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SCHUBERT, C., I.V.I.C., Caracas, Venezuela, R. ESTEVEZ, Universidad de los Andes, Merida, Venezuela, and H. G. HENNEBERG, Universidad del Zulia, Maracaibo, Venezuela

ABSTRACT: The Bocono Fault Zone, Western Venezuela

The Bocono Fault Zone, the western part of the Bocono -Moron-El Pilar Fault System of the southern Caribbean plate boundary, consists of aligned valleys, linear depressions, pull-apart basins and other morphological features, which extend for about 500 km in a N45 degrees E direction, between the Tachira depression (Venezuela-Colombia border) and the Caribbean Sea. It crosses obliquely the Cordillera de Merida and cuts across the Caribbean Mountains, two different geologic provinces of Late Tertiary-Quaternary and Late Cretaceous-Early Tertiary age, respectively. Therefore, the maximum age that can be assigned to the Bocono Fault Zone is Late Tertiary (probably Pliocene). A total maximum right-lateral offset of less than 100 km has been documented along the zone. Radiocarbon dated gla ial sediments suggest a Holocene right-lateral offset rate of 3.3 mm/a. The age of the sedimentary fill o~ the La Gonzalez pull-apart basin suggests that the 7-9 km right-lateral offset necessary to produce it took place in Middle to Late Pleistocene time. The majority of seismic events are well aligned with the main fault trace; minor events are distributed in a belt several kilometers wide. Focal depth is typically 15 km and focal mechanisms indicate an average east-west compression across the zone. Return periods of 135-460 a (Richter M = 8), 45-70 a (M = 7), and 7-15 a (M =6) have been calculated. Geodetic studies of several sites along the zone indicate compressive and right-lateral components; at Mucubaji the rate of right-lateral displacement observed is about 1 mm every 5 months 15 a of measurements).

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.