Petrology of Cenomanian basalts on the Brazilian equatorial margin: Implications for the tectonomagmatic evolution of the drift phase

Olivine basalts from the Serra do Cuó magmatism in the onshore Potiguar basin exhibit SiO₂ = 46–53 wt%, MgO = 9–12 wt%, and total alkalis = 3.5–6 wt%, combined to elevated concentrations of large ion lithophile elements (Rb, Ba, Th, U, K), positive anomalies of Nb and Ta, and fractionated heavy rare earth elements. These lavas constitute a single volcanic event with evidence of fractional crystallization primarily involving olivine and pyroxene. Whole rock ⁴⁰Ar/³⁹Ar geochronology provided a minimum crystallization age of 99 ± 1 Ma, which is chronologically compatible with other Albian/Cenomanian igneous activity in NE Brazil. Clinopyroxene geothermobarometry indicates a range of crystallization depths from 23 km to 6 km, supporting crystal growth in a magma plumbing system before the emplacement. Radiogenic isotopes reveal enriched mantle-type source, akin to Paleogene/Neogene alkali basalts elsewhere in NE Brazil. Rare earth element inverse modeling hints that Serra do Cuó melts originated at a mantle potential temperature of 1350 °C, approximately 60 km depth. The long-lived alkali basaltic volcanism across the NE Brazil likely resulted from decompression melting of the mantle due to a combination of geodynamic factors, including episodes of hotspot influence and changes in South America's drift pattern.