Geological and petrological studies on the Tanzawa mountainland (3),

Abstract

Three stages metamorphism of the Tanzawa metamorphic rocks are discriminated from the data of the field and microscopic observations, regional metamorphism, contact metamorphism, and hydrothermal metamorphism. The geologic relationships among these different stages of metamorphism are obtained by examining the structure of original rocks and their metamorphism. The conclusions are as follows. 1) Regional metamorphism of the first stage was not followed immediately by the contact metamorphism of the second stage, and the meta-morphosed areas of the two stages do not coinside to each other. The plutonic mass of this district is a composite mass composed of acidic and basic facies, of which the basic plutonic rock is closely related to the regional metamorphism, while the acidic plutonic rock is related to the contact metamorphism. 2) Hydrothermal metamorphism of the third stage gave an effect over-lappling with the effects due to the metamorphism during the preceeding stages. 3) Original rocks are divided into two groupes, i.e., the rocks of the inner zone and the rocks of the outer zone. The metamorphosed area of the first stage coincide to the rocks of the inner zone, while the metamorphosed area of the second stage do not coincide to that and moreover seem to extend to the rocks of the outer zone. 4) Judging from the presence of debris of plutonic rocks in the lower part of the rocks of the outer zone, it is suggested that there might have been some geologic gap between the rocks of the outer zone and those of the inner zone. The gap is compared to that between the two stages of metamorphism, i.e. the first regional metamorphism and the second contact metamorphism.