Shallow subduction of the Cocos Ridge below southeastern Costa Rica (a process that was initiated ca. 5 Ma) has elevated the central segment of the Chorotega arc (the Cordillera de Talamanca) to heights over 3,500 m. Rapid uplift and associated faulting exposed the remains of volcanic arcs predating the Quaternary volcanics that dominate in the northwestern and eastern segments of the Chorotega arc. Because of extensive cover by cloud forests and generally steep topography, collection of fresh samples remains problematic. Access has become easier, however, in the last few years because of development of a network of logging roads that enabled collection along several transects. The geochemical and isotope data indicate that at least three, possibly four, phases of igneous activity occurred in the Cordillera de Talamanca. Evidence for the earliest Paleocene-early Eocene arc is provided indirectly by the volcanic contents of both the forearc (Fila Costena) and back-arc (Limon Sur) basins. Steep subduction appears to have been responsible for formation of this presently severely segmented volcanic arc. Intermediate-angle subduction gave rise to volcanics arcs in the mid-Oligocene and mid-Miocene. Igneous rocks emplaced during these periods are similar, but their contents of the element Zr differ. On chondrite-normalized spider diagram, the Oligocene intrusives display a negative, the Miocene intrusive rocks (Talamanca suite sensu stricto) a positive Zr anomaly.

Low-angle subduction characterized the Plio-Pleistocene. Associated volcanism is quite distinct from that in the Miocene and consists predominantly of intermediate to felsic magmas with geochemical signatures suggesting partial melting of a MORB source. The four volcanic phases are separated by periods of relative quiescence that correlate with periods during which the plate tectonic configuration in the east-central Pacific changed.