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Santa Luzia island is essentially formed by erosional remnants of, at least, one volcanic edifice: the Old Edifice. The remains of this edifice are now a NW-SE trending mountain range. It is a fisural edifice that follows this trend and is formed by hundreds of meters of aa-type lava flows crosscut by dikes. Lithologic compositions are basic and ultrabasic (picrobasalts, basanites, basalts and trachybasalts), intermediate (trachyandesites) and felsic (trachytes and phonolites). The main process generating these compositional differences is fractional crystallization, La isla de Santa Luzia está formada esencialmente por los restos erosivos de, al menos, un edificio volcánico: el Edificio Antiguo. Los restos de este edificio forman en la actualidad una alineación montañosa de dirección NWSE. Se trata de un edificio fisural alineado en la mencionada dirección formado por centenares de metros de coladas de lava de tipo aa y por diques que lo atraviesan. Las rocas que lo forman son básicas y ultrabásicas (basaltos picríticos, basanitas, basaltos y traquibasaltos), intermedias (traquiandesitas) y félsicas (traquitas y fonolitas). El principal proceso generador de estas diferencias composicionales es la cristalización fraccionada

A more than 1000m thick pile of basaltic lava flows and pyroclasts dipping seawards rises on the western sector of San Vicente. Several systems of dikes cut across the succession that is composed of two different sequences. The lower sequence (Lazareto Formation), about 400 m thick, is formed mainly by pahoe-hoe, frequently ankaramitic, basalt lavas and some breccias intercalated. This sequence is exposed in small hills and low rounded ridges of gentle slopes. The upper sequence (Monte Cara Formation), some 700 m thick, consisting in individually thicker basaltic lava flows with typical scoria levels is well exposed in high scarps. Numerous subvertical dikes cross the entire succession. The dikes vary increasingly their strike from south to north. Frequent sills (one every 3-5 m) also intrude the lower sequence. The distribution of the lava flow dip strikes as well as the dike strikes suggests that the succession as a whole was part of a central volcanic edifice, of which the eruptive centre was once located south of the city of Mindelo. This giant volcanic edifice, 16-20 km in diameter and 1600-2000m high, would have extended off the present coast. According to the radiometric ages obtained the volcano built up between 6,1Ma and 4,6 Ma with maximum activity concentrated between 5,5 and 5 Ma

The first data about the composition of lava flows from Branco Island (Cabo Verde) are presented in this work. Most lava flows in the sequence are alkali basalts (Fo84-76 olivine, En44-36 diopside, An83-31 plagioclase) showing geochemical affinity of typical ocean island basalts. The scarce most evolved members are mugearites (olivine absent, En41-31 clinopyroxene, An51-26 plagioclase, and kaersutite). The compositional variations between both the types are explained by crystal fractionation and extraction of pyroxene (up to 29%) and lesser proportions of olivine and Fe and Ti oxides (Cpx: 75; Ol: 21; OxFeTi: 4). The transition to mugearites from the most evolved basalts would mainly be due to extraction of pyroxene (24%) and Fe and Ti oxides (Cpx: 68; Ol: 3; Plag: 5; OxFeTi: 30)

The morphological, structural and volcanological aspects of Branco, an island of the Cape Verde Archipelago, are described and interpreted in this work. The isle consists of a 700 m thick pile of basalt lava flows and scarce pyroclastics crossed by several families of dikes. The structure of the island could correspond to the remaining fragment of a primitive large shield volcano. The main hypothetical emission centre could once be situated between the present islands of Santa Luzia and Branco