海洋地殻の磁化 : 海洋地磁気縞状異常の起源について

抄録

The location of the magnetized rocks of the oceanic crust that are responsible for sea-floor spreading magnetic anomalies has been a long-standing problem in geophysics. The recognition of these anomalies was a keystone in the development of the theory of plate tectonics. Our present concept of oceanic crustal magnetization is much more complex than the original, uniformly magnetized model of Vine-Matthwes-Morley. Magnetic inversion studies indicated that the upper oceanic extrusive layer (layer 2A, 0.5 km thick) was the only magnetic layer and that it was not necessary to postulate any contribution from deeper parts of oceanic crust. Direct measurements of the magnetic properties from the sea floor, however, have shown that (i) the magnetization of layer 2A is insufficient to give the required size of observed magnetic anomalies and (ii) some contribution from lower intrusive rocks is necessary. Recent ODP studies reported high magnetization intensities in the gabbroic rocks and the peridotites. The source of the lineated magnetic anomalies must reside in most of the oceanic crust and in the upper portion of upper mantle.