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Abstract

Global Positioning System (GPS) measurements suggest the existence of a rigid Panama- Costa Rica microplate that is moving northward relative to the stable Caribbean Plate. Northward motion of South America relative to the Caribbean plate is independently suggested by the April 1991 Costa Rica earthquake, active folding in the North Panama deformed belt, and a south-dipping Wadati-Benioff zone beneath Panama. Panama may also be continuing to collide eastward with the northern Andes. Rapid subduction is occurring at the Middle America (72mm/yr), Ecuador (70mm/yr), and Colombia (50mm/yr) trenches. The northern Andes are moving northeastward relative to stable South America. Preliminary GPS results also suggest Caribbean-North Andean convergence and an independent North Nazca plate.

About 6 Ma the Panama-Choco island arc collided with the northwestern margin of South America, eventually forming a land bridge between the Americas; closed the Pacific-Caribbean seaway, changing ocean circulation patterns and perhaps the world's climate; folded the East Panama deformed belt; and uplifted the Eastern Cordillera of Colombia. An interpretation of the paleo-Romeral suture in southern Colombia as a low-angle fault dipping to the west into the lower crust under the Cordillera Occidental is compatable with seismic velocity and gravity data. During the Late Cretaceous the Western Cordillera oceanic terrain was obducted eastward on the fault system over continental crust.

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