Magmatism of the Beka Volcanic Massifs (Cameroon Volcanic Line, West-Central Africa): New Petrographical and Mineralogical Data  

作　　者：Jacques Dili-Rake Sahabo Aboubakar Abdoulaye Joseph Legrand Tchop Merlin Isidore Teitchou Christian Mana Bouba Oumarou Faarouk Nkouandou Daouda Dawaï Eddy Ferdinand Mbossi Jacques Dili-Rake;Sahabo Aboubakar Abdoulaye;Joseph Legrand Tchop;Merlin Isidore Teitchou;Christian Mana Bouba;Oumarou Faarouk Nkouandou;Daouda Dawaï;Eddy Ferdinand Mbossi(Research Centre for Geophysics and Volcanology, Institute of Geological and Mining Research, Buea, Cameroon;Faculty of Sciences, University of Maroua, Maroua, Cameroon;Centrer for geological and Mining Research, Institute of Geological and Mining Research, Garoua, Cameroon;Faculty of Sciences, University of Ngaoundere, Ngaoundere, Cameroon)

机构地区：[1]Research Centre for Geophysics and Volcanology, Institute of Geological and Mining Research, Buea, Cameroon [2]Faculty of Sciences, University of Maroua, Maroua, Cameroon [3]Centrer for geological and Mining Research, Institute of Geological and Mining Research, Garoua, Cameroon [4]Faculty of Sciences, University of Ngaoundere, Ngaoundere, Cameroon

出　　处：《Journal of Geoscience and Environment Protection》2022年第7期198-228,共31页地球科学和环境保护期刊（英文）

摘　　要：The Beka volcanic massifs are located northeast of Ngaoundere region, within the Adamawa plateau. It consists mainly of basanites, trachytes and phonolites. The petrographic study shows that all the basanite lavas have porphyritic microlitic textures with a more pronounced magmatic fluidity than the felsic lavas displaying trachytic textures. The lavas are composed of phenocrysts, microlites and microphenocrysts of olivine, clinopyroxene, plagioclase and iron-titanium oxides for the basanites and of greenish clinopyroxene, alkali feldspar, and titanomagnetite for the felsic lavas. Chemical microprobe analysis indicates that the olivine crystals are magnesian (Fo_73-78). Clinopyroxene crystals have a composition of diopside (Wo_47-) in the basaltic lavas and diopside near the hedenbergite pole in the trachytes phonoliths and titanomagnetite (TiO₂: 21.13% - 22.36% and FeO: 68% - 68%). Chemical analyses on whole rocks show that all the lavas belong to the same series and the felsic lavas come from the differentiation of basanite lavas by fractional crystallization of the minerals therein. The basanites originate from a low rate of partial melting of an OIB-type mantle. Contamination and mixing processes are suspected. Lavas of similar composition are found in other volcanic centres of the Adamawa plateau and the continental and oceanic sectors of the Cameroon Volcanic Line, in particular the Kapsiki plateau, Mounts Cameroon and Bamenda.The Beka volcanic massifs are located northeast of Ngaoundere region, within the Adamawa plateau. It consists mainly of basanites, trachytes and phonolites. The petrographic study shows that all the basanite lavas have porphyritic microlitic textures with a more pronounced magmatic fluidity than the felsic lavas displaying trachytic textures. The lavas are composed of phenocrysts, microlites and microphenocrysts of olivine, clinopyroxene, plagioclase and iron-titanium oxides for the basanites and of greenish clinopyroxene, alkali feldspar, and titanomagnetite for the felsic lavas. Chemical microprobe analysis indicates that the olivine crystals are magnesian (Fo_73-78). Clinopyroxene crystals have a composition of diopside (Wo_47-) in the basaltic lavas and diopside near the hedenbergite pole in the trachytes phonoliths and titanomagnetite (TiO₂: 21.13% - 22.36% and FeO: 68% - 68%). Chemical analyses on whole rocks show that all the lavas belong to the same series and the felsic lavas come from the differentiation of basanite lavas by fractional crystallization of the minerals therein. The basanites originate from a low rate of partial melting of an OIB-type mantle. Contamination and mixing processes are suspected. Lavas of similar composition are found in other volcanic centres of the Adamawa plateau and the continental and oceanic sectors of the Cameroon Volcanic Line, in particular the Kapsiki plateau, Mounts Cameroon and Bamenda.

关 键 词：Cameroon Volcanic Line Adamawa Plateau Beka Volcanic Massif Fractional Crystallization OIB-Type Mantle 

分 类 号：P58[天文地球—岩石学]