IGNEOUS PETROGENESIS AND TECTONIC SETTING OF PLUTONIC AND VOLCANIC-ROCKS OF THE CORDILLERA DE TALAMANCA, COSTA-RICA PANAMA, CENTRAL-AMERICAN ARC

The Cordillera de Talamanca represents the largest and highest mountai n belt in Costa Rica and Panama. This study presents petrologic descri ption and petrogenetic interpretation of the plutonic and volcanic roc ks of the Talamancas. The Late Miocene Talamanca Intrusive Suite (TIS) represents one of the youngest and most extensively exposed plutonic suites associated with orogenesis in the world, Rapid uplift associate d with subduction of the Cocos Ridge (approx 5 Ma) is primarily respon sible for exposing this plutonic core to the Chorotega tectonic block. In addition, a combination of Pleistocene glacial and recent rain for est conditions have provided an efficient erosional mechanism for unro ofing the Cordillera de Talamanca and generating an eclectic mix of ge omorphological features. On the basis of petrographic, geochemical, an d geochronological information, four major lithologic groupings are ma de on igneous rocks of the Cordillera de Talamanca, which include mid- Oligocene tholeiitic gabbros, mid-Oligocene El Baru plutonic rocks, La te Miocene calc-alkaline TIS, and a Plio-Pleistocene volcanic group. T he mid-Oligocene intrusives are are igneous activity by following the initial ophiolite obduction event(s) recorded by the basement Nicoya C omplex. The next major igneous episode is represented by the TIS (17-6 Ma), which is the focus of this study. A integrated study of major an d trace element and isotopic (Nd and Sr) modeling indicates enriched) mantle source. Magmatic differentiation of the TIS was primarily a fun ction of fractional crystallization of a plagioclase-hornblende-biotit e-magnetite assemblage generating the gabbro to granite compositional variation. Estimated intensive parameters of the TIS crystallization s uggest epizonal (<1 kb) intrusion at temperatures of 805 degrees to 86 0 degrees C. Coeval (12-9 Ma) calc-alkaline dacites have been found in the Talamancas and may represent volcanism cogenetic with the TIS, su ggesting that the TIS intruded into its own volcanic ejecta. Talamanca volcanic rocks are primarily represented by Plio-Pleistocene andesite s that display geochemical characteristics consistent with derivation from a subducted oceanic crustal source, such as hot, young Cocos Ridg e material. Petrogenetic evolution of the recognized igneous suites fr om the Talamancas records the tectonic evolution of Chorotega block fr om an intraoceanic island arc to a continental arc setting.