北部九州,白亜紀香春花崗閃緑岩牛斬山岩体(牛斬山花崗閃緑岩)のマグマ過程と成因  [in Japanese] Magma processes and genesis of the Cretaceous Kawara granodiorite Ushikiri-yama body (Ushikiri-yama granodiorite), North Kyushu, SW Japan  [in Japanese]

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Abstract

<p>香春花崗閃緑岩牛斬山岩体(牛斬山花崗閃緑岩)は福岡県田川市に分布し,北部九州バソリスの一部を形成する.牛斬山花崗閃緑岩は岩体中央部の細粒相を境に南部・北部岩体に区分され,岩体内には斑状細粒花崗岩,斑状細粒トーナル岩および斑状細粒閃緑岩が小規模岩脈として貫入する.本研究では,牛斬山花崗閃緑岩と小規模岩脈類の成因関係を検討した.斑状細粒花崗岩は南部岩体の斜長石・角閃石および黒雲母が取り去られる分別結晶作用により形成可能である.一方,斑状細粒トーナル岩は南部岩体と斑状細粒閃緑岩の混合・または斑状細粒閃緑岩が同化作用を受けることにより形成したと推察される.斑状細粒閃緑岩はSanukitic HMA組成に類似した組成であり,北部九州に点在する高Mg安山岩組成の岩石と類似した組成を示す.よって,牛斬山花崗閃緑岩と岩脈類は混合,分化および同化作用の様々なマグマ過程へて形成したと推察される.</p>

<p>The Cretaceous Ushikiri-yama granodiorite is exposed in the northern part of Tagawa city (Fukuoka Prefecture, SW Japan) and is part of the North Kyushu batholith. Three types of dikes with varying compositions are associated with the Ushikiri-yama granodiorite: porphyritic fine-grained diorite (Pr Fine Di), porphyritic fine-grained tonalite (Pr Fine To), and porphyritic fine-grained granite (Pr Fine Gr). The granodiorite intrudes the pre-Cretaceous basement rocks as an isolated stock, which can be divided into two bodies (North and South bodies), separated by a fine-grained granodiorite unit with a hypidiomorphic granular texture. The South body, which contains magmatic epidote, was intruded by the North body. Higher initial Sr isotope ratios of the South body, relative to the North body, indicate that sedimentary rocks were assimilated in the magma of the South body during its emplacement in the middle/upper crust. Geochemical data indicate that the Pr Fine To resulted from mixing of the magmas that produced the South body and the Pr Fine Di, with minor crustal contamination by host sedimentary rocks. Fractional crystallization of plagioclase, biotite, and hornblende in the South body resulted in the differentiation of the evolved Pr Fine Gr. In addition, Pr Fine Di has a sanukitic high-Mg andesite composition that is similar to Cretaceous high-Mg diorite bodies from the North Kyushu batholith. Overall, the results indicate that a variety of igneous processes including magma mixing, fractional crystallization, and assimilation with the host rocks, were responsible for the formation of the Ushikiri-yama granodiorite.</p>

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 125(3), 237-253, 2019

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130007660924
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • ISSN
    0016-7630
  • NDL Article ID
    029690395
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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