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EAS00288 - TEXTURAL AND PETROGRAPHIC STUDIES OF GRANITE AROUND ILE-OGBO, OSUN STATE SOUTHWESTERN NIGERIA


CHAPTER ONE

  •         INTRODUCTION

The study area forms a portion of the Precambrian complex which is located around ILE - OGBO, Osun State, Southwestern Nigeria and it’s situated at Telemu town at latitudes 070 38’ to 070 44’N of the equator and longitudes 040 12’ to 040 18’E Greenwich meridian.

The geological field investigation of Ile - ogbo area has a unique and high potential geological setting with significant occurrences of different rock units and structural features that shows imprint of regional trend mass into bands of different chemical and mineralogical composition.

This work presents the field and petrographic study of Granite around Ile-Ogbo. The petrography is the detailed study of rocks most commonly the microscopic scale. Granite in the study area is coarse to medium grained (phaneritic) in texture, it contains minerals like Quartz, Microcline, Plagioclase, Hornblende, Muscovite and Biotite which are revealed by hand specimen. Mafic mineral is predominant, brown feldspar appears like a weathered surface, quartz remain colorless, flakes of biotite maintain a silvery black coloration in a sheet like manner and vitreous luster of hornblende is also present in a rod like manner.

A circular prismatic of hornblende exhibit random orientation within the biotite and quartz crystal of size about 216.4c.m/2.2cm from the flat line to a boulder rising surface .Granite color depends on their chemistry and mineralogy

The term granite is consequently not the name of the rock but of an assemblage of rock types. The assemblage is connected by origin, the differentiation of the same parent magma. The banded structure which these rocks commonly present in the field is only in a small measure due to plastic deformation, but is to large extent original, and has been by flow in a viscous crystallizing intrusive magma, together with differentiation or segregation of the mass into bands of different chemical and mineralogical composition. Granite are widely distributed especially in the southern hemisphere and even in the southwestern part of Nigeria.

The Older Granite of Nigeria includes a wide spectrum of rocks varying in composition from tonalite through granodiorite to granite, syenite and charnockite rocks (Truswell et. al, 1963). The granitoids have been emplaced into both the migmatite-gneiss complex and the schist belts, and they occur in all parts of Nigeria (Ajibade, 1982).                                                                                                                                                                             

1.1 AIM AND OBJECTIVES OF STUDY

AIM

To conduct a textural and petrographic investigation on granite around Ile - Ogbo

OBJECTIVE

  • To carry out geological mapping of the study area.
  • To collect representative rock samples.
  • To interpret the result obtained using modal composition and QAPF diagram.
  • To compare the data obtained with established values from other study areas.

1.2       Location and Accessibility

            The study area is located around Ile - Ogbo in  Osun State, Southwestern Nigeria. It is surrounded by towns and villages. Telemu town is geographically bounded by latitudes 070 38’ to 070 44’N of the Equator and longitudes 040 12’ to 040 18’E Greenwich meridian.

It is accessible by network of major and minor roads and footpaths that connects the neighboring villages, farms and forest in the study area. It is accessible to major town like Iwo, Ede, Osogbo and Ibadan.

Fig. 1.1: Location and Accessibility Map of the Study Area.

 

 

 

 

 

 

1.3       Climate and Vegetation

            The area is situated within the tropical climate belt with characteristics of heavy rain during wet season and less rain during the dry season. About 1260mm of precipitation falls annually.

Precipitation is the lowest in January, with an average of 8mm. The greatest amount of precipitation occurs in September with an average of 199mm. at an average temperature of 28.20C, March is the hottest month of the year. The lowest average temperatures in the year occur in August, when it is around 23.90C.  The area is covered with vegetation ranging from sparse to thick woody rain forest with some being cleared as a result of farming.

1.4       DRAINAGE

            The area is entirely drained by small rivers, streams which are seasonal in flow. The source of the rivers can be traced to the cracks and joint in the rock bodies. The drainage patterns of these streams conform to the dendritic pattern which forms network branching and anastomosing water pathways. Most of the rivers and streams get drained into the Osun River.

 

 

 

Figure 1.2: Map showing the drainage of the study Area

 

 

 

 

1.5       SCOPE OF STUDY

            The scope of the work entails geological mapping of the study area, collection of rock sample, studying the field occurrence of the rocky outcrops, examine the hand specimen of the sample using aided eye as to identify structure, feature and mineralogical components of the rock. It involves petrographical analysis of the rock samples in order to investigate and study the various elements by use of microscope present in the rock.