Structural controls of the migration of mantle-derived CO₂ offshore in the Santos Basin (Southeastern Brazil)

We present a multi-scale conceptual model based on structural controls of the migration of mantle-derived CO2 offshore in the Santos Basin (Southeastern Brazil). We assembled the model from a regional 2D seismic reflection line integrated with potential gravimetric field data and a local 3D seismic reflection volume integrated with well data (lithologies and in situ stress). (i) The geochemical isotope range of delta C-13(CO2) falls mostly within -7 parts per thousand and -5 parts per thousand and shows relatively high values for He-3/He-4 represented by an R/Ra rate of up to 5.60, indicating CO2 mantle generation and degassing. (ii) Seismic interpretation feasibly validated by potential gravimetric responses of the crustal structure (Moho discontinuity) show CO2 migration through deep-seated faults in a region of highly stretched continental crust with oceanward mantle uprising. (iii) Early Cretaceous basement highs generated in an obliquely syn-rift faulting system control CO2 accumulation in thermogenic travertines (hydrothermal carbonate reservoirs of continental lakes), and Aptian evaporites subsequently trap it.