Petrology and Geochemistry of Basement Complex Rocks in Okom-Ita Area, Oban Massif, Southeastern Nigeria

Abstract

The determination of the mineralogical composition of rocks that underlie Okom-Ita area, in Oban Massif became necessary for the interpretation of the petrogenesis and protoliths of rocks in the area. Twelve representative rock samples were selected for thin section petrography and bulk rock geochemical analysis. The results reveal that the dominant intrusive rocks in Okom-Ita area are pegmatites, quartz veins and dolerites emplaced within gneisses, schists and phyllites host rocks. The quartz veins and pegmatites are leucocratic consisting predominantly of quartz, plagioclase and subordinate amount of Muscovites. The dolerite is dark grey, fine to medium grained and texturally ophitic and consists dominantly of pyroxenes, olivine and opaques. Three varieties of gneisses were recognized: feldspathic, banded and biotite gneisses. The gneisses, schists, and phyllites are dominated by SiO2 in the range of (60% -75%). The rocks exhibit higher molecular concentration {Al 2 O 3 > (CaO + Na 2 O + K 2 O)}, high alkali concentration with Na 2 O > K 2 O, high Al 2 O 3 to alkali ratios and low TiO 2 , CaO and MgO concentrations. These distribution trends suggest a compensation for the high silica and alumina concentrations and support a granitic protolith for the pegmatites and their host gneisses and schists. The dolerites and amphibolites are impoverished in SiO 2 , but relatively enriched in lime and alkali oxides. Plots in the AFM, TiO diagrams show that the pegmatite was derived from calc-alkaline magmatic source, while the dolerite was derived from tholeiitic basalt magma.

Mineralogy and organic geochemistry of phyllite from the Dewon–Pokrzywna deposit, the Opava Mountains (SW Poland)

“…So dium and po tas sium vary con sid er ably in phyllites from var i ous lo cal i ties. Iron pre dom i nates over mag ne sium with few ex cep tions (e.g., Rasul, 1963;Opara et al, 2014).…”

Petrology Of Intrusive Rocks Of Oban Massif, Southeastern Nigeria

“…The most recent event was the Pan-African tectonothermal event. Each of these events has left structural imprints on the basement rocks of the complex as suggested by several workers on the Nigerian basement including Rahaman et al, 1981;Onyeagocha and Ekwueme, 1982;Ephraim, 2009;Igonor, et al, 2011;Ukwang et al, 2012;Oden 2012;Opara et al,;Obi et al, (2014) Edem et al, 2015;Asinya et al, 2016;Edem et al, 2016;Ekwueme and Okoro, 2019. It is however, thought that the Pan-African deformation event was widespread and very pervasive to the extent that it probably, totally obliterated all preceding structural imprints of earlier orogenies. Consequently, the geometric characteristic of structures in the Oban Massif is expected to reflect mainly the Pan-African event of 600 ± 150 Ma.…”

Assessment and delineation of groundwater potential zones using integrated geospatial techniques and analytic hierarchy process

“…The earlier mentioned lithologic units of the study area's geology have two major fracture orientations, one NE-SW and NW-SE (Opara et al 2014). These fractures are parallel to the Schists Belts of the country and Cretaceous Bida Basin which controls the directions of flow and drainage of surface water sources in the area.…”