四万年以来南海西北次海盆地磁场古强度演化及其地球动力学意义

海洋沉积物能够记录较为连续的古地磁信息.对沉积物记录的天然剩磁(NRM)进行归一化处理,可以构建过去较为连续的地磁场相对古强度(RPI)信息,这对于研究地磁场演变与全球记录对比具有重要的科学意义.本文以南海西北次海盆地区L07岩芯作为研究对象,利用等温剩磁(IRM)作为NRM的归一化参数,构建了南海西北次海盆地区37ka以来的RPI曲线.实验结果显示,L07岩芯中载磁矿物的成分较为单一,以单畴(SD)-细粒准单畴(PSD)低矫顽力磁铁矿为主,能够作为古强度记录的载体.此外,在11.5ka处RPI出现峰值.进一步结合东亚地区鄂霍茨克海岩芯的RPI记录以及中国黄土10Be的丰度变化,我们认为该RPI峰值是由于地球非偶极子场影响所致.这说明东亚正磁异常的影响范围可以达到中国南海等中低纬度地区,这为理解东亚地区磁场演化提供了新证据,同时也为该区千年尺度RPI记录变化特征提供了新机制.

Geomagnetic paleointensity and its geodynamic significance for the last 40 ka recorded in the northwestern sub-sea basin of the South China Sea

Marine sediments can record relatively continuous paleomagnetic information. Normalized natural remanent magnetization (NRM) records of sediments can be used to construct continuous relative paleointensity (RPI) information of the paleomagnetic field, which facilitates studying evolution of the geomagnetic field and global record correlations. This paper investigated the gravity core L07 drilled from the northwestern sub-sea basin of the South China Sea. By using isothermal remanent magnetization (IRM) as the normalization parameter, RPI curve was constructed for the past 37 ka. Results show that the dominant magnetic minerals in the L07 are mainly (pseudo) single domain (PSD/SD) magnetite particles. In addition, RPI value maximized at 11.5 ka. By further combining the RPI records of the Okhotsk sea core in East Asia and the abundance changes of ¹⁰Be in China Loess, we attribute the RPI peak to the Earth's non-dipole field. Our results indicate that the influence of positive magnetic anomalies in East Asia can reach to low latitude area such as the South China Sea. This greatly improves our understanding the evolution of magnetic fields in East Asia and provides a possible mechanism for change in the millennium scale's RPI characteristics in this region.