Results of geomagnetic survey and magnetic properties of dredged rocks at sea around Iwo-zima.
A land magnetic survey and a three-component aeromagnetic survey of Iwo-zima and its adjacent areas were conducted in 1980. Geomagnetic anomalies obtained show remarkable features of strong normal magnetization for the greater area of the seamount of lwo-zima, except for the summit portion. On the contrary, the summit area of about 20 km in diameter, including Iwo-zima in its center, shows remarkable anomalies of opposite polarity compared with the surrounding normally magnetized area. Magnetization of an uniformly magnetized seamount can be computed if its shape and magnetic anomaly are known. On the other hand, the shape of the magnetized body can be computed by two-dimensional Fourier’s analysis from its magnetic anomaly if the magnetization is known. Both of these techniques were used to estimate the shape of the magnetized portion and magnetization of the seamount under Iwo-zima. The computed intensity of magnetization is roughly I×10-2 emu/cc. The estimated shape of the magnetized portion of the seamount shows a deep cavity at its center from the topographic surface to about 2 km in depth, which would be attributable to high temperature of the core of the seamount. In June 1981, a geological and geophysical investigation in the sea around Iwo-zima was conducted. Dredged rock samples during the cruise were judged as trachyandesites from the results of observation of thin section and chemical analysis. Magnetic properties of the rock samples were also measured, and a maximum intensity of NRM (Natural Remanent Magnetization) of about 2.8×10-2 emu/cc was found for rock which contained many small grains of magnetites in the groundmass. Key Words: Geomagnetism-property of the dredged rocks-Iwo-Zima
| Main Authors: | , , , , , , |
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| Format: | Journal Contribution biblioteca |
| Language: | Japanese |
| Published: |
1982
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| Online Access: | http://hdl.handle.net/1834/16261 |
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