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Outline of landforms and geology of Japan
Hida and Oki Belts
The Hida Belt and the Oki Belt are the oldest units mainly consisting
of metamorphic rock (gneiss). Some of the rocks are of the Precambrian,
which are considered fragments of South China (Yangtze) block. Rock
aged two billion years was found in both belts. Rocks in the Hida Belt
were remetamorphosed at least three times and intruded by granite (220
Ma–180 Ma). The belt also includes Carboniferous-Permian sedimentary
rocks.
Hida Marginal, Renge, Joetsu, and Kurosegawa Belts
These belts consist of high-pressure type metamorphic rock, ophiolite,
terrigenous sedimentary rocks including tuff and limestone, and igneous
rocks formed in the subduction zone. The ages of the rocks range from
500 to 300 million years old. The metamorphic rocks include metamorphic
rock related to subducted mid-ocean ridge. The Hida Marginal Belt and
the Renge Belt are adjacent to the Hida Belt and the Oki Belt, but the
Kurosegawa Belt is located in a Jurassic accretionary complex zone
(Chichibu Belt), lying from the eastern Kii Peninsula to western
Kyushu. The Kurosegawa Belt is considered a klippe without the root.
Akiyoshi, Maizuru, Sangun, and Ultra-Tamba Belts
These belts are Permian accretionary complex zones aged 300 to 200
million years. The Akiyoshi Belt is dominated by limestone including
fossils such as coral and fusulinid inhabiting in the tropics. Since it
is underlain by oceanic basalt and includes no terrigenous deposit, the
limestone derives from accreted seamounts formed in the tropical sea
far away from the land. The Maizuru Belt is characterized by ophiolite.
The Sangun Belt is a high P/T metamorphic rock zone (high P/T: high
ratio of pressure to temperature, showing high-pressure and
low-temperature metamorphic condition). Subducted accretionary deposits
of the Akiyoshi Belt and the Maizuru Belt were metamorphosed under
high-pressure condition to be the Sangun metamorphic rocks. The Ultra-Tamba
Belt consists of chert, sandstone, and mudstone.
Mino-Tamba, Chichibu, and Ashio Belts
These belts are Jurassic accretionary complex zones aged 200 million
years or younger. Ocean-floor basalt, limestone, chert, mudstone,
terrigenous sediment (sand and mud) constitute the belts. The Chichibu
Belt situated to the south of the Mino-Tamba Belt is considered as a
nappe.
Ryoke and Sambagawa Belts
These belts are metamorphic rock zones. Metamorphic rock type in the
Ryoke Belt is the low P/T type (low-pressure and high-temperature type
metamorphism), formed by massively granitic intrusion about 100 million
years ago. Metamorphic rock type in the Sambagawa Belt is the high P/T
type. The parent rocks (protolith) of the Sambagawa metamorphic rock
are accretionary complex formed 140 million years ago. The subducted
accretionary complex was metamorphosed by about 110 million years ago,
and uplifted 80 to 70 million years ago.
Shimanto Belt
This belt is a accretionary complex zone formed 100 to 30 million years
ago (Cretaceous to Paleogene), distributed in the outermost end
(Pacific side) of southwest Japan from the Boso Peninsula in Kanto to
the Nansei Islands (1800 km in length and 100 km in maximum width).
Oceanic basalt, pelagic sediments (chert and limestone), and
terrigenous sediments (sandstone and mudstone) constitute the belt.
Trench-fill sediments of sand and mud principally occur as alternating
beds of sand and mud (turbidite). Mélange zones containing blocks of
oceanic crust (basalt and chert) are sandwiched in turbidite zones.
(See "Tei mélange and Muroto")
[Northeast Japan (Tohoku and western Hokkaido)]
The boundary between southwest Japan and northeast Japan as basement geology is the Tanakura Tectonic Line, although the Itoigawa-Shizuoka Tectonic Line is the border between the Southwest Japan Arc and the Northeast Japan Arc. Geotectonic units obliquely across the island arc (not parallel to the trench), but these are considered to have formed in the margin of the Asian continent with accretionary complexes in southwest Japan.
Hitachi-Takanuki, Matsugadaira-Motai, and South Kitakami Belts
Rocks (500-300 million years old) formed in a subduction zone
constitute these belts. The Hitachi-Takanuki Belt is composed of
metamorphic rocks, sedimentary rocks including tuff and limestone, and
igneous rocks. The Matsugadaira-Motai Belt is a high P/T metamorphic
rock zone. The South Kitakami Belt is comprised of various type rocks
including metamorphic rocks, igneous rocks, and terrigenous
(shallow-sea) sedimentary rocks. These belts are distributed on the
Pacific side. In southwest Japan, pre-Permian rocks, other than rocks
in the Kurosegawa Belt are found on the Sea of Japan side.
North Kitakami and Oshima Belts
The North Kitakami Belt is a Jurassic accretionary complex zone. The
Oshima Belt in southwestern Hokkaido is regarded as the extension of
the North Kitakami Belt.
Gosaisho Belt
This belt is composed of a low P/T metamorphic rock with granite aged
200 to 100 million years, which is considered to be related to the
Ryoke Belt.
[Hokkaido]
Geotectonic units in Hokkaido are distributed north-south, not parallel to the Kuril Trench. It is thought that the tectonic settings of areas in which the basement rocks of Hokkaido were formed differed from southwest and northeast Japan. Therefore, the characteristics of the geotectonic units are distinct from those in other regions.
Oshima Belt
The Oshima Belt situated in westernmost Hokkaido is a Jurassic
accretionary complex zone regarded as the extension of North Kitakami
Belt as mentioned above.
