RT Journal Article
T1 A basic radial dike swarm of Boa Vista (Cape Verde Archipelago); its significance inthe evolution of the island
A1 Ancochea Soto, Eumenio
A1 Hernán Reguera, Francisco
A1 Huertas Coronel, María José
A1 Brandle, J.L.
AB A basic radial dike swarm unrelated to other basic units of Boa Vista (Cape Verde Archipelago) has been localizedand characterized in the central sector of the island.According to new radiometric data three main stages in the evolution of Boa Vista are distinguished: the earlier(the Old Volcanic Complex: 17–16 Ma) is equivalent to the shield building stage of Hawaii and the later(the Recent Volcanics (8–4 Ma) is in some aspects comparable to the post-erosional stage. An important intermediateessentially felsic stage (the Trachytic–Phonolitic Complex: 14.3–12.8 Ma) followed the basalticshield stage. This felsic stage has equivalents in some other oceanic islands as the Canary Islands, speciallyGran Canaria, Tenerife, and La Gomera. The central sector of Boa Vista is also occupied by the FelsicSubvolcanic Complex, a unit consisting of phonolitic breccias, syenites and monzonites that represent theTrachytic–Phonolitic Complex hypabyssal roots. The felsic rocks as a whole constitute half of the total amountof igneous rocks on the island making up Boa Vista, the island with the highest percentage of felsic rocks inthe Central Atlantic Ocean.More than 200 dikes of the basic radial swarm intruding the Felsic Subvolcanic Complex have been measured.The intensity of the multiple dike injection is sometimes rather high, roughly a dike every 5 m. The individualdikes have an observable mean length of about 300 m. The composition of these dikes is always foiditic (nephelinites,melilitites, and limburgites), slightly different in composition (more alkaline and richer in incompatibleelements) to the other basic units of the island (the Old Volcanic Complex and the Recent Volcanics).The radial dikes converge in an area located NW of the geometrical center of Boa Vista, a zone where the hypotheticalcenter of the Old Volcanic Complex and the Trachytic–Phonolitic Complex edifices must also havebeen situated. The ages obtained from the dikes (between 14.8 and 11.5 Ma) indicate that the radial injectionsare contemporary with the phonolites and the trachytes of the Trachytic–Phonolitic Complex and yetare part of the intermediate evolutionary stage of Boa Vista.
PB Elsevier Science Publishers
SN 0377-0273
YR 2012
FD 2012
LK https://hdl.handle.net/20.500.14352/42509
UL https://hdl.handle.net/20.500.14352/42509
LA eng
DS Docta Complutense
RD 30 abr 2024