热带海洋学报 ›› 2012, Vol. 31 ›› Issue (3): 103-112.doi: 10.11978/j.issn.1009-5470.2012.03.014

• 海洋地球物理学 • 上一篇    下一篇

南海北部陆缘下侏罗统古地磁与岩石磁学结果*

张伙带1, 谈晓冬2, 周蒂2, 黎铭汉3, 陈汉宗2, 汤贤赞2   

  1. 1.广州海洋地质调查局, 广东 广州 510760; 2. 中国科学院南海海洋研究所边缘海地质重点实验室, 广东 广州 510301; 3. 广东省佛山地质局, 广东 佛山 528000
  • 收稿日期:2011-04-19 修回日期:2011-06-02 出版日期:2012-09-11 发布日期:2012-09-11
  • 作者简介:张伙带(1985—), 女, 广东省云浮市人, 硕士学历, 主要从事古地磁学研究。E-mail: z183514387@126.com
    通信作者: 谈晓冬。E-mail: xdtan@scsio.ac.cn
    * 两位匿名评阅人对本文原稿提出了建设性意见, 作者由衷地表示感谢。
  • 基金资助:

    国家重点基础研究发展计划项目(2007CB41170401)

Paleomagnetic results and magnetic characteristics of rocks from Lower Jurassic rocks in the northern margin of the South China Sea

ZHANG Huo-dai1, TAN Xiao-dong2, ZHOU Di2, LI Ming-han3, CHEN Han-zong2, TANG Xian-zan2   

  1. 1. Guangzhou Marine Geological Survey, Guangzhou 510760, China; 2. Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;3. Foshan Geological Bureau of Guangdong Province, Foshan 528000, China
  • Received:2011-04-19 Revised:2011-06-02 Online:2012-09-11 Published:2012-09-11

摘要: 前人研究表明,粤东海盆、南沙地块东部、加里曼丹西部存在晚三叠—早侏罗世海相地层, 并且沉积相和古生物的对比认为它们在晚三叠—早侏罗世可能属同一海盆。文章对广东梅县、惠州和东莞的下侏罗统进行了古地磁研究, 试图从古地磁的角度探讨粤东海盆、南沙地块东部、加里曼丹西部是否同属一个海盆。本文退磁结果表明,梅县玄武岩样品分离出低温剩磁和高温特征剩磁; 惠州样品只有少数能分离出低温剩磁,难以统计方向;东莞红层样品分离出低温剩磁、中温剩磁和高温特征剩磁。梅县和东莞低温剩磁方向与当地现代地磁场方向一致,为现代地磁场的重磁化结果。所有采点中,只有2个采点分离出了高温特征剩磁, 难以用褶皱检验方法检验高温特征剩磁是否原生剩磁。若用华南地块早侏罗世、中—晚侏罗世和白垩纪参考极限定东莞和梅县磁倾角大小, 对比东莞中温剩磁、高温特征剩磁和梅县高温特征剩磁褶皱展平0—100%的倾角范围, 讨论各剩磁在褶皱展平的形成阶段, 结果为东莞中温剩磁在褶皱展平70%—80%时获得; 东莞高温特征剩磁可能在褶皱展平后获得; 但无法确定梅县高温特征剩磁最可能在哪个褶皱展平阶段获得。磁组构揭示了东莞红层沉积和压实特征, 增加了东莞高温特征剩磁为原生剩磁的可能性。等温剩磁曲线、热退磁曲线和交变退磁曲线表明, 东莞红层的携磁矿物为赤铁矿; 梅县玄武岩部分样品携磁矿物为磁铁矿, 部分样品携磁矿物为赤铁矿。文章的古地磁结果虽然未能回答“粤东海盆、南沙地块东部、加里曼丹西部是否同属一个海盆”的科学问题,但为今后进一步的古地磁工作提供了有用信息。

关键词: 南海北部陆缘, 早侏罗世, 古地磁, 岩石磁学

Abstract: Previous study has showed that Late Triassic and Early Jurassic marine sediments exist in the northern margin of the South China Sea (SCS), the eastern part of Nansha Block and the western part of the Kalimantan Islands. Similarities of lithofacies and fossil types between these areas indicate that they probably belonged to a unified basin in the Late Triassic and Early Jurassic. To test this hypothesis, paleomagnetic data are required from these three crustal blocks, and here we report Early Jurassic paleomagnetic data from the northern margin of the SCS. Seven sites (98 samples) of volcaniclastic sediments and basalts were collected from Meixian; two sites (48 samples) of siltstones were collected from Huizhou and Dongguan. Single, recent overprint component was found in the volcaniclastic sediments from Meixian. Low temperature component (LTC) and high temperature component (HTC) can be isolated from basalts in Meixian. LTC, intermediate temperature component (ITC) and HTC can be isolated from siltstones in Dongguan. The LTC directions from Meixian and Dongguan are distributed near the present geomagnetic field, indicating that they are recent viscous remanence. HTCs can be isolated from these two sites. However, it is hard to know whether the HTCs are primary components because fold tests are not available. If reference poles of Early Jurassic, Mid-Late Jurassic and Cretaceous from the South China Block (SCB) were used to confine the magnetic inclination of Meixian and Dongguan, we could estimate which phase the components were formed in during 0?100% unfolding of the strata by comparing the confined inclination to the magnetic inclination during unfolding. With this method, we conclude that the ITC of Dongguan was formed when the strata was unfold by 70%?80% and HTC of Dongguan was probably formed before the folding, but we cannot determine when the HTC of Meixian was formed because the range of magnetic inclination during unfolding is wide. Results of anisotropy of magnetic susceptibility (AMS) are consistent with lava flow fabrics, sediment deposition and compaction fabrics. Curves of isothemal remanent magnetism (IRM), thermal demagnetization and alternative field demagnetization indicate that the main magnetic mineral of red beds from Dongguan is hematite and that the main magnetic mineral of some specimen from Meixian is magnetite while the main magnetic mineral of other specimen from Meixian is hematite. Though our result can’t answer the question that whether the northern margin of SCS, the eastern part of Nansha Block and the western part of the Kalimantan Islands belonged to the same basin in the Late Triassic and Early Jurassic due to the limited paleomagnetic data, it is still important to report the result to provide information for further paleomagnetic research of those areas.

Key words: northern margin of the South China Sea, Early Jurassic, paleomagnetism, magnetic characteristics of rocks

中图分类号: 

  • P738