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[1] The age and origin of magmatic complexes along the Pacific Coast of Central America have important implications for the origin and tectonic evolution of this convergent plate margin. Here we present new 40 Ar/ 39 Ar laser age dates, major and trace element data, and initial Sr-Nd-Pb isotope ratios. The 124-109 Ma tholeiitic portions of the Santa Elena complex formed in a primitive island arc setting, believed to be part of the Chortis subduction zone. The geochemical similarities between the Santa Elena and Tortugal alkaline volcanic rocks suggest that Chortis block may extend south of the Hess Escarpment. The Nicoya, Herradura, Golfito, and Burica complexes and the tholeiitic Tortugal unit formed between 95 and 75 Ma and appear to be part of the Caribbean Large Igneous Province, thought to mark the initiation of the Galápagos hotspot. The Quepos and Osa complexes (65-59 Ma) represent accreted sections of an ocean island and an aseismic ridge, respectively, interpreted to reflect part of the Galápagos paleo-hotspot track. An Oligocene unconformity throughout Central America may be related to the mid-Eocene accretion of the Quepos and Osa complexes.

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We present the results of volcanological, geochemical, and geochronological studies of volcanic rocks from Malpelo Island on the Nazca plate (15.8-17.3 Ma) belonging to the Galápagos hotspot tracks, and igneous complexes (20.8-71.3 Ma) along the Pacific margin of Costa Rica and Panama. The igneous complexes consist of accreted portions of ocean island and seamount volcanoes and aseismic ridges, representing the missing (primarily subducted) history of the Galápagos hotspot. The age and geochemical data directly link the Galápagos hotspot tracks on the Pacific Ocean floor to the Caribbean large igneous province (ca. 72-95 Ma), confirming a Pacific origin for the Caribbean oceanic plateau from the Galápagos hotspot. We propose that emplacement of this oceanic plateau between the Americas and interaction of the Galápagos hotspot tracks with the Central American Arc played a fundamental role in the formation of land bridges between the Americas in Late Cretaceous-Paleocene and Pliocene-Holocene time. The land bridges allowed the exchange of terrestrial faunas (e.g., dinosaurs, mastodons, saber-tooth cats, and ground sloths) between the Americas and served as barriers for the exchange of marine organisms between the central Pacific Ocean and the Caribbean Sea and the central Atlantic Ocean.

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