群馬県西部新第三紀秋間層・相間川層の古地磁気

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Palaeomagnetic stability tests of rocks have been made shift with thermal and alternating field demagnetizations. In this case, however, the memories of original or secondary magnetizations acquired during geological times are often destroyed in the processes of the demagnetization. There may be various degrees of secondary magnetization of rocks that are obtained in various stages of rock alteration. Stability tests of rock magnetization must be carried out using various kinds of altered rocks. Akima Collaborative Research Group has investigated the geology of the western part of Gunma Prefecture. The geology of this area consists of the Akima and Aimagawa Formations of Upper Miocene age. There are a great many lava flows which have suffered from a low grade of rock alteration and dislocation of bedding planes. Magnetization of these rocks was measured by an astatic magnetometer and magnetic barrance. The results of the geological investigation and measurement of rock magnetization are as follows. 1) All the lava flows of the Akima and Aimagawa Formations indicate reversed magnetization. It seems to be probable that the two formations were formed in an epoch of geomagnetic reversal in Late Miocene. 2) The orientation of natural remanent magnetization has been influenced neither by dislocation of bedding planes in the Yakehoda Member nor by the occurrence of maghemite in magnetite grains of the Yakehoda and Omine Members.
日本地質学会の論文
1976-12-30

群馬県西部新第三紀秋間層・相間川層の古地磁気

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