Mineralogy and Magmatic Processes of Cenozoic Intraplate Alkaline Volcanic Rocks of Bafang and Its Environs (Cameroon Volcanic Line, West Africa)

Pierre Kamgang,Gilles Chazot,Merlin Patrick Njombie Wagsong,Innocent Badriyo,Natalie Love Ngongang Tchikankou,Dieudonné Youmen,Nicaise Blaise Tchuimegnie Ngongang,François Mvondo Owono,Philippe Essomba

doi:10.4236/ojg.2021.116013

Abstract

Alkaline basalts of Bafang and its environs are consisted of feldspars, olivines, pyroxenes and oxides which appear as phenocrysts, microphenocrysts and microcrysts. Feldspars are plagioclases (An67.97-15.84Ab69.19-30.43Or20.59-1.51) and anorthoclases (Ab68.11-61.20Or33.87-20.91An10.98-4.93). Plagioclases are the most abundant amount these feldspars. Anorthoclases appear only in mugearite (BAF 3 and BAF 37) the most differentiated of the studied alkaline-basalts. In High Magnesian basalt, (HMg-B) plagioclases are labradorites (An67.97-59.30Ab38.74-30.43Or2.75-1.60) and sanidine (An45.44-31.82Ab62.66-51.79Or5.52-2.77), whereas in Low Magnesian basalt (LMg-B) there are labrador (An67.4.75-51.96Ab44.98-33.72Or3.06-1.51), andesine (An45.44-31.82Ab62.66-51.79Or5.52-2.77), oligoclase (An26.65-15.84Ab69.19-63.57Or20.59-8.55) and anarthoclase (Ab68.11-61.20Or33.87-20.91An10.98-4.93). Olivines are magnesian (Fo86.7-50.1) and ferriferous (Fo48.8-37.8). In HMg-B, olivine are only magnesian. These olivines are chrysolites and hyalositerite. In LMg-B, olivines are magnesian and ferriferous with the predominance of ferriferous. They are chrysolites, hyalositerite and hortonolite. Pyroxenes are Ca, Mg and Fe clinopyroxenes. There are diopsides (Wo51.94-45.02En44.41-33.16Fs16.42-10.70) and augites (Wo44.88-43.64En41.03-37.04Fs18.25-14.43). Oxides are magnetites represented by ulvospinel (Usp90-75Sp2-7Mt5-23). Fractionation of ferromagnesian minerals (opaque oxide, olivine and pyroxene) is the main differentiation process. Two stages of fractional crystallization can be distinguished: the first stage comes with basanites and the second with hawaiites to mugearites. Chemical compositions of phenocrystals in studied basaltics lavas record signatures of magma recharge by pulsatory intrusions of new magma into the existing magma reservoir before the eruptions.

Highlights

The generation and the evolution of magma are known to be two stages related to the formation of igneous rocks
Mineralogical studies of basaltic rocks provide informations for the better understanding of petrogenitic processes developed in the Cameroon Volcanic Line (CVL)
According to % MgO and their mantle sources, these basaltic rocks are subdivided into two groups: the high MgO basalts (HMg-B) and the low MgO basalts (LMg-B)

Summary

Introduction

The generation and the evolution of magma are known to be two stages related to the formation of igneous rocks. Mineralogical studies of basaltic rocks provide informations for the better understanding of petrogenitic processes developed in the Cameroon Volcanic Line (CVL). We present mineral chemistry of alkaline volcanic rocks of Bafang and its environs. These volcanic rocks are basanites, alkali basalts, hawaiites and mugearites [2]. According to [2], the basaltic lavas of Bafang and its environ are alkaline volcanic rocks with Na (Na2O/K2O = 1.5 - 3.0) and Ne-Ol-Di-Hy normative. According to % MgO and their mantle sources, these basaltic rocks are subdivided into two groups: the high MgO basalts (HMg-B) and the low MgO basalts (LMg-B). Mineral chemistry is used in this study to give new constraints into magmatic processes beneath the volcanic region of Bafang and its environs

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Discussion

Conclusion