PETROGRAPHY AND MICROTEXTURAL CHARACTERISTICS OF GRANODIORITE FROM WASIMI, SOUTHWESTERN NIGERIA

E J Oziegbe,A P Adebisi,O O Ocan

doi:10.26480/esmy.02.2020.82.89

Abstract

Rock samples of granodiorite from Wasimi were studied in detail to determine the minerals, mineral associations and the different micro-texture present in order to unravel the processes that were involved during the cooling of the magma. The following minerals were observed; plagioclase feldspars, K-feldspars, biotite, pyroxene, amphiboles, with zircon and sphene as accessory minerals. The pyroxene are engulfed in amphiboles and have reaction rims. Pyroxene occur as inclusions in plagioclase feldspars. Amphiboles are poikilitic with inclusions of quartz. Symplectic texture exits between the following minerals; plagioclase and K-feldspar, biotite and quartz, plagioclase and amphibole. The plagioclase feldspars have fractured and bent twin lamellae. Crystals of plagioclase feldspars are zoned and also exhibit both Carlsbad and albite form of twinning. It can be said that there was an initial slow cooling of the magma which was responsible for the large crystals of feldspars which was later followed by rapid cooling as the magma rises close to the surface which gave rise to zoned plagioclase feldspars and indication of high level intrusive.

Highlights

Granodiorite is an intrusive rock, intermediate in composition between diorite and granite
Amphiboles is poikilitic with inclusions of quartz (Figure 11)
There is a symplectic texture between biotite & plagioclase, and between biotite & quartz (Figure 16 & 17)

Summary

INTRODUCTION

Granodiorite is an intrusive rock, intermediate in composition between diorite and granite. The study of microtextures has contributed to the understanding of geological and geochemical magmatic processes (Lee and Parsons, 1997; Dini et al, 2004; Sable et al, 2006). These microtextures are sources of information on crystal growth T, cooling rates, and isochemical and non-isochemical replacement reactions which are in a way associated with late magmatic or externally derived aqueous fluids (Parsons et al, 2015). There are reported cases of microtextures in feldspar that have shown great complexity (Parsons et al, 2013; Parsons et al, 2015). Quick Response Code microtextures to interpret the processes that occurred during the cooling of the magma

MATERIALS AND METHODS

Petrography

DISCUSSION

CONCLUSION