Magnetic studies on mesozoic dike swarms from the coastline of São Paulo state (SE Brazil)

Abstract: The Mesozoic magmatism in Southern Brazil is represented mainly by the basaltic flows of the Serra Geral Formation, the tholeiitic dikes swarms from the Ponta Grossa Arch, Florianópolis, and along the coast between São Paulo and Rio de Janeiro, and several alkaline complexes that lie along tectonic features associated with the evolution of the Paraná Basin. This magmatism is called as Paraná-Etendeka Magmatic Province. The emplacement of the dike swarms and the alkaline complexes is related to the processes of separation between South America and Africa, and with the opening of Atlantic Ocean. We are performing an intensive magnetic study (magnetic fabrics, paleomagnetism and rock-magnetism) in all dike swarms from the coastline of São Paulo state, in which the dikes with different chemical composition (tholeiitic, lamprophyre and alkaline) are widespread along the Serra do Mar and beaches between São Paulo and Rio de Janeiro. The principal purpose of this study is to apply both AMS and AARM techniques to investigate the magma flow, to provide information on its mode of emplacement, and to investigate the relative position of magma sources and fractures, and to determine the paleomagnetic pole(s) of the dike swarms to compare it with available poles from Ponta Grossa (Raposo and Ernesto, 1995a, b) and Florianópolis (Raposo et al., 1998) to verify whether they can be the same age since it is believed that the tholeiitic activity occurred during the Early Cretaceous and was then partly coeval with Ponta Grossa and Florianópolis dikes (e.g