New Ar-Ar geochronology of the Catanda carbonatitic magmatism (Angola) and implications on its origin

1. Introduction

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The Catanda Carbonatite Complex (CCC) represents one of the few examples of extrusive carbonatites in the world, constituting a unique volcanic carbonatite complex in west Angola (Woolley & Church, 2005Woolley, A. R., & Church, A. A. (2005). Extrusive carbonatites: a brief review. Lithos, 85(1-4), 1-14.
; Bambi, 2015Bambi, A.C.J.M. (2015). Metalogenia de las carbonatitas en dominios plutónicos, subvolcánicos y volcánicos: Tchivira, Bonga y Catanda, Angola. Tese de doutorado. Universitat de Barcelona. 705 pp.
; Campeny, 2016Campeny, M. (2016). Caracterización del vulcanismo carbonatítico de Catanda (Angola). Tésis de Doutoramento, Universitat de Barcelona, 66 pp.
). This carbonatitic volcanic system has a complex structure associated to explosive and effusive volcanic activity. It is made up of eight main eruptive centres, whose carbonatite magmas have a high content of F, Nb and Rare Earth Elements (Bambi, 2015Bambi, A.C.J.M. (2015). Metalogenia de las carbonatitas en dominios plutónicos, subvolcánicos y volcánicos: Tchivira, Bonga y Catanda, Angola. Tese de doutorado. Universitat de Barcelona. 705 pp.
; Campeny, 2016Campeny, M. (2016). Caracterización del vulcanismo carbonatítico de Catanda (Angola). Tésis de Doutoramento, Universitat de Barcelona, 66 pp.
; Campeny et al., 2014Campeny, M., Mangas, J., Melgarejo, J. C., Bambi, A., Alfonso, P., Gernon, T., & Manuel, J. (2014). The Catanda extrusive carbonatites (Kwanza Sul, Angola): an example of explosive carbonatitic volcanism. Bulletin of Volcanology, 76, 1-15.
, 2015Campeny, M., Kamenetsky, V.S., Melgarejo, J.C., Mangas, J., Alfonso, P., Kamenetsky, M.B., Bambi, A.C.J.M., & Gonçalves, A.O. (2015). Carbonatitic lavas in Catanda (Kwanza Sul, Angola): Mineralogical and geochemical constraints on the parental melt. Lithos, 232, 1-11.
). For that reason and with the aim of enhancing the geological knowledge of SW Angola, the Catanda volcanic complex has been an intriguing subject of study during the PLANAGEO Project (National Geology Plan of Angola).

Catanda is one of the three main regions in Angola that contains carbonatitic complexes (Issa Filho et al., 1991Issa Filho, A., Dos Santos, A.B.R.M.D., Riffel, B.F., Lapido-Loureiro, F.E.V., & McReath, I. (1991). Aspects of the geology, petrology and chemistry of some Angolan carbonatites. J. Geochem. Explor., 40, 205-226.
). These carbonatite-rich areas are the central (Monte Verde, Bailundo, Coola, Longonjo, Tchivira-Bonga), southwest (Virulundo, Lupongola), and central-west (Catanda) regions. These areas are usually associated with the alkaline-carbonatitic magmatism that occurred during Mesozoic times in SW Angola. This magmatism is distributed along a series of tectonic alignments that were active at least during the Upper Jurassic and Lower Cretaceous (155 Ma, 138-130 Ma; Lapido-Loureiro, 1973Lapido-Loureiro, F.E. (1973). Carbonatitos de Angola. Memórias e Traballos. I.I.C.A., 11.
; Cahen et al., 1984Cahen, L., Snelling, N.J., Delhal, J., & Vail, J.R. (1984). The geochronology and evolution of África: London, Oxford University Press, 512 p.
; Allsopp & Hargraves, 1985Allsopp, H.L., & Hargraves, R.B. (1985). Rb-Sr ages and palaeomagnetic data for some Angolan alkaline intrusives. Transactions Geological Society South Africa, 88, 295-299.
; Issa Filho et al., 1991Issa Filho, A., Dos Santos, A.B.R.M.D., Riffel, B.F., Lapido-Loureiro, F.E.V., & McReath, I. (1991). Aspects of the geology, petrology and chemistry of some Angolan carbonatites. J. Geochem. Explor., 40, 205-226.
; Coltorti et al., 1993Coltorti, M., Alberti, A., Beccaluva, L., Dos Santos, A.B., Mazzucchelli, M., Morais, E., Rivalenti, G., & Siena, F. (1993). The Tchivira Bonga alkaline-carbonatite complex (Angola): petrological study and comparison with some Brazilian analogues. Eur. J. Mineral., 5, 1001-1024.
; Alberti et al., 1999Alberti, A., Castorina, F., Censi, P., Comin-chiaramonti, P., & Gomes, C.B. (1999). Geochemical characteristics of Cretaceous carbonatites from Angola. Journal África Earth Sciences, 29(4), 735-759.
; Comin-Chiaramonti et al., 2005Comin-Chiaramonti, P., Gomes, C. B., Marques, L. S., Censi, P., Ruberti, E., & Antonini, P. (2005). Carbonatites from southeastern Brazil: geochemistry, OC, Sr-Nd-Pb isotopes and relationships with the magmatism from the Paraná-Angola-Namibia Province. Mesozoic to Cenozoic alkaline magmatism in the Brazilian Platform. Edusp/Fapesp, São Paulo, 657-688.
, 2007Comin-Chiaramonti, P., Barros Gomes, C., Cundari, Al., Castorina, F., & Censi, P. (2007). A review of carbonatitic magmatism in the Paraná-Angola-Namibia (PAN) system. Periodico di Mineralogia, 76(2-3), 25-78.
). These large-scale tectonic structures control the distensive Lucapa structure, the Alkaline-carbonatitic Diagonal Trans-Angola Province (Woolley, 1987Woolley, A. R. (1987). Alkaline rocks and carbonatites of the world. Part 3. The Geological Society of London. 372 p.
; Lapido-Loureiro, 1967Lapido-Loureiro, F.E.V. (1967). Nota prévia sobre as estruturas carbonatiticas de Angola. Bol. Inst. Invest. Cient., Angola, Luanda 4(2), 45-66.
, 1968Lapido-Loureiro, F.E.V. (1968). Sub-volcanic carbonatite structures of Angola. In: XXIII International Geological Congress. Praga, pp. 147-161.
, 1973Lapido-Loureiro, F.E. (1973). Carbonatitos de Angola. Memórias e Traballos. I.I.C.A., 11.
, 1995Lapido-Loureiro, F.E.V. (1995). A mega-província carbonatítica Brasil-Angola e os seus recursos minerais; geologia, petrografia, geoquímica, geologia económica. Universidade de Lisboa, PhD Thesis, 191 pp.
), and the Volcanic Belt of Angola (Machado, 1959Machado, A. D. B. (1959). New Systematic and Biogeo-graphical Studies of Glossina. Publicacoes Culturais Com-panhia Diamantes de Angola, (46), 13-90.
), which are associated with the destabilisation and crustal break-up of Pangaea promoted by the opening of the South Atlantic Ocean (Guardado et al., 1989Guardado, L. R., Gamboa, L. A. P., & Lucchesi, C. F. (1989). Petroleum geology of the Campos Basin, Brazil, a model for a producing atlantic type basin: In: Edwards, J.D., and Santogrossi, P.A. (eds.), Divergent/Passive Margin Basins. American Association of Petroleum Geologists 48. https://doi.org/10.1306/M48508C1
; Brownfield & Charpentier, 2006Brownfield, M. E., & Charpentier, R. R. (2006). Geology and total petroleum systems of the west-central coastal province (7203), West Africa (No. 2207-B). US Geological Survey.
, Torsvik et al., 2009Torsvik, T. H., Rousse, S., Labails, C., & Smethurst, M. A. (2009). A new scheme for the opening of the South Atlantic Ocean and the dissection of an Aptian salt basin. Geophysical Journal International, 177(3), 1315-1333.
; Bryant et al., 2012Bryant, I., Herbst, N., Dailly, P., Dribus, J. R., Fainstein, R., Harvey, N., & Tapponnier, P. (2012). Basin to basin: Plate tectonics in exploration. Oilfield Review, 24(3), 38-57.
).

The petrographic and geochemical features of the CCC have been widely studied in the works of Melgarejo et al. (2012)Melgarejo, J. C., Costanzo, A., Bambi, A. C., Gonçalves, A. O., & Neto, A. B. (2012). Subsolidus processes as a key factor on the distribution of Nb species in plutonic carbonatites: The Tchivira case, Angola. Lithos, 152, 187-201.
, Bambi (2015)Bambi, A.C.J.M. (2015). Metalogenia de las carbonatitas en dominios plutónicos, subvolcánicos y volcánicos: Tchivira, Bonga y Catanda, Angola. Tese de doutorado. Universitat de Barcelona. 705 pp.
, Campeny et al. (2015Campeny, M., Kamenetsky, V.S., Melgarejo, J.C., Mangas, J., Alfonso, P., Kamenetsky, M.B., Bambi, A.C.J.M., & Gonçalves, A.O. (2015). Carbonatitic lavas in Catanda (Kwanza Sul, Angola): Mineralogical and geochemical constraints on the parental melt. Lithos, 232, 1-11.
, 2017)Campeny, M., Melgarejo, J.C., Mangas, J., & Gonçalves, A.O. (2017). Recent carbonatitic magmatism in Angola: the dykes of the Chiva lagoon maar. Boletín de la Sociedad Geológica Mexicana, 209-220.
, Campeny (2016)Campeny, M. (2016). Caracterización del vulcanismo carbonatítico de Catanda (Angola). Tésis de Doutoramento, Universitat de Barcelona, 66 pp.
and Giuliani et al. (2017)Giuliani, A., Campeny, M., Kamenetsky, V. S., Afonso, J. C., Maas, R., Melgarejo, J. C., & Manuel, J. (2017). Southwestern Africa on the burner: Pleistocene carbonatite volcanism linked to deep mantle upwelling in Angola. Geology, 45(11), 971-974.
. Nevertheless, the existing geochronological data regarding the Catanda magmatism may be contradictory. For example, the phonolite dikes found near the CCC presumably associated with this carbonatitic magmatism, were dated at 92 ± 7 Ma by whole-rock K-Ar geochronology (Silva & Pereira, 1973Silva, M.V.S., & Pereira, E. (1973). Estrutura Vulcânico-Carbonatítica da Catanda (Angola). Boletim dos Serviços de Geologia e Minas, 24, 5-14.
; Torquato & Amaral, 1973Torquato, J.R., & Amaral, G. (1973). Idades K/Ar em rochas das regiões de Catanda e Vila do Almoster. Bol. Inst. Invest. Cient., Angola, Luanda, vol. 10, Pub. IICA 308.
; in Torquato, 1977Torquato, J. R. (1977). Geotectonica Outline of Angola. Cah. O.R.S.T.O.M., sér. Geól., vol. IX, nº 1/2, 15-34.
), indicating association with the opening of the Atlantic Ocean. However, recent ³⁹Ar-⁴⁰Ar and (U-Th-Sm)/He mineral dating of the Catanda lavas (Campeny, 2016Campeny, M. (2016). Caracterización del vulcanismo carbonatítico de Catanda (Angola). Tésis de Doutoramento, Universitat de Barcelona, 66 pp.
; Giuliani et al., 2017Giuliani, A., Campeny, M., Kamenetsky, V. S., Afonso, J. C., Maas, R., Melgarejo, J. C., & Manuel, J. (2017). Southwestern Africa on the burner: Pleistocene carbonatite volcanism linked to deep mantle upwelling in Angola. Geology, 45(11), 971-974.
), which yield extrusion ages ranging from 0.78 to 0.56 Ma (Pleistocene), suggests a relationship with the reactivated ancient NE-SW extensional structures in the context of the crustal fracturing and alkaline- carbonatitic magmatism currently occurring in the East African Rift. Nevertheless, Ar-Ar ages from phlogopite separates recently obtained in PLANAGEO, together with additional whole-rock Ar-Ar dating of the same carbonatitic sample, provide a new insight on the geological history of the Catanda region in central west Angola. In any case, the variability of the radiometric values encourages discussion for future geological and geochronological work in the area.

2. Geological setting

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The CCC is located in the Kwanza Sul province (Angola), approximately 60 km southeast of the town of Sumbe (Fig. 1). This complex comprises a cluster of relatively eroded volcanic cones, covering an area of 50 km², composed of carbonatitic lavas and pyroclastic materials unconformably deposited over a Paleoproterozoic igneous and metasedimentary basement (Fig. 1). The CCC preserves the morphology of a volcanic building, although intense alteration and erosion have caused the development of eluvial-alluvial deposits on the slopes of this building. In the Chiva lagoon area, to the east of the main volcanic building, there are carbonatite dikes associated with the complex (Campeny et al., 2017Campeny, M., Melgarejo, J.C., Mangas, J., & Gonçalves, A.O. (2017). Recent carbonatitic magmatism in Angola: the dykes of the Chiva lagoon maar. Boletín de la Sociedad Geológica Mexicana, 209-220.
). In the vicinity of this volcanic complex, active hot springs have also been described associated with a NNW-SSE fault system that emanates CO₂-rich waters, resulting in the formation of thick travertine deposits on top of the Palaeoproterozoic basement (Bambi, 2015Bambi, A.C.J.M. (2015). Metalogenia de las carbonatitas en dominios plutónicos, subvolcánicos y volcánicos: Tchivira, Bonga y Catanda, Angola. Tese de doutorado. Universitat de Barcelona. 705 pp.
).

Geographic location and geological map of the Catanda area. It is also indicated the location of the stratigraphic sections A and B performed during the PLANAGEO project.

Figure 1. Geographic location and geological map of the Catanda area. It is also indicated the location of the stratigraphic sections A and B performed during the PLANAGEO project.

Figura 1. Localización geográfica y mapa geológico del área de Catanda. También se indica la ubicación de las columnas estratigráficas A y B realizadas durante el proyecto PLANAGEO.

The basement and country rock of the CCC comprise slightly foliated, porphyritic and medium-grained Palaeoproterozoic granitoids affected by a complex system of brittle, occasionally ductile, fracturing with WNW-ESE, NNW-SSE and ENE-WSW directions. In some of these sectors, the granite intrusions display medium- to high strain deformational textures, showing cataclastic to mylonitic textures, and more sparsely preserved migmatitic structures. Metasedimentary rocks and quartz-feldspar porphyries occur within a WNW-trending high-strain deformational corridor. The granitoid basement is intruded by a set of NNW-SSE and ENE-WSW trending microgabbros and phonolite dikes. These latter alkaline dikes provided an age of 92 ± 7 Ma by whole-rock K-Ar (Torquato & Amaral, 1973Torquato, J.R., & Amaral, G. (1973). Idades K/Ar em rochas das regiões de Catanda e Vila do Almoster. Bol. Inst. Invest. Cient., Angola, Luanda, vol. 10, Pub. IICA 308.
). Given the spatial association with these alkaline dykes, the CCC was interpreted as Cretaceous in age.

3. The Catanda Carbonatite Complex: field and petrographic features.

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The Catanda Carbonatite Complex (CCC) stands out as a topographic height with an elevation of < 200 m over the surrounding countryside (Fig. 2). Carbonatitic pyroclastites and lavas of calciocarbonatite, silicocarbonatite and natrocarbonatite composition form a composite volcanic structure, as a result of different extrusive and effusive events (Fig. 3; Bambi, 2015Bambi, A.C.J.M. (2015). Metalogenia de las carbonatitas en dominios plutónicos, subvolcánicos y volcánicos: Tchivira, Bonga y Catanda, Angola. Tese de doutorado. Universitat de Barcelona. 705 pp.
; Campeny, 2016Campeny, M. (2016). Caracterización del vulcanismo carbonatítico de Catanda (Angola). Tésis de Doutoramento, Universitat de Barcelona, 66 pp.
), defining anticlinal structures associated with the flanks of the volcanic building. Campeny et al. (2017)Campeny, M., Melgarejo, J.C., Mangas, J., & Gonçalves, A.O. (2017). Recent carbonatitic magmatism in Angola: the dykes of the Chiva lagoon maar. Boletín de la Sociedad Geológica Mexicana, 209-220.
cite the presence of explosive and effusive maar-type structures, located in the Chiva lagoon, related to the carbonatitic magmatism of Catanda. The petrography of these rocks is described in detail in the works of Melgarejo et al. (2012)Melgarejo, J. C., Costanzo, A., Bambi, A. C., Gonçalves, A. O., & Neto, A. B. (2012). Subsolidus processes as a key factor on the distribution of Nb species in plutonic carbonatites: The Tchivira case, Angola. Lithos, 152, 187-201.
, Bambi (2015)Bambi, A.C.J.M. (2015). Metalogenia de las carbonatitas en dominios plutónicos, subvolcánicos y volcánicos: Tchivira, Bonga y Catanda, Angola. Tese de doutorado. Universitat de Barcelona. 705 pp.
, Campeny et al. (2014Campeny, M., Mangas, J., Melgarejo, J. C., Bambi, A., Alfonso, P., Gernon, T., & Manuel, J. (2014). The Catanda extrusive carbonatites (Kwanza Sul, Angola): an example of explosive carbonatitic volcanism. Bulletin of Volcanology, 76, 1-15.
, 2015Campeny, M., Kamenetsky, V.S., Melgarejo, J.C., Mangas, J., Alfonso, P., Kamenetsky, M.B., Bambi, A.C.J.M., & Gonçalves, A.O. (2015). Carbonatitic lavas in Catanda (Kwanza Sul, Angola): Mineralogical and geochemical constraints on the parental melt. Lithos, 232, 1-11.
, 2017)Campeny, M., Melgarejo, J.C., Mangas, J., & Gonçalves, A.O. (2017). Recent carbonatitic magmatism in Angola: the dykes of the Chiva lagoon maar. Boletín de la Sociedad Geológica Mexicana, 209-220.
, Campeny (2016)Campeny, M. (2016). Caracterización del vulcanismo carbonatítico de Catanda (Angola). Tésis de Doutoramento, Universitat de Barcelona, 66 pp.
and Giuliani et al. (2017)Giuliani, A., Campeny, M., Kamenetsky, V. S., Afonso, J. C., Maas, R., Melgarejo, J. C., & Manuel, J. (2017). Southwestern Africa on the burner: Pleistocene carbonatite volcanism linked to deep mantle upwelling in Angola. Geology, 45(11), 971-974.
.

Panoramic view of the Catanda Carbonatitic Complex (CCC) from the NE. The shape of the volcanic edifice is partially preserved and the carbonatite outcrops can be seen at the top of the image, whereas the eluvial deposits covering the entire area appear at the bottom of the image.

Figure 2. Panoramic view of the Catanda Carbonatitic Complex (CCC) from the NE. The shape of the volcanic edifice is partially preserved and the carbonatite outcrops can be seen at the top of the image, whereas the eluvial deposits covering the entire area appear at the bottom of the image.

Figura 2. Vista panorámica del Complejo Carbonatítico de Catanda desde el NE. Se conserva parcialmente la forma del edificio volcánico y se pueden ver los afloramientos de carbonatitas en la parte superior de la imagen, y los depósitos eluviales que cubren toda el área en la parte inferior de la imagen.

The pyroclastic deposits of the CCC seem to be linked to explosive episodes related to the high volatile content of the carbonatitic magmas. These deposits consist of fine- to medium-grained pyroclastites with cinerite levels, the latter typically deposited at the top of the sequence (figs. 3A, E and 4). They usually show pale, fiery to slightly yellowish colours (figs. 3A, B). The tuff levels and pyroclastites may present carbonate cement, which increases their competence and resistance to weathering. They usually present parallel, grain-decreasing, lamination and planar or cross stratification (figs. 3C, D). These deposits are composed of calcite, apatite, pyroxene, quartz and amphibole crystals (Bambi, 2016Bambi, A. C. J. M. (2016). Metalogenia de las carbonatitas en dominios plutónicos, subvolcánicos y volcánicos: Tchivira, Bonga y Catanda, Angola.
). The pyroclastic levels usually include heterolithic fragments of foliated granitoids and porphyritic granites, and more sparsely, gabbros and serpentinised ultramafic rocks, associated with host-rock brecciation during the carbonatite magma ascent, and extrusion of volcanic products (Fig. 3E). Some of these fragments show signs of metasomatism related to the circulation of hydrothermal fluids and/or volatile enrichment occurring after the extrusion of the carbonatitic pulses.

Mesoscopic and microscopic features of the Catanda volcanic rocks. a) Fine- to medium-grained pyroclastic deposits, forming a steep slope of the volcanic edifice. b) Alternation of fine- to medium-grained pyroclastites and cinerites, showing greyish to slightly yellowish light colours. c) Carbonatite pyroclastites deposited unconformably over the Palaeoproterozoic granitic basement. d) Cross-bedded fine- to medium-grained pyroclastites. e) Detail of a fragment of a porphyritic granite included in the pyroclastite deposits. f) Competent levels of carbonatite lavas, showing dark colours and high relief. g) Carbonatite lava flow corresponding to the upper half of stratigraphic column B. h) Detail of the carbonatite lava flow, showing apatite and calcite phenocrysts and mafic xenocrystic (olivine, pyroxene), with reaction halos at the edges. i) Microphotograph of the carbonatite lava flow, showing phlogopite, hornblende, clinopyroxene and olivine phenocrysts in a matrix composed of carbonates, opaque minerals and zeolites. j) Scanning electron microscope (SEM) microphotograph of a pyroclastic flow, showing abundant phenocrysts within a fine-grained matrix. Reaction halos in grain edges are observed in the phenocrysts.

Figure 3. Mesoscopic and microscopic features of the Catanda volcanic rocks. a) Fine- to medium-grained pyroclastic deposits, forming a steep slope of the volcanic edifice. b) Alternation of fine- to medium-grained pyroclastites and cinerites, showing greyish to slightly yellowish light colours. c) Carbonatite pyroclastites deposited unconformably over the Palaeoproterozoic granitic basement. d) Cross-bedded fine- to medium-grained pyroclastites. e) Detail of a fragment of a porphyritic granite included in the pyroclastite deposits. f) Competent levels of carbonatite lavas, showing dark colours and high relief. g) Carbonatite lava flow corresponding to the upper half of stratigraphic column B. h) Detail of the carbonatite lava flow, showing apatite and calcite phenocrysts and mafic xenocrystic (olivine, pyroxene), with reaction halos at the edges. i) Microphotograph of the carbonatite lava flow, showing phlogopite, hornblende, clinopyroxene and olivine phenocrysts in a matrix composed of carbonates, opaque minerals and zeolites. j) Scanning electron microscope (SEM) microphotograph of a pyroclastic flow, showing abundant phenocrysts within a fine-grained matrix. Reaction halos in grain edges are observed in the phenocrysts.

Figura 3. Características mesoscópicas y microscópicas de los materiales volcánicos de Catanda. a) Materiales piroclásticos de grano fino a medio, que forman una pendiente pronunciada del edificio volcánico. b) Alternancia de piroclastitas y cineritas de grano fino a medio, con colores claros, grises a ligeramente amarillentos. c) Piroclastitas carbonatíticas depositadas en discordancia sobre las unidades del basamento granítico Paleoproterozoico. d) Piroclastitas de grano fino a medio con estratificación cruzada. e) Detalle de un fragmento de granito porfídico (roca encajante) incluido en los depósitos piroclásticos. f) Niveles competentes de lavas carbonatíticas, de tonalidades oscuras y elevado relieve. g) Colada carbonatítica correspondiente a la mitad superior de la columna B () Detalle de la colada carbonatítica, mostrando fenocristales de apatito, calcita y xenocristales de minerales máficos (olivino, piroxeno), con halos de reacción en los bordes. i) Lámina delgada de la colada de lava carbonatítica, mostrando fenocristales de flogopita, hornblenda, clinopiroxeno y olivino en una matriz compuesta por carbonatos, minerales opacos y zeolitas. j) Microfotografía con microscopio electrónico de barrido (SEM) de una muestra piroclástica, donde se pueden observar abundantes fenocristales dentro de una matriz de grano fino. Se observan bordes de reacción en los fenocristales.

Effusive carbonatite lava flows tend to occur at high structural levels within the volcanic edifice. The dark grey to greenish colours of these materials, together with their high competence, make them more visible in the most prominent heights of the sequence (figs. 3F, G). They have an inequigranular porphyritic holocrystalline texture, with subhedral to anhedral apatite, calcite and phlogopite phenocrysts, and olivine, magnetite and pyroxene xenocrysts, the latter showing reaction rims (figs. 3H, J).

The matrix forms a micro- to cryptocrystalline carbonate-rich mesostasis with brownish to violet colours, together with larger crystals of olivine, apatite, clinopyroxene, opaque minerals, and zeolites (Fig. 3H). Bambi (2015)Bambi, A.C.J.M. (2015). Metalogenia de las carbonatitas en dominios plutónicos, subvolcánicos y volcánicos: Tchivira, Bonga y Catanda, Angola. Tese de doutorado. Universitat de Barcelona. 705 pp.
and Campeny (2016)Campeny, M. (2016). Caracterización del vulcanismo carbonatítico de Catanda (Angola). Tésis de Doutoramento, Universitat de Barcelona, 66 pp.
mentioned the presence of pyrochlore, fluorite, fluorapatite, spinel, baddeleyite and barite.

During PLANAGEO field work, two stratigraphic columns were made (Fig. 4; see location in Fig. 1). The column A-Gonjomba was studied in the NW area of the carbonatitic complex, with a total thickness of 58 meters. This section is dominated by pyroclastites rather than lava flows. The lower part (30 m) of the column consists of lenticular pyroclastic bodies with variable thickness and a lateral continuity of up to 18 m (Fig. 4A). These pyroclastite layers show a tendency to decrease in grain size towards the top, displaying planar cross-bedding and parallel lamination (Fig. 3D). The upper part of the section (28 m) is formed by pyroclastites of variable granulometry and laminated cinerites of massive appearance (Fig. 3B), interbedded with an approximately 5 m thick pyroclastic flow level with a large lateral continuity.

Stratigraphic columns of the Catanda Carbonatite Complex (CCC). Column A - Gonjomba is located on the NW of the area whereas the B-column is located on the SE of the complex. See location on Figure 1.

Figure 4. Stratigraphic columns of the Catanda Carbonatite Complex (CCC). Column A - Gonjomba is located on the NW of the area whereas the B-column is located on the SE of the complex. See location on .

Figura 4. Columnas estratigráficas del Complejo Carbonatítico de Catanda. La columna A - Gonjomba está ubicada en el NO del área, mientras que la columna B está ubicada en el SE del complejo. Ver localización en la

The second column (B-Ungongué) was constructed on the southern slope of a volcanic eruptive centre located in the eastern part of the complex, reaching a total thickness of almost 70 m. This section contains a higher concentration of pyroclastic materials compared to column A, covering almost 55 m of the section. The pyroclastite levels are heterometric and have an overall massive appearance (Fig. 4B). The presence of heterolithic fragments in the pyroclastic materials of the surrounding basement (gabbros, foliated granites and porphyritic granites) is constant along the two columns (Fig. 3E). The upper half of this section is dominated by massive carbonatite lava flows (figs. 3F, H). The sample dated in this study (UTEMC33U015I; UTM coordinates: (X) 441538 (Y) 8708575) was taken from this carbonatitic level.

4. Ar-Ar methodology

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Sample preparation for Ar-Ar dating, including rock crushing and mineral separation (phlogopite in this case), was performed at the IGME laboratories in Tres Cantos (Madrid, Spain) and sent to the Pacific Center for Isotopic and Geochemical Research (PCIGR), University of British Columbia (Vancouver, Canada).

Samples were crushed and sieved to obtain fragments ranging in the size from 0.1 to 0.5 mm. A hand-magnet was passed over the samples to remove magnetic minerals and metallic crusher fragments/spall. The samples were rinsed in dilute nitric acid, washed in deionized water and then air-dried at room temperature. Mineral separates were hand-picked, wrapped in aluminium foil and stacked in an irradiation capsule with similar-aged samples and neutron flux monitors (Fish Canyon Tuff sanidine, 28.02 Ma; Renne et al., 1998Renne, P.R., Swisher, C.C., III, Deino, A.L., Karner, D.B., Owens, T., & DePaolo, D.J. (1998). Intercalibration of standards, absolute ages and uncertainties in ⁴⁰Ar/³⁹Ar dating. Chemical Geology, 145, 117-152.
). The samples were irradiated at the McMaster Nuclear Reactor in Hamilton, Ontario, for 56 MWH, with a neutron flux of 3x1016 neutrons/cm². Analyses (n=54) of 18 neutron flux monitor positions produced errors of <0.5% in the J value. The mineral separates were step-heated at incrementally higher powers in the defocused beam of a 10W CO₂ laser (New Wave Research MIR10) until fused, at the Noble Gas Laboratory of the PCIGR facilities from the University of British Columbia. The gas evolved from each step was analysed with a VG5400 mass spectrometer equipped with an ion-counting electron multiplier. All measurements were corrected for total system blank, mass spectrometer sensitivity, mass discrimination, radioactive decay during and after irradiation, as well as interfering Ar from atmospheric contamination and the irradiation of Ca, Cl and K. Isotope production ratios were (⁴⁰Ar/³⁹Ar) K=0.0302, (³⁷Ar/³⁹Ar) Ca=1416.4306, (³⁶Ar/³⁹Ar) Ca=0.3952, Ca/K=1.83(³⁷ArCa/³⁹ArK). The plateau and correlation ages were calculated using Isoplot 3.09 software (Ludwig, 2003Ludwig, K.R. (2003). Isoplot 3.00 A Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center, Special Publication No. 4.
). Errors are quoted at the 2σ (95% confidence) level and are propagated from all sources except mass spectrometer sensitivity and age of the flux monitor.

5. Ar-Ar geochronological results

⌅

A carbonatite sample from a lava flow from an eruptive centre located in the eastern part of the CCC was selected for Ar-Ar isotopic analyses (sample UTEMC33U015I; Fig. 3H). Ar-Ar dating was performed on whole-rock and phlogopite separates of the same sample (figs. 5, 6). The whole-rock Ar-Ar spectra shows a “U” shape pattern of gas steps with different apparent ages (Fig. 5A). The first two initial heating steps display an average age of 1483 ± 67 Ma, due to the low ³⁹Ar (4.42-3.51 %) and radiogenic ⁴⁰Ar content (15.95-12.34%; Table 1), while the next two steps and the final one yield an average age of 471 ± 28 Ma. The remaining three continuous steps with 61% of the Ar released provide an Ar-Ar plateau age of 203 ± 19 Ma (MSWD = 0.028, probability = 0.97; Fig. 5A). The normal isochron age of the whole data reveals an inaccurate age of 170 ± 78 Ma (MSWD = 10.5; Fig. 5B). After pooling the concordant ⁴⁰Ar*/³⁹Ar results and discriminating the two age spectra, the corresponding inverse isochrons yield Ar-Ar ages of 461 ± 63 Ma for the oldest data (Fig. 5C), and 203 ± 49 Ma for the youngest steps (Fig. 5D), which are within the error of the Ar-Ar plateau ages.

A) Whole-rock Ar/Ar plateau age obtained for the Catanda carbonatite lava flow (sample UTEMC33U015I) (203 ± 19 Ma); B) Whole-rock, normal isochron of the whole data, reporting an Ar-Ar age of 170 ± 78 Ma. C) Inverse isochron of the old concordant age data, giving an Ar-Ar age of 461 ± 63 Ma. D) Inverse isochron of the youg concordant data, showing an age of 203 ± 49 Ma.

Figure 5. A) Whole-rock Ar/Ar plateau age obtained for the Catanda carbonatite lava flow (sample UTEMC33U015I) (203 ± 19 Ma); B) Whole-rock, normal isochron of the whole data, reporting an Ar-Ar age of 170 ± 78 Ma. C) Inverse isochron of the old concordant age data, giving an Ar-Ar age of 461 ± 63 Ma. D) Inverse isochron of the youg concordant data, showing an age of 203 ± 49 Ma.

Figura 5. A) Edad de plateau Ar/Ar en roca total de una colada carbonatítica de Catanda (muestra UTEMC33U015I). Magmatismo carbonatítico de Catanda (203 ± 19 Ma); B) Edad de isocrona Ar-Ar obtenida a partir de todos los datos de edades, aportando una edad de 170 ± 78 Ma. C) Isocrona inversa de los datos concordantes antiguos, obteniéndose una edad Ar-Ar de 461 ± 63 Ma. D) Isocrona inversa de los datos concordantes jóvenes, mostrando una edad de 203 ± 49 Ma.

A) Ar/Ar Plateau age from phlogopite phenocrysts of the Catanda lava flow (UTEMC33U015I) (3.01 ± 0.53 Ma), B) Inverse isochron obtained from the concordant Ar-Ar age data, giving an age of 2.83 ± 0.66 Ma.

Figure 6. A) Ar/Ar Plateau age from phlogopite phenocrysts of the Catanda lava flow (UTEMC33U015I) (3.01 ± 0.53 Ma), B) Inverse isochron obtained from the concordant Ar-Ar age data, giving an age of 2.83 ± 0.66 Ma.

Figura 6. A) Edad de plateau Ar/Ar en separados de flogopita de la misma colada de Catanda (UTEMC33U015I) (3.01 ± 0.53 Ma), B) Isocrona inversa obtenida a partir de los datos de edad Ar-Ar concordantes, aportando una edad de 2.83 ± 0.66 Ma.

Table 1. Results of whole rock Ar-Ar studies on sample: UTEMC33U015I.

Tabla 1. Resultados de los estudios Ar-Ar en roca total en la muestra: UTEMC33U015I.

Laser	Isotope Ratios
Power(%)	⁴⁰ Ar/ ³⁹ Ar	2s	³⁶ Ar/ ³⁹ Ar	2s	³⁹ Ar/ ⁴⁰ Ar	2s	³⁶ Ar/ ⁴⁰ Ar	2s	Rho	K/Ca	%⁴⁰Ar rad	f ³⁹Ar	⁴⁰ *Ar/ ³⁹ ArK**	Age	2s
2,30	1721,39	35,15	4,86	0,12	0,0006	0,00001	0,0028	0,00004	0,053	0,01	15,95	4,42	281,893	1457,80	± 79,57
2,60	2305,16	135,51	6,80	0,41	0,0004	0,00003	0,0029	0,00004	0,026	0,00	12,34	3,51	307,483	1546,83	± 127,34
3,00	433,71	6,23	1,26	0,03	0,0022	0,00003	0,0028	0,00006	0,223	0,01	14,99	11,14	69,072	477,93	± 56,00
3,40	257,89	3,91	0,72	0,02	0,0035	0,00007	0,0026	0,00008	0,193	0,00	23,02	11,16	66,716	463,53	± 43,95
3,80	118,32	3,32	0,34	0,04	0,0080	0,00023	0,0026	0,00033	0,183	0,01	21,61	9,80	27,004	201,95	± 88,25
4,50	56,56	1,31	0,11	0,01	0,0172	0,00040	0,0018	0,00018	0,213	0,02	47,17	25,72	27,353	204,42	± 22,93
5,20	73,59	1,92	0,18	0,01	0,0131	0,00035	0,0022	0,00020	0,108	0,01	34,82	25,43	26,670	199,59	± 33,66
6,00	160,77	3,81	0,36	0,02	0,0058	0,00014	0,0020	0,00014	0,248	0,01	39,59	8,83	68,469	474,26	± 48,50
J = 0.00431950 ± 0.00000864								Volume ³⁹ArK = 0,078 x E-13 cm³ NPT
Integrated Date = 343,76 ± 15,09 Ma
Plateau age = 203 ± 19 Ma				(2σ, including J-error of .4%)				MSWD = 0.028, probability=0.97				Includes 60.9% of the ³⁹Ar steps 5 through 7
Inverse isochron (correlation age) results: Model 1 Solution (± 95%-conf.) on 3 points
Age = 461 ± 63 Ma				Initial ⁴⁰Ar/³⁶Ar =299 ± 12				MSWD = 0.18				Probability = 0.67
Inverse isochron (correlation age) results: Model 1 Solution (± 95%-conf.) on 3 points
Age = 203 ± 49 Ma				Initial ⁴⁰Ar/³⁶Ar =295 ± 49				MSWD = 0.034				Probability = 0.85

The phlogopite separate provides an Ar-Ar plateau age of 3.01 ± 0.53 Ma (MSWD = 0.39, probability = 0.91, including 98.9% of ³⁹Ar; Fig. 6A). The two first steps were discarded for age calculations, due to their low ³⁹Ar (0.24 % and 0.81 %) and erratic radiogenic ⁴⁰Ar values (-237.9 % and -310.09 %) (Table 2). However, the remaining data showed a consistent average age throughout all heating stages, within error, supporting the confidence of the Ar-Ar plateau age obtained. In fact, the produced inverse isochron from the concordant Ar-Ar age data provides a similar age (i.e., 2.83 ± 0.66 Ma; Fig. 6B) to that obtained by the Ar-Ar plateau age, reinforcing the consistency of the age data.

Table 2. Results of Ar-Ar studies on phlogopite separates from the sample: UTEMC33U015I.

Tabla 2. Resultados de los estudios Ar-Ar en separados de flogopita de la muestra: UTEMC33U015I

Laser	Isotope Ratios
Power(%)	⁴⁰ Ar/ ³⁹ Ar	2s	³⁶ Ar/ ³⁹ Ar	2s	³⁹ Ar/ ⁴⁰ Ar	2s	³⁶ Ar/ ⁴⁰ Ar	2s	Rho	K/Ca	%⁴⁰Ar rad	f ³⁹Ar	⁴⁰ *Ar/ ³⁹ ArK**	Age	2s
2,40	56,61	2,33	0,64	0,14	0,02	0,0007	0,0113	0,0025	0,052	0,12	-237,95	0,24	135,153	-2052,03	± 1173,29
2,80	35,11	0,28	0,48	0,07	0,03	0,0002	0,0137	0,0021	0,009	0,30	-310,09	0,81	109,027	-1436,38	± 438,71
3,20	5,11	0,04	0,0157	0,0021	0,20	0,0015	0,0030	0,0004	0,035	2,59	8,98	4,13	0,459	4,19	± 5,75
3,50	5,30	0,05	0,0168	0,0041	0,19	0,0019	0,0032	0,0008	0,032	1,78	5,65	3,25	0,299	2,73	± 11,08
3,90	2,13	0,02	0,0064	0,0009	0,47	0,0037	0,0030	0,0004	0,033	4,50	10,47	9,13	0,222	2,03	± 2,56
4,30	2,27	0,02	0,0061	0,0011	0,44	0,0042	0,0027	0,0005	0,038	6,06	19,90	7,63	0,452	4,12	± 3,07
4,80	2,43	0,02	0,0065	0,0010	0,41	0,0031	0,0027	0,0004	0,031	8,08	20,17	8,27	0,490	4,47	± 2,69
6,20	0,79	0,01	0,0022	0,0004	1,26	0,0113	0,0021	0,0005	0,021	0,37	38,24	24,26	0,303	2,76	± 1,10
7,20	0,54	0,00	0,0012	0,0002	1,84	0,0169	0,0013	0,0005	0,019	0,38	60,97	32,39	0,332	3,02	± 0,68
8,20	0,72	0,01	0,0017	0,0009	1,40	0,0254	0,0019	0,0013	0,025	0,67	42,55	9,91	0,305	2,78	± 2,54
J = 0.00498690 ± 0.00000997								Volume ³⁹ArK = 1,326 x E-13 cm³ NPT
Integrated Date = 3,01 ± 0,53 Ma
Plateau age = 3.01 ± 0.53 Ma				(2σ, including J-error of .4%)				MSWD = 0.39, probability=0.91				Includes 98.9% of the ³⁹Ar steps 3 through 10
Inverse isochron (correlation age) results: Model 1 Solution (±95%-conf.) on 8 points
Age = 2.83 ± 0.66 Ma				Initial ⁴⁰Ar/³⁶Ar =307 ± 26				MSWD = 0.37				Probability = 0.9

6. Discussion

⌅

The Catanda volcanic complex was commonly considered to be formed during Cretaceous times (e.g., Silva & Pereira, 1971Silva, M.V.S., & Pereira, E. (1971). Notícia Explicativa da carta Nº 207 GUNGO, escala 1:100 000. Direcção Provincial dos Serviços de Geologia e Minas, Luanda.
; Issa Filho et al., 1991Issa Filho, A., Dos Santos, A.B.R.M.D., Riffel, B.F., Lapido-Loureiro, F.E.V., & McReath, I. (1991). Aspects of the geology, petrology and chemistry of some Angolan carbonatites. J. Geochem. Explor., 40, 205-226.
; Alberti et al., 1999Alberti, A., Castorina, F., Censi, P., Comin-chiaramonti, P., & Gomes, C.B. (1999). Geochemical characteristics of Cretaceous carbonatites from Angola. Journal África Earth Sciences, 29(4), 735-759.
), according to the whole-rock K-Ar crystallisation age of 92 ± 7 Ma reported for the tinguaite dikes located southeast of Catanda (Torquato & Amaral, 1973Torquato, J.R., & Amaral, G. (1973). Idades K/Ar em rochas das regiões de Catanda e Vila do Almoster. Bol. Inst. Invest. Cient., Angola, Luanda, vol. 10, Pub. IICA 308.
). The U-Pb geochronological works performed in kimberlites from the Catoca region, to the east of Catanda, provided an eruption age of 117.9 ± 0.7 Ma (Robles-Cruz et al., 2012Robles-Cruz, S. E., Escayola, M., Jackson, S., Galí, S., Pervov, V., Watangua, M., & Melgarejo, J. C. (2012). U-Pb SHRIMP geochronology of zircon from the Catoca kimberlite, Angola: implications for diamond exploration. Chemical geology, 310, 137-147.
). Other works provide crystallisation ages of some alkaline-carbonatitic massifs in Angola comprised between 130 and 155 Ma, using Rb-Sr isochron or Ar-Ar plateau ages (Cahen et al., 1984Cahen, L., Snelling, N.J., Delhal, J., & Vail, J.R. (1984). The geochronology and evolution of África: London, Oxford University Press, 512 p.
; Allsopp & Hargraves, 1985Allsopp, H.L., & Hargraves, R.B. (1985). Rb-Sr ages and palaeomagnetic data for some Angolan alkaline intrusives. Transactions Geological Society South Africa, 88, 295-299.
; Merino-Martínez, 2022Merino-Martínez, E. (2022). Carta Geológica de Angola à escala 1:100.000, folha 336 (Lubango), e memória explicativa. UTE (IGME, LNEG, Impulso) - IGEO, Luanda, 172 p.
; Merino-Martínez et al., 2025Merino-Martínez, E., Valverde-Vaquero, P., Beranoaguirre, A., Galán, G., Gabites, J., & Manuel, J. (2025). Preliminary Ar-Ar geochronology of Cretaceous alkaline-carbonatitic to tholeiitic magmatism in the Quilengues area, SW Angola. Boletín Geológico y Minero, (136).
), suggesting a clear relationship between this magmatism and the breakup of Gondwana and the opening of the South Atlantic Ocean. Nevertheless, the works of Campeny (2016)Campeny, M. (2016). Caracterización del vulcanismo carbonatítico de Catanda (Angola). Tésis de Doutoramento, Universitat de Barcelona, 66 pp.
and Giuliani et al. (2017)Giuliani, A., Campeny, M., Kamenetsky, V. S., Afonso, J. C., Maas, R., Melgarejo, J. C., & Manuel, J. (2017). Southwestern Africa on the burner: Pleistocene carbonatite volcanism linked to deep mantle upwelling in Angola. Geology, 45(11), 971-974.
attributed an extrusion age for the Catanda carbonatite lavas between 0.56 and 0.78 Ma based on ³⁹Ar-⁴⁰Ar in phlogopite and (U-Th-Sm)/He in apatite isotopic dating. These authors considered these ages to be associated with the reactivation of Cretaceous structures, such as the Lucapa corridor, during the middle Pleistocene.

The Ar-Ar data obtained in the PLANAGEO project, presented in this study, together with the previously reported Ar-Ar data (Campeny, 2016Campeny, M. (2016). Caracterización del vulcanismo carbonatítico de Catanda (Angola). Tésis de Doutoramento, Universitat de Barcelona, 66 pp.
; Giuliani et al., 2017Giuliani, A., Campeny, M., Kamenetsky, V. S., Afonso, J. C., Maas, R., Melgarejo, J. C., & Manuel, J. (2017). Southwestern Africa on the burner: Pleistocene carbonatite volcanism linked to deep mantle upwelling in Angola. Geology, 45(11), 971-974.
) suggest that this magmatism took place between 3 and 0.5 Ma. Excess argon is responsible for the U-shaped Ar-Ar spectra displayed by the whole-rock sample. This feature is commonly associated with low potassium rocks or the presence of melt or fluid inclusions, which would release far more argon during stepwise heating, producing anomalously old ages (e.g., Kelley, 2002Kelley, S. (2002). Excess argon in K-Ar and Ar-Ar geochronology. Chemical Geology, 188, 1-22.
, and references therein). Also, it can be attributed to the presence of excess Ar in the mantle source of these magmas (e.g., Coltice & Ricard, 2002Coltice, N., & Ticard, Y. (2002). On the origin of noble gases in mantle plumes. Phil. Trans.R.Soc. Lond. A, 360, 2633-2648.
). Thus, although the whole rock Ar-Ar plateau ages displayed in the Catanda carbonatite lava flow could reflect distinct incorporation mechanisms for the excess argon (Fig. 5A), they may be also indicative of old magmatic events and/or mantle metasomatic imprints recorded by the carbonatitic magmas, these latter without connection to any precise tectono-thermal event identified at the surface of the region so far.

The younger Ar-Ar plateau ages of 203 ± 19 are similar to the whole-rock K-Ar age of 222 ± 16 Ma reported in basaltic lava flows found in the Kwanza Basin (Torquato & Amaral, 1973Torquato, J.R., & Amaral, G. (1973). Idades K/Ar em rochas das regiões de Catanda e Vila do Almoster. Bol. Inst. Invest. Cient., Angola, Luanda, vol. 10, Pub. IICA 308.
). It is worth noting that within the PLANAGEO project other recent Ar-Ar dating in basaltic samples south to the Sumbe area also reveal an Ar-Ar plateau age of 210 ± 6 Ma (Merino-Martínez et al., 2021Merino-Martínez, E., Chinchilla, D., and Chamizo, M. (2021). Carta Geológica de Angola à escala 1:250.000, folha Sul C-33/U (Ucu Seles, metade Sul), e memória explicativa. UTE (IGME, LNEG, Impulso) - IGEO, Luanda, 175 p.
), which closely aligns with the results obtained in the Catanda samples. These ages are also alike to those reported in dolerite dikes from the Espinhaço Region and Santos Basin of Brazil (220-193 Ma; Dossini et al., 1995Dossini, T.M., Dossini, I.A., Charvet, J., & Bonhomme, M.G. (1995). K-Ar chronology of a Mesozoic dike swarm from southern Espinhaço Region (SE Brazil). Journal of South American Earth Sciences, 8(1), 47-53.
; Guedes et al., 2005Guedes, E., Heilbron, M., Vasconcelos, P.M., Valeriano, C.M., Horta de Almeida, J.C., Teixeira, W., & Thomaz Filho, A. (2005). K-Ar and ⁴⁰Ar/³⁹Ar ages of dikes emplaced in the onshore basement of the Santos Basin, Resende area, SE Brazil: implications for the south Atlantic opening and Tertiary reactivation. Journal of South American Earth Sciences, 18(3-4), 371-382.
) and closely resemble those documented in the Central Atlantic Magmatic Province (204-192 Ma; Svensen et al., 2017Svensen, H.H., Torsvik, T.H., Callegaro, S., Augland, L., Heimdal, T.H., Jerram, D.A., Planke, S., & Pereira, E. (2017). Gondwana Large Igneous Provinces: plate reconstructions, volcanic basins and sill volumes. Em: Sensarma, S. e Strorey, B.C. (eds). Large Igenous Provinces from Gondwana and Adjacent Regions. Geological Society, Special Publications, 463.
; Oliveira et al., 2023Oliveira, A.L., Schmitz, M.D., Wall, C.J., Crowley, J.L., Macêdo Filho, A.A., & Hollanda, M.H.B.M. (2023). New U-Pb geochronology for the Central Atlantic Magmatic Province, critical reevaluation of high-precision ages and their impact on the end-Triassic extinction event. Science Reports, 13, 5485. https://doi.org/10.1038/s41598-023-32534-3
). This would suggest that: i) the Catanda magmatism was related to the pre-Karoo magmatism recorded in the Central Atlantic Magmatic Province, and may correspond to the first basaltic pulses occurred during the early stages of crustal break-up of the Pangaea supercontinent during the Triassic-Jurassic transition (Svensen et al., 2017Svensen, H.H., Torsvik, T.H., Callegaro, S., Augland, L., Heimdal, T.H., Jerram, D.A., Planke, S., & Pereira, E. (2017). Gondwana Large Igneous Provinces: plate reconstructions, volcanic basins and sill volumes. Em: Sensarma, S. e Strorey, B.C. (eds). Large Igenous Provinces from Gondwana and Adjacent Regions. Geological Society, Special Publications, 463.
); or ii) that high-temperature xenolith minerals and/or inclusions were incorporated in the carbonatite materials, revealing a late-Triassic metasomatism event in the lithospheric mantle beneath the Catanda volcanics, similar to that suggested for other Cenozoic alkaline volcanics (e.g., Villaseca et al., 2018Villaseca, C., Belousova, E.A., Barford, D.N., & González-Jiménez, J.M. (2018). Dating metasomatic events in the lithospheric mantle beneath the Calatrava volcanic field (central Spain). Lithosphere, 11(2), 192-208.
).

Possible evidence for mantle metasomatic events could be also recorded in this Ar spectra. The initial whole-rock Ar ages constrained between 1547 and 1458 Ma (average age of 1483 ± 67 Ma) would probably attest for erratic measurements due to excess Ar (Fig. 5A; Table 1). Nevertheless, similar ages are documented in SW Angola and NW Namibia, related to the emplacement of distinct igneous intrusions and MT to HT metamorphic events registered in the Epupa Complex during the late-Palaeoproterozoic and Early-Mesoproterozoic (1534-1447 Ma Brandt et al., 2003Brandt, S. (2003). Metamorphic evolution of ultrahigh-temperature granulite facies and upper amphibolite facies rocks of the Epupa Complex, NW Namibia. Unpublished PhD Thesis, University of Würzburg, Germany, 289 p.
; Seth et al., 2003Seth, B., Armstrong, R.A., Brandt, S., Villa, I.M., & Kramers, J.D. (2003). Mesoproterozoic U-Pb and Pb-Pb ages of granulites in NW Namibia: reconstructing a complete orogenic cycle. Precambrian Research, 126, 147-168. https://doi.org/10.1016/S0301-9268(03)00193-1
, 2005Seth, B., Armstrong, R.A., Büttner, A., & Villa, I.M. (2005). Time constraints for Mesoproterozoic upper amphibolite facies metamorphism in NW Namibia: a multi-isotopic approach. Earth and Planetary Science Letters, 230, 355-378. https://doi.org/10.1016/j.epsl.2004.11.022
).

In addition, some steps of the whole-rock Ar-Ar dating performed in the carbonatitic lavas of Catanda also display an average age of 471 ± 28 Ma. This age matches the ages recorded in the post-orogenic stages of the Pan-African/Brasiliano orogeny (Heilbron et al., 2008Heilbron, M., Valeriano, C. D. M., Tassinari, C. C. G., Almeida, J., Tupinamba, M., Siga Jr, O., & Trouw, R. (2008). Correlation of Neoproterozoic terranes between the Ribeira Belt, SE Brazil and its African counterpart: comparative tectonic evolution and open questions. Geological Society, London, Special Publications, 294(1), 211-237.
; Bento dos Santos et al., 2010Bento dos Santos, T. M., Munhá, J. M., Tassinari, C. C., Fonseca, P. E., & Neto, C. D. (2010). Thermochronology of central Ribeira Fold Belt, SE Brazil: Petrological and geochronological evidence for long-term high temperature maintenance during Western Gondwana amalgamation. Precambrian Research, 180 (3-4), 285-298.
, 2015Bento dos Santos, T. M. B., Tassinari, C. C., & Fonseca, P. E. (2015). Diachronic collision, slab break-off and long-term high thermal flux in the Brasiliano-Pan-African orogeny: Implications for the geodynamic evolution of the Mantiqueira Province. Precambrian Research, 260, 1-22.
). It is interesting to note that other similar ages have been determined within the PLANAGEO Project (i.e., 509-475 Ma; Chamizo & Buzzi, 2021Chamizo, M., & Buzzi, J. (2021). Carta Geológica de Angola à escala 1:100.000, folha 250-251 (Benguela), e memória explicativa. UTE (IGME, LNEG, Impulso) - IGEO, Luanda, 156 pp.
; Lopes et al., 2021Lopes, R., Pereira, L. F., Caessa, P., & Correia, J. (2021). Carta Geológica de Angola à escala 1:250.000, folha Sul D-33/G (Equimina), e memória explicativa. UTE (IGME, LNEG, Impulso) - IGEO, Luanda, 296 pp.
; Merino-Martínez, 2022Merino-Martínez, E. (2022). Carta Geológica de Angola à escala 1:100.000, folha 336 (Lubango), e memória explicativa. UTE (IGME, LNEG, Impulso) - IGEO, Luanda, 172 p.
) in distinct gneissic rocks from the Angolan coastal region and in dolerite dikes from SW Angola. Torquato & Amaral (1973)Torquato, J.R., & Amaral, G. (1973). Idades K/Ar em rochas das regiões de Catanda e Vila do Almoster. Bol. Inst. Invest. Cient., Angola, Luanda, vol. 10, Pub. IICA 308.
also reported equivalent K-Ar ages ranging from 508 ± 59 to 490 ± 8 Ma in granite and gneissic rocks to the west of Catanda. In fact, these ages are described in the coastal Angolan counterparts, the Ribeira Belt/Mantiqueira Province in SE Brazil and northern Uruguay, related to the cooling ages of long-term magmatism (540-490 Ma; Bento dos Santos et al., 2010Bento dos Santos, T. M., Munhá, J. M., Tassinari, C. C., Fonseca, P. E., & Neto, C. D. (2010). Thermochronology of central Ribeira Fold Belt, SE Brazil: Petrological and geochronological evidence for long-term high temperature maintenance during Western Gondwana amalgamation. Precambrian Research, 180 (3-4), 285-298.
, 2015Bento dos Santos, T. M. B., Tassinari, C. C., & Fonseca, P. E. (2015). Diachronic collision, slab break-off and long-term high thermal flux in the Brasiliano-Pan-African orogeny: Implications for the geodynamic evolution of the Mantiqueira Province. Precambrian Research, 260, 1-22.
) or in the Cabo Frio tectonic domain, associated to the latest deformational events of the Brasiliano orogeny (505-490 Ma; Schmitt et al., 2004Schmitt, R. S, Trouw, R. A., Van Schmus, W. R., & Pimentel, M. M. (2004). Late amalgamation in the central part of West Gondwana: new geochronological data and the characterization of a Cambrian collisional orogeny in the Ribeira Belt (SE Brazil). Precambrian Research, 133(1-2), 29-61.
, 2008Schmitt, R.S, Trouw, R. A. J., Medeiros, S. R., & Dantas, E. L. (2008). Age and geotectonic setting of Late Neoproterozoic juvenile mafic gneisses and associated paragneisses from the Ribeira belt (SE Brazil) based on geochemistry and Sm-Nd data—implications on Gondwana assembly. Gondwana Research, 13(4), 502-515.
).

On the contrary, the accurate Ar-Ar plateau age obtained from the phlogopite suggests an extrusion age for the carbonatitic lava flow of 3.01 ± 0.53 Ma (Fig. 6A). This age is older than the phlogopite Ar inverse isochron and U-Th-Sm/He apatite ages of 0.8-0.5 Ma obtained by Campeny (2016)Campeny, M. (2016). Caracterización del vulcanismo carbonatítico de Catanda (Angola). Tésis de Doutoramento, Universitat de Barcelona, 66 pp.
and Giuliani et al. (2017)Giuliani, A., Campeny, M., Kamenetsky, V. S., Afonso, J. C., Maas, R., Melgarejo, J. C., & Manuel, J. (2017). Southwestern Africa on the burner: Pleistocene carbonatite volcanism linked to deep mantle upwelling in Angola. Geology, 45(11), 971-974.
for other carbonatitic lavas of the CCC. Hence, the ages recorded in the CCC lava flows would suggest that distinct episodes of carbonatitic volcanism occurred during the Pliocene and Pleistocene in the Catanda region.

However, the Pliocene-Pleistocene age for the complex needs to be taken with caution, as Bambi (2015)Bambi, A.C.J.M. (2015). Metalogenia de las carbonatitas en dominios plutónicos, subvolcánicos y volcánicos: Tchivira, Bonga y Catanda, Angola. Tese de doutorado. Universitat de Barcelona. 705 pp.
and Campeny et al. (2014Campeny, M., Mangas, J., Melgarejo, J. C., Bambi, A., Alfonso, P., Gernon, T., & Manuel, J. (2014). The Catanda extrusive carbonatites (Kwanza Sul, Angola): an example of explosive carbonatitic volcanism. Bulletin of Volcanology, 76, 1-15.
, 2015)Campeny, M., Kamenetsky, V.S., Melgarejo, J.C., Mangas, J., Alfonso, P., Kamenetsky, M.B., Bambi, A.C.J.M., & Gonçalves, A.O. (2015). Carbonatitic lavas in Catanda (Kwanza Sul, Angola): Mineralogical and geochemical constraints on the parental melt. Lithos, 232, 1-11.
described diverse alteration textures in the Catanda lavas, including the phlogopite crystals, as well as evidence of geochemical and isotopic (δ¹³C-δ¹⁸O) mobility related to hydrothermal processes. This hydrothermalism could account for the disturbance of the age spectra and spread of the Ar phlogopite and U-Th-Sm/He apatite ages reported for the Catanda carbonatites. In addition, it should be noted that several meteoric alteration and erosion phenomena occurred from the Cretaceous to the Pleistocene (Pereira, 1977Pereira, E. (1977). Serra da Neve, Angola: nota sobre a geomorfologia da regiao e idade das aplanaçoes.(Serra da Neve, Angola: note sur la géomorphologie de la région et notes sur les aplanissements). Boletim da Sociedade geologica de Portugal Lisboa, 20(3), 277-282.
), and a significant crustal uplift, which formed the so-called Chela Escarpment, was described between Miocene and Pliocene times (Jackson et al., 2005Jackson, M. P. A., Hudec, M. R., & Hegarty, K. A. (2005). The great West African Tertiary coastal uplift: Fact or fiction? A perspective from the Angolan divergent margin. Tectonics, 24(6), TC6014, 24 pp.
; Guiraud et al., 2010Guiraud, M., Buta-Neto, A., & Quesne, D. (2010). Segmentation and differential post-rift uplift at the Angola margin as recorded by the transform-rifted Benguela and oblique-to-orthogonal-rifted Kwanza basins. Marine and Petroleum Geology, 27, 1040-1068.
). Thus, further geochronological and isotopic work is required to better constrain the timing of the carbonatitic volcanism and associated hydrothermalism in the CCC and its connection with the Cenozoic volcanism in central Africa (Giuliani et al., 2017Giuliani, A., Campeny, M., Kamenetsky, V. S., Afonso, J. C., Maas, R., Melgarejo, J. C., & Manuel, J. (2017). Southwestern Africa on the burner: Pleistocene carbonatite volcanism linked to deep mantle upwelling in Angola. Geology, 45(11), 971-974.
).

7. Conclusions

⌅

The newly acquired Ar-Ar dates within the PLANAGEO project prompt further discussion on the geochronology of the carbonatitic lavas found in the Catanda volcanic complex of central west Angola. The Ar-Ar data determined in whole-rock and phlogopite mineral separates from a carbonatitic lava provide significantly different ages. The whole-rock analysis provides a U-shape Ar-Ar spectra characteristic of excess Ar, with a plateau age of 210 ± 6 Ma. The geological significance of this age is arguable, but it could suggest that a late-Triassic metasomatic event could have been recorded in the lithospheric mantle beneath the CCC, related to the initial stages of magmatism during the opening of the South Atlantic Ocean. Initial whole-rock Ar steps with an average age of 1483 ± 67 Ma and an inverse Ar isochron age of 471 ± 28 Ma, although probably derived from excess Ar, could also attest for older thermal and/or metasomatic events registered in the lithospheric mantle or the presence of Mesoproterozoic and/or Palaeozoic sources beneath the Catanda region. A separate set of phlogopite crystals have provided an Ar-Ar plateau age of 3.01 ± 0.53 Ma, that is alike to the obtained concordant inverse isochron Ar age of 2.83 ± 0.66 Ma. This newly acquired Ar data, together with the previously reported ages in mineral separates (0.78-0.56 Ma in phlogopite and apatite), suggests a Pliocene-Pleistocene extrusion age for the Catanda Carbonatite Complex.

Authorship contribution statement

⌅

Darío Chinchilla-Benavides: Writing - Original Draft, Investigation, Conceptualization, Methodology, Data Curation, Visualization, Supervision, Writing - Review & Editing.

Enrique Merino-Martínez: Writing - Original Draft, Investigation, Methodology, Data Curation, Investigation, Project administration, Formal analysis, Supervision.

Manuela Chamizo-Borreguero: Investigation, Supervision, Review & Editing.

Pablo Valverde-Vaquero: Investigation, Data Curation, Formal analysis, Writing - Review & Editing. Aratz Beranoaguirre: Data Curation, Investigation, Formal analysis.

Janet Gabites: Data Curation, Investigation, Visualization.

José Manuel: Supervision, Project administration, Funding acquisition.