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

Enrique Merino-Martínez; Pablo Valverde-Vaquero; Aratz Beranoaguirre; Gustavo Galán; Janet Gabites; José Manuel

doi:10.21701/bolgeomin/136.1/009

Authors

Enrique Merino-Martínez Departamento de Geología y Subsuelo, Centro Nacional Instituto Geológico y Minero de España (IGME-CSIC) https://orcid.org/0000-0002-2032-6353
Pablo Valverde-Vaquero Departamento de Geología y Subsuelo, Centro Nacional Instituto Geológico y Minero de España (IGME-CSIC) https://orcid.org/0000-0002-2184-0848
Aratz Beranoaguirre UTE-PLANAGEO (IGME/LNEG/Impulso). Department of Geosciences, Goethe-University Frankfurt https://orcid.org/0000-0002-1137-6498
Gustavo Galán UTE-PLANAGEO (IGME/LNEG/Impulso)
Janet Gabites Pacific Center for Isotopic and Geochemical Research, The University of British Columbia https://orcid.org/0000-0003-3698-3275
José Manuel Instituto Geologico de Angola (IGEO) https://orcid.org/0000-0001-5509-5068

DOI:

https://doi.org/10.21701/bolgeomin/136.1/009

Keywords:

Ar-Ar geochronology, Alkaline-carbonatitic magmas, Bimodal magmatism, Mesozoic, Angola

Abstract

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.

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