Laboratoire de Géologie du socle et de Métallogénie, UFR STRM, Université Félix Houphouët Boigny de Cocody Abidjan, 22 BP 582 Abidjan 22, Côte d’Ivoire
Our study area in southwestern Côte d’Ivoire in SASCA domain is part of the Archean-Paleoproterozoic transition zone and consists mainly of metasediments, grey gneisses, metabasites and granitoids. We present new data on the petrographic characterization and origin of metasediments in this area. Both field and petrographic observations indicate that metasediments consist of garnet-sillimanite-cordierite paragneisses and staurolite and/or garnet mica schists. The major elements made it possible to constrain the origin of these metasediments by showing: (i) their belonging to the group of iron-rich shales in majority and secondarily to the Fe-rich sandstones, (ii) their provenance from basalt and andesitic rocks moderately weathered (60
The petrographic and geochemical study of the geological formations of Tabou and Grand-Béréby area located in SASCA domain (south-west of the Ivory Coast) show a strong foliated paragneisses. These gneisses are characterized by an alternation of dark layers of garnet-biotite-sillimanite and millimeter-thick leucocratic quartz-feldspar-cordierite bands. The mineralogical assembly thus described indicates a high grade metamorphism (granulite-facies). The major and traces elements made it possible to force the paragneisses protoliths. Thus this study shows that paragneisses are composed by greywackes and derived from source areas of felsic to intermediate composition. Their chondrite normalized REE patterns show a moderate LREE enrichment (LaN/YbN= 6,90-38,36) and a flat heavy rare earth patterns (HREE) This spectrum is almost identical to those of the Post-Archean average Australian Shale and Early Proterozoic Greywackes. Geochemical data also suggest that paragneisses are set up in a tectonic environment of active continental margin and continental island arc.
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