Cocos Ridge

Using recently acquired marine magnetic data and existing magnetic and bath ymetric data sets together with ODP Leg 170 age determinations we present a revised plate tectonic model for the southern Cocos and northern Nazca pla te area. According to this model the formation of the southern Cocos plate was governed by spreading at different ridge axes with alternations between spreading ridges producing a complex magnetic anomaly pattern. In the Coco s and Malpelo ridge area we have identified two precursors of the recently active Cocos-Nacza spreading system which were active from 22.8 to 14.7 Ma, with a change in spreading direction from NW-SE to ENE-WSW at 19.5 Ma. The oceanic crust of these abandoned spreading systems was subsequently thicke ned and overprinted by hotspot volcanism that formed the Cocos and Malpelo ridges. The centre of this hotspot volcanism is about 500 km away from, but most probably related to, the Galapagos hotspot.