藏东卡贡地区早侏罗世似斑状钾长花岗岩LA-ICP-MS锆石U-Pb年龄及地球化学特征

于涛; 徐佳丽; 高强; 樊炳良; 徐长昊

藏东卡贡地区早侏罗世似斑状钾长花岗岩LA-ICP-MS锆石U-Pb年龄及地球化学特征

于涛^1,,
徐佳丽^2, ,,
高强³,
樊炳良⁴,
徐长昊⁵

1.
西藏大学理学院, 西藏拉萨 850000
2.
中国地质大学(武汉)环境学院, 湖北武汉 430074
3.
河北省地矿局第四地质大队, 河北承德 067000
4.
西藏自治区地质矿产勘查开发局地热地质大队, 西藏拉萨 850000
5.
成都理工大学地球科学学院, 四川成都 610059

基金项目:

中国地质调查局项目《西藏卡贡地区1:5万四幅区域地质调查》 DD20160016-21

详细信息

作者简介:
于涛(1987-), 男, 硕士, 讲师, 从事地理教学和固体勘查勘查工作。E-mail:1034125709@qq.com

通讯作者:
徐佳丽(1983-), 女, 博士, 讲师, 从事环境地质分析测试工作。E-mail:52094108@qq.com

中图分类号: P534.52;P588.12
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出版历程
- 收稿日期: 2019-05-05
- 修回日期: 2019-07-07
- 网络出版日期: 2023-08-15
- 刊出日期: 2020-05-14

LA-ICP-MS zircon U-Pb age and geological characteristics of the Early Jurassic potassium porphyritic granites in Kargang area, eastern Tibet

1.
College of Science, Tibet University, Lhasa 850000, Tibet, China
2.
School of environmental studies, China University of Geosciences(Wuhan), Wuhan 430074, Hubei, China
3.
The Fourth Geological Brigade of Hebei Geological and Mining Bureau, Chengde 067000, Hebei, China
4.
Geothermal Geological Survey Party, Tibet Bureau of Geology and Mineral Exploration and Development, Lhasa 850000, Tibet, China
5.
Department of Geology College of Earth Sciences, Chengdu University of Technology, Chengdu 610059, Sichuan, China

摘要

摘要:
用LA-ICP-MS技术测得卡贡地区似斑状钾长花岗岩锆石的²⁰⁶Pb/²³⁸U年龄为178±2 Ma（MSWD=3.7，n=20），属于早侏罗世的产物。岩石地球化学特征表明，岩石具富碱富钾（K₂O+Na₂O=8.02%~8.76%，K₂O/Na₂O=1.71~2.11）、低铝（Al₂O₃=14.08%~14.73%，A/CNK=1.01~1.04），不含透辉石和刚玉分子较低的特征；岩石普遍富集Rb、Th、K、U等大离子亲石元素，明显亏损Ba、Nb、Sr、P、Ti等元素，高场强元素Zr、Nb、Ta含量极低，（Ga/Al）×10⁴值为4.48~5.06，Rb/Sr值为1.84~2.29，均显示出岩浆分异程度较高的特征；岩石的形成与俯冲消减作用有关，其构造环境由挤压环境逐渐向相对伸展环境转变，伴随着地壳深部压力减小，幔源岩浆上涌，并与上覆地壳发生部分熔融作用而形成。
- 似斑状钾长花岗岩 /
- 地球化学特征 /
- 锆石U-Pb /
- LA-ICP-MS /
- 岩石成因
Abstract:
In this paper, LA-ICP-MS zircon U-Pb age test was carried out on the potassium porphyritic granites in the Kargang area, which shows that the ²⁰⁶Pb/²³⁸U age weighted average value of the rock mass is 178±2 Ma(MSWD=3.7, n=20), suggesting a product of Early Jurassic.The geochemical characteristics of the rocks show that the rocks have alkali-rich potassium(K₂O+Na₂O=8.02%~8.76%, K₂O/Na₂O=1.71~2.11), but low aluminum(Al₂O₃=14.08%~14.73%, A/CNK=1.01~1.04), without pyroxene and with lower corundum molecules.The rocks are generally characterized by rich Rb, Th, K, U and other large ionic pro-stone elements, obvious loss of Ba, Nb, Sr, P, Ti and other elements, and very low values of high field strength elements Zr, Nb, with(Ga/Al)×10⁴ values of 4.48~5.06 and Rb/Sr ratios of 1.84~2.29, which shows the characteristics of high magma differentiation; in addition, the formation of rocks was related to subduction reduction, and its tectonic environment changed gradually from extrusion environment to relative stretching environment, accompanied by the decrease of deep crustal pressure, which led to the upwelling of mantle source magma and the partial melting of the overlying crust.
- potassium porphyritic granites /
- geochemical characteristics /
- zircon U-Pb /
- LA-ICP-MS /
- rock genesis

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图 1 研究区大地构造位置图(a)和区域地质简图(b)(据参考文献[3]修改)

1—上三叠统-侏罗系碎屑岩；2—上三叠统碎屑岩；3—中三叠统竹卡组安山岩、岩屑凝灰岩；4—下石炭统卡贡组变质砂岩、千枚岩；5—下石炭统卡贡岩组变质砂岩、千枚岩夹大理岩、玄武岩岩块；6—下石炭统邦达岩组+错绒沟口岩组变质砂岩、千枚岩；7—下古生界酉西群；8—新元古界吉塘群；9—古-中元古界卡穷岩群；10—晚白垩世二长花岗岩、似斑状二长花岗岩；11—早侏罗世二长花岗岩、似斑状钾长花岗岩；12—晚三叠世花岗闪长岩；13—晚三叠世二长花岗岩；14—中三叠世二长花岗岩；15—中奥陶世二长花岗岩；16—晚寒武世石英闪长岩；17—区域次级断裂；18—区域分区断裂

Figure 1. Tectonic Location(a)and geological sketch map(b) of the study area

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图 2 卡贡地区早侏罗世似斑状钾长花岗岩地质简图(a)和显微镜下照片(b、c)

Qtz—石英；Pl—斜长石；Afs—碱性长石

Figure 2. Geological map of the Early Jurassic potassium porphyritic granites in Kargang area(a)and photographs under microscopes(b, c)

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图 3 卡贡地区早侏罗世似斑状钾长花岗岩锆石阴极发光图像及U-Pb年龄

Figure 3. Cathodoluminescence images and U-Pb ages of the Early Jurassic potassium porphyritic granites

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图 4 卡贡地区早侏罗世似斑状钾长花岗岩锆石²⁰⁶Pb/²³⁸U年龄图解

Figure 4. Zircon²⁰⁶Pb/²³⁸U age diagram of the Early Jurassic potassium porphyritic granites in Kargang area

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图 5 卡贡地区早侏罗世似斑状钾长花岗岩SiO₂-K₂O图解(a)和A/CNK-A/NK图解(b)

Figure 5. SiO₂-K₂O(a)and A/CNK-A/NK(b)plots of the Early Jurassic potassium porphyritic granites in Kargang area

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图 6 卡贡地区早侏罗世似斑状钾长花岗岩稀土元素球粒陨石标准化配分图(a)和微量元素原始地幔标准化蛛网图(b)(标准化值据参考文献[9])

Figure 6. Chondrite-normalized REE patterns(a)and primitive mantle-normalized trace element patterns(b) of the Early Jurassic potassium porphyritic granites in Kargang area

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图 7 卡贡地区早侏罗世似斑状钾长花岗岩成因判别图

Figure 7. The genetic discriminant map of the Early Jurassic potassium porphyritic granites in Kargang area

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图 8 卡贡地区早侏罗世似斑状钾长花岗岩构造环境判别图

Figure 8. The illustration of tectonic environment discrimination of the Early Jurassic potassium porphyritic granites in Kargang area

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表 1 卡贡地区早侏罗世似斑状钾长花岗岩LA-ICP-MS锆石U-Th-Pb分析结果

Table 1 LA-ICP-MS zircon U-Th-Pb analytical data of the Early Jurassic potassium porphyritic granites in Kargang area

测点号	Pb	Th	U	Th/U	同位素比值						年龄/Ma
测点号	/10^-6			Th/U	²⁰⁷Pb/²⁰⁶Pb	1σ	²⁰⁷Pb/²³⁵U	1σ	²⁰⁶Pb/²³⁸U	1σ	²⁰⁷Pb/²⁰⁶Pb	1σ	²⁰⁷Pb/²³⁵U	1σ	²⁰⁶Pb/²³⁸U	1σ
01	8.13	246	216	1.14	0.0504	0.0026	0.1972	0.0101	0.0283	0.0004	217	114	183	8.6	180	2.5
02	10.36	383	274	1.40	0.0511	0.0023	0.1907	0.0082	0.0271	0.0003	256	102	177	7.0	173	2.1
03	12.18	335	333	1.01	0.0557	0.0022	0.2177	0.0086	0.0285	0.0004	443	89	200	7.2	181	2.6
04	10.46	346	280	1.23	0.0522	0.0021	0.1985	0.0076	0.0276	0.0003	295	86	184	6.4	175	2.0
05	13.33	401	361	1.11	0.0510	0.0021	0.1986	0.0074	0.0283	0.0003	243	101	184	6.3	180	1.9
06	7.65	235	205	1.15	0.0546	0.0029	0.2112	0.0108	0.0282	0.0004	394	88	195	9.1	179	2.4
07	9.79	291	279	1.04	0.0541	0.0025	0.2057	0.0102	0.0274	0.0003	376	106	190	8.6	174	2.1
10	20.83	349	664	0.53	0.0504	0.0014	0.1900	0.0054	0.0273	0.0002	213	67	177	4.6	173	1.5
11	8.23	236	222	1.06	0.0520	0.0027	0.2079	0.0113	0.0288	0.0004	283	116	192	9.5	183	2.5
12	19.5	623	500	1.24	0.0539	0.0020	0.2152	0.0080	0.0288	0.0003	369	87	198	6.7	183	1.7
13	11.81	277	344	0.81	0.0544	0.0022	0.2106	0.0084	0.0280	0.0003	387	91	194	7.0	178	2.0
17	15.03	469	405	1.16	0.0532	0.0020	0.2030	0.0069	0.0278	0.0003	345	83	188	5.8	177	1.8
18	6.40	197	166	1.19	0.0536	0.0026	0.2136	0.0105	0.0289	0.0004	354	109	197	8.8	184	2.8
19	9.48	230	275	0.84	0.0519	0.0024	0.1969	0.0090	0.0277	0.0005	283	107	182	7.6	176	2.8
20	7.89	254	206	1.24	0.0485	0.0025	0.1894	0.0093	0.0284	0.0004	124	79	176	8.0	180	2.3
21	37.36	570	1137	0.50	0.0551	0.0015	0.2202	0.0059	0.0289	0.0003	417	61	202	4.9	184	1.9
22	22.33	235	705	0.33	0.0551	0.0016	0.2153	0.0061	0.0282	0.0002	417	67	198	5.1	180	1.4
23	11.43	314	322	0.97	0.0541	0.0019	0.2046	0.0075	0.0273	0.0003	376	77	189	6.3	174	1.8
24	17.14	415	509	0.81	0.0549	0.0018	0.2066	0.0067	0.0272	0.0002	406	76	191	5.7	173	1.6
25	8.61	252	230	1.10	0.0540	0.0025	0.2110	0.0094	0.0285	0.0004	369	108	194	7.9	181	2.5
08	9.26	285	229	1.24	0.0753	0.0032	0.3008	0.0128	0.0289	0.0004	1077	85	267	10.0	184	2.3
09	15.02	528	398	1.33	0.0570	0.0020	0.2163	0.0076	0.0275	0.0003	500	76	199	6.4	175	1.7
14	10.46	212	235	0.90	0.0687	0.0030	0.2619	0.0112	0.0277	0.0004	900	89	236	9.0	176	2.3
15	8.49	304	280	1.08	0.0669	0.0028	0.2561	0.0110	0.0278	0.0004	835	87	232	8.9	177	2.4
16	12.17	321	342	0.94	0.0586	0.0019	0.2237	0.0073	0.0276	0.0003	554	77	205	6.0	176	1.9

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表 2 卡贡地区早侏罗世似斑状钾长花岗岩主量、微量和稀土元素分析结果

Table 2 Whole-rock major, trace elements and REE data of the Early Jurassic potassium porphyritic granites in Kargang area

样号	H1	H2	H3	H4	H5
SiO₂	69.78	70.80	69.37	70.26	68.89
TiO₂	0.39	0.33	0.39	0.41	0.52
Al₂O₃	14.40	14.25	14.73	14.08	14.61
Fe₂O₃	2.31	1.92	2.27	2.43	2.90
MnO	0.06	0.05	0.06	0.06	0.08
MgO	1.09	0.91	1.11	1.18	1.40
CaO	1.97	1.77	1.82	1.75	2.04
Na₂O	2.77	2.77	2.82	2.71	2.96
K₂O	5.66	5.76	5.95	5.63	5.06
P₂O₅	0.13	0.11	0.13	0.14	0.17
烧失量	0.67	0.63	0.61	0.66	0.92
总量	99.24	99.30	99.25	99.31	99.53
A/NK	1.35	1.32	1.33	1.33	1.41
A/CNK	1.01	1.02	1.02	1.02	1.04
Li	58.8	56.3	61.0	65.9	74.8
Be	8.21	8.12	7.79	8.38	9.85
Sc	6.05	4.38	5.39	5.67	6.47
V	37.0	30.9	35.7	37.8	47.1
Cr	15.0	12.0	13.8	15.1	19.6
Co	4.78	4.01	4.77	5.07	6.14
Ni	8.35	7.14	8.27	8.60	11.5
Cu	2.86	2.79	3.48	2.90	4.13
Zn	38.1	33.2	39.7	41.7	50.5
Ga	19.2	19.1	19.6	19.6	21.8
Rb	362	366	382	373	367
Sr	180	181	176	163	199
Y	21.4	19.2	20.0	21.1	30.4
Zr	222	185	207	234	267
Nb	23.5	20.5	21.7	23.5	31.1
Sn	12.1	10.2	11.3	12.2	15.5
Cs	13.4	12.4	13.9	14.6	14.4
Ba	615	607	551	494	430
La	50.4	52.4	59.2	57.2	69.9
Ce	94.3	94.6	105	102	136
Pr	10.2	10.4	11.7	11.5	16.3
Nd	34.9	34.8	38.6	38.6	50.6
Sm	5.22	5.16	5.42	5.72	7.98
Eu	0.91	0.89	0.89	0.85	0.96
Gd	3.70	3.43	3.64	3.72	5.17
Tb	0.60	0.54	0.56	0.58	0.88
Dy	3.41	3.14	3.32	3.32	5.07
Ho	0.69	0.61	0.65	0.66	1.00
Er	2.03	1.85	1.90	2.02	2.93
Tm	0.30	0.28	0.29	0.30	0.45
Yb	2.10	1.88	1.95	2.04	2.96
Lu	0.29	0.29	0.29	0.31	0.42
Hf	6.84	5.75	6.33	7.20	8.09
Ta	2.10	1.89	1.91	2.02	3.10
Tl	2.32	2.33	2.45	2.41	2.45
Pb	34.1	36.1	35.3	34.2	31.9
Th	45.9	44.6	48.4	53.2	68.9
U	8.93	7.75	9.40	8.99	10.4
ΣREE	209	210	233	229	300
LREE	196	198	220	216	281
HREE	13.1	12.0	12.6	12.9	18.9
LREE/HREE	14.9	16.5	17.5	16.7	14.9
La_N/Yb_N	17.2	20.0	21.8	20.1	16.9
δEu	0.60	0.61	0.58	0.53	0.43
δCe	0.96	0.94	0.92	0.92	0.95
注：主量元素含量单位为%，微量和稀土元素含量单位为10^-6

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