Geochemical Characterization of Boula Ibi Granitoids and Implications in Geodynamic Evolution

Jean Paul Sep Nlomngan,Sebastien Owona,Augustin Patrice Moussango Ibohn,Emmanuel N. Nsifa,Toteu Sadrack Félix,Joseph Penaye,Rigobert Tchameni

doi:10.5539/jgg.v11n4p13

Abstract

Petrographical and geochemical study, consistent with observed field relations show that the Boula Ibi syn- and post-kinematic granitoids in north Cameroon, occurred in banded gneisses. These syn- and post-kinematic granitoids consist of deformed monzonites typified by its granoblastic texture, diorites, syenites, granites and basic xenoliths of dioritic and monzonitic composition. They are calc-alkaline, hyperpotassic, metaluminous to slightly peraluminous and I-Type granitoids. They display high content in Fe2O3 + MgO + CaO (2.16 &ndash; 23.24 %) that reveals their intermediate affinity, magnesian and metaluminous character whilst the low A/CNK (&lt; 1.1) content indicates their mantle origin. Harker diagrams and La/Sm vs La define the fractional crystallization and partial melting as the two main processes that led the geodynamic evolution of the Boula Ibi syn- and post-kinematic granitoids. These are consistent with low-content of Cs, Ta, Nb, Tb and Hf, supporting high melting rates ranging between 20 and 40% as well as molar Al2O3/(MgO + FeOt) vs CaO/(MgO + FeOt) plot showing magmatic evolutions from metabasaltic and metagreywackes sources.

Highlights

The Pan African Central Fold Belt (PACFB) located between the West African craton, Congo/Sao-Francisco craton and Saharan metacraton, is a large domain that has been remobilized during the Pan African orogeny following the collision of above cratons between 700 and 500 Ma (Castaing et al, 1994; Abdelsalam et al, 2002)
The Boula Ibi region consists of metamorphites in which are intruded four generations of granitoids; the orthogneiss of monzonitic composition; undeformed diorites, granites and syenites (Figure 1c)
Sr/Ba ratios slightly vary (0,33 – 1,07), whereas Rb/Sr ratios increase strongly (0,055 – 1,81) with increasing concentrations of SiO2. These charateristics are compatible with magma evolution by fractional crystallization (Figure 7b; Bowden et al, 1974; Provost & Allegre, 1979) of basic to acidic magma and indicate that the fractionation of plagioclase and K-feldspar was the important mechanism in the course of the magmatic evolution of the I-Type granitoids (Djouka-Fonkwé et al, 2008)

Summary

Introduction

The Pan African Central Fold Belt (PACFB) located between the West African craton, Congo/Sao-Francisco craton and Saharan metacraton, is a large domain that has been remobilized during the Pan African orogeny following the collision of above cratons between 700 and 500 Ma (Castaing et al, 1994; Abdelsalam et al, 2002). Several granitoids within the three domains have been classified as pre-, syn- to post- kinematic (Kwekam, 1993; Nguiessi Tchankam et al, 1994; Toteu et al, 2001; Tagne Kamga, 2003; Nzolang et al, 2003; Njanko et al, 2006; Djouka-Fonkwe et al, 2008; Njiekak et al, 2008; Kouankap et al, 2010; Kankeu et al, 2012). The Boula Ibi area that includes several granitoids and seems to be a suitable area for petrology and geodynamic evolution of granitoids is still poorly known

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