New Discovery of the Middle Devonian I-Type Xiwuqi Quartz Diorite in Inner Mongolia and Its Geological Significance

doi:10.19657/j.geoscience.1000-8527.2020.051

Abstract

Abstract:

The Xiwuqi area,situated in the southern section of the Paleozoic Hegenshan suture zone,is a key tectonic unit for revealing the evolution of the Paleozoic Hegenshan ocean,a branch of the Paleo-Asian Ocean.There are a few Devonian magmatic rocks in this area,and the evolution of the Devonian Hegenshan ocean is not well studied.In the regional geological survey,a quartz diorite body was newly discovered at Uhelchulu and Xiwuqi.Here,we studied the petrography,zircon U-Pb chronology and geochemistry of the quartz diorite samples.LA-ICP-MS zircon U-Pb dating obtained the weighted average ²⁰⁶Pb/²³⁸U age of 395.8±7.5 Ma (MSWD=1.4, n=8),indicating an Early Devonian pluton emplacement.Geochemistry of the quartz diorite indicates that it is calc-alkaline,characterized by high Si and Na and metaluminous.The pluton is enriched in LILEs(e.g.,Rb,Ba,Th,U,Pb,and Sr) and depleted in HFSEs(e.g.,Zr,Hf,Nb,Ta,and Ti).The ΣREE content is relatively low with moderate LREE/HREE fractionation and weak negative Eu anomalies.Basing on this study and published data,we considered the quartz diorite to be I-type.The Y-Nb and(Y+Nb)-Rb granite discrimination diagrams suggest that the pluton was formed in the volcanic arc setting related to oceanic plate subduction.The discovery of the quartz diorite indicates that the Hegenshan ocean basin probably had existed in the Early Devonian,and it undergone southward subduction beneath the Xilinhot micro-continent.This new finding is different from the conventional understanding that the Hegenshan ocean has only subducted northward.

Key words: Devonian Hegenshan ocean, bidirectional subduction, I-type granite, volcanic arc

CLC Number:

CHENG Tianshe, YANG Wenjing, TENG Chao, ZHANG Xuebin, YANG Xinjie, LAI Lin, WU Rongze, ZHOU Changhong. New Discovery of the Middle Devonian I-Type Xiwuqi Quartz Diorite in Inner Mongolia and Its Geological Significance[J]. Geoscience, 2023, 37(06): 1624-1633.

Figures/Tables 11

References 37

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U01 测点	元素含量(10^-6)			Th/U	同位素比值						同位素比值				年龄(Ma)
U01 测点	Pb	Th	U	Th/U	²⁰⁶Pb/ ²³⁸U	1σ	²⁰⁷Pb/ ²³⁵U	1σ	²⁰⁷Pb/ ²⁰⁶Pb	1σ	²⁰⁸Pb/ ²³²Th	1σ	²³²Th/ ²³⁸U	1σ	²⁰⁶Pb/ ²³⁸U	1σ	²⁰⁷Pb/ ²³⁵U	1σ	²⁰⁷Pb/ ²⁰⁶Pb	1σ
1	8.75	54.77	135.89	0.41	0.0643	0.0007	0.4792	0.0136	0.0540	0.0015	0.0158	0.0003	0.4135	0.0013	401.80	4.24	397.52	11.28	370.75	63.11
2	16.92	70.00	272.45	0.26	0.0638	0.0005	0.4936	0.0083	0.0561	0.0009	0.0164	0.0002	0.2636	0.0009	398.53	3.24	407.36	6.87	457.14	36.44
3	14.76	40.18	237.50	0.17	0.0649	0.0007	0.5159	0.0091	0.0559	0.0010	0.0183	0.0004	0.1736	0.0007	405.58	4.41	422.38	7.44	446.56	37.86
4	17.90	68.62	277.43	0.25	0.0647	0.0006	0.5257	0.0095	0.0572	0.0010	0.0240	0.0004	0.2537	0.0009	404.15	3.72	428.97	7.75	497.91	38.69
5	15.51	96.97	197.72	0.50	0.0757	0.0008	0.6044	0.0134	0.0579	0.0013	0.0208	0.0002	0.5031	0.0017	470.20	4.76	480.02	10.62	527.13	47.85
6	10.72	87.33	154.10	0.58	0.0645	0.0006	0.5007	0.0198	0.0563	0.0021	0.0207	0.0003	0.5814	0.0024	403.21	3.89	412.19	16.29	462.79	83.93
7	13.91	40.31	157.81	0.26	0.0757	0.0008	0.5950	0.0119	0.1278	0.0024	0.0623	0.0014	0.2620	0.0009	470.14	4.78	474.03	9.45	2068.29	33.14
8	5.12	31.47	61.82	0.52	0.0735	0.0013	0.8845	0.0606	0.0867	0.0059	0.0300	0.0010	0.5222	0.0018	456.93	7.95	643.43	44.07	1354.87	131.09
9	18.78	104.50	280.74	0.38	0.0622	0.0006	0.6960	0.0111	0.0811	0.0013	0.0260	0.0004	0.3818	0.0012	389.03	3.52	536.39	8.55	1224.51	30.56
10	18.10	115.89	286.01	0.42	0.0610	0.0006	0.4551	0.0087	0.0541	0.0010	0.0209	0.0002	0.4157	0.0015	381.83	3.52	380.86	7.28	374.96	42.21
11	23.26	182.40	350.51	0.53	0.0621	0.0005	0.4628	0.0077	0.0541	0.0009	0.0208	0.0001	0.5338	0.0022	388.21	3.29	386.21	6.43	374.22	37.01
12	22.72	134.90	306.63	0.45	0.0707	0.0006	0.5431	0.0090	0.0557	0.0009	0.0241	0.0002	0.4513	0.0015	440.25	3.47	440.47	7.29	441.64	35.62
13	12.00	72.66	182.68	0.41	0.0622	0.0007	0.4835	0.0153	0.0563	0.0017	0.0247	0.0003	0.4080	0.0013	389.18	4.26	400.45	12.70	466.03	67.69

U01 测点	元素含量(10^-6)			Th/U	同位素比值						同位素比值				年龄(Ma)
U01 测点	Pb	Th	U	Th/U	²⁰⁶Pb/ ²³⁸U	1σ	²⁰⁷Pb/ ²³⁵U	1σ	²⁰⁷Pb/ ²⁰⁶Pb	1σ	²⁰⁸Pb/ ²³²Th	1σ	²³²Th/ ²³⁸U	1σ	²⁰⁶Pb/ ²³⁸U	1σ	²⁰⁷Pb/ ²³⁵U	1σ	²⁰⁷Pb/ ²⁰⁶Pb	1σ
1	8.75	54.77	135.89	0.41	0.0643	0.0007	0.4792	0.0136	0.0540	0.0015	0.0158	0.0003	0.4135	0.0013	401.80	4.24	397.52	11.28	370.75	63.11
2	16.92	70.00	272.45	0.26	0.0638	0.0005	0.4936	0.0083	0.0561	0.0009	0.0164	0.0002	0.2636	0.0009	398.53	3.24	407.36	6.87	457.14	36.44
3	14.76	40.18	237.50	0.17	0.0649	0.0007	0.5159	0.0091	0.0559	0.0010	0.0183	0.0004	0.1736	0.0007	405.58	4.41	422.38	7.44	446.56	37.86
4	17.90	68.62	277.43	0.25	0.0647	0.0006	0.5257	0.0095	0.0572	0.0010	0.0240	0.0004	0.2537	0.0009	404.15	3.72	428.97	7.75	497.91	38.69
5	15.51	96.97	197.72	0.50	0.0757	0.0008	0.6044	0.0134	0.0579	0.0013	0.0208	0.0002	0.5031	0.0017	470.20	4.76	480.02	10.62	527.13	47.85
6	10.72	87.33	154.10	0.58	0.0645	0.0006	0.5007	0.0198	0.0563	0.0021	0.0207	0.0003	0.5814	0.0024	403.21	3.89	412.19	16.29	462.79	83.93
7	13.91	40.31	157.81	0.26	0.0757	0.0008	0.5950	0.0119	0.1278	0.0024	0.0623	0.0014	0.2620	0.0009	470.14	4.78	474.03	9.45	2068.29	33.14
8	5.12	31.47	61.82	0.52	0.0735	0.0013	0.8845	0.0606	0.0867	0.0059	0.0300	0.0010	0.5222	0.0018	456.93	7.95	643.43	44.07	1354.87	131.09
9	18.78	104.50	280.74	0.38	0.0622	0.0006	0.6960	0.0111	0.0811	0.0013	0.0260	0.0004	0.3818	0.0012	389.03	3.52	536.39	8.55	1224.51	30.56
10	18.10	115.89	286.01	0.42	0.0610	0.0006	0.4551	0.0087	0.0541	0.0010	0.0209	0.0002	0.4157	0.0015	381.83	3.52	380.86	7.28	374.96	42.21
11	23.26	182.40	350.51	0.53	0.0621	0.0005	0.4628	0.0077	0.0541	0.0009	0.0208	0.0001	0.5338	0.0022	388.21	3.29	386.21	6.43	374.22	37.01
12	22.72	134.90	306.63	0.45	0.0707	0.0006	0.5431	0.0090	0.0557	0.0009	0.0241	0.0002	0.4513	0.0015	440.25	3.47	440.47	7.29	441.64	35.62
13	12.00	72.66	182.68	0.41	0.0622	0.0007	0.4835	0.0153	0.0563	0.0017	0.0247	0.0003	0.4080	0.0013	389.18	4.26	400.45	12.70	466.03	67.69

样号	岩性	SiO₂	Al₂O₃		TiO₂	Fe₂O₃		FeO	CaO		MgO	K₂O		Na₂O	MnO		P₂O₅
A01	石英闪长岩	60.44	14.66		0.73	1.76		4.67	5.59		3.73	2.39		2.48	0.13		0.15
A02		55.71	15.15		0.99	2.55		6.27	6.76		5.23	1.72		2.47	0.17		0.20
A03		55.39	15.43		0.96	2.50		6.32	6.01		5.62	1.87		2.63	0.18		0.20
A04		60.53	14.33		0.81	2.01		5.56	5.11		4.58	1.77		2.18	0.16		0.17
样号	岩性	烧失量	总量		FeO^*/ MgO	Na₂O/ K₂O		A/ CNK	A/NK		Ba	Rb		Sr	Y		Zr
A01	石英闪长岩	3.08	99.81		1.68	1.04		0.87	2.20		682.9	82.8		257.3	28.23		163.0
A02		2.60	99.81		1.64	1.44		0.83	2.56		339.9	70.3		298.4	43.29		174.1
A03		2.75	99.84		1.53	1.41		0.89	2.43		349.8	74.1		320.5	36.32		167.9
A04		2.68	99.86		1.61	1.23		0.97	2.61		223.9	66.1		241.6	31.03		164.6
样号	岩性	Nb	Th		Pb	Ga		Zn	Cu		V	Cr		Hf	Ta		Co
A01	石英闪长岩	11.31	5.16		10.3	20.05		79.3	36.3		170.2	118.7		10.20	0.76		24.82
A02		11.17	2.94		6.3	19.99		91.9	46.8		184.0	117.2		11.40	0.65		29.92
A03		11.09	3.96		7.7	19.66		91.8	49.3		199.4	153.9		9.85	0.71		31.53
A04		10.39	13.81		9.4	16.78		75.0	33.4		161.5	115.9		9.55	0.85		23.54
样号	岩性	U	W		Mo	Bi		Ti	La		Ce	Pr		Nd	Sm		Eu
A01	石英闪长岩	0.87	0.62		0.30	0.09		4359	17.97		46.51	6.08		25.38	5.53		1.46
A02		0.56	0.44		0.30	0.07		5918	25.47		64.36	8.89		37.91	8.49		2.01
A03		0.76	0.63		0.31	0.09		5744	23.72		54.91	7.28		31.07	6.97		1.75
A04		0.94	0.81		0.29	0.20		4833	20.05		54.14	6.06		25.48	5.87		1.42
样号	岩性	Gd	Tb		Dy	Ho		Er	Tm		Yb	Lu		δEu	(La/Yb)_N		ΣLREE
A01	石英闪长岩	4.88	0.89		5.82	1.14		3.29	0.55		3.30	0.42		0.84	3.67		102.93
A02		7.48	1.37		8.98	1.74		5.09	0.82		4.89	0.64		0.75	3.51		147.13
A03		6.28	1.16		7.53	1.49		4.33	0.71		4.15	0.54		0.80	3.85		125.71
A04		5.15	0.96		6.34	1.22		3.60	0.58		3.42	0.46		0.77	3.96		113.01
样号	岩性	ΣHREE		ΣLREE/ΣHREE			ΣREE			T_Zr(℃)			10000×Ga / Al			Zr+Nb+Ce+Y
A01	石英闪长岩	20.30		5.07			123.22			748			1.37			249.1
A02		31.00		4.75			178.12			734			1.32			292.9
A03		26.19		4.80			151.89			740			1.27			270.2
A04		21.73		5.20			134.74			762			1.17			260.2

样号	岩性	SiO₂	Al₂O₃		TiO₂	Fe₂O₃		FeO	CaO		MgO	K₂O		Na₂O	MnO		P₂O₅
A01	石英闪长岩	60.44	14.66		0.73	1.76		4.67	5.59		3.73	2.39		2.48	0.13		0.15
A02		55.71	15.15		0.99	2.55		6.27	6.76		5.23	1.72		2.47	0.17		0.20
A03		55.39	15.43		0.96	2.50		6.32	6.01		5.62	1.87		2.63	0.18		0.20
A04		60.53	14.33		0.81	2.01		5.56	5.11		4.58	1.77		2.18	0.16		0.17
样号	岩性	烧失量	总量		FeO^*/ MgO	Na₂O/ K₂O		A/ CNK	A/NK		Ba	Rb		Sr	Y		Zr
A01	石英闪长岩	3.08	99.81		1.68	1.04		0.87	2.20		682.9	82.8		257.3	28.23		163.0
A02		2.60	99.81		1.64	1.44		0.83	2.56		339.9	70.3		298.4	43.29		174.1
A03		2.75	99.84		1.53	1.41		0.89	2.43		349.8	74.1		320.5	36.32		167.9
A04		2.68	99.86		1.61	1.23		0.97	2.61		223.9	66.1		241.6	31.03		164.6
样号	岩性	Nb	Th		Pb	Ga		Zn	Cu		V	Cr		Hf	Ta		Co
A01	石英闪长岩	11.31	5.16		10.3	20.05		79.3	36.3		170.2	118.7		10.20	0.76		24.82
A02		11.17	2.94		6.3	19.99		91.9	46.8		184.0	117.2		11.40	0.65		29.92
A03		11.09	3.96		7.7	19.66		91.8	49.3		199.4	153.9		9.85	0.71		31.53
A04		10.39	13.81		9.4	16.78		75.0	33.4		161.5	115.9		9.55	0.85		23.54
样号	岩性	U	W		Mo	Bi		Ti	La		Ce	Pr		Nd	Sm		Eu
A01	石英闪长岩	0.87	0.62		0.30	0.09		4359	17.97		46.51	6.08		25.38	5.53		1.46
A02		0.56	0.44		0.30	0.07		5918	25.47		64.36	8.89		37.91	8.49		2.01
A03		0.76	0.63		0.31	0.09		5744	23.72		54.91	7.28		31.07	6.97		1.75
A04		0.94	0.81		0.29	0.20		4833	20.05		54.14	6.06		25.48	5.87		1.42
样号	岩性	Gd	Tb		Dy	Ho		Er	Tm		Yb	Lu		δEu	(La/Yb)_N		ΣLREE
A01	石英闪长岩	4.88	0.89		5.82	1.14		3.29	0.55		3.30	0.42		0.84	3.67		102.93
A02		7.48	1.37		8.98	1.74		5.09	0.82		4.89	0.64		0.75	3.51		147.13
A03		6.28	1.16		7.53	1.49		4.33	0.71		4.15	0.54		0.80	3.85		125.71
A04		5.15	0.96		6.34	1.22		3.60	0.58		3.42	0.46		0.77	3.96		113.01
样号	岩性	ΣHREE		ΣLREE/ΣHREE			ΣREE			T_Zr(℃)			10000×Ga / Al			Zr+Nb+Ce+Y
A01	石英闪长岩	20.30		5.07			123.22			748			1.37			249.1
A02		31.00		4.75			178.12			734			1.32			292.9
A03		26.19		4.80			151.89			740			1.27			270.2
A04		21.73		5.20			134.74			762			1.17			260.2