Paleomagnetic properties of basalts of ODP Hole 111-504B (Table 3)@en

Downhole magnetic field measurements were conducted in Hole 504B on the Costa Rica Ridge during ODP Leg 111. Three magnetic groups within oceanic basement at this site are tentatively defined, based on the interval mean values of the downhole magnetic field. Statistical analyses show that there are significant differences in the inclinations of natural remanent magnetization (NRM) among the three magnetic groups. Although this could be caused by various factors, we explain the inclination difference among the three groups by simple tectonic displacements of basement by faulting after its formation, about 5.9 Ma ago. Based on the intensities of NRM and inclinations measured in the basement core samples drilled in Hole 504B on DSDP Legs 69, 70, and 83 and ODP Leg 111, the investigated section of basement formation can be divided into three or four magnetic zones that parallel the zones defined by the downhole magnetic field, alteration, and lithology. Downhole magnetic field and paleomagnetic data generally correlate positively, in spite of some discrepancies. The magnetic susceptibility values of the core samples were used to derive the insitu NRM from the downhole magnetic field data.在大洋钻探计划（Ocean Drilling Program, ODP）第111航次期间，研究人员于哥斯达黎加海脊的504B钻孔开展了井下磁场测量。基于井下磁场的区间平均值，本站位洋壳基底内暂划分出三个磁组。统计分析表明，三个磁组的天然剩余磁化强度（natural remanent magnetization, NRM）倾角存在显著差异。尽管该差异可能由多种因素导致，但我们将三个磁组间的倾角差异归因于约590万年前基底形成后，断层作用引发的简单构造位移。结合深海钻探计划（Deep Sea Drilling Project, DSDP）第69、70、83航次及大洋钻探计划第111航次在504B钻孔采集的基底岩芯样品所测得的NRM强度与倾角，本次研究的基底形成剖面可划分为三个或四个磁带，这些磁带与井下磁场、蚀变作用及岩性所划分的带具有一致性。尽管存在部分偏差，但井下磁场与古地磁数据总体呈正相关关系。研究人员利用岩芯样品的磁化率数值，从井下磁场数据反演得到原位天然剩余磁化强度。