CHAPTER ONE

1.0    INTRODUCTION

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 mega structures 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. 

1.1  OBJECTIVES

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 latitudes 10000’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 employed 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. 

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