Abstract
The petrographic and structural study of Gbowé (Grand-Béréby) formations located in the SASCA domain (South-West of Côte d’Ivoire) revealed migmatitic paragneisses. For an in-depth understanding of the petrographic, structural and metamorphic characteristics, six (6) thin sections were made from these paragneisses. These gneisses are characterized by paleosomes and neosomes (leucosome and melanosome), consisting of quartz, garnet, plagioclase, biotite, cordierite, sillimanite, myrmekite and microcline. The mineralogical assemblage thus described indicates a retrograde metamorphism (transition from granulitic facies to amphibolitic facies). The structural and microstructural study identified two types of deformation (ductile and brittle). The ductile deformation is characterized by phases D1 (NE-SW flattening) and D2 (NW-SE flattening), materialized by foliations (N140˚, N050˚), folds (asymmetrical folds, similar folds, concentric folds, ptymatic folds) and boudins. Fracture schistosity and fold fracture schistosity are characteristic of the brittle deformation (phase D3). The microstructural study coupled with the metamorphic study shows that the deformations had an impact on the texture of the minerals (recrystallization and mineral reactions). It also allowed giving the paragenesis of phases D1 and D2. The D1 phase is characterized by garnet1, biotite1, quartz1, sillimanite1 and cordierite1 and the D2 phase is characterized by garnet1, quartz2, sillimanite2, biotite2, garnet2 and orthose2. These parageneses thus highlighted bear witness to a polydeformation and polymorphism that affects the study area.
Highlights
The geological formations of south-west Côte d’Ivoire consist of several metamorphic units, and Eburnean plutonic rocks grouped into two domains (Papon, 1973): the Man domain and the SASCA domain
The petrographic and structural study of Gbowé (Grand-Béréby) formations located in the SASCA domain (South-West of Côte d’Ivoire) revealed migmatitic paragneisses
The geological formations of south-west Côte d’Ivoire consist of several metamorphic units, and Eburnean plutonic rocks grouped into two domains (Papon, 1973): the Man domain and the SASCA domain
Summary
The geological formations of south-west Côte d’Ivoire consist of several metamorphic units, and Eburnean plutonic rocks grouped into two domains (Papon, 1973): the Man domain and the SASCA domain (named after the Sassandra and Cavally rivers which limit this area). The SASCA domain is composed of an old Liberian granitic and metamorphic basement (Koffi et al, 2020, Kouamelan et al, 2018) over which birimian formations of pelitic, tuffaceous, acidic and/or basic origin have transgressed, to which the micaschists of Kounoukou are associated (Papon, 1973) This zone is characterized by the coexistence of high and medium grade metamorphic units (Papon, 1973, Kouamelan et al, 2015; Kouadio, 2017) with the presence of Archean crustal relics (Kouamelan, 1996; Kouamelan et al, 1997a, 2015, Petersson et al, 2016, 2017). The geological formations in this sector raise several questions, namely: 1) What are the petrographic characteristics of the main formations encountered?, 2) What are the deformations and metamorphisms that have affected these formations and their relative chronology? and 3) How can we explain the formation of these formations?
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