NORTH VENEZUELAN COLLISIONAL CRUSTAL BLOCK - THE BOUNDARY BETWEEN THE CARIBBEAN AND SOUTH-AMERICAN PLATES

The internal organization of the crust in the region between 66-degrees and 70-degrees-W and 7-degrees and 14-degrees-N (northern Venezuela and southern Caribbean areas) is reviewed according to a model in which a paleo-island-are collides with and is obducted over the continental shelf. The model incorporates geological and physiographical constraints and was constructed to accommodate gravimetric and magnetic data. Earthquake foci were interpreted and integrated with the latter to describe the geodynamics of the plate boundary zone. The data are interpreted as indicating dynamic coupling of the Caribbean and South American plates through an interposed crustal block: the Bonaire Block. The northern limit of this crustal block is the South Caribbean Marginal Fault (estimated convergence rate of O.7 cm/yr); the southern limit is the 100-km-wide north Venezuelan fault belt, centered about 40 km south of the central Venezuelan coastline (estimated right-lateral slip-rate of 1.5 cm/yr). The three-dimensional outline of the Bonaire Block is that of an inverted triangular prism, with an east-west axis and a vertical plane facing the Caribbean Mountains. Depths to the Moho are calculated as ranging from 38 km beneath the continent to 14 km beneath the Caribbean Sea.