西藏雅拉香波早白垩世变质基性岩和斜长角闪岩的发现及其地质意义

doi:10.13745/j.esf.sf.2022.2.63

摘要/Abstract

摘要：

特提斯喜马拉雅带内雅拉香波地区首次发现白垩纪的变质基性岩。为进一步探讨雅拉香波变质基性岩的岩石成因、岩浆源区以及其经历的变质过程,本文报道了雅拉香波变质基性岩及斜长角闪岩岩石地球化学、锆石U-Pb年代学及电子探针成分数据。研究表明,雅拉香波变质基性岩锆石U-Pb等时线年龄为(127.97±0.47) Ma,形成于早白垩世。变质基性岩可分为弱变形(组1)和强变形(组2)两种类型。组1具有较低含量的SiO₂(41.82%~48.23%)、Na₂O(0.48%~3.06%)、K₂O(0.05%~0.12%),相对较高含量的Al₂O₃(11.31%~13.88%)、CaO(8.87%~15.36%)、MgO(4.62%~7.47%);相比于组1,组2的Al₂O₃含量(19.65%、22.46%)明显升高,MgO含量(3.26%、3.5%)降低,其他元素含量差异不大。斜长角闪岩的SiO₂含量为47.41%~48.53%,Na₂O(3.41%~3.84%)、K₂O(0.56%~0.6%)含量低,具有较高的Al₂O₃(13.98%~14.24%)、CaO(10.88%~11.40%)、MgO(6.12%~6.15%)含量。变质基性岩和斜长角闪岩均属于玄武岩,具有洋中脊玄武岩(MORB)的性质。组1和斜长角闪岩显示出平缓的稀土元素配分形式,与正常型洋中脊玄武岩(N-MORB)非常类似,而组2则具有富集型洋中脊玄武岩(E-MORB)的特征;地壳组分对变质基性岩的贡献很小,而斜长角闪岩表现出明显的壳源物质混染特征。雅拉香波变质基性岩为一退变质演化过程,经历了石榴子石相变质作用阶段及绿帘角闪岩相变质作用阶段。变质基性岩同时具有N-MORB和E-MORB的特征,在地球化学性质上可以与Comei大火成岩省内已报道的基性岩进行很好地对比,暗示它们具有相似的岩浆源区和地球动力学背景,形成于地幔柱活动条件下与大印度从澳大利亚裂解出来有关的伸展背景。

关键词: 地球化学, 锆石年代学, 基性岩浆活动, 雅拉香波, 特提斯喜马拉雅

Abstract:

Cretaceous metamorphic basic rocks have been discovered for the first time in the Yalaxiangbo area of the Tethyan Himalayan belt. In order to study their petrogenesis, magmatic source and metamorphism process, this paper reports the petrogeochemistry, zircon U-Pb geochronology and electron microprobe composition of Yalaxiangbo metamorphic basic rocks and plagioclase amphibolite. The metamorphic basic rocks have a zircon U-Pb isochron age of (127.97±0.47) Ma, indicating their formation in the early Cretaceous. They can be divided into two types: weak deformation (Group 1) and strong deformation (Group 2). Group 1 basic rocks have low contents of SiO₂ (41.82%-48.23%), Na₂O (0.48%-3.06%) and K₂O (0.05%-0.12%), and relatively high contents of Al₂O₃ (11.31%-13.88%), CaO (8.87%-15.36%) and MgO (4.62%-7.47%). Compared to Group 1, Group 2 rocks have significantly higher Al₂O₃ (19.65%-22.46%) and lower MgO (3.26%-3.5%) contents. In plagioclase amphibolite, SiO₂ content ranges from 47.41% to 48.53%, while the contents of Na₂O (3.41%-3.84%) and K₂O (0.56%-0.6%) are low, and the contents of Al₂O₃ (13.98%-14.24%), CaO (10.88%-11.40%) and MgO (6.12%-6.15%) are relatively high. The metamorphic basic rock and plagioclase amphibolite belong to basalts with the characteristics of mid-ocean ridge basalt (MORB). Group 1 rocks and plagioclase amphibolite show gentle REE patterns, which are similar to normal mid-ocean ridge basalts (N-MORB), while Group 2 rocks are characterized by enriched mid-ocean ridge basalts (E-MORB). The contribution of crustal components of metamorphic basic rocks is very small, while plagioclase amphibolite shows obvious contamination of crustal materials. The Yalaxiangbo metamorphic basics represent a retrograde metamorphic evolutionary process through stages of garnet and epidote-amphibolite facies metamorphism. Metamorphic basic rocks of Yalaxiangbo, with both N-MORB and E-MORB characteristics, can be well correlated with the known basic rocks of the Comei giant igneous province in terms of their geochemical properties, which suggest they share similar magmatic source and geodynamic background and formed in the extensional setting related to the splitting of great India from Australia controlled by mantle plume activity.

Key words: geochemistry, zircon geochronology, basic magmatism, Yalaxiangbo, Tethyan Himalayan

中图分类号:

P581
P597.3

赵晓燕, 杨竹森, 杨洋, 曹煜, 范建彪, 赵苗. 西藏雅拉香波早白垩世变质基性岩和斜长角闪岩的发现及其地质意义[J]. 地学前缘, 2023, 30(2): 163-182.

ZHAO Xiaoyan, YANG Zhusen, YANG Yang, CAO Yu, FAN Jianbiao, ZHAO Miao. Discovery of Early Cretaceous metamorphic basic rock and plagioclase amphibolite in Yalaxiangbo, Tibet and its geological significance[J]. Earth Science Frontiers, 2023, 30(2): 163-182.

图/表 15

图1 青藏高原和喜马拉雅地体区域构造简图图(a,b图据文献[13])及雅拉香波穹窿地质图(c图据文献[20])

Fig.1 Simplified tectonic map of (a) Tibetan Plateau and (b) Himalayan terrane (Fig.a and Fig.b adapted from [13]) and (c) geological map of the Yalaxiangbo dome (Fig.c adapted from [20])

图2 雅拉香波变质基性岩及斜长角闪岩岩石学特征 (a)变质基性岩野外露头;(b)弱变形的变质基性岩;(c)强变形的变质基性岩;(d)斜长角闪岩手标本特征;(e-f)弱变形的变质基性岩镜下特征,变质矿物包括石榴子石、角闪石,少量绿帘石;(g)强变形的变质基性岩,变质矿物主要由绿帘石和角闪石组成;(h)斜长角闪岩镜下特征,主要组成矿物为角闪石及斜长石。

Fig.2 Petrological characteristics of metamorphic basic rocks and amphibolites from Yalaxiangbo. (a) Outcrop of metamorphic basic rocks. (b) Weakly deformed metamorphic basic rocks. (c) Strongly deformed metamorphic basic rocks. (d) Hand specimens of amphibolite. (e-f) Microscopic characteristics of weakly deformed metamorphic basic rocks containing garnet, hornblende and a small amount of epidote. (g) Microscopic characteristics of strongly deformed metamorphic basic rocks composed of epidote and hornblende. (h) Microscopic characteristics of amphibolite composed of hornblende and plagioclase.

图3 雅拉香波变质基性岩锆石CL特征(a)及U-Pb年龄(b,c)

Fig.3 Zircon CL characteristics (a) and U-Pb ages (b, c) of Yalaxiangbo metamorphic basic rocks

表1 雅拉香波变质基性岩锆石U-Pb年龄

Table 1 Zircon U-Pb age of metamorphic basic rock in Yalaxiangbo

表2 雅拉香波变质基性岩和斜长角闪岩主微量元素组成

Table 2 Major (%) and trace element (10-6 ) compositions of metamorphic basic rock and plagioclase amphibolite from the Yalaxiangbo

图4 雅拉香波变质基性岩及斜长角闪岩Nb/Y-Zr/TiO2图解(a图据文献[23])、Co-Th图解(b图据文献[24])、Th/Yb-Zr/Y图解(c图据文献[25])及Zr-Ti图解(d图据文献[26])

Fig.4 Nb/Y-Zr/TiO2 (a, adapted from [23]), Co-Th (b, adapted from [24]), Th/Yb-Zr/Y (c, adapted from [25]) and Zr-Ti (d, adapted from [26]) diagrams for metamorphic basic rocks and plagioclase amphibolites from Yalaxiangbo

图5 雅拉香波变质基性岩及斜长角闪岩球粒陨石标准化稀土元素配分模式图(a)和原始地幔标准化微量元素蛛网图(b)(球粒陨石、原始地幔、OIB、N-MORB 和 E-MORB 数据来自文献[27])

Fig.5 Chondrite-normalized REEs (a) and primitive mantle-normalized trace elements (b) variation diagrams for metamorphic basic rock and plagioclase amphibolite from Yalaxiangbo. Chondrite, primitive mantle, OIB, N-MORB and E-MORB data from [27].

表3 变质基性岩中石榴子石电子探针成分

Table 3 Electron probe composition of garnet from metamorphic basic rock in Yalaxiangbo

样品号	w_B/%
样品号	SiO₂	Na₂O		K₂O			Cr₂O₃	Al₂O₃			MgO		CaO		MnO		TiO₂			FeO	P₂O₅		NiO			总和
YLXB18-1-6	37.36	0.02		0.01			0.03	20.89			0.67		10.97		3.57		0.20			26.28	0.01		0.00			99.98
	37.26	0.01		0.01			0.00	20.77			0.55		10.17		6.46		0.15			23.70	0.02		0.01			99.11
	36.97	0.00		0.01			0.00	20.66			0.55		10.48		5.63		0.20			24.63	0.00		0.03			99.17
	37.40	0.05		0.00			0.00	20.83			0.88		10.25		1.82		0.18			28.12	0.02		0.07			99.61
	36.69	0.00		0.00			0.00	21.02			0.64		10.49		4.27		0.18			26.81	0.00		0.04			100.14
	37.17	0.02		0.01			0.04	20.40			0.54		10.22		5.71		0.24			24.82	0.00		0.01			99.16
	37.48	0.01		0.00			0.00	20.79			0.51		10.28		6.19		0.19			24.16	0.05		0.00			99.65
	37.62	0.02		0.00			0.00	20.75			0.75		10.35		2.89		0.19			27.46	0.02		0.00			100.04
样品号	以23个氧为基础计算的阳离子数
样品号	阳离子应带电荷Si		阳离子应带电荷Ti			阳离子应带电荷Al				阳离子应带电荷Cr		Fe³⁺				Fe²⁺			阳离子应带电荷Mn			阳离子应带电荷Mg			阳离子应带电荷Ca
YLXB18-1-6	2.99		0.01			1.97				0.00		0.02				1.74			0.24			0.08			0.94
	3.02		0.01			1.98				0.00		-0.03				1.63			0.44			0.07			0.88
	2.99		0.01			1.97				0.00		0.02				1.64			0.39			0.07			0.91
	3.01		0.01			1.97				0.00		-0.01				1.91			0.12			0.11			0.88
	2.94		0.01			1.98				0.00		0.11				1.68			0.29			0.08			0.90
	3.01		0.01			1.95				0.00		0.00				1.68			0.39			0.06			0.89
	3.02		0.01			1.97				0.00		-0.03				1.66			0.42			0.06			0.89
	3.01		0.01			1.96				0.00		-0.01				1.85			0.20			0.09			0.89
样品号	各成分含量/%
样品号	铁铝榴石				钙铝榴石				锰铝榴石					镁铝榴石				钙铁榴石						钙铬榴石
YLXB18-1-6	57.95				31.01				8.05					2.66				0.30						0.02
	54.00				29.61				14.65					2.19				-0.44						0.00
	54.70				29.88				12.85					2.21				0.36						0.00
	63.13				29.47				4.11					3.50				-0.21						0.00
	57.06				28.87				9.83					2.60				1.64						0.00
	55.61				29.29				12.94					2.14				-0.02						0.04
	54.79				29.77				13.93					2.01				-0.50						0.00
	61.20				29.54				6.49					2.95				-0.18						0.00

表4 变质基性岩中绿帘石电子探针成分

Table 4 Electron probe composition of epidote from metamorphic basic rock in Yalaxiangbo

样品号	w_B/%
样品号	SiO₂	Na₂O	K₂O	Cr₂O₃	Al₂O₃	MgO	CaO	MnO	TiO₂	FeO	P₂O₅	NiO	总和	Fe₂O₃	XFe
YLXB18-1-6	38.22	0.03	0.01	0.03	26.28	0.01	23.53	0.03	0.09	8.22	0.01	0.01	96.46	9.13	0.26
	38.72	0.00	0.00	0.00	26.46	0.01	23.45	0.16	0.13	7.99	0.03	0.03	96.97	8.88	0.25
	38.54	0.01	0.01	0.04	26.23	0.01	23.55	0.09	0.07	8.32	0.04	0.00	96.90	9.25	0.26
	38.29	0.02	0.00	0.00	25.97	0.00	23.58	0.00	0.12	8.21	0.03	0.00	96.20	9.12	0.26
	38.74	0.02	0.01	0.05	26.28	0.01	23.42	0.09	0.04	7.94	0.00	0.00	96.61	8.82	0.25
	38.70	0.00	0.00	0.05	26.55	0.01	23.27	0.07	0.12	8.08	0.01	0.00	96.85	8.98	0.25
	38.40	0.00	0.00	0.00	26.57	0.01	23.53	0.05	0.08	7.74	0.00	0.04	96.43	8.60	0.24
	38.51	0.00	0.00	0.03	26.80	0.01	23.54	0.09	0.00	7.75	0.03	0.01	96.77	8.62	0.24
	38.36	0.03	0.01	0.02	26.61	0.00	23.44	0.16	0.07	7.92	0.06	0.06	96.73	8.80	0.25
	38.56	0.02	0.01	0.00	26.28	0.01	23.52	0.12	0.07	8.25	0.04	0.00	96.88	9.17	0.26
YLXB18-2-1	38.20	0.00	0.00	0.05	26.41	0.00	23.62	0.10	0.05	7.92	0.04	0.00	96.40	8.81	0.25
	38.44	0.00	0.02	0.04	26.87	0.04	23.37	0.27	0.18	7.07	0.03	0.04	96.37	7.86	0.23
	38.35	0.00	0.01	0.00	26.40	0.03	23.52	0.13	0.11	7.88	0.03	0.00	96.45	8.76	0.25
	38.67	0.01	0.01	0.04	26.40	0.00	23.63	0.06	0.03	7.68	0.02	0.01	96.56	8.53	0.24
	38.38	0.00	0.01	0.01	26.47	0.01	23.50	0.22	0.03	7.75	0.00	0.03	96.40	8.61	0.25
	38.82	0.02	0.01	0.00	26.55	0.00	23.55	0.07	0.04	7.97	0.02	0.00	97.04	8.86	0.25
	38.62	0.00	0.01	0.09	26.53	0.02	23.47	0.10	0.04	7.81	0.01	0.00	96.68	8.68	0.25
	38.56	0.01	0.01	0.03	26.62	0.00	23.51	0.05	0.07	7.94	0.04	0.00	96.82	8.82	0.25
	38.86	0.00	0.00	0.06	26.60	0.01	23.56	0.14	0.06	8.08	0.00	0.00	97.37	8.98	0.25
YLXB18-3-1	38.84	0.00	0.00	0.02	27.12	0.02	23.63	0.01	0.03	7.47	0.01	0.04	97.18	8.30	0.23
	38.67	0.03	0.00	0.00	27.08	0.01	23.74	0.11	0.11	7.22	0.06	0.01	97.03	8.03	0.23
	38.66	0.00	0.01	0.00	27.87	0.01	23.38	0.15	0.06	6.42	0.12	0.03	96.68	7.13	0.20
	38.93	0.00	0.01	0.05	27.18	0.02	23.61	0.05	0.08	6.98	0.07	0.00	96.96	7.76	0.22
	38.64	0.03	0.01	0.03	27.33	0.04	23.69	0.12	0.18	6.46	0.01	0.03	96.56	7.18	0.21
	38.71	0.00	0.01	0.04	27.42	0.03	23.42	0.11	0.04	6.65	0.03	0.02	96.48	7.39	0.21
	38.72	0.00	0.00	0.07	27.35	0.02	23.55	0.09	0.06	6.44	0.07	0.00	96.36	7.15	0.21
	38.74	0.03	0.00	0.00	27.44	0.02	23.48	0.08	0.01	6.83	0.03	0.04	96.68	7.58	0.22
YLXB18-5-1	38.27	0.03	0.00	0.00	27.01	0.02	23.28	0.14	0.14	6.99	0.03	0.00	95.89	7.76	0.22
	38.70	0.00	0.00	0.05	26.74	0.02	23.50	0.05	0.10	7.63	0.05	0.00	96.84	8.48	0.24
	38.67	0.02	0.01	0.01	26.95	0.03	23.53	0.09	0.08	7.39	0.00	0.00	96.76	8.21	0.23
	38.95	0.00	0.00	0.02	28.39	0.05	23.64	0.09	0.25	5.33	0.00	0.03	96.75	5.93	0.17
	38.35	0.00	0.00	0.00	26.77	0.01	23.46	0.10	0.14	7.45	0.03	0.00	96.31	8.28	0.24
	38.40	0.02	0.00	0.02	27.03	0.04	23.48	0.07	0.07	6.44	0.02	0.05	95.65	7.15	0.21
	38.59	0.00	0.00	0.03	27.72	0.02	23.63	0.06	0.02	6.38	0.06	0.02	96.53	7.09	0.20
	38.51	0.00	0.00	0.00	27.06	0.00	23.64	0.01	0.14	6.85	0.03	0.00	96.23	7.61	0.22

表4 变质基性岩中绿帘石电子探针成分

Table 4 Electron probe composition of epidote from metamorphic basic rock in Yalaxiangbo

样品号	w_B/%
样品号	SiO₂	Na₂O	K₂O	Cr₂O₃	Al₂O₃	MgO	CaO	MnO	TiO₂	FeO	P₂O₅	NiO	总和	Fe₂O₃	XFe
YLXB18-1-6	38.22	0.03	0.01	0.03	26.28	0.01	23.53	0.03	0.09	8.22	0.01	0.01	96.46	9.13	0.26
	38.72	0.00	0.00	0.00	26.46	0.01	23.45	0.16	0.13	7.99	0.03	0.03	96.97	8.88	0.25
	38.54	0.01	0.01	0.04	26.23	0.01	23.55	0.09	0.07	8.32	0.04	0.00	96.90	9.25	0.26
	38.29	0.02	0.00	0.00	25.97	0.00	23.58	0.00	0.12	8.21	0.03	0.00	96.20	9.12	0.26
	38.74	0.02	0.01	0.05	26.28	0.01	23.42	0.09	0.04	7.94	0.00	0.00	96.61	8.82	0.25
	38.70	0.00	0.00	0.05	26.55	0.01	23.27	0.07	0.12	8.08	0.01	0.00	96.85	8.98	0.25
	38.40	0.00	0.00	0.00	26.57	0.01	23.53	0.05	0.08	7.74	0.00	0.04	96.43	8.60	0.24
	38.51	0.00	0.00	0.03	26.80	0.01	23.54	0.09	0.00	7.75	0.03	0.01	96.77	8.62	0.24
	38.36	0.03	0.01	0.02	26.61	0.00	23.44	0.16	0.07	7.92	0.06	0.06	96.73	8.80	0.25
	38.56	0.02	0.01	0.00	26.28	0.01	23.52	0.12	0.07	8.25	0.04	0.00	96.88	9.17	0.26
YLXB18-2-1	38.20	0.00	0.00	0.05	26.41	0.00	23.62	0.10	0.05	7.92	0.04	0.00	96.40	8.81	0.25
	38.44	0.00	0.02	0.04	26.87	0.04	23.37	0.27	0.18	7.07	0.03	0.04	96.37	7.86	0.23
	38.35	0.00	0.01	0.00	26.40	0.03	23.52	0.13	0.11	7.88	0.03	0.00	96.45	8.76	0.25
	38.67	0.01	0.01	0.04	26.40	0.00	23.63	0.06	0.03	7.68	0.02	0.01	96.56	8.53	0.24
	38.38	0.00	0.01	0.01	26.47	0.01	23.50	0.22	0.03	7.75	0.00	0.03	96.40	8.61	0.25
	38.82	0.02	0.01	0.00	26.55	0.00	23.55	0.07	0.04	7.97	0.02	0.00	97.04	8.86	0.25
	38.62	0.00	0.01	0.09	26.53	0.02	23.47	0.10	0.04	7.81	0.01	0.00	96.68	8.68	0.25
	38.56	0.01	0.01	0.03	26.62	0.00	23.51	0.05	0.07	7.94	0.04	0.00	96.82	8.82	0.25
	38.86	0.00	0.00	0.06	26.60	0.01	23.56	0.14	0.06	8.08	0.00	0.00	97.37	8.98	0.25
YLXB18-3-1	38.84	0.00	0.00	0.02	27.12	0.02	23.63	0.01	0.03	7.47	0.01	0.04	97.18	8.30	0.23
	38.67	0.03	0.00	0.00	27.08	0.01	23.74	0.11	0.11	7.22	0.06	0.01	97.03	8.03	0.23
	38.66	0.00	0.01	0.00	27.87	0.01	23.38	0.15	0.06	6.42	0.12	0.03	96.68	7.13	0.20
	38.93	0.00	0.01	0.05	27.18	0.02	23.61	0.05	0.08	6.98	0.07	0.00	96.96	7.76	0.22
	38.64	0.03	0.01	0.03	27.33	0.04	23.69	0.12	0.18	6.46	0.01	0.03	96.56	7.18	0.21
	38.71	0.00	0.01	0.04	27.42	0.03	23.42	0.11	0.04	6.65	0.03	0.02	96.48	7.39	0.21
	38.72	0.00	0.00	0.07	27.35	0.02	23.55	0.09	0.06	6.44	0.07	0.00	96.36	7.15	0.21
	38.74	0.03	0.00	0.00	27.44	0.02	23.48	0.08	0.01	6.83	0.03	0.04	96.68	7.58	0.22
YLXB18-5-1	38.27	0.03	0.00	0.00	27.01	0.02	23.28	0.14	0.14	6.99	0.03	0.00	95.89	7.76	0.22
	38.70	0.00	0.00	0.05	26.74	0.02	23.50	0.05	0.10	7.63	0.05	0.00	96.84	8.48	0.24
	38.67	0.02	0.01	0.01	26.95	0.03	23.53	0.09	0.08	7.39	0.00	0.00	96.76	8.21	0.23
	38.95	0.00	0.00	0.02	28.39	0.05	23.64	0.09	0.25	5.33	0.00	0.03	96.75	5.93	0.17
	38.35	0.00	0.00	0.00	26.77	0.01	23.46	0.10	0.14	7.45	0.03	0.00	96.31	8.28	0.24
	38.40	0.02	0.00	0.02	27.03	0.04	23.48	0.07	0.07	6.44	0.02	0.05	95.65	7.15	0.21
	38.59	0.00	0.00	0.03	27.72	0.02	23.63	0.06	0.02	6.38	0.06	0.02	96.53	7.09	0.20
	38.51	0.00	0.00	0.00	27.06	0.00	23.64	0.01	0.14	6.85	0.03	0.00	96.23	7.61	0.22

表5 变质基性岩及斜长角闪岩中角闪石电子探针成分

Table 5 Electron probe composition of hornblende from metamorphic basic rock and plagioclase amphibolite in Y alaxiangbo

图6 雅拉香波变质基性岩及斜长角闪岩中角闪石Si-Mg/(Mg+Fe2+)分类图解(底图据文献[30])

Fig.6 Si-Mg/(Mg+Fe2+) classification diagram for hornblende in metamorphic basic rocks and amphibolites from Yalaxiangbo. Adapted from [30].

图7 雅拉香波变质基性岩及斜长角闪岩(Th/Nb)PM -(La/Nb)PM图解 (底图据文献[34];MC—中地壳和LC—下地壳据文献[31])

Fig.7 (Th/Nb)PM vs. (La/Nb)PM diagram for metamorphic basic rocks and amphibolites from Yalaxiangbo (adapted from [34]). MC (middle crust) and LC (lower crust) data from [31].

图8 雅拉香波变质基性岩及斜长角闪岩La-La/Sm(a)和La-La/Zr(b)图解

Fig.8 La-La/Sm (a) and La-La/Zr (b) diagrams for metamorphic basic rock and plagioclase amphibolite from Yalaxiangbo

图9 雅拉香波变质基性岩及斜长角闪岩La/Yb-Dy/Yb(a)和La/Sm-Sm/Yb(b)图解图中熔融曲线运用[40]批式熔融模型计算得到[41],每条曲线上的数字对应给定源区部分熔融程度(%),亏损的MORB地幔(DMM)、富集的DMM(E-DMM)据文献[42],原始地幔数据据文献[27]。

Fig.9 La/Yb-Dy/Yb (a) and La/Sm-Sm/Yb (b) diagrams for metamorphic basic rocks and plagioclase amphibolites from Yalaxiangbo, showing the partial melting curves obtained using the nonmodal batch melting equations. Tick marks on each curve correspond to degrees of partial melting (%) for a given mantle source. Depleted MORB mantle (DMM) and enriched DMM (E-DMM) compositions from [42]; primitive mantle compositions from [27].

图10 雅拉香波变质基性岩及斜长角闪岩构造判别图解 (a)Th/Yb-Nb/Yb图解,底图据文献[26];(b)2Nb-Zr/4-Y图解,底图据文献[44],A1—板内碱性玄武岩,A2—板内碱性玄武岩+板内拉斑玄武岩,B—E-MORB,C—板内拉斑玄武岩+火山弧玄武岩,D—火山弧玄武岩+N-MORB;(c)Hf/3-Th-Ta和(d)Hf/3-Th-Nb/16图解,底图据文献[45],A—正常洋中脊玄武岩,B—富集型洋中脊玄武岩或板内拉斑玄武岩,C—板内碱性玄武岩,D—岛弧拉斑玄武岩。

Fig.10 Discrimination diagram of tectonic setting for metamorphic basic rocks and plagioclase amphibolites from Yalaxiangbo. (a) Th/Yb-Nb/Yb diagram (adapted from [26]). (b) 2Nb-Zr/4-Y diagram (adapted from [44]). A1—Intraplate alkaline basalt; A2—Intraplate alkaline basalt + Intraplate tholeiite. B—E-MORB; C—Intraplate tholeiite + Volcanic arc basalt; D—Volcanic arc basalt + N-MORB. (c) Hf/3-Th-Ta diagram (adapted from [45]). (d) Hf/3-Th-Nb/16 diagrams (adapted from [45]). A—N-MORB; B—E-MORB/Intraplate tholeiite; C—Intraplate alkaline basalt; D—Island arc tholeiite.

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