地質学雑誌
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
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115 巻, 6 号
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  • 結晶方位配列と亜結晶粒回転軸によるかんらん石すべり系の推定～秋田県男鹿半島一の目潟火山かんらん岩捕獲岩を例として～
    佐津川 貴子, 道林 克禎
    2009 年115 巻6 号 p. 288-291
    発行日: 2009年
    公開日: 2009/10/29
    DOIhttps://doi.org/10.5575/geosoc.115.288
    ジャーナル フリー
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    In this study of peridotite xenoliths from Ichinomegata volcano, Oga peninsula, NE Japan, we used electron backscattered diffraction to assess the validity of two methods of identifying the olivine slip system that operated during deformation. The xenoliths are harzburgite in composition and contain a distinct foliation and lineation defined by aligned spinel and pyroxene grains. Using the first method, the dominant slip system in olivine was estimated based on the crystallographic preferred orientation (CPO) of olivine with respect to the foliation and lineation. The second method was based on an analysis of subgrain rotation: given that intracrystalline subgrain boundaries were observed within several olivine grains, we measured the misorientation angles across these boundaries to define sets of slip planes, slip directions, and rotation axes. The olivine slip systems estimated using the two methods are essentially identical. The CPO pattern provides an important constraint on the dominant slip system that operated during deformation, whereas the analysis of subgrain rotation yields the slip system responsible for the development of individual subgrain boundaries composed of edge dislocations. The two methods are therefore complementary.
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  • Upper Triassic reefal limestone from the Sambosan accretionary complex in Japan and its geological implication
    Tetsuji Onoue, Jérôme Chablais, Rossana Martini
    2009 年115 巻6 号 p. 292-295
    発行日: 2009年
    公開日: 2009/10/29
    DOIhttps://doi.org/10.5575/geosoc.115.292
    ジャーナル フリー
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    Upper Triassic limestone within the Sambosan accretionary complex in Japan contains reefal facies that accumulated on a mid-oceanic seamount in the Panthalassa Ocean. Such limestone is found at the Inaba Cave locality along the Shimanto River, central Shikoku. The reefal limestone occupies part of a bioclast-rich limestone that occurs as an allochthonous tectonic slab. The reefal limestone is characterized by sponge-algal rudstone-floatstone and coral bafflestone rich in Retiophyllia. Megalodonts floatstone also occurs in association with the reefal facies. Although the lateral continuity and exact relationship between the Megalodonts floatstone and the reefal facies remain uncertain, this is the first report in which this unique facies association has been described in the Sambosan accretionary complex.
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