Formation history of the Japanese Islands
11 to 2 million years ago (Late Miocene - Pliocene)
Fig. 12
Pliocene paleogeographic map [
]
The volcanic front and the trenches were situated near the present
positions and the shoreline was similar to the modern line in this
period. The Japanese Islands, except for a few areas including
Beppu-Shimabara Graben, have been dominated by compression owing to the
subduction of the Pacific Plate and the Philippine Sea Plate since this
period. As a result, reverse or strike-slip faulting and folding formed
mountain ridges and basins. The active island-arc volcanism occurred;
in northeastern Honshu and Hokkaido, eruptions with large scale
pyroclastic flow produced volcanoes with a caldera, and in Kyushu,
grabens developed in the Hohi volcanic zone (on the north of the
Beppu-Shimabara Graben), which may be regarded as the pre-subsidence of
the Okinawa Trough extending to the southwest of these grabens.
In northeast Japan, the Ou Range began uplifting 10 million years ago
and grew to mountains six million years ago. Since the uplift rate
increased in the Late Pliocene, depression areas in the Miocene have
inversely changed into heights. The mountain areas (Dewa Mountains) on
the west of the Ou Range upheaved above the sea level 2.5 million years
ago (Late Pliocene).
In southwest Japan, tectonic movement was milder compared to northeast
Japan. Gentle warping occurred in the island arc direction in the
inland five million years ago. Lacustrine and fluvial deposits
accumulated in depression areas formed by this warping. The developed
depression area resulted in the Seto Inland Sea. Neogene deposits
except shallow-marine sediment of the Middle Miocene are hardly found
in northern and central Kyushu. Therefore, Kyushu is thought to have
been broadly land in this period. In the Nansei Islands, the Okinawa
Trough began to be formed in the Late Miocene-Pliocene (or 10 million
years ago).
In central Honshu, the collision of the Izu-Bonin Arc, which started 15
million years ago, still continued. The Tanzawa block and the Izu block
accreted to the Honshu island to be the Tanzawa Mountains eight million
years ago and the Izu Peninsula 1.5 million years ago, respectively.
These multiple collision of the blocks markedly deformed the Honshu
island, bended geotectonic structure such as the Shimanto Belt, the
Chichibu Belt, and the Median Tectonic Line. The collision also
effected on major configuration including the Akaishi, the Kiso, and the Hida Ranges to the west of the collision zone.
2 million years ago to the present (Quaternary) and future
Fig. 12
Pleistocene paleogeographic map []
The Japanese Islands has been strongly compressed by the
eastward movement of the sea floor of the Sea of Japan as well as the
westward subduction of the Pacific Plate and the Philippine Sea Plate since
two million years ago. The uplift rates of mountain ranges formed
between the end of the Miocene and the Pliocene increased because of
this powerful compression. As a result, an abundance of clastic material
from mountains was provided in lowlands. There are also considerably
subsiding areas. The Kanto Plain, for example, has sunk over 1000 m in
the Quaternary, being the largest plain in Japan. The uplift rates of
mountains in northern and central Honshu (Tohoku and Chubu Regions) are
greater than those in western Honshu (Chugoku Region).
The earth repeatedly experienced ice ages in the Quaternary. The
Japanese Islands were connected with the continent by land during the
last ice age (tens of thousands to 10000 years ago) because the sea
level fell by 120 m. Mammoths came to Hokkaido from Siberia, and various
animals came and went between southwest Japan and the Korean Peninsula.
Glaciers developed in high mountain areas of Hokkaido to central Honshu,
forming glacial landforms. Some of them remain in those areas.
Most Quaternary volcanoes are active in current positions and create
characteristic landforms of the Japanese volcanic islands.
[In the future]
It is predicted that Australia will collide with the Asian continent
about 50 million years later and the North American continent will meet
with the Asian continent 200 million years later, based on the motion of
the present continents. As a result, a supercontinent will be formed and
the Pacific Ocean will be closed. The Japanese Islands will disappear
because they assimilate with the supercontinent.
References
*Titles of the following references
[Pre-Cambrian - Cretaceous]
Isozaki et al., 2010 (in English)
Isozaki, 2000
Kanagawa Prefectural Museum of Natural History, 2010
Taira, 1990
[Paleogene - Quaternary]
Yonekura et al., 2001
Nohda, 2008
Taira,1990
Iijima and Tada, 1990
