Seisme du Japon
11 Mars, 2011

Main shock (9.1)
and after shocks
with tsunami(port wave)

Intern. WS Geoneutrino Research (Sendai; Oct. 25, 2016)

Geotectonic evolutionof the Japanese Islands
significance not only for Japan but also for the whole mantle

Yukio Isozaki
Dept. Earth Science & Astronomy
The University of Tokyo

Maruyama et al. (1989)

North China

South China
Asia is a composite continent
composed of 9-10 blocks

Old Japan along South China (Yangtze) block(Isozaki et al., 2011)

Geotectonic subdivision of Japan (Isozaki,1996 The Island Arc)ca. 900 million year-long history of the JapaneseIslands in 1 minute
Ma: million years ago

birth @a rift: ７00 Ma
early growth @passive margin: ７00-５00 Ma
tectonic
conversion: ５00 Ma
accretionary growth: ５00 Ma-50
MaAP
demise in collision: 50-200 MaAP

700 Ma breakup of
the supercontinent Rodinia(Rino et al., 2009)

birth @ S. China margin
counterpart: western
N. America (Laurentia)

“Say Good-bye to Hollywood!”

Isozaki (1996)

Initiation of oceanic subduction (500 Ma)

Isozaki (1996)

essential geologic elements formed along arc–trench system(Isozaki et al., 2010, 2011)

accretionary complex (AC)blueschists (high-pressure meta-AC)
fore-arc +back-arc basin sediments

arc granite: factory of continental crust beneath volc. arc

oceanward growthof continental crustalong active continental margin
net continental growth:juvenile addition of arc granite

(100 Ma)

lifetime of Pacific Ocean

Grand finale @ ca. 200 m.y. after present

50 m.y. AP

250 m.y. AP

end of Japan = end of the Pacific Ocean= formation of the next supercontinent

America + Asia = Amasia

Dewey & Bird (1970) Jour. Geophys. Res.
highly cited classic paper on mountain building processes
based on plate tectonics
collision-type vs. Cordilleran-type

Alpine-Himalaya
Variscan/Hercynian
Caledonian

California, B.C.,
Japan
circum-Pacificconundrum
disagreement between
elapsed time andremaining continental
crust

Paleozoic: 290 m.y.
Mesozoic: 185 m.y.
Cenozoic: 65 m.y.

400

Paleozoic

Zircon (sand) and grains with U-Pb ages (granite provenance)

depositionalage
500

300

200

Mesozoic

mineral zirocn forms mostly in granite.

1000 Ma

Cenozoic

Nakama et al. (2009)older arc granite belt：
exposed extensively, then gone….

Without vaporizing to the outer space,to somewhere else?

Light-weighed continental (granitic) material
can subduct into mantle with heavy rocks??

Indication of the existence of second continent
densityUppermantlePressureLower
mantleAt 300-800km depth,
Granite becomes much denser
than mantle peridotite

・Across the lower transition
zone, seismic velocity (Vp, Vs)
becomes faster than PREM
・May indicate
the presence of 6-7 timesof granitic crustal material
in mantle tansition zone.

First principle calculation（Kawai et al., 2009; 2010）tectonic erosion
構造浸食
how to slim continentsvon Huene & Scholl (1990)

Seismic cross-section
across the Japan Trench
XXYY

Modern subduction zones in the world△： Erosive (non-accreting) margins （~75％）▲： Accreting margins（~25％）(Scholl and von Huene, 2007; 2009)tectonic erosion

Losing arc crust means
disappearance ofgranitic continental
crust……..

Where to dump
the lightest rocks
like granite
in solid Earth?

No worries,
we can bury
continents intothe mantle!

New view: another continent in mid-mantle (Maruyama, 2012)
Lost Atlantis??
Previously we imagined without doubt ….
・ granitic continent. crust is more buoyant than mantle rocks
・ low-density continents never subduct into mantle
Second continent：
accumulated continental
material is 6 times ofextant continents on
surface(Rino et al., 2007)
Another heat source formantle convection

Tectonic erosion：
destructtion of continent
at subduction zone
（e.g. Scholl & von Huene,2007）

Conclusions
1) Geology of Japan recorded the history of a Pacificcontinental margin that added continental crust, apparently
for 400 km wide during the last 500 m.y.
2) Typical/general growth pattern of continental crust by active
plate subsuction, with growth and retreat, was demonstrated.
3) The main implication is in the burial of a large amount ofcontinental crust (with high content of U and Th) into themantle, which was totally overlooked for years.
4) The claimed second continent in mid-mantle may provide a
possible hunting target for geoneutrino researchers.