TITLE:
Petrology and Geochemistry of Basement Complex Rocks in Okom-Ita Area, Oban Massif, Southeastern Nigeria
AUTHORS:
Kelechi Denis Opara, Young E. Obioha, Samuel Okechukwu Onyekuru, Chikwendu Okereke, Sabinus Ikechukwu Ibeneme
KEYWORDS:
Okom-Ita, Oban Massif, Petrology, Geochemistry, Petrogenesis, Protolith, Tectonics
JOURNAL NAME:
International Journal of Geosciences,
Vol.5 No.4,
April
24,
2014
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 {Al2O3 > (CaO + Na2O + K2O)}, high alkali concentration with
Na2O > K2O, high Al2O3 to alkali
ratios and low TiO2, 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 SiO2,
but relatively enriched in lime and alkali oxides. Plots in the AFM, TiO2-K2O-P2O5 and Na2O/Al2O3-K2O/Al2O3 diagrams show that the pegmatite was derived from calc-alkaline magmatic
source, while the dolerite was derived from tholeiitic basalt magma.