Plate tectonics of the Northeastern Caribbean sea region

Abstract

Previous geologic literature and the results of the Puerto Rico Seismic Network are synthesized into a plate tectonic model of the northeastern Caribbean Sea region. The Puerto Rico Seismic Network has detected earthquakes which form a well defined zone of seismicity dipping 45 to 50 degrees from the Puerto Rico Trench to a depth of about 150 km under Puerto Rico. This inclined zone of seismicity is interpreted to represent a lithospheric plate. However, focal mechanism solutions have shown that plate motion along the Puerto Rico Trench is directed in an east-to-west sense similar to that expected in a transform fault zone. A plate tectonic model is developed which shows that a portion of the North American plate, originally subducted under the northern Lesser Antilles, underrides the northern edge of the Caribbean plate. When this underriding plate reaches the Hispaniola subduction zone it sinks deeper taking on a plow-shaped configuration. The Puerto Rico type of 'transform' trench is not unique to the Caribbean, but also occurs in the western Aleutian Trench, Puysegur Trench, northern Sunda Trench, and possibly the Scotia Sea region.