The geological history of Maio, Cape Verde Islands

Abstract

The oldest igneous rocks on Maio are pillow lavas of Mid-Ocean Ridge pillow basalts character which have been tilted and uplifted about 4 km from the ocean floor to outcrop as a partial ring, dipping steeply away from a central plutonic complex made up of pyroxenites, essexites, syenites and carbonatites. The ocean floor volcanic rocks are overlain conformably by a stratigraphically continuous pelagic carbonate succession which demonstrates a shallowing depositional environment from the Upper Jurassic to Upper Cretaceous times, when tuffaceous beds indicate renewed volcanism. The tuffs are associated with rudites demonstrating the emergence of the island and amongst the clasts are plutonics indicating Upper Cretaceous magmatism and the unroofing of the volcano to a substantial depth. Deformation under compressive stress resulted in the folding and local repetition by thrusting of this sedimentary cover, which, together with the plutonic core, had been intensively injected by major sills. The Mesozoic succession has been planed off and overlain with marked unconformity by a largely Neogene sequence of volcanic and terrestrial sedimentary rocks. There is a hiatus throughout the Palaeogene, and constructional activity appears to recommence with ankaramitic hyaloclastite and lava deltas and subaerial ankaramitic flows. These are overlain by fluvial sediments and tuffs. Stratigraphically above these is an extensive plateau of silica-undersaturated lavas, olivine-melilitites and nephelinites, which rest on a planed and locally lateritized surface. At topographically higher levels in the eastern part of the island there are thick ankaramitic lavas and pyroclasts which evidently flowed eastward through valleys cut down into the Mesozoic strata, and appear to be of Pliocene age. The subsequent history of the island appears to be non-volcanic.

Tracers of Uplift and Subsidence in the Cape Verde Archipelago

“…The first full stratigraphic description of the island was produced by Serralheiro (1970) and was later revised and redefined by Stillman et al (1982). According to Stillman et al (1982), it includes: Mesozoic Basement Complex; Central Igneous Complex; Casas Velhas Formation;…”

“…According to Stillman et al (1982), it includes: Mesozoic Basement Complex; Central Igneous Complex; Casas Velhas Formation;…”

“…Figure S3: Geological map of Maio, after Serralheiro (1970), Stillman et al (1982) and Holm et al (2008).…”

“…The mechanism responsible for its upheaval is not yet completely understood, but is thought to be related to updoming associated with plutonic activity and island volcanism (Serralheiro 1970; Stillman et al 1982). …”

“…The Central Igneous Complex corresponds to a series of intrusive bodies composed of pyroxenites, essexites and syenites, densely cut by a swarm of sills and dykes of varied composition (Serralheiro 1970;Stillman et al 1982). The age of these intrusions is still debatable but the 18-21 Ma interval seems to best represent it (Holm et al 2008).…”