Geophysical-structural framework of the Campo Alegre basin (Santa Catarina State, southern Brazil)

Abstract

Numerous syn- to post-collisional basins originated as a response to crust stabilization processes after the collisions between Apiaí, Curitiba and Luis Alves Cratons during the Neoproterozoic in Brazil. The late Neoproterozoic Campo Alegre Basin represents one of these so called transitional-stage basin in the southern Brazil. The structural record of this basin is an important clue for understanding the regional geological development after the Western Gondwana supercontinent agglutination. An integrated study of airborne geophysical data, ground gravimetry and structural analysis of the basin and its basement outlined its magnetic-structural framework and its tectonic evolution. Thus, it was possible to present a basin 3-event tectonic evolution history. The first event (E1) is marked by WNW and ENE normal faults as a response to conjugated extension stress fields (σ3 and σ2). The normal faults generated in (E1) conditioned the deposition of the coarse-grained basal deposits close to basin borders. A second event (E2) was recognized through EW normal faults and ENE-WSW right-lateral strike-slip faults on basin intermediate formations. Hydrothermalism from volcanism final fluids is associated with these faults, especially on the south portion. The last tectonic event (E3) that affected basin rocks is characterized by the reactivation of E1 normal faults as inverse and occurred in Mesozoic Era associated with South Atlantic Ocean opening. This event is also marked by NNW e EW strike-slips faults. Besides the gravimetric model and the magnetic interpretation, field data allow us to conclude that the nucleation of Campo Alegre Basin began as a conjugated rift system.