赤石山地北部の花崗岩類と糸魚川-静岡構造線 : 赤石山地北部の地質(その2)

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In the northern part of the Akaishi Massif, granitic intrusives of two series are developed in limited area. Kaikoma-Hoo Granite intrudes discordantly into undivided Mesozoic Group (Shimantogawa Group) and the contact metamorphic effect is recognized within 2-6 km from the margin of the granitic mass. The recrystallized minerals in pelitic and psammitic sediments are biotite, muscovite, cordierite, andalusite, garnet, and potashfeldspar. In this aureole, it is noteworthy that the helicitic cordierite grows in concordant with the cleavage of the pelitic phyllite. The fact is, therefore, suggestive that the development of phyllite in the Shimanto Province is followed, at least partly, succesive intrusion of the Kaikoma-Hoo Granite. Yakejizo Granite intrudes into Kaikoma-Hoo Granite and undivided Mesozoic Group. The eastern margin of Yakejizo Granite in contact with the Itoigawa-Shizuoka Tectonic Line is transformed into mylonite for 20-100 m in width as well as Kaikoma-HOO Granite. No contact metamorphic effect by this granite is detectable in the undivided Mesozoic Group. On the other hand, in the Momonoki Formation, the Misaka Group of southern Fossa Magna, contact metamorphism of Yakejizo Granite is recognized in the east side of the Itoigawa-Shizuoka Tectonic Line. In this case, the recrystallized minerals are cordierite, muscovite, and biotite in pelitic rocks, muscovite and biotite in arkose sandstone and granophyre, and biotite and actinolite in porphyrite intrusives, respectively. The Itoigawa-Shizuoka Tectonic Line which is the eastern border of the granitic complex in this region is characterized by the low-angle thrust. The granitic mass thrusts up the Momonoki Formation, towards the east. The geologic history of this region with special reference to the development of the Itoigawa-Shizuoka Tectonic Line is traced as follows ; Sedimentation of the Shimantogawa Group and the folding of the strata. Completion of zonal arrangement of the Shimanto Zone.→Formation of phyllite in the Shimantogawa Group and successive intrusion of Kaikoma-Hoo Granite. Following uplift of the Akaishi Massif. Occurrence of primary Itoigawa-Shizuoka Tectonic Line.→Sedimentation of the Momonoki Formation in the eastern side of uplifting Akaishi Massif. -> Porphyrite and granophyre injections into the Momonoki Formation.>Intrusion of Yakejizo Granite in the Shimanto Province.→Completion of the Itoigawa-Shizuoka Tectonic Line as the low-angle thrust towards the east, and the formation of mylonite in front of the granitic mass accompanied with the thrust up.
地学団体研究会の論文
1965-01-30

赤石山地北部の花崗岩類と糸魚川-静岡構造線 : 赤石山地北部の地質(その2)

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