Geochemistry of the Bayonplutonic Complex – Western Cameroon

Z Itiga,M Thoni,S Owona,F Koller,Jp Tchouankoue,Nas Wambo,Rnn Belnoun

doi:10.4314/gjgs.v11i1.7

Abstract

The BayonNeoproterozoic plutonic complex located in Western Cameroon intrudes gneisses of Paleo to Neo Proterozoic age. The complex is composed of gabbro, monzogabbro and monzonites frequently crosscut by trachytic and granitic veins. The primary mineral assemblages of the gabbro and monzogabbro is plagioclase (An30 - An69), clinopyroxene (En40 – 42 Fs 12 – 18 Wo 45 - 47) hypersthene (En62 – 65 Fs34 – 37 Wo1- 4) and orthoclase (Or78-Or91) whilebiotite, magnetite, Ilmenite and apatite constitute accessory minerals. Monzonite is formed of plagioclase (An22 to An39), orthoclase (Or80-Or87),clinopyroxene (En38-39 Fs14-20 Wo45-46), biotite and quartz. Amphiboles occur as secondary minerals. Ilmenite and apatite are accessory minerals in monzonite.The rocks are mafic to intermediate in composition (41 – 61 wt % SiO2) and transalkaline with high-K and have shoshonitic features. Bayon plutonic rocks have highabundance of Ba, Sr ,V and Zr but possesses low concentrations of Rb, Sc, Y and Th.Gabbroic rocks show moderately fractioned REE patterns (LaN/LuN= 14 – 27) with none or negligible Eu anomalies. The monzonite shows also moderate fractionatedpatterns (LaN/LuN= 20 – 27) with fairly positive Eu anomalies. All the studied rocks show flat HREE features. The primitive mantle- normalized element patterns are almost homogeneous with negative anomalie in Ta, Nb, Th, P and Ti. Sm/Nd-wr-Cpx-Pl ages of the complex are 580 ± 13 Ma; 553 ± 32 Ma for the monzogabbro and 547 ± 26 Ma for the monzonite. The Nd/Sr isotopic compositions show that the Bayon plutonic rocks were generated by partial melting of subcontinental lithospheric mantle. The depleted mantle Nd model age TDM of 1.6 – 1.7 Ga indicates that the studied rocks originated by partial melting of Mesoproterozoic mantle.KEYWORDS: West Cameroon, Panafrican, Pluton, Geochemistry, partial meting

Highlights

The Bayon plutonic complex belongs to the Neoproterozoic fold belt of Cameroon
That collision structured the Pan-African North Equatorial belt which extends in Sudan, Central African Republic, Cameroon and through correlations with North-East Brazil (Castaing et al, 1994; Nzenti et al, 1998; Toteu et al.,2001; Abdelsalam et al, 2002; Oliveira et al, 2006).In West Cameroon, Pan-African massifsare widely distributed (Fig.1b) andare described as syn to post–collisional, calc-alkaline, ferro-potassic and metaluminous(Tchouankoue, 1992; Nguiessi et al.,1997; Tagne – Kamga, 2003; Nzolang et al, 2003; Tetsopgang, 2003; Djouka Fonkwe et al, 2008).According to available ages, the massifswere emplaced during the Pan – African D2 deformation event
The Bayon plutonic complex is composed of gabbroic and monzonite rocks.The major minerals areplagioclase, augite, diopside, pigeonite, clinoenstatite, and biotite

Summary

Introduction

The Bayon plutonic complex belongs to the Neoproterozoic fold belt of Cameroon This fold belt is associated with the Pan-African tectonothermalevent 650-500 Ma and is related to the collision of the Congo Craton with the West African Craton (Fig.1a). That collision structured the Pan-African North Equatorial belt which extends in Sudan, Central African Republic, Cameroon and through correlations with North-East Brazil (Castaing et al, 1994; Nzenti et al, 1998; Toteu et al.,2001; Abdelsalam et al, 2002; Oliveira et al, 2006).In West Cameroon, Pan-African massifsare widely distributed (Fig.1b) andare described as syn to post–collisional, calc-alkaline, ferro-potassic and metaluminous(Tchouankoue, 1992; Nguiessi et al.,1997; Tagne – Kamga, 2003; Nzolang et al, 2003; Tetsopgang, 2003; Djouka Fonkwe et al, 2008).According to available ages, the massifswere emplaced during the Pan – African D2 deformation event. In this paper we reportthe geochemistry of the Bayon plutonic complex, Rose Noel Ngo Belnoun, Department of Earth Sciences, University of Yaoundé I, P.O. Box 812, Yaoundé Cameroon.

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Conclusion