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This paper examines the application of the theory of plate tectonics for a specific part of the Earth’s surface: the Caribbean region. Gravity anomalies, topography, volcanoes, seismicity, and the terrestrial flow of heat are inferred to be indicators of present tectonic activity, and maps illustrating these parameters are presented herein. Examination and comparison of the maps indicate that there are large variations in parameter magnitudes along presumed plate boundaries and that different data sets in many instances suggest different locations as sites of significant tectonic activity.

Free-air gravity anomalies in the Caribbean region are among the largest in the world, ranging from −355 mgal north of Puerto Rico over the Puerto Rico Trench to greater than +200 mgal on the adjacent Greater Antilles. Although large positive and negative free-air anomalies are associated with portions of the margins of the Caribbean lithospheric plate, the interior regions of the Caribbean and Atlantic plates generally have anomalies within ±50 mgal of zero and hence are close to being in isostatic equilibrium. The Cayman Trough also is in nearly isostatic equilibrium, which is compatible with its origin by sea-floor spreading. Variations of the gravity field are interpreted to indicate that the easternmost end of Cuba, Jamaica, parts of Hispaniola, Puerto Rico, the Lesser Antilles, the Sierra Nevada de Santa Marta, the Eastern, Central, and Western Cordillera of the Colombian Andes, the Coast Range of Colombia, central Panama, and the Nicoya Peninsula of Costa Rica are sites of mass excess and are probably being uplifted. Mass deficiency in the eastern Caribbean is associated with the negative anomaly belt east of the Lesser Antilles, and the east-trending zones along the Puerto Rico Trench north of Puerto Rico and in eastern Venezuela and Trinidad. The mass deficiency east of the Lesser Antillean island arc is due to the underthrusting of the Atlantic plate beneath the arc. The east-trending zones lie away from the Caribbean plate on the other side of transform faults. It is inferred that compressive forces across the transform faults may be responsible for the east-trending negative free-air anomalies. These anomalies may result, north of the Greater Antilles, from depressed lithosphere caused by a former period of underthrusting and, in Trinidad and eastern Venezuela, from a viscoelastic downwarping of the crust. Differential motion between the North and South American plates is inferred to explain the compression across the transform faults bordering the eastern part of the Caribbean plate.

A speculative attempt at defining the present boundaries of the Caribbean plate is made within the concepts of plate tectonics. The variations in topography, gravity anomalies, seismicity, and heat flow along the borders of the Caribbean plate, as well as the lack of consistency in location of the major variations between the data sets, suggest that some degree of nonrigid deformation is important locally in the development of some of the plate boundaries. Principal areas of inconsistency are Jamaica, eastern Cuba, western and central Hispaniola, northeastern Venezuela, the Santa Marta mountains, the Isthmus of Panama, and the vicinity of Central America. The cause of the local variability in topography, gravity, seismicity, and heat flow is not well known. The curvature of the Isthmus of Panama and its structures may have formed through nonrigid northward motion of the north end of the Panama block over the Caribbean plate. Such a northward flow may have occurred in part because of subduction beneath Panama of a spreading center that had previously existed south of Panama. The subduction of thin lithosphere may have made this crust easier to deform laterally (northward).

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