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Geology and Rare Earth Element Geochemistry of Magnesian Granitoids Within Proterozoic Schist Belt of Southwest Nigeria

Olufemi Williams Okunola
Olufemi Williams Okunola
, 
Akinade Shadrach Olatunji
Akinade Shadrach Olatunji
 y 
Adegoke Olukayode Afolabi
Adegoke Olukayode Afolabi
   | 26 jul 2023
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Article Category: Original Scientific Article
Publicado en línea: 26 jul 2023
Páginas: -
Recibido: 01 ene 2023
Aceptado: 20 feb 2023
DOI: https://doi.org/10.2478/rmzmag-2023-0002
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© 2023 Olufemi Williams Okunola et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Figure 1:

Geological map of the study area.
Geological map of the study area.

Figure 2:

a) Plane polar photomicrograph of the granodiorite reveals biotite (Bt) as the main mineral phase. b) Plagioclase (Pl), muscovite (Ms), and quartz (Qz) are identified as other major mineral phases under cross-polar. c) Biotite crystals forming mantle around large phenocrysts of feldspar are identified in plane polar. d) Porphyroclast of microcline shows evidence for grain size reduction in cross-polar. The magnification of photomicrographs is x40.
a) Plane polar photomicrograph of the granodiorite reveals biotite (Bt) as the main mineral phase. b) Plagioclase (Pl), muscovite (Ms), and quartz (Qz) are identified as other major mineral phases under cross-polar. c) Biotite crystals forming mantle around large phenocrysts of feldspar are identified in plane polar. d) Porphyroclast of microcline shows evidence for grain size reduction in cross-polar. The magnification of photomicrographs is x40.

Figure 3:

Photomicrograph of syenite. a) Plane-polarised light reveals euhedral grains of biotite (Bt) around subhedral grains of hornblende (Hb). b) Cross-polar view reveals plagioclase (Pl) and quartz (Qt) as the main mineral phases. c) and d) reveal large hornblende and microcline grains. The magnification of photomicrographs is x40.
Photomicrograph of syenite. a) Plane-polarised light reveals euhedral grains of biotite (Bt) around subhedral grains of hornblende (Hb). b) Cross-polar view reveals plagioclase (Pl) and quartz (Qt) as the main mineral phases. c) and d) reveal large hornblende and microcline grains. The magnification of photomicrographs is x40.

Figure 4:

Harker's plot of SiO2 vs. other oxides in wt. %.
Harker's plot of SiO2 vs. other oxides in wt. %.

Figure 5:

TAS plot (after Middlemost [19]).
TAS plot (after Middlemost [19]).

Figure 6:

An adapted QAP diagram using CIPW normative mineralogy [20].
An adapted QAP diagram using CIPW normative mineralogy [20].

Figure 7:

a) Plot of SiO2 vs. FeO(tot) [24]. b) Plot of Al2O3 /SiO2 vs. MgO/SiO2 (adapted after Paulick et al. [25]).
a) Plot of SiO2 vs. FeO(tot) [24]. b) Plot of Al2O3 /SiO2 vs. MgO/SiO2 (adapted after Paulick et al. [25]).

Figure 8:

a) SiO2 vs. (FeO+0.9Fe2O3)/(FeO+0.9Fe2O3+MgO) (after Frost & Frost [30]); b) SiO2 vs. Modified Alkali Lime Index (MALI) (Na2O+K2O-CaO) [10], and; c) SiO2 vs. K2O (after Peccerillo & Taylor [31]).
a) SiO2 vs. (FeO+0.9Fe2O3)/(FeO+0.9Fe2O3+MgO) (after Frost & Frost [30]); b) SiO2 vs. Modified Alkali Lime Index (MALI) (Na2O+K2O-CaO) [10], and; c) SiO2 vs. K2O (after Peccerillo & Taylor [31]).

Figure 9:

A/CNK vs. A/NK plot (after Shand [32]).
A/CNK vs. A/NK plot (after Shand [32]).

Figure 10:

The trilinear plot of La/10-Y/15-Nb/8 from Cabanis & Lecolle [33] describes geodynamic boundaries for the rocks of the study.
The trilinear plot of La/10-Y/15-Nb/8 from Cabanis & Lecolle [33] describes geodynamic boundaries for the rocks of the study.

Figure 11:

Ta/Yb vs. Th/Yb diagram characterising magma from volcanic arcs [34].
Ta/Yb vs. Th/Yb diagram characterising magma from volcanic arcs [34].

Figure 12:

Granite tectonic discrimination diagram suggests post-orogenic environment for the granitoid rocks of the study [12].
Granite tectonic discrimination diagram suggests post-orogenic environment for the granitoid rocks of the study [12].

Figure 13:

R1 = (4Si – 11(Na + K) – 2(Fe + Ti) vs. R2 = (6Ca + 2Mg + Al) diagram discriminates geotectonic environment for rocks of the study (after Batchelor & Bowden [35]).
R1 = (4Si – 11(Na + K) – 2(Fe + Ti) vs. R2 = (6Ca + 2Mg + Al) diagram discriminates geotectonic environment for rocks of the study (after Batchelor & Bowden [35]).

Figure 14:

REE plot normalised using Boynton's [39] chondrite values.
REE plot normalised using Boynton's [39] chondrite values.

Figure 15:

a) CaO vs. LREE/HREE; b) K2O vs. LREE/HREE, and; c) (La/Yb)N vs. (Eu/Eu*)N.
a) CaO vs. LREE/HREE; b) K2O vs. LREE/HREE, and; c) (La/Yb)N vs. (Eu/Eu*)N.

Elemental concentrations of the studied granitoids. Granodiorite (Pg1–Pg3) and Syenite (Sy1–Sy7) (major oxides are in wt. % and trace element in ppm).

Sample id Pg1 Pg2 Pg3 Av. Sy1 Sy2 Sy3 Sy4 Sy5 Sy6 Sy7 Av. Ave*
SiO2 63.70 61.82 61.65 62.39 55.04 59.77 56.95 56.23 59.03 57.88 57.84 57.53 58.99
Al2O3 14.41 15.79 14.73 14.98 10.71 14.90 13.73 12.47 13.77 13.83 13.35 13.25 13.77
Fe2O3 7.38 6.41 5.65 6.48 7.48 5.94 6.45 7.80 6.07 6.08 6.30 6.59 6.56
MgO 3.67 3.36 3.25 3.43 8.93 3.19 4.57 6.17 3.62 4.09 4.76 5.05 4.56
CaO 2.73 3.71 3.67 3.37 8.02 3.66 5.36 6.13 4.93 5.33 5.67 5.59 4.92
Na2O 2.01 2.60 1.82 2.14 1.00 2.76 2.86 1.87 2.50 2.28 2.15 2.20 2.19
K2O 3.35 3.23 5.84 4.14 5.24 6.95 6.50 6.09 6.75 6.89 6.76 6.45 5.76
TiO2 1.13 0.98 0.94 1.02 1.27 0.96 1.26 0.87 1.02 1.16 1.09 1.09 1.07
P2O5 0.27 0.67 0.31 0.42 0.47 0.38 0.48 0.44 0.35 0.49 0.50 0.44 0.44
MnO 0.11 0.09 0.07 0.09 0.12 0.09 0.09 0.13 0.09 0.08 0.10 0.10 0.10
Ba 677.00 685.00 1629.00 997.00 1407.00 1313.00 1387.00 1370.00 1288.00 1402.00 1638.00 1400.71 1279.60
Ni 60.10 57.80 51.90 56.60 114.50 33.10 38.70 26.20 17.40 44.90 44.50 45.61 48.91
Co 22.00 18.90 18.90 19.93 34.10 16.20 22.10 23.30 18.70 19.50 21.30 22.17 21.50
Nb 20.50 16.60 21.60 19.57 21.10 38.90 55.80 22.10 50.20 39.10 31.40 36.94 31.73
Rb 150.50 144.00 250.70 181.73 221.40 341.90 324.70 247.00 388.00 351.70 329.00 314.81 274.89
Sn 3.00 3.00 4.00 3.33 6.00 9.00 11.00 5.00 5.00 6.00 6.00 6.86 5.80
Sc 13.00 12.00 13.00 12.67 21.00 11.00 11.00 16.00 11.00 9.00 13.00 13.14 13.00
Sr 219.00 293.80 387.00 299.93 338.10 449.90 461.80 403.10 402.20 450.70 472.40 425.46 387.80
Ta 1.20 1.20 1.00 1.13 0.90 1.70 2.50 1.50 3.30 2.40 1.80 2.01 1.75
Th 17.20 38.80 26.00 27.33 25.20 48.80 92.90 46.30 53.80 50.20 80.90 56.87 48.01
U 4.10 5.80 5.80 5.23 7.90 5.30 5.20 4.70 6.20 6.70 7.90 6.27 5.96
V 139.00 79.00 82.00 100.00 122.00 73.00 93.00 105.00 87.00 79.00 93.00 93.14 95.20
W 1.40 0.80 0.70 0.97 0.90 1.80 1.50 4.40 1.50 1.70 1.50 1.90 1.62
Hf 15.80 15.00 11.30 14.03 15.30 18.40 17.80 9.30 19.70 15.10 14.30 15.70 15.20
Zr 612.20 605.30 431.70 549.73 625.70 694.10 681.60 324.10 731.60 579.30 559.00 599.34 584.46
Y 69.40 67.40 22.50 53.10 29.00 33.70 47.60 37.60 59.70 34.70 36.50 39.83 43.81
Cu 16.40 13.90 46.50 25.60 104.10 34.80 45.70 23.70 6.60 35.30 37.30 41.07 36.43
Pb 3.90 5.40 12.60 7.30 11.20 34.30 62.50 16.30 10.40 4.80 6.30 20.83 16.77
Zn 104.00 95.00 73.00 90.67 25.00 57.00 35.00 22.00 34.00 55.00 49.00 39.57 54.90
Au 2.10 1.90 0.60 1.53 2.30 0.80 3.20 1.80 0.80 13.90 1.70 3.50 2.91
La 57.8 101.3 76.3 78.47 45.5 149.9 183.5 106.2 248.7 151.2 123.4 144.06 124.38
Ce 99.1 200.9 146.3 148.77 105.6 295.6 350.4 221 421.1 282.4 247 274.73 236.94
Pr 12.86 24.44 17 18.10 14.33 32.95 40.53 26.73 51.53 32.92 29.02 32.57 28.23
Nd 50.3 93.3 61.6 68.40 63.3 115.9 150.6 102.1 181.5 116.9 105.4 119.39 104.09
Sm 9.96 17.78 10.09 12.61 12.63 17.38 24.75 17.08 27.72 17.64 16.89 19.16 17.19
Eu 1.68 2.37 2.09 2.05 2.57 3.17 4.32 2.9 4.4 3.11 2.81 3.33 2.94
Gd 10.49 15.86 7.46 11.27 9.3 11.09 16.1 12.25 20.63 11.99 12.03 13.34 12.72
Tb 1.79 2.35 0.9 1.68 1.16 1.36 2.01 1.57 2.33 1.4 1.44 1.61 1.63
Dy 11.01 13.05 4.66 9.57 5.94 6.7 9.67 7.7 11.54 6.87 7.19 7.94 8.43
Ho 2.48 2.49 0.77 1.91 1.07 1.11 1.62 1.37 1.9 1.1 1.21 1.34 1.51
Er 7.27 7.16 2 5.48 2.92 3.12 4.2 3.54 4.98 3.13 3.16 3.58 4.15
Tm 1.01 1 0.32 0.78 0.4 0.44 0.58 0.5 0.68 0.42 0.42 0.49 0.58
Yb 6.16 6.15 1.95 4.75 2.61 2.88 3.65 2.98 4.18 2.6 2.62 3.07 3.58
Lu 0.9 0.85 0.28 0.68 0.38 0.43 0.51 0.45 0.61 0.38 0.4 0.45 0.52
ASI 1.21 1.09 0.92 1.07 0.49 0.8 0.64 0.6 0.68 0.66 0.63 0.64 0.77
Zr/Hf 38.75 40.35 38.20 39.10 40.90 37.72 38.29 34.85 37.14 38.36 39.09 38.05 38.37
Nb/Ta 17.08 13.83 21.60 17.51 23.44 22.88 22.32 14.73 15.21 16.29 17.44 18.90 18.48
LREE 242.2 456 320.84 339.66 253.23 625.99 770.2 488.26 955.58 616.16 536.55 606.57 526.50
HREE 30.62 33.05 10.88 24.85 14.48 16.04 22.24 18.11 26.22 15.9 16.44 18.49 20.40
LREE/HREE 7.91 13.80 29.49 17.06 17.49 39.03 34.63 26.96 36.44 38.75 32.64 32.28 27.71
REE(tot) 272.81 489.00 331.72 364.51 267.71 642.03 792.44 506.37 981.80 632.06 552.99 625.06 546.89
(Eu/Eu*)N 0.50 0.42 0.71 0.54 0.69 0.65 0.62 0.59 0.54 0.62 0.57 0.61 0.59
(La/Yb)N 6.33 11.11 26.38 14.60 11.75 35.09 33.89 24.03 40.11 39.21 31.75 30.83 25.96

Cross, Iddings, Pirsson, and Washington (CIPW) normative mineralogy normative mineralogy for the studied granitoids.

Norm Pg1 Pg2 Pg3 Sy1 Sy2 Sy3 Sy4 Sy5 Sy6 Sy7
Q 28.634 23.272 17.188 5.931 7.31 2.392 5.254 7.09 5.593 5.531
C 3.16 2.875 0 0 0 0 0 0 0 0
Or 19.798 19.088 34.513 30.967 41.073 38.413 35.99 39.891 40.718 39.95
Ab 17.008 22 15.4 8.462 23.354 24.201 15.823 21.154 19.293 18.193
An 11.78 14.029 14.774 9.258 7.74 5.428 7.644 6.414 7.152 6.81
Di 0 0 0 18.297 3.849 10.891 13.522 9.775 9.623 11.402
Hy 9.142 8.37 8.096 13.763 6.163 6.335 9.102 4.487 5.728 6.572
Il 0.235 0.193 0.15 0.257 0.193 0.193 0.278 0.193 0.171 0.214
Hm 7.381 6.411 5.65 7.481 5.94 6.451 7.801 6.07 6.08 6.301
Tn 0 0 0.993 2.786 2.108 2.844 1.776 2.255 2.627 2.399
Ru 1.007 0.879 0.457 0 0 0 0 0 0 0
Ap 0.64 1.587 0.734 1.113 0.9 1.137 1.042 0.829 1.161 1.184
Sum 98.784 98.704 97.955 98.315 98.629 98.284 98.233 98.158 98.145 98.556

Modal mineralogy for the studied granitoids.

Min/Sample Id Pg1 Pg2 Pg3 Sy1 Sy2 Sy3 Sy4 Sy5 Sy6 Sy7
Quartz 44 46 47 4 2 4 8 10 7 8
Microcline 13 7 12 42 43 42 41 44 45 42
Plagioclase 12 13 11 20 30 16 15 20 20 20
Hornblende 7 6 5 15 13 17 16 14 13 15
Pyroxene – – – 3 2 5 6 6 5 4
Biotite 21 23 20 15 9 15 12 5 8 9
Opaque 3 5 5 1 1 1 2 1 2 2
Garnet – – – 1 1 1 3 2 2 3
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