TITLE:
Petrographic and Geochemical Characterization of the Fianga Granitoids (Mayo Kebbi) in the Pan-African Range of Central Africa in Chad: Geodynamic Implication
AUTHORS:
Moussa Ngarena Klamadji, Diondoh Mbaguedje, Nenadji Félix Djerossem, Ronang Gustave Baïssemia, Djoum Temoua
KEYWORDS:
Granitoids, Calc-Alkaline, Fianga Massif, Mayo-Kebbi, Pan-African Range
JOURNAL NAME:
Open Journal of Geology,
Vol.15 No.12,
December
26,
2025
ABSTRACT: The Fianga Massif belongs to the Pan-African Range of Central Africa in Chad. The Fianga Massif belongs to the Chadian sector of the Pan-African Range of Central Africa. The Fianga area has not been the subject of a detailed geological study. Many gaps remain in terms of the petrography and geochemistry of the massif. The Fianga Massif is composed of small, elongated NW-SE plutons. It consists of granitoids (granodiorites, hornblende and biotite granites, biotite granites and biotite microgranites) intruding into metamorphic rocks (quartz chlorite schists and massive amphibolites). These granitoids contain enclaves of metamorphic rocks and are cut by aplite and pegmatite veins. Geochemistry demonstrates that the Fianga granitoids are highly potassic and peraluminous. These studied rocks originate from a single magmatic source that evolved and differentiated by fractional crystallization in a magmatic reservoir. REE profiles show weakly enriched REEs (LaN/YbN = 0.69 - 40.29) while heavy REEs show a nearly flat profile (DyN/YbN = 0.52 - 1.13), and the La/Sm and Sm/Yb ratios led to the proposal that the Fianga rocks were derived from the partial melting of a mantle source enriched in spinel-garnet lherzolite. The partial melting of this mantle source is linked to large-scale movements along the Central Cameroon or Adamawa-Yadé shear zone and the Tchollire-Banyo shear zone, which controlled the emplacement of the pluton in the study area during the Pan-African period. This partial melting would be the origin of the emplacement of the granitoids of the Fianga massif. The high La/Nb (0.30 - 8.66) and low La/Ba (0.012 - 0.36) ratios of these granitoids are consistent with their origin by partial melting of the subcontinental lithospheric mantle modified by subduction. Pink granites (A/CNK = 0.91 - 0.96), pink microgranites (A/CNK = 0.98 - 0.07), syenites (A/CNK = 0.02), and granodiorites (A/CNK = 0.94 - 1.40) are metaluminous to perataluminous. The data suggest emplacement of this Fianga pluton in a subduction zone. The granitoids occur in the domains of volcanic arc granitoids and syn-collisional granites.