EVOLUTION OF THE CRETACEOUS TO RECENT OROGENIC BELT OF NORTHERN VENEZUELA

The Caribbean Mountain system (Venezuela) is both a Modern and Ancient Plate Boundary and Orogen. At first glance, this mountain range appears to be a classical orogenic belt with a metamorphic "Hinterland" and a non-metamorphic "Foreland" fold and thrust belt. However, extensive dating (mostly 40Ar/39Ar) indicates that metamorphism of the hinterland belt took place in mid-Cretaceous time, whereas the non-metamorphic foreland rocks were deformed in Cenozoic time. This situation resulted from marked right-oblique convergence of the Caribbean and South American plates along their mutual EW-trending plate boundary zone. The metamorphic rocks contain blueschists and eclogites and have formed in the Leeward Antilles subduction zone along which the Atlantic plate was subducted. Blueschists and eclogites were partially exhumed by arc-parallel stretching resulting from displacement partitioning along an oblique plate margin. The collision of the Leeward Antilles arc with South America resulted in obduction of the accretionary wedge onto the South American margin and change of subduction polarity. This obduction took place in Paleocene time in the west and is still occurring in the east. The development of foreland basins and the foreland fold and thrust belt was diachronous as well and young from west to east. The oblique convergence rate vector was strongly partitioned into a plate-boundary normal component that resulted into the south-vergent fold and thrust belt and a plate-boundary parallel component resulting in boundary parallel right-lateral strike slip faults along which the metamorphic belts were displaced toward the east.

In addition, subduction related processes vary along strike. In the west, two high-pressure belts (Cordillera de la Costa and Villa de Cura belts) occur whereas in the east, (Margarita Island) only one exists. The Cordillera de la Costa belt contains eclogites that were formed at ~70 km depth. Eclogites on Margarita formed at ~45 km depth. The Villa de Cura belt blueschist formed at ~30 km depth. The age of exhumation varies from mid-Cretaceous (Villa de Cura and Margarita) to Eocene (Cordillera de la Costa). The dependence of depth of metamorphism and timing of exhumation of these high-P rocks on plate tectonic configuration is complicated, because of Tertiary overprint.