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

E.J. Oziegbe
E.J. Oziegbe
, 
O.O. Ocan
O.O. Ocan
 and 
A.O. Buraimoh
A.O. Buraimoh
   | Jul 27, 2020
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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
© 2020 Oziegbe E.J. et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Figure 1

Map of Iwo region within Basement Complex of Nigeria. Stippled pattern indicates Cretaceous and younger sedimentary cover [1].
Map of Iwo region within Basement Complex of Nigeria. Stippled pattern indicates Cretaceous and younger sedimentary cover [1].

Figure 2

Geologic map of Iwo region modified after 1: 250,000 sheet 60 (Iwo) of Geological Survey of Nigeria (GSN). 1, Migmatite-gneiss complex; 2, charnockite; 3, early granitic phases of Older Granite Cycle; 4, younger granitic phases of Older Granite Cycle; 5, amphibolite, amphibolite schist, and pelitic schist; 6 quartzite, quartz-schist, and quartzofeldspathic gneiss; 7, granitic-gneiss-dominated regions; p, pegmatite; T, tonalite. Thick broken lines indicate major faults [1].
Geologic map of Iwo region modified after 1: 250,000 sheet 60 (Iwo) of Geological Survey of Nigeria (GSN). 1, Migmatite-gneiss complex; 2, charnockite; 3, early granitic phases of Older Granite Cycle; 4, younger granitic phases of Older Granite Cycle; 5, amphibolite, amphibolite schist, and pelitic schist; 6 quartzite, quartz-schist, and quartzofeldspathic gneiss; 7, granitic-gneiss-dominated regions; p, pegmatite; T, tonalite. Thick broken lines indicate major faults [1].

Figure 3

Field photograph showing tonalite. Take note of the vein quartz at the centre.
Field photograph showing tonalite. Take note of the vein quartz at the centre.

Figure 4

Hand specimen of tonalite from Iwo area.
Hand specimen of tonalite from Iwo area.

Figure 5

Photomicrographs showing: (a) zoned allanite (Aln) surrounded by biotite (Bt) crystals; biotite is darker at the edges closer to allanite than those away (PPL). (b) Zoned allanite (Aln), biotite (Bt), plagioclase (Pl) and quartz (Qtz) (XPL). (c) Opaque (Opq) minerals within a zoned allanite (Aln), take note of the close relationship between biotite and allanite (PPL). (d) Inclusions of opaque (Opq) minerals within a zoned allanite (Aln) (XPL).
Photomicrographs showing: (a) zoned allanite (Aln) surrounded by biotite (Bt) crystals; biotite is darker at the edges closer to allanite than those away (PPL). (b) Zoned allanite (Aln), biotite (Bt), plagioclase (Pl) and quartz (Qtz) (XPL). (c) Opaque (Opq) minerals within a zoned allanite (Aln), take note of the close relationship between biotite and allanite (PPL). (d) Inclusions of opaque (Opq) minerals within a zoned allanite (Aln) (XPL).

Figure 6

Photomicrographs showing: (a) numerous fractures within zoned allanite (Aln), there are inclusions of apatite in biotite (Bt) and the edges of biotite touching allanite are darker (PPL). (b) Opaque (Opq) minerals within allanite (Aln) (XPL). (c) Biotite (Bt) surrounding allanite (Aln), there are inclusions of allanite within biotite (XPL). (d) Close association between plagioclase (Pl) and allanite (Aln) (XPL).
Photomicrographs showing: (a) numerous fractures within zoned allanite (Aln), there are inclusions of apatite in biotite (Bt) and the edges of biotite touching allanite are darker (PPL). (b) Opaque (Opq) minerals within allanite (Aln) (XPL). (c) Biotite (Bt) surrounding allanite (Aln), there are inclusions of allanite within biotite (XPL). (d) Close association between plagioclase (Pl) and allanite (Aln) (XPL).

Figure 7

Photomicrograph showing sericitisation of plagioclase feldspars (Pl) in close association with allanite (Aln) (XPL).
Photomicrograph showing sericitisation of plagioclase feldspars (Pl) in close association with allanite (Aln) (XPL).

Figure 8

Photomicrographs showing: (a) close association between biotite (Bt) and chlorite (Chl), as well as titanite (Ttn) (PPL). (b) Microcline (Mc) in close relationship with altered biotite (XPL). (c) Compositional zoning of plagioclase, there are biotite (Bt) inclusion in the plagioclase feldspar (Pl) (XPL). (d) Plagioclase with deformed twin lamellae and preferred orientation of the biotite (Bt) (XPL).
Photomicrographs showing: (a) close association between biotite (Bt) and chlorite (Chl), as well as titanite (Ttn) (PPL). (b) Microcline (Mc) in close relationship with altered biotite (XPL). (c) Compositional zoning of plagioclase, there are biotite (Bt) inclusion in the plagioclase feldspar (Pl) (XPL). (d) Plagioclase with deformed twin lamellae and preferred orientation of the biotite (Bt) (XPL).

Figure 9

Photomicrograph showing a close relationship between biotite (Bt) and titanite (Ttn). Take a note of reaction rim of titanite (Ttn) round the opaque (Opq) (PPL).
Photomicrograph showing a close relationship between biotite (Bt) and titanite (Ttn). Take a note of reaction rim of titanite (Ttn) round the opaque (Opq) (PPL).

Figure 10

Photomicrograph showing reaction rim of titanite (Ttn) on opaque (Opq) (PPL).
Photomicrograph showing reaction rim of titanite (Ttn) on opaque (Opq) (PPL).

Figure 11

Photomicrograph showing reaction rim of titanite (Ttn) on opaque (Opq) (XPL).
Photomicrograph showing reaction rim of titanite (Ttn) on opaque (Opq) (XPL).
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