Abstract
Characterization and tectonic implications of Mesozoic-Cenozoicoceanic assemblages of Costa Rica and Western PanamaThe Pacific face of Costa Rica and western Panama has been extensively studied because of the wide occur-rence of oceanic assemblages. In Northern Costa Rica, the Santa Elena Nappe made by ultramafic and maficassociations overthrusts the Santa Rosa Accretionary Complex. The Nicoya Complex corresponds to a pre-Campanian oceanic plateau association, cropping out in the Nicoya Peninsula and the outer Herradura Block.The 89 Ma high MgO Tortugal Komatiitic Suite corresponds to 14-km long, 1.5-km wide body, with no clearrelation with to the NicoyaComplex. The Tulín Formation (Maastrichtian to Lower Eocene) forms the mainedifice of an accreted ancient oceanic island of the Herradura Block. The Quepos Block was formed by theaccretion of a late Cretaceous-Paleocene seamount. In the Osa and Burica peninsulas, Caño Island and Golfitoarea, a series of Upper Cretaceous to Eocene accreted plateau and seamount blocks crop out. In western Pana-ma, the oceanic assemblages range from Upper Cretaceous to Miocene, and their geochemical signature showtheir oceanic plateau association. The Costa Rica and western Panama oceanic assemblages correspond to afragmentary and disrupted Jurassic to Miocene sequences with a very complicated geological and geotectonichistory. Their presence could be interpreted as a result of accretionary processes rather than tectonic erosion;despite this last process is nowadays active in the Middle American Trench. The whole picture has not beencompleted yet, but apparently, most of the igneous rocks have a geochemical signature similar to the Galapagosmantle plume. The later has been acting in pulses, or otherwise the outcropping occurrences could be part of several plateaus somehow diachronically formed in the Pacific basin.