<abstract xmlns="http://www.w3.org/1999/xhtml"><p>Primary, secondary and accessory minerals in tonalitic rocks from Iwo region of the Precambrian Basement Complex of Southwestern Nigeria were identified and analysed with the aim of determining the various processes involved during the crystallisation of magma. Thin sections of tonalite were prepared and studied with the aid of a petrographic microscope. The mineral assemblages observed are biotite, plagioclase, alkali-feldspar, amphiboles, pyroxene, quartz, muscovite and chlorite. Allanite, titanite, apatite and zircon occur as accessory minerals. Muscovite and chlorite are found to be secondary minerals. The mineral allanite has a characteristic form of zoning and shows evidence of metamictisation, and is surrounded by dark-coloured biotite having radioactive haloes. Titanite is anhedral to subhedral crystals and forms reaction rim round opaque minerals. Plagioclase shows evidence of compositional zoning as well as plastic deformation of the twin lamellae. The allanite observed is primary in nature and has undergone radioactive disintegration; chlorite and muscovite are formed by secondary processes of chloritization and sericitisation, respectively. The tonalite is formed as a result of rapid cooling of magma close to the Earth's surface.</p></abstract>

Primary, secondary and accessory minerals in tonalitic rocks from Iwo region of the Precambrian Basement Complex of Southwestern Nigeria were identified and analysed with the aim of determining the various processes involved during the crystallisation of magma. Thin sections of tonalite were prepared and studied with the aid of a petrographic microscope. The mineral assemblages observed are biotite, plagioclase, alkali-feldspar, amphiboles, pyroxene, quartz, muscovite and chlorite. Allanite, titanite, apatite and zircon occur as accessory minerals. Muscovite and chlorite are found to be secondary minerals. The mineral allanite has a characteristic form of zoning and shows evidence of metamictisation, and is surrounded by dark-coloured biotite having radioactive haloes. Titanite is anhedral to subhedral crystals and forms reaction rim round opaque minerals. Plagioclase shows evidence of compositional zoning as well as plastic deformation of the twin lamellae. The allanite observed is primary in nature and has undergone radioactive disintegration; chlorite and muscovite are formed by secondary processes of chloritization and sericitisation, respectively. The tonalite is formed as a result of rapid cooling of magma close to the Earth's surface.

Petrography of Allanite-bearing Tonalite from Iwo Region, Osun State, Nigeria

Department of Geosciences, Faculty of Science

Department of Geological Science, College of Science, Engineering and Technology

Materials and Geoenvironment

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

Petrografija tonalita z alanitom iz območja Iwo, Osun State, NIgerija

Primary, secondary and accessory minerals in tonalitic rocks from Iwo region of the Precambrian Basement Complex of Southwestern Nigeria were identified and...

Petrography of Allanite-bearing Tonalite from Iwo Region, Osun State, Nigeria

Article Category: Original scientific paper

Published Online: Jul 27, 2020

Page range: 79 - 89

Received: Apr 30, 2020

Accepted: May 18, 2020

DOI: https://doi.org/10.2478/rmzmag-2020-0006

Keywords
zoning, titanite, radioactive haloes, chloritization, sericitisation

© 2020 Oziegbe E.J. et al., published by Sciendo

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

Petrography of Allanite-bearing Tonalite from Iwo Region, Osun State, Nigeria

Article Category: Original scientific paper

Published Online: Jul 27, 2020

Page range: 79 - 89

Received: Apr 30, 2020

Accepted: May 18, 2020

DOI: https://doi.org/10.2478/rmzmag-2020-0006

Keywordszoning, titanite, radioactive haloes, chloritization, sericitisation

© 2020 Oziegbe E.J. et al., published by Sciendo

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

Keywords
zoning, titanite, radioactive haloes, chloritization, sericitisation