Boletín de la Sociedad Geológica Mexicana

Volumen 69, núm. 1, 2017, p. 209 ‒ 222

Recent carbonatitic magmatism in Angola: the dykes of the Chiva lagoon maar

Marc Campeny1,2,*, Joan C. Melgarejo2, José Mangas3, José Manuel4, Antonio O. Gonçalves4

1 Museu de Ciències Naturals de Barcelona (Departament de Mineralogia). Passeig Picasso s/n 08003 – Barcelona, Catalonia.
2 Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona. c/Martí i Franquès s/n 08028 - Barcelona, Catalonia.
3 Departamento de Física, Instituto de Oceanografía y Cambio Global, Universidad de Las Palmas de Gran Canaria, Campus universitario de Tafira 35017 – Las Palmas de Gran Canaria, Spain.
4 Departamento de Geologia, Universidade Agostinho Neto, Avenida 4 Febreiro, 71, CP815 – Luanda (Angola).

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Abstract

Chiva is a circular lagoon with a diameter of 900 m, located in the vicinity of the Catanda graben (Angola). This area is largely covered by Quaternary lacustrine sediments, however, a few dykes of carbonatitic composition have been found near the SE shore of the lagoon. The intrusion of these carbonatitic dykes has been linked to the occurrence of recent volcanic events in the Chiva area and interpreted as feeding channels of an eruptive centre with maar morphology. The Chiva carbonatitic dykes show a finely porphyritic texture formed by phenocrysts of subhedral calcite (60 %), apatite (30 %) and magnetite (10 %) hosted in a fine calcite-rich ground mass that also contains accessory minerals such as pyrochlore, perovskite and kimzeyite. The mineralogical and compositional features of the Chiva dykes are similar to those described in some of the carbonatitic lavas from the Catanda graben, suggesting that both volcanic events are genetically related. The finding of this new eruptive centre enlarges the carbonatitic domain of Catanda and opens the door to the discovery of new carbonatitic outcrops in this region of Western Angola.

Keywords: carbonatites, carbonatitic dykes, maar, Angola, Catanda, Chiva.