Tectonics changes in NW South American Plate and their effect on the movement pattern of the Bocono Fault System during the Merida Andes evolution

The NE-SW trending Merida-Andes fold-and-thrust belt, in the southern boundary of the Maracaibo Block, formed by a collisional event in Late Miocene at the boundary of the Maracaibo Block and Guyana Shield in the northwestern South American plate. The 500 km long, NE-SW striking right-lateral strike-slip Bocono Fault System lies in the Merida-Andes area. Mylonitic fault rocks along the Bocono Fault System developed during pre-Late Miocene-Early Pliocene. Microscopic and mesoscopic structures such as mica fish, asymmetrical porphyroclasts, S-C shear bands, and asymmetrical ductile folds in Bocono Fault mylonite indicate a sinistral movement along the fault. The movement is probably related to pre-collision extensional tectonics that began in the Late Triassic-Jurassic interval, and continued until the late Cretaceous or Middle Eocene. Following the collision of the Panama Arc and the South American plate in the Late Miocene, and the change from extensional to contractional tectonic regime, the Bocono was reactivated as a dextral fault system. (C) 2011 Elsevier Ltd. All rights reserved.