Preliminary Ar-Ar geochronology of Mesozoic alkaline-carbonatitic to tholeiitic magmatism in the Quilengues area, SW Angola

New geochronological data have been obtained on kimberlitic units related to the Bonga carbonatite massif and basaltic dikes in the Quilengues region of southwestern Angola as part of the National Geological Plan of Angola (PLANAGEO). Ar-Ar dating of mineral separates (phlogopite, amphibole) indicates distinct intrusion pulses for the alkaline-carbonatite magmas of the Bonga Complex (155.2 ± 2.9 Ma) and a NNE-SSW dike assemblage (124.7 ± 2.2 Ma). These ages agree with those reported from coeval volcanic materials in the coastal region, suggesting a direct correlation with lithospheric destabilisation processes induced by the ascent of deep melts, during incipient to progressive stages of the Atlantic rifting and Pangea’s breakup. The basaltic dikes may represent the feeding channels of mantle-derived melts that extruded as Large Igneous Provinces (LIPs), forming the Paraná-Angola-Etendeka Province. The spatio-temporal relationships of the studied bodies are consistent with the intrusion of mantle melts during the early stages of rifting, in directions equivalent to the Lucapa structure and the Atlantic margin. The new age data reinforce the existing dataset of Jurassic-Cretaceous alkaline-carbonatite and bimodal (alkaline to tholeiitic) pulses in Angola and their South American counterparts. A structural control is also suggested, with the later alkaline pulses emplaced along ~E-W directions, related to the progress of rifting and the action of deep transform faults during continental breakup.