| 菲律宾海西北部岩芯记录的125 ka以来的地磁场强度及其影响因素 |
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| 引用本文： | 葛淑兰,L.菲律宾海西北部岩芯记录的125 ka以来的地磁场强度及其影响因素[J].地球物理学报,2013,56(2):542-557. |
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| 作者姓名： | 葛淑兰 L |
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| 作者单位： | 1. 国家海洋局第一海洋研究所, 青岛 266061;
2. 挪威卑尔根大学地球科学系, 卑尔根 |
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| 基金项目： | 国家自然科学基金重点项目(40431002)和面上项目(40574029,40876036)联合资助 |
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| 摘 要： | 沉积物记录的地磁场强度首先提供了模拟地磁场演化的数据约束,其次提供了沉积物的年龄信息. 本文报道了菲律宾海西北部岩芯记录的地磁场相对强度,并结合岩石磁学和沉积学性质探讨了影响强度的各个因素. 除底部红粘土层的局部磁偏角偏转可能揭示了沉积后改造以外,磁化率各向异性和地磁场方向特征表明沉积物为原状沉积. 岩石磁学性质表明沉积物符合磁性均一性,可以记录可靠的地磁场强度. 由于红粘土层及其下部的磁偏角异常,本文讨论其上部约125 ka的结果. 常规归一方法获得的两个地磁场强度参数NRM/ARM(特征剩磁和非磁滞剩磁比值)和NRM/κ(特征剩磁和磁化率比值)与其它记录对比得到时间-深度对比点,对比点之间的年龄为线性内推或者外推. 地磁场强度时间模型上的岩芯氧同位素与全球氧同位素综合曲线一致证明强度结果的有效性和对比的正确性. 磁化率为归一参数的强度大多低于以非磁滞剩磁为归一参数的强度,频谱和相关分析证明NRM/ARM不与ARM和磁性矿物粒度(ARM/κ)相关,也没有轨道周期性,而NRM/κ却与κ和ARM/κ相关,而且有13~12 ka的周期. 由此我们认为NRM/ARM记录的地磁场强度比NRM/κ更好地消除了气候印记. 进一步探讨了超顺磁含量、碳酸钙含量、磁性矿物组成以及磁性矿物粒度变化与地磁场强度差值的关系,发现末次间冰期较高的超顺磁含量和磁性矿物粒度的较大范围变化造成了地磁场强度差值,后者至少造成了90%差异. 中等含量的碳酸钙和较小的磁性矿物组成变化不是磁场强度差值产生的原因. 如何校正磁性矿物粒度变化的影响将是下一步工作的重点.
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| 关 键 词： | 菲律宾海西北部 地磁场相对强度 低温和室温磁化率比值 磁性矿物粒度 |
| 收稿时间： | 2012-02-22 |
Relative paleointensity recorded in the core of northwestern Philippine Sea for the last 125 ka and its influencing factors |
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| GE Shu-Lan
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LVLIE Reidar
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SHI Xue-Fa
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FANG Xi-Sheng
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CHEN Zhi-Hua
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WU Yong-Hua.Relative paleointensity recorded in the core of northwestern Philippine Sea for the last 125 ka and its influencing factors[J].Chinese Journal of Geophysics,2013,56(2):542-557. |
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| Authors: | GE Shu-Lan LVLIE Reidar SHI Xue-Fa FANG Xi-Sheng CHEN Zhi-Hua WU Yong-Hua |
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| Institution: | 1. First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China;
2. Department of Earth Sciences, Bergen University, Bergen, Norway |
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| Abstract: | Relative paleointensity from sediments provides constraints for geomagnetic field modeling and also the age information of the deposit. The relative paleointensity in a core of the northwestern Philippine Sea was reported and its possible influencing factors including rock magnetic and sedimentological property are examined. Except for the rotation of declination in the brown clay at lower part of the core, both directions of anisotropy of magnetic susceptibility and of geomagnetic field indicate original sedimentary nature. The magnetically uniform sediment conforms to the requirement for relative paleointensity study and the correlation of relative paleointensity proxies NRM/ARM and NRM/κ with PISO1500 and SINT800 produce depth-age tie points. The sparse oxygen isotopes on paleointensity chronology in this core agree with global stack LR04, confirming the correlation of paleointensity. NRM/κ is usually lower than NRM/ARM, and the latter has no correlation with ARM and ARM/κ and also no astronomical period, but the former is correlated with ARM/κ and κ and a period of 13~12 ka by spectrum and coherence analysis. Therefore NRM/ARM is regarded to shun off imprint of climate. Further investigations between the intensity difference and its affecting elements find that difference between NRM/ARM and NRM/κ covaries with super-paramagnetic content and magnetic size variation, and the latter contributing 90% of the difference. Other elements like carbonate percentage and mineralogy change are not responsible for the difference. How to adjust the effect of magnetic size on paleointensity estimation is the focus of further work. |
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| Keywords: | Northwest Philippine Sea Relative paleointensity Low temperature and room temperature susceptibility Magnetic grain size |
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