(Table 1) Paleomagnetic properties of specimens from DSDP Holes 69-504B and 70-504B@en

Paleomagnetic and rock magnetic measurements of basalt specimens from DSDP Hole 504B, associated with the Costa Rica Rift, have a mean natural remanence intensity (Jn) between 5 and 10 x 10**-3 gauss, consistent with the presence of a magnetized layer that is 0.5 to 1 km thick, which produces the observed magnetic anomalies. A mean Koenigsberger ratio (Qn) greater than 10 indicates that the remanence dominates the magnetic signal of the drilled section. The susceptibility (x) increases with depth, and the median demagnetizing field (MDF) decreases with increasing depth in Hole 504B, congruent with the downhole increase in the relative abundance of massive flow units. Hole 504B is composed of at least 12 units with distinct stable average inclinations (Is), which probably represent extrusion at times of different geomagnetic field directions and possibly also the effects of faulting. The thickness of basalt associated with these inclination units varies from less than 9 meters to possibly as much as 160 meters. Two relatively thick magnetic units (40 m and 45 m, separated by 100 m) have anomalously high Is values of -53° and -63°, in contrast with the near zero inclinations expected for the equatorial latitude of Site 504. For this reason and because the average inclination of all the magnetic units is skewed to a negative value, it might be that the entire section at Hole 504B was tilted by approximately 30°.

针对与哥斯达黎加裂谷（Costa Rica Rift）相关的深海钻探计划（Deep Sea Drilling Project, DSDP）504B孔的玄武岩标本开展的古地磁与岩石磁学测量结果显示：其天然剩余磁化强度（natural remanence intensity, Jn）的平均值介于5×10⁻³至10×10⁻³高斯之间，该结果与厚度为0.5至1千米的磁化层的存在相吻合，该磁化层正是观测到的磁异常的成因。柯尼斯伯格比（Koenigsberger ratio, Qn）的平均值大于10，表明剩余磁化主导了该钻探段的磁信号。504B孔的磁化率（susceptibility, χ）随深度增加而升高，而中位退磁场（median demagnetizing field, MDF）则随深度增加而降低，这一变化规律与块状熔岩流单元相对丰度随井深升高的趋势相一致。504B孔至少由12个具有独特稳定平均倾角（stable average inclinations, Is）的单元构成，这些单元大概率对应着不同地磁场方向时期的熔岩喷发，同时也可能受到断层作用的影响。这些倾角单元对应的玄武岩厚度从不足9米到可达160米不等。两个相对较厚的磁单元（厚度分别为40米与45米，二者间距100米）呈现出异常偏高的Is值——-53°与-63°，这与504站位所在赤道纬度预期的近零倾角形成显著反差。基于上述原因，加之所有磁单元的平均倾角整体偏向负值，推测504B孔的整个钻探段可能发生了约30°的倾斜。