The Precambrian basement complex of Nigeria as an integral part of the west African craton is known to have been subjected to various episode of deformation. These activities reflect in the presence of geological structures like folds, foliations and fractures of varying magnitudes. Remote sensing can be applied in the study of regional structures particularly those that extend over hundreds of kilometers. One of such megastructures is the Ife Wara-Zungeru fault which extends in the western and northern parts if Nigeria. The magnitude of the fault and its extent over a complex litho-structural terrain make the area a good subject of study.
The following are the objectives for carrying out this study;
a) To identify and analyse lineaments over the study area.
b) To establish the continuity of the lineaments on the southern and northern parts of the Nupe basin.
c) To compare the effectiveness of different remotely sensed images in detecting and interpreting lineaments.
d) T o evolve a model on the tectonic evolution of the Ifewara-Zungeru megalineament.
1.2 AREA OF STUDY
The area of study lies on the western half of Nigeria bounded by longitudes 4030’E to 7030’E, and latitudes 7000’N to 11000’N. An area bounded by longitudes 6000’E to 7030’E and latitudes10000’N to 11000’ was included to investigate the continuity or otherwise of the fracture zone. The study area is underlain by Precambrian basement complex rocks and a part of the cretaceous Nupe Basin. Prominent in the area are the Idanre hills and Efon ridges which extend northwards to Oke Onigbin ridges and Kisheriki hills in north central Nigeria. These hills serve as catchment and sources for the rivers that drain the area. The Osun, Owena, Ogbese and Ose rivers flow southwards into the atlantic ocean while the Asa, Oyi and Oro rivers flow northwards into the river Niger. Rivers Koriga and Sarkin Pawa drain into the Kaduna river which in turn empties into the river Niger. The study area is covered by various vegetation types ranging from rain forest in the south, through Guinea savanna to sudan savanna characterized by grassland with scattered shrubs in the north. A few forest reserves dot some parts of the southern area. Some major towns in the study area include Akure, Ibadan, ilesa, Ilorin, jebba, Kaduna, minna, mokwa, osogbo and zunger.
1.3 PREVIOUS WORK
Although the basement complex rocks in the western half of Nigeria have been studied through geological mapping very little work has been done using remote sensing. The schist belts in particular have received a lot of attention apparently due to its complex nature and mineralization. It has been known to consist of low to medium grade schists, metaconglomerate, quartzites, calc silicate gneises, banded-iron formation, amphibolites and other meta-igneous rocks ( Truswell and Cope, 1963; McCurry, 1976; Rahaman, 1973, 1976; Turner, 1983; Odeyemi, 1976,1977,1988,1988;Adekoya, 1993). In addition, prominent workers have studied other parts of the basement complex (Hubbard, 1975; Odeyemi, 1981; Fitches et al., 1985; Braide, 1992; Okonkwo, 1992). The geology and structural disposition of rocks in the Ilesha schist belt have been earlier studied and various evolution models have been suggested ( Elueze; 1977; Odeyemi, 1981; Ajibade, 1976; 1982; Turner, 1983; Ajibade et al, 1986; Ananaba and Ajakaiye, 1987). For example, Hubbard (1975) first recognized a major NNE-SSW trending Ifewara fault that separates the rocks of Ilesha schist belt into two structural units with contrasting lithologies. Geophysical methods have also been employes in the study of this area. Ako et al, (1978) first established a lithostructural break among the rock units, but ascribed it to silicification which itself is indicative of healing along a fault zone.
Olasehinde et al. (1990) studied aeromagnetic anomalies and their correlation with some lineaments in the basement complex of Nigeria. Folami (1992) also carried out aeromagnetics mapping over a part of the Ilesha schist belt. Results of the study show the presence of a continuous structure which trend and location agree with the Ifewara fault earlier recognized by hubbard (1975). Idornigie and Olorunfemi (1992) carried out geoelectrical survey which indicates a high degree of the Nupe Basin. Also, two sets of fault trending along the NW-SE and NE-SW directions were recognized. A regional aeromagnetic mapping of crustal lineaments was carried out by Ananaba (1991) in an attempt to assess the possible risks of dam failure in Nigeria. A lineament study of northern Nigeria using landsat images was carried out by Ananaba and Ajakaiye (1987) to correlate lineament density with mineral occurrences, results of the study suggest that primary mineralization in Nigeria is tectonically controlled.
1.4 JUSTIFICATION FOR THE STUDY
None of the previous works in the study area was aimed at establishing the regional continuity of any particular structural feature by combining satellite-based and aircraft-based data sources for a study. Therefore this effort is focused at studying the Ifewara-Zungeru megalineament through a combination of many remote sensing techniques. Such a study would provide more information on the Precambrian evolution, tectonics as well as mineral and energy resources within the study area. In addition, the results can be useful in mineral exploration since the presence and types of minerals depends on geologic antecedents along the megalinear. This is the reason for choosing this trend of study.
AJIBADE, A.C. 1976. Provisional classification and correlation of the schist belts of northwestern Nigeria. In; C.A. Kogbe(ed.), Geology of Nigeria, Elizabethan Publishing Co., Lagos, pp. 85-90
AJIBADE, A.C., WOAKES, M. and RAHAMAN, M.A. 1986. Proterozoic crustal development in the Pan-African regime of Nigeria. Amer Geophy. Union, pp 259-271
AKO, B.D., AJAYI, T.R. and ALABI, A.O. 1978. A geoelectrical study of the ifewara area. Jour.Min.Geol.Vol. 15, No. 2, pp84-89
ANANABA, S.E. and AJAKAIYE, D.E. 1987.E vidence of tectonic control of mineralization in Nigeria from lineament density analysis. Inter. Jour. Rem. Sens. Vol. 8, No. 10, pp 1445-1453
BRAIDE, S.P. 1992. Geological development, origin and energy mineral resources potential of the Lokoja Formation in the southern Nupe Basin. Jour.Min.Geol.Vol.28, No. 1, pp.33-34
ELUEZE, A.A. 1977.Geological and geochemical studies in the Ife-Ilesa schist belt in relation to gold mineralization in Nigerian schist Belts. Jour.Min.Geol. Vol.18,No 1,pp 31-36
FITCHES, W.R., AJIBADE, A.C, EGBUNIWE, I.E., HOLT, R.W. and WRIGHT, J.B. 1985. Late Proterozoic schist belts and plutonism in Nigeria. Jour. Geol. Soc. Lond. Vol. 142, pp. 319-337