A Tectonic Cross-Section of the Costa Rican Pacific Littoral as a Key to the Structure of the Landward Slope of the Middle America Trench off Guatemala

Abstract

Pre-upper Senonian basement of Costa Rica crops out in the Santa Elena and Nicoya peninsulas. From south to north and from base to top the basement includes the Esperanza, Matapalo, and Santa Elena units. The Esperanza unit is Albian-Santonian in age and consists mainly of pillow basalt and massive basalt flows. The Matapalo unit includes Callovian-Cenomanian radiolarite and exhibits a massive basalt flow, pillow basalt, and dolerite basement. The Santa Elena unit contains ultramafic and mafic rocks in which harzburgite is the major component. The most important tectonic features of the Nicoya Complex are the large Santa Elena and Matapalo nappes. Nappe emplacement was from north to south during late Santonian time. The sedimentary cover of the Nicoya Complex comprises (1) the Campanian El Viejo Formation, which consists of shallow-water sediments to the north on Santa Elena Peninsula and the Campanian-Maestrichtian Sabana Grande Formation of deep-water origin to the south on Nicoya Peninsula; (2) Paleocene sediments, which indicate deposition in a deep-water environment and which comprise the Rivas, Las Palmas, and Samara formations; and (3) post-upper Eocene(?) sediments, which consist of the shallow-water Barra Honda and Montezuma formations. Two unconformities are the major geologic features of the upper Senonian-Tertiary sequence of Costa Rica. The lower one is at the base of the Sabana Grande Formation and marks a major change in the geologic conditions (basalt is scarce in the Campanian-Tertiary series); the upper unconformity at the base of the Barra Honda and Montezuma formations is not as pronounced as the lower one. During post-Campanian time, normal faulting occurred in two stages separated by a phase of strong erosion.The geology of the landward slope of the adjacent Middle America Trench is outlined in this chapter through interpretation of multifold seismic reflection records taken off the west coast of Costa Rica and from the DSDP Legs 67 and 84 transects off Guatemala. The western Caribbean Plate boundary may have been under extensional stress for the last 75 m.y. The strong landward-dipping reflectors of the landward slope of the Middle America Trench off Guatemala could be equivalent to the on-land pre-Campanian overthrusts of Costa Rica. The available data are consistent with the convergent extensional margin concept.

Costa Rica Accretionary Wedge

“…data). In contrast, other workers in the Costa Rica area interpret that the forearc is composed dominantly of ophiolite, on the basis originally of comparisons to the Guatemala forearc (Azema et al, 1985;Corrigan et al, 1990;R. von Huene, pers.…”

Three-dimensional velocity structure of the upper mantle beneath Costa Rica from a teleseismic tomography study

“…The convergent margin changes its geodynamic character from north to south, passing from a 'convergent extensional margin' in northern Costa Rica (Azema et al 1985) to a 'collisional' one in southern Costa Rica, where folding and compressional low-angle faults are predominant. The collision of the Cocos Ridge with the Caribbean Plate began in the Pliocene (Van Andel et al 1971;De Boer 1979), and evidence of the present subduction of the Cocos Ridge has been found by Giiendel et al (1984,1989 propagated from the forearc area to the back arc and offshore into the Caribbean sea, joining the North Panama Deformed Belt system (Jacob et al 1991;Gardner et al 1992).…”

“…area with thick sequences of volcaniclastic turbidites and marine sediments of Tertiary age that are partially involved in the back-arc thrusting of the Caribbean seafloor under northern Panama and southeastern Costa Rica (Case & Holcombe 1980); (6) the 'Panama Fault Zone' (PFZ), a north-south dextral transcurrent fault system which forms the boundary between the Cocos and Nazca plates. The convergent margin changes its geodynamic character from north to south, passing from a 'convergent extensional margin' in northern Costa Rica (Azema et al 1985) to a 'collisional' one in southern Costa Rica, where folding and compressional low-angle faults are predominant. The collision of the Cocos Ridge with the Caribbean Plate began in the Pliocene (Van Andel et al 1971;De Boer 1979), and evidence of the present subduction of the Cocos Ridge has been found by Giiendel et al (1984,1989).…”

Geologia de las margenes de la placa del Caribe: generalidades en Guatemala, Costa Rica, la Española y resultados preliminares del analisis de una transversal en la cordillera de la costa de Venezuela

“…3. Esquema tectónico de las penínsulas de S. Elena y Nicoya, Costa Rica (de Kuijpers, 1980;Azema et al, 1984;Gursky, 1988;Meschede et al, 1988). características de arco insular. El conjunto está intruido por magmas ácidos que afloran en voluminosos cuerpos de tonalitas.…”

“…3) se realizó una campaña regional sobre la Unidad de Santa Elena y el Complejo de Nicoya (Azema et al, 1984;Gursky, 1988;Kujpers, 1980;Meschede et al, 1988).…”