Petro-Structural Characterization of Bonguen Area, Nyong Series, Cameroon: Insight into the Northern Extension of Kribi-Campo Shear Zone

Abstract

The west Bonguen area is located within latitudes 03°25’N to N03°39’N and longitudes 10°04’E to 10°09’ E in South Cameroon. It belongs to the Nyong Series which is the north-western extension of the Congo Craton in Cameroon. In order to highlight the extension of the Kribi-Campo shear zone, petrographic studies and structural analysis were carried out. Mylonitic metagranodiorite outcropping as a large dome in biotite gneiss basement rocks, it is the main rock type in the study area, it is made up of Kfs + Qtz + Bt + Pl + Op. Majority of the minerals shows deformation marks such as sigmoidal shape of Kfs, rolling extension of Qtz ribbons, Subgrains of Qtz and kink-band of Bt. Three (03) deformation phases (D1, D2, and D3) were denoted in Bonguen west. The D1 deformation developed S1 foliation in biotite gneiss basement rocks and is characterized by the alternation of parallel compositional bands and lithological units. The D2 deformation developed S2 mylonitic shistosity, Shear bands (C2-planes) develop oblique to the main S2 mylonitic schistosity (S2-plane) showing dextral ductile shear, V2 veins and B2 boudins. The D3 phase is exclusively highlighted by brittle features such as V3 veins, F3 joints and faults. The area consequently underwent a polyphases ductilo-fragile tectonism dominated by a dextral thrusting kinematics. Bonguen area is here considered as a segment of the northern extension of the Kribi-Campo fault.