内蒙古乌兰乌台花岗闪长岩U-Pb年龄、地球化学特征及地质意义

doi:10.19657/j.geoscience.1000-8527.2020.052

摘要/Abstract

摘要：

内蒙古乌兰乌台花岗闪长岩位于兴蒙造山系内蒙古中部弧盆系锡林浩特岩浆弧中段。为探讨其成因类型和构造背景,开展了1:50 000区域地质调查工作,对其进行了年代学、岩石矿物学及岩石地球化学研究。结果表明,花岗闪长岩的LA-ICP-MS锆石U-Pb谐和年龄为(384.8±5.1) Ma,形成于晚泥盆世。主要矿物为斜长石、钾长石、石英、黑云母及角闪石,副矿物组合属锆石-钛铁矿-磷灰石型,此外还含少量独居石、磁铁矿,其矿物特征与Barbarin花岗岩分类中CPG(含堇青石过铝质花岗岩类)较相近。另外,乌兰乌台花岗闪长岩富钾(K₂O含量为3.10%~3.94 %),富铝(Al₂O₃为11.70%~12.89%),属过铝质岩石,其A/CNK=1.16~1.25,含黑云母,副矿物中含有磷灰石、独居石、钛铁矿,岩体见闪长岩包体,指示乌兰乌台花岗闪长岩可能来源于壳-幔混源岩浆,与西伯利亚板块同华北板块陆-陆碰撞有关。

关键词: 兴蒙造山带, 花岗闪长岩, U-Pb定年, 晚泥盆世, 陆-陆碰撞

Abstract:

The Wulanwutai granodiorite in Inner Mongolia is located in the middle part of Xilinhot magmatic arc of an arc-basin system, in the middle part of Xingmeng orogen. To discuss its genetic type and tectonic background, 1:50,000 regional geological survey was conducted and the petrology, mineralogy, geochronology and petrochemistry of the granodiorite were studied. The LA-ICP-MS zircon U-Pb age of (384.8±5.1) Ma indicates a Late Devonian granodiorite emplacement. The rocks mainly contain plagioclase, K-feldspar, quartz, biotite, and amphibole, with accessory zircon, ilmenite, apatite, monazite, and magnetite. The mineral contents resemble typical CPG (cordierite-bearing peraluminous granites) in Barbarin granite classification. In addition, the granodiorite is rich in K₂O(3.10%-3.94%) and Al₂O₃(11.70%-12.89%), and is peraluminous (A/CNK=1.16-1.25). The rocks also contain diorite xenolith. Hence, it is considered that the primary magma of the granodiorite may have derived from partial melting of a crust-mantle mixed source, and formed during the continent-continent collision between the Siberian and North China plates.

Key words: Xingmeng orogenic belt, granodiorite, U-Pb dating, Late Devonian, continent-continent collision

中图分类号:

P588.1
P597

程天赦, 杨文静, 张学斌, 吴荣泽, 周长红. 内蒙古乌兰乌台花岗闪长岩U-Pb年龄、地球化学特征及地质意义[J]. 现代地质, 2021, 35(05): 1231-1239.

CHENG Tianshe, YANG Wenjing, ZHANG Xuebin, WU Rongze, ZHOU Changhong. Zircon U-Pb Age and Geochemical Characteristics of the Granodiorite in Wulanwutai, Inner Mongolia and Its Geological Significance[J]. Geoscience, 2021, 35(05): 1231-1239.

图/表 11

图1 内蒙古大地构造分区及工作区位置

Fig.1 Tectonic division of Inner Mongolia and location of the study area

图2 乌兰乌台花岗闪长岩地质概图(实测) 1.第四系坡洪积物; 2.宝格达乌拉组;3.白音高老组流纹质熔结凝灰岩;4.哲斯组;5.大石寨组;6.寿山沟组;7.本巴图组;8.晚三叠世中细粒二长花岗岩;9.晚三叠世中粗粒花岗岩;10.中三叠世花岗斑岩;11.中三叠世斑状花岗岩;12.中三叠世中粗粒二长花岗岩;13.晚二叠世闪长岩;14.晚石炭世闪长岩;15.晚泥盆世花岗闪长岩;16.采样位置及编号

Fig.2 Sketch of the granodiorite in Wulanwutai

图3 花岗闪长岩显微结构(正交偏光,半自形粒状结构) Kfs.钾长石;Pl.斜长石;Qtz.石英;Am.角闪石云母

Fig.3 Photos showing the microstructure of the granodiorite (XPL)

图4 乌兰乌台花岗闪长岩锆石阴极发光图像(CL)及分析点位和年龄

Fig.4 Cathodoluminescence images and analysis spots of zircons from the Wulanwutai granodiorite sample

表1 乌兰乌台花岗闪长岩(样品WGHS.37)LA-ICP-MS锆石 Ub-Pb年龄分析结果

Table 1 LA-ICP-MS zircon U-Pb age data of the Wulanwutai granodiorite (sample WGHS.37)

测试点	同位素比值						年龄/Ma
测试点	²⁰⁶Pb/²³⁸U	²⁰⁷Pb/²³⁵U	²⁰⁷Pb/²⁰⁶Pb	²⁰⁸Pb/²³²Th	²³²Th/²³⁸U		²⁰⁶Pb/²³⁸U	1σ	²⁰⁷Pb/²³⁵U	1σ	²⁰⁷Pb/²⁰⁶Pb	1σ
1	0.06	0.54	0.06	0.02	0.41	390.4		3.5	440.0	13.2	708.6	61.7
2	0.07	0.51	0.06	0.04	0.12	408.2		5.5	419.3	10.5	480.8	58.6
3	0.06	0.51	0.06	0.04	0.19	381.8		4.3	420.6	19.3	639.8	95.7
4	0.06	0.54	0.06	0.03	0.17	393.0		3.8	435.5	8.4	667.0	38.5
5	0.06	0.57	0.06	0.03	0.42	396.2		3.6	455.1	9.3	764.4	42.0
6	0.06	0.46	0.06	0.02	0.27	375.3		3.4	384.5	9.3	440.4	53.9
7	0.07	0.53	0.06	0.02	0.51	423.0		4.1	430.8	14.8	472.5	75.6
8	0.06	0.50	0.06	0.02	0.33	378.8		4.0	414.5	11.2	618.5	60.0
9	0.06	0.52	0.06	0.05	0.21	375.7		7.7	427.0	32.9	714.0	143.1
10	0.06	0.50	0.06	0.03	0.21	397.4		3.7	411.8	14.3	493.3	75.0
11	0.06	0.50	0.06	0.01	0.96	399.6		5.0	414.0	6.8	495.0	39.4
12	0.06	0.44	0.05	0.02	0.26	371.4		4.2	372.0	6.7	375.7	43.0
13	0.06	0.46	0.06	0.02	0.44	374.6		3.9	381.2	14.0	421.4	81.3
14	0.06	0.46	0.05	0.02	0.41	380.7		3.9	381.5	14.9	386.2	84.4
15	0.07	0.55	0.06	0.03	0.61	431.5		4.6	444.0	14.2	509.2	73.7
16	0.06	0.45	0.05	0.02	0.26	383.0		3.5	380.3	11.1	363.7	63.0
17	0.06	0.48	0.05	0.02	0.37	396.0		5.8	396.7	12.7	401.3	70.1
18	0.06	0.45	0.05	0.02	0.33	374.0		4.3	375.2	6.7	382.6	39.0
19	0.06	0.50	0.06	0.02	0.18	401.5		4.8	414.3	9.3	486.6	49.3
20	0.06	0.45	0.05	0.02	0.34	375.3		4.2	380.3	7.4	410.8	42.5

图5 乌兰乌台花岗闪长岩锆石U-Pb测年结果

Fig.5 Zircon U-Pb concordia diagram (weighted average age in the inset diagram) for the Wulanwutai granodiorite

表2 乌兰乌台花岗闪长岩主量元素(%)、稀土元素(10-6)和微量元素(10-6)丰度

Table 2 Contents of major (%) and trace (incl. REE) elements (10-6) of the Wulanwutai granodiorite

样品编号	SiO₂	TiO₂	Al₂O₃	Fe₂O₃	FeO	FeO_t	MnO	MgO	CaO	Na₂O	K₂O	P₂O₅	总量	A/CNK
A01 A02	73.01 70.48	0.64 0.67	11.70 12.89	0.88 0.59	2.84 3.71	3.63 4.25	0.06 0.07	1.71 2.12	1.27 1.75	2.15 2.29	3.94 3.10	0.11 0.08	100.00 100.00	1.16 1.25
样品编号	Ba	Rb	Sr	Y	Zr	Nb	Th	Pb	Ga	Zn	Cu	V	Cr	Hf
A01 A02	481.20 376.90	212.00 194.50	89.45 134.00	34.13 45.89	195.00 234.10	16.33 20.02	22.01 41.22	20.04 22.04	16.06 19.03	51.36 68.74	15.64 19.23	76.33 94.09	50.05 63.17	7.07 8.61
样品编号	Ta	Co	U	W	Mo	Bi	Ti	La	Ce	Pr	Nd	Sm	Eu	Gd
A01 A02	1.50 1.85	11.04 12.45	3.07 2.90	1.88 2.02	0.39 0.26	0.44 0.48	3 813.39 4 029.24	33.02 67.62	72.66 127.08	8.12 15.97	31.36 57.60	6.65 10.86	1.03 1.19	5.98 9.09
样品编号	Tb	Dy	Ho	Er	Tm	Yb	Lu	δEu	LR/HR	(La/Yb)_N		LREE	HREE	REE
A01 A02	1.11 1.51	7.17 9.13	1.35 1.83	3.95 5.31	0.66 0.85	4.00 5.10	0.56 0.73	0.49 0.36	6.17 8.36	5.57 8.94		152.84 280.32	24.78 33.55	177.62 313.87

图6 乌兰乌台花岗闪长岩QAPF图解(底图据Streckeisen & Le Maitre[9]) 1.富石英花岗岩;2.碱性长石花岗岩;3.花岗岩;3a.钾长石花岗岩或普通花岗岩;3b.二长花岗岩;4.花岗闪长岩;5.英云闪长岩;6.石英碱性长石正长岩;7.石英二长岩;8.石英二长闪长岩;9.石英二长闪长岩/石英二长辉长岩;10.石英闪长岩/石英辉长岩;6*.碱性长石正长岩;7*.正长岩;8*.二长岩;9*.二长闪长岩/二长辉长岩;10*.闪长岩/辉长岩/斜长岩;6'.含似长石碱性长石正长岩;7'.含似长石正长岩;8'.含似长石二长岩;9'.含似长石二长岩/二长辉长岩;10'.含似长石闪长岩/辉长岩;11.似长石正长岩;12.似长二长正长岩;13.似长二长闪长岩;14.似长石辉长岩; 15.似长辉长岩;Q.石英;A.碱性长石;P.斜长石;F.似长石

Fig.6 QAPF diagram for the Wulanwutai granodiorite(base map after Streckeisen & Le Maitre[9])

图7 乌兰乌台花岗闪长岩AFM图解(底图据Brown[10])

Fig. 7 AFM diagram for the Wulanwutai granodiorite(base map after Brown[10])

图8 乌兰乌台花岗闪长岩稀土元素球粒陨石标准化配分曲线(a)和微量元素原始地幔标准化配分曲线(b)(底图据文献[10,11])

Fig.8 Chondrite-normalized REE distribution patterns and Primitive mantle-normalized trace elements distribution patterns of the granodiorite of Wulanwutai(base map after refs.[10,11])

图9 乌兰乌台花岗闪长岩(Y+Nb)-Rb(a)和Y-Nb(b)判别图解(底图据Pearce等[18]) Syn-COLG.同碰撞花岗岩;WPG.板内花岗岩;VAG.火山弧花岗岩;ORG.洋中脊花岗岩

Fig.9 (Y+Nb)-Rb (a) and Y-Nb (b) tectonic discrimination diagrams for the Wuherichulu granodiorite(base map after Pearce et al.[18] )

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