山口県後期白亜紀防府バソリスの三次元形態:地質・岩石と重力異常からの推定  [in Japanese] Three-dimensional geometry of the Late Cretaceous Hofu batholith (Yamaguchi Prefecture, Japan) inferred from geological, petrographic, and gravity anomaly observations  [in Japanese]

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Abstract

後期白亜紀防府バソリスの三次元形態と貫入・定置機構を解明するために,地質・岩石と重力異常を検討した.本バソリスは岩石組織や鉱物粒度などの岩相の違いによって粗粒花崗岩,中粒花崗岩,花崗閃緑岩,斑状花崗岩および細粒花崗岩に区分され,それらはシート状花崗岩の累重により構成される.最上部の定置深度は同時代の火山岩層に貫入することから地下2 km以内と考えられる.防府バソリスの分布域は負の重力異常域とよく一致し,とくに椹野川−大原湖断層と佐波川断層に挟まれた北東部でそれが顕著である.本バソリスは水平方向に33 × 48 kmにわたって広がり,重力異常を使ったモデル計算から,厚さ500−3,500 mと見積もられることから,水平に広がった薄い平板状岩体であると見なされる.バソリス下底面の深度が3,000 mを超える部分が断層近傍に見られることから,花崗岩マグマの供給口は断層に規制されていると考えられる.

Geology, petrography, and gravity data have been used to determine the 3D geometry and emplacement mechanisms involved in the formation of the Late Cretaceous Hofu batholith. Grain size distributions and textures have been used to classify granites of the batholith into five lithofacies: coarse-, medium-, and fine-grained granites, porphyritic granite, and granodiorite. These granites are vertically stacked sheet-like bodies that were emplaced at a depth of < 2 km, as determined from their intrusive relationships with surrounding volcanic rocks.<br>The batholith is associated with a negative gravity anomaly, particularly the northern part of the intrusion that is bounded by the Fushinogawa–Oharako and Sabagawa faults. The batholith has an areal extent of 33 × 48 km, with the base of the batholith estimated using a gravity data inversion to be at a depth of ca. −500 to −3500 m, suggesting that the batholith is tabular. The fact that the deep parts of the batholith occur at depths of −3000 m near both faults suggests that the granite magma may have been transported along near-vertical fault-controlled conduits.

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 118(12), 782-800, 2012

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130003363889
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • Article Type
    journal article
  • ISSN
    0016-7630
  • NDL Article ID
    024188974
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  IR  J-STAGE 
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