Petrology of the Volcanic Rocks from Bioko Island (“Cameroon Hot Line”)

Fadimatou Ngounouno Yamgouot^1*, Bernard Déruelle², Isaac Bertrand Gambie Mbowou³, Ismaïla Ngounouno³

¹Département des Sciences de la Terre, Faculté des Sciences, Université de Ngaoundéré, Ngaoundéré, Cameroun.
²Laboratoire de Magmatologie et Géochimie Inorganique et Expérimentale (MAGIE), Institut de Physique du Globe de Paris, Université Pierre et Marie Curie, Paris, France.
³Département des Mines et de la Géologie, Ecole de Géologie et d’Exploitation Minière (EGEM), Université de Ngaoundéré, Meiganga, Cameroun.

DOI: 10.4236/ijg.2015.63019                

Abstract

Bioko island (3008 m a.s.l.), is composed of the alkaline basaltic lavas (basalts and hawaiites) with xenoliths. These lavas have a microlitic textureand consisted of euhedral to subhedral phenocrysts (>1 mm) of olivine (0.83 < Mg# < 0.87) and diopside ± Ti-augite. Plagioclase (An_62-67Ab_35-32Or_3-1) phenocrysts are present only in hawaiites. In Harker diagrams, SiO₂, Al₂O₃, Na₂O and K₂O contents of the lavas increase and Fe₂O₃, MgO and CaO decrease with increasing differentiation from basalts to hawaiites. The compatible elements Ni, Cr and V decrease strongly in basalts and remain at low levels in hawaiites. Basaltic lavas from Bioko lavas have low Hf contents (4.2 - 9.2 ppm) and consequently higher Hf/Zr ratios (50 - 90) than those (<50) of similar lavas from other volcanoes of the Cameroon Hot Line. Such high ratios are commonly observed in alkaline basaltic lavas associated with carbonatitic and/or nephelinitic magmatism. The Sr and Nd isotopic compositions point to a slightly depleted mantle source.

Keywords

Petrology, Geochemistry, Lavas, Bioko, Cameroon Hot Line

Conflicts of Interest

The authors declare no conflicts of interest.

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