西南印度洋中脊玄武岩地球化学特征及其对岩浆过程的指示意义

韩宗珠; 孙苑高; 王传; 孙晓霞; 刘明; 来志庆

doi:10.16028/j.1009-2722.2020.045

西南印度洋中脊玄武岩地球化学特征及其对岩浆过程的指示意义

1.
中国海洋大学海洋地球科学学院，青岛 266100

2.
海底科学与探测技术教育部重点实验室，青岛 266100

基金项目: 国家自然科学基金（41376053）；山东省自然科学基金（ZR2017PD002）

详细信息

作者简介: 韩宗珠（1964—），男，教授，主要从事岩石学和地球化学方面的研究工作. E-mail：hanzongzhu@ouc.edu.cn

中图分类号: P736.4；P595

收稿日期: 2020-05-06

刊出日期: 2021-01-31

GEOCHEMICAL CHARACTERISTICS OF THE MORBS OF THE SWIR AND THEIR IMPLICATIONS FOR MAGMATIC PROCESS

1.
College of Marine Geosciences, Ocean University of China, Qingdao 266100, China

2.
Key Laboratory of Submarine Geosciences and Prospecting Techniques, Qingdao 266100, China

Received Date: 06 May 2020

Publish Date: 31 January 2021

摘要

摘要:
对采自西南印度洋中脊（SWIR）50°E附近5个站位的玄武岩样品进行了岩石学和元素地球化学研究。样品主量元素、TAS分类图解和AFM图解显示，SWIR研究区样品类型主要为低钾拉斑玄武岩。相对原始地幔SWIR区玄武岩具有Ba、Nb、Sr负异常，K表现为正异常。稀土元素分配模式均为左倾型，具有轻微的Eu、Ce正异常；SWIR区玄武岩都起源于上地幔，SWIR玄武岩则明显向EMⅡ端元偏移。SWIR玄武岩地幔源区相对最为富集，可能为DM和EMⅡ的混合源区，存在少量的陆壳成分。研究区玄武质岩浆起源深度为尖晶石橄榄岩区域处于中度还原环境下，经历了明显的橄榄石+单斜辉石+斜长石的分离结晶。
- 西南印度洋中脊 /
- 地球化学 /
- 玄武岩 /
- 岩浆过程 /
- 结晶分异
Abstract:
Five fresh MORBs samples collected from the 50°E of the SWIR have been studied for petrology and geochemistry. The major elements, TAS and AFM diagrams suggest that the samples from the SWIR are dominated by low potassic tholeiite. The primitive mantle-normalized sprider diagram shows negative anomalies of Ba, Nb and Sr, while K is positive in all of the samples. The MORBs of the SWIR show a depleted pattern of light REE in chondrite-normalized REE diagram, with slightly positive Eu and Ce anomalies; The MORBs from the SWIR are all derived from the upper mantle and obviously migrate to the end member of EMII. Most of the SWIR basalts enriched in the region are sourced from mantle. It is composed of both DM and EMII, includes small amount of continental crustal components. The basaltic magmas of SWIR are originated from the spinel peridotite zone. The samples of the SWIR are formed under a moderate reducing environment, experienced obvious fractional crystallization from olivine, clinopyroxene to plagioclase.
- SWIR /
- Geochemistry /
- basalt /
- magmatic processes /
- crystallization differentiation

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图 1 西南印度洋洋中脊岩石类型分布图^[12]

Figure 1.

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图 2 SWIR研究区玄武岩代表性样品偏光镜下特征

Figure 2.

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图 3 SWIR研究区玄武岩TAS分类图

Figure 3.

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图 4 SWIR研究区玄武岩AFM图解

Figure 4.

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图 5 稀土元素球粒陨石标准化配分模式及微量元素原始地幔标准化蛛网图

Figure 5.

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图 6 SWIR研究区玄武岩Nb*-Ta*、εNd-⁸⁷Sr/⁸⁶Sr图解

Figure 6.

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图 7 SWIR玄武岩εNd-²⁰⁶Pb/²⁰⁴Pb、²⁰⁶Pb/²⁰⁴Pb -⁸⁷Sr/⁸⁶Sr、²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb图解

Figure 7.

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图 8 SWIR玄武岩（Tb/Yb）_N-（La/Sm）_N图解^[29]

Figure 8.

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图 9 ¹⁴³Nd/¹⁴⁴Nd-⁸⁷Sr/⁸⁶Sr图解^[27]

Figure 9.

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图 10 SWIR玄武岩（La/Yb）_N-（Dy/Yb）_N和La/Yb-Yb图解

Figure 10.

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图 11 SWIR玄武岩CaO/Al₂O₃-Na₈图解

Figure 11.

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表 1 SWIR研究区样品采样位置及采样方法

Table 1. Sample locations from SWIR and sampling methods

样品编号	经度	纬度	采样方式
B01	50.42585°E	37.60980°S	电视抓斗
B03	50.37599°E	37.552317°S
B04	50.46777°E	37.67918°S
B05	50.47244°E	37.67936°S
S31	48.5802°E	38.13244°S

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表 2 SWIR研究区玄武岩元素地球化学数据分析结果

Table 2. Element geochemistry of the basalt in the study area

元素/指标		B01	B03	B04	B05	S31
主量元素/%	SiO₂	47.13	43.72	48.93	48.4	48.04
	TiO₂	1.52	1.41	1.4	1.43	1.14
	Fe₂O₃	14.67	12.72	12.83	13.57	14.62
	MgO	8.36	5.96	7.76	8.63	10.98
	Al₂O₃	12.21	14.94	14.57	13.61	13.36
	Na₂O	3.33	3.46	3.35	3.67	3.43
	CaO	10.77	12.48	11.13	11.29	10.65
	K₂O	0.28	0.35	0.37	0.28	0.31
	MnO	0.21	0.45	0.19	0.21	0.37
	P₂O₅	0.15	0.22	0.15	0.17	0.13
	Total	98.63	95.71	100.68	101.26	103.03
	Mg#	53	48	55	56	60
微量元素/10⁻⁶	Ba	14.4	21	25.07	26.95	17.1
	Cr	231.85	248.65	290.85	326.87	576.19
	Ni	89.14	95.99	114.65	117.82	220.23
	Sr	111.27	226.37	96.58	96.38	94.72
	V	431.92	426.03	393.05	411.36	346.54
	Nb	1.89	3.73	2.82	3.66	4.84
	Ta	0.13	0.12	0.15	0.15	0.16
	Hf	3.78	7.08	2.23	2.15	1.74
	Zr	89.67	78.96	78.6	74.9	57.4
稀土元素/10⁻⁶	La	2.84	7.49	2.14	2.32	3.48
	Ce	8.77	27.6	7.22	7.42	14.6
	Pr	1.62	2.47	1.41	1.46	1.39
	Nd	8.9	12.24	8.12	8.28	7.35
	Sm	3.21	3.78	3.04	3.1	2.54
	Eu	1.22	1.36	1.16	1.17	0.98
	Gd	3.69	4.37	3.54	3.49	3.02
	Tb	0.81	0.91	0.78	0.78	0.65
	Dy	5.72	6.3	5.52	5.64	4.54
	Ho	1.29	1.41	1.25	1.27	1.02
	Er	3.57	3.92	3.52	3.57	2.83
	Tm	0.57	0.61	0.56	0.57	0.45
	Yb	3.54	3.89	3.6	3.67	2.91
	Lu	0.57	0.64	0.59	0.58	0.47
	∑REE	46.31	76.99	42.45	43.32	46.22
	LREE/HREE	1.34	2.49	1.19	1.21	1.91
	La_N/Yb_N	0.54	1.3	0.4	0.43	0.81
	δEu	1.08	1.02	1.08	1.08	1.08
	δCe	0.97	1.54	0.97	0.94	1.6

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表 3 SWIR研究区玄武岩Sr-Nd-Pb同位素分析结果

Table 3. The analysis results of Sr-Nd-Pb isotope on the SWIR

同位素	B04	B05	S31	DM	EM	HIMU	N-MORB
²⁰⁸Pb/²⁰⁴Pb	38.282 1	38.529 4	38.746 3	37.2～37.4	38～38.2		37.891
2SE	0.005 5	0.001 9	0.002
²⁰⁷Pb/²⁰⁴Pb	15.563 2	15.623 6	15.649 8	15.4	15.46～15.49		15.485
2SE	0.002	0.000 7	0.000 7
²⁰⁶Pb/²⁰⁴Pb	18.327 2	18.377 6	18.706 1	17.2～17.7	17.6～17.7	>20.8	18.6
2SE	0.002 2	0.000 7	0.000 8
²⁰⁸Pb/²⁰⁶Pb	2.088 81	2.096 5	2.071 2
2SE	0.000 07	0.000 05	0.000 04
²⁰⁷Pb/²⁰⁶Pb	0.849 19	0.850 1	0.836 5
2SE	0.000 02	0.000 01	0.000 01
⁸⁷Sr/⁸⁶Sr	0.702 692	0.702 7	0.704 1	0.702～0.702 4	0.704 5～0.706	0.702 9	0.702 84
±2σ	14	15	12
¹⁴³Nd/¹⁴⁴Nd	0.513 126	0.513 1	0.512 9	0.513 1～0.513 3	0.511 2	<0.512 8	0.513 13
±2σ	6	14	8
εNd（t）	9.519 388	9.285 3	5.715 5
注：DM、EM、HIMU数据来自ZINDLER等^[17]和WEAVER^[18]；N-MORB数据来自ITO和李彬贤^[19]。

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表 4 SWIR玄武岩部分熔融程度

Table 4. The partial melting of the SWIR basalt

/%
采样位置	样品号	Na₈	Ca₈	Al₈	F
SWIR	B01	3.39	10.57	11.89	15.45
	B03	3.03	14.29	16.78	16.76
	B04	3.31	11.28	14.79	13.95
	B05	3.78	10.98	13.07	12.69
	S31	3.95	10.64	11.97	12.57

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西南印度洋中脊玄武岩地球化学特征及其对岩浆过程的指示意义

1. 中国海洋大学海洋地球科学学院，青岛 266100 2. 海底科学与探测技术教育部重点实验室，青岛 266100

作者简介: 韩宗珠（1964—），男，教授，主要从事岩石学和地球化学方面的研究工作. E-mail：hanzongzhu@ouc.edu.cn

GEOCHEMICAL CHARACTERISTICS OF THE MORBS OF THE SWIR AND THEIR IMPLICATIONS FOR MAGMATIC PROCESS

1. College of Marine Geosciences, Ocean University of China, Qingdao 266100, China 2. Key Laboratory of Submarine Geosciences and Prospecting Techniques, Qingdao 266100, China

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1.
中国海洋大学海洋地球科学学院，青岛 266100

2.
海底科学与探测技术教育部重点实验室，青岛 266100

1.
College of Marine Geosciences, Ocean University of China, Qingdao 266100, China

2.
Key Laboratory of Submarine Geosciences and Prospecting Techniques, Qingdao 266100, China