基底岩系和花岗岩类Pb-Nd同位素组成限制祁连山带的构造属性

张宏飞; 靳兰兰; 张利; 袁洪林; 周炼; 张本仁

基底岩系和花岗岩类Pb-Nd同位素组成限制祁连山带的构造属性

1.
中国地质大学地质过程与矿产资源国家重点实验室，湖北武汉 430074
2.
西北大学大陆动力学实验室，陕西西安 710069

基金项目:

国家自然科学基金重点项目 40234052

详细信息

作者简介:
张宏飞(1962-), 男, 教授, 博士生导师, 主要从事造山带地球化学研究.E-mail: hfzhang@cug.edu.cn

中图分类号: P59
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出版历程
- 收稿日期: 2005-09-23
- 刊出日期: 2006-01-25

Pb and Nd Isotopic Compositions of Basement and Granitoid in the Qilianshan: Constraints on Tectonic Affinity

1.
State Key Laboratory of Geological Processes and Mineral Resources, china Univences, Wuhan 430074, China
2.
Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069, China

摘要

摘要: 对扬子陆块的西北部边界至今尚未得到有效的限定.中央山系西段祁连山带基底岩系和花岗岩类的Pb-Nd同位素组成为限定扬子陆块的西北边界提供限制.祁连山带前寒武纪基底岩系的Nd同位素亏损地幔模式年龄(T_DM)主要分布于0.75-2.5 Ga之间, 峰值为2.1 Ga左右; 该带古生代花岗岩类的T_DM变化于1.07-2.14 Ga之间.由此表明, 祁连山带地壳增长主要发生于元古宙, 缺乏太古宙地壳增长的信息.祁连山带前寒武纪基底和花岗岩类全岩均以高放射成因的铅同位素组成为特征, 极大多数样品的²⁰⁶Pb/²⁰⁴Pb > 18.0, ²⁰⁷Pb/²⁰⁴Pb > 15.5, ²⁰⁸Pb/²⁰⁴Pb > 38.0.因此, 祁连山带地壳增长特征和铅同位素组成特征与华北陆块存在明显的差异, 而与扬子陆块一致, 从而表明祁连山带具有扬子型陆块的构造属性.因此, 扬子陆块的西北部边界扩大至祁连山带的北侧.自新元古代以来, 祁连山带经历了岩石圈裂解作用, 并有洋盆形成, 但这些构造事件均发生在扬子型陆块内部的地质背景.
- 祁连山 /
- 基底岩系 /
- 花岗岩类 /
- Pb-Nd同位素 /
- 构造属性
Abstract: The northwestern boundary of the Yangtze (South China) block has not been efficiently constrained yet. Pb and Nd isotopic compositions of the Qilianshan Precambrian basements and granitoids in the western segment of the Central Oro-genie System (COS) of China provide constraints on the northwestern boundary of the Yangtze block. Most samples from the Qilianshan Precambrian basement have mantle-depleted Nd isotopic model ages (T_DM)ranging from 0. 75 to 2. 5 Ga, with a peak value of -2. 1 Ga. The Qilianshan Paleozoic granitoids have T_DM values ranging from 1. 07 to 2. 14 Ga. They show that crustal growth of the Qilianshan mainly occurred in the Proterozoic, without significant Archean information. The Precambrian basement rocks and the Paleozoic granitoids are characterized by high radiogenic Pb isotopic composition. Most samples have ²⁰⁶Pb/²⁰⁴Pb > 18. 0, ²⁰⁷Pb/²⁰⁴Pb > 15. 5 and ²⁰⁸Pb/²⁰⁴Pb > 38. 0. The T_DM values and Pb isotopic compositions of the Qilianshan basement and granitoids are similar to those of the Yangtze block but distinct from those of the North China block, indicating that the crustal basement of Qilianshan has an affinity with the Yangtze block. It is suggested that the northwestern boundary of the Yangtze block is located along the north side of the Qilianshan belt. Since the Proterozoic, the Qilianshan belt had experienced lithospheric rifting and subsequent Qilian ocean opening. These tectonic events had thus happened within the Yangtze block.
- Qilianshan /
- basement /
- granitoid /
- Pb-Nd isotope /
- tectonic affinity

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图 1 祁连山带构造简图

1.前寒武基底岩系采样位置; 2.花岗岩类采样位置; 内插图示研究区在中国的大地构造位置

Fig. 1. Simplified tectonic map of Qilianshan belt

下载: 全尺寸图片幻灯片

图 2 Nd同位素模式年龄(T_DM)分布直方图

Fig. 2. Histogram of Nd isotope model age (T_DM)distribution

下载: 全尺寸图片幻灯片

图 3 ²⁰⁷ Pb/²⁰⁴ Pb分布直方图

a.华北陆块中生代花岗岩(张理刚, 1995); b.扬子陆块中生代花岗岩(张理刚, 1995); c.祁连山花岗岩类(数据见表 4); d.祁连山前寒武基底(数据见表 3)

Fig. 3. Histogram of²⁰⁷Pb/²⁰⁴ Pb distribution

下载: 全尺寸图片幻灯片

表 1 祁连山带前寒武纪变质岩系Nd同位素资料

Table 1. Whole-rock Nd isotope data of Precambrian basement from Qilianshan belt

表 2 祁连山带古生代和中生代花岗岩类Nd同位素资料

Table 2. Whole-rock Nd isotope data of Paleozoic and Mesozoic granitoid from Qilianshan belt

表 3 祁连山带前寒武纪变质岩系全岩Pb同位素资料

Table 3. Whole-rock Pb isotope data of Precambrian basement from Qilianshan belt

表 4 祁连山带古生代和中生代花岗岩类全岩Pb同位素资料

Table 4. Whole-rock Pb isotope data of graniroid from Qilianshan belt

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