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Surface geology of the Japanese Islands
Shigeru Otoh (Graduate School of Science and Engineering, University of Toyama)
International Workshop on KamLAND Geoscience;Toward Enhanced Reference Earth Models for Geoneutrino AnalysisJanuary 16, 2015
Introduction
My research career started 30 years ago.I study the tectonic evolution of East Asia from the perspective of global geodynamics.
Methods- Comparative stratigraphy- Paleobiogeography- Structural geology (age and kinematics of
major shear zones)- Detrital zircon geochronology- Paleomagnetism
Contents of my talk
Geology around KamLAND
Main constituent geologic units of the
Japanese Islands
- Gondwana-derived fragments
- Accretionary complex
- Supra-subduction-zone igneous rocks
- Rocks related to the Sea of Japan (East Sea)
Vertical extension of surface geology
Uranium deposits
Surface geology around KamLAND
: Uranium deposits
KamLAND
Geo
log
ic m
ap a
rou
nd
Kam
LA
ND
(htt
ps:
//g
ban
k.g
sj.j
p/g
eon
avi/
geo
nav
i.p
hp
)
KamLAND
Ro
cks
rela
ted
to
Go
nd
wan
a-d
eriv
ed
frag
men
ts (
mai
nly
470
–230
Ma
(Myr
ago
))
KamLAND
Acc
reti
on
ary
com
ple
x(m
ain
ly 2
70–1
40 M
a )
KamLAND
Ro
cks
rela
ted
to
th
e o
pen
ing
of
the
Sea
of
Jap
an (
Eas
t S
ea;
20–5
Ma)
KamLAND
main
ly M
ioce
ne ro
cks
Su
pra
-su
bd
uct
ion
-zo
ne
ign
eou
s an
d
sed
imen
tary
ro
cks
(230
–0 M
a)
KamLAND
Mt. Ontake
Main constituent geologic units ofthe Japanese Islands
Gondwana-derived fragments and related rocksAccretionary complex causing growth of a continental marginSupra-subduction-zone igneous rocks covering or intruding into the older rocksVolcanic and sedimentary rocks related to the opening of the Sea of Japan (East Sea)
Geology around KamLAND shows major geohistory and main constituent geologic units of the Japanese Islands.
◆Hida and Hida Gaien belts◆Khanka Belt (Sikhote Alin)◆South Kitakami Belt◆Sergeevka Belt (Sikhote Alin)
Geologic elements of Japan
Inner side
Outer side
CSF: Central Sikhote-Alin FaultPF: Partizansk FaultHTL: Hatakawa Tectonic LineTTL: Tanakura Tectonic LineMTL: Median Tectonic Line
Gondwana-derived fragments
Gondwana
Gondwana-derived fragments and related rocks
Gondwana was built up through the Grenville and Pan-African “Orogenic” ( collisional) ≒events (1250–550 Ma Meso- to Neoproterozoic)⊆ .
Geologic units with sandstone and volcaniclastic rocks containing Meso- to Neoproterozoic zircons are interpreted to have been derived from or related to Gondwana.
Gondwana
https://www.uwgb.edu/dutchs/platetec/plhist94.htm
Arrangement of continents inthe Silurian (ca. 450 Ma)
Caled
onian O
r.
Avalon Arc
★
Proto-Japan
Peri-Gondwana
Mongolia
Laurentia
Siberia (Angara)
Baltica
Gondwana450 Ma
Gondwana
Drift history of the South Kitakami Paleoland (SKP)Gondwana
Drift history of the SKP in the Mesozoic Era Gondwana
Accretionary complex
An accretionary complex is a geologic body consisting of oceanic and/or terrigenous materials that were most likely accreted to a continental crust along an active continental margin (ACP: continental margin above a subducting oceanic crust).
The framework of the Japanese Islands consistsmainly of Mesozoic to Cenozoic (250 Ma or younger) accretionary complexes.
Strasser et al. (2009) →
Accretionary complex
◆Tamba–Mino–Ashio Belt◆ Samarka Belt (Sikhote Alin)◆ Southern Chichibu–Northern
Kitakami Belt◆Taukha Belt
Inner side
Outer side
CSF: Central Sikhote-Alin FaultPF: Partizansk FaultHTL: Hatakawa Tectonic LineTTL: Tanakura Tectonic LineMTL: Median Tectonic Line
Jurassic accretionarycomplex
Accretionary complex
Geologic elements of Japan
Oceanic-plate stratigraphy inthe Jurassic accretionary complex of Japan
Accretionary complex
How to makethe oceanic-plate stratigraphy
BasaltRadiolarian
testsTerrigenous
sand and mud
Accretionary complex
tectonic erosion
Geological setting of the Nankai accretionary wedge (Strasser etal., 2009)
accretion (off-scraping)
Accretionary complex
Vo
lcan
ic f
ron
t in
Jap
an(E
ach
arc
–tr
en
ch
sy
ste
m h
as
a v
olc
anic
fro
nt
du
e t
o
the
de
pth
of
de
hy
dra
tio
n/m
elt
ing
of
su
bd
uc
ted
oce
an
ic p
late
.)
Jap
an T
ren
chNankai Trough
Igneous rocks
Distribution of 100–45-Magranite bodies in SW Japan
Paleogene: Magnetite-series
Cretaceous: Ilmenite-series
Base map: Ishihara and Matsuhisa (2002)
Large granite bodies occur only on the north of the Median Tectonic Line (fault with a large displacement).
Outer Zone of Southwest Japan
Igneous rocks
◆ Okinawa Trough
◆ SW Japan →Intra-arc deformation
◆ NE Japan →Submarine topography
Eastern margin ofAsia at 20 Ma
Process of Restoration
Compiled from Yamakita and Otoh (1998, 2000)and Otoh et al. (1999)
Sea of Japan
Ro
cks
rela
ted
to
th
e o
pen
ing
of
the
Sea
of
Jap
an (
Eas
t S
ea;
20–5
Ma)
KamLAND
Miocene (23–5 Ma) rocks related tothe opening of the Sea of Japan
(https://gbank.gsj.jp/geonavi/geonavi.php)
Miocene volcanic and sedimentary rocks widely occupy the western to central part of Northeast Japan.
Tohoku University●Yamagata
Sea of Japan
Assessment of radioactivity
Granite and granitic metamorphic rocks, forming upper continental crust, tend to contain many radioactive minerals.
- Zircons in granite: 100 wt ppm + monazite, xenotime, uraninite … - Zircons in sandstone: 100 wt ppm or more - Zircons in volcanic rocks: less than 100 wt ppm
Sandstone may partly contains more radioactive heavy minerals, and there may be some concentrations of radioactive minerals in carbonaceous (reductive) mudstone.
Radioactivity
Accretionary complexes:Assessment of radioactivity
The Gondwana-derived fragments and related rocks, consisting mostly of sedimentary and volcaniclastic rocks may be equally or less radioactive than normal upper continental crust.
Basalt and pelagic to hemipelagic sediments, forming the lower part of the oceanic-plate stratigraphy, contain small amount of radioactive minerals.
The radioactivity caused by granite should be very low in the Outer Zone of Southwest Japan.
Radioactivity
Seismic lines (yellow) and integrated cross section line (red)
★
KamLAND
Jap
an T
ren
ch
Nankai Trough
Sea of Japan(East Sea)
Sikhote
Alin
A
B
CD
E
Seismic profiles (Ito and Sato, 2010)
Thickness of the upper
crust < 15 km
Crust of the Sea of Japan was horizontally extended and thinned; upper crust < 10 km, lower crust = 10 km or a little thicker.
Uranium deposits
Could be small but many uranium deposits in North Korea (850–1100 km from KamLand)
Some uranium deposits in the Ogcheon Belt of South Korea (ca. 800 km from KamLand)
The Ningyo-toge deposits (ca. 330 km from KamLand)
The Tono deposits (ca. 110 km from KamLand)
Conclusions
Surface geology of the Japanese Islands consists mainly of (1) Gondwana-derived fragments, (2) accretionary complex, (3) supra-subduction-zone igneous and sedimentary rocks, and (4) volcanic and sedimentary rocks related to the opening of the Sea of Japan .
The lithology of constituent rocks as well as laterally extended nature of the upper crust suggest that the radioactivity of the surface geological units is lower than normal continental crust.
We can measure the radioactivity of samples from all the surface geologic unit if needed.
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