Geological constraints for the geodynamic evolution of the southern margin of the Caribbean plate

The southern margin of the Caribbean plate, cropping out in the Venezuela belt, consists of an assemblage of four main terranes: the Dutch-Venezuelan Islands, Margarita Island, Cordillera de la Costa, and Serrania del Interior. These terranes have been located, since the middle Cretaceous, along the transform boundary between the Caribbean and South American plates. On the basis of both new data and the literature, a critical review of the complex and long-lived evolution recorded in different units of these terranes is herein provided in order to highlight the Mesozoic-early Tertiary geodynamic evolution of the southern Caribbean. The analysis of the lithostratigraphic, petrologic, and tectono-metamorphic features of the terranes, as well as their regional correlations, allows us to define the main geotectonic elements (as oceanic basins, magmatic arcs, subduction zones, continental margins, continental microplates, etc.) involved in the evolution of the southern Caribbean margin. The magmatic, tectonic, and metamorphic histories of these elements provide valuable constrains for the evolution of the southern Caribbean, as, for instance, the beginning of the convergence during the Early Cretaceous, the atypical evolution of the suprasubduction system during the middle Cretaceous, the role of the middle Cretaceous strike-slip tectonics, the exhumation histories of the high-pressure/low-temperature (HP-LT) units. The collected data suggests a Middle Jurassic-Early Cretaceous location of these elements in a westernmost, "near mid-America" position, almost at the northwestern corner of the South American plate. Starting from the middle Cretaceous, the elements have been affected by a right-oblique convergence along the transform boundary connecting the two oppositely dipping subduction zones of the Andes and Aves-Lesser Antilles. According to the geologic constraints, three possible geodynamic scenarios can be proposed for the beginning of the convergence during the middle Cretaceous, taking into account the different locations of the transform fault in the geodynamic setting of the southern Caribbean. The collisional belt, resulting from the middle Cretaceous tectonics, has been dissected in different terranes, progressively rotated clock-wise, reciprocally juxtaposed, and then eastward displaced. The geodynamic framework was closely related to the progressive eastward motion of the Caribbean plateau which, in turn, was associated with the development of a west-southwest-dipping, intraoceanic subduction of the proto-Caribbean oceanic crust below the plateau, and related island-arc calc-alkaline magmatism, today preserved in the Dutch-Venezuelan Islands and Aves-Lesser Antilles. At that time, the terranes were already emplaced onto the South America continental margin. Northward, the dextral strike-slip tectonics of the Caribbean southern margin increasingly involved the southern part of the magmatic arc, which gradually became inactive and underwent a progressive rotation clockwise. In contrast, the Aves-Lesser Antilles were gradually bent eastward by the oblique convergence occurring at the southern end of the magmatic arc. Since the late Paleocene, the whole marginal belt was already completely identifiable with the large shear zone occurring today at the transform boundary between the Caribbean and South American plates.