eng Science and Education Publishing Journal of Geosciences and Geomatics 2373-6704 2020-04-13 8 1 35 44 10.12691/jgg-8-1-5 JGG2020815 article Ominigbo O. E. ominigboedafe@gmail.com 1 Ukwang E. E. 1 Okumoko D. P. 2 Ukpai U. J. 2 Department of Geology, Faculty of Physical Sciences, University of Calabar, Calabar, Nigeria Department of Earth Sciences, College of Sciences, Federal University of Petroleum Resources, Effurun, Nigeria 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 (¡Ý70.11 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. http://pubs.sciepub.com/jgg/8/1/5/jgg-8-1-5.pdf petrogenesis tectonic setting magmatism syn-collisional Obudu Plateau Bamenda massif