Tectonic-Igneous Sequence in Costa Rica

Abstract

Costa Rica forms a large part of the Southern Central American orogen, a mountain system that links Nuclear Central America with northern South America and resulted from intensive diastrophic and igneous activity since the middle of the Cretaceous. It provides, therefore, an excellent ground for studying relationships between igneous activity and tectonic events. The igneous-tectonic sequence is outlined as follows: A prototectonic phase started with the formation of a volcanic island arc during Jurassic or Early Cretaceous time, resulting in a complex association of igneous and sedimentary rocks. The sedimentary rocks are characterized by graywackes, cherts, and siliceous limestones. The igneous rocks belong to the ophiolitic suite and are mostly spilitic basalts, gabbroic intrusive rocks, and serpentinized peridotite. The peridotite was emplaced along a fault zone continuous with the Clipperton fracture zone of tne Pacific Ocean during early deformational stages, prior to deposition of Late Cretaceous marine sediments. An orogenic phase began during Late Cretaceous time with upwarping of the axis of the orogen and eastward shifting of the main depositional area, forming a basin on the eastern, concave side of the arc. Orogenic movements continued during the Eocene epoch, contemporaneously with volcanic activity which was mostly andesitic. The climax of the orogenic phase, in Miocene time, was accompanied by granodiorite-type intrusions along the axial area of the orogen. Late orogenic stages during late Miocene and Pliocene times were marked by basalt-andesite volcanic activity and by basalt dikes. A post-tectonic phase from late Pliocene to Recent time was marked by general uplift, normal faulting, and calc-alkalic volcanism along the central part of the orogen. The orogen was developed along an unstable margin of an intermediate-type crust; this accounts for the kinds of igneous rocks. The tectonic-igneous history of the Southern Central American orogen resembles that of the Sunda Mountain system of Indonesia.