n African Journal of Science, Technology, Innovation and Development - Remote sensing and geological investigation of Okemesi area, southwestern Nigeria

Volume 2, Issue 2
  • ISSN : 2042-1338
  • E-ISSN: 2042-1346
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Lithological and structural studies of the area around Okemesi were carried out using a remotely sensed Landsat Thematic Mapper (Landsat ™) imagery coupled with geological ground truth. The ground truth exercise was essentially a reconnaissance geological mapping of the area done after the completion of the digital image processing of the landsat imagery.

Four lithological units including quartzites, granites, schists and migmatites with well-defined boundaries were recognised on the landsat imagery. This is in contrast to the five lithologies-quartzite, granite, schist, migmatite and gneiss mapped in the area during ground truth. Structures such as fractures (lineaments) and folds were also observed in the area from the Landsat imagery and during ground truth. The recognised folds in the area include overturned folds and assymetrical folds. The fold axial plane trends in a NNE-SSW on the imagery and bears imprints of different episodes of tectonic deformation. The most striking megascopic feature on the imagery is the Okemesi antiform, which forms N-S trending ridge and the Imesi-Ile granite batholith which also occupies the north western portion on the imagery.
Two distinct fault sets were recognised on the imagery. The major one is a part of Ifewara fault which is curvilinear and runs nearly parallel to the strike of the quartzites; while the minor ones occur as fractures and are found on the quartzite limbs. A tectonic model of evolution involving the existence of proto oceans is proposed for the area. The opening of one of the oceans enables the deposition of metasediments of pelitic to greywacke affinity in a quiet environment coupled with back-arc subduction, the back-arc subduction of the metasediments and the accompanying metamorphism in addition with other geological processes in the mantle led to the emplacement of rocks of different varieties in the area. The existence of a weathered ultramafic rock south east of Ilesha represents an ophiolite suture zone marked by the Ifewara fault.
The study has shown the benefits of the applications of remote-sensing technology for socio-economic development in a developing country like Nigeria, and also other African countries.

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