鉱脈による新第三紀東北本州弧の造構応力場復元

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More than 3,300 metalliferous veins were analyzed to reconstruct the Neogene tectonic stress fields of Northeast Honshu Arc based on the basic knowledge of fracture mechanics. Not only the stratigraphic data of country rocks but also more than 40 isotopic ages of veins, altered country rocks and igneous rocks which have genetical relations to the mineralization were used to estimate the age of stress fields. The distribution of veins is limitted on the east by "metalliferous vein front" which coincides with the middle and late Miocene volcanic front. More than 80% of veins are distributed within the lower Miocene series, and concentrated on the Ou-backbone Range and NW-trending uplift zones with about 50km wavelength in backarc side. Veins are distinguished in to the most dominant NE-system and subordinate EW-, NS- and NW systems. Most of them are Cu・Pb・Zn and Au・Ag veins. The NW-system in southwest Hokkaido is characterized by manganiferous veins. There is no vein of thrust fault. The NE-system is an assemblage of conjugate strike-slip faults, extension joints and normal faults. They suggest that σ_3 was NW〜NNW in trend and virtually tensional, and that σ_1 or σ_2 was NE〜ENE in trend. The NE〜ENE-trending compressional stress may have not been intense, and σ_1 and σ_2 may have been easily exchanged. Such a stress field prevailed through out the period from 15 Ma to late Miocene. Thereafter, it was replaced by a different stress field; EW〜ENE-trending compression which is transitional from the Miocene stress field to the present one.
日本地質学会の論文
1989-03-15

鉱脈による新第三紀東北本州弧の造構応力場復元

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