Lithospheric Structure of Northwestern Venezuela From Wide-Angle Seismic Data: Implications for the Understanding of Continental Margin Evolution

Northwestern Venezuela is located in the complex deformation zone between the Caribbean and South American plates. Several models regarding the lithospheric structure of the Merida Andes have been proposed. Nevertheless, they lack relevant structural information in order to support the interpretation of deeper structures. Therefore, a 560-km-long refraction profile across the northern part of Merida Andes, oriented in a NNW direction, covering areas from the Proterozoic basement in the south, to both Paleozoic and Meso-Cenozoic terranes of northwestern Venezuela to the north, is analyzed in this contribution. Thirteen land shots were recorded by 545 short-deployment seismometers, constraining P wave velocity models from first-arrival seismic tomography and layer-based inversion covering the whole crust in detail, with some hints to upper mantle structures. The most prominent features imaged are absence of a crustal root associated to the Merida Andes, as the Northern Andes profile is located marginal to the Andean crustal domain, and low-angle subduction of the Caribbean oceanic slab (similar to 10-20 degrees) beneath northwestern South America. Further crustal structures identified in the profile are (a) crustal thinning beneath the Falcon Basin along the western extension of the Oca-Ancon fault system interpreted as a back-arc basin; (b) suture zones between both the Proterozoic and Paleozoic provinces (Ouachita-Marathon-related suture?), and Paleozoic and Meso-Cenozoic terranes (peri-Caribbean suture) interpreted from lateral changes in seismic velocity; and (c) evidence of a deep Paleozoic(?) extensional basin, underlying thick Mesozoic and Cenozoic sequences (beneath the Guarico area).