7. Plate Tectonic Evolution
of the Cocos-Nazca Spreading Center¹

Martin Meschede² and Udo Barckhausen³

ABSTRACT

Paleogeographic restorations for the oceanic crust formed by the Cocos-Nacza spreading center and its precursors were performed in steps of 0.5 m.y. The breakup of the Farallon plate into the Cocos and Nazca plates occurred at ~23 Ma and was followed by three subsequent spreading systems: CNS-1, ~23-19.5 Ma; CNS-2, 19.5-14.7 Ma; and CNS-3, 14.7 Ma-present. Based on the spreading history, we reconstructed the evolution and ages of submarine aseismic ridges in the Eastern Pacific Basin—the Carnegie, Coiba, Cocos, and Malpelo Ridges, which overprint oceanic crust formed at the subsequent Cocos-Nazca spreading system. The mophological bipartition of the Carnegie Ridge reflects the jump from CNS-2 to CNS-3 at 14.7 Ma and the later increasing distance of the CNS-3 spreading axis from the Galápagos hotspot. The Cocos Ridge is mainly composed of products from the Galápagos hotspot but also contains material from a suggested less productive second center of volcanic activity that is located ~600 km northeast of Galápagos. The Malpelo Ridge is a product of the second center of volcanic activity, whereas the Coiba Ridge probably formed directly at the Galápagos hotspot. The geometric relationship of the Cocos and Carnegie Ridges indicates symmetric spreading and a constant northward shift of the presently active CNS-3 system since its formation at 14.7 Ma.