近畿中央部,初瀬深成複合岩体の定置過程  [in Japanese] Emplacement process of the Hatsuse plutonic complex, central Kinki Province, SW Japan.  [in Japanese]

近畿中央部の初瀬深成複合岩体は,主に片麻状黒雲母花崗閃緑岩とそれと同時形成の苦鉄質岩類から構成されており,E-W方向とNW-SE方向の2つのシンフォームによって特徴づけられるベースン構造を形成している.花崗閃緑岩の片麻状構造は,主に黒雲母クロットの形態定向配列によって定義され,マグマ流〜亜マグマ流によって形成されている.花崗閃緑岩中の角閃石の化学組成から,花崗閃緑岩マグマの定置深度は,およそ20kmと見積もられる.花崗閃緑岩中には,高温の塑性変形組織が見出されている.マグマ流〜亜マグマ流による変形と高温塑性変形の最大伸長方向が一致しており,これらの変形作用は花崗閃緑岩の定置に関連して,マグマの固結後に温度の低下とともに連続して生じたと推測される.E-W方向のシンフォーム構造は,領家変成帯中に広く認められるD3期鉛直褶曲構造と平行であることから,片麻状黒雲母花崗閃緑岩は,領家変成帯の鉛直褶曲時の広域応力場において定置したと考えられる.

Hatsuse plutonic complex in the Ryoke metamorphic belt, central Kinki Province, SW Japan, is composed mainly of the Cretaceous gneissose biotite granodiorite and hornblende gabbros. The biotite granodiorite is a syn-kinematic pluton during the deformation forming upright folds and the hornblende gabbros are syn-plutonic dykes intruded subparallel to the gneissosity of the surrounding granodiorite. The trends of the gneissose structure in the granodiorite and of the lithological boundaries between the granodiorite and gabbros exhibit basin structure possibly divided into major E-W trending synform and minor N-S trending synform. The gneissose structure in the granodiorite is defined mainly by the alignment of the long-axis of the biotite clots. Based on the microstructural analyses, the gneissose structure was formed by the magmatic to submagmatic flow during the emplacement of the granodiorite magma. Based on the amphibole chemistry, emplacement depth of the granodiorite magma was estimated to be 450-600 MPa that corresponds to crustal depth of about 20 km. In the granodiorite, since high-temperature plastic deformation conditions determined by the c-axis fabric of quartz grains (X-maximum and type-II crossed girdle patterns) are observed in the quartz grains and the maximum elongation directions between the magmatic/submagmatic flow and the high-temperature plastic deformation structures are consistent with each other, the deformation related to the emplacement of the granodiorite magma lasted just after the solidification of the magmas. The basin axis of the major E-W trending synform is parallel to the regional upright folds observed elsewhere in the Ryoke metamorphic belt ; the emplacement of the plutonic complex may be governed by the regional stress fields to form the upright folds in the Ryoke metamorphic belt.