| 2 | Magnetic Characterization of Amphibolites from the Fomopéa Pluton(West Cameroon):Their Implication in the Pan-African Deformation of the Central African Fold Belt显示文摘The Fomopea granitic pluton is emplaced in gnessic and amphibolitic basement.These gneissic and amphibolitic basement rocks are represented in the pluton's body as sub-rounded,elongated or stretched xenoliths.Amphibolitic xenoliths display testimonies of two main tectonic events namely:(i) E1 flattening deformation event characterized by a NW-SE to E-W foliation with a best pole at 246/57 and a mineral stretched lineation with a best line at 293/47;and(ii) E2 compressive event typified by(1) N-S to NNE-SSW steeply dipping foliation;(2) S-type flexion-fold indicating a sinistral shear movement.These amphibolite rocks indicate a magnetic susceptibility magnitude(Km) range from 418 μSI to 90092 μSI for 87% of the stations showing a ferromagnetic behavior.K-T curves reveal the presence of Ti-poor magnetite as susceptibility mineral carrier.Magnetic foliation and lineation suggest that the N-S strike direction observed in the Bamendou amphibolite is,as pointed out elsewhere in the Central African Fold Belt,of paramount importance in the tectonic evaluation of the Fomopea area,since it has most likely acted as major deformation phase in the second tectonic event in the belt. | NJANKO Théophile FOZING Eric Martial KWéKAM Maurice YAKEU SANDJO Angéline Flore NJONFANG Emmanuel | 2012 | Acta Geologica Sinica(English Edition)2012，86，1： | 0 |
| 3 | Kinematic Evolution of the Nyakong-Manyi Shear Zone(Adamawa,Cameroon): Constraints from Field Observations and Microstructures,and Implication for Metamorphic P-T-t Estimation显示文摘The Nyakong-Manyi Shear Zone(NMSZ) is a NE-SW elongated corridor found to the northwest of the Foumban-Bankim Shear Zone(FBSZ) along the Central Cameroon Shear Zone. Controversial chronology models has been proposed for the kinematic evolution of the sinistral and dextral shear phases in the Tikar Plain, thus in the FBSZ;early dextral and late sinistral shear phases for some authors and early sinistral and late dextral shear for others. Moreover, the NMSZ kinematic evolution implication on the mylonitization P-T-t path in the area seem to be problematic and the present paper aim is to clear enough those problems;since this shear zone is the main mylonitic corridor that registered the left and right lateral movement in this area. The NMSZ comprises amphibolites, protomylonites, strict sensus mylonites(garnet-kyanite-sillimanite mylonite and garnet-pyroxene mylonite), ultramylonites kyanite-sillimanite and garnet-kyanite-sillimanite gneiss. Field structures testify that the investigated area recorded three deformation phases:(i) the D1deformation phase which is marked by NW-SE to N-S trending S1metamorphic foliation with low to moderate dips(15°–45°) that was transposed during the D2phase, is responsible for a regional metamorphism whose mineral paragenesis is garnet-kyanite-sillimanite;(ii) the early sinistral NNE-SSW to NE-SW shear phase D2marked by S2metamorphic and mylonitic foliations;responsible for, L2stretching mineral lineation, F2fold axes and B2boudins structures;(iii) the late dextral NE-SW shear phase D3, characterized by F3folds, B3boudins and ductile dextral C3shear planes. Mineral paragenesis garnet + kyanite + sillimanite and microstructures within gneiss testify that this rock underwent high grade regional metamorphism whose peak conditions are estimated at 11.5–13.5 kbar/850–900 ℃. After the peak of metamorphism gneiss was overprinted by high grade pressure mylonitization during the early sinistral and late dextral shear deformations. Microstructural data here indicate a high-grade mylonitization whose P-T conditions are estimated at least at around 10 kbar/750 ℃ attained during the D2. Shear markers, indicates that the studied area underwent an intense mylonitization at deep crustal deformation level, probably at the ductile-brittle boundary structural level during a major dextral shear deformation. | Belmien Robinson Sobze Yemdji Jules Tcheumenak Kouémo Eric Martial Fozing Ludovic Achu Megnemo Julios Efon Awoum Agnes Blandine Kamgang Tchuifong Brice Rostant Tepi Yemele Maurice Kwékam | 2023 | Journal of Earth Science2023，34，5： | 0 |
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