The Santa Catarina Plateau and the nature of its basement

摘要

The Santa Catarina Plateau is a prominent undersea feature of the Brazilian Southern Margin with approximately 340,000 km(2) that interrupts the lower continental slope between depths of 2900 and 3200 m. The plateau's morphology and basement were unknown until new geophysical data were acquired for the Brazilian Continental Shelf Survey Program (LEPLAC). The multibeam bathymetry, sub-bottom profile, and mini-airgun data allowed the identification of important morphologic features, such as the Santa Catarina Drift and Pelotas Drift, and the study of their sedimentary processes, especially related to slope instabilities and mass movement. The seismic and gravimetric datase.ts allowed the study of the Torres High, an important structural feature that supports most of the Santa Catarina Plateau. With this new dataset, it was possible to develop different gravimetric models, controlled by the ultra-deep seismic information, to analyze the two competing hypotheses for the nature of Torres High: (1) thickened oceanic crust or (2) continental crust. The crustal and the Moho character below the Torres High, observed in strike- and dip-oriented ultra-deep seismic lines, and the results of the gravimetric model, support the interpretation of its continental nature. Additionally, the analysis of the basement depth and the interpretation of the Bouguer gravity map clearly show the Torres High as a continuous structural feature attached to the South American continent, in a northwest-southeast direction, constituting a continental promontory of the Brazilian land mass and part of the basement of the Santa Catarina Plateau.