No abstract

La région de Sangmélima est une portion du Complexe du Ntem, la terminaison septentrionale du craton du Congo d'âge archéen. Elle est située entre 2 °45' et 3 °02' N et 11 °55' et 12 °15' E. L'étude morphotectonique réalisée dans cette zone est fondée sur les techniques de traitement des images ETM+ de landsat-7 et les méthodes classiques de prospection géologique croisées à travers un système d'information géographique (SIG). L'objectif est d'évaluer l'apport de ces images dans la cartographie structurale. Les résultats obtenus mettent en évidence une déformation polyphasée D1 -D4 où D1 est soulignée par une foliation S1 globalement orientée E-W à NW-SE dans l'encaissant. D2 est représenté par les foliations S1 /2 transposées dans l'encaissant et foliation S2 dans les plutonites. L'ensemble est reprist par un épisode décrochant et transpressif conjugué D3 caractérisé par un cisaillement N-S à NE-SW. A cette D3 fait suite un épisode de déformation cassante D4 , induite par une double compression conjuguée NNW-SSE et NNE-SSW. L'extension de la télédétection à l'ensemble du domaine archéen du sud Cameroun dont l'apport s'est avéré conséquent dans la région de Sangmélima, devrait améliorer la cartographie géologique de cette région.

This study presents the new petrology and geochemistry data for the comprehension of the origin and emplacement conditions of the Lolodorf mafic rocks whitin the Nyong Complex. The meta-mafic rocks consist of fine-grained garnet meta-mafic (FGM) and coarse-grained garnet meta-mafic (CGM) rocks presenting nearly similar mineral composition. They are made up of quartz, plagioclase, garnet orthopyroxene, clinopyroxene, amphibole, opaques, apatite and rutile. They also present recrystallization features such as quartz ribbons, corroded grain mineral, cuspate plagioclase boundary and necklace garnets in the matrix. These mineral assemblages suggest that the recrystallization took place under granulite facies condition. The meta-mafic rocks have basaltic and tholeiitic composition like the magmas (SiO2 FGM = 48.20–50.70 wt% and SiO2CGM = 46.68–50.27 wt% and MgFGM = 43.24–62.27 and MgCGM = 40.85–69.70) emplaced in the active continental margin context. The low La/Th ratio observed in the FGM and the high La/Th ratio in the CGM together with low Hf content imply that the FGM are reworked plutonic rocks that recorded both high grade partial melting and metamorphism whereas CGM recorded only metamorphism imprints. Thermobarometry results suggest that the partial melting and metamorphic peak occurred around the amphibolite-granulite facies transition. The fine-grained garnet meta-mafic rocks emplaced under pressure estimated at around 2.7–14.89 kbar with temperature interval between 672 and 952 °C while the coarse-grained garnet meta-mafics settled at around 1.5–16.09 kbar and 631–909 °C. The selected amphiboles display low water content (1.92–2.10 wt%) and plot between NNO and NNO + 2 buffers indicating that they crystallized under high oxidizing conditions. These results coupled with previous geochronological study suggest that the FGM may have occurred at the Mesoarchean and have been reworked during Eburnean whereas the CGM may have been formed at the Eburnean.

Structural data, meso‑ and micro-photographics were collected from Archean basement of the Memve'ele area (Ntem Complex, southwestern Cameroon). The analyses were acquired using field and laboratory investigations. Meso-photographics were obtained by a camera Canon SX160 IS , 16X digital zoom, HD 16.0 Mega pixels. Micro-photographics were carried out by electronic microscope Olympus BX60 type with a camera and entire thin section picture scan. Structural data were acquired by a topochaix compass type and stereographic data were obtained by a stereonet program. The data presented in this paper are further interpreted and discussed in the Ntomba et al., 2020 [1] .