PETROLOGY OF SOME METACONGLOMERATES IN IGARRA AND ENVIRONS, SOUTHWESTERN NIGERIA

ABSTRACT

Field mapping was carried out in which the area is bounded by lattitudes 7⁰16^’N – 7⁰18^’N and longitudes 6⁰4^’E – 6⁰7^’E which revealed the major rock types in the area namely; quartz biotite schist, calc-silicate gneiss, marble, mica-schist, quartzite and metaconglomerates which is the case study for this work. Metaconglomerates were studied in detail with particular interest in the clasts which are quartzitic, carbonate and granitic in composition. The clasts in the metaconglomerates indicate that they are derived from surrounding rocks. Classification of the metaconglomerates shows that most of the metaconglomerates in the area are polymictic-matrix-supported-metaconglomerates. They also show that the area is a high strained environment that has undergone polyphase deformation. The occurrence of carbonates and clastics and also the absence of volcanics suggest a miogeosynclinal environment. Petrographic evidence showsthat mineral assemblages defined by quartz + hornblende + plagioclase  actinolite indicate that they are low-medium grade metasediments that belong to the green-schist facies (Buchan-Barrovian type of metamorphism).