Petrology and geochemistry of I-type granitoids from the Makassa area, Far North Cameroon: new insights into late-orogenic Pan-African magmatism along the Mayo-Kébbi arc

Abstract The Makassa area, in the North Cameroon domain of the Central African Fold Belt (CAFB), preserves Pan-African plutonic and metamorphic rock whose petrogenesis and geodynamic significance remain poorly constrained. We present petrographic and whole-rock geochemical data for 12 representative samples (selected from 22 collected) of amphibole-biotite granite, biotite granite, gneiss and amphibolite. The rocks form a continuous compositional series (53.83–74.97 wt% SiO 2 ); the gneiss and amphibolite are ortho-derived and are treated together with the plutonic suite. Decreasing Al 2 O 3 , Fe 2 O 3 , MgO, CaO and TiO 2 with increasing SiO 2 is consistent with fractional crystallization of amphibole, biotite, plagioclase, Fe-Ti oxides and apatite from a common parental magma. The granitoids are predominantly metaluminous, ferroan, high-K calc-alkaline to shoshonitic I-type rocks (A/CNK = 0.79–1.17), with one peraluminous S-type sample. They show LREE enrichment, flat HREE segments, negative Eu anomalies (Eu/Eu* = 0.10–0.47) and depletion in Ba, Nb-Ta, Sr and Ti, indicating a dominantly crustal, tonalitic-granodioritic source with a subordinate mantle contribution. In Rb versus (Y + Nb) and Rb versus (Ta + Yb) diagrams the samples plot across the volcanic-arc, syn-collisional and within-plate fields, a pattern interpreted as a post-collisional setting that inherits an arc-like source signature. The Makassa magmatism therefore records the transition from a late-collisional to a post-collisional stage of the Pan-African orogeny. These data provide the first geochemical characterization of Pan-African magmatism in the Far North Cameroon sector of the Mayo-Kébbi/North Cameroon arc, previously known only from Rb/Sr ages.