氷上花崗複合岩体

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  • 許 成基
    札幌支部:北海道大学理学部地質学鉱物学教室

書誌事項

タイトル別名
  • The Hikami Granitic Complex
  • ヒョウジョウ カコウ フクゴウガンタイ

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抄録

The Hikami Granitic Complex, which extends for about 8 km E-W and 14 km N-S in the Southern Kitakami Mountains, northeast Japan, is petrographically described in detail. The Complex is petrographically divided into two granitic masses, namely A and B. Mass A mainly consists of tonalite to granite. Although the author subdivided this mass into three sub-facies, I, I' and II, according to rock facies and lithologic characters, most rocks are revealed cataclastic in texture and have undergone extensive hydrothermal alteration. Weak flow structure is characteristic throughout this mass. No contact effect on the country sedimentary rocks is apparent. The granitic mass A occupies more than two-thirds of the exposed surface of the Complex and is surrounded by Palaeozoic and Mesozoic sedimentary sequences. The Upper Carboniferous Nagaiwa series is obviously intruded by the granitic mass A in the studied area. The Ono type granite, which is petrographically equivalent to the granitic mass A, intrudes into Lower Permian rocks (Ishii et al,, 1960). The granitic mass B consists of tonalite to granite and includes the Tsubonosawa Metamorphics. It is lithologically subdivided into two subfacies and has conspicuous flow structures. Granitic rocks of the mass B are protoclastic in texture, and rarely unaltered. The mass B intrudes into the Upper Permian Toyoma series and also into the granitic mass A, while no contact effect by these granitic rocks is apparent in the host rocks. On the contrary, both the Toyama series sedimentary rocks and the granitic mass B are thermally metamorphosed by the Kesengawa type granodiorite, another granitic mass, of Middle Cretaceous age. Although the mass A is revealed as an intrusion of early Permian age, pebbles apparently derived from granitic rocks of this mass are frequently found in Middle to Upper Silurian (Kawauchi and Takainari Series) and in Lower Devonian (Ono ser.) sedimentary strata. These conflicting observations possibly signify that the granitic mass A is once was the basement of the pre-Middle Silurian stratified formations. Afterwards the mass A was partially remelted and its product (mass B) intruded into Upper Permian formations with the almost concomitant uplift of the remaining solid granitic mass A.

収録刊行物

  • 地球科学

    地球科学 30 (1), 39-53, 1976

    地学団体研究会

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