English

A Oyawale A,O Ocan O

doi:10.5897/jgmr2020.0334

Abstract

The Ikare area is underlain by rocks of the migmatite-gneiss-quartzite complex and older granite lithologic groups and charnockites. Categorization of these rocks in the literature and published map is generalized and the rocks are undifferentiated. Though reported in few literature as an area with rocks composed of granulite facie grade, the nature of transition is not well documented. Field and petrographic studies were carried out to properly characterize the different rock types, evaluate the migmatization processes and elucidate the nature of amphibolite to granulite facie transition. Major rock types recognized and mapped includes grey gneiss, charnockitic gneiss, granite gneiss, pelitic gneiss, porphyritic granite and quartzite. Minor rock types are the mafic and ultramafic components which are made up of basic schist and amphibolites. The area suffered at least four episodes of deformation (D1, D2, D3 and D4) and at least three episodes of metamorphism (M1, M2 and M3). Petrographic studies further show that the mineral assemblage within the quartzo-feldspathic rocks changed from hydrous to anhydrous phases as one traverses from the southern part of the study area to the northern part. Reaction textures indicate that the transition zone between the amphibolite and granulite facie rocks is achieved by a prograde dehydration reaction while rehydration reactions took place during the waning retrograde stage. Anatexis and metamorphic differentiation were mainly responsible for the migmatization process in Ikare area while the charnockitization process was a product of dehydration reactions aided by reduction in water fugacity due to influx of CO2. Key words: Structure, migmatites, granulite facies, deformational episodes, metamorphism, charnockitic gneiss.  

Highlights

High grade metamorphic terrains in most parts of the world are made up of migmatitic rocks and associated charnockitic rocks
Observations of small-scale structures on outcrops in this study suggest that the study area was affected by at least four episodes of ductile deformation D1-D4 and a later episode of brittle deformation producing joints and other fractures
The rock types differentiated in this study within the MGQC are: grey gneiss, charnockitic gneiss, granite gneiss, pelitic gneiss, porphyritic granite and quartzite

Summary

Introduction

High grade metamorphic terrains in most parts of the world are made up of migmatitic rocks and associated charnockitic rocks. In spite of the lack of economic importance, embedded in migmatites are clues and evidences for better understanding of past thermal regimes and structural evolution of the continental crust (Lee and Cho, 2003). Determination of previous P-T conditions of such rocks gives some insights on the associated tectonic processes (Thompson and Ridley, 1987; Harley, 1989). Exposed granulite-facies terrains are often regarded as windows into the middle to lower continental crust (Fountain and Salisbury, 1981; Percival et al, 1992). In-depth analysis of the pressuretemperature paths of granulites enables evaluation of the deep crustal processes responsible for the formation and stabilization of the continental crusts

Methods

Results

Conclusion