Neotectonics of the Caribbean

Abstract

A compilation of earthquake focal mechanism solutions together with the interpretation of inclined, intermediate‐depth seismic zones, Neogene strike‐slip faults, fault‐controlled basins, and volcanism is used to test three existing models for the neotectonic (i.e., Neogene or post‐Oligocene) development of the Caribbean. The current models, although based on different hypotheses using different data sets, are similar and suggest varying degrees of convergence between the Caribbean and either North or South American plates or convergence between the Caribbean plate and continental fragments of the northwestern corner of South America. Using model 1, previous workers have interpreted the disposition of fracture zones and magnetic anomalies in the central and South Atlantic as indicating that the Caribbean plate is being compressed by north‐south convergence between the Americas with the result that it is being driven eastward relative to the Americas along strike‐slip faults while producing east‐west trending subductionlike convergent zones along northern and southern plate margins. Using model 2, previous workers have interpreted the azimuths of active strike‐slip faults and focal mechanism solutions and closure of three‐plate velocity circuits as indicating that the South American plate converges in a west‐northwesterly direction on the southern margin of the Caribbean plate and has produced compressional features, while strike‐slip motion dominates along the northern boundary. Using model 3, previous workers have interpreted focal mechanism solutions and the pattern of strike faulting and basin development in northwestern South America to suggest right‐lateral displacement of the northwestern corner of South America relative to the craton with convergence and compression in the south central Caribbean. Our integration of geologic information on faults, basins, and volcanism considerably extends the limited record of plate interactions known from historical reports of the past few hundred years and recorded earthquakes and suggests that (1) relative motion between the North American and Caribbean plates is dominantly east‐west strike‐slip motion, although areas of complex internal deformation associated with restraining bend or compressional strike‐slip fault segments have been identified in Jamaica, Hispaniola and Central America (2) relative motion between the South American and Caribbean plates is dominantly east‐west strike‐slip motion, although an area of restraining bend deformation has been identified in the Araya Peninsula of Venezuela; (3) relative motion between a triangular continental fragment of northwestern South America (the “Maracaibo Block”) ranges from northwest to northeast along the south central margin of the Caribbean and appears to be driven mostly by the late Miocene‐Pliocene collision of the Panama arc, although additional driving forces may include the collision of the Carnegie Ridge and/or oblique subduction (to the northeast) in Ecuador; and (4) relative motion (internal deformation) may be occurring at a very slow rate between fault‐bounded blocks within the Caribbean plate as a result of the convergence of the Maracaibo Block and/or eastward motion of the Caribbean plate relative to a continental promontory of North America in northern Central America. Because the Caribbean margins are composed mainly of anisotropic, easily deformed continental and arc lithosphere, plate boundaries are zones of diffuse deformation, and it is difficult to assess the degree of convergence between the Americas, although data from the Caribbean itself suggest that it may be smaller than the amount inferred by some workers using model 1 (fracture zone and magnetic anomalies in the Atlantic). Some of the compressional features cited as evidence for the relative convergence of the Americas may be instead related to the convergence between the Maracaibo Block relative to the southern margin of the Caribbean. Many aspects of Caribbean neotectonics remain less than completely understood, but more integration of seismic and geologic studies (particularly exploratory fault trenching of onshore faults and seismic profiling of offshore faults) should lead to rapid advances.