Main Article Content
Very little research has been carried out and reported on the Irruan granitoids. Geological field mapping and laboratory analyses were carried out to ascertain the petrological, geochemical and structural attributes of the Irruan Basement Rocks in southern Obudu Plateau, southeastern Nigeria. Five petrological units: granite gneiss, banded gneiss, migmatite gneiss, granodiorite and biotite granite were identified in the area. The rocks are generally siliceous and quartzofeldspathic, recording ≥70.11 wt.% of SiO2 except the biotite granite that records 61.10 wt.% of SiO2; quartz ranges from 25 – 35%, 30%, 20 – 27%, 22 – 35% and 30% for granite gneiss, banded gneiss, migmatite gneiss, granodiorite and biotite granite respectively. Feldspar ranges from 20 – 35%, 22 – 25%, 20 – 27%, 20 – 30% and 25% respectively for the granite gneiss, banded gneiss, migmatite gneiss, granodiorite and biotite granite. Relative to plagioclase, orthoclase is more dominant in many of the samples. Biotite and muscovite range from 5 – 15%. The metamorphosed rocks are predominantly peraluminous, showing aluminum saturation index (ASI) ranging from 1.05 to 3.37 and (Na2O + CaO)/Al2O3 ratios of 0.27 – 0.95 and average A/CNK of 1.13. Generally, there are marked variations in the distribution of trace elements with Rb/Nb, Rb/Zr and Rb/Sr ratios of ≤25,000, ≤0.5319 and ≤0.7377 respectively. The granitoids have resulted from the partial melting of the crust with possible contribution from mantle-derived, crust-contaminated magma. On the outcrop scale, fractures occur in NW-SE, NE-SW, NNE-SSW, E-W and N-S orientations. Evidences of primary and secondary structures were observed. The dominant NE-SW fractures were developed contemporaneously with the foliations and lineaments. The N-S and fairly weak E-W fracture sets were developed from a later episode.
Kroner A, Ekwueme BN. The Oldest Rocks in West Africa: SHRIMP zircon age for early Archean Migmatitic Orthogneiss at Kaduna, Northern Nigeria. Journal of Geology. 2001;109:399–406.
Ekwueme BN, Kroner A. Single zircon ages of migmatitic gneisses and granulites in the Obudu Plateau: Timing of granulite-facies metamorphism in Southeastern Nigeria. Journal of African Earth Sciences. 2006;44:459–469. DOI:10.1016//j.jafrearsci.2005.11.013
Ominigbo OE, Ukwang EE, Okumoko JP, Ukpai UJ. Petrogenesis and Tectonic Setting of the Basement Rocks around Irruan area, Bamenda massif, SE Nigeria. Journal of Geosciences and Geomatics. 2020;8(1):35–44. DOI:10.12691/jgg-8-1-5
Egesi N, Ukaegbu UV. Petrologic and structural features of basement of rocks of Mukuru Area, South-eastern Nigeria. Earth Science. 2013;2(4);96–103. DOI: 10.11648/j.earth.20130204.11
Egesi N, Ukaegbu VU. Petrology and major element geochemistry of late to post Neoproterozoic Peraluminous Granitoids in parts of Bansara, Southeastern Nigeria. The IUP Journal of Earth Sciences. 2011;5(3):7-19.
Anor AE, Freeth SJ. Thermo-tectonic evolution of the basement complex around Okene, Nigeria, with special reference to deformation mechanism. Precambrian Research. 1985;28:269–281.
Aydan O, Kawamoto T. Discontinuities and their effects on rock mass. Rock Joints, Barton N. & Stephansson, O. (eds.), Balkema, Rotterdam. 1990;149–156.
Ominigbo OE, Asadu AN, Omo-Irabor OO, Emudianughe JE, Ofuyah WN, Overare B. Sedimentology and Petrographic Attributes of Outcropping Coastal Plain Sands from Abudu and Environs, Southern Nigeria. Nigerian Journal of Science and Environment. 2017;15(1):130–140. DOI: 10.5987/UJ-NJSE
Ajibade AC, Wright JB. The Togo-Benin-Nigeria Shield: Evidence of Crustal Aggregation in the Pan-African Belt. Tectonophysics. 1989;165:125-129.
Odeyemi I. A review of the Orogenic events in the precambrian basement of Nigeria, West Africa. Geologische Rundschau.1981;70(3):897-909, DOI: 10.1007/bf01820170
Rahaman MA. Review of the Basement Geology of South Western Nigeria. In Kogbe, C. A. Geology of Nigeria (2nd Edition), Rock View. 1989;39–56. Jos.
Rahaman MA. Recent advances in the study of the basement complex of Nigeria. In Precambrian Geology of Nigeria, Geological Survey of Nigeria, Kaduna South. 1988;11-43.
Rahaman MA. Recent advances in the study of the basement complex of Nigeria. In Oluyide, et al. (Eds.) Precambrian Geology of Nigeria. Publication of the Geological Survey Nigeria, Esho Printers, Kaduna; 1981.
Ukwang EE, Ekwueme BN. Trace element geochemistry and tectonic characterization of the granulite facies rocks from southwest Obudu Plateau, Southeastern Nigeria. Chinese Journal of Chemistry. 2009;28:248–257.
Gok NG, Dada SS, Oha AI, Moumouni A. An interpretation of tectonic elements of the Kanke Basement, central Nigeria. Online Journal of Earth Sciences. 2010;4 (2):89–94. DOI:10.3923/ojesci.2010.89.94
Oden MI, Okpamu TA, Amah EA. Comparative analysis of fracture lineaments in Oban and Obudu areas, SE Nigeria. Journal of Geography and Geology. 2012;4(2):36–47. DOI: 10.59539/jgg.v4n2p36
Ekwueme BN. Basaltic magmatism related to the early stages of rifting of the BenueTrough: The Obudu dolerites of Southeastern Nigeria. Geological Journal. 1994;29:269–276.
Egesi N, Ukaegbu VU. Petrologic and structural characteristics of the basement units of Bansara Area, Southeastern Nigeria. The Pacific Journal of Science and Technology. 2010;11(1): 510–525.
Ogunyele AC, Oluwajana OA, Ehinola IQ, Ameh BE, Salaudeen TA. Petrochemistry and petrogenesis of precambrrian basement rocks around Akungba-Akoko, southwestern Nigeria. Material & Geoenvironment. 2019;66(13):173–183. DOI: 10.2478/rmzmag-2019-0036
Obiora SC. Chemical Characterization and Tectonic Evolution of Hornblende-Biotite Granitoids from the Precambrian Basement Complex around Ityowanye and Katsina-Ala, Southeastern Nigeria. Journal of Mining and Geology. 2012;48(1):13–29.
Rahaman MAO. Field work as a basic geological tool. in proceedings of field mapping standardization workshop, Lambert-Aikhionbare and Olayinka, AI. (Eds.), Ibadan University Press, Ibadan. 2009;2.
Tsuchiya N, Shibata T, Koide Y, Owada M, Takazawa E, Goto Y, Choi JH, Terada S, Hariya Y. Major element analysis of rock samples by X-ray fluorescence spectrometry, using Scandium Anode Tube. Journal of Faculty of Science, Hokkaido University. 1989;22(3):489–502.
Obasi RA. Geochemistry, S-Type Classification and Petrography of Granites from Idanre, Ondo State, South West Nigeria. International Journal of Scientific and Engineering Research. 2016;7(12):859–879.
Frost BR, Barnes CG, Collins WJ, Arculus RJ, Ellis DJ, Frost CD. A Geochemical Classification for Granitic Rocks. Journal of Petrology. 2001;42(11):2033–2048.
Nazemi E, Arian MA, Jafarian A, Pokermani M. Petrology and Geochemistry of Igneous Rocks of Zarinkamar Area, NE Shahrood, Iran. Open Journal of Geology. 2017;7:348–359.
Katongo C, Koller F, Kloetzli U, Koeberl C, Tembo F, Waele BD. Petrography, geochemistry and geochronology of granitoid rocks in the neoproterozoic-paleozoic lufilian-zambezi belt, Zambia: Implications for Tectonic Setting and Regional Correlation. Journal of African Earth Sciences.2004; 40:219–244.
Wilson G. The Tectonic Significance of Small Scale Structures, and their Importance to the Geologist in the Field. Annals, Societe’ Ge’ologique de Belgique, 1961;84:423–548.
Oden MI, Umagu CI, Udinmwen E. The use of jointing to infer deformation episodes and relative ages of minor cretaceous intrusive in the Western Part of Ikom-Mamfe Basin, Southeastern Nigeria. Journal of African Earth Sciences. 2016;121:316–329.
Hubbard FH. Precambrian crustal development in Western Nigeria: Indications from the Iwo region. Geological Society of America Bulletin. 1975;8:548–554.
Omasanya KO, Ariyo SO, Kaigama U, Mosuro GO,Laniyan TA. An outcrop evidence for polycyclic orogenies in the basement complex of southwest Nigeria. Journal of Geography and Geology. 2015; 7(3): 24 – 34.
Kamgang P, Njonfang E, Nono A, Dedzo MG, Tchoua FM. Petrogenesis of silicic magma system: Geochemical evidence from Bamenda Mountains, NW Cameroon, Cameroon Volcanic Line. Journal of African Erath Sciences. 2010;58:285–304. DOI: 10.1016/j.jafrears.sci.2010.03.008
Girei MB, Najime T, Ogunleye PO. Geochemical characterization and origin of Neoproterozoic high-K calc-alkaline granitoids in the northern part of Mandara hills, northeastern Nigeria. Acta Geochemica; 2019. DOI: 10.1007/s11631-019-00365-7
Dada SS. Proterozoic evolution of the Nigeria-Boborema province. Geological Society of London Special Publication. 2008;294:121–136. DOI: 10.1144/SP294.7
Ekwueme BN, Kroner A. Single zircon evaporation ages from the Oban massif, Southeastern Nigeria. Journal of African Earth Sciences. 1998;26:195–205.
Obiora SC. Petrology and geotectonic setting of the basement complex rocks around Ogoja, southeastern Nigeria. Ghanaian Journal of Science. 2006;46:13–46.
Oden MI, Igonor EE, Ukwang EE. Geochemical evaluation of the Pan-African pegmatites from parts of the Oban massif, Southeast Nigeria. Materials and Geoenvironment. 2013;60:39–46.
Ekwueme BN. Petrology of intermediate igneous rocks in the Oyioba-Uganga area, Southeastern Benue Trough. Journal of Mining and Geology. 1992;28(1):141–147.