Petrogênese e Contexto Geodinâmico das Suítes Basálticas Toleíticas (de alto-TiO2 e baixo-TiO2) do Cretáceo Inferior da Porção Centro-oriental do Enxame de Diques da Serra do Mar

Abstract

Tholeiitic basalts of Early Cretaceous age integrate the Serra do Mar Dyke Swarm (SMDS) in Southeastern Brazil. These rocks occur as dykes that intrude the Neoproterozoic, Brasiliano-Pan/African rocks of the Ribeira orogen. The SMDS can be divided in a low- and high-TiO2 suite. The petrological studies revealed the ocurrance of two low-TiO2 suite (A and B) and four high-TiO2 suite (A, B, C and D). This geochemical provinciality indicates a mantelic heterogenety in a local scale. The results of the petrogenetic modeling indicate ATA (Assimilation by Turbulent Ascent) as the likely evolutionary process for the B low-TiO2 suite. In the case of the other low- and high-TiO2 suite, it is important to note the existence of processes involving assimilation and concomitant fractional crystallisation. The building of multi- elementar diagrams, modal-batch partial melting models and discrimination of mantelic reservoir showed that the petrogenesis of the majority of the low- and high- TiO2 are related to mixing process of mantelic sources. The only exception correspond to the B low-TiO2 suite which is generated exclusively by a enriched reservoir (EM I). Binary mixing models and assimilation tests revealed that the petrogenesis of the A low-TiO2 suite involved a large amount of participation of a depleted component with small contribution of a enriched component. In contrast, the generation of the tholeiitic basalts of all the high-TiO2 suite are related to a possible mixing between enriched and fertile sources. Finally, the elaborated petrogenetic modeling in association with recent litogeochemical, geocronological and isotope data (Sr-Nd-Pb) to the tholeiitic series of SDMS permit the construction of a geodynamic scenario that must contribute to the refining of the recent proposed modeling to the mafic magmatism of Cretaceous in the center-south portion of South America Plate.