Abstract
Samples of mafic intrusive rock were analyzed for their mineralogical and chemical properties. The textural relationship was studied using the petrographic microscope, elemental composition of minerals was determined using the Electron Microprobe and the whole rock chemical analysis was done using the XRF and ICP-MS. The following minerals were observed in order of abundance; pyroxene, amphibole, plagioclase, biotite, opaque minerals, quartz and chlorite, with apatite and zircon occurring as accessory mineral. Two types of pyroxenes were observed; orthopyroxene (hypersthene) and clinopyroxene. Texturally, amphiboles have inclusions of plagioclase and pyroxene. The plagioclase has undergone sericitization. The chemical composition of the pyroxene is En51.95Fs44.53Wo3.52, biotite has Fe/(Fe+Mg):0.42, Mg/(Fe+Mg):0.59, and plagioclase is Ab63.5An34.55Or1.95. Whole rock chemistry shows a chemical composition; SiO2: 45.15 %, Al2O3: 14.04 %, Fe2O3: 16.01 %, MgO: 5.65 %, CaO: 7.58 % and TiO2: 3.59 %. There is an enrichment of LREE and a depletion of HREE. Based on the minerals, mineral chemistry and the geochemistry of the studied rock, the rock is mafic and hydrous minerals formed by hydration recrystallization of pyroxene. The rock has extensively retrogressed but has not been affected by any form of deformation.
Highlights
The Basement complex of Nigeria comprises some components of mafic to ultramafic in addition to other rock units which some believed to be remnants of mantle diapirs
Under the microscope the mafic rock is generally granoblastic in texture and consists of the following minerals: pyroxene, amphiboles, plagioclase, biotite, chlorite, opaque minerals, and quartz with zircon and apatite occurring as accessory mineral
The pyroxene is surrounded by amphiboles and with some occurring as inclusions in amphiboles
Summary
The Basement complex of Nigeria comprises some components of mafic to ultramafic in addition to other rock units which some believed to be remnants of mantle diapirs. Erusu is a town in Akoko North West of Ondo State, which is part of the Basement Complex of Southwestern Nigeria. The Basement Complex of Southwestern Nigeria is believed to have formed in a back-arc basin (Oyinloye and Odeyemi, 2001). Mafic intrusive were first mentioned in this area in a study, in which it was described as one of the rock units of Ikare area (Rahaman and Ocan, 1988). The petrography, mineral chemistry, and geochemistry (major, trace and REE elements) of samples collected from the mafic intrusive rock at Erusu Akoko is presented in this article
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