Ominigbo O. E.^1,, Ukwang E. E.¹, Okumoko J. P.², Ukpai U. J.¹

The basement rocks around Irruan in southern Obudu Plateau, southeastern Nigeria were studied using field mapping and geochemical data. Both igneous (granodiorite and biotite granite) and metamorphic rocks (granite gneiss, banded gneiss and migmatite gneiss) were mapped in the area. The rocks are generally quartzofeldspathic and range from alkali-calcic to calc-alkali. Fairly strong negative correlation exists between Al₂O₃ and Na₂O with SiO₂ as well as between Al₂O₃ and Fe₂O₃. The magma source for the Irruan granitoids is continental as indicated by the high SiO₂ content (≥70.11 wt.% except the biotite granite that records 61.10 wt.% of SiO₂) and discriminant plots for the area. A sedimentary protholith has been interpreted for the gneissic rocks. Magmatism in the area commenced during the later stages of the Pan-African orogeny and continued much into the post-orogenic period, leaving behind, imprints of syn-collosional and post-orgenic tectonic settings.

petrogenesis, tectonic setting, magmatism, syn-collisional, Obudu Plateau, Bamenda massif