海洋地殻1kmの掘削と古地磁気測定

抄録

Paleomagnetic reference profile over 1 km through the upper part of the oceanic crust is constructed by the magnetic measurement of 256 Deep Sea Drilling Project samples ot Hole 504 B drilled by three DSDP/IPOD Legs 69, 70 and 83. Hole 504 B is composed of at least four magnetic groups with magnetic properties of stable inclination (Is), intensity of natural remanent magnetization (Jn), and initial susceptibility (k), whose natures are demonstrated by the peculiarities of each group. The upper two groups have the remanent intensity around of 6 A/M and magnetized reversal polarity, consistent with the presence of observed marine magnetic anomalies. The middle part of the hole, which was suffered from intense hydrothermal alteration, has a quite low NRM intensity, and it is insufficiently magnetized to be contributors of magnetic anomalies. In this part, stable inclination is also disturbed and observed inclination may not indicate their original phases. The lower part of the hole, which consists of sheeted dike complexes, has around 1 A/M NRM intensity, of which value may be evaluated as a source layer of magnetic anomaly, inconsistent with recent magnetic study of ophiolite suites.