Subduction of the Caribbean Plate and basement uplifts in the overriding South American Plate

Abstract

The new tectonic interpretations presented in this paper are based on geologic field mapping and gravity data supplemented by well logs, seismic profiles, and radiometric and earthquake data. The present Caribbean‐South American plate boundary is the South Caribbean marginal fault, where subduction is indicated by folding and thrusting in the deformed belt and a seismic zone that dips 30° to the southeast and terminates 200 km below the Maracaibo Basin. The Caribbean‐South American convergence rate is estimated as 1.9 ± 0.3 cm/yr on the basis of the 390‐km length of the seismic zone and a thermal equilibration time of 10 m.y. The Caribbean‐South American convergence has produced a northwest‐southeast maximum principal stress direction σ1 in the overriding South American plate. The mean σ1 direction for the Maracaibo‐Santa Marta block is 310° ± 10° based on earthquake focal mechanism determinations, and structural and gravity data. On the overriding South American plate, basement blocks have been uplifted 7–12 km in the last 10 m.y. to form the Venezuelan Andes, Sierra de Perija, and the Colombian Santa Marta massif. Crystalline basement of the Venezuelan Andes has been thrust to the northwest over Tertiary sediments on a fault dipping about 25° and extending to the mantle. In the Sierra de Perija, Mesozoic sediments have been thrust 16–26 km to the northwest over Tertiary sandstones along the Cerrejon fault. A thrust fault dipping 15° ± 10° to the southeast is consistent with field mapping, and gravity and density data. The Santa Marta massif has been uplifted 12 km in the last 10 m.y. by northwest thrusting over sediments. The basement block overthrusts of the Perijas, Venezuelan Andes, and the Santa Marta massif are Pliocene‐Pleistocene analogs for Laramide orogenic structures in the middle and southern Rocky Mountains of the United States. The nonmagmatic basement block uplifts along low‐angle thrust faults reveal horizontal compression in the overriding plate over 500 km from the convergent margin. Present‐day east northeast‐west southwest (080°) compression is indicated by earthquake focal mechanisms and strike slip motion on the Bocono fault. These earthquakes are intraplate deformation associated with east‐west (080°) Nazca‐South American convergence.