Petrography and chemical evidence for multi-stage emplacement of western Buem volcanic rocks in the Dahomeyide orogenic belt, southeastern Ghana, West Africa. (December 2015)

• Record Type: Journal Article
• Authors: Nude, Prosper M.; Kwayisi, Daniel; Taki, Naa A.; Kutu, Jacob M.; Anani, Chris Y.; Banoeng-Yakubo, Bruce; Asiedu, Daniel K.
• Is Part Of: Journal of African earth sciences. Volume 112:Part A(2015:Dec.)
• Page Start: 314
• Page End: 327
• Publication Date: 2015-12
• Subjects: Pan-African orogeny -- Dahomeyide belt -- Buem structural unit -- Ghana -- West Africa; Earth sciences -- Africa -- Periodicals; Earth sciences -- Middle East -- Periodicals; Geology -- Africa -- Periodicals; Geology -- Middle East -- Periodicals; Sciences de la terre -- Afrique -- Périodiques; Sciences de la terre -- Moyen-Orient -- Périodiques; Géologie -- Afrique -- Périodiques; Géologie -- Moyen-Orient -- Périodiques; Earth sciences; Geology; Africa; Middle East; Periodicals; Electronic journals; 556.05
• DOI: 10.1016/j.jafrearsci.2015.09.019
• Languages: English
• ISSNs: 1464-343X

Abstract

Abstract: The volcanic rocks of the Buem Structural Unit in the Dahomeyide orogenic belt of southeastern Ghana, constitute a unique assemblage among the monocyclic sedimentary formations of this structural unit. Representative volcanic rock samples were collected from the Asukawkaw, Bowiri-Odumase and Nkonya areas which form a roughly north-south trend. The volcanic rocks comprise spherulitic, amygdaloidal, vesicular, phyric and aphyric varieties. Whole rock geochemistry shows that these volcanic rocks exhibit both alkaline and subalkaline characteristics. The alkaline varieties are relatively enriched in REE and incompatible trace element concentrations, similar to OIB; the subalkaline varieties show E-MORB and N-MORB REE and incompatible element characteristics. The rocks have low La/Nb (<1), low K/Nb (<450) and high Nb/U (averagely 47.3) values, suggesting no significant effect of crustal contamination. The key characteristics of these volcanic rocks are the distinct petrography and geochemistry, shown from the three separate localities, which may suggest source fractionation at different depths or modes of emplacement. The association of volcanic rocks of OIB, E-MORB and N-MORB affinities, with no significant crustal contamination, may suggest mantle derived magma that may have been related to rifting event and eventual emplacement at the eastern passive margin of the West African Craton. Highlights: First published petrographic and geochemical data on the entire western Buem volcanics. Four categories of volcanic rocks identified. Formation of the volcanic rocks linked to rifting event and emplacement at the eastern margin of the West African Craton. Multi-stage emplacement of the volcanic rocks proposed.