Browsing by Author "Okonkwo, CT"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Microstructural and Mineralogical Evolution of the Oke Awon Shear Zone in the Jebba Area, S.W. Nigeria(Akamia University, 2014) Okonkwo, CT; Adetunji, A; Folorunso, IOThe Jebba area of southwestern Nigeria is underlain by metasedimentary and metaigneous rocks which have been intruded by probable Pan-African (ca.600 Ma) granitic rocks. Locally, in the west, these rocks have been tectonised within two N – S trending brittle-ductile shear zones. Granitic mylonites contain elongate quartz ribbons surrounded by finer grained groundmass of microcline, quartz and plagioclase. Metabasic mylonites contain fine-grained hornblende and plagioclase defining the mylonitic, S2, fabric. Locally, the assemblage is epidote, actinolite, albite, and quartz indicating a marked retrogression. Semi-pelitic rocks, the mineralogy contain syntectonically rotated garnets with sigmoidal inclusion trails, fractured and elongated garnet, fine-grained biotite and muscovite, late porphyroblastic muscovite, and locally, minor epidote and chlorite resulting from partial retrogression. The quartzites are marked by microstructures ranging from cataclasites to ultracataclasites. These observations indicate two generations of shearing, an earlier one under amphibolites facies conditions at deeper structural levels which was locally overprinted by brittle deformation under greenschist facies conditions following exhumation.Item Petrochemistry and geotectonic setting of granitic rocks in Aderan Area, SW Nigeria(Canadian Center of Science and Education, 2013) Okonkwo, CT; Folorunso, IOAderan area, southwestern Nigeria is underlain by metaigneous and metasedimentary rocks which have been intruded by granitic rocks of probable Pan-African (ca. 600 Ma) age. Four types of granitic rocks have been identified in the area, including granitic gneisses, medium-grained granite, porphyritic granite and granodiorite. Geochemical analysis show that the rocks are largely calc-alkaline. The granodiorite is less siliceous and more calcic, and also contains less Ba, Nb and Rb, and more Sr, Ce and La than the granites. Tectonically, the rocks classify as volcanic arc and syn-collisional and possibly late-to- post-collisional granitic rocks with respect to the Pan-African orogeny. Chemical characteristics indicate that these rocks were derived from partial melting of mafic to semi-pelitic (metasedimentary) crustal rocks under conditions of intermediate oxygen fugacity and activities of H2OItem Petrographic Investigation of Oke-Awun Rocks, Southwestern Nigeria(Faculty of Science, Adeleke University, Ede, 2015) Folorunso, IO; Okonkwo, CTThe Oke-Awun area is underlain by older units of Migmatitic gneisses, Augen gneisses, Quartz-biotitemuscovite schists, Quartzites and Amphibolites which have been intruded by Granites, Granodiorites and Pegmatites of probable Pan African (ca 600 Ma) age. The Gneisses are medium grained rocks with mineral constituent which include quartz, plagioclase, biotite, hornblende, microcline with accessory minerals such as chlorite, sericite, sphene, epidote and ore minerals. Amphibolites are medium-fine grained and are characterised mainly by hornblende and plagioclase with minor quartz while the metasediments are characterized by quartz, plagioclase, biotite, muscovite, microcline and epidote. The granites are made of quartz, biotite, plagioclase, microcline, chlorite, epidote, sericite and muscovite. The metamorphic rocks of Oke-Awun have been subjected to Amphibolite facies regional metamorphism which has been locally overprinted by greenschist facies retrogression.Item Structural Geology of Oke-Awun Rocks, Southwestern Nigeria(Published by Faculty of Pure and Applied Science, Ladoke Akintola University of Technology, Ogbomoso, 2015) Folorunso, IO; Okonkwo, CTRocks found in Oke-Awun area include older units of gneisses; migmatitic gneisses, augen gneisses, metasediment; quartz-biotite-muscovite schists, and quartzites and amphibolites which have been intruded by granites, granodiorites and pegmatites of probable Pan African (ca 600 Ma) age. Three episodes of deformation have been recognized in the area. The first deformation (D1) was associated with the development of penetrative foliation in the metamorphic rocks. The second deformation (D2) gave rise to asymmetric folds in the migmatitic gneisses and quartz-biotite- muscovite schists which locally deformed D1. The third deformation (D3) involved the formation of transcurrent faults which cuts all the rocks in the area. The metamorphic rocks have been deformed into a NNE-SSW trending synform and cut by two major approximately N-S trending sub-parallel dextral transcurrent faults.