Nb-Zr enrichment in Jabal Al Bayda A-type granites, western Arabian Shield, Saudi Arabia: interplay of magmatic and hydrothermal processes

Figures & data

Figure 1. Location map of the study area; image provided by Google Earth.

Figure 2. Geologic map of the studied district; Modified after pellaton [11].

Table 1. Lithostratigraphic units in the Al Bayda area.

Era and Epoch	Lithostratigraphic units		Intrusive and extrusive rock units	Age in M.Y	Lithology
Cenozoic			Neogene volcanic rocks	<10–22 m.y	Olivine and alkali olivine basalt
Thermal contact
NEOPROTEROZOIC			Post-granitic dikes		Basic, intermediate and acidic dikes
	Late to post tectonic intrusions	Peralkaline granite Alkali granite Altered mica granite	560 ± 16 m.y.
	Thermal contact
	Al Ays group	Urayfi Formation		<750–>700 m.y	Rhyolite-ignimbrite members and detrital sedimentary members (reworked lithic tuffs)
		Farshah Formation			Epiclastic rocks, andesite, basalt, and different tuffs

Age-related references are given in the text.

Figure 3. The main geologic features of Al Bayda granites; (a) general view of the studied granites; (b) NW trending NFS cutting through Al Bayda granite; (c) Al Bayda granitic exfoliation; (d) The contact between the studied granites and Neogene basaltic rocks; (e) Altered granites and alteration sites. Gr = Granite & Bs = Basalt.

Figure 4. The modal analysis of the studied granites on the ternary diagram of Streckeisen [15].

Table 2. The modal analyses (mineral %) of the studied alkaline granites.

▪ Alkali feldspar	K-fel.	Qz	Hb.	Musc.	Biotite	Acc.	Op.	Total
1Ak	55.43	37.24	6.36	0.31	0.08	0.15	0.43	100
2 Ak	57.76	36.21	4.56	0.96	0.07	0.17	0.27	100
3Ak	57.48	36.00	5.36	0.42	0.06	0.00	0.68	100
4 Ak	57.70	35.22	5.32	0.39	0.07	0.35	0.95	100
5Ak	54.39	37.97	5.41	0.61	0.04	0.43	1.15	100
11 Ak	59.44	35.73	3.22	0.61	0.07	0.08	0.85	100
13 Ak	60.62	34.36	3.24	0.90	0.02	0.21	0.65	100
▴ Peralkaline	K-fel.	Neph.	Alk. Pyx.	Alk. Amp.	Zircon	Op.	Acc.	Total
19 Pk	61	27	7	2	0.10	2.10	0.80	100
20 Pk	64	25	5	3	0.20	2.2	0.60	100
21 Pk	65	22	6	2	0.25	1.82	0.93	100
23 Pk	70	18	6	3	0.20	2.10	0.70	100
25 Pk	68	22	5	2	0.10	1.98	0.92	100

K-fel = K feldspars + albite; Qz = quartz; Hb = Hornblende; Acc. =  Accessories; Op. = opaques; Neph = nepheline; Alk = Alkali; Pxy = pyroxenes; Amp = amphiboles.

Figure 5. Photomicrographs showing alkali feldspar granite essential, accessory, and opaque minerals and their mutual relationships.

Figure 6. Photomicrographs showing peralkaline granite essential, accessory, and opaque minerals and their mutual relationships.

Figure 7. Photomicrographs showing altered muscovite granite essential, accessory, and opaque minerals and their mutual relationships.

Figure 8. Photomicrographs showing the pegmatite-aplite sheet rock-forming minerals and their mutual relationships.

Figure 9. Variation diagrams of selected major and trace elements of Al Bayda fresh and altered younger granitoid rocks.

Table 3. Major (wt.%) and trace elements (ppm) abundance in Al Bayda fresh and altered granitoids.

Rock type	Alkali feldspar granite							Peralkaline granite
Oxides	1Ak	2Ak	3Ak	4Ak	5Ak	6Ak	Avg	1Pk	2Pk	4Pk	3Pk	5Pk	Avg
SiO2	78.71	75.04	76.23	75.29	77.58	75.86	76.45	73.22	73.56	72.95	73.35	74.22	73.46
TiO2	0.13	0.23	0.15	0.17	0.08	0.15	0.15	0.43	0.38	0.41	0.31	0.41	0.39
Al2O3	11.87	11.92	11.46	11.78	11.25	11.23	11.59	10.35	9.60	9.40	10.22	9.50	9.81
Fe2O3	0.65	0.72	0.98	0.85	1.07	0.69	0.83	2.53	2.89	3.11	2.65	3.22	2.88
FeO*	0.58	0.65	0.88	0.76	0.96	0.62	0.74	2.28	2.60	2.80	2.38	2.90	2.59
MnO	–	–	–	–	–	–	–	0.06	0.08	0.05	0.05	0.04	0.06
MgO	0.18	0.16	0.12	0.17	0.11	0.14	0.15	0.63	0.56	0.65	0.76	0.35	0.59
CaO	0.27	0.64	0.49	0.25	0.24	0.33	0.37	1.23	0.95	1.36	1.25	1.33	1.22
Na2O	3.67	3.54	3.72	4.12	3.89	3.65	3.77	4.87	5.12	4.81	4.98	4.56	4.87
K2O	4.30	5.86	5.04	5.86	4.75	5.24	5.18	5.23	4.89	5.26	5.22	5.02	5.12
P2O	U.D.	U.D.	U.D.	U.D.	U.D.	U.D.	U.D.	0.12	0.11	0.15	0.21	0.08	0.13
LOI	1.07	1.28	1.26	1.12	0.98	1.05	1.13	0.70	0.95	1.25	0.89	0.98	0.95
Sum	100.92	99.46	99.52	99.68	100.02	98.41	99.67	99.44	99.16	99.47	99.96	99.78	99.56
Cr	–	–	–	–	–	–	–	9	7	5	8	6	6.96
Cu	4	3	4	3	2	4	3	3	3	4	3	3	3
Zr	360	286	415	389	379	412	374	731	685	632	715	584	669
Nb	43	62	48	65	57	65	57	70	52	81	67	65	67
Y	51	45	50	58	46	69	53	50	78	64	76	59	65
Hf	11	10	14	16	11	17	13	14	18	16	20	17	17
Ga	26	22	24	20	23	18	22	13	15	13	15	16	13
La	51	72	68	84	65	71	68	36	42	38	51	45	42
Ce	44	30	25	42	38	46	37	78	82	75	89	79	81
Dy	10	9	10	8	12	7	9	6	6	4	5	6	5
Er	5	4	6	5	4	5	5	4	3	4	2	4	3
Eu	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Gd	10	13	11	10	14	12	12	5	5	7	6	5	6
Ho	2	2	2	1	2	3	2	–	–	–	–	–	–
∑REE + Y	173	175	172	208	181	213	186	179	216	192	229	198	202
Rocks	Altered muscovite granites								Pegmatite-aplite
Oxides	1Ad	2Ad	3Ad	4Ad	5Ad	6Ad	7Ad	Avg	1Ap	2Ap	Avg
SiO2	80.20	79.05	78.30	76.85	80.25	77.45	76.12	78.42	78.60	77.69	78.15
TiO2	0.07	0.09	0.12	0.05	0.06	0.11	0.22	0.13	0.11	0.09	0.10
Al2O3	11.31	9.86	11.54	10.58	10.22	10.76	10.86	10.89	11.42	12.45	11.94
Fe2O3	0.69	1.68	1.27	1.85	0.75	1.68	2.23	1.47	1.23	1.29	1.26
FeO*	0.62	1.51	1.14	1.66	0.67	1.51	2.01	1.32	1.11	1.16	1.13
MnO	–	–	–	–	–	–	–	–	–	–	–
MgO	0.16	0.15	0.15	0.17	0.15	0.14	0.22	0.17	0.25	0.38	0.32
CaO	0.33	0.32	0.44	0.42	0.35	0.73	0.38	0.37	0.60	0.56	0.58
Na2O	3.60	3.92	3.98	3.84	3.62	3.87	3.91	3.85	3.76	3.45	3.61
K2O	4.12	4.18	4.42	5.26	4.25	4.15	4.56	4.32	3.72	4.14	3.93
P2O	0.03	0.06	0.04	0.07	0.04	0.08	0.07	0.05	0.05	0.05	0.05
L.O.I	0.98	1.12	0.65	1.35	1.08	1.12	1.42	1.04	0.69	0.79	0.74
Sum	101.56	100.50	100.98	100.51	100.84	100.16	100.06	100.78	100.50	100.96	100.73
Li	6	11	14	10	16	12	18	12	35	28	31
Cr	4	7	5	4	6	4	3	4.75	<1	<1	<1
Cu	2	3	3	4	2	3	<1	<1	2	<1	1
Zr	405	398	375	402	425	396	384	391	95	80	88
Nb	65	58	54	67	82	61	63	60	46	44	45
Y	94	100	96	85	102	89	96	97	56	72	64
Hf	7	12	12	9	12	7	10	10	8	6	7
Ga	22	16	18	14	13	21	16	18	21	24	23
La	44	52	41	46	43	50	47	46	20	22	21
Ce	64	76	68	59	74	73	65	68	39	32	36
Dy	9	12	11	9	14	10	12	11	9	7	8
Er	4	5	7	4	6	5	4	5	5	5	5
Eu	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1	<1
Gd	11	13	11	10	9	13	13	12	7	5	6
Ho	1	3	2	3	2	3	3	2	1	1	1
∑REE + Y	227	261	236	216	250	243	240	241	137	144	141

FeO* is recalculated total iron as Fe²⁺. & (-) = under detection limit.

Figure 10. Classification, Magma type and tectonic setting of the studied granites. (a) Middlemost, [18], (b) Batchelor & Bowden [19], (c) Rickwood [20], (d) Agapitic index (AI) vs. SiO₂ diagram [21]. The post-collision granite field is added by Farahat et al., [22]., (e) Maniar and Piccoli [23], (f&g) Whalen et al., [24], (h) Pearce et al., [25], VAG-volcanic arc granite, syn-COLG-syn collision granite, ORG-oceanic ridge granite, WPG-within plate granite. Symbols as Figure (9).

Figure 11. (a) Anorogenic and post-orogenic A-type granite discrimination diagram, Eby [28]. (b) Granitic source binary diagram, modified after Altherr et al. [30]. Symbols as Figure (9).

Figure 12. Chondrite-normalized multi-elements diagram for the studied granites. Normalizing values from Sun and McDonough [32]. Symbols as Figure (9).

Figure 13. Primitive mantle-normalized multi-elements diagrams for the studied granite. Normalizing values from Sun and McDonough [32]. Symbols as Figure (9).

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