Acceso abierto

Retrogression of Orthopyroxene-bearing Gneiss of Iboropa Akoko, Southwestern Nigeria

E.J. Oziegbe
E.J. Oziegbe
, 
V.O. Olarewaju
V.O. Olarewaju
, 
O.O. Ocan
O.O. Ocan
 y 
G. Costin
G. Costin
   | 27 jul 2020
Materials and Geoenvironment's Cover Image
Acerca de este artículo
Artículo anterior
Artículo siguiente
Cite
Article Category: Original scientific paper
Publicado en línea: 27 jul 2020
Páginas: 119 - 134
Recibido: 04 jun 2020
Aceptado: 16 jun 2020
DOI: https://doi.org/10.2478/rmzmag-2020-0009
Palabras clave
© 2020 E.J. Oziegbe et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Figure 1

Sketch geological map of the Hoggar-Aïr-Nigeria Province showing the Neoproterozoic Trans-Saharan belt, resulting from terrane amalgamation between the cratons of West Africa and Congo and the East Saharan block [26].
Sketch geological map of the Hoggar-Aïr-Nigeria Province showing the Neoproterozoic Trans-Saharan belt, resulting from terrane amalgamation between the cratons of West Africa and Congo and the East Saharan block [26].

Figure 2

Location map of the study area.
Location map of the study area.

Figure 3

Field photograph of charnockitic gneiss with quartzo-feldspathic material at Iboropa Akoko.
Field photograph of charnockitic gneiss with quartzo-feldspathic material at Iboropa Akoko.

Figure 4

Photomicrographs showing (a) porphyroblast of pyroxene (Px) having numerous fractures. Pale biotite (Bt) along cleavage planes (PPL). (b) Plagioclase (Pl) occurring as inclusions in pyroxene (XPL). PPL, plane polarised light; XPL, crossed polarised light.
Photomicrographs showing (a) porphyroblast of pyroxene (Px) having numerous fractures. Pale biotite (Bt) along cleavage planes (PPL). (b) Plagioclase (Pl) occurring as inclusions in pyroxene (XPL). PPL, plane polarised light; XPL, crossed polarised light.

Figure 5

(a) Photomicrograph showing pyroxene (Px) rimmed by amphibole (Am). The opaque mineral (Opq) (PPL). (b) Backscattered electron image of minerals shown in (a). PPL, plane polarised light; XPL, crossed polarised light.
(a) Photomicrograph showing pyroxene (Px) rimmed by amphibole (Am). The opaque mineral (Opq) (PPL). (b) Backscattered electron image of minerals shown in (a). PPL, plane polarised light; XPL, crossed polarised light.

Figure 6

The compositional maps of minerals shown in Figure 5, showing elemental levels of Si, Mg, Na, Ca, Fe, Al, K, Mn and Ti.
The compositional maps of minerals shown in Figure 5, showing elemental levels of Si, Mg, Na, Ca, Fe, Al, K, Mn and Ti.

Figure 7

Photomicrographs showing: (a) amphiboles (Am) with inclusions of pyroxene (Px) (PPL). (b) Amphiboles with inclusions of pyroxene, surrounded by plagioclase (Pl) (XPL). (c) Biotite having inclusions of plagioclase feldspar (XPL). (d) Biotite having inclusions of plagioclase feldspar (PPL). PPL, plane polarised light; XPL, crossed polarised light.
Photomicrographs showing: (a) amphiboles (Am) with inclusions of pyroxene (Px) (PPL). (b) Amphiboles with inclusions of pyroxene, surrounded by plagioclase (Pl) (XPL). (c) Biotite having inclusions of plagioclase feldspar (XPL). (d) Biotite having inclusions of plagioclase feldspar (PPL). PPL, plane polarised light; XPL, crossed polarised light.

Figure 8

Photomicrographs showing: (a) pyroxene in close contact with areas occupied by transparent minerals: plagioclase and K-feldspar. Altered biotite (brownish mineral) surrounded by transparent mineral (PPL). (b) Pyroxene (Px), perthitic K-feldspar (Kfs) and plagioclase feldspar (Pl). The straight lamellae in the perthite (XPL). (c) Biotite (Bt) and apatite. The smaller needle-shaped apatite crystals (PPL). (d) K-feldspar (Kfs), quartz (Qtz), apatite (Ap) and plagioclase (Pl) (XPL). PPL, plane polarised light; XPL, crossed polarised light.
Photomicrographs showing: (a) pyroxene in close contact with areas occupied by transparent minerals: plagioclase and K-feldspar. Altered biotite (brownish mineral) surrounded by transparent mineral (PPL). (b) Pyroxene (Px), perthitic K-feldspar (Kfs) and plagioclase feldspar (Pl). The straight lamellae in the perthite (XPL). (c) Biotite (Bt) and apatite. The smaller needle-shaped apatite crystals (PPL). (d) K-feldspar (Kfs), quartz (Qtz), apatite (Ap) and plagioclase (Pl) (XPL). PPL, plane polarised light; XPL, crossed polarised light.

Figure 9

Ternary diagram showing feldspar solid solution.
Ternary diagram showing feldspar solid solution.

The chemical composition of pyroxene and amphibole

Pyroxene Amphibole
Sample 1c 1r Crystal 1 2 3 4 5 6
SiO2 49.680 49.830 SiO2 42.453 41.804 43.680 42.904 43.139 42.786
TiO2 0.037 0.114 TiO2 2.038 1.450 1.505 1.669 1.826 1.993
Al2O3 0.618 0.682 Al2O3 10.389 10.342 9.819 10.039 10.174 10.186
FeO 32.470 31.910 FeO 18.095 17.894 17.156 18.178 18.975 18.580
Cr2O3 0.000 0.010 Cr2O3 0.000 0.000 0.043 0.132 0.053 0.101
MnO 0.585 0.712 MnO 0.058 0.016 0.111 0.132 0.049 0.054
MgO 15.200 15.070 MgO 9.163 9.361 9.943 9.474 9.399 9.622
CaO 0.618 0.495 CaO 11.305 11.394 11.575 11.465 11.431 11.455
Na2O 0.014 0.055 Na2O 1.533 1.338 1.108 1.386 1.406 1.443
K2O 0.057 0.030 K2O 1.409 1.430 1.215 1.411 1.347 1.349
Total 99.290 98.900 Cl 0.071 0.085 0.063 0.077 0.043 0.140
TSi 1.958 1.970 Total 96.510 95.110 96.180 96.740 97.79 97.610
TAl 0.029 0.030 O_Cl 0.020 0.020 0.010 0.020 0.010 0.030
TFe3+ 0.014 0.000 TSi 6.553 6.517 6.681 6.580 6.556 6.512
M1Al 0.000 0.002 TAl 1.447 1.483 1.319 1.420 1.444 1.488
M1Ti 0.001 0.003 Sum_T 8 8 8 8 8 8
M1Fe3+ 0.044 0.026 CAl 0.442 0.416 0.449 0.393 0.377 0.337
M1Fe2+ 0.062 0.080 CFe+3 0.000 0.038 0 0 0 0
M1Cr 0.000 0.000 CTi 0.237 0.170 0.173 0.193 0.209 0.228
M1Mg 0.893 0.888 CMg 2.109 2.176 2.267 2.166 2.129 2.183
M2Mg 0.000 0.000 CFe+2 2.213 2.201 2.106 2.232 2.279 2.240
M2Fe2 0.950 0.949 Sum_C 5 5 5 5 5 5
M2Mn 0.020 0.024 BFe+2 0.123 0.095 0.089 0.099 0.132 0.125
M2Ca 0.026 0.021 BMn 0.008 0.002 0.014 0.017 0.006 0.007
M2Na 0.001 0.004 BCa 1.870 1.903 1.897 1.884 1.861 1.868
M2K 0.003 0.002 Sum_B 2 2 2 2 2 2
Sum (cat) 3.997 3.998 ANa 0.459 0.404 0.329 0.412 0.414 0.426
Ca 1.337 1.069 AK 0.277 0.284 0.237 0.276 0.261 0.262
Mg 45.770 45.260 Sum_A 0.736 0.689 0.566 0.688 0.675 0.688
Fe2_Mn 52.890 53.670 Sum_cat 15.736 15.689 15.566 15.688 15.675 15.688
JD1 0.000 0.108 CCl 0.019 0.022 0.016 0.020 0.011 0.036
AE1 0.202 0.186 Sum_oxy 23.102 23.000 23.023 23.031 23.016 23.002
CFTS1 2.056 1.168
CTTS1 0.056 0.174
CATS1 0.000 0.000
WO1 0.000 0.000
EN1 45.780 45.560
FS1 51.902 52.800
Q 1.931 1.939
J 0.002 0.008
WO 1.299 1.055
EN 44.460 44.670
FS 54.240 54.280
WEF 99.890 99.570
JD 0.000 0.032
AE 0.100 0.396

The composition of ilmenite in a charnockitic gneiss

Sample 1
SiO2 0.046
TiO2 50.787
Al2O3 0.02
FeO 46.372
Cr2O3 0.075
MnO 0.477
MgO 0.267
CaO 0
Na2O 0.061
Total 98.11
Si 0.001
Al 0.001
Ti 0.986
Fe2+ 1.001
Cr 0.002
Mn 0.01
Mg 0.01
Ca 0
Na 0.003
Cations 2.014

Chemical composition of biotite crystals

Crystal 1 2 3 4 5 6 7 8
SiO2 35.20 35.10 35.19 34.71 35.52 35.34 35.95 35.42
TiO2 5.23 5.15 4.97 4.84 4.84 4.97 5.09 5.00
Al2O3 13.63 13.79 14.14 13.75 13.92 13.35 13.82 13.83
Cr2O3 0.04 0.06 0.00 0.03 0.02 0.05 0.03 0.00
FeO 21.02 20.48 20.75 20.96 19.97 20.59 20.41 20.72
MnO 0.00 0.04 0.03 0.03 0.00 0.01 0.00 0.02
MgO 9.88 9.95 10.15 9.93 10.00 10.07 9.99 9.64
CaO 0.01 0.07 0.00 0.04 0.02 0.00 0.00 0.04
Na2O 0.13 0.11 0.09 0.14 0.09 0.08 0.14 0.11
K2O 9.74 9.71 9.57 9.62 9.56 8.54 9.63 9.74
Cl 0.15 0.11 0.12 0.15 0.09 0.09 0.10 0.10
H2O 1.80 1.81 1.81 1.78 1.81 1.80 1.83 1.81
Total 95.03 94.57 95.01 94.2 94.03 93.09 95.16 94.62
Si 5.739 5.735 5.717 5.714 5.803 5.823 5.812 5.782
AlIV 2.261 2.265 2.283 2.286 2.197 2.177 2.188 2.218
AlVI 0.356 0.388 0.423 0.380 0.481 0.414 0.443 0.441
Ti 0.641 0.633 0.607 0.599 0.595 0.616 0.619 0.614
Fe2+ 2.866 2.798 2.819 2.885 2.729 2.837 2.759 2.829
Cr 0.005 0.008 0.000 0.004 0.003 0.007 0.004 0.000
Mn 0.000 0.006 0.004 0.004 0.000 0.001 0.000 0.003
Mg 2.401 2.423 2.458 2.437 2.436 2.474 2.408 2.346
Ca 0.002 0.012 0.000 0.007 0.004 0.000 0.000 0.007
Na 0.041 0.035 0.028 0.045 0.029 0.026 0.044 0.035
K 2.026 2.024 1.984 2.020 1.993 1.795 1.986 2.028
Cations 16.338 16.327 16.323 16.381 16.270 16.170 16.263 16.303
CCl 0.083 0.061 0.066 0.084 0.050 0.050 0.055 0.055
OH 1.959 1.970 1.967 1.958 1.975 1.975 1.973 1.972
O 24 24 24 24 24 24 24 24
Fe/(Fe + Mg) 0.5400 0.54 0.530 0.540 0.530 0.530 0.530 0.550
Mg/(Fe + Mg) 0.460 0.460 0.470 0.460 0.470 0.470 0.470 0.450

The chemical composition of plagioclase crystals

Crystal 1 2 3 4 5 6 7 8 9 10 11 12 13 14
SiO2 58.96 59.05 59.39 59.47 58.84 58.19 58.45 59.22 59.23 58.7 59.76 60.19 58.14 58.57
TiO2 0.02 0 0 0 0.04 0 0.37 0.01 0 0 0.04 0 0.03 0
Al2O3 25.53 25.59 25.55 25.03 25.72 25.77 25.8 25.65 25.34 25.26 24.06 24.78 25.24 25.49
FeO 0.12 0.07 0.05 0.15 0.02 0.07 0.24 0.07 0.11 0.17 0 0.08 0.01 0.01
MnO 0.01 0.01 0.05 0.02 0.01 0.04 0 0.03 0 0.04 0.02 0 0 0
MgO 0 0.01 0 0 0.01 0 0 0 0.02 0 0 0.01 0 0
BaO 0.01 0.04 0.08 0.05 0.07 0 0.07 0.03 0.09 0 0.06 0.01 0.08 0.03
CaO 8.05 8.04 7.98 7.82 8.13 8.58 8.49 8.21 7.78 7.88 7.18 7.3 8.34 8.15
Na2O 6.87 6.88 5.99 7.04 6.75 6.7 6.26 6.62 6.93 7.01 7.35 7.35 6.07 6.53
K2O 0.38 0.37 0.39 0.39 0.34 0.37 0.36 0.34 0.37 0.36 0.49 0.41 0.37 0.39
Total 99.95 100.06 99.48 99.97 99.93 99.72 100.04 100.18 99.87 99.42 98.96 100.13 98.28 99.17
Si 2.639 2.64 2.659 2.661 2.633 2.616 2.617 2.642 2.651 2.642 2.697 2.683 2.642 2.639
Al 1.346 1.347 1.347 1.319 1.356 1.364 1.36 1.347 1.336 1.339 1.279 1.301 1.351 1.353
Fe3+ 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ti 0.001 0 0 0 0.001 0 0.012 0 0 0 0.001 0 0.001 0
Fe2+ 0.004 0.003 0.002 0.006 0.001 0.003 0.009 0.003 0.004 0.006 0 0.003 0 0
Mn 0 0 0.002 0.001 0 0.002 0 0.001 0 0.002 0.001 0 0 0
Mg 0 0.001 0 0 0.001 0 0 0 0.001 0 0 0.001 0 0
Ba 0 0.001 0.001 0.001 0.001 0 0.001 0.001 0.002 0 0.001 0 0.001 0.001
Ca 0.386 0.385 0.383 0.375 0.39 0.413 0.407 0.392 0.373 0.38 0.347 0.349 0.406 0.393
Na 0.596 0.596 0.52 0.611 0.586 0.584 0.543 0.573 0.602 0.612 0.643 0.635 0.535 0.571
K 0.022 0.021 0.022 0.022 0.019 0.021 0.021 0.019 0.021 0.021 0.028 0.023 0.021 0.022
Cations 4.994 4.995 4.937 4.997 4.989 5.003 4.971 4.979 4.992 5.002 4.998 4.995 4.958 4.98
X 3.986 3.987 4.006 3.98 3.99 3.98 3.989 3.989 3.987 3.981 3.977 3.984 3.994 3.992
Z 1.008 1.007 0.93 1.016 0.998 1.023 0.981 0.989 1.003 1.021 1.02 1.011 0.963 0.987
Ab 59.4 59.5 56.2 60.6 58.9 57.4 55.9 58.2 60.4 60.4 63.2 63.1 55.6 57.9
An 38.4 38.4 41.4 37.2 39.2 40.6 41.9 39.8 37.4 37.5 34.1 34.7 42.2 39.9
Or 2.2 2.1 2.4 2.2 1.9 2.1 2.2 1.9 2.1 2.1 2.8 2.3 2.2 2.2

Bulk rock composition of charnockitic gneiss; major elements (%), trace elements (ppm), REE (ppm)

Major element 1 Trace element 1 REE 1
Wt% ppm ppm
SiO2 50.93 V 188.28 La 57.71
Al2O3 15.51 Cr 95.31 Ce 119.2
CaO 7.79 Co 107.09 Pr 14.13
Fe2O3 12.3 Ni 52.36 Nd 54.64
MgO 5.14 Cu 41.17 Sm 9.05
K2O 1.01 Zn 124.1 Eu 2.27
MnO 0.15 Rb 18.36 Gd 7.325
Na2O 3.33 Sr 583.8 Tb 0.856
TiO2 2.15 Zr 294.09 Dy 4.365
P2O5 0.65 Nb 20.61 Ho 0.8
Cr2O3 0.02 Mo 1.54 Er 2.02
LOI 0.34 Cs 0.31 Tm 0.251
Total 99.32 Ba 479.77 Yb 1.63
Hf 6.49 Lu 0.22
Ta 1.08 Total 274.4
Pb 8.51 LaN/YbN 25.39
Th 2.89 GdN/YbN 3.72
U 0.45 EuN/EuN* 0.852
Ce/Ce* 1.153
eISSN:
1854-7400
Idioma:
Inglés
Calendario de la edición:
4 veces al año
Temas de la revista:
Computer Sciences, Databases and Data Mining, Geosciences, Geodesy, Geology and Mineralogy, Materials Sciences, Materials Characterization and Properties
RSS Feed de revista