羌北地块上志留统龙木措上组岩石磁学特征

王保锋; 程鑫; 姜南; 卫弼天; 张伟杰; 吴珂; 许鹏祥; 周亚楠; 刘雨纯; 吴汉宁

doi:10.19509/j.cnki.dzkq.tb20220102

羌北地块上志留统龙木措上组岩石磁学特征

doi: 10.19509/j.cnki.dzkq.tb20220102

1.
西北大学地质学系, 西安 710069
2.
南方科技大学海洋科学与工程系海洋磁学中心(CM²), 广东深圳 518055

基金项目:

国家自然科学基金项目 41774073

国家自然科学基金项目 91855211

国家自然科学基金项目 42074075

第二次青藏高原综合科学考察研究 2019QZKK0704

详细信息

作者简介:
王保锋(1997—), 男, 现正攻读地球探测与信息技术专业硕士学位, 主要从事古地磁学研究工作。E-mail: 614975769@qq.com

通讯作者:
程鑫(1982—), 男, 教授, 主要从事古地磁学与区域大地构造的教学与科研工作。E-mail: chenxin@nwu.edu.cn

中图分类号: P318.41;P534.43
计量
- 文章访问数: 346
- PDF下载量: 29
- 被引次数: 0
出版历程
- 收稿日期: 2022-03-11
- 录用日期: 2022-06-17
- 修回日期: 2022-05-26

Rock magnetic properties of the Upper Silurian Longmu Co Upper Formation in the North Qiangtang Terrane

1.
Department of Geology, Northwest University, Xi'an 710069, China
2.
Department of Ocean Science and Engineering, Centre for Marine Magnetism(CM²), Southern University of Science and Technology, Shenzhen Guangdong 518055, China

摘要

摘要:
开展羌北地块早古生代古地磁学研究, 定量约束出其古生代以来的古地理位置, 可为研究青藏高原古构造格局、显生宙特提斯演化和古地理重建等提供重要基础和关键制约。在进行古地磁研究之前, 首先进行岩石磁学特征的研究, 明确岩石中载磁矿物的组合类型和特征, 为后续退磁实验方案的选择以及剩磁的原生性的讨论提供岩石磁学基础。对羌北地块上志留统龙木措上组灰岩和砂岩进行岩石磁学特征研究, 包括等温剩磁获得曲线、磁化率随温度变化(χ-T)曲线、三轴等温系统热退磁实验、低温磁学性质测试以及扫描电镜(SEM)和能谱分析(EDS)等。实验结果表明, 龙木措上组灰岩样品中的磁性矿物以磁铁矿为主, 另外还有少量的磁赤铁矿和磁黄铁矿, 砂岩样品中的磁性矿物较为复杂, 主要为磁铁矿, 可能还含有磁黄铁矿等其他磁性矿物。研究结果表明龙木措上组地层中灰岩样品可以分离出稳定的高温剩磁分量, 适宜开展进一步古地磁学研究。
- 青藏高原 /
- 岩石磁学 /
- 羌北地块 /
- 上志留统 /
- 龙木措上组
Abstract: Objective
Palaeomagnetic study of the early Palaeozoic North Qiangtang Terrane can quantitatively constrain its palaeogeographic location since the Palaeozoic, which serves as an important foundation and key constraint for studying of the palaeotectonic pattern of the Qinghai-Tibet Plateau, the evolution of the Phanerozoic Tethys and palaeogeographic reconstruction.
Methods
Prior to palaeomagnetic study, it is essential to investigate the magnetic properties of rocks to identify the types and assemblages of magnetic carriers present in rocks, which will facilitate the selection of demagnetization experimental protocols and discussions on the primary nature of remanent magnetization. This paper focuses on the magnetic properties of limestone and sandstone from the Late Silurian Longmu Co Upper Formation in the North Qiangtang Terrane, through analyses of isothermal remanence acquisition curves, magnetic susceptibility with temperature(χ-T) curves, triaxial thermal demagnetization experiments, low-temperature magnetic properties tests, scanning electron microscopy (SEM) and energy dispersive spectral (EDS) analysis.
Results
Results show that magnetite is the predominant magnetic carrier in the limestone samples of the Longmu Co Upper Fm, with small amounts of pyrrhotite. The magnetic assemblage in the sandstone samples is more complex, dominated by magnetite, possibly with other magnetic minerals such as pyrrhotite.
Conclusion
Moreover, it demonstrates that stable high-temperature remanent magnetization components can be isolated from the limestone samples in the Longmu Co Upper Formation, making them suitable for further palaeomagnetic researches.
- Qinghai-Tibet Plateau /
- rock magnetism /
- North Qiangtang Terrane /
- Upper Silurian /
- Longmu Co Upper Formation
注释:

(所有作者声明不存在利益冲突)

HTML全文

图 1 羌北地块及邻区大地构造简图(a)和采样区地质简图(b)

Figure 1. Simplified tectonic map of the North Qiangtang Terrane and adjacent areas (a) and simplified geological map of the sampling area (b)

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图 2 龙木措上组地层柱状图和野外露头照片

Figure 2. Stratigraphic column and field outcrop photographs of the Longmu Co Upper Formation

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图 3 龙木措上组灰岩(a~f)和砂岩(g~l)样品等温剩磁及反向场退磁曲线、累计高斯模型获得曲线

Figure 3. Acquisition curves of isothermal remanent magnetization(IRM), back-field demagnetization curves of IRM and cumulative log Gaussian analysis curves for the limestone(a-f) and sandstone(g-l) samples from the Longmu Co Upper Formation

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图 4 龙木措上组灰岩(a~d)和砂岩(e, f)样品三轴等温剩磁系统热退磁曲线

Figure 4. Thermal demagnetization of three-axis IRM for limestone(a-d) and sandstone(e, f) samples from the Longmu Co Upper Formation

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图 5 龙木措上组灰岩(a~d)和砂岩(e, f)样品磁化率随温度变化(χ-T)曲线

Figure 5. χ-T curves for limestone(a-d) and sandstone(e, f) samples from the Longmu Co Upper Formation

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图 6 龙木措上组灰岩样品扫描电镜与能谱分析图

Figure 6. Scanning electron microscope images and energy dispersive spectra of the limestone samples from the Longmu Co Upper Formation

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图 7 灰岩样品的ZFC和FC磁化强度随温度变化曲线

Figure 7. Field-cooled (FC) and zero-field-cooled (ZFC) heating curves of RTSIRM of limestone samples from the Longmu Co Upper Formation

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图 8 龙木措上组灰岩(a, b)和砂岩(c, d)样品退磁结果

NRM为天然剩磁强度；实心、空心点分别代表正、负半球的投影

Figure 8. Demagnetization result for limestone(a, b) and sandstone(c, d) samples from the Longmu Co Upper Formation

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