Elastic thickness and residual gravity anomaly applied to the northern Brazilian basins: Unravelling the volcanic-sedimentary history linked to the Central Atlantic Ocean opening

Abstract

The opening of the Central Atlantic Ocean during the Mesozoic caused voluminous outpouring of lava flows related to the Central Atlantic Magmatic Province (CAMP). Despite that, volcanic influence on the depositional evolution of northern Brazilian sedimentary basins is poorly-understood, as well as the interactions of volcanic and recurrent sedimentary deposits between lava flows. This region exhibits diverse magmatic expressions, including exclusively subsurface intrusions confined to the Amazonas and Solimões basins (Penatecaua magmatism) and lava spills, dykes, and sills interbedded with intertrap deposits (Mosquito Formation) in the Parnaíba Basin. In this context, forward gravity modeling was applied to derive residual gravity anomalies to better understand the emplacement and subsurface distribution of CAMP lithotypes. Crustal elastic thickness maps for the Amazonas, Solimões, and Parnaíba basins were constructed through cross-correlation of observed and modeled gravity signals. High values in the residual gravity maps are likely associated with volcanic rocks, enabling the reinterpretation of internal basin structures previously described to tectonic origins, such as the Monte Alegre Dome. The elastic thickness maps reveal a thinner crust in the Parnaíba Basin, closer to magma sources, which facilitated lava spills following magma accumulation along the basin’s western edge. This basin experienced three distinct magmatic pulses, interspersed with quiescent periods of subsidence and sedimentary deposition. In contrast, the Amazonas and Solimões basins exhibit thicker crusts, where magma was predominantly emplaced as sills, reaching up to 1 km in thickness. This is attributed to crustal densification and increased mechanical resistance. The heightened elastic resistance in the Amazonas and Solimões basins contributed to epeirogenic uplift and erosion of overlying sedimentary layers. Variations in crustal thickness and elastic resistance likely governed the styles and durations of magmatic activity, subsequently influencing the uplift or subsidence dynamics of the northern Brazilian basins.