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

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)

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

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o

the

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of

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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.