国立科博専報，(51), pp. 1–24 , 2016 年 3 月 28 日
Mem. Natl. Mus. Nat. Sci., Tokyo, (51), pp. 1–24, March 28, 2016

Uraninite and Thorite Ages of Around 400 Granitoids
in the Japanese Islands
Kazumi Yokoyama1*, Masako Shigeoka1, Yukiko Otomo2,
Kouta Tokuno3 and Yukiyasu Tsutsumi1
1

Department of Geology and Paleontology, National Museum of Nature and Science,
4–1–1 Amakubo, Tsukuba, Ibaraki 305–0005, Japan
2
Faculty of Education, Art and Science, Yamagata University,
1–4–12 Kojirakawa-machi, Yamagata-shi, Yamagata 990–8560, Japan
3
Earth and Planetary Science, Kyushu University,
744 Motooka, Nishiku, Fukuoka 819–0395, Japan* E-mail: yokoyama@kahaku.go.jp

Abstract. Systematic dating of around 400 granitoids in the Japanese Islands have been made on
the basis of total UO2, ThO2 and PbO contents of uraninite and anhydrous thorite using an electron
microprobe analyzer (EPMA) at the National Museum of Nature and Science, Tokyo. The ages
range from ca. 5 Ma to 300 Ma. From the granitoid ages, the Japanese Islands were divided into
many terranes. In northern Japan, granitoids with ages of approximately 110–120 Ma occur in the
Kitakami Mountains, southwest Hokkaido and eastern Abukuma Mountains, and granitoids withages of approximately 100–110 Ma occur at the western Abukuma Mountains and its northern
extension. The granitoids that are around 90–100 Ma old occur sporadically in the JapaneseIslands: mainly in the Asahi Mountains, the Nikko area, northern Shikoku and northern Kyushu. In
central and northern Japan, the younger Cretaceous granitoids, partly Paleogene, with an age ofaround 65 Ma occur along the western part of the Asahi Mountains and Tsukuba–Nikkou area. In
western Japan, granitoids that are 60–70 Ma old occur linearly along the coastal zone of the Sea ofJapan. However, other granitoids with similar ages do not always show a linear or zone arrangement, but are concentrated in relatively restricted regions. These divisions by granitoid ages using
uraninite and thorite are essentially similar to those determined by K–Ar ages, but the former ages
are much more concentrated in each area than the latter ones.
Key words: uraninite, thorite, age, EPMA, granitoid

Introduction
Yokoyama et al. (2010) reconﬁrmed the age
method for uraninite and thorite in granitoids
based on the UO2, ThO2 and PbO contents thatwere obtained via an electron microprobe analyzer (EPMA). Holmes (1911) ﬁrst established amethod for dating minerals through normal wet
chemical analyses on the basis of the assumptionthat inherited Pb was negligible at the time ofmineral crystallization. Holmes (1931) later dealt
exhaustively with the application of radioactivity
to the measurement of geologic time. The
method was used by many researchers and wasreferred to as the chemical age. After the isotope
methods had been established for many minerals,
the Holmesʼs method was not applied for uraninite and thorite until 1990. Bowles (1990) developed accurate age calculations for uraninite
through EPMA analyses. Uraninite, thorianite,thorite and huttonite contain high concentrationsof radiogenic Pb even in Paleogene and Neogene
rocks. In most of the dating studies, the EPMA
ages for these minerals were consistent withthose obtained by isotopic methods (Yokoyama
et al., 2010).
Iimori (1941) analyzed uraninite in a granitoidfrom Iisaka, Fukushima Prefecture, using the wet2

Kazumi Yokoyama et al.

chemical method and calculated using the simple
Holmesʼs equation. The age was 103 Ma, similar
to the age obtained by the K–Ar method. Since
1965, the K–Ar method has been widely used forage analyses of granitoids in Japan (e.g. Kawano& Ueda, 1964 & 1966). Based mostly on the K–
Ar method of the Kawano group, radiometric age
data of granitoids in the Japanese Islands weresummarized by Nozawa (1975). From the K–Ar
method, it is well known that Cretaceous granitoids are the most ubiquitous in the islands,
whereas Neogene granitoids occur mostly inSouthwest Japan along the Paciﬁc Ocean. Permian to Triassic granitoids occur only in the Hida
Terrane, and ages of far older granitic rocks,
Cambrian to Silurian, occur as small plutonic
bodies.
The EPMA age method, i.e. U-Th-total Pb or
chemical method, has attracted attention for its
quickness, high spatial resolution and relatively
high precision similar to isotopic methods. In thispaper, we studied mainly uraninite and thorite
ages of granitoids in the Japanese Islands and try
to clarify age variation in each province. The age
method was described in detail by Yokoyama etal. (2010). They demonstrated the validity of the
EPMA method, which yields age results comparable to those obtained by isotopic methods suchas Sensitive High Resolution Ion Microprobe(SHRIMP) and the K–Ar method. There aremany methods used to obtain the ages of granitoids. Among them, SHRIMP and Laser Abration
Inductively Coupled Plasma (LA-ICP-MS) are
the most reliable and useful for this study
because of the common presence of zircon. However, LA-ICP-MS and SHRIMP methods have,so far, only been applied to restricted samples orterranes. The present age method has a disadvantage that uraninite and thorite are not always
present in the granitoids. It is, however, important to summarize the ages of the granitoids in
the Japanese Islands by the same method as was
performed for the K–Ar age method. In thisstudy, the granitoid age is obtained by the samemachine in the National Museum of Nature andScience and by the same analytical conditions

and standards as reported by Yokoyama et al.
(2010). Most granitoids older than the Cretaceous rarely contain uraninite and thorite. In suchrocks, monazite ages are obtained by the EPMA
method. Monazite ages comparing the results
obtained by the same EPMA machine and isotopic ages have been reported by Santosh et al.
(2006).
Paleomagnetic measurements showed that
Southwest Japan was rotated clockwise, whereas
Northeast Japan was rotated anticlockwise at thetime of the opening of the Sea of Japan at around
20 Ma (e.g. Otofuji & Matsuda, 1983 & 1984).
However, the boundary between the Southwest
and Northeast terranes has not yet been clariﬁed.
In the Japanese Islands, Cretaceous granitoids
are most common. The study of the spatial distribution of the granitoids will contribute to thereconstruction of the terranes in the islands andPrymorye, Far East Russia, before the opening of
the Sea of Japan. Even if only a little, the present
study will ﬁnd a solution to the problem of thetectonic boundary between the Southwest andNortheast Japan.
Samples
Cretaceous and Cenozoic granitoids arewidely distributed in the Japanese Islands (Fig.
1), whereas Jurassic to Permian granitoids occur
only in the Hida terrane. Far older granitoids
occur sporadically in the islands. Most of the
granitoid samples used for this study are registered samples at the National Museum of Natureand Science. Some are preserved in storages at
few universities. In total, around one thousand
granitoids were crushed to check for radiogenic
minerals such as uraninite, thorite and monazite.
In the granitoids, uraninite (UO2) and thorite(ThSiO4) are usually rare minerals. Uraninite, if
present, occurs mostly as a euhedral grain in theheavy fraction, rarely surrounded by pyrite.
Although thorite was found in most of the granitoids in the Japanese Islands, it is commonly
altered into hydrous thorite, especially in older
granitoids. Anhydrous thorite is well preserved inUraninite and thorite ages of granitoids in the Japanese Islands

Fig. 1.

3

Distribution of granitoids in the Japanese Islands and index map for the following ﬁgures.

the Neogene granitoids, but it is preserved partly
in hydrated thorite grains in Cretaceous or older
granitoids. Finally, we obtained ages from about
400 granitoid samples.

Age results
Ages of granitoids in the Japanese Islands are
summarized according to the six provinces asshown in Fig. 1: southern Hokkaido–Tohoku,
Asahi–Abukuma, Chubu–Kansai, Hida, Chugoku–
northern Shikoku and northern Kyushu. All theKazumi Yokoyama et al.

4

Table 1. Locality and age data of the analyzed granitoids in the Japanese Islands. The samples with registerednumber are stocked at the National Museum of Nature and Science.
sample No

rockreg. No

locality

Uraninite

ThoriteMonaziteAge data in Figs. 2, 3 and 4
DN-01

granite134109DN-02

granodiorite

134110

DN-07
OK-6

granitegranodiorite

134115135359AO-6

granite134279AO-7

granite134280

AO-8

granite134281

AO-9

granite134282

AO-10

aplite134283

AO-11

granite134284

AO-14

granodiorite

134287

KTK–13
AK-2
AK-3
AK-5
AK-8
AK-9
TH-06
TH-01
TH-02
TH-04
TH-07
TH-08
AK-11
AK-12
AK-13
8605
8612
8608
8609
6515
7294
SK-1

granitegranitegranitegraniteQz diorite
Qz diorite
granitic rock
granitic rock
granitic rock
granitic rock
granitic rock
granitic rock
granitegranitegranitoid
granodiorite
granodiorite
granodiorite
granodiorite
granodiorite
adamelite
adamelite

135408135409135411135414135415134472134464134465134467134470134471135417135418135419
8605
8612
8608
8609
6515
7294
127853

SK-2
SK-5
SK-19

adamelite
granitegranite127854
127857
127871

SK-32
SK-14
SK-16
SK-18

granitegranitegranitegranite127884
127866
127868127870

SK-25
SK-29

granitebiotite gneiss

127877127881

SK-30

biotite gneiss

127882

YT-5

granite133770

SK-52
SK-53
SK-57
SK-59
SK-61
SK-62
SK-64

granitegranitegranodiorite
granodiorite
granodiorite
granodiorite
granodiorite

127904127905128618128620128622128623128625

Kenichi-onsen, Yakumo-cho, Futami-gun,
121.1±1.7
Hokkaido
Kumaishitomarikawa, Yakumo-cho, Futami-gun, 119.6±1.2
Hokkaido
Pirika, Imakane-cho, Seta-gun, Hokkaido
122.2±1.5Kamoishi Coast, Okushiri-cho, Okushiri-gun,
103.1±0.6
Hokkaido
Ohmagoe-rindo, Fukaura-machi, Nishitugaru-gun, 104.6±0.7
AomoriOhmagoe-rindo, Fukaura-machi, Nishitugaru-gun, 106.1±1.6
AomoriOhmagoe, Fukaura-machi, Nishitugaru-gun,
106.8±1.7
AomoriOhmagoe, Fukaura-machi, Nishitugaru-gun,
108.8±0.9
AomoriOhmagoe, Fukaura-machi, Nishitugaru-gun,
107.7±1.1
AomoriOhmagoe, Fukaura-machi, Nishitugaru-gun,
92~107
Aomori
Ajigasawa-machi, Fukaura-machi, Nishitugaru107.0±1.0
gun, Aomori
Hashikami-cho, Sannohe-gun, Aomori
Nibetsushinrin Museum, Akita-shi, Akita
Sannai River, Kawabesannai, Akita-shi, Akita
101.9±1.5
Idemaisawa, Kawabesannai, Akita-shi, Akita
101.6±0.9
Kobuchigasawa, Akinomiya, Yuzawa-shi, Akita
103.0±1.3
Kosawa, Akinomiya, Yuzawa-shi, Akita
Obonai, Tazawako, Senboku-shi, Akita
Hondera, Genbi-cho, Ichinoseki-shi, Iwate
111.8±1.2
Yuda Dam, Nishiwaga-machi, Waga-gun, Iwate
Toyosawa Dam, Hanamaki-shi, Iwate
115.3±1.4
Sawauchi, Nishiwaga-machi, Waga-gun, Iwate
109.0±1.8
Sawauchi, Nishiwaga-machi, Waga-gun, Iwate
108.4±1.5
Koishizawa, Izawa-ku, Oshu-shi, Iwate
111.6±1.2
Hosoturusawa, Izawa-ku, Oshu-shi, Iwate
Kazayodosawaguchi, Izawa-ku, Oshu-shi, Iwate
111.2±2.4
Fujikirisawa, Tsukimoshi-cho, Thono-shi, Iwate
118.4±2.4
Sarugaishikawa, Tsukimoshi-cho, Thono-shi, Iwate 119.5±2.3
Shimoarisu, Sumita-cho, Kesen-gun, Iwate
Sarugaishikawa, Tsukimoshi-cho, Thono-shi, Iwate
Koidenakataki, Tsukimoshi-cho, Thono-shi, Iwate
Himegamidake, Tamayama-ku, Morioka-shi, Iwate
Higashidake-toge, Hiraizumi-machi, Nishiiwaigun, Iwate
Nakajima, Ichinoseki-shi, Iwate
Orikabe, Murone-machi, Ichinoseki-shi, Iwate
Kamitubo, Takekoma-cho, Rikuzentakada-shi,
Iwate
Maide, Yokota-cho, Rikuzentakada-shi, Iwate
Mt.Hikami, Rikuzentakada-shi, Iwate
Mt.Hikami, Rikuzentakada-shi, Iwate
Seisou-Center, Takekoma-cho, Rikuzentakada-shi,
Iwate
Mt.Raishin, Rikuzentakada-shi, Iwate
Kamitubo, Takekoma-cho, Rikuzentakada-shi,
Iwate
Kamitubo, Takekoma-cho, Rikuzentakada-shi,
Iwate
Tamayamakogenr Takekoma-cho, Rikuzentakadashi, Iwate
Rainai, Kamigo-cho, Thono-shi, Iwate
117.2±1.9
Nagaoka, Ayaori-cho, Thono-shi, Iwate
115.1±1.9
Tahara-toge, Daito-cho, Ichinoseki-shi, Iwate
118.5±2.3
Ogayu, Morioka-shi, Iwate
Takazudou, Towa-cho, Hanamaki-shi, Iwate
Yanagawa, Esashi-ku, Ohshu-shi, Iwate
Ide, Esashi-ku, Ohshu-shi, Iwate

118.2±1.7
5.0±2.2

23.4±2.0
109.1±2.1112.5±2.0

111.1±7.3
112.2±6.0

114.4±2.4110.6±2.2118.9±4.4118.0±1.4125.0±4.0
116.4±4.9116.8±2.0126.3±4.7121.9±4.5116.6±4.3118.7±4.0119.6±4.4117.1±1.4454.8±13.5455.7±6.3
447.6±11.7
125.1±16.8449.4±14.6451.9±16.4445.8±11.7

114.4±5.3
117.0±6.6118.0±2.3119.0±2.5117.0±2.7118.0±3.7118.0±4.0

Uraninite and thorite ages of granitoids in the Japanese Islands
Table 1.
sample No
KTK–1
KTK–5
KTK–6
KTK–7
KTK–9
KTK–10
KTK–12
KTK–14
KTK–15
KK-4
KK-16

rock
granitegranitegranitegranitegranitegranitegranitegranitegranitegranodiorite
granodiorite

reg. No

127605127617

5(continued)

locality

Uraninite

ThoriteFujisawa-cho, Ichinoseki-shi, Iwate
Toni-cho, Kamaishi-shi, Iwate
Hakizaki-cho, Kamaishi-shi, Iwate
Tashiro, Miyako-shi, Iwate
123.2±0.9
Iwaizumi-cho, Shimohei-gun, Iwate
Fudai-mura, Shimohei-gun, Iwate
Hirono-cho, Kunohe-gun, Iwate
Hanamaki-shi, Iwate
Tsukimoshi-cho, Thono-shi, Iwate
Ayukawa-hama, Kinkazan, Ishinomaki-shi, Miyagi
Ayukawa-hama, Kinkazan, Ishinomaki-shi, Miyagi

116.3±2.3
117.2±3.7116.5±2.6118.4±2.9117.4±2.4118.9±2.2120.1±2.5114.8±3.2
113.2±2.5116.4±3.7118.6±5.2

Age data in Figs. 5 and 6031107-4
041122-2

granitoid
granitoid

041122-3

granitoid

050609-12

granitoid

050906-3

granitoid

051128-6

granitoid

051128-3

granitoid

051130-5

granitoid

051130-6051130-7

granitoid
granitoid

051130-9060426-2
061115-1

granitoid
granitoid
granite061115-5b

granite061021-19

granitoid

061105-1

granitoid

061108-13
070627-29
070719-2
070726-4

granitoid
granitoid
granitoid
granitoid

070726-11061201-4
061201-5
061115-806120-1c
ER6-4
111206-3
111207-6
091022-1

granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid

111012-3

granitoid

Nihon-2
Nihon-3
Nihon-15
Kita-1Ashi-6Ashi-4Ashi-7Ashi-5Ashi-3Ashi-2
ABK-7

granitegranitegranitedioriteadamelite
granitegranitegraniteaplitegranitegranitoid

130674130675130686129956127850127848127851
127849127847127846

Jinzu-kyou, Ooe-cho, Nishimurayama-gun, Yamagata 101.5±0.9
Ooisawa, Nishikawa-machi, Nishimurayama-gun, 93.4±1.4
Yamagata
Ooisawa, Nishikawa-machi, Nishimurayama-gun,
92.5±1.6
Yamagata
Ooisawa, Nishikawa-machi, Nishimurayama-gun, 95.7±1.6
Yamagata
Ooisawa, Nishikawa-machi, Nishimurayama-gun, 95.5±1.5
Yamagata
Yanagawa, Ooe-machi, Nishimurayama-gun,
102.4±1.6
Yamagata
Yanagawa, Ooe-machi, Nishimurayama-gun,
107.9±2.8
Yamagata
Sirakura, Asahi-machi, Yamagata
97.7±2.2core,
92.4±1.3rim
Sirakura, Asahi-machi, Yamagata
91.1±1.4
Yanagawa, Ooe-machi, Nishimurayama-gun,
91.7±1.1
Yamagata
Zao-dam, Kamihosawa, Yamagata-shi, Yamagata
93.3±1.3
Oura-hashi, Tsuruoka-shi, Yamagata
67.9±1.0
65.6±1.9
Ooisawa, Nishikawa-machi, Nishimurayama-gun, 95.8±1.2
91.3±2.6
Yamagata
Ooisawa, Nishikawa-machi, Nishimurayama-gun, 67.3±1.7
66.3±2.2
Yamagata
Asahi-kosen, Asahi-machi, Nishimurayama-gun,
91.0±1.6
Yamagata
Oohagemoriyama, Asahi-machi, Nishimurayama92.5±2.1
gun, Yamagata
Asahi-machi, Nishimurayama-gun, Yamagata
97.2±1.0
97.6±2.5
Nishikawa-machi, Nishimurayama-gun, Yamagata
66.9±3.6
Oguni-machi, Nishiokitama-gun, Yamagata
80.7±1.6
Iide-machi, Nishiokitama-gun, Yamagata
80.2±1.7 core, 65.6±4.3
68.0±0.7rim
Teraizumi, Nagai-shi, Yamagata
63.0±3.0
Nakaisazawa, Nagai-shi, Yamagata
97.9±1.3
Urushiyama, Nanyou-shi, Yamagata
98.2±1.3
Nishikawa-machi, Nishimurayama-gun, Yamagata 91.0±1.7
Shirataka-machi, Nishiokitama-gun, Yamagata
103.8±1.4
Yamaguchi, Tendo-shi, Yamagata
101.8±1.3
Kamihigashiyama, Yamagata-shi, Yamagata
95.1±1.4
Daimon, Kaminoyama-shi, Yamagata
101.6±1.3
Tachiyazawa, Shonai-machi, Higashitagawa-gun,
97.2±1.0
Yamagata
Nagaioohashi, Hinode-machi, Nagai-shi,
97.2±0.6
Yamagata
Oodai, Murayama-shi, Nigata
65.6±1.3
Omata, Murakami-shi, Nigata
65.0±1.2
Ganjiki, Murayama-shi, Nigata
65.5±0.6
Nyotaisan, Nakagawa-machi, Nasu-gun, Tochigi
105.1±3.7
Chyugushi, Nikko-shi, Tochigi
63.5±2.563.6±3.0
Ashio-machi, Nikko-shi, Tochigi
63.7±2.0
65.2±3.7
Sasamekura, Nikko-shi, Tochigi
65.1±2.2
65.7±3.2
Chyugushi, Nikko-shi, Tochigi
97.9±1.8
Hara, Ashio-machi, Nikko-shi, Tochigi
99.2±1.7
Kusaki lake, Azuma-cho, Midori-shi, Gunma
99.2±2.5
Yokokawa-machi, Koriyama-shi, Fukushima
103.4±1.0

MonaziteKazumi Yokoyama et al.

6

Table 1.
sample No

rockreg. No

ABK-8
ABK-10
ABK-11
ABK-12
ABK-15

granitoid
granitoid
granitoid
granitoid
granitoid

ABK-16
ABK-17
ABK-24
ABK-25
YK24

granitoid
granitoid
granitoid
granitoid
granodiorite

127564

Yk27
K44
I-A
I-B
I-C
I-E
I-4

granodiorite
metaporphyry
granitegranitegranodiorite
granitegranodiorite

127568127480128636128637128638128639128643

I-11
I-12
I-14
Z-4
Z-6
Z-7
Z-9
Z-13
Z-14

granodiorite
granodiorite
granodiorite
granitegranodiorite
granitegranitegranitegranite128650128651128653
128658128660128661
128663
128667
128668

ABK-18
ABK-20granitegranite(continued)

locality

Uraninite

ThoriteTamura-machi, Koriyama-shi, FukushimaOno-machi, Tamura-gun, Fukushima
Hirata-mura, Ishikawa-gun, Fukushima
Ishikawa-machi, Ishikawa-gun, Fukushima
Samekawa-mura, Higashishirakawa-gun,
Fukushima
Tabito-machi, Iwaki-shi, Fukushima
Furudono-machi, Ishikawa-gun, Fukushima
Katsurao-mura, Futaba-gun, Fukushima
Tokiwa-machi, Tamura-shi, Fukushima
Mt.Takakura, Yaguki, Yotsukura-machi, Iwakishi, Fukushima
Shiosawa, Ogawa-machi, Iwaki-shi, Fukushima
Mt.Haguro, Soma-shi, Fukushima
Oda, Tsukuba-shi, Ibaraki
Shiio, Makabe-cho, Sakuragawa-shi, Ibaraki
Sakurabo, Makabe-cho, Sakuragawa-shi, Ibaraki
Inada, Kasama-shi, Ibaraki
Iwafune, Shirosato-machi, Higashiibaraki-gun,IbarakiShimokimita, Takahagi-shi, Ibaraki
Ishioka, Nakago-cho, Kitaibaraki-shi, Ibaraki
Takahara, Juoo-cho, Hitachi-shi, Ibaraki
Inada, Kasama-shi, Ibaraki
Iwase, Sakuragawa-shi, Ibaraki
Kurusu, Kasama-shi, Ibaraki
Ohirominami, Kasama-shi, Ibaraki
Hojo, Tsukuba-shi, Ibaraki
Usui, Tsukuba-shi, Ibaraki

124.1±1.2120.9±2.6113.3±2.4

Oda, Tsukuba-shi, Ibaraki
Makabe-cho, Sakurakawa-shi, Ibaraki

106.5±1.0110.3±1.5114.4±1.2
106.5±3.0
110.3±1.0110.4±1.5104.2±1.0117.9±3.5115.8±1.5116.0±0.05
65.1±1.365.8±1.5
65.0±1.2

105.2±0.8
106.1±2.1
66.5±1.1

64.6±2.3
68.5±2.1
65.2±0.979.7±1.4

102.5±1.7

80.0±7.4
69.5±2.7
105.0±0.8102 (1grain)
68.2±1.467.2±3.8
69.3±4.5
67.7±1.080.5±2.2core,
67.8±4.5rim
81.0±1.9

Age data in Figs. 7 and 8
S-1
91030804
98031201
YG-118

granodiorite
granitoid
granitoid
granitoid

YG-120B
YG-121B

granitoid
granitoid

S-2
5763
E-1
TG-2
TG-3
TG-4
TG-5
TG-6
TS-3
98031401
98031402
98031403
98031405
98031501
OG-3
RZ-2
SZ-1
SZ-2
OM-5
HA-4
IN-08
IDM-1
KO-1
GY-4
Ik-5
KTN

granitegranitegranitegranitegranitegranitegranitegraniteporphyry
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitegranitoid
granitoid
granitoid
granodiorite
granitoid

1286281286295763
128626134087133088132089131090130091134453135895

Mt.Eimeiji, Chino-shi, Nagano
Kashimata, Takagi-mura, Shimoina-gun, Nagano
Ogawa, Agematsu-machi, Kiso-gun, Nagano
Momiji lake, Minowa-machi, Kamiina-gun,
NaganoKuwabara fall, Kamiina-gun, Nagano
Koshibu lake, Minowa-machi, Kamiina-gun,
NaganoHakusyu-cho, Hokuto-shi, Yamanashi
Taguchi, Shidara-cho, Kitashidara-gun, Aichi
Kerokubo, Kasagi-cho, Ena-shi, Gifu
Tateishi, Tsuruga-shi, Fukui
Irohama, Tsuruga-shi, Fukui
Kutsu, Tsuruga-shi, Fukui
Takekawa, Mihama-cho, Mikata-gun, Fukui
Kurokawagawa quarry, Tsuruga-shi, Fukui
Hachimangu, Masuya, Echizen-shi, Fukui
Tanokami, Otsu-shi, Shiga
Tanokami, Otsu-shi, Shiga
Tanokami, Otsu-shi, Shiga
Mt.Hiei, Otsu-shi, Shiga
Hira, Otsu-shi, Shiga
Ogi, Otsu-shi, Shiga
Ryozen, Otsu-shi, Shiga
Mandokoro-cho, Higashiomi-shi, Shiga
Tuchiyama-cho, Koga-shi, Shiga
Ide-cho, Tsuzuki-gun, Kyoto
Hanasebetsusho-cho, Sakyou-ku, Kyoto
Mie, Omiya-cho, Kyotango-shi, Kyoto
Ide-cho, Tsuzuki-gun, Kyoto
Somada, Wazuka-cho, Soura-gun, Kyoto
Mt.Gyoja, Kameoka-shi, Kyoto
Taishi-cho, Minamikawachi-gun, Osaka
Kisabe, Katano-shi, Osaka

72.6±0.911.5±0.871.6±2.1
72.3±2.772.2±1.2
71.6±1.0
101.0±2.3

66 (1grain)
77.3±1.077.7±1.1
101.1±1.0

98.0±1.0
98.8±1.2

Monazite

14.1±1.2
69.4±1.568.6±2.768.3±2.467.9±2.3
69.3±1.967.8±2.565.5±1.579.7±2.1
101.9±1.8
77.0±2.1
102.4±3.8
74.1±2.073.0±2.073.4±2.5
104.2±2.3105.6±1.9
65.7±4.790.1±2.0
94.4±3.380.9±1.6
84.2±1.574.7±12.5
68.6±1.5

Uraninite and thorite ages of granitoids in the Japanese Islands
Table 1.
sample No

rockreg. No

98031502
98031503
98031504
Ik-1

granitoid
granitoid
granitoid
granite129930

Ik-2
Ik-3

granitegranite129931
129932

IK-9
Ik-11
SK-02
SK-03
SK-04
S-3
S-4
S-5
S-6

graniteqz diorite
granitoid
granitoid
granitoid
granitegranitegranodiorite
granodiorite

129938129940128630128631128632
128633

S-8

granodiorite

128635

S-9

granodiorite

134085

7(continued)

locality
Ibaraki-shi, Osaka
Ibaraki-shi, Osaka
Ibaraki-shi, Osaka
Kitasanjyoguchi-station, Heguri-cho, Ikoma-shi,
NaraIchihara tunnel, Heguri-cho, Ikoma-shi, Nara
Kitasanjyoguchi-station, Heguri-cho, Ikoma-shi,
Nara
Hondo, Sango-cho, Ikoma-gun, Nara
Kyuanji, Heguri-cho, Ikoma-shi, Nara
Nakatani, Sakurai-shi, NaraKasa, Sakurai-shi, NaraKasa, Sakurai-shi, Nara
Kamiobina-cho, Kofu-shi, Yamanashi
Yoshizawa, Kai-shi, Yamanashi
Yanagidaira, Makioka-cho, Yamanashi-shi, Yamanashi
Kanazakura shrine, Makioka-cho, Yamanashi-shi,
Yamanashi
Narusawa, Makioka-cho, Yamanashi-shi,
Yamanashi
Kaiyamato statim, Yamato-cho, Kosyu-shi,
Yamanashi

Uraninite

86.7±0.9

ThoriteMonazite80.9±1.982.2±1.881.5±2.786.0±0.6
86.6±0.581.2±2.2
89.0±1.789.3±1.474.7±1.3

86.0±1.415.8±1.7
16.9±2.1
4.1±0.8
4.8±1.2
12.8±1.2
12.1±1.5

Age data in Figs. 9 and 10
98031301

granite98052212
98052217
98112501
98112504
99040905

granitegranitegranitegranitegranite99042210

granite99082802aplite99100705
99100707

granitegranite5760
98112201

granitegranite99042801
99042805
99091807
99111304
99111305
99111306
98092905
98092906
98092907

granitegranitegranitegranitegranitegranitegranitegranitegranite98092908
98092910
98092911
98092913
98100304
98100308
98100309
98100310
98100311
99042103
99042106

granitegranitegranitegranitegranitegranitegranitegranitegranitegranitegranite99042107
9904210899082901
99093003
99093004

granitegranitegranitegranitegranite5760

129249129248129250129252

Niho power station, Yatsuo-machi, Toyama-shi,
195.5±3.2
ToyamaIori, Kamiichi-machi, Nakaniikawa-gun, Toyama
66.8±2.0
67.1±3.1
Iori, Kamiichi-machi, Nakaniikawa-gun, Toyama 198.7±2.5
Minamimata vally, Sanga, Uozu-shi, Toyama
232.4±4.4
Minamimata, Sanga, Uozu-shi, Toyama
236.3±5.5
Mt.Shiridaka, Kamiichi-machi, Nakashinkawa241.0±3.6
gun, Toyama
Kufusu river, Kiritani, Yatsuo-machi, Toyama-shi, 189.9±3.2
ToyamaShona river, Tateyama-machi, Nakashinkawa-gun, 198.1±3.0
195.4±6.5
ToyamaOtozawa, Unazuki-machi, Kurobe-shi, Toyama
255.8±2.9
Unazuki-machi, Kurobe-shi, Toyama
core:241.1±4.2,
sec:191.8＋5.9
Aimoto, Unazuki-machi, Kurobe-shi, Toyama
95.9±2.4
Isurugiyama, Nakanoto-machi, Kashima-gun,
183.5±3.7
Ishikawa
Mt.Hotatu, Hakui-shi, Ishikawa
188.5±7.1
Mt.Hotatu, Hakui-shi, Ishikawa
234.3±2.8
Notokongo, Shika-machi, Hakui-gun, Ishikawa
189.2±7.0
Metuke vally, Aratani, Hakusan-shi, Ishikawa
188.9±3.1
Metuke vally, Aratani, Hakusan-shi, Ishikawa
161.1±4.5215.2±13.6
Metuke vally, Aratani, Hakusan-shi, Ishikawa
196.5±9.8
Horatani, Miyagawa-cho, Hida-shi, Gifu
198.3±4.1
Horatani, Miyagawa-cho, Hida-shi, Gifu
196.5±3.8
Horatani, Miyagawa-cho, Hida-shi, Gifu
245.2±5.0core,
196.7±7.4rim
Horatani, Miyagawa-cho, Hida-shi, Gifu
206.8±2.4
Utsubo, Miyagawa-cho, Hida-shi, Gifu
204.4±4.3
Utsubo, Miyagawa-cho, Hida-shi, Gifu
208.5±2.5
Utsubo, Miyagawa-cho, Hida-shi, Gifu
189.6±3.6
Azukizawa, Miyagawa-cho, Hida-shi, Gifu
189.6±4.0
Hongo, Kamitakara-cho, Takayama-shi, Gifu
201.7±2.8
Shimosatani, Kamitakara-cho, Takayama-shi, Gifu 198.8±3.5
Shimosatani, Kamitakara-cho, Takayama-shi, Gifu 191.5±2.9
Kuzuyama, Kamitakara-cho, Takayama-shi, Gifu 194.2±3.3
Morimo, Kamioka-cho, Hida-shi, Gifu
198.9±2.6Sugoroku river, Kamitakara-cho, Takayama-shi,
205.4±7.8
Gifu
Kasatani, Kamitakara-cho, Takayama-shi, Gifu
205.2±3.6
Kamitakara-cho, Takayama-shi, Gifu
267.8±10.1
Kagasawa, Utubo, Miyakawa-cho, Hida-shi, Gifu 190.2±4.0
193.4±4.9
Osaka-toge, Furukawa-maci, Hida-shi, Gifu
215.2±13.6
Furukawa-cho, Hida-shi, Gifu
196.1±11.9

Kazumi Yokoyama et al.

8

Table 1.
sample No
HD31
KM133

rock
granitegranitereg. No(continued)

locality
Asoya, Kamioka-cho, Hida-shi, Gifu
Mannami river, Miyagawa-cho, Hida-shi, Gifu

Uraninite

Thorite201.6±3.1
233.4±3.4core,
191.4±1.8rim

Age data in Figs. 11 and 12
D2000408
GY-05
GY-06
TSHY-60
9803170313
98031702
MIKAGETSHYG-42
Akou
Tatsuno-1
TSTAU-1
TSTAU-7
NGM-2
AW-58cSZUKI-1
YG-41
YG-43
YG-58
YG-59
YG-81
YG-87
YG-88
YG-89
GY-02
GY-03
GY-05
GY-06
Mannari
GY-12
GY30-2
GY-65
GY-86
YG-07
YG-08

granitoid
granitoid
granitoid
granitoid
granitoid
granitoidqz-diorite
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitegranitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitegranitoid
granitoid
granitoid
granitoid
granitoid
granitoid

YG-09
YG10-1
YG-12
YG-17
YG-18

granitoid
granitoid
granitoid
granitoid
granitoid

YG-19
YG-20
YG-105
YG-106
YG-130
YG-132
YG-135
YG-137
YG-138
YG-13984101601
84101804
84102702
84102901
GY-21-3
GY-53
GY-56-1
GY-58
GY-59
GY-61
GY-62
GY-63

granitoid
granitoid
granitegranitegranitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitegranitoid
granitegranitegranitegranitegranitegraniteAioi, Aioi-shi, Hyogo
Okuyane, Tanto-cho, Toyooka-shi, Hyogo
Tanto-cho, Toyooka-shi, Hyogo
Nada-ku, Kobe-shi, Hyogo
Kita-ku, Kobe-shi, Hyogo
Mt.Rokko, Higashinada-ku, Kobe-shi, Hyogo
Mt.Rokko, Higashinada-ku, Kobe-shi, Hyogo
Mt.Rokko, Higashinada-ku, Kobe-shi, Hyogo
Tenwa, Akou-shi, Hyogo
Shinmiya-cho, Tatsuno-shi, Hyogo
Shiosaki, Miya, Ienaga-cho, Himeji-shi, Hyogo
Hishinohana, Ienaga-cho, Himeji-shi, Hyogo
Nojima-Hirabayashi, Awaji-shi, Hyogo
Oomachi, Awaji-shi, Hyogo
Shio, Awaji-shi, Hyogo
Iwaya, Shinmura, Awaji-shi, Hyogo
Iwaya, Shinmura, Awaji-shi, Hyogo
Takenokuchi, Sumoto-shi, Hyogo
Shio, Awaji-shi, Hyogo
Shio, Awaji-shi, Hyogo
Iwaya, Shinmura, Awaji-shi, Hyogo
Nojima Hikinoura, Awaji-shi, Hyogo
Higashiyama, Shinmura, Awaji-shi, Hyogo
Shimonomiya, Toyooka-shi, Hyogo
Hokkeiji, Toyooka-shi, Hyogo
Okuyane, Tanto-cho, Toyooka-shi, Hyogo
Okuyane, Tanto-cho, Toyooka-shi, Hyogo
Mannai, Kita-ku, Okayama
Kamisaibara, Kagami-cho, Tomata-gun, Okayama
Ushiroyama, Mimasaka-shi, Okayaam
Hiruzen-Nishikayabe, Maniwa-shi, Okayama
Fujimori, Maniwa-shi, Okayama
Kashino, Ushimado-cho, Setouchi-shi, Okayama
Yomogisaki, Ushimado-cho, Setouchi-shi,
OkayamaOka, Ushimado-cho, Setouchi-shi, Okayama
Kashino, Ushimado-cho, Setouchi-shi, Okayama
Tamahara, Tamano-shi, Okayama
Miyaura, Minami-ku, Okayama-shi, Okayama
Mt.Hachijyoiwa, Minami-ku, Okayama-shi,
Okayama
Hase lake, Kamiyamasaka, Tamano-shi, Okayama
Kamo-cho, Tsuyama-shi, Okayama
Kamisaibara, Kagami-cho, Tomata-gun, Okayama
Kamisaibara, Kagami-cho, Tomata-gun, Okayama
Okutsu, Kagamino-cho, Tomata-gun, Okayama
Okutsu, Kagamino-cho, Tomata-gun, Okayama
Okutsu, Kagamino-cho, Tomata-gun, Okayama
Okutsu, Kagamino-cho, Tomata-gun, Okayama
Okutsu, Kagamino-cho, Tomata-gun, Okayama
Kamisaibara, Kagami-cho, Tomata-gun, Okayama
Kaita-cho, Aki-gun, Hiroshima
Jhoge-cho, Fuchu-shi, Hiroshima
Fukutomi-cho, Higashihiroshima-shi, Hiroshima
Higashihiroshima-shi, Hiroshima
Iwamoto, Iwami-cho, Iwami-gun, Tottori
Yamaguchi, Mochigase-cho, Toori-shi, Tottori
Tanigawa, Hoki-cho, Saihaku-gun, Tottori
Asakane, Aimi-cho, Saihaku-gun, Tottori
Ikeno, Aimi-cho, Saihaku-gun, Tottori
Neubara, Hoki-cho, Saihaku-gun, Tottori
Kakibara, Kofu-cho, Hino-gun, Tottori
Furuyashiki, Kofu-cho, Hino-gun, Tottori

82.9±1.6
84.0±0.784.8±1.885.4±1.2
84.3±1.4
88.1±0.581.2±1.181.9±0.982.8±2.1

72.6±2.664.3±1.3
68.0±1.287.5±1.187.2±1.684.8±0.973.4±1.1
63.8±1.564.5±1.571.6±0.972.4±1.0
72.2±1.272.5±1.0

92.9±1.1
32.4±0.886.3±2.3
89.9±2.865.4±1.1
65.0±1.0
66.1±0.768.2±0.8

86.8±2.4
66.2±2.6
67.4±2.3
81.6±2.579.3±2.081.6±1.1
82.2±1.0
81.6±2.588.2±1.787.6±2.085.4±2.085.8±1.886.1±1.787.0±3.087.3±2.581.2±2.185.8±2.1
81.7±1.287.8±3.3
66.4±1.574.8±2.566.2±2.6
67.4±2.387.8±1.965.9±3.0
83.9±2.3
86.6±2.6
88.7±1.885.8±1.2
85.1±2.187.8±2.487.0±1.771.6±0.871.9±2.1
72.4±2.1
72.7±2.075.3±3.789.5±1.994.7±2.3
94.8±1.888.0±2.071.2±2.0
65.0±1.8

MonaziteUraninite and thorite ages of granitoids in the Japanese Islands
Table 1.
sample No

rockreg. No

GY-64
GY-85
YG93-1
YG93-2
YG-95
YG-96
YG-98
YG-104
YG-141
YG-142
YG-143
YG-144
YG-145
YG-14692072301
92072403
95101802
Do-2
YG-21
YG-22-1
YG-22-2
YG-23

granitegranitegranitegranitegranitegranitegranitegranitegranitegranitegranitegranitegranitegranitegranitegranitegranitegranitegranitoid
granitoid
granitoid
granitoid

YG-24
YG-26-2

granitoid
granitoid

YG-27
YG-28
YG-29
YG-30
YG-31
YG-33-2
YG-53
YG-54
YG-55
YG-56
87S34B
87S36A
87S36BYG-61
YG62-1
YG-65
YG-68
6415
KK-11

granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
aplitesheard granite

6415
130794

Ko-16

gneiss1307091306919(continued)

locality
Sukesawa, Kofu-cho, Hino-gun, Tottori
Yamaguchi, Sekikane-cho, Kurayoshi-shi, Tottori
Kuro pass, Okumoto, Chizu-cho, Yazu-gun, Tottori
Kuro pass, Okumoto, Chizu-cho, Yazu-gun, Tottori
Hazi, Chizu-cho, Yazu-gun, Tottori
Kuchiunami, Chizu-cho, Yazu-gun, Tottori
Kuchiunami, Chizu-cho, Yazu-gun, Tottori
Oshikakei, Misasa-cho, Tohaku-gun, Tottori
Kijiyama, Misasa-cho, Tohaku-gun, Tottori
Kijiyama, Misasa-cho, Tohaku-gun, Tottori
Misasa-cho, Tohaku-gun, Tottori
Simonishidani, Misasa-cho, Tohaku-gun, Tottori
Shimohata, Misasa-cho, Tohaku-gun, Tottori
Fukumoto, Misasa-cho, Tohaku-gun, Tottori
Hirao-cho, Kumage-gun, Yamaguchi
Totu, Iwakuni-shi, Yamaguchi
Suoshima-cho, Ooshima-gun, Yamaguchi
Fuse, Okinoshima-cho, Oki-gun, Shimane
Kinosho, Shodoshima-cho, Shozu-gun, Kagawa
Yoshino, Shodoshima-cho, Shozu-gun, Kagawa
Yoshino, Shodoshima-cho, Shozu-gun, Kagawa
Kamano, Shodoshima-cho, Shozu-gun, Kagawa

Uraninite64.1±1.3
83.3±1.3
83.0±1.3
83.0±1.564.6±0.9

65,6±0.866.5±1.0
70.2±0.766.9±1.1
94.2±1.1
92.9±1.1
94.5±1.818.7±2.0
86.5±1.2
84.9±2.987.7±1.3
93.0±1.6,
88.6±1.6
Futaomote, Shodoshima-cho, Shozu-gun, Kagawa 92.0±1.7
Un-misaki, Furuo, Shodoshima-cho, Shozu-gun,
90.1±2.1
KagawaSakate, Shodoshima-cho, Shozu-gun, Kagawa
92.2±2.4
Tachibana, Shodoshima-cho, Shozu-gun, Kagawa
94.2±1.1
Tachibana, Shodoshima-cho, Shozu-gun, Kagawa 104.4±2.2
Tachibana, Shodoshima-cho, Shozu-gun, Kagawa 105.6±1.7
Tachibana, Shodoshima-cho, Shozu-gun, Kagawa
Fukuda, Shodoshima-cho, Shozu-gun, Kagawa
Sue, Sanuki-shi, Kagawa
92.4±1.5
Shido, Sanuki-shi, Kagawa
90.8±1.2
Shirotori, Higashikagawa-shi, Kagawa
90.1±1.0
Nyunoyama, Higashikagawa-shi, Kagawa
89.1±0.9
Matsuyama-shi, Ehime
100.5±2.4
Matsuyama-shi, Ehime
99.0±2.0
Matsuyama-shi, Ehime
96.8±2.0
Takabe, Imabari-shi, Ehime
95.6±2.4
Namikata, Namikata-cho, Imabari-shi, Ehime
92.9±1.9
Moriue, Namikata-cho, Imabari, Ehime
95.3±1.0
Kugawa, Matsuyama-shi, Ehime
97.0±1.3
Ashizurimisaki, Tosashimizu-shi, Kochi
Heimiyaganaro, Niyodogawa-cho, Agawa-gun,
Kochi
Umanohara, Sagawa-cho, Takaoka-gun, Kochi

ThoriteMonazite

66.6±3.2
90.2±1.487.7±2.642.1±2.343.7±2.085.6±2.4

92.2±1.892.5±2.584.3±1.690.2±1.5

91.1±2.2
96.2±4.4
13.7±1.9

465.8±15.8456.5±17.1

Age data in Figs. 13 and 14
YG-04
Kyu-1
Kyu-5
Kyu-7
09-3-01
09-3-02
09-3-03
09-3-04
09-3-06
09-3-07
09-3-08
09-3-09
09-3-16

granitegranitoid
granitoid
granitoid
pegmatite
pegmatite
graniteaplitegranitepegmatite
granitepegmatite
granite13581313373013373413373613420013420113420213420413420513420613420713420813421509-8-01

granite134217

09-8-02

granite13421809-8-05

qz diorite

134221

Onihara, Hekishimo, Nagata-shi, Yamaguchi
Isozaki, Nijofukui, Itoshima-shi, Fukuoka
Mikasa, Dazaifu-shi, Fukuoka
Kakishita, Kawara-machi, Tagawa-gun, Fukuoka
Imajuku-Nagataru, Nishi-ku, Fukuoka-shi, Fukuoka
Hakoshima, Nijohamakubo, Itoshima-shi, Fukuoka
Nijomatusue, Itoshima-shi, Fukuoka
Nijyoufukui, Itoshima-shi, Fukuoka
Haisaki, Nijofukui, Itoshima-shi, Fukuoka
Haisaki, Nijofukui, Itoshima-shi, Fukuoka
Kushisaki, Nijoshikaka, Itoshima-shi, Fukuoka
Kushisaki, Nijoshikaka, Itoshima-shi, Fukuoka
Kankake pass, Tanushimaru-machi, Kurume-shi,
Fukuoka
Tsufune, Itoshima, Nishi-ku, Fukuoka-shi,
Fukuoka
Tsugami, Itoshima, Nishi-ku, Fukuoka-shi,
Fukuoka
Masaki, Kawasaki-machi, Tagawa-gun, Fukuoka

87.3±4.6
101.5±3.0
103.0±1.8
93.9±1.1
105.5±1.2
98.5±1.0
107.2±1.1107.7±2.8

105.8±5.3
95.2±1.2
105.5±1.8
106.0±2.7

100.5±7.6

98.0±6.7
106.8±8.987.2±15.0

95.0±1.4
106.3±2.4
97.9±1.4

99.4±6.8
87.8±4.4

97.6±2.4

Kazumi Yokoyama et al.

10

Table 1.
sample No(continued)

rock

reg. No

locality

Uraninite09-8-06
09-8-07
09-10-04

qz diorite
granitegranite13422213422313422794.9±1.2

09-10-05

granite13422809-10-07

granite13423009-10-08
09-10-09
09-10-10
09-10-11
09-10-12
09-10-13
09-10-14
09-10-16
09-10-17
09-10-19
09-10-26
09-10-27
09-10-28
09-10-29
09-10-30

aplitegranodiorite
aplitegranitegraniteaplitegranodiorite
aplitepegmatite
granitegranitegranitegranitegranitegranite134231
134232134233134234134235134236134237134238134241134242134249134250134251134252134253

09-11-01
09-11-02

granitepegmatite

134254134255

09-11-03
09-11-04
09-11-05
09-11-06
09-11-07
09-11-08

granitegranitegranitegranitegranitegranodiorite

134256134257134258134259134260134261

09-11-09
09-11-10
09-11-11
09-11-12
09-11-13

granodiorite
granitegranitegranitegranite134262134263134264134265134266

09-11-15
09-11-16
09-11-17
09-12-01
09-12-02
Kyu-3
09-3–11
09-10-21
09-10-22
QK-1
QK-5
QK-6
QK-7
QK-8
QK-9
1574
6396
TSM-17

granitegranodiorite
granitegranitegranitegranitoid
granitegranitepegmatite
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitoid
granitegranite134268134269134270134271134272133732134210134244134245

Naiju-kyo, Naiju, Iisuka-shi, Fukuoka
Mt. Sangun, Yusubaru, Chikushino-shi, Fukuoka
Kitashima, Itoshima, Nishi-ku, Fukuoka-shi,
Fukuoka
Tsugami, Itoshima, Nishi-ku, Fukuoka-shi,
Fukuoka
Karadomari, Itoshima, Nishi-ku, Fukuoka-shi,
Fukuoka
Kafuri, Itoshiro-shi, Fukuoka
Kafuri, Itoshiro-shi, Fukuoka
Nijohamakubo, Itoshima-shi, Fukuoka
Nijohamakubo, Itoshima-shi, Fukuoka
Nijomatusue, Itoshio-shi, Fukuoka
Nijofukui, Itoshiro-shi, Fukuoka
Nijyoufukui, Itoshima-shi, Fukuoka
Maeda, Nijofukui, Itoshima-shi, Fukuoka
Haisaki, Nijofukui, Itoshima-shi, Fukuoka
Ishikama, Sagara-ku, Fukuoka-shi, Fukuoka
Kamihoman, Hondoji, Chikushio-shi, Fukuoka
Hondoji, Chikushio-shi, Fukuoka
Anraku temple, Hondoji, Chikushio-shi, Fukuoka
Kitaya dam, Kitaya, Dazaifu-shi, Fukuoka
Byobu, Shioji, Usami-machi, Kasuya-gun,
Fukuoka
Mt. Ganjaku, Soeda-machi, Tagawa-gun, Fukuoka
Aburagi dam, Soeda-machi, Tagawa-gun,
Fukuoka
Tsuno, Soeda-machi, Tagawa-gun, Fukuoka
Jinya dam, Soeda-machi, Tagawa-gun, Fukuoka
Jinya dam, Soeda-machi, Tagawa-gun, Fukuoka
Jinya dam, Soeda-machi, Tagawa-gun, Fukuoka
Chugenji, Soeda-machi, Tagawa-gun, Fukuoka
Toya-natural park, Kawsaki-machi, Tagawa-gun,
Fukuoka
Amagi, Kawasaki-machi, Tagawa-gun, Fukuoka
Amagi, Kawasaki-machi, Tagawa-gun, Fukuoka
Amagi, Kawasaki-machi, Tagawa-gun, Fukuoka
Tateishi-toge, Aka-mura, Tagawa-gun, Fukuoka
Yusubaru station, Aka-mura, Tagawa-gun,
Fukuoka
Mt. Toshiro, Aka-mura, Tagaw-gun, Fukuoka
Uchida, Aka-mura, Tagawa-gun, Fukuoka
Uchida, Aka-mura, Tagawa-gun, Fukuoka
Inokuni, Kawsaki-machi, Tagawa-gun, Fukuoka
Amagi, Kawasaki-machi, Tagawa-gun, Fukuoka
Mitsuse, Mitsuse-mura, Saga-shi, Saga
Mt. Kurosaki, Ura, Karatsu-shi, Saga
Mitsuse, Mitsuse-mura, Saga-shi, Saga
Mitsuse, Mitsuse-mura, Saga-shi, Saga
Hinokage-cho, Nishiusuki-gun, Miyazaki
Kitakata-cho, Nishiusuki-gun, Miyazaki
Kitakata-cho, Nishiusuki-gun, Miyazaki
Kitakata-cho, Nishiusuki-gun, Miyazaki
Hinokage-cho, Nishiusuki-gun, Miyazaki
Hinokage-cho, Nishiusuki-gun, Miyazaki
Kiurakozan, Ume, Saiki-shi, Oita
Kitamura, Yamagashi-shi, Kumamoto
Uchiyama, Izuhara-machi, Tsushima-shi,
Nagasaki

1574
6396
135872Thorite111.9±1.7112.9±1.9

Monazite
97.2±5.6
94.0±4.8

107.9±3.0112.6±0.9107.5±1.6105.86±1.5

106.9±1.4105.6±2.8103.5±1.0

104.4±2.9104.6±5.2

95.1±2.8
100.5±1.7

99.0±1.2
98.5±1.2
99.8±1.3
100.3±0.9100.3±1.3
102.1±1.3

14.7±0.6

113.4±1.2
15.5±0.5

111.6±9.7
107.0±6.0108.2±7.9100.1±4.7
95.7±13.3
98.2±9.7
92.7±6.5
103.2±10.1
92.3±10.3
90.8±0.11.7
102.2±7.6102.1±0.7
99.6±0.8
102.1±1.8
98.1±1.3
99.4±2.2

110.7±6.3

10.16±12.0
98.8±1.2

97.6±6.0

99.2±1.7

99.1±.2.0

101.1±9.0
100.2±7.8

97.1±0.699.2±2.895.4±6.893.4±6.3
98.3±7.7
86±17109.7±7.2
94.4±8.915.6±1.7
15.6±1.515.5±1.915.7±1.6
15.0±1.6
14.4±3.0
15.5±1.4116±6

Age data out of the ﬁgures
6644

granite

6644

3624
H-7

granitegranite3624
128038

Kosugidani, Yakushima-cho, Kumage-gun,Kagoshima
Kinko-cho, Kimotsuki-gun, Kagoshima
Idenohana, Ashikita-machi, Ashikita-gun,
Kumamoto

14.9±0.3
16.3±1.5

426.3±14.8

Uraninite and thorite ages of granitoids in the Japanese Islands

data in the granitoids were summarized as anaverage and standard deviation. The standard
deviation is usually 1 sigma calculated from a
Gaussian distribution in probability theory. The
age data and localities of about 400 granitoids
are summarized in Table 1. Age data and their
histograms in each province are plotted in Figs. 2
to 16.
Uraninite and thorite ages obtained from theJapanese Islands range from ca. 5 to 300 Ma. In
some granitoids, monazite age determined by
EPMA analyses and zircon age determined by
LA-ICP-MS are used. Their analytical methods
were presented by Santosh et al. (2006) and Tsutsumi et al. (2010), respectively. In the present
study, the standard deviations of uraninites arefound to be around 4 Ma at around 200 Ma, 1 Ma
at around 70 Ma, and less than 1 Ma at around
5 Ma, which is comparable to those obtained byisotopic methods. The standard deviation for thorite is roughly double that for uraninite. In somesamples, bimodal age distributions were obtained
due to a later stage thermal event as found by
Yokoyama et al. (2010).
Southern Hokkaido and Tohoku Province:
Granitoids in Southern Hokkaido and Tohoku
Province are mostly Lower Cretaceous in age(Figs. 2 & 3). Neogene granitoids and Ordovician granitoids rarely occur. The Cretaceous andNeogene ages were obtained using uraninite andthorite whereas ages of the Ordovician granitoids
in the Hikami Area (Fig. 4) were obtained bymonazite analyses. The age of one diorite dyke
rock at the Shimokita Peninsula, Aomori prefecture, was obtained by LA-ICP-MS because of theabsence of both uraninite and anhydrous thorite.
Except for Neogene and Ordovician granitoids,
the Lower Cretaceous granitoids are divided into
two terranes based on age: the Kitakami Mountains area and the western Tohoku area. The former granitoids exceed 110 Ma and the latter isless than 110 Ma. The boundary between themextends in a N–S direction along the middle of
the Ou Mountains. The age range of the westernpart of Tohoku is from 101 Ma to 109 Ma. Creta-

11

ceous granitoids younger than 101 Ma were notfound in the area. As far as age is concerned,
granitoids with ages＞110 Ma extend to southern
Hokkaido except for Okushiri Island. In southern
Hokkaido, the boundary between the two types ispresent between Esashi and the Okushiri Island.
The oldest Cretaceous granitoid was found in the
Himegami body in the Kitakami Mountains andis 126 Ma. The age histogram by uraninite is different from that by thorite as shown in Fig. 3.
This is due to the strong alteration of thorite in
the granitoids from the western part of Tohoku.
Many K–Ar ages were obtained from Southern
Hokkaido and from Tohoku Province. In the
Kitakami Mountains, K–Ar ages of granitoids
range from 89 to 128 Ma (Kawano & Ueda,
1965a). Although their oldest age is similar topresent results, about 30% of the ages are lessthan 110 Ma, which corresponds to the westernpart of the Tohoku group of granitoids. K–Ar
ages in the western part of Tohoku are also variable ranging from ca. 80 Ma to 110 Ma, which isdifferent from present results that are concentrated well in a narrow range: 101 Ma to 109 Ma.
The variable range is because the Cretaceous
granitoids suffered from a late stage thermal
event or alteration that caused younger results
due to Ar loss. The division of the area by uraninite and thorite ages will be important when we
discuss the extension of the terrane or comparison of the granitoids in Primorye, Far East Russia, because the Japanese Islands were a part of
the Eurasia continent and were in contact with
Primorye before the opening of the Sea of Japan
during the early Neogene.
Granitoid ages at Hikami Mountain wereobtained only by studying the monazite (Fig. 4),even though thorite was commonly present. The
thorite was completely altered into a hydrous
state making it unsuitable for age dating. The
monazite age is 451±4 Ma, which is almost consistent with the SHRIMP age of 442.5±3.5 Ma
determined by Watanabe et al. (1995). Cambrian
granitoids were found as a small block from theIsawa and Nagasaka areas, Iwate Prefecture (Isozaki et al., 2015), in the terrane with an age

Kazumi Yokoyama et al.

12

Fig. 2. Sample localities of the studied granitoids in the southern Hokkaido and Tohoku Province. Numbers are
age data of granitoids. Most of the ages are obtained by EPMA analyses of uraninite and thorite. Zircon age in
one sample is obtained by LA-ICP-MS method.

Uraninite and thorite ages of granitoids in the Japanese Islands

13(e.g. Tsutsumi et al., 2012; Tagiri et al., 2010;
Isozaki et al., 2015). Isozaki et al. (2015) discussed such Early Paleozoic granitoids as remnants of the arc plutonic belt from the Early
Paleozoic Japan that developed near the continental margin.
Neogene granitoid occurs sporadically in Hokkaido and in Tohoku Province. Only two Neogene granitoids were analyzed. Their uraninite
ages are 23 and 5 Ma. They are probably relatedwith the opening of the Sea of Japan and laterstage igneous events, respectively, but regional
study is necessary to discuss their origin.

Fig. 3. Histograms of the uraninite and thorite ages
from the granitoids in southern Hokkaido andTohoku Province.

Fig. 4. Monazite ages of the Hikami granitoids andassociated metamorphic rocks. Average age ofthe rocks are 451 Ma with a standard deviationof 4 Ma as one sigma.

＞110 Ma as well as the Hikami Granitoids.
Although the geological relations of the old granitoids are unknown, such old granitoids occur
sporadically in the Japanese Islands such as in
the Maizuru, Hitachi areas and Kurosegawa Belt

Asahi Mountains, Abukuma Mountains andTsukuba–Nikko area: Fig. 5 shows the ages of
granitoids in the Asahi Mountains, the Abukuma
Mountains and the Tsukuba–Nikko area. A histogram of the Cretaceous age is shown in Fig. 6. In
this area, the Tanakura Tectonic Line (Fig. 1)
runs along the western margin of the Abukuma
Mountains. The tectonic line divides the Japanese Islands into two blocks. It was conﬁrmedthat the two blocks moved in different ways at
the time of the opening of the Japan Sea (e.g.
Otofuji & Matsuda, 1983 & 1984). Even though
the line is important, its northern extension has
not been clariﬁed. In this area, we can divide thearea into several terranes based on uraninite andthorite age. In the Asahi Mountains, the westernpart is composed of granitoids younger than
70 Ma, between 65 and 68 Ma, whereas granitoids in the eastern part are between 90 Ma and
98 Ma with one exception at 103 Ma. Two granitoids with an age around 80 Ma occur near the
younger granitoid terrane mentioned above.
Granitoids in the Abukuma Mountains areroughly classiﬁed into two groups based only on
the uraninite and thorite ages: 100–107 Ma and
110–124 Ma, with one exception at 301 Ma fromthe Soma area (Tsutsumi et al., 2012). The latterolder granitoid was further analysed and the age
was conﬁrmed by the LA-ICM-MA method(Tsutsumi et al., 2012). If this division is available, the western part of the Abukuma Mountains
is consistent with those from the western part of

14

Kazumi Yokoyama et al.

Fig. 5. Age data of granitoids in the Asahi Mountains, Abukuma Mountains and Nikko–Tsukuba area. Explanation of the age data is shown in Fig. 2.

Tohoku in Fig. 2, whereas the eastern part of the
Abukuma Mountains corresponds to the Kitakami Mountains and its northern extension.

In addition to the K–Ar ages for the granitoids
determined by Kawano & Ueda (1965b), there
are many studies about the granitoid ages in the

Uraninite and thorite ages of granitoids in the Japanese Islands

Fig. 6. Histograms of the uraninite and thorite ages
from the granitoids in the Asahi Mountains,
Abukuma Mountains, and Nikko–Tsukuba area.

Abukuma Mountains determined via zircon analyses by recent LA-ICM-MA and SHRIMP methods (Tagiri et al., 2010; Kon & Tagiri, 2012; Konet al., 2015; Ishihara & Orihashi, 2015). Tagiri etal. (2010) reported a Cambrian metagranitoidfrom the Hitachi metamorphic terrane at thesouthern end of the Abukuma Mountains with anage of around 500 Ma. Many other papers presented Cretaceous granitoid ages from the central
part of the Abukuma Mountains (Kon & Tagiri,
2012; Kon et al., 2015; Ishihara & Orihashi,2015). The Cretaceous age ranges from 97 Ma to
121 Ma similar to our results of 100–124 Ma.
However, they reported a younger age from theeastern part of the mountains where the uraninite
and thorite ages are 110–124 Ma. Kon et al.
(2015) concluded that the spatial distribution of
hornblende-biotite granitoids had no correlation
with their intrusive ages. In contrast, the leucocratic granitoids with an age of around 110 Ma
were located at the eastern part of the Abukuma
Mountains, whereas those with an age around
100 Ma were at the western part. Our results may
be comparable with the leucocratic granitoids.
In the Tsukuba area (Fig. 5), at the southernend of the Yamizo Mountains, granitoids haveages ranging from 65 Ma to 70 Ma with the15

exception of two samples that had ages of 80 Ma.
Granitoids in the Yamizo Mountains were studied using the K–Ar method by Shibata et al.
(1973). The K–Ar ages are similar to uraninite
and thorite ages, i.e. mostly less than 70 Ma. Two
samples in this study were found to have an ageof 80 Ma, which was found to be a relict age. The
combination with 65–70 Ma and 80 Ma may becorrelated with granitoids from the western partof the Asahi Mountains. One granitoid that had
an age of 105 Ma occurs at the eastern part of the
Yamizo Mountains, close to the Tanakura Tectonic Line. Although the age shows correlation
with those in the Abukuma Mountains, it isclearly different because the Yamizo Mountains
belonged to western Japan at the time of the
opening of the Sea of Japan, whereas the Abukuma Mountains were in eastern Japan.
In the western part of the Nikko area, granitoids have an age of 99 Ma, whereas in the easternpart the ages are around 64 Ma. These age data
show that the western part of the Nikko corresponds to the Asahi Mountain, whereas eastern
Nikko, including the Tsukuba area, corresponds
to the western part of the Asahi Mountains. It is
well accepted that metamorphic rocks in the Tsukuba area belong to the Ryoke belt and its extension is the Nihonkoku area of northern Niigata
Prefecture; western part of the Asahi Mountains(Fig. 5). Hence, it will be reasonable to conclude
that the Tsukuba and Nihonkoku will be formed
as the same igneous province. Granitoids that are
80 Ma in both areas will be treated same.
Many granitoids in this area have not been
analyzed yet, especially in the region between
Nikko and the Asahi Mountains (Fig. 5). Analyses of such granitoids will be important to study
the spatial distribution between the Nikko andAsahi Mountains granitoids.
Chubu and Kansai provinces: Fig. 7 shows theages of granitoids in the Chubu and Kansai provinces. Histogram of the Cretaceous age is shownin Fig. 8. In this area, the granitoid age ranges
from 4 Ma to 106 Ma. The youngest granitoids
occur along the Fossa Magna region, Yamanashi

Kazumi Yokoyama et al.

16

Fig. 7.

Age data of granitoids in Chubu and Kansai provinces. Explanation of the age data is shown in Fig. 2.

Fig. 8. Histograms of the uraninite and thorite ages
from the granitoids in the Chubu and Kansai
provinces.

Prefecture. Their ages range from 4.1 Ma to
16.9 Ma, which is comparable to the K–Ar dataof 4.5–13.0 Ma by Shibata et al. (1984) andUchiumi et al. (1990). Cretaceous granitoids arevariable in age, but they are divided roughly into

four groups: ＞70 Ma, 70–80 Ma, 80–90 Ma and
98–106 Ma. The granitoids with ages younger
than 70 Ma occur around the Wakasa Bay. Granitoids that are 70–80 Ma occur at the Ina district,around Lake Biwa and at the Suzuka Mountains.
Granitoids that are 80–90 Ma are found aroundthe Ikoma Mountains where SHRIMP analyses
by Watanabe et al. (2000) presented similar ages.
Granitoids with ages of 98–106 Ma occur southeast of Lake Biwa. Suzuki & Adachi (1998)
obtained granitoid ages in the Ryoke metamorphic belt analyzing monazite by EPMA. Theirages range from 67 Ma to 95 Ma, which is mostly
much older than the K–Ar age. They thought thatthe difference was due to the cooling rate due tothe difference of closure temperature of monazite
and mica. As presented by Suzuki and Adachi,
there is younger granitoid terrane in the Ryoke
belt than in the present data. Although more age
data were necessary in the other areas to conﬁrm
the regional differences, we tentatively divide thegranitoids only by means of the present age data.
In the western part of the Chubu and Kansai
areas shown in Fig. 7, it is expected that theUraninite and thorite ages of granitoids in the Japanese Islands

granitoid age will be getting younger northwards.
In the inner zone of southwest Japan, granitoids
are generally divided into three zones: the Ryoke
belt, the Sanyo belt and the Sanin belt from south
to north as discussed later. Generally speaking,age of granitoids becomes younger from south tonorth. However, granitoids with ages over 98 Ma
occur surrounded by young granitoid regions
such as 73 Ma to 80 Ma and 80–87 Ma. Such
relatively old granitoids, 102–107 Ma, werereported from the same area by Imaoka et al.
(2014). The complex spatial distribution of the
granitoids shows that igneous activity is not consistent with the geological belts such as the
Ryoke metamorphic belt and Mino Jurassic Belt.
Apparently the older granitoids, 98–106 Ma,
occur locally and were surrounded by younger
granitoids that are 70–80 Ma and 80–90 Ma.
Hida terrane: There were many studies about
the age of granitoids in the Hida terrane. Ota &Itaya (1989) summarized age data of K–Ar, Rb–
Sr, U–Pb and other methods in the terrane. Fig. 9shows uraninite, thorite and monazite ages of
granitoids in the Hida terane. The histogram ofFig. 9. Age data of granitoids in the Hida area.
Explanation of the age data is shown in Fig. 2.
The number in the box shows ages obtained
from monazite by EPMA analyses.

17

the age data is shown in Fig. 10. In this analysis,
we found that the granitoids are older than
180 Ma except for a local intrusion of Cretaceous
granitoids with an age of around 60–70 Ma and100 Ma. Uraninite and thorite ages in four granitoids from the Hida terrane were reconﬁrmed by
SHRIMP analyses (Yokoyama et al., 2010). In
the Hida terrane, two granitoid types were recognized based on the geological relations. They are
the Funatsu and Simonomoto types. Ota & Itaya(1989) concluded that Funatsu type is 170–
180 Ma in age, whereas the Shimonomoto type isaround 190 Ma. Our study could not conﬁrm agranitoid younger than 180 Ma except for a granitoid that is 160 Ma, which is much younger thanthe other age data. Because the granitoid with auraninite age of 160 Ma has monazite ages of
215±15 Ma, the uraninite age will be due toresetting by a later stage thermal event different
from the main metamorphic or igneous events in
the Hida terrane.
Histogram in Fig. 10 shows a roughly bimodal
distribution: 180–210 Ma and 230–260 Ma. The

Fig. 10. Histograms of the uraninite, thorite andmonazite ages from the granitoids in the Hida
area.

18

Kazumi Yokoyama et al.

Fig. 11. Age data of granitoids in the Chugoku and northern Shikoku provinces. Explanation of the age data isshown in Fig. 2.

two age groups are conﬁrmed often by the coreand rim relationships in the uraninite and thorite
grains (Fig. 9 and Yokoyama et al., 2010). Thereis no areal distinction between the two groups in
the map. It is difﬁcult from the uraninite and thorite ages to conclude whether early stage igneous
activity occurred in all the areas or only at the
local level. These data will be important for
future age studies or for determining the tectonic
setting of the Hida terrane.
Chugoku and northern Shikoku provinces:Fig. 11 shows the granitoid ages in the Chugoku
and northern Shikoku provinces. A histogram of
the granitoid ages is shown in Fig. 12. The innerzone of Southwest Japan is geologically divided
into three belts: Ryoke, Sanyo and Sanin fromthe south to north. Even though there are manyage data in the Ryoke and Sanyo belts, a reliablecorrelation with age has not been obtained. On
the other hand, in the Sanin belt, Imaoka et al.

Fig. 12. Histograms of the uraninite and thorite
ages from the granitoids in the Chugoku andnorthern Shikoku provinces.

Uraninite and thorite ages of granitoids in the Japanese Islands(2011) obtained detailed ages of the Eocene–
Oligocene granitoids by the K–Ar method androughly found their linear arrangement as well as
the granitoids that are 60–70 Ma. In the present
analyses, granitoids younger than 70 Ma develop
along the coast of the Sea of Japan. Except for a
few granitoids that have ages of 30–45 Ma and
73–83 Ma in the Sanin Belt, the area almost overlaps with those of the Eocene–Oligocene granitoids by Imaoka et al. (2011). As far as the granitoid that is 60–70 Ma is concerned, the belt willcontinue to the 60–70 Ma granitoid region around
Wakasa Bay in Fig. 7. Imaoka et al. (2011) concluded that the lineation of the granitoids that are
30–45 Ma was related to the plate subduction at
the time of formation of the Shimanto Belt running parallel to the Paciﬁc Ocean. The granitoids
that are 30–45 Ma occur only in the rather
restricted area of the Sanin Belt, which is different from the elongation of the Shimanto Belt that
continues from Okinawa to the Boso Peninsula,
Kanto Province. Distribution of such granitoids
is too local to deduce a close correlation with the
Shimanto Belt.
In contrast to the Sanin Belt, it is hard to ﬁnd alinear arrangement on the basis of the granitoid
age in the Ryoke and Sanyo belts. Murakami(1987) summarized K–Ar ages of the granitoids
in the belts: 75–95 Ma in the Ryoke Belt and
70–115 Ma in the Sanyo Belt. There is no spatial
distribution about the age in both the belts asshown in Fig. 11. The Ryoke Belt has uraninite
and thorite ages from 90 to 105 Ma except for
granitoids from Awaji Island. The oldest age
observed is 106 Ma from the northeastern part of
Shodo Island. Only granitoids with an age ofaround 80–85 Ma continue eastwards: Ikoma
Mountains in Fig. 9. In the Sanyo Belt, most of
the age data are from 70 to 95 Ma and there arethree areas that collect together based on granitoid age. The oldest area is at the western part ofHiroshima and most of the granitoids are older
than 90 Ma. The youngest are with 70–73 Ma,
and they occur in a narrow area of the Sanin
Mountain, close to the Sanin Belt. In the otherarea, granitoid ages are mostly 80–90 Ma, similar

19

to the Awaji Island of the Ryoke Belt. Linear
arrangement of the granitoids simply by uraninite
and thorite age is not recognized in both the
Ryoke and Sanyo belts, but it seems that granitoids with similar ages have concentrated in
restricted areas.
Northern Kyushu Province: Fig. 13 shows agesof granitoids in northern Kyushu. A histogram of
the granitoids is shown in Fig. 14. Most of Cretaceous granitoids in northern Kyushu have a narrow age range determined by uraninite and thorite from 95 Ma to 108 Ma. A few granitoids haveages around 113 Ma. Karakida (1992) summarized K–Ar ages of granitoids in northern
Kyushu. The range of the K–Ar age was from 75
to 115 Ma. As found in the other terranes, theoldest age obtained by the K–Ar age in each terrane is similar to that of the uraninite or thorite
age, which is probably because a fresh granitoid
gives a reasonable age for K–Ar dating. As far as
the age is concerned, this terrane will be one
igneous province similar to the western part of
the Ryoke belt (Fig. 11) and the Abukuma Mountains. The granitoids younger than 20 Ma concentrate in the Okueyama Mountains. Such young
granitoids occur at the Osumi Peninsula and in
Yakushima Island (Table 1), Kagoshima Prefecture, as well as granitoids in the Shimanto belt,
namely along the Paciﬁc coast. In addition to theyoung granitoids from the Fossa Magna region(Fig. 7), they were formed after or during the
opening of the Sea of Japan.
Other granitoid ages: Most of the age data areplotted in Figs. 2–13. Some granitoids analyzed
in this study are not included in the ﬁgures. They
are younger than 20 Ma and occur at the southernparts of Kyushu, Shikoku and the Kii Peninsula.
Furthermore, some old granitoids occurring in
the Maizuru and Kurosegawa belts are not presented in the ﬁgures. Their ages were obtained bymonazite or LA-ICP-MS. The granitoids from
the Maizuru belt were reported by Tsutsumi et al.
(2014). The other age data are shown in Table 1.

Kazumi Yokoyama et al.

20

Fig. 13.

Age data of granitoids in the northern Kyushu Province. Explanation of the age data is shown in Fig. 2.

Discussions
Ages of about 400 granitoids in the JapaneseIslands were obtained through EPMA analyses ofuraninite and thorite. Although the age data are
not enough to discuss a spatial distribution of
granitoids in the islands, the present study isimportant because the ages of the granitoids are
obtained by the same method and machine
throughout this study. Age data obtained by LAICP-MS or SHRIMP will be available. But so far
it is difﬁcult to compare their age data with present data because of differences in method, standard, machine and other experimental differ-ences. In the near future, it will be best to use acommon mineral in granitoids such as zircon
when we summarize more detailed distributionsin the islands by a more reliable method such as
LA-ICP-MS or SHRIMP. Among the obtained
data, it is concluded that the uraninite and thorite
ages are much more concentrated in each province than by ages obtained by the K–Ar method.
The K–Ar method involves a few problems. One
is the Ar loss during later stage thermal eventsand alteration. The others are an age difference
among minerals used for the age analyses andlow closure temperature. Uraninite and thorite
ages also have a closure temperature problem as

Uraninite and thorite ages of granitoids in the Japanese Islands

Fig. 14. Histograms of the uraninite and thorite
ages from the granitoids in the northern Kyushu
Province.

shown by Yokoyama et al. (2010). Uraninite andthorite are lower in closure temperature than zircon and monazite, but higher than micaceous
minerals. For the other problem, uraninite andanhydrous thorite are usually rare and are notalways present in the granitoids. In spite of these
problems, the ages obtained by EPMA analysesof uraninite and thorite are available because ofequivalent results to the SHRIMP age or K–Ar
age for Neogene granitoids (Yokoyama et al.,2010). Therefore, we try to discuss the spatial
distribution of the granitoids only through uraninite and thorite ages.
Devonian and Cambrian granitoids occur only
sporadically in the islands and were summarized
by Isozaki et al. (2015). The other younger granitoids in the Japanese Islands are roughly summarized by the present study mainly using theuraninite and thorite ages and are divided into
several terranes. Spatial distribution by granitoid
ages in the islands is summarized in Fig. 15. It
will be probable that the age boundaries are
eventually more ambiguous and the zones withsimilar ages may overlap more or less with eachother. The oldest terrane is the well-known Hida
terrane that has an age older than 180 Ma. The

21

terrane will be further divided into two events:
180–220 Ma and 230–260 Ma (Fig. 10). As presented in the histograms (Figs. 10 and 16), it will
be noteworthy that the granitoids with ages from
126 Ma to 180 Ma are absent in the JapaneseIslands. Cretaceous granitoids that also partly
include Paleogene in age are widely distributed
throughout the islands. Their ages range from
60 Ma to 126 Ma that appears almost continuous
in the summarized data (Fig. 16), indicating
almost continuous igneous activity including volcanism in the islands. The Kitakami granitoids
with 110–126 Ma show a zone from southern
Hokkaido to the eastern Abukuma Mountains.
Ages older than 110 Ma are only and locallyfound in northern Kyushu, though there may be
no continuous relation with the Kitakami granitoids. Granitoids with ages of 100–110 Ma
roughly form a zone from the Okushiri Island,
Hokkaido, to the western Abukuma Mountains
through the Akita area. Similar granitoids that are
100–110 Ma occur sporadically along the Median
Tectonic Line and in a restricted area at thesouthwest part of Lake Biwa. Similar granitoids
are well concentrated in northern Kyushu. Granitoids that are 90–100 Ma are found in several
areas: the Asahi Mountains, Nikko and sporadically across southwest Japan along the Median
Tectonic Line. So far, clear zonation has not beenrecognized among them.
Granitoids that are 80–90 Ma occur mostly in
the Chugoku to Kinki provinces and may begrouped as the same igneous province. Granitoids that are 70–80 Ma occur in two areas: Shinshu on the northern side of the Median Tectonic
Line, and the central part of the Sanin Province.
Granitoids that are 60–70 Ma in age are well concentrated along the coast of the Sea of Japan andin the Tsukuba–Nikko area.
Igneous activity including volcanism in theJapanese Islands and along the continental margin of Asia has been treated as a result of subduction of the oceanic plate as an analogue of thepresent plate tectonics (e.g. Imaoka et al., 2015;
Kon et al., 2015). Spatial distribution of granitoids with similar ages, especially Cretaceous

Kazumi Yokoyama et al.

22

Fig. 15.

Spatial distribution of granitoids summarized by uraninite and thorite ages in the Japanese Islands.

ones, does not always show a linear arrangement
and is not related with the geological province.
Hence, the correlation with subduction has notbeen solved yet. The youngest granitoids occur
along the Paciﬁc coast of western Japan andalong the Fossa Magna zone and are related tothe events that occurred after the opening of the

Sea of Japan. Unfortunately, we could not
develop a clear model for the youngest granitoids. This study of the spatial distribution of
granitoids in the Japanese Islands is still on theway and will be reﬁned or reconﬁrmed by LAICP-MS, SHRIMP and/or new age techniques.
The present data will be available as a prelimi-

Uraninite and thorite ages of granitoids in the Japanese Islands

Fig. 16. Histograms of the uraninite and thorite
ages from the granitoids in the Japanese Islands.

nary study for the compilation of the granitoids
in the Japanese Islands in the near future.
Acknowledgements
This paper was conducted as a part of theresearch project “Research on the Earthʼs surface
processes and biota in and near the Sea of Japan”
launched by the Museum. We wish to express
our thanks to Dr. A. Goto & Dr. S. Kiyokawa forproviding us granitoid samples.
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日本列島の花崗岩質岩 400 資料の閃ウラン鉱とトールによる年代測定
横 山 一 己・重 岡 昌 子・大 友 幸 子・徳 野 康 太・堤之 恭

日本列島の花崗岩質岩 400 資料が閃ウラン鉱とトールの EPMA 分析により年代測定された．年代は，5 百万年から 3 億年の範囲で，狭い年代の範囲で地域ごとに纏められた．日本の北部では，海溝沿いに年代が並ぶ地域があるが，西南日本では，一部を除き，帯状配列は見られず，点状に分布する年代地域があることが判明した．これらの年代データは，
日本海対岸の花崗岩質岩の年代との比較で古地理の復元に利用されるものである．