<abstract xmlns="http://www.w3.org/1999/xhtml">

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.
</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.

Mineral Chemistry of Pyroxene Gneiss in Obudu, SE Nigeria, and Its Petrological Significance

Alex Ekwueme Federal University Ndufu-Alike

Materials and Geoenvironment

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Mineralna kemija piroksenitnega gnajsa iz Obuduja, JV Nigerija in njegov petrološki pomen

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...

Mineral Chemistry of Pyroxene Gneiss in Obudu, SE Nigeria, and Its Petrological Significance

Published Online: Aug 29, 2023

Page range: -

Received: Jan 23, 2023

Accepted: Feb 14, 2023

DOI: https://doi.org/10.2478/rmzmag-2023-0001

Keywords
mineral chemistry, pyroxene gneiss, electron microprobe, Obudu

© 2023 Ifeoma Agbi et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Mineral Chemistry of Pyroxene Gneiss in Obudu, SE Nigeria, and Its Petrological Significance

Published Online: Aug 29, 2023

Page range: -

Received: Jan 23, 2023

Accepted: Feb 14, 2023

DOI: https://doi.org/10.2478/rmzmag-2023-0001

Keywordsmineral chemistry, pyroxene gneiss, electron microprobe, Obudu

© 2023 Ifeoma Agbi et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Keywords
mineral chemistry, pyroxene gneiss, electron microprobe, Obudu