毛北榴辉岩古地磁及岩石磁学初探

孟小红; 余钦范; 郭友钊; 周姚秀

毛北榴辉岩古地磁及岩石磁学初探

孟小红^{1, 2,},
余钦范^{1, 2},
郭友钊³,
周姚秀⁴

1.
地质过程与矿产资源国家重点实验室和地下信息探测技术与仪器教育部重点实验室, 北京 100083
2.
中国地质大学地球物理与信息技术学院, 北京 100083
3.
国土资源部地球物理地球化学勘探研究所, 河北廊坊 065000
4.
国土资源部航空物探遥感中心, 北京 100083

基金项目: 北京市重点学科“地球探测与信息技术(XK104910598)”资助

详细信息

作者简介:
孟小红(1958-), 女, 教授, 主要从事勘探地球物理学领域的教学和研究.E-mail: mxh@cugb.edu.cn

中图分类号: P631.2
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出版历程
- 收稿日期: 2007-04-12
- 刊出日期: 2007-07-25

A Pilot Study on Paleomagnetism and Rock Magnetism of Maobei Eclogite

1.
State Key Laboratory of Geological Processes and Mineral Resources; Geo-detection Laboratory of the Ministry of Education, Beijing 100083, China
2.
School of Geophysics and Information Technology, China University of Geosciences, Beijing 100083, China
3.
Institute of Geophysical and Geochemical Exploration, CAGS, Langfang 065000, China
4.
China Aero Geophysical Survey and Remote Sensing Center for Land and Resources, Beijing 100083, China

摘要

摘要: 对中国大陆科学钻探孔区——江苏省东海县毛北地区的55块榴辉岩样品进行了古地磁研究, 并从中抽样测试了等温剩磁、磁滞迴线、磁组构、热磁化率以及电子探针和镜下分析, 结果表明, 毛北榴辉岩有两组稳定的剩磁, 即反向磁化和正向磁化, 稳定剩磁方向分别为: D=94.3°, I=-29.1°和D=273.7°, I=15.4°, 携带正向磁化与携带反向磁化样品的磁化强度和密度变化很大; 毛北榴辉岩的磁各向异性度非常弱, 最小轴方向很难确定; 等温剩磁和磁滞迴线显示磁铁矿可能是毛北榴辉岩的主要载磁矿物, 且在以M_r/M_s和H_cr/H_c的对数为纵、横坐标的图上落在视单畴(PSD)区域.根据磁性特征, 对毛北榴辉岩的磁性载体成因、剩磁获得机制及构造意义进行了讨论.
- 古地磁 /
- 岩石磁学 /
- 榴辉岩 /
- 超高压变质带
Abstract: In this paper, a pilot study of paleomagnetism and rock magnetism is done on 55 eclogite samples collected from Maobei area, Donghai County, Jiangsu Province. Synchronously, some of the samples are analyzed by electron-probe and scanning electric microscope, and tested for the isothermal remanence, hysteresis loop, magnetic fabric, thermal magnetic properties. The result indicates that there are two groups of stable remanence, i. e- the normal polarity and reversed polarity. The remanence orientations are: D=94. 3°, I=-29. 1° and D=273. 7°, I=15. 4° respectively. The magnetization and the density of the samples with normal polarities are very different from that of the samples with reversed polarities. The magnetic anisotropy is weak, and the minimum axis is hardly confirmed. The isothermal remanence and the hysteresis loop show that the magnetic carriers of the eclogite may be SD (single domain) and PSI) (pseudo-single domain) magnetite. According to the magnetic property, the cause of the formation of magnetic carrier, the causation of the remanence, and the significance for the geotectonic are discussed at the end of the paper.
- paleomagnetism /
- rock magnetism /
- eclogite /
- ultrahigh-pressure metamorphic zone.

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图 1 毛北榴辉岩及围岩退磁曲线

a₁，a₂，a₃为剩磁强度归一化衰减曲线；b₁，b₂，b₃为正交矢量投影图；C₁，C₂，C₃为退磁矢量赤平投影图

Fig. 1. The demagnetization curves of Maobei eclogite and its surrounding rocks

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图 2 毛北榴辉岩稳定剩磁方向赤平投影图

Fig. 2. Stereographic projection of the stable remanence orientations of Maobei eclogite

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图 3 (a) 磁化率与剩余磁化强度散点图; (b)磁化率与密度散点图

Fig. 3. (a)Scatter plot of susceptibility and remanence; (b)Scatter plot of susceptibility and density

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图 4 (a) 榴辉岩等温剩磁获得曲线及反向磁场退磁曲线; (b)围岩等温剩磁获得曲线及反向磁场退磁曲线; (c)磁滞廻线; (d)κ-t曲线

图 3c中H_r=236.4 mT, H_c=63.6 mT, H_r/H_c=3.71, M_r=2.35×10^-6A·m², M_s=6.91×10^-6A·m², M_r/M_s=0.34

Fig. 4. (a)The curve gotten from isothermal remanence and the demagnetization curves gotten from reversed polarities of the eclogite; (b)The curve gotten from isothermal remanence and the demagnetization curves gotten from reversed polarities of the surrounding rocks; (c)Hysteresis loop; (d)κ-t curve

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表 1 毛北榴辉岩样品磁组构测量结果

Table 1. The measured magnetic fabric of Maobei eclogite samples

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