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 Analysis January 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

Geologic map around KamLAND ( KamLAND

Rocks related to Gondwana-derived fragments (mainly 470–230 Ma (Myr ago)) KamLAND

Accretionary complex (mainly 270–140 Ma ) KamLAND

Rocks related to the opening of the Sea of Japan (East Sea; 20–5 Ma) KamLAND mainly Miocene rocks

Supra-subduction-zone igneous and sedimentary rocks (230–0 Ma) KamLAND Mt. Ontake

Main constituent geologic units of the Japanese Islands Gondwana-derived fragments and related rocks Accretionary complex causing growth of a continental margin Supra-subduction-zone igneous rocks covering or intruding into the older rocks Volcanic 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 Fault PF: Partizansk Fault HTL: Hatakawa Tectonic Line TTL: Tanakura Tectonic Line MTL: 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

Arrangement of continents in the Silurian (ca. 450 Ma) Caledonian Or. Avalon Arc ★ Proto-Japan Peri-Gondwana Mongolia Laurentia Siberia (Angara) Baltica Gondwana 450 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 consists mainly 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 Fault PF: Partizansk Fault HTL: Hatakawa Tectonic Line TTL: Tanakura Tectonic Line MTL: Median Tectonic Line Jurassic accretionary complex Accretionary complex Geologic elements of Japan

Oceanic-plate stratigraphy in the Jurassic accretionary complex of Japan Accretionary complex

How to make the oceanic-plate stratigraphy Basalt Radiolarian tests Terrigenous sand and mud Accretionary complex

tectonic erosion Geological setting of the Nankai accretionary wedge (Strasser et al., 2009) accretion (off-scraping) Accretionary complex

Volcanic front in Japan (Each arc–trench system has a volcanic front due to the depth of dehydration/melting of subducted oceanic plate.) Japan Trench Nankai Trough Igneous rocks

Distribution of 100–45-Ma granite 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 of Asia at 20 Ma Process of Restoration Compiled from Yamakita and Otoh (1998, 2000) and Otoh et al. (1999) Sea of Japan

Rocks related to the opening of the Sea of Japan (East Sea; 20–5 Ma) KamLAND

Miocene (23–5 Ma) rocks related to the opening of the Sea of Japan ( 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 Japan Trench Nankai Trough Sea of Japan (East Sea) Sikhote Alin A B C D 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.