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

The NE–SW trending Mérida–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 Boconó Fault System lies in the Mérida–Andes area.Mylonitic fault rocks along the Boconó 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 Boconó 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 Panamá Arc and the South American plate in the Late Miocene, and the change from extensional to contractional tectonic regime, the Boconó was reactivated as a dextral fault system.

► The NE–SW striking right-lateral strike-slip Boconó Fault System lies in the Mérida–Andes axis. ► The mechanism of Bocono Fault System has changed from left-lateral to right-lateral. ► The time of slip sense inversion, is coincident with the inversion of extensional regime to compressional.