Bimodal volcanism during the Early Cretaceous in Santos Basin, Brazil: Mantle-crust interaction, thermal regimes, CO2 influx and coeval magma generation onshore and offshore the South Atlantic volcanic rifted margins

There are many sedimentary basins along the South Atlantic rifted margins with voluminous hydrocarbon reservoirs. It evolves from rift to drift tectonic stages give rise to geological processes that control part of their petroleum systems. Some of these processes are related to changes in thermal regimes due to long-standing tectono-magmatic events associated to mantle-crust interactions. The Santos Basin, offshore southeast Brazil, contains the country's largest oil and gas reservoirs. Its origin is related to the rift process that led to the Gondwana breakup during the Early Cretaceous. This paper presents wellbore, petrographic, geochemical, isotopic and geochronological data obtained for an 800m-tick magmatic section recorded along the so-called pre-salt sedimentary sequence in the well 6-BG-6P-SPS in the Santos Basin. This magmatic section comprises effusive mafic and composite felsic rocks associated with long-standing bimodal volcanism (135-122 Ma). The geochemical models allowed to propose that the basic mafic and acid felsic rocks are no-cogenetic by differentiation processes, although some of the basic and intermediate liquids can be linked by AFC within the upper continental crust. The enriched isotope signature of the basic rocks can be explained by geodynamic processes involving the Tristan da Cunha plume and enriched portions of the SCLM (EMII-like mantle reservoir). The data were used to propose conceptual models for the mantle geodynamics and the tectono-magmatic settings from the Hauterivian to Aptian. These models show how mantle-crust tectonic and magmatic interactions imposed thermal regimes that may have controlled geological processes, hydrothermalism and CO₂ influx recorded in the pre-salt petroleum systems in the Santos Basin.