Abstract

Abstract The pyroxene gneiss which forms part of the basement cover in southeast Nigeria is a coarse-grained weakly foliated rock that has experienced high-grade metamorphism and anatexis. Electron microprobe data obtained from samples of this pyroxene-bearing gneiss confirm that the essential minerals are plagioclase (andesine, An30 – 37), orthopyroxene (hypersthene, En55.3 – 61.2, Wo1.0 – 2.6, Fs36.3 – 43.7), and clinopyroxene (augite, En39.7 –42.3, Wo42.0 – 45.1, Fs14.2 – 17.0). This assemblage is a typical granulite facies mineralogy produced by igneous rocks with intermediate to mafic composition that have been metamorphosed at medium pressure. Other minerals are calcic amphibole (XMg = 0.56–0.59), biotite (XMg = 0.58–0.69), orthoclase, and quartz. Orthoclase occurs mainly in leucocratic bands and clinopyroxene absent samples and may have resulted from dehydration reaction and thus dissolved in the melt phase. Fe-Ti oxides of ilmenite, hematite, and magnetite occur as accessory minerals, giving the imprint of metamorphism under oxidizing conditions. The presence of exsolved titanohematite in ilmenite indicates retrogressive metamorphism.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.