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

Olufemi Williams Okunola; Akinade Shadrach Olatunji; Adegoke Olukayode Afolabi

doi:10.2478/rmzmag-2023-0002

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

Materials and Geoenvironment

AHEAD OF PRINT

By: Olufemi Williams Okunola, Akinade Shadrach Olatunji and Adegoke Olukayode Afolabi

Open Access

|Jul 2023

Figures & Tables

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.

Table 1:

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

Table 2:

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

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.

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

Table 3:

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

[i] Av. Pg – Average for Granodiorite only

[ii] Av. Sy – Average for Syenite only

[iii] Ave* - Average for all the granitoid samples

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

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

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]).

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

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

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

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]).

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

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

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DOI: https://doi.org/10.2478/rmzmag-2023-0002 | Journal eISSN: 1854-7400

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Language: English, Slovenian

Submitted on: Jan 1, 2023

Accepted on: Feb 20, 2023

Published on: Jul 26, 2023

Published by: Sciendo

In partnership with: Paradigm Publishing Services

Publication frequency: 4 issues per year

Keywords:

major oxides,

REE,

syenite,

granodiorite,

orogenic-setting

Related subjects:

Computer sciences,

Databases and data mining,

Geosciences,

Geodesy,

Geology and mineralogy,

Materials sciences,

Materials characterization and properties

© 2023 Olufemi Williams Okunola, Akinade Shadrach Olatunji, Adegoke Olukayode Afolabi, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

AHEAD OF PRINT

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

Figures & Tables

Figure 1:

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Table 1:

Table 2:

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Table 3:

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