Zircon U-Pb Ages, Geochemistry and Tectonic Implications of Adamellite in Ophiolite Mélange Belt in South Altyn Tagh

doi:10.19657/j.geoscience.1000-8527.2019.012

Abstract

Abstract:

The large Yusupuleke Tagh batholiths intruded the Mangya ophiolite mélange belt in South Altyn Tagh. We carried out detailed geochronologic and geochemical analyses on the adamellite from the Yusupuleke Tagh batholiths. LA-ICP-MS zircon U-Pb dating yielded a Late Ordovician to Early Silurian weighted average age of (443.7±2.3) Ma. Geochemical analysis show that the rocks are characterized by high SiO₂(73.72%-75.08%), low TiO₂(0.11%-0.21%), low CaO (0.63%-1.45%), alkali-rich(N₂O+K₂O=7.19%-8.16%),high K₂O(K₂O/Na₂O=1.32-1.56) and low Mg^#(15.95-28.94) contents and A/CNK=1.11-1.26, suggesting high-K calc-alkaline and peraluminous affinities. REE distribution patterns show negative Eu anomalies, and distinctly high value of LREE/HREE. The chondrite-normalized REE patterns are right-inclined, with a clear V trough. The adamellite is rich in large ion lithophile elements (LILEs, e.g., Cs, K, Pb) as well as Th and Nd and depleted in high field strength elements (HFSEs, e.g., Nb, Ce, Ti) as well as Ba and P. Such geochemical features indicate that the rocks were formed by the partial melting of metamorphic sandstones in the middle-lower crust under a post-collisional setting. Considering the regional geology, the adamellite was likely formed in a compressional to extensional transition tectonic regime, younger than the previously reported ages in South Altyn Tagh. This suggests that the subduction and collision between the Azhong Block and Qaidam Block had occurred, and that the South Altyn Tagh ocean basin had completely closed at about 443 Ma.

Key words: adamellite, LA-ICP-MS zircon U-Pb dating, geochemistry, post-collisional tectonic, ophiolite mélange belt

CLC Number:

P588.12

LI Qi, WANG Jiangtao, ZENG Zhongcheng, SHI Wei, LI Hui, GUO Qianyi. Zircon U-Pb Ages, Geochemistry and Tectonic Implications of Adamellite in Ophiolite Mélange Belt in South Altyn Tagh[J]. Geoscience, 2020, 34(01): 51-63.

Figures/Tables 13

References 39

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点号	Th/U	同位素比值									t/Ma
点号	Th/U	²⁰⁷Pb/²⁰⁶Pb	σ	²⁰⁷Pb/²³⁵U	σ	²⁰⁶Pb/²³⁸U	σ	²⁰⁸Pb/²³²Th	σ		²⁰⁷Pb/ ²⁰⁶Pb	σ	²⁰⁷Pb/ ²³⁵U	σ	²⁰⁶Pb/ ²³⁸U	σ	²⁰⁸Pb/ ²³²Th	σ
1	0.35	0.058 27	0.002 32	0.567 50	0.015 81	0.070 62	0.001 03	0.024 39	0.000 51	539		86	456	10	440	6	487	10
2	0.96	0.056 89	0.001 89	0.554 64	0.009 75	0.070 70	0.000 94	0.021 75	0.000 28	487		72	448	6	440	6	435	6
3	0.66	0.054 90	0.001 96	0.541 50	0.011 74	0.071 53	0.000 98	0.022 05	0.000 34	408		77	439	8	445	6	441	7
4	0.46	0.055 59	0.001 86	0.556 76	0.010 08	0.072 63	0.000 97	0.022 39	0.000 32	436		73	449	7	452	6	448	6
5	0.63	0.057 88	0.001 86	0.577 60	0.008 97	0.072 36	0.000 95	0.021 98	0.000 28	525		69	463	6	450	6	439	6
6	0.55	0.056 34	0.001 84	0.560 96	0.009 44	0.072 19	0.000 96	0.022 06	0.000 30	465		71	452	6	449	6	441	6
7	0.50	0.056 05	0.001 83	0.554 35	0.009 22	0.071 72	0.000 95	0.021 72	0.000 29	454		71	448	6	447	6	434	6
8	0.53	0.058 28	0.001 90	0.574 40	0.009 63	0.071 47	0.000 95	0.022 70	0.000 31	540		71	461	6	445	6	454	6
9	0.60	0.056 83	0.001 84	0.556 81	0.009 04	0.071 05	0.000 94	0.021 65	0.000 28	484		71	449	6	443	6	433	6
10	0.56	0.058 70	0.001 89	0.575 76	0.009 14	0.071 13	0.000 94	0.021 81	0.000 29	556		69	462	6	443	6	436	6
11	0.41	0.056 52	0.001 93	0.556 83	0.010 88	0.071 44	0.000 97	0.022 58	0.000 35	472		75	450	7	445	6	451	7
12	0.62	0.054 80	0.001 78	0.537 27	0.008 98	0.071 10	0.000 94	0.021 97	0.000 29	404		71	437	6	443	6	439	6
13	1.01	0.057 71	0.002 20	0.562 86	0.014 53	0.070 73	0.001 01	0.014 96	0.000 25	518		82	453	9	441	6	300	5
14	0.51	0.056 74	0.001 81	0.559 78	0.008 77	0.071 54	0.000 95	0.021 72	0.000 29	481		70	451	6	445	6	434	6
15	0.69	0.055 79	0.001 78	0.549 49	0.008 56	0.071 42	0.000 94	0.021 19	0.000 27	444		69	445	6	445	6	424	5
16	0.44	0.057 21	0.001 83	0.564 93	0.008 90	0.071 60	0.000 95	0.022 18	0.000 30	499		69	455	6	446	6	443	6
17	0.50	0.058 16	0.001 92	0.570 71	0.010 10	0.071 15	0.000 95	0.021 56	0.000 31	535		71	459	7	443	6	431	6
18	0.52	0.054 10	0.001 75	0.526 03	0.008 70	0.070 51	0.000 94	0.021 50	0.000 29	375		71	429	6	439	6	430	6
19	0.90	0.054 85	0.001 84	0.533 67	0.010 04	0.070 56	0.000 95	0.020 53	0.000 28	406		73	434	7	440	6	411	6
20	0.46	0.055 54	0.001 86	0.543 15	0.010 15	0.070 92	0.000 96	0.021 34	0.000 32	434		73	441	7	442	6	427	6
21	0.99	0.055 33	0.001 83	0.541 21	0.009 87	0.070 94	0.000 95	0.021 09	0.000 28	425		72	439	7	442	6	422	6
22	0.49	0.054 97	0.001 82	0.541 17	0.009 89	0.071 40	0.000 96	0.021 67	0.000 32	411		72	439	7	445	6	433	6
23	0.63	0.058 28	0.001 94	0.572 64	0.010 55	0.071 26	0.000 96	0.022 57	0.000 32	540		72	460	7	444	6	451	6
24	0.46	0.058 26	0.001 99	0.570 36	0.011 39	0.071 00	0.000 97	0.022 25	0.000 35	539		74	458	7	442	6	445	7
25	0.62	0.054 85	0.001 75	0.530 62	0.008 55	0.070 15	0.000 93	0.021 17	0.000 28	406		69	432	6	437	6	424	6

点号	Th/U	同位素比值									t/Ma
点号	Th/U	²⁰⁷Pb/²⁰⁶Pb	σ	²⁰⁷Pb/²³⁵U	σ	²⁰⁶Pb/²³⁸U	σ	²⁰⁸Pb/²³²Th	σ		²⁰⁷Pb/ ²⁰⁶Pb	σ	²⁰⁷Pb/ ²³⁵U	σ	²⁰⁶Pb/ ²³⁸U	σ	²⁰⁸Pb/ ²³²Th	σ
1	0.35	0.058 27	0.002 32	0.567 50	0.015 81	0.070 62	0.001 03	0.024 39	0.000 51	539		86	456	10	440	6	487	10
2	0.96	0.056 89	0.001 89	0.554 64	0.009 75	0.070 70	0.000 94	0.021 75	0.000 28	487		72	448	6	440	6	435	6
3	0.66	0.054 90	0.001 96	0.541 50	0.011 74	0.071 53	0.000 98	0.022 05	0.000 34	408		77	439	8	445	6	441	7
4	0.46	0.055 59	0.001 86	0.556 76	0.010 08	0.072 63	0.000 97	0.022 39	0.000 32	436		73	449	7	452	6	448	6
5	0.63	0.057 88	0.001 86	0.577 60	0.008 97	0.072 36	0.000 95	0.021 98	0.000 28	525		69	463	6	450	6	439	6
6	0.55	0.056 34	0.001 84	0.560 96	0.009 44	0.072 19	0.000 96	0.022 06	0.000 30	465		71	452	6	449	6	441	6
7	0.50	0.056 05	0.001 83	0.554 35	0.009 22	0.071 72	0.000 95	0.021 72	0.000 29	454		71	448	6	447	6	434	6
8	0.53	0.058 28	0.001 90	0.574 40	0.009 63	0.071 47	0.000 95	0.022 70	0.000 31	540		71	461	6	445	6	454	6
9	0.60	0.056 83	0.001 84	0.556 81	0.009 04	0.071 05	0.000 94	0.021 65	0.000 28	484		71	449	6	443	6	433	6
10	0.56	0.058 70	0.001 89	0.575 76	0.009 14	0.071 13	0.000 94	0.021 81	0.000 29	556		69	462	6	443	6	436	6
11	0.41	0.056 52	0.001 93	0.556 83	0.010 88	0.071 44	0.000 97	0.022 58	0.000 35	472		75	450	7	445	6	451	7
12	0.62	0.054 80	0.001 78	0.537 27	0.008 98	0.071 10	0.000 94	0.021 97	0.000 29	404		71	437	6	443	6	439	6
13	1.01	0.057 71	0.002 20	0.562 86	0.014 53	0.070 73	0.001 01	0.014 96	0.000 25	518		82	453	9	441	6	300	5
14	0.51	0.056 74	0.001 81	0.559 78	0.008 77	0.071 54	0.000 95	0.021 72	0.000 29	481		70	451	6	445	6	434	6
15	0.69	0.055 79	0.001 78	0.549 49	0.008 56	0.071 42	0.000 94	0.021 19	0.000 27	444		69	445	6	445	6	424	5
16	0.44	0.057 21	0.001 83	0.564 93	0.008 90	0.071 60	0.000 95	0.022 18	0.000 30	499		69	455	6	446	6	443	6
17	0.50	0.058 16	0.001 92	0.570 71	0.010 10	0.071 15	0.000 95	0.021 56	0.000 31	535		71	459	7	443	6	431	6
18	0.52	0.054 10	0.001 75	0.526 03	0.008 70	0.070 51	0.000 94	0.021 50	0.000 29	375		71	429	6	439	6	430	6
19	0.90	0.054 85	0.001 84	0.533 67	0.010 04	0.070 56	0.000 95	0.020 53	0.000 28	406		73	434	7	440	6	411	6
20	0.46	0.055 54	0.001 86	0.543 15	0.010 15	0.070 92	0.000 96	0.021 34	0.000 32	434		73	441	7	442	6	427	6
21	0.99	0.055 33	0.001 83	0.541 21	0.009 87	0.070 94	0.000 95	0.021 09	0.000 28	425		72	439	7	442	6	422	6
22	0.49	0.054 97	0.001 82	0.541 17	0.009 89	0.071 40	0.000 96	0.021 67	0.000 32	411		72	439	7	445	6	433	6
23	0.63	0.058 28	0.001 94	0.572 64	0.010 55	0.071 26	0.000 96	0.022 57	0.000 32	540		72	460	7	444	6	451	6
24	0.46	0.058 26	0.001 99	0.570 36	0.011 39	0.071 00	0.000 97	0.022 25	0.000 35	539		74	458	7	442	6	445	7
25	0.62	0.054 85	0.001 75	0.530 62	0.008 55	0.070 15	0.000 93	0.021 17	0.000 28	406		69	432	6	437	6	424	6

样品号	SiO₂	TiO₂	Al₂O₃	Fe₂O₃	FeO	MnO	MgO	CaO	Na₂O	K₂O
PM022/18-1	74.44	0.13	13.53	0.53	1.03	0.03	0.16	0.84	3.06	4.77
PM022/18-2	74.27	0.11	13.55	0.66	0.74	0.03	0.16	0.87	3.47	4.59
PM022/18-3	75.08	0.12	13.78	0.78	0.54	0.02	0.14	0.70	2.99	4.38
PM022/18-4	74.78	0.11	13.67	0.69	0.64	0.02	0.21	0.63	3.04	4.75
PM022/18-5	73.72	0.21	13.82	0.48	1.19	0.03	0.37	1.45	3.09	4.10
样品号	P₂O₅	烧失量	总量	AR	σ	A/NK	A/CNK	K₂O + Na₂O	Na₂O/K₂O	Mg^#
PM022/18-1	0.03	0.80	99.35	3.39	1.95	1.33	1.15	7.83	0.64	15.95
PM022/18-2	0.03	0.96	99.43	3.53	2.08	1.27	1.11	8.06	0.76	17.64
PM022/18-3	0.03	0.89	99.45	3.07	1.69	1.43	1.26	7.37	0.68	16.73
PM022/18-4	0.04	0.80	99.38	3.39	1.91	1.35	1.21	7.79	0.64	22.91
PM022/18-5	0.05	0.91	99.41	2.78	1.68	1.45	1.14	7.19	0.75	28.94

样品号	SiO₂	TiO₂	Al₂O₃	Fe₂O₃	FeO	MnO	MgO	CaO	Na₂O	K₂O
PM022/18-1	74.44	0.13	13.53	0.53	1.03	0.03	0.16	0.84	3.06	4.77
PM022/18-2	74.27	0.11	13.55	0.66	0.74	0.03	0.16	0.87	3.47	4.59
PM022/18-3	75.08	0.12	13.78	0.78	0.54	0.02	0.14	0.70	2.99	4.38
PM022/18-4	74.78	0.11	13.67	0.69	0.64	0.02	0.21	0.63	3.04	4.75
PM022/18-5	73.72	0.21	13.82	0.48	1.19	0.03	0.37	1.45	3.09	4.10
样品号	P₂O₅	烧失量	总量	AR	σ	A/NK	A/CNK	K₂O + Na₂O	Na₂O/K₂O	Mg^#
PM022/18-1	0.03	0.80	99.35	3.39	1.95	1.33	1.15	7.83	0.64	15.95
PM022/18-2	0.03	0.96	99.43	3.53	2.08	1.27	1.11	8.06	0.76	17.64
PM022/18-3	0.03	0.89	99.45	3.07	1.69	1.43	1.26	7.37	0.68	16.73
PM022/18-4	0.04	0.80	99.38	3.39	1.91	1.35	1.21	7.79	0.64	22.91
PM022/18-5	0.05	0.91	99.41	2.78	1.68	1.45	1.14	7.19	0.75	28.94

样品号	La	Ce	Pr	Nd	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm
PM022/18-1	26.1	51.0	5.93	20.2	4.68	0.53	4.17	0.60	3.05	0.59	1.61	0.29
PM022/18-2	19.3	37.6	4.58	15.0	4.20	0.49	3.71	0.61	3.75	0.82	2.18	0.42
PM022/18-3	32.0	61.7	7.11	24.0	5.41	0.57	5.20	0.71	3.66	0.72	1.89	0.37
PM022/18-4	23.5	48.1	5.39	18.6	4.63	0.50	3.76	0.58	3.18	0.68	1.64	0.34
PM022/18-5	31.3	58.4	6.55	23.0	4.73	0.79	4.12	0.55	2.92	0.58	1.65	0.30
样品号	Yb	Lu	Y	∑REE	LREE	HREE	LREE/HREE	δEu	δCe	(La/Yb)_N	(La/Sm)_N	(Gd/Yb)_N
PM022/18-1	0.11	0.020	0.88	138.51	108.44	30.07	3.61	0.36	0.95	10.41	3.51	1.99
PM022/18-2	0.11	0.021	0.85	120.16	81.17	39.00	2.08	0.37	0.93	5.44	2.89	1.25
PM022/18-3	0.11	0.020	0.87	166.27	130.79	35.48	3.69	0.32	0.95	12.77	3.72	2.48
PM022/18-4	0.11	0.020	0.87	132.72	100.72	32.00	3.15	0.36	0.99	9.21	3.19	1.76
PM022/18-5	0.11	0.020	0.88	154.63	124.77	29.86	4.18	0.54	0.93	13.61	4.16	2.14