青藏高原北羌塘地区古近纪火山岩中埃达克岩的地球化学特征及其构造意义

赵振明; 李荣社; 计文化; 伊海生; 林金辉; 朱同兴

青藏高原北羌塘地区古近纪火山岩中埃达克岩的地球化学特征及其构造意义

1.
西安地质矿产研究所, 陕西西安 710054
2.
成都理工大学沉积地质研究所, 四川成都 610059
3.
成都地质矿产研究所, 四川成都 610082

基金项目:

中国地质调查局“青藏高原北部空白区基础地质综合研究”项目 1212010510110

详细信息

作者简介:
赵振明(1965-), 男, 硕士, 从事构造和环境方面的工作. E-mail: xazzhenming@cgs.gov.cn

中图分类号: P542
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出版历程
- 刊出日期: 2007-09-25

The Characteristics of Geochemical and Its Tectonic Significance from the Adakite of Palaeogene Volcanic Rocks in Northern Qiangtang Area, Qinghai-Tibetan Plateau

1.
Xi′an Institute of Geology and Mineral Resources, Xi′an 710054, China
2.
Chengdu University of Technology, Institute of Sedimentary Geology, Chengdu 610059, China
3.
Chengdu Institute of Geology and Mineral Resources, Chengdu 610082, China

摘要

摘要: 为了研究青藏高原北羌塘地区分布的新生代火山岩形成的时代、物质来源和构造环境, 通过各种年代学和地球化学测试方法获得的资料进行综合研究, 结果表明该地区的火山岩主要形成时代为古近纪, 常量、微量和稀土元素特征显示该区发育一定比例的标准埃达克岩(adakite), 代表地区的12件埃达克岩样品, 其SiO₂含量≥56%(59.05%~67.80%), Al₂O₃≥15%(15.43%~16.63%), MgO < 3%(0.47%~2.98%, 1件样品3.21%), Mg#>20(21.2~56.5), Na₂O/K₂O>1(1.03~1.76), Sr>400×10^-4(609.6×10^-6~3008.0×10^-6), Y≤18×10^-6(4.53×10^-6~13.76×10^-6), Yb≤1.9×10^-6(0.44×10^-6~1.35×10^-6), Sr/Y≥40(44.3-314.68), La/Yb≥20(20.11-69.26), δSr正异常(1.02~7.66, 3件样品0.82、0.93、0.97), δEu正异常或微弱的负异常(0.77~1.36), LREE富集, HREE亏损, 高场强元素HFSEs(Nb、Ta、Ti)明显亏损⁸⁷Sr/⁸⁶Sr>0.704(0.707101-0.707923), ¹⁴³Nd/¹⁴⁴Nd < 0.5126(0.512382-0.512448)⁴⁰K-⁴⁰Ar、⁴⁰Ar-³⁹Ar测定时代分别为28.2~32.2Ma, 38.1~46.8Ma.上述特征除表明该套古近系埃达克岩岩浆源处于加厚的下地壳环境外, 可能还代表了在高原演化过程中, 北羌塘地区滞留在下地壳和上地幔的“洋壳残片”部分熔融并在地表喷发的构造过程.
- 青藏高原 /
- 北羌塘 /
- 古近系 /
- 埃达克岩
Abstract: Studies on the formation times, resources and tectonic environment of the Cenozoic volcanic rocks in the northern Qiantang area, Qinghai-Tibetan Plateau, formed mostly in Plaeogene, show that these rocks have presented characteristics of typical adakite, according to major and trace elements data tested by many dating and geochemical methods. Of the 12 typical adakite samples in important area, SiO₂≥56%(59. 05%-67. 80%), Al₂O₃≥15%(15.43%-16.63%), MgO < 3% (0. 47%-2. 98%, 1 sample is 3.21%), Mg#>20(21.2-56.5), Na₂O/K₂O>1(1.03-1.76), Sr>400 × 10^-6 (609. 6 × 10^-6-3 008. 0× 10^-6), Y≤18 × 10^-6 (4. 53 × 10^-6-13.76 × 10^-6), Yb≤1. 9 × 10^-6 (0.44 × 10^-6-1.35 × 10^-6), Sr/Y≥ 40(44. 3-314. 68), La/Yb≥20(20. 11-69. 26), δSr positive anomaly(1.02-7.66, 3 samples are 0. 82, 0. 93, 0. 97), δEu positive anomaly or weak anomaly(0. 77-1.36), LREE enrichment, HREE depletion, HFSEs (Nb, Ta, Ti) strong depletion, ⁸⁷Sr/⁸⁶Sr>0. 704(0. 707 101-0. 707 923), ¹⁴³Nd/¹⁴⁴Nd < 0. 512 6(0. 512 382-0. 512 448), ⁴⁰K-⁴⁰Ar, ⁴⁰Ar-³⁹Ar ages are 28. 2-32.2 Ma, 38. 1-46. 8 Ma. The above geochemical features of adakite indicate a primitive magmatic generation process responsible for the partial melting of lower thickened crust of northern Qinghai-Tibetan Plateau and perhaps also represent the process in which the remains in lower crust-up mantle melted and erupted in surface after the subduction of ocean crust in the plateau evolvement during early period.
- Qinghai-Tibetan plateau /
- northern Qiangtang area /
- Palaeogene /
- adakite

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图 1 青藏高原北羌塘地区古近系火山岩分布

①乌兰乌拉湖地区氩-氩法测年4个样品由中国地震局地质研究所测试, 钾-氩法测年1个样品由成都地质矿产研究所测试; ②多格错仁地区氩-氩法测年1个样品由中国科学院广州地球化学研究所测试, 钾-氩法测年5个样品由国土资源部中南矿产资源检测中心测试; ③黑虎岭地区钾-氩法测年2个样品由宜昌地质矿产研究所测试. 图中火山岩形状和断层线以潘桂棠和丁俊(2004)为准

Fig. 1. Map of Palaeogene volcanic rocks in the northern Qiangtang area of Qinghai-Xizang plateau

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图 2 SiO₂-(K₂O+Na₂O)(a)和SiO₂-K₂O(b)图解

Fig. 2. SiO₂-(K₂O +Na₂O)(a) and SiO₂-K₂O (b) diagrams

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图 3 Na-K-Ca图解(a)和埃达克岩MgO-SiO₂图解(b)

Fig. 3. Na-K-Ca ternary diagram (a) and The adakites MgO-SiO₂ diagram (b)

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图 4 埃达克岩Sr /Y-Y图解(据Defant and Drummond, 1990; Defant et al., 2002)

Fig. 4. Sr /Y-Y diagrams for the adakites

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图 5 微量元素蛛网图

a. 乌兰乌拉与多格错仁岩区; b. 黑虎岭岩区

Fig. 5. Spider diagrams of primitive mantle normalized trace element distribution patterns

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图 6 微量元素蛛网图(乌兰乌拉与多格错仁岩区)

Fig. 6. Roke normalized trace element distribution patter

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图 7 埃达克岩稀土分配曲线(a)和埃达克岩La /Sm-La图解(b)

Fig. 7. Diagrams of chondrite normalized rare each element distribution patterns (a) and discriminating diagram of La /Sm-La for the adakites (b)

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表 1 青藏高原北羌塘地区古近系埃达克岩元素地球化学测试数据

Table 1. Major and trace element analy ses of Palaeogene adakite from the northern Qiang tang area of Qinghai-Xizang plateau

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表 2 新生代火山岩Sr、Nd、Pb同位素组成

Table 2. Compositions of Sr、Nd、Pb isotope for the Cenozic rocks

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表 3 青藏高原北羌塘地区部分火山岩同位素年龄数据表

Table 3. The part of isotopic ages of volcanic rocks from the northern Qiangtang area of Qinghai-Xizang Plateau

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