Abstract
This research involved the 1: 50 000 scale topographic sheets of Abra, Caraigres, Candelaria and Río Grande, covering 2 000 km2 of the central regioon of Costa Rica.
The regional basement corresponds to the Ophiolitic Complex of Nicoya, which is overlied by Tertiary rocks. In the SW ocurred turbiditic sediments (Punta Serrucho Formation) and shallow marine deposits (Punta Carballo Formation). In the Candelaria basin, the Nicoya Complex is overlied by a thick sequence that begin with limestones of the Parrillita Formation and breccias of the Caraigres Formation. A further increase of the volcanic activity originated the Pacacua Formation. The reactivitation of faults like Candelaria Fault caused the Coyolar Green Breccias. Cooling after tectonic movements started up continuos susidence during sedimentation of Peña Negra Formation and its lateral equivalent (San Miguel Formation). Another volcanic period is evidenced in the Coris, Turrúcares and La Cruz Formations.
The deformation in the Miocene-Pliocene corresponds to the arrival of the Cocos Rise to the Meso-American Trench and it resulted in the homoclinal of the Candelaria Basin at the same time that the Escazú Intrusive was arising. The post-deformation volcanism is represented by the Grifo Alto Formation. Afther that event, the north migration of the magmatic arc (Lavas Intracañón and Depósitos de Avalancha Ardiente Formations) concluded in the volcanism of the Cordillera Volcánica Central (Barva Formation) and the associated ash and mud flows that filled up the central depression named the Valle Central.