Open-System Magmatic Evolution of The Morro de São João Alkaline Complex, SE Brazil: Insights from Magnetometric Signatures Combined to Petrographic Analysis

The present study integrates the magnetometric with petrographic data from the Morro de São João (MSJ) Alkaline Complex to investigate the magmatic evolution of the complex. The findings emphasize the critical role of magma mixing processes in shaping the textural and compositional diversity of MSJ rocks. The complex is a circular and conical body of approximately 10 km² located southeast of Rio de Janeiro composed of alkaline rocks strongly-silica undersaturation. The study used conventional petrographic analysis and aeromagnetic data processing, such as the Total Gradient Amplitude (TGA) and Reduction to the pole (RTP) maps to reveal the presence of multiple anomalous domains, supporting the hypothesis of non-cogenetic magmatic bodies that interacted during magma mixing events. To accomplish these objectives, this study employs a cross-correlation method to estimate the magnetization direction of the magnetic source. From a geodynamic perspective, the evolution of the MSJ’s evolution is supposed to be closely linked to geomagnetic polarity reversals, mantle plume activity, and extensional tectonic processes associated with the break-up of the Gondwana paleocontinent. These factors contributed to the generation of alkaline magmatism through the decompression of the subcontinental lithospheric mantle and the thermal influence of deep mantle plumes.