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

International Journal of Geosciences 2014年第4期5卷 394-407页

作者： Kelechi Denis Opara Young E. Obioha Samuel Okechukwu Onyekuru Chikwendu Okereke Sabinus Ikechukwu Ibeneme Department of Geosciences Federal University of Technology Owerri Nigeria

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.

关键词： Okom-Ita oban Massif Petrology Geochemistry Petrogenesis Protolith Tectonics

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