Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena Paleoweathering of intrusive carbonatites (4.5 Ma) from Fogo Island, Cape Verde – Mineralogy and geochemistry R. Marques a,b, ⁎ , M.I. Prudêncio a,b , M.I. Dias a,b , D. Russo a,b , J.G. Marques a,b , F. Ruiz a,c , M. Abad d , T. Izquierdo d , M.L. González-Regalado c , F. Rocha e,f a Centro de Ciências e Tecnologias Nucleares (C2TN), Instituto Superior Técnico, Universidade de Lisboa, EN10 (139.7 km), 2695-066 Bobadela, Portugal b Departamento de Engenharia e Ciências Nucleares (DECN), Instituto Superior Técnico, Universidade de Lisboa, EN 10 (km 139.7), 2695-066 Bobadela, Portugal c Departamento de Ciencias de la Tierra, Universidad de Huelva, Avda. Tres de Marzo s/n, 21071 Huelva, Spain d Departamento de Geología, Facultad de Ingeniería, Universidad de Atacama, Avda. Copayapu 485, Copiapó, Chile e Departamento de Geociências, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal f GeoBioTec – GeoBiociências, GeoTecnologias e GeoEngenharias, Universidade de Aveiro, 3810-193 Aveiro, Portugal ARTICLE INFO Keywords: Oceanic intrusive carbonatite Fogo Island Paleoweathering Mineralogy and geochemistry Size fractions Cape Verde ABSTRACT Intrusive carbonatites from a fluvial valley near Monte Almada (Fogo Island, Cape Verde), corresponding to the oldest unit of the island (≈4.5 Ma) occur under alkaline lavas and tuffs of more recent age in two slopes, with a very steep inclination. Its exposure with the water line fitting led to the weathering of the outcrops, and the materials are currently retained in small terraces with shrubs and trees. The motivation that drives this work was the absence of paleoweathering materials studies of these carbonatites in Fogo Island. Mineralogical and che- mical analyses of paleoweathered carbonatites samples with different weathering degrees were performed by means of X-ray diffraction (XRD) and instrumental neutron activation analysis (INAA). The results obtained from fresh rock to near paleosurface samples showed that chemical contents could vary significantly in the fresh rock, particularly the trace elements, including the rare earth elements (REE), as well as in the size fractions. Besides calcite, pyroxenes and phyllosilicates, traces of anatase and K-feldspars also occur in the < 2 mm fraction; dolomite was detected in one sample. Smectite, illite and kaolinite were found in the < 2 μm fraction. Carbonatites weathered products are easily distinguished from other volcanic soils of Fogo Island due to higher REE contents, particularly the light and middle ones, and to higher K, Rb, Cs, W, and Th contents. Higher concentrations of Zn and Cs are observed in the silt-clay and clay-size fractions where phyllosilicates dominate, particularly smectite and illite. 1. Introduction Carbonatites usually occur in association with alkalic silicate ig- neous rocks, namely alkaline ultramafic rocks like pyroxenites or ne- phelinites (and/or ijolites), or more evolved types such as phonolites and nepheline syenites (Harmer, 1999). The carbonate minerals are the major constituent of intrusive carbonatites, and almost 60% of the in- trusive carbonatites are calcitic, while the remaining 40% are dolomite- ankerite (Chakhmouradian et al., 2016a). Some previous works, fo- cused on calcite and dolomite of intrusive carbonatites contributed for an enhanced characterization (chemical and textural) of terrestrial ig- neous carbonate materials (Chakhmouradian et al., 2016a, 2016b). According to Jørgensen and Holm (2002), interaction between carbonatites and the oceanic mantle was found in Polynesia and Grande Comoro, but oceanic carbonatites outcrops were only found in Canary and Cape Verde archipelagos. This scarcity of oceanic carbonatites suggests that the subcontinental lithosphere may serve as the source for at least some carbonatites (Hoernle et al., 2002). In fact, carbonatites only form in hotspots with the lowest Si and highest alkali contents among their primitive melts, which are the case of these two archipe- lagos, as described by Schmidt and Weidendorfer (2018). The way carbonatites are formed is still debateable (Doucelance et al., 2010; Halama et al., 2005; Jørgensen and Holm, 2002; Woolley and Church, 2005). They may form directly from the mantle (by low-degree partial melting) or through a combination of fractionation and immiscible se- paration from CO 2 -bearing alkaline silicate melts, as described in Schmidt and Weidendorfer (2018, and references herein). The different types of carbonatites can be classed as: (i) calcite-carbonatite, including https://doi.org/10.1016/j.catena.2020.104778 Received 11 March 2019; Received in revised form 25 June 2020; Accepted 29 June 2020 ⁎ Corresponding author. E-mail address: rmarques@ctn.tecnico.ulisboa.pt (R. Marques). Catena 194 (2020) 104778 0341-8162/ © 2020 Elsevier B.V. All rights reserved. T