シコク セイブ ウチコ オダ チイキ ノ ミカブ リョクショク ガンルイ ノ チシツ コウゾウ

Geological structures of the Mikabu greenstones were studied in the Uchiko-Oda Area in West Shikoku. Greenstones near Mt. Takamori, to the east of Ikazaki, consist of basaltic tuff breccia, tuff and gabbro. They continue eastward, through Umezu, to the widely distributed Mikabu greenstones near Mt. Rohgajo and Mimido. Therefore, the greenstones near Mt. Takamori and Umezu can be correlative with the Mikabu greenstones. The Mikabu greenstones of the Uchiko-Oda Area are intercalated in the Jurassic accretionary complex as a sheet-like unit, and are folded by the Utsumukiyama and Odagawa antiforms. The Mikabu greenstones should be included in the northern Chichibu Terrain in the sight of geological structures. The Kiyomizu Tectonic Line, which runs along the northern margin of the Mikabu greenstones, is probably a large fault, dividing the Sanbagawa Terrain from the Northern Chichibu Terrain

シコク セイブ チチブタイ トリガタヤマ オオノガハラ セッカイ ガンタイ ト シンキ イノ ヘンセイ コンプレックス ノ チシツ コウゾウ

Geological structures of the Torigatayama-Onogahara limestone body of the Permian accretionary complex and the Younger Ino metamorphic complex were studied in the Chichibu Terrain in West Shikoku. The Torigatayama-Onogahara limestone body consists of six limestone bodies, which occur in a convex way toward south. The limestone bodies are northward facing and form southward thrust sheet, and do not occur in the axial part of a synform. An antiform and a synform occur in the distributional area of the Younger Ino metamorphic complex. The antiform does not extend westward to the distributional area of the Yusugawa Unit of the Jurassic accretionary complex. The Permian accretionary complex and the Younger Ino metamorphic complex do not occupy the highest tectonic horizon in the Chichibu Terrain in West Shikoku

シコク チュウオウブ ニシイシハラ チイキ ニオケル ミカブ リョクショク ガンルイ ノ チシツ コウゾウ

Geological structures of the Mikabu greenstones and northern margin of the Chichibu Terrain are studied in the Nishi-ishihara Area, Central Shikoku. The Mikabu greenstones are not considered to occur in the area between Nishi-ishihara and Kamiyakawa in Central Shikoku, because of the existence of the Nishi-ishihara thrust. This study, however, clarified that the Mikabu greenstones composed of tuff and tuff breccia occur in a narrow zone there. Therefore, the Mikabu greenstones are considered to expose continuously from Nishi-ishihara to west of Kamidoi. The Mikabu greenstones are intercalated in the Jurassic accretionary complex, and form an antiform. The antiform of the Nishi-ishihara area can be traced to the Nanokawa area in Middle West Shikoku, and also affects the Mikabu greenstones near Mt. Zohshi-yama. Jurassic complex under the Mikabu greenstones lies in the axial part of the antiform. The complexes of the northern and southern limbs have the same lithologic characters with each other. The Kamiyakawa-Ikegawa Tectonic Line, which runs along the antiformal hinge, is not a fault separating the Sanbagawa Metamorphic Terrain from the Northern Chichibu Terrain

Mitaki Igneous Rocks and Younger Ino Metamorphic Complex of the Torigatayama-Onogahara Area in the Kurosegawa Terrain, West Shikoku

Small granitic bodies of the Mitaki igneous rocks of the Kurosegawa Terrain occur in the area to the north of Mt Mitaki, in the Onogahara-Torigatayama Area, West Shikoku. These granitic bodies measure 40-60 m wide and 350-600 m long. They are metamorphosed under pumpellyite-actinolite facies conditions to form pumpellyite, actinolite, chlorite and albite. Phyllites, calcareous sandstones and greenstones with actinolite occur around the granites. They possibly constitute the Permian accretionary complex. The Permian accretionary complex underlies the Jurassic accretionary complex by fault. Amphiboles of the greenstones, which are thought to be the Younger Ino metamorphic complex of the Kurosegawa Terrain, are glaucophane or ferroglaucophane, and coexist with pumpellyite. These greenstones are correlated with those of the Kurosegawa Terrain in Central Shikoku. On the other hand, amphiboles of the Permian accretionary complex near the Torigatayama-Onogahara limestone body are actinolite-ferroactinolite or winchite-ferrowinchite, showing lower-grade metamorphism than the Ino Metamorphic Complex

Nanokawa thrust of the Northern Chichibu Terrain in Middle West Shikoku

In the Northern Chichibu Terrain in Middle West Shikoku, the Nanokawa thrust occurs in the Jurassic accretionary complexes. Along the Nanokawa thrust, greenstones and pelitic semi-schists of the Nakatsuyama Unit are thrust over chaotic formations, sandstones and greenstones of the Niyodogawa Unit. The strata of the Nakatsuyama Unit dip gently and are slightly folded, whereas those of the Niyodogawa Unit dip steeply to the north. Metamorphic minerals of the greenstones of the hanging wall and footwall of the Nanokawa thrust are examined. The greenstones of the hanging wall contain alkali amphibole, alkali pyroxene, stilpnomelane and pumpellyite, and have undergone the pumpellyite-actinolite facies metamorphism. On the other hand, those of the footwall contain prehnite and pumpellyite, and have undergone the prehnite-pumpellyite facies metamorphism. The Nanokawa thrust is a large overthrust, which has a different metamorphic grades between the hanging wall and footwall. The Nanokawa thrust extends toward west to the north of the Torigatayama limestones. The thrust does not extend to the Kurofujigawa thrust, which occurs near the Mikabu greenstones

シコク チュウオウブ ササガタニ チイキ ニオケル チチブ ホクタイ ノ チシツ コウゾウ

The Sasagatani fault in central Shikoku was considered to be a tectonic boundary between the Sanbagawa high-P/T metamorphic belt and the Chichibu non-high-P/T belt. Metamorphic minerals of the greenstones around the Sasagatani fault are examined. Alkali amphibole, alkali pyroxene, actinolite, stilpnomelane and pumpellyite are found not only on the north side of the fault, but also on the south side. Strata around the Sasagatani fault have undergone the pumpellyite-actinolite facies metamorphism. Thus, the Sasagatani fault is not an upper boundary fault of the Sanbagawa metamorphic rocks. The Nanokawa thrust occurs in the Jurassic accretionary complexes of the Northern Chichibu Terrain in the Sasagatani Area. The greenstones of the hanging wall of the thrust have undergone the pumpellyite-actinolite facies metamorphism, whereas those of the footwall have undergone the prehnite-pumpellyite facies metamorphism. The Nanokawa thrust is a large overthrust, which has a different metamorphic grade between the hanging wall and footwall. The thrust is probably a southern boundary of the Jurassic accretionary deposits which have undergone the Sanbagawa metamorphism

シコク チュウオウブ セイブ カミドイ チイキ ト オダ チイキ ニオケル ミカブ リョクショク ガンルイ ノ チシツ コウゾウ

Geological structures of the Mikabu greenstones and northern margin of the Chichibu Terrain were studied in the Kamidoi and Oda Areas in Central to West Shikoku. It has been thought that the Mikabu greenstones did not occur in the Kamidoi and Nishi-ishihara Areas in Central Shikoku, because of the existence of the Nishi-ishihara and Ikegawa thrusts. This study, however, clarified that the Mikabu greenstones composed of tuff and tuff breccia occur in a narrow zone there. The Mikabu greenstones are intercalated in the Jurassic accretionary complex as a layered unit, and are folded by the Kamiyakawa-Ikegawa antiform. The Mikabu greenstones of the Oda Area are also intercalated in the Jurassic complex and form the Odagawa antiform, which is the same as the Kamiyakawa-Ikegawa antiform. There is no large thrusts along the southern margin of the Mikabu greenstones. The Jurassic complexes under the Mikabu greenstones of the Kamidoi and Oda Areas have undergone the pumpellyite-actinolite facies metamorphism, like as the Mikabu greenstones and the overlying Jurassic complex. The Kiyomizu Tectonic Line, which runs along the northern margin of the Mikabu greenstones, is probably a large fault, dividing the Sanbagawa Terrain from the Mikabu greenstones and the Nortner Chichibu Terrain