The granodiorite outcrops as rounded masses and is characterized by a coarse-grained porphyroid texture, displaying feldspar and quartz phenocrysts embedded in a fine-grained matrix composed of ferromagnesian and felsic minerals ( Figure 3(a) ). It is in sharp contact with the biotite microgranite. Under the microscope, the granodiorite exhibits a granular texture and consists of plagioclase, quartz, biotite, and oxides ( Figure 4(a) , Figure 4(b) ). Plagioclase (30% - 45%) occurs as subhedral to euhedral crystals, typically in lath-like forms of variable size. Rounded grain edges indicate an advanced degree of alteration. Quartz (20% - 30%) appears as large, elongated grains with lobate margins and neograins, suggesting crystallization under high-temperature conditions. Biotite (10% - 20%) is present as interstitial micrograins or as inclusions within plagioclase and quartz crystals. Opaque minerals (<5%) are observed as subrounded grains, often included within plagioclase and quartz.

The deformed biotite granite crops out as blocks or slabs, generally weathered, and covers a large area within the study zone ( Figure 3(b) ). It displays a granoblastic texture typical of metamorphosed rocks, with a mineralogical composition dominated by plagioclase, quartz, biotite, and secondary minerals such as chlorite and calcite ( Figure 4(c) , Figure 4(d) ). Plagioclase (~60%) forms subhedral to euhedral crystals arranged in laths of varying dimensions and constitutes the dominant phase of the rock. Quartz (10% - 20%) occurs as elongated, interstitial grains between plagioclase crystals, indicating recrystallization under ductile conditions. Biotite (<10%) is generally found as inclusions within plagioclase phenocrysts, suggesting crystallization prior to or synchronous with plagioclase formation. Secondary minerals, including chlorite and calcite, are present in variable amounts and are associated with alteration processes.

The biotite granite outcrops as rounded masses, blocks, and small hills aligned along a north-south axis ( Figure 3(c) ). It is locally crosscut by dolerite dykes, indicating magmatic events that postdate its emplacement. Thin-section analysis reveals a coarse-grained heterogranular texture, characterized by medium to coarse grains and interlocking phenocrysts ( Figure 4(e) , Figure 4(f) ). The primary mineralogical composition includes plagioclase, quartz, and biotite, accompanied by accessory minerals such as zircon, sphene, and opaque minerals. Plagioclase (30% - 40%) occurs as more or less elongated lath-shaped crystals with well-developed polysynthetic twinning, forming the dominant phase of the rock. Quartz (20% - 35%) is present in two distinct generations: the first generation consists of phenocrysts spatially associated with plagioclase, while the second generation comprises neograins arranged in coronas around plagioclase crystals, suggesting late-stage recrystallization. Biotite (10% - 15%) appears as elongated flakes located in the interstices between plagioclase and quartz crystals. Some biotite grains are also observed as inclusions within plagioclase crystals. Accessory minerals (<3%) include zircon, sphene, and opaque phases, typically found as inclusions within the main mineral phases (plagioclase, quartz, biotite), indicating early or synchronous crystallization.

Biotite microgranites crop out as north-south trending dykes that crosscut both the granodiorite and the biotite granite ( Figure 3(d) ). These well-defined dykes range in thickness from 10 to 30 cm. They are also found at the summits of certain hills, whose bases consist of rocks with dioritic to granodioritic compositions. The microgranite is distinguished by a fine-grained texture, typical of rapidly cooled facies ( Figure 4(g) , Figure 4(h) ). Its mineralogical composition is similar to that of the biotite granite, dominated by plagioclase, quartz, and biotite, along with accessory minerals. Plagioclase (>50%) occurs as euhedral to subhedral lath-shaped crystals, sometimes showing surface alteration, and represents the dominant phase of the rock. Quartz (>20%) is present in two forms: medium-grained interstitial quartz associated with plagioclase, and neograins surrounding plagioclase crystals, indicative of post-magmatic recrystallization. Biotite (<10%) appears as interstitial flakes located between plagioclase and quartz crystals, with some grains also observed as inclusions within plagioclase. Accessory minerals (<3%), including zircon, sphene, and opaque phases, are found as inclusions within the main mineral phases, suggesting early or synchronous crystallization.

To characterize petrogenetic processes in geochemistry, it is essential to evaluate rock weathering, even when samples appear fresh in the field. The Chemical Index of Alteration (CIA), introduced by [23] , provides a quantitative measure based on the following molar ratio: CIA = [Al₂O₃/(Al₂O₃ + CaO* + Na₂O + K₂O)] × 100 (where CaO* represents the concentration of CaO incorporated within the silicate fraction of the rock).

According to [24] , three levels of weathering can be distinguished based on CIA values: 1) Intense weathering (feldspar transformation into clay minerals) when CIA > 92; 2) Moderate atmospheric weathering when CIA ranges between 60 and 80 and 3) Low or negligible weathering when CIA < 60. All analyzed granitoid samples exhibit CIA values below 60, indicating minimal to no alteration. This interpretation is further supported by their position within the unweathered rock domain of the CN-K-A ternary diagram ( Figure 5 ).

Geochemical analyses were conducted on 13 representative samples, including 2 granodiorites, 3 deformed biotite granites, 6 biotite granites, and 2 biotite microgranites. Major element concentrations for these granitoids are presented in Table 1 and are characterized by Loss on Ignition (LOI) values ranging from 0.33 to 1.78 wt.%. These granitoids are predominantly intermediate to acidic rocks, with SiO₂ contents ranging from 67.2 to 78 wt.%. TiO₂, P₂O₅, MnO, and CaO values are relatively low across all samples. K₂O concentrations are slightly lower in granodiorites (1.29 - 1.80 wt.%) and deformed biotite granites (0.86 - 1.02 wt.%) compared to biotite granites (2.86 - 3.75 wt.%) and biotite microgranites (4.37 - 4.76 wt.%). Al₂O₃ and Na₂O contents are slightly higher in granodiorites and deformed biotite granites (14.8 - 19 wt.% and 5.62 - 7.54 wt.%, respectively) than in biotite granites and microgranites (11.8 - 13.2 wt.% and 3.95 - 4.32 wt.%). Total alkali contents range from 6.74 to 8.74 wt.%, with K₂O/Na₂O ratios between 0.13 and 1.20, and very low Mg# values (6.43 - 39.27).

In the [26] classification diagram for plutonic rocks ( Figure 6(a) ), the samples plot within the granodiorite and granite fields, corresponding to subalkaline domains. In the A/CNK vs A/NK diagram [27] , the analyzed granitoids are metaluminous and fall within the I-type granitoids field for the granodiorite, biotite granite and biotite microgranite ( Figure 6(b) ). Deformed biotite granite is peraluminous and fall winthin the I-type granitoids field. They are characterized by K₂O/Na₂O ratios ranging from 0.13 to 1.20, consistent with strongly potassic calc-alkaline granitoids for the granodiorites, biotite granites, and biotite microgranites ( Figure 6(c) ). The deformed biotite granites are weakly potassic.

According to the [28] classification diagram, the Goueygoudoum-Fianga granitoids exhibit calcic to calc-alkaline affinities ( Figure 6(d) ). In the Harker-type diagram ( Figure 7 ), oxide concentrations show two trends with increasing SiO₂ content: a negative correlation for Al₂O₃, TiO₂, Fe₂O₃, MgO, CaO, Na₂O, and P₂O₅, and a positive correlation for K₂O. In both cases, the deformed biotite granites are slightly offset from the other granitoid types.

The Goueygoudoum-Fianga granitoids are characterized by elevated concentrations of barium (Ba), ranging from 44.5 to 859 ppm. Strontium (Sr) values are moderately high in granodiorites and deformed biotite granites (109.5 - 704 ppm), compared to lower concentrations in biotite granites and biotite microgranites (7.1 - 121.5 ppm). Rubidium (Rb) concentrations are high in granodiorites (34 - 109.5 ppm) and biotite microgranites (116.5 - 245 ppm), while they remain low in deformed biotite granites and biotite granites (8 - 81.2 ppm).

In the chondrite-normalized rare earth element (REE) diagram [32] ( Figure 8 ), all granitoid samples exhibit parallel REE patterns with enrichment in light rare earth elements (LREE) ((La/Yb)_N = 1.09 - 11.80) relative to middle and heavy rare earth elements (MREE and HREE) ((Gd/Yb)_N = 0.42 - 3.03). Granodiorites (Eu/Eu* = 0.55 - 0.70), biotite granites (Eu/Eu* = 0.41 - 0.46), and biotite microgranites (Eu/Eu* = 0.05 - 0.13) display negative europium anomalies, whereas deformed biotite granites show positive Eu anomalies (Eu/Eu* = 1.08 - 2.18).

In the primitive mantle-normalized multi-element diagram [32] ( Figure 9 ), the Goueygoudoum-Fianga granitoids exhibit negative anomalies in Nb, Sr, Ti, Ta, Eu, Tb, and Ba. Positive anomalies are also observed in Ba, Pb, Sr, Zr, Y, and Th.

Petrographic and geochemical characteristics of major and trace elements indicate that the Goueygoudoum-Fianga granitoids are primarily composed of granodiorite, deformed biotite granite, biotite granite, and biotite microgranite. These rocks are generally ferroan and peraluminous, displaying a weakly to high-K calc-alkaline nature, predominantly of I-type affinity. However, the granitoids also exhibit high concentrations of SiO₂, K₂O, Na₂O + K₂O, FeO, Ga/Al ratios, and high field strength elements (HFSEs), along with low contents of CaO, MgO, P₂O₅, and Al₂O₃, and negative anomalies in Sr, Eu, and Ti. These geochemical signatures are consistent with A-type granites as described in the literature [28] [33] [34] . In the Zr vs. 10000*Ga/Al diagram ( Figure 10(a) , Figure 10(b) ), granodiorites, biotite granites, and biotite microgranites plot within the A-type granite field. This classification is consistent with that proposed by [12] for the Mayo Kebbi massif, emplaced at 567 ± 10 Ma under very high temperatures (ranging from 744 ˚C to 923 ˚C), suggesting a highly differentiated magma. Similar granite types were also identified by [35] in the Guéra massif, where they were dated at 554 ± 8 Ma and 546 ± 8 Ma, respectively.

In contrast, the deformed biotite granites correspond to I-type granitoids, as indicated by their molar ratio Al₂O₃/(CaO + Na₂O + K₂O) > 1.1. These characteristics are complemented by high concentrations of incompatible elements such as Rb, Ba, and Sr, which are typical of pre-collisional arc-type granites. These rocks were dated at 668 ± 8 Ma by [36] , implying a significant contribution from an older basement in their genesis.

This section uses major, trace, and rare earth element concentrations to discuss magmatic evolution processes such as fractional crystallization and crustal contamination/assimilation.

I-type granitoids composed of deformed biotite granite exhibit decreasing concentrations of Al₂O₃, CaO, Na₂O, and K₂O as SiO₂ content increases. These correlations likely reflect fractional crystallization of plagioclase, feldspars, and apatite. In contrast, concentrations of TiO₂, Fe₂O₃, MgO, and P₂O₅ are highly scattered and variations in immobile element ratios such as Zr/Nb and La/Yb suggest an origin linked to partial melting [38] . This geochemical behavior highlights heterogeneity among the deformed biotite granites, possibly resulting from complex partial melting processes or an atypical magmatic source. I-type granites (deformed biotite granites) span both lower continental crust (LCC) and upper continental crust (UCC) domains, as shown in the CN-K-A diagram ( Figure 11(c) ). This trend is also evident in the Rb/Th vs. Rb diagram ( Figure 11(d) ), where deformed biotite granites display signs of crustal contamination.

A-type granitoids reveals linear negative trends for Al₂O₃, CaO, Na₂O, TiO₂, Fe₂O₃, MgO, and P₂O₅, and a positive trend for K₂O in the Harker-type diagrams. According to [39] , these correlations play a significant role in mineral phase crystallization. The low CaO content suggests plagioclase and apatite fractionation. Amphibole fractionation accounts for the low MgO levels. Depletion in TiO₂ and P₂O₅ reflects the fractionation of ilmenite and apatite, respectively, while low Fe₂O₃ concentrations are linked to magnetite fractionation.

Overall, the negative oxide trends with increasing SiO₂ content, as described by [40] , support fractional crystallization of plagioclase and magnetite. Negative anomalies in Eu, Nb, Ta, and Ti, along with positive anomalies in Eu and Sr, further indicate the fractionation of minerals such as plagioclase, hornblende, biotite, apatite, allanite, and titanite.

Immobile element ratios such as Zr/Nb and La/Yb typically remain constant during fractional crystallization but tend to increase with higher degrees of partial melting [38] [41] . In this study, these ratios remain stable in granodiorites, biotite granites, and fine-grained microgranites ( Figure 11(a) , Figure 11(b) ), reflecting a fractional crystallization process. Additionally, the analyzed A-type granitoids exhibit low MgO contents and particularly low Mg# values. Cr, Ni, and Co concentrations are also low. These parameters, well below those of the primitive mantle, indicate an advanced stage of magmatic differentiation, typical of fractional crystallization with or without crustal contamination [42] .

Crustal contamination is clearly illustrated in the Nb/U vs. Nb diagram [43] ( Figure 11(c) ), where the granitoids plot within a field indicative of upper continental crust composition, especially for A-type granites. This is also observed in the Rb/Th vs. Rb diagram, where the granodiorites, biotite granites, and fine-grained granites fall within a field likely affected by fractional crystallization with crustal assimilation ( Figure 11(d) ).

I-type granitoids, particularly the deformed biotite granite, exhibit trace element concentrations such as V = 5 - 15 ppm, Cr = 95 - 200 ppm, Co ≤ 1 ppm, Ni ≤ 1 ppm, Mg# = 19.31 - 34.29, Nb/U = 2.07 - 23.33, and Ce/Pb = 0.56 - 2.04. These values are significantly lower than those typical of mantle-derived magmas (V = 151 ppm; Cr = 151 ppm; Co = 94 ppm; Ni = 81 ppm; Mg# = 60; Nb/U = 30; Ce/Pb = 10.2 [40] [45] , indicating a dominantly crustal geochemical signature. The Ta/U ratio (0.71 - 2) is also lower than or equal to mantle values, suggesting a mixed origin. These granites are further distinguished by enrichments in Br and Sr, low Rb/Sr ratios, high concentrations of large-ion lithophile elements (LILE), and light rare earth elements (LREE), along with negative anomalies in Nb, Ta, and Ti. Elevated Rb/Th ratios, low La/Sm and (Ta/La)_N ratios, and high alkali contents reinforce this interpretation.

According to [46] , these geochemical signatures suggest that the parental magma may have originated from partial melting of a metasomatized mantle, combined with crustal contamination. This hypothesis supports a magma mixing model involving mantle-derived melts and crustal inputs. On discriminant diagrams such as Hf–Nb/4–Rb/30, Rb vs. Y + Nb, and (Nb/Zr)_N vs. Zr ( Figure 11(b) , Figure 11(c) ), the deformed biotite granites plot within the volcanic arc granite field. Moreover, La/Ta (16 - 38), La/Nb (2.46 - 13.10), and Nb/Ta (2.9 - 14) ratios, along with low Rb contents, reflect a subduction-related genesis [47] . This interpretation is supported by the Zr vs (Nb/Zr)_N diagram, which highlights geochemical signatures indicative of partial melting. ( Figure 11(d) ). Similar granitoid sources have been identified in the Central African orogenic belt, notably in the Guéra massif [16] [18] .

A-type granitoids, including granodiorites, biotite granites, and fine-grained granites, show trace element concentrations of V = 5 - 77 ppm, Cr = 112 - 233 ppm, Co = 1 - 5 ppm, Ni = 1 - 9 ppm, and Mg# = 6.43 - 39.27. These values are also lower than those of mantle-derived magmas, indicating a crustal origin. This is further supported by low Ta/U (0.33 - 0.76), Nb/U (3.64 - 11.17), and Ce/Pb (1.91 - 9.59) ratios, compared to mantle values (Ta/U = 1.1 - 1.8; Nb/U = 30; Ce/Pb = 10.2 [40] .

According to [48] , the molar ratio diagram of CaO/(MgO + FeOt) vs. Al₂O₃/(MgO + FeOt) helps identify source rocks formed under varying melting conditions. The distribution of Goueygoudoum-Fianga granitoids in this diagram ( Figure 12(a) ) indicates derivation from partial melting of metagreywackes and metapelites, consistent with a crustal source. Similar sources have been reported in the Ouaddaï massif [15] , Baïbokoum [17] and Mayo Kebbi [11] [12] [49] . Granodiorite indicates derivation from partial melting of metabasic and tonalitic sources.

Structural analysis using the ternary Hf-Nb/4-Rb/30 diagram ( Figure 12(b) ) shows that most studied granitoids fall within the volcanic arc granite field. One notable exception is a fine-grained granite sample that plots in the post-collisional granite domain. In the (Y + Nb) vs. Rb diagram ( Figure 12(c) ), granodiorites, biotite granites, and biotite microgranites display characteristics typical of A-type granites, suggesting emplacement in a post-collisional tectonic setting. The (Nb/Zr)_N vs. Zr diagram ( Figure 12(d) ) indicates that biotite granites fall within the subduction-related magmatic field. Overall, granodiorites, biotite granites, and microgranites are compatible with a continental collision magmatic context. However, one microgranite and one granodiorite sample plot in a transitional zone between subduction and collision fields, suggesting mixed geodynamic conditions during their formation. Finally, a fine-grained granite sample shows a transitional signature between collisional and intraplate settings, reflecting a complex tectono-magmatic evolution possibly linked to lithospheric thinning or reactivation processes.