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Journal of Geosciences and Geomatics. 2018, 6(2), 65-76
DOI: 10.12691/JGG-6-2-4
Original Research

Contrasting Ba-Sr Granitoids from Bamenda Area, NW Cameroon: Sources Characteristics and Implications for the Evolution of the Pan African Fold Belt

Gus Djibril KOUANKAP NONO1, , Pierre WOTCHOKO1, Alice MAGHA1, Sylvestre GANNO2, Ndam NJOYA1, Aloysius AFAHNWIE NGAMBU3, Jean Paul NZENTI2 and Veronique KAMGANG KABEYENE2

1Department of Geology, HTTC, University of Bamenda, P.O.Box 39 Bambili, Bamenda, Cameroon

2Department of Earth Sciences, Faculty of Sciences, University of Yaoundé 1, P.O.Box 812, Yaoundé, Cameroon

3Department of Geology, University of Buea, P.O.Box 63 Buea, Cameroon

Pub. Date: August 13, 2018
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Gus Djibril KOUANKAP NONO, Pierre WOTCHOKO, Alice MAGHA, Sylvestre GANNO, Ndam NJOYA, Aloysius AFAHNWIE NGAMBU, Jean Paul NZENTI and Veronique KAMGANG KABEYENE. Contrasting Ba-Sr Granitoids from Bamenda Area, NW Cameroon: Sources Characteristics and Implications for the Evolution of the Pan African Fold Belt. Journal of Geosciences and Geomatics. 2018; 6(2):65-76. doi: 10.12691/JGG-6-2-4

Abstract

The basement rocks of Bamenda town are mainly covered by volcanic rocks and are made up of two distinct types of granitoids: granites and leucogranites. These basement rocks belong geochemically to the same granite field. The studied granitoids are silica rich, with concentrations ranging from 70 to 73% in granite and 73 to 76% in leucogranite. Both belong to high-K calc-alcaline series with granite being magnesian and more potassic (Na2O/K2O < 1) whereas the leucogranite is ferriferous and similar to Na-granitoids (Na2O/K2O >1). Leucogranites are low Ba-Sr granitoids, strongly peraluminous (A/CNK > 1.1) and plot in the field of S-type granites, while granites are high Ba-Sr granitoids, slightly peraluminous and plot in the field of I-type granitoids. The chondrite-normalized REE patterns show more LREE enrichment in granites (>100*chondrite) than in leucogranites (>10*chondrite). Major and trace element compositions of the leucogranites and granites indicate crustal derivation from the partial melting of metapelite and metagreywacke respectively. The REE patterns display pronounced negative Eu anomalies (Eu/Eu* = 0.23-0.36) in leucogranites due to low degree of partial melting of a plagioclase depleted crustal source, and weakly negative to null Eu anomalies (Eu/Eu* = 0.81-1.08) in granites due to high degree of partial melting. The estimated temperatures of Bamenda granitoids magma range between 800°C and 950°C. Bamenda I-type granites are syn-tectonic and are similar to the other granitoids of the central domain of the Pan-African North-Equatorial Fold belt in Cameroon. Bamenda S-type peraluminous leucogranites are post-tectonic and chemically similar to the Himalayan peraluminous leucogranites. Furthermore, decompression model may be related to Bamenda leucogranite formation. Tectonically, the studied granitoids are related to crustal delamination characterizing the post-collisional event within the Pan African Fold Belt.

Keywords

granites, High-K calc-alcaline series, peraluminous, metaluminous, crustal source, bamenda

Copyright

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