南海西北次海盆古地磁场长期变化及其环境磁学研究

LONG-TERM MAGNETIC FIELD CHANGE AND ENVIRONMENTAL MAGNETIC STUDY IN THE NORTHWESTERN SUB-SEA BASIN OF THE SOUTH CHINA SEA

王浩森

11749140

硕士

环境科学与工程

刘青松

2019-06-01

2019-07-05

哈尔滨工业大学

深圳

海洋沉积物能够记录到较为连续的古地磁与古洋流的演变信息。其中，通过对沉积物中磁性矿物记录的天然剩磁（Natural Remanent Magnetisation, 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（Relative Paleointensity, RPI）信息，这对于地磁场演变与全球记录的对比具有重要意义。目前在中国南海，尤其是在西北次海盆地区，缺乏高精度的 RPI 记录，这在一定程度上制约了我们对该区域地磁场演化精细特征的理解。为此，本论文以南海西北次海盆地区 L07 岩芯作为主要的研究对象，综合古地磁学和岩石磁学的研究方法。利用等温剩磁（Isothermal Remanent Magnetisation, IRM）作为天然剩磁（NRM）的归一化参数，构建了南海西北次海盆地区 37 ka 以来的 RPI 曲线。结果显示，L07 岩芯中载磁矿物的成分较为单一，以单畴（Single Domain, SD）低矫顽力磁铁矿为主。古地磁倾角数据显示在 220 cm 处出现了倾角负值并伴随着RPI 的低值，这与南海西北次海盆的 PC83 岩芯结果一致。我们认为此处的 RPI 最低值和倾角负值对应地磁场在 28.5ka 出现的”Mono Lake”极性事件。此外，我们还发现在 10.5 ka 年前 RPI 显示出一个峰值，通过结合东亚地区鄂霍茨克海岩芯的 RPI 记录，我们认为此 RPI 峰值是由于地球非偶极子场变化影响所致。这表明高纬度区域的磁通量变化对中-低纬区域的古地磁场信息有显著影响。

Marine sediments could record relatively continuous information on paleomagne tic and paleoceanographic changes. By normalizing the natural remanent magnetization (NRM) recorded by marine sediments by magnetic concentration-related parameters, it is possible to reconstruct the relative paleointensity (RPI) record of the geomagnetic field, which is of great significance for studying the evolution of the geomagnetic field and the comparison of global RPI records.At present, because of the lack of high-precision RPI records in the South China Sea, especially in the Northwest Sub-basin, understanding of fine features of the geomagnetic field evolution in this region has been hindered. To this end, this project systematically investigated the gravity core L07 collected form the northwestern basin of the South China Sea using both rock magnetism and paleomagnetism. The isothermal remanent magnetization (IRM) was used as the normalized parameter of NRM to reconstruct the RPI curve since the 37 ka BC in the northwestern basin of the South China Sea.Our results show that the magnetic bearing minerals in the L07 core sediments are relatively uniform and are mainly pseudo-single domain (PSD) low-coercivity magnetites. The paleomagnetic inclination data shows that the inclination is negative at 220 cm and is accompanied by the low value of RPI, which is consistent with the data of the Core PC83 in the northwestern basin of the South China Sea. We believe that the lowest RPI and negative inclination values at 200 cm correspond to the geomagnetic excursion event: “Mono Lake” polarity event.In addition, we also found that a RPI peak is shown at 10.5 ka By combining the RPI records from the Okhotsk sea in East Asia, we contribute this RPI peak to effects of the non-dipole field. More specifically, the magnetic flux anomaly at high latitudes could have significant impacts on paleomagnetic information at the mid-low latitudes.

南海西北次海盆 地磁场相对古强度 非偶极子场 古地磁学 岩石磁学

northwest sub-basin in the South China Sea relative paleomagnetic intensity of geomagnetic field non-dipole field paleomagnetism rock magnetism

中文

联合培养

南方科技大学

王浩森. 南海西北次海盆古地磁场长期变化及其环境磁学研究[D]. 深圳. 哈尔滨工业大学,2019.