Programme des sessions > Recherche par auteur correspondant > Adissin Glodji Cossi Luc

The Kandi shear zone (KSZ) crossing the entire Benin from South to North and possibly connected to the 4°50' shear zone in the Hoggar Mountains and to the “Transbrasiliano lineamento” in northeastern Brazil, is a large right-lateral N-S trend transcurrent domain about forty kilometers wide in Central Benin and is one of the major late Pan-African shear zone worldwide. The geological and geodynamic evolution of this major shear-zone in the framework of the Pan-African Dahomeyide orogen remains poorly documented, largely due to the limited investigations on the timing of its deformation from ductile to ductile-brittle conditions. The KSZ exposes an association of high-grade gneisses and migmatites, together with granitoids, low-grade metavolcanic and sedimentary formations and low-temperature tectonites bands. This almost crustal shear zone and potentially rooted in the lithosphere constitutes one exceptional fault connecting lower structural unit (granulite facies rocks) toward very shallow sedimentation. To better understand geodynamic evolution of the KSZ, U-Pb dating of zircons using LA-ICP-MS was carried out on metamorphic and igneous rocks from Central Benin. Zircons from the orthopyroxene-garnet-biotite granulite of Savalou yielded a Paleoproterozoic ages of 2091 ± 14 Ma and 2057 ± 8 Ma interpreted as crystallization and metamorphic recrystallization in granulite facies condition. The amphibole-biotite gneiss of Govi provided a Neoproterozoic age of 606 ± 5 Ma, interpreted as the HT mylonitic deformation associated with the onset of the Kandi shearing. Dating coupled with geochemical and microstructural analysis of granitoids and rhyolite shows that the KSZ controlled the ascent and emplacement of intrusive and volcanic magmas until about 570 Ma by the localisation of the deformation along the kilometric-scale wide shear bands. About four hundred kilometers north of these plutons, a granite with an age of 547 ± 15 (207Pb/206Pb age on zircon; Kalsbeek et al. 2012) is currently studied and may represent the youngest known magmatic event along the KSZ. To further understand the magmatic activity, its relationship with deformation, the role of fluids and to better constrain the late-stage history of the KSZ at low-temperature, dating using in situ U-Th-Pb on monazite and Rb-Sr on micas techniques is being carried out.