Deformation of the Caribbean region: One plate or two?

New deep-penetrating high-resolution multichannel seismic reflection data collected in the eastern Caribbean during RN Ewing cruise EW9501 imaged both the crustal structure and overlying stratigraphic successions. On the basis of this new multichannel seismic data, we define the geologic development of the Beata Ridge and Venezuelan basin. The Caribbean crust was formed by seafloor spreading in Late Jurassic-Early Cretaceous time. Prior to the Senonian, widespread and rapid eruption of basaltic flows began in concert with extensional deformation of the Caribbean crust. Thick volcanic wedges characterized by divergent reflectors are observed along the boundary that separates rough from smooth oceanic crust, are coincident with an abrupt shallowing of the Moho, and appear to be bounded by a large, northwest-dipping fault system. The locus of major extensional deformation migrated through time from the Venezuelan basin to the western flank of the Beata Ridge. Extensional unloading of the Beata Ridge footwall caused uplift and rotation of the ridge. Sediment thicknesses and stratal geometry observed across the Venezuelan basin and Beata Ridge suggest that the majority of the deformation in this region occurred during and soon after the emplacement of the volcanics. Minor fault reactivation in the Neogene along the eastern flank of the Beata Ridge is associated with an accommodation zone (i.e., tear fault) that records a change in the deformation style from bending and subduction of the Caribbean plate along the Muertos Trough south of Puerto Rico to compressional deformation and obduction of the Caribbean plate south of Hispaniola. We propose that this difference in deformational style is, in part, a consequence of the thicker crust on the Beata Ridge, which is more resistant to subduction.