Abstract
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.
