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Natural Occurrence of Titanomaghemite and Its Relevance to the Unstable Magnetization of Rocks

1960; Society of Geomagnetism and Earth, Planetary and Space Sciences; Volume: 11; Issue: 3 Linguagem: Inglês

10.5636/jgg.11.94

2185-5765

Syun-iti Akimoto, Ikuo Kushiro,

Geochemistry and Geochronology of Asian Mineral Deposits

Physical mechanism causing the scattered polarization or the unstable magnetization of some dolerite sheets was investigated through various magnetic measurements and microscopic observation. It was found from X-ray and chemical analyses that titanomaghemite exclusively occurs in the rocks showing unstable magnetization. This implies that the scattered polarization or the unstable magnetization of the rocks may be attributable to the following mechanism: the thermoremanent magnetization is destroyed by natural oxidation from original titanomagneite to titanomaghemite with the result that the remanent magnetization measured in the laboratory is only the isothermal remanent magnetization produced by the magnetic after effect under the geomagnetic field. The situations that the magnetic instability of rocks varies systematically according to the degree of the alteration or weathering were also elucidated.