ORIGIN OF THE CARIBBEAN PLATE

Bathymetry and seismic imaging indicate that the Caribbean plate is significantly thicker, on the order of 10-20 km in aggregate thickness, than normal oceanic crust. Geochemical studies of widely dispersed basaltic igneous rocks believed to be accreted fragments of the Caribbean plate are interpreted to indicate a within plate oceanic plateau origin. Some recent models suggest that the plateau formed in the Pacific from the ancestral Galapagos hot spot. In these models, arrival of the plateau at the subducting boundary of a west-facing arc led to subduction reversal trapping the overthickened plateau crust behind the newly formed east-facing arc, thereby forming the Caribbean plate. Basaltic lavas and diabasic intrusions on the Leeward Antilles islands of Aruba and Curacao are believed to represent fragments of the Caribbean plate. Detailed mapping coupled with ongoing geochronological investigations of these islands, leads us to an alternative model for the development of the Caribbean plate. Field relations on Aruba and Curacao indicate that both islands became emergent in the Late Cretaceous. Basalt and diabase on both islands have exhibit abundant evidence for weathering that can be constrained to have occurred in the Late Cretaceous. In addition, on Aruba a distinctive unit of Late Cretaceous basaltic accretionary tuff overlies weathered basalt and diabase, further indicating subaerial conditions. Following emergence , the geologic evolution of the two islands significantly diverged. Aruba underwent regional deformation and metamorphism prior to emplacement of a tonalite batholith at 89 ± 1Ma, whereas Curacao records subsidence and deep marine sedimentation. We suggest that the basalt and diabase units on Aruba and Curacao formed at the intersection of a spreading ridge and mantle plume. While both islands were above the plume thermal anomaly they ultimately became emergent and underwent subaerial erosion. Following this Aruba was partially subducted beneath an east-facing arc along with the mantle plume. Curacao moved off the axis of the thermal anomaly due to sea-floor spreading, subsided and continued to receive hemipelagic sedimentation while Aruba was still at depth. Subduction of the mantle plume led to crustal thickening in the backarc region producing the overthickened crust of the Caribbean plate.