The geometry of the Archean, Paleo- and Neoproterozoic tectonics in the Southwest Cameroon

Abstract

The foliations, lineations, fold axes trajectories and shear zones kinematics vary from the Archean Ntem and Paleoproterozoic Nyong complexes to Neoproterozoic Oubanguide complex. The S 1 , S 2 and S 3 typified foliations are folded in F 2 , F 3 and F 4 cartographic folds equivalent to thrust slices while the L 1 , L 2 and L 3 lineations are oriented SSE-NNW, westeast and sub-north-south in the above complexes, respectively. Both, the foliations and lineations confirm the transport top-to-the east of the Nyong nappe onto the Congo craton during the Eburnean orogeny under amphibolitic conditions and as the transport top-tothe SSE of the Yaounde nappe onto the Ntem and Nyong complexes during the Pan-African event under granulitic to green schist conditions. The paleostress of fault and shear zones display crustal thinning and horizontal extension oriented east-west, NW-SE and subnorth-south in the Ntem, Nyong and Oubanguide complexes. All these tectonic features, completed by north-south and east-west cross sections, demonstrate litho-chronostratigraphical, structural and angular discordances between the three complexes.

Evidence of Quartz, Feldspar and Amphibole Crystal Plastic Deformations in the Paleoproterozoic Nyong Complex Shear Zones Under Amphibolite to Granulite Conditions (West Central African Fold Belt, SW Cameroon)

“…Granoblastic textures in BIF and metagranodiorites provide evidence of reactivation related to Eburnean/Transamazonian orogeny (Feybesse et al, 1998;Owona et al, 2011;Penaye et al, 2004). Protolith, metamorphic and retromorphic parageneses were identified in BIF and metagranodiorites, associated to their emplacement, deformation and uplift.…”

“…Magnetite-bearing quartzite, metagranodiorite and synkinematic clinopyroxene syenite petrographic studies from the Kama and Akongo group reveal in the NyC, the coexistence of the magmatic, metamorphic and retromorphic fabrics, respectively (Feybesse et al, 1998;Owona, 2008;Owona et al, 2011;Penaye et al, 2004). Granoblastic textures in BIF and metagranodiorites provide evidence of reactivation related to Eburnean/Transamazonian orogeny (Feybesse et al, 1998;Owona et al, 2011;Penaye et al, 2004).…”

“…This orogeny can be extended until 1742 Ma (Ar/Ar-Bt) because of recent age obtained in Akongo (Ow310) synkinematic syenite (Owona, 2008). D 4 was dominated by retromorphic processes related to uplift and by brittle deformation occurring under cool thermal conditions (Owona et al, 2011). Retromorphic blasts such as epidote, sericite, biotite, calcite and opaques are derived from saussuritization and damouritization of feldspars; chloritisation of biotite and alteration of amphibole under epidote-amphibolite facies.…”

“…This Eburnean thermotectonic phase is responsible for the overall uralitization of pyroxene to amphibole between 2169-2000 Ma in the NyC (Ar/Ar-Hbl, Owona, 2008). D 2 is accompanied by the antiperthitic K-feldspar exsolution from plagioclase, F 2 folds, quartz and amphibole L 2 mineral and stretching lineations (Owona, 2008;Owona et al, 2011). D 3 is characterized by crystal plastic deformations varying in term of features, intensity and thermal conditions, in protoliths and from outer to inner shear zones.…”

“…The Nyong Complex (NyC) studied here, results from the Eburnean/Transamazonian tectonothermal event (2400-1800 Ma) associated to the collision between the Congo and São Francisco cratons (Nédélec et al, 1993;Feybesse et al, 1998;Lopez et al, 2001;Penaye et al, 2004;Lerouge et al, 2006;Neves et al, 2006;Owona et al, 2011). It belongs to the Paleoproterozoic mobile belt or West Central African Fold Belt (-WCAFB-, Feybesse et al, 1998), which includes other provinces such as Franceville-Ogoué in Gabon, West Congo in Republic of Congo and Carnot basin in the Central African Republic (Poidevin & Pin, 1986;Bassot et al, 1987;Morin et al, 1991;Caen-Vachette et al, 1988;Owona, 2008).…”