Evidence of adakitic signature in Pan-African basement rocks from the Mbengwi region (NW Cameroon): constraints from whole rock chemistry and Sr–Nd isotopes

Bulk rock geochemical characteristics and Sr–Nd isotopic data were used as a proxy to evidently ascertain the adakitic affinity or signature of the basement rock samples from the Mbengwi region, located within the Pan-African North Equatorial fold belt. In the present study, numerous granitoids display low MgO (<3.0 wt.%) and Mg# (mostly < 45), moderate to high Sr/Y (avg.: 23), moderate to high La/Yb (avg.: 62), high Zr/Sm (10.86–328.9; avg.: 43.8) high Na 2 O contents (2.2–5.5 wt.%) and 87 Sr/ 86 Sr ≤0.7045 in addition to high K 2 O/Na 2 O (avg.: 1.5) ratio, typical of adakites or adakite-like rocks. The samples referred to as adakite-like are assigned both as K-rich adakite and high-Si adakite (HSA), and consequently of crustal origin. The large variation of Sr/Y and La/Yb ratios, the range of their Rb/Sr ratio (0.27–0.53) in addition to the plots of bulk rocks Mg number, FeO T /MgO and MgO vs. SiO 2 likewise evidence that they are mainly C-type adakitic rocks, and almost all derived from partial melt of lower thickened crust.