Seismic Refraction and Reflection in Caribbean Sea

The results of 30 seismic refraction profiles are presented in five seismic sections in the Caribbean Sea. Particular attention was given to areas of complex structure such as Tobago Island, Aves Swell, Netherlands West Indies, Los Roques and Bonaire Trenches, Curaçao Ridge, Beata Ridge, Nicaragua Rise, and Cayman Trough. Previous surveys have established that the Colombia and Venezuela Basins crustal structures consist of a 6.1 km/sec layer over a 7.2 km/sec layer, which is underlain by a mantle of normal velocity, 8.1 km/sec. This survey demonstrated that the Nicaragua Rise and Beata Ridge have a 5.4 km/sec layer overlying a 6.7 km/sec layer. Only the upper crustal layer was recorded beneath the Aves Swell and it has a velocity of 6.0 km/sec, similar to that of the basins. The Cura;ao Ridge overlies a sediment-filled trough that contains up to 14.5 km of low-and high-velocity sediments and rock. The Netherlands West Indies are underlain by material having a velocity of about 5.5 km/sec. large accumulations of sediments surround the Islands. An average nonturbidite basin sedimentary sequence includes velocities of 1.9, 2.7, and 3.9 km/sec. The reflection profiler shows two acoustically transparent beds in the Venezuela and Colombia Basins (1.9 and 2.7 km/sec layers), separated by a strong reflector representing approximately the Mesozoic-Cenozoic boundary. The surface of the layer underlying the transparent beds is a smooth coherent reflector suggestive of a sedimentary horizon. It is postulated that the Caribbean is a relict of Mesozoic Pacific crust that was emplaced between North and South America during separation from Europe and Africa. The interaction of the Caribbean plate with the circum-Caribbean lands resulted in the formation of geosynclines. The Caribbean plate subsequently has decoupled from the parent Pacific spreading system and is protected from being assimilated into the mantle by the presence of crustal sinks on both the east and west margins.