Récent structural data on Meta sédiments in the western part of Yaoundé (Cameroun) : Nouvelles données structurales sur les Meta sédiments de Yaoundé-ouest (Cameroun)

Abstract

This study presents the western part of Yaounde as a portion of the southern domain, found within the PNEFB. It aims is to bring new structural information concerning the tectonic evolution of the western part of Yaounde, based on the combined field survey, lithological and satellite image processing methods. Petrographic study revealed two lithological units: (i) the metasedimentary units (migmatites) composed of Kyanite-biotite gneiss, Garnet-biotite gneiss, garnetite and quartzite and (ii) the meta-igneous unit (metadiorites) composed of amphibolites. Mineralogical assemblages range from amphibolite facies (Amp +Kfs +Qtz ±Grt , Kfs +Qtz +Amp + Bt+ Pl+ Spn + Grt ± Cd ± Std) to granulite facies that is Kyanite-biotite gneiss (Bt+ Grt+ Qtz+ Ky+ And +Kfs ±Px), biotite–garnet gneiss (Bt + Grt+ Kfs + Qtz + Pl), garnetite (Grt + Bt +Qtz+ Ky+ And+ Kfs+ Pl± Px) and finally quartzite (Qtz +Bt ± 0p).These assemblage shows that the target site is characterized by medium-pressure(MP), medium-temperature (MT) to high temperature (HT) metamorphic facies. The target site where emplaced during continental Syn-collisional zone preceded by subduction. Analysis of the metamorphic rocks based on structural information, characterized the rocks as an imprint of poly-phased progressive deformation with 6 phases of monocyclic tectonic evolution. Here, D1 and D2 showed two major events of ductile deformation in which the D1 characterize compression that led to an S1 horizontal to sub horizontal foliation, B1 intra-foliated boudins, on one hand while the D2 marked transposition of D1 structures by dextral C2 shears, symmetrical F2 folds. The ductile-brittle D3 is marked by the development of dextral C3 shear, F3 fold. While D4 consist of F4 fracture, C4 shear. The D5 deformation phased is characterized by a brittle-ductile deformation which is composed of C5 shearing and finally, a D6 deformation phase characterized by vertical brittle deformation.