The Earth’s crust is predominantly composed of Archean and Paleoproterozoic materials, with over 75% of the continental crust having differentiated from the mantle during this period [1] . However, recent studies suggest limited crustal evolution during the Hadean [2] [3] . The Archean domain of the West African Craton (COA) mainly consists of orthogneisses and charnockites, particularly within the Réguibat and Man Ridges. These high-grade metamorphic formations are often associated with intrusive magmatic rocks. The geothermal gradients during the Archean were higher than those of the Paleoproterozoic [4] , making this era distinct in terms of petrology, tectonics, and mineralization. Petrologically, Archean terrains are characterized by TTG (tonalite-trondhjemite-granodiorite) suites and komatiites. While komatiites are associated with greenstone belts, TTGs dominate granito-gneissic complexes. TTG studies remain significant for determining rock protoliths [5] . Gneissic formations, among the oldest rocks [6] , are widespread in the Archean domain of Côte d’Ivoire but also occur in the transition zone between Archean and Paleoproterozoic terrains. Tectonically, Archean terrains exhibit predominantly vertical structures [7] - [10] . The Kenema-Man domain hosts Banded Iron Formations (BIFs), indicating a previously reducing atmosphere. The disappearance of BIFs corresponds to increased atmospheric oxygen levels [11] [12] . Petrogeochemical, structural, and geochronological studies [13] have provided insights into the lithological composition, geochemical characteristics, and tectonic evolution of this domain. This study aims to further contribute by analyzing the petrographic and geochemical properties of the gneisses in the Biankouma-Kouibli sector and assessing their emplacement context.

The study area is located in western Côte d’Ivoire, between longitudes 7˚ and 8˚ West and latitudes 8˚ and 8˚30' North ( Figure 1 ). It lies approximately 700 km north of Abidjan and 40 km north of Man. It is bordered by Touba to the north, Man to the south, Danané to the west, and Séguéla to the east.

The West African Craton includes two principal Precambrian domains: the Réguibat Rise to the North and the Leo-Man Rise to the South [14] [15] . The Leo-Man Rise is composed by an Archean cratonic nucleus in the southwest, the so-called Kéména-Man domain (KMD), surrounded by some Paleoproterozoic belts in the north and east forming the Baoulé-Mossi domain ( Figure 2 ) [16] . Following this first stage of crustal growth, the craton was affected by two major metamorphic and magmatic events; the Leonian cycle at ca. 3.2 - 3.0 Ga [17] and the Liberian cycle at ca. 2.9 - 2.8 Ga [17] [18] . The Baoulé-Mossi domain is made up by an association of mainly low-grade Birimian (ca. 2.20 - 2.13 Ga) and Tarkwaian (ca. 2.10 - 2.09 Ga) sediments and plutono-volcanic rocks, which emplaced during a major juvenile crust-forming event, referred as the Eburnean orogeny, and dated between ca. 2250 and 1980 Ma [15] [19] - [21] .

Volcanic rocks geochemical signature is compatible with the evolution from tholeiitic oceanic crust or oceanic plateau to juvenile calc-alkaline volcanic island arcs [15] .

The Baoule-Mossi Paleoproterozoic domain of the West African Craton (WAC) was accreted to the Archean nucleus of The WAC During the Eburnean orogeny [22] - [26] ( Figure 2 ). The Baoule-Mossi domain is composed of Birimian greenstone belts made of metavolcanic, metavolcanosedimentary, and metasedimentary rocks, emplaced between 2220 and 2160 Ma [15] [27] , And Bandamian Volcanic rocks aged between 2120 And 2080 Ma [24] [28] [29] . The study area is part of the Kenema-Man domain. The Archean domain or Kenema-Man domain is delimited by the Monts Trou fault trending SW-NE and the south-meridian Sassandra fault up to the height of Odienné. It is located north of the Man-Danané fault. The region is governed mainly by gray granulitic gneisses, pink granulites, charnockites and some granitoids [30] ( Figure 3 ).

These formations are intruded by pink granites, basic-ultrabasic complexes, granodiorites, and granites. Supracrustal rocks such as aluminous gneisses, amphibolo-pyroxenites, and ferruginous quartzites have undergone catazonal metamorphism during significant folding events [31] . Additionally, Birimian formations, including the Ity-Toulépleu unit (Danané region) and the layered mafic-ultramafic Yacouba complex (Biankouma-Sipilou region), have intruded the gneissic granulites of the Archean Man domain (3.6 - 2.78 Ga) [32] .

The northern domain of the Man-Danané fault primarily consists of gray granulitic gneiss, charnockite, and pink granulite, with SiO₂ contents ranging from 68.6% to 73.4% and A/CNK ratios between 0.98 and 1.05.

In contrast, the southern domain of the fault comprises migmatitic biotite gneisses and hypersthene gneisses, displaying SiO₂ contents between 59.16% and 74.6%, with A/CNK ratios ranging from 0.81 to 1.03. These rock formations are generally weakly peraluminous, except for charnockite (CIS 26) and migmatitic biotite gneiss (CIS 44), which exhibit a metaluminous affinity ( Figure 5 ).

In the K₂O versus SiO₂ diagram of [33] , CIS 25A, CIS 26, CIS 27A, and CIS 46 fall within the strongly potassic calc-alkaline series, CIS 25B and CIS 27B belong to the Shoshonitic series, CIS 44 aligns with the moderately potassic calc-alkaline series, CIS 45 follows a weakly potassic tholeiitic series ( Figure 6 ).

The northern domain of the Man-Danané fault is mainly composed of gray granulitic gneiss, charnockite and pink granulite with SiO₂ contents ranging from 68.6% to 73.4%. The A/CNK ratios = 0.98 - 1.05. In addition, the petrographic study carried out in the domain south of this fault has revealed migmatitic biotite gneisses and hypersthene gneisses with SiO₂ contents ranging from 59.16% and 74.6% as well as A/CNK ratios = 0.81 - 1.03. All these rock formations are weakly peraluminous except for the Charnockite CIS 26 and the migmatitic biotite gneiss CIS 44 which have a metaluminous affinity ( Figure 5 ). In the K₂O versus SiO₂ [33] , CIS 25A, CIS 26 and CIS 27A, CIS 46 are located in the strongly potassic calc-alkaline series, samples CIS 25B and CIS 27B are located in the shoshonitic series, CIS 44 in the moderately potassic calc-alkaline series and finally CIS 45 follows a tholeiitic series which is weakly potassic ( Figure 6 ).

The multi-element spectra of Biankouma and Kouibli samples, normalized to the primitive mantle (McDonough et al., 1992) [34] , exhibit a similar geochemical pattern. These rocks are notably enriched in large-ion lithophile elements (LILEs) such as Rb, Ba, and K, while showing depletions in high-field strength elements (HFSEs) like Nb, P, and Ti ( Figure 7 ). Among them, CIS 27B displays a more pronounced depletion in heavy rare earth elements (HREEs). Additionally, the lithologies show a non-negligible enrichment in radioactive elements, particularly Th.

The observed Ba enrichment is likely linked to the granulitic metamorphic event responsible for their formation [35] , suggesting that alkali feldspar fractionation over time was minimal. The negative anomalies in Ti, P, and Nb may indicate the presence of magnetite, sphene, apatite, and ilmenite in the melt residue or cumulate phases. Furthermore, the Ta-Nb depletion trend across all samples suggests that these granulitic gneisses originated from a subduction-related environment.

The total rare earth element content (ΣREE) varies from 107.7 ppm to 528.3 ppm. REE spectra, normalized to chondrites [34] ( Figure 8 ), indicates a light rare earth element (LREE) enrichment, with (La/Sm) N ratios ranging from 7.99 to 8.45 and (La/Yb) N values spanning from 6.08 to 252.4. In contrast, there is a noticeable HREE depletion. Additionally, the granulitic gneisses exhibit a negative Eu anomaly (Eu/Eu = 0.39 - 1.67), indicative of plagioclase fractionation during fractional crystallization.

The multi-element spectra of the Biankouma and Kouibli samples normalized to the primitive mantle [34] show a similar pattern. These rocks are enriched in LILEs (Rb, Ba and K) and depleted in HFSE (Nb, P and Ti) ( Figure 7 ). The depletion of heavy rare earths is more pronounced in the CIS 27B sample. The enrichment of these lithologies in radioactive elements (Th) is not negligible.

The enrichment in Ba could be due to the granulitic event that allowed the formation of these rocks [35] and would exclude a fractionation of the alkali feldspars over time. The negative anomalies in Ti, P and Nb could be assimilated to the presence of magnetite, sphene, apatite and ilmenite in the melt residue or in the cumulate. The depression observed between Ta-Nb for all of these formations would indicate that these granulitic gneisses would come from a subduction environment.

The amount of rare earths (ƩREE) varies respectively from 107.7 ppm to 528.3 ppm. The rare earth spectra of the different rocks were normalized to the chondrites of [34] ( Figure 8 ). These spectra are marked by an enrichment in light earths (LREE) with (La/Sm) N ratios that vary between 7.99 and 8.45; (La/Yb) N range from 6.08 to 252.4 and a depletion in heavy rare earths (HREE). Granulitic gneisses show a depletion in Eu (Eu/Eu* = 0.39 - 1.67). This depletion in Eu reflects a fractionation of plagioclase during fractional crystallization.

The aim of this study was to characterize the gneissic formations of the Biankouma and Kouibli areas, investigate their geochemical properties, and propose a model for their emplacement. From a petrographic perspective, the Archean domain of the Biankouma area extending into the Kouibli area is primarily composed of granulitic gneiss, charnockites, and pink granulite in Biankouma, with biotite migmatite gneiss and charnockitic gneiss in Kouibli. The mineralogy of these metamorphic formations includes quartz, alkali feldspar, hypersthene, plagioclase, and biotite, all formed under granulite facies conditions. Geochemical analysis reveals that the studied formations are Archean TTGs with granodioritic, tonalitic, and granitic compositions. These rocks are characterized by low aluminum content (Al₂O₃ < 15%) and exhibit a strongly potassic to tholeiitic calc-alkaline affinity. The formations display a weakly metaluminous to weakly peraluminous nature. Trace element distributions show enrichments in light rare earth elements (LREEs) and depletions in heavy rare earth elements (HREEs). The negative anomalies in Ta-Nb and Eu further support the hypothesis that these formations originated from the partial melting of a basic source rock containing garnet and hornblende. The composition of all samples suggests an arc and collision granite signature, consistent with their formation in a subduction zone.

The analyses and fieldwork were financially supported by PRESED-CI T2GEM research grant “Geophysical and Geochemical Techniques for Mining Exploration”. We would like to thank the PASRES (Strategic Support Program for Scientific Research) for contributions to the field campaign.