GEOLOGY OF AKING AND ITS ENVIRONS

GEOLOGY OF AKING AND ITS ENVIRONS

CHAPTER ONE

INTRODUCTION

The study area is located in the Akampka Local Government Area of Cross River State (figure 1), and it is part of the Oban Massif, which is the foundation complex of south eastern Nigeria (fig2) The area is approximately 72km2 in size and is located between latitudes 050 221N and 050 261N and longitudes 0080 361E and 0080 381E greenwich.

The study area consists of such amphibolitesfacies rocks as gneisses, amphibolites intruded by quartz veins, Pegmatites veins, and dolerite (Rahman et al, 1981, Ekwueme, 1990)

The Oban massif is bounded to the north by the Mamfe Embayment, to the west by the Benue trough, to the south by the Calabar flank, and to the east by Cameroon. The Oban Massif is located in Scotland.

1.1LOCATION AND ACCESSIBILITY

The study area is limited to Aking-Westand and its environs, and it covers an area of land that includes three major settlements: Osomba, Mankor, and Aking, all of which are located in Akamkpa L.G.A of Cross River State.

The study area is accessible via the Calabar-Ekang Road, which runs all the way to the Cameroon border. Several other minor roads provide access to various locations throughout the study area.

REVIEW OF LITERATURE

The Nigerian basement complex, which includes the Oban massif in the southern part of Nigeria where the study area is located, has received the least attention and is thus depicted as an undifferentiated basement complex on the region’s geological map (geological survey Nigeria sheet 50). In the Nigeria Basement, Oyawoye (1964) identified three subdivisions.

(I) Prehistoric Metasediments

(II) Gneisses, Migmatites, and Older Granite

(III) Metasediments of a Younger Age

Rahman (1976) identified four major Petrologicalunits in Nigeria’s Basement Complex as follows:

1. Complex of migmatic gneiss and quartzite (Esurnean,2000ma )

Meta-igneous rocks are the second type of rock.

3. Paraschist that is slightly magmatized to non-magmatized

4. Granite and diorites that are older

Rahman et al. (1981) identify the following Major lithologic Rock Units from preliminary studies of the west and northwestern parts of the Oban Massif:

I. intrusive unmetamorphoseddolorite to meso-diorite

II. paraschist,phyllites,quartzites, and metaconglomerates, amphibolites and metadiorite, aplites, and foliated pegmatites.

III. Older granite intrusive series composed of granodioritemetadiorite, mellitus to granitic rocks, weakly to unfoliated pegmatites, aplites, and quartz veins.

Nigeria is located in the Pan-African belt, which has been assigned an age of 450-750Ma, though Cohen et al (1984) proposed a 450-1100Ma age for the occurrence of Bauchite-Charnokiteintrusive at Akor along the Calabar-Ekang Road.

The mineralogy and petrography of the rocks here are strikingly similar to those reported in northern Nigeria. The striking similarities in the lithologic and lithotectonic settings between the basement rocks of the Oban massif and those in Northern Nigeria suggest that the basement rocks were metamorphosed through tectonism, magmatism, and metasomatism.

were subjected to the same (Rahmanet al, 1980).

Ekwueme and Onyeagocha (1986) identified two types of metamorphic rocks based on their age in the Uwetarea (Oban Massif) that extends to the study area: older and younger metasediments.

(1)The older metasedimentary series is 2,500 million years old and is composed of gneiss and migmatites of low grade metamorphism ranging from middle green schist to uppermost amphibolitesfacies grade (products of barrovian type of regional metamorphism), which some authors refer to as the gneiss migmatites – quartzite complex.

(2)The younger metasediments are low grade metasediments deposited between 1000 and 800 million years ago and are referred to as the newer sedimentary series, which includes pelites and semi-peleles.

This age relationship between metasedimentarysequence and the occurrence of garnet, staurolite, hornblende, biotite and fayatite

Rahman’s point of view is correct (1986)

Ekwueme et al. (1988) used whole rock rubidium – strontium geochronology to obtain ages of 52716ma and 67626ma for gneisses and schist in parts of the Oban massif, respectively. The data of 67626ma represents the main phase of Pan-African orogeny in the area, whereas the data of 52716Ma depicts retrogression, which could have occurred during the warring stages of the same orogeny. The age data presented above are used to compare other similar rocks in Nigeria.

In terms of crustal evolution, the region is underlain by rocks influenced by the pan-African thermotectonic event (650 – 450 million years ago), which primarily involved the reactivation of an older crust. Ekwueme (1988) reported charnochite Pb-Srwhole rockisochron ages of 128153 and 54624Ma.

of the eastern Oban massif and regard them as kibiran. Ekwueme (1995) also reported on the basis of recent isotopic studies that there are early protozoic crustal components in the Oban massif using 207 Pb/206Pb evaporation techniques on single zircons. The oban village banded gneiss yielded a zircon age of 58420Ma.

According to Ekwueme and Onyeagucha (1986), the structural trend of foliation, lineation, and fold axis in the Oban basement complex rocks is approximately constant in the N-S direction with variations in the NW-SE and NE-SW directions.