冈底斯印支期造山事件: 花岗岩类锆石U-Pb年代学和岩石成因证据

张宏飞; 徐旺春; 郭建秋; 宗克清; 蔡宏明; 袁洪林

冈底斯印支期造山事件: 花岗岩类锆石U-Pb年代学和岩石成因证据

1.
中国地质大学地质过程与矿产资源国家重点实验室和地球科学学院, 湖北武汉 430074
2.
中国地质大学地质调查研究院, 湖北武汉 430074
3.
西藏地质矿产勘查开发局地热地质大队, 西藏拉萨 850000
4.
西北大学大陆动力学国家重点实验室, 陕西西安 710069

基金项目:

国家自然科学基金项目 40521001

教育部长江学者和创新团队发展计划 IRT0441

详细信息

作者简介:
张宏飞(1962 -), 男, 教授, 主要从事岩石圈地球化学的教学和科研工作.E-mail: hfzhang@cug.edu.cn

中图分类号: P597
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出版历程
- 收稿日期: 2007-02-03
- 刊出日期: 2007-03-25

Indosinian Orogenesis of the Gangdise Terrane: Evidences from Zircon U-Pb Dating and Petrogenesis of Granitoids

1.
State Key Laboratory of Geological Processes and Mineral Resources, and Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China
2.
Academe of Geological Survey, China University of Geosciences, Wuhan 430074, China
3.
Team of Geothermy and Geology, Tibet Bureau of Geology and Mineral Resource Exploration and Development, Lhasa 850000, China
4.
State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069, China

摘要

摘要: 对冈底斯中部地区二云母花岗岩和花岗闪长岩进行了LA-ICP-MS锆石U-Pb定年、主量元素、微量元素和锆石Hf同位素组成的测定.结果表明, 二云母花岗岩的岩浆结晶年龄为(205± 1)Ma, 岩石属于强过铝质花岗岩, A/CNK= 1.16~ 1.20, K₂O/Na₂O= 1.67~ 1.95.岩石富Rb、Th和U等元素, Eu/Eu^* = 0.29~ 0.41, (La/Yb)_N= 22.62~ 35.08.锆石ε_Hf(t)= -12.4~ -1.8.二云母花岗岩的岩浆产生于地壳中泥质岩类在无外来流体加入的情况下云母类矿物脱水反应所诱发的部分熔融作用, 其岩石形成机制类似于喜马拉雅新生代淡色花岗岩.花岗闪长岩的岩浆结晶年龄为(202± 1)Ma, 岩石属于准铝质(A/CNK= 0.96~ 0.98), K₂O/Na₂O= 1.42~ 1.77, Eu/Eu^* = 0.54~ 0.65, (La/Yb)_N= 6.76~ 13.35.锆石ε_Hf(t)= -8.2~ -5.5.根据花岗闪长岩的地球化学特征和锆石Hf同位素组成, 花岗闪长岩的岩浆来自于地壳中基性岩类的部分熔融.冈底斯印支晚期强过铝质花岗岩的确定, 表明了冈底斯在印支晚期以前曾发生地壳的缩短与加厚作用, 从而进一步明确了冈底斯印支早期的造山事件及冈底斯经历了多期造山作用的演化.
- 印支期花岗岩类 /
- 锆石U-Pb定年 /
- 锆石Hf同位素 /
- 地球化学 /
- 构造意义 /
- 冈底斯 /
- 西藏
Abstract: This paper reports LA-ICP-MS zircon U-Pb ages, whole-rock major and trace element and zircon Hf isotopic com- positions from two-mica granite and granodiorite plutons occurring in the middle part of the Gangdise terrane, Tibet. Magma zircons from the two-mica granite yielded a weighted 206Pb/238 U mean age of(205± 1)Ma(MSWD= 0.47), which is inter- preted as its magma crystallization age(Late Indosinian). The two-mica granite is strongly peraluminous, with Al index(A/ CNK)= 1.16 -1.20 and K₂O/Na₂O= 1.67 -1.95. The two-mica granite is characterized by enrichments of Rb, Th and U etc. Rare earth element(REE)data display Eu/Eu^*= 0.29 -0.41 and(La/Yb)_N= 22.62 -35.08.ε_Hf(t)(205 Ma)values from the dated zircons range from -12.4 to -1.8. It is suggested that the magma for the two-mica granite was dominately derived from patial melting of argillaceous rocks in crust, induced by dehydration of mica minerals. The petrogenesis of the two-mica granite is similar to that of the Himalayan Tertiary leucogranites. Magma zircons from the granodiorite yielded a weighted 206Pb/238 U age of(202± 1)Ma, representing its magma crystallization age. The granodiorite is metaluminous, with Al index(A/CNK)= 0.96 -0.98, K₂O/Na₂O= 1.42 -1.77. REE data show Eu/Eu^* = 0.54 -0.65 and(La/Yb)_N= 6.76 -13.35. Dated zircon Hf isotopic compositions exhibitε_Hf(202 Ma)values ranging from -8.2 to -5.5. The geo- chemical signatures and zircon Hf isotopic compositions suggest that the magma of granodiorite formed by partial melting of basaltic rocks in crust. The Late Indosinian stronlgly peralumineous granite is the first report in the Gangdise terrane. The occurring of the stronlgly peralumineous granite reveals Gangdise crustal thickening prior to Late Indosinian, and gives an impelling evidence that the Gangdise terrane took place an Early Indosinian orogenic event.
- Indosinian granitoids /
- U-Pb zircon dating /
- Hf isotope /
- geochemistry /
- tectonic implication /
- Gangdise terrane /
- Tibet

HTML全文

图 1 冈底斯中部洛扎-仁堆地区地质简图

Fig. 1. Simplified geological map of Loza-Rende area in middle part of Gangdise terrane

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图 2 代表性锆石阴极发光图像

a.样品T450;b.样品T457

Fig. 2. CL images of representative zircon of sample T450 and sample T457

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图 3 锆石U-Pb谐和图

Fig. 3. U-Pb zircon concordia diagram of sample T450 and sample T457

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图 4 原始地幔标准化的元素组成模式

a.二云母花岗岩; b.花岗闪长岩; 原始地幔标准化值据Sun and McDonough(1989)

Fig. 4. Primitive mantle normalized elemental compositional patterns of two-mica granite(a) and granodiorite(b)

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图 5 稀土元素组成模式

a.二云母花岗岩; b.花岗闪长岩; 球粒陨石标准化值据Taylor and McLennan(1985)

Fig. 5. Chondrite-normalized REE patterns of two-mica granite(a) and granodiorite(b)

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表 1 样晶T450和T457 LA-ICP-MS锆石U-Pb同位素资料

Table 1. U-Pb zircon LA-ICP MS chronoiogical data of samples T450 and T457

表 2 冈底斯印支期花岗岩类主量元素(%)和微量元素(μg/g)资料

Table 2. Major element (%) and Lracc clerment (μg/g) data of Gangdise Indosinian granitoid

表 3 样品T450和T457锆石Lu-Hf同位素资料

Table 3. Zircon Lu-Hf isotopic data of samples T450 and T457

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