Zircon U-Pb Age of Granite Porphyry Within Youhulugou Ophiolite in the Suture Zone of North Qilian Mountains and Its Geological Implications

Abstract

Abstract:

Ophiolites as on-land or arc slices of oceanic lithosphere, are the production of the mid ocean ridge expansion or subduction of the plates. The granitoids can be formed during the formation of ophiolites and are important for studying origin of the ophiolites, especially dating the precise ages of the ophiolites formation and evolution. The Youhulugou ophiolite is one of the representative ophiolite fragments in the suture zone of the North Qilian Mountain. In this study, major and trace elements geochemical study indicates that the granite porphyry within Youhulugou ophiolite has high Al₂O₃ and K₂O content characteristics. According to the moderate LREE-enrichment patterns, the granite porphyry is similar to the obduction-type granitoids rocks within ophiolites. LA-ICP-MS U-Pb dating was carried out for zircons from isotropic granite porphyry within Youhulugou ophiolite. Twenty point analyses yield a relatively consistent and apparent ²⁰⁶Pb/²³⁸U weighted mean age of (497.5±1.5) Ma, which is considered to be the forming age of the granite porphyry and the obduction age of the Youhulugou ophiolite onto the continental crust. Combined with regional geological characteristics, chronological and geochemical data,we concluded that the Youhulugou ophiolite obducted during the Late Cambrian era, and the acquisition of forming age and determination of tectonic setting for Youhulugou ophiolite provide significant constraints on the age of intra-oceanic subduction system in the North Qilian Ocean.

Key words: North Qilian suture zone, Youhulugou ophiolite, obduction-type granite porphyry, zircon U-Pb age

CLC Number:

P588.1
P597

LI Bing, HU Daogong, CHEN Xuanhua, ZHANG Yaoling, WU Huanhuan, WANG Chaoqun. Zircon U-Pb Age of Granite Porphyry Within Youhulugou Ophiolite in the Suture Zone of North Qilian Mountains and Its Geological Implications[J]. Geoscience, 2017, 31(06): 1170-1176.

Figures/Tables 7

References 36

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测点	w_B/10^-6		Th/U	同位素比值							年龄/Ma
测点	Pb	U	Th/U	²⁰⁶Pb/²³⁸U	1σ	²⁰⁷Pb/²³⁵U	1σ	²⁰⁷Pb/²⁰⁶Pb	1σ		²⁰⁶Pb/²³⁸U	1σ	²⁰⁷Pb/²³⁵U	1σ
1	92	936	1.37	0.079 3	0.000 4	0.646 1	0.059 1	0.059 1	0.000 8	492		3	506	7
2	60	622	1.09	0.080 7	0.000 4	0.650 5	0.058 5	0.058 5	0.000 8	500		2	509	7
3	39	422	0.93	0.079 8	0.000 4	0.628 0	0.057 1	0.057 1	0.001 1	495		2	495	10
4	81	812	1.37	0.079 9	0.000 3	0.662 6	0.060 1	0.060 1	0.000 8	496		2	516	7
5	37	407	0.90	0.080 7	0.000 4	0.642 3	0.057 7	0.057 7	0.000 9	500		2	504	8
6	68	718	1.09	0.080 6	0.000 4	0.634 9	0.057 1	0.057 1	0.000 8	500		2	499	7
7	51	549	1.03	0.080 4	0.000 4	0.633 8	0.057 2	0.057 2	0.000 8	498		2	498	7
8	45	474	1.11	0.080 9	0.000 4	0.637 0	0.057 1	0.057 1	0.000 9	501		3	500	8
9	76	790	1.23	0.079 5	0.000 3	0.625 9	0.05 71	0.057 1	0.000 8	493		2	494	7
10	73	779	1.02	0.080 0	0.000 4	0.624 9	0.056 6	0.056 6	0.000 8	496		3	493	7
11	74	784	1.08	0.079 8	0.000 4	0.630 8	0.057 4	0.057 4	0.000 8	495		2	497	7
12	88	870	1.31	0.080 1	0.000 5	0.624 8	0.056 6	0.056 6	0.000 8	497		3	493	7
13	104	1022	1.26	0.079 4	0.000 3	0.625 5	0.057 2	0.057 2	0.000 8	492		2	493	7
14	62	607	1.15	0.080 6	0.000 3	0.633 1	0.057 0	0.057 0	0.000 8	500		2	498	7
15	99	850	1.82	0.079 5	0.000 3	0.633 8	0.057 8	0.057 8	0.000 8	493		2	498	7
16	87	843	1.18	0.080 8	0.000 3	0.641 5	0.057 6	0.057 6	0.000 8	501		2	503	7
17	88	854	1.13	0.080 9	0.000 4	0.655 6	0.058 8	0.058 8	0.000 8	501		2	512	7
18	37	397	0.75	0.080 8	0.000 4	0.646 2	0.058 0	0.058 0	0.001 0	501		2	506	9
19	67	696	0.97	0.080 8	0.000 3	0.653 0	0.058 6	0.058 6	0.000 8	501		2	510	7
20	51	545	0.85	0.080 3	0.000 3	0.639 9	0.057 8	0.057 8	0.000 9	498		2	502	8

测点	w_B/10^-6		Th/U	同位素比值							年龄/Ma
测点	Pb	U	Th/U	²⁰⁶Pb/²³⁸U	1σ	²⁰⁷Pb/²³⁵U	1σ	²⁰⁷Pb/²⁰⁶Pb	1σ		²⁰⁶Pb/²³⁸U	1σ	²⁰⁷Pb/²³⁵U	1σ
1	92	936	1.37	0.079 3	0.000 4	0.646 1	0.059 1	0.059 1	0.000 8	492		3	506	7
2	60	622	1.09	0.080 7	0.000 4	0.650 5	0.058 5	0.058 5	0.000 8	500		2	509	7
3	39	422	0.93	0.079 8	0.000 4	0.628 0	0.057 1	0.057 1	0.001 1	495		2	495	10
4	81	812	1.37	0.079 9	0.000 3	0.662 6	0.060 1	0.060 1	0.000 8	496		2	516	7
5	37	407	0.90	0.080 7	0.000 4	0.642 3	0.057 7	0.057 7	0.000 9	500		2	504	8
6	68	718	1.09	0.080 6	0.000 4	0.634 9	0.057 1	0.057 1	0.000 8	500		2	499	7
7	51	549	1.03	0.080 4	0.000 4	0.633 8	0.057 2	0.057 2	0.000 8	498		2	498	7
8	45	474	1.11	0.080 9	0.000 4	0.637 0	0.057 1	0.057 1	0.000 9	501		3	500	8
9	76	790	1.23	0.079 5	0.000 3	0.625 9	0.05 71	0.057 1	0.000 8	493		2	494	7
10	73	779	1.02	0.080 0	0.000 4	0.624 9	0.056 6	0.056 6	0.000 8	496		3	493	7
11	74	784	1.08	0.079 8	0.000 4	0.630 8	0.057 4	0.057 4	0.000 8	495		2	497	7
12	88	870	1.31	0.080 1	0.000 5	0.624 8	0.056 6	0.056 6	0.000 8	497		3	493	7
13	104	1022	1.26	0.079 4	0.000 3	0.625 5	0.057 2	0.057 2	0.000 8	492		2	493	7
14	62	607	1.15	0.080 6	0.000 3	0.633 1	0.057 0	0.057 0	0.000 8	500		2	498	7
15	99	850	1.82	0.079 5	0.000 3	0.633 8	0.057 8	0.057 8	0.000 8	493		2	498	7
16	87	843	1.18	0.080 8	0.000 3	0.641 5	0.057 6	0.057 6	0.000 8	501		2	503	7
17	88	854	1.13	0.080 9	0.000 4	0.655 6	0.058 8	0.058 8	0.000 8	501		2	512	7
18	37	397	0.75	0.080 8	0.000 4	0.646 2	0.058 0	0.058 0	0.001 0	501		2	506	9
19	67	696	0.97	0.080 8	0.000 3	0.653 0	0.058 6	0.058 6	0.000 8	501		2	510	7
20	51	545	0.85	0.080 3	0.000 3	0.639 9	0.057 8	0.057 8	0.000 9	498		2	502	8

样品号	SiO₂	TiO₂	Al₂O₃	Fe₂O₃	FeO	MnO	MgO	CaO	Na₂O	K₂O	P₂O₅	CO₂	H₂O⁺	总计
B063-7	70.01	0.37	14.11	1.24	1.78	0.02	1.76	1.44	2.53	2.69	0.08	0.94	2.02	98.99
样品号	Sr	Rb	Ba	Th	Ta	Nb	Zr	Hf	Sc	Cr	Ni	Co	V	U
B063-7	38.8	106	323	22.3	1.25	13.9	200	6.03	7.2	23.1	12.8	8.37	49.1	5.55
样品号	La	Ce	Pr	Nd	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu	Y
B063-7	41.9	81.3	8.45	29.4	4.68	0.78	6.14	0.67	3.58	0.67	1.94	0.34	1.95	0.32	21.6

样品号	SiO₂	TiO₂	Al₂O₃	Fe₂O₃	FeO	MnO	MgO	CaO	Na₂O	K₂O	P₂O₅	CO₂	H₂O⁺	总计
B063-7	70.01	0.37	14.11	1.24	1.78	0.02	1.76	1.44	2.53	2.69	0.08	0.94	2.02	98.99
样品号	Sr	Rb	Ba	Th	Ta	Nb	Zr	Hf	Sc	Cr	Ni	Co	V	U
B063-7	38.8	106	323	22.3	1.25	13.9	200	6.03	7.2	23.1	12.8	8.37	49.1	5.55
样品号	La	Ce	Pr	Nd	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu	Y
B063-7	41.9	81.3	8.45	29.4	4.68	0.78	6.14	0.67	3.58	0.67	1.94	0.34	1.95	0.32	21.6