北京大学学报（自然科学版） ›› 2018, Vol. 54 ›› Issue (3): 521-534.DOI: 10.13209/j.0479-8023.2017.100

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华北地块沁水盆地下三叠统刘家沟组古地磁倾角浅化研究

周庭红1, 黄宝春1,†, 贾舒斐1, 梁雅伦1, 张东海1, 赵千1, 张也1, 闫永刚2   

  1. 1. 造山带与地壳演化教育部重点实验室, 北京大学地球与空间科学学院, 北京 100871
    2. 岩石圈演化国家重点实验室, 中国科学院地质与地球物理研究所, 北京 100029
  • 收稿日期:2017-03-31 修回日期:2017-05-09 出版日期:2018-05-20 发布日期:2018-05-20
  • 通讯作者: 黄宝春, E-mail: bchuang(at)pku.edu.cn
  • 基金资助:
    国家自然科学基金(41190071)资助

Paleomagnetic Inclination Shallowing in Lower Triassic Liujiagou Formation from Qinshui Basin, North China Block

ZHOU Tinghong1, HUANG Baochun1,†, JIA Shufei1, LIANG Yalun1, ZHANG Donghai1, ZHAO Qian1, ZHANG Ye1, YAN Yonggang2   

  1. 1. The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing100871
    2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029
  • Received:2017-03-31 Revised:2017-05-09 Online:2018-05-20 Published:2018-05-20
  • Contact: HUANG Baochun, E-mail: bchuang(at)pku.edu.cn

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摘要：

对华北地块沁水盆地下三叠统刘家沟组红层样品进行系统的岩石磁学、磁组构和古地磁学研究, 并用E/I (elongation/inclination)方法对其进行磁倾角浅化的识别与校正, 获得刘家沟组红层磁倾角浅化因子f = 0.6。岩石磁学结果显示, 刘家沟组红层的主要载磁矿物是赤铁矿及磁铁矿, 其磁组构具有典型的静水沉积特征。经地层校正后, 15个采样点特征剩磁分量的平均方向为Ds=318.8°, Is=30.9°(α95= 6.9°), 对应的古地磁极为49.3°N, 5.5°E (A95=6.7°), 磁倾角浅化校正后的古地磁极为53.5°N, 18.0°E。对包括本文数据在内的高质量的华北早三叠世古地磁极数据(Q≥4)进行平均, 得到校正前的古地磁极为55.3°N, 357.1°E (A95=5.5°), 校正后的古地磁极为60.8°N, 13.4°E (A95=5.8°)。经过古地磁倾角浅化校正, 华北地块早三叠世的古纬度有约10°的明显提高, 指示其东部早三叠世时与华南地块之间可能存在一定的纬度差, 但是该纬度差很可能并不代表华北地块东部早三叠世时与华南地块尚未对接, 而是指示华南地块下三叠统灰岩同样存在显著的磁倾角浅化现象。

关键词: 华北地块, 磁倾角浅化, 早三叠世, 刘家沟组, 古地磁

Abstract:

A combined paleomagnetic, rock magnetic and magnetic fabrics study is conducted on the redbeds of Early Triassic Liujiagou Formation from Qinshui Basin, North China Block (NCB). The E/I (elongation/inclination) method indicates that the characteristic remanent magnetizations (ChRM) was significantly affected by inclination shallowing with a flattening factor f=0.6. Rock magnetic analysis indicates that hematite and magnetite are the main magnetic carriers. Anisotropy of magnetic susceptibility (AMS) result shows typical depositional fabrics in water. The chRM has been successfully isolated from 15 sites with tilt-corrected mean direction of Ds=318.8°, Is=30.9° (α95=6.9°) and a corresponding paleomagnetic pole at 49.3°N, 5.5°E (A95=6.7°). The pole after E/I correction is 53.5°N, 18.0°E. Combining with published high quality Early Triassic pole (Q≥4) for NCB, the mean Early Triassic pole for NCB before and after inclination shallowing correction is 55.3°N, 357.1°E (A95=5.5°) and 60.8°N, 13.4°E (A95=5.8°), respectively. The paleolatitude of NCB is obviously higher at Early Triassic after inclination shallowing correction with ~10° increase. Furthermore, the corrected Early Triassic paleolatitude of NCB seems to be different from that of South China Block (SCB) at the east, which may result from the inclination shallowing error in Early Triassic limestone rocks of SCB instead of the real separation between the two blocks.

Key words: North China Block, inclination shallowing, Early Triassic, Liujiagou Formation, paleomagnetism

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