Platanar is a volcanic centre located in the Cordillera Central of Costa Rica. The centre is ~330 km3 composed of the slightly N-S elongated Chocosuela Caldera enclosing two stratovolcanoes: Platanar and Porvenir. Most of the complex is dominated by rocks of a calc-alkaline, basalt-andesite-dacite-rhyolite magma series. Minor alkaline rocks can be found in both the centre of the complex near Porvenir and a cinder cone field spanning the northern flank of Platanar to the alluvial fan of the Aguas Zarcas river. The nine northern cinder cones are mafic and form part of the Aguas Zarcas subunit, the two easternmost cones are shoshonitic, and the remainder containing normative nepheline, hypersthene and are more Na-rich. Rocks of this subunit are mostly classified as LIL- and LREE-enriched transitional to alkaline basalts. The alkaline magma is believed to have mixed with the magma of the Platanar pluton resulting in some unusual hybrid rock types and geochemical properties of the main calc-alkaline series. Petrography, whole rock major and trace element data, and detailed description of rock units can be found in Alvarado & Carr (1993).