Joseph Mvondo Ondoa

Quantification of Strain of the Pan-African in Mvog-Betsi Area (Yaoundé Group, Cameroon)

The ductile deformation in the paragneissic bed of Mvog-Betsi in the north-eastern part of Yaounde (Cameroon) appears to be intensive and may be traduced by a high shear rate (more than 10%). Some marker subjects that may quantify this strain are observed. Those are elliptical quartz and feldspar, and folds. The study of elliptical markers shows their preferential orientation. The initial rate R i of the markers before the strain approaches 3.76, and the harmonic value of R f is between 1.51 and 1.71. Main orientation O f of strain’s ellipse from the direction of stretching in actual position is situated between -10 and -19. The strain’s rate R S is comprised between 1.1 and 1.7. The orientation O S of the strain’s ellipse is situated between N10E and N20E. The rate of shortening varies between 20% and 75%.

Evidence of the ~NE-SW extension in the Sa’a - Monatélé Region as in the Bafia and Yaounde groups within the Central African Fold belt (Cameroon): Implication for the Southern Cameroon Neoproterozoic extension

1 Abstract The Sa’a-Monatélé Region within the Neoproterozoic North Equatorial Fold Belt located between the Bafia and Yaounde groups, highlights a polyphase D1D4 Pan-African deformation that emplaced the Yaounde tectonic nappe transported top-to the SSW onto the Congo Craton and responsible for its actual geometry. D1 is a compression tectonic phase dominated by the simple shear type, represented by S0/1 foliation and F1 folds. D2 is a general flattening under a pure shear regime associated to the exhumation of D1 nappe due to the NE-SW extension; responsible for L2 lineations, B2 boudins, F2 folds, S0/1/2 and S2 foliations in metapelites and metagranitoids, respectively and C2 shear planes. D3 mainly an ~E-W shortening and a ~NE-SW extension, emplaced F3 mesoand large-scale folds that form tectonic units of the Yaounde nappe. D4 was an N-S to NE-SW shortening, perpendicular to the D3 once and represented by F4 large-scale folds. C3 shear zones as the NE-SW Central Cameroon shear zone was emplaced under the same regime. The Sa’a-Monatélé Region may correspond mostly accordingly to a thrusting zone than a real tectonic suture between the Bafia and Yaounde groups. In comparison, D1-D4 stages show similar geometry and kinematics in Bafia and Yaounde groups. Both groups are composed of similar rock types made of lowto high grade metapelites, amphibolites and metagranitoids with comparable volcano-sedimentary origin for metapelites and amphibolites; Archean to Proterozoic (Nd model ages 3500-2100 Ma) in metapelites, crustal rocks with minor mantle contributions origin for metagranitoids; the Neoproterozoic as the same maximum deposit age fixed at ~1600 Ma (U/Pb-, Pb/Pb-detrital zircons) as well as a comparable syntectonic granitoids emplaced between ~625 – 600 Ma (U/Pb-, Pb/Pbzircons); an analogous Pan-African orogeny (650-542 Ma) with the retrograde phase from the granulite to amphibolite facies that ranges 616 – 540 Ma (Sm/Nd-garnet, EMP-monazite, Rb/Srwhole rock biotite ± muscovite). The admitted Bafia and Yaounde groups that outline the similar litho-chemistry nature and origin, a comparable Pan-African thermotectonic evolution can therefore be considered as a single and a same litho-chrono-thermo-structural unit: the Yaounde Group. ISSN 1029–2225©2014 Sciences, Technologies et Développementos