地質調査研究報告/Bulletin of the Geological Survey of Japan

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1 ,*,, Takahiro Yamamoto 1, Jun-ichi Itho 1, Mitsuhiro Nakagawa 2, Takeshi Hasegawa 2 and Hiroshi Kishimoto (2010) 14 C ages for the ejecta from Kutcharo and Mashu calderas, eastern Hokkaido, Japan. Bull. Geol. Surv. Japan, vol. 61 (5/6), p , 4 figs, 3 tables. Abstract: Eruption ages of the ejecta from Kutcharo and Mashu calderas were systematically determined by 14 C dating. 16 charred samples were newly obtained from the Mashu and Nakashumbetsu Tephra Formations around the calderas and dated by AMS and β-counting methods. Examined units are Ma-d, Ma-e, Ma-f, Ma-j, Ma-k, Ma-l and Ml-a in the Mashu ejecta and 6 Nakashumbetsu tephra layers including Kutcharo Pumice Flow Deposit I (KpI), which is the youngest caldera-forming product from Kutcharo caldera. Results of the 14 C dating range from 3,660 ±40 ybp to 36,080±1,300 ybp, and are consistent with the tephrostratigraphy. Calendar age for KpI was newly calculated at almost 40 ka and this age shows there was about 70,000 years recurrence interval between KpI and KpIV caldera-forming eruptions. Mashu caldera has appeared on the eastern part of Kutcharo caldera immediately after the KpI eruption, and calendar age for its main caldera-forming eruption were determined at ca. BC 5,600. Keywords: Kutcharo caldera, Mashu caldera, 14 C age, tephrostratigraphy C AMS Ma-d Ma-e Ma-f Ma-j Ma-k Ma-l Ml-a KpI KpI C C, ybp,, ybp KpI ka KpIV KpI. Cal BC VIII I KpVIII I km AIST, Geological Survey of Japan, Institute of Geology and Geoinformation, GSJ Hokkaido University, Graduate School of Science, Department of Natural History Sciences Asia Air Survey Company, Department of Disaster Prevention Ibaraki University, College of Science * Corresponding autor: T. YAMAMOTO, Central, - - Higashi, Tsukuba, Ibaraki -, Japan.

7 Shibecha Nakashunbetsu Shibetsu Loc.4 Loc.

E Loc. =. N,. E Loc. =. N,. E Loc. =. N,. E Loc. =. N,. E Loc. =. N,. E Kushiro 20km N Fig.

0 E); Loc. 2 = Chibecha (43 18 7.0 N, 144 32 57.

4 N, 145 3 39.7 E); Loc. 4 = Kikusui (43 31 44.

8 N, 145 15 8.3 E); Loc. 6 = Konan (43 47 26.

2 Shari Koshimizu Loc.6 Akan Kutcharo Mashu Teshikaga Loc.2 Loc.7 Shibecha Nakashunbetsu Shibetsu Loc.4 Loc.1 Loc.3 Loc.5 Nemuro Loc. =. N:. E Loc. =. N,. E Loc. =. N,. E Loc. =. N,. E Loc. =. N,. E Loc. =. N,. E Loc. =. N,. E Kushiro 20km N Fig. 1 Topographic image around Kutcharo and Mashu calderas and location of outcrops. Loc. 1 = Kenebetsu ( N: E); Loc. 2 = Chibecha ( N, E); Loc. 3 = Nakashumbetsu ( N, E); Loc. 4 = Kikusui ( N, E); Loc. 5 = Tokotan ( N, E); Loc. 6 = Konan ( N, E); Loc. 7 = Yoroushi ( N, E). C a IV KpIV KpIV e Toya ka km KpIV a KpIV Nl Nu Ch Ml Ma II/III KpII/III I KpI Ymb HkP TyP a

3 Ch-a -d = Ds-Oh = HkP = ; Kc-Hb = ; Kc-Sr = Ma-b -l = Ml-a -e = Na-P = Ng = Nu-a -r = Spfa- = TyP = YmP = Fig. 2 Tephrostratigraphic sections through the Mashu, Chanai and Nakashumbetsu Tephra Formations. Ch-a to -d = Chanai tephra series; Ds-Oh = Daisetsu-Ohachidaira tephra; HkP = Higashikayano pumice; Kc-Hb = Kutcharo-Haboro tephra; Kc-Sr = Kutcharo- Shiyoro tephra; Ma-b to -l = Upper Mashu tephra series; Ml-a to -e = Lower Mashu tephra series; Na-P = Nakashari pumice; Ng = Nigorikawa tephra; Nu-a to -r = Upper Nakashumbetsu tephra series; Spfa-1 = Shikotsu 1 tephra; TyP = Toyozumi pumice; YmP = Yanbetsu pumice. See Fig. 1 for location. Ds-Oh Ds-Oh YmP HkP Ds-Oh YmP HkP cm Loc. cm cm Ds-Oh Loc. Nu-q a Loc. Ml-b Ml-e cm Ml-d a

4 Ch-a = Ng = Nu-a & -d = Spfa = Ap = Bt = Cpx = Hb = Min = Opq = Opx = tr = Table 1. Characteristics of pyroclastic deposits within the Mashu, Chanai and Nakashumbetsu Tephra Formations. Ch-a = Chanai tephra Ch-a; Ng = Nigorikawa tephra; Nu-a & -d = Upper Nakashumbetsu tephra series; Spfa-1 = Shikotsu 1 tephra. Ap = apatite; Bt = biotite; Cpx = clinopyroxene; Hb = hornblende; Min = minerals; Opq = opaque minerals; Opx = orthopyroxene; tr = trace. Ng km Loc. KpI. KpI a (Spfa- ) DHT101 Loc. cm d Ma-d Ma-d Katsui et al.,. g DHT102 Loc. cm e Ma-e Ma-e Katsui et al.,. g DHT103 Loc. cm j Ma-j Ma-j i h g Ma-i Ma-h Ma-g. g AMS DHT104 Loc. cm k Ma-k Ma-k

5 Katsui et al.,. g DHT105 Loc. cm l Ma-l Ma-l Ma-l Katsui et al.,. g DHT106 Loc. cm Ml-a a Ml-a cm Ma-l Katsui et al.,. g DHT107 Loc. cm Ml-a a Ml-a cm Ma-l Katsui et al.,. g DHT108 Loc. cm Nu-h a Nu-h cm cm Nu-h. g DHT109 Loc. cm Nu-l a Nu-l cm cm -. cm cm cm Nu-l. g DHT110 Loc. cm Nu-n a Nu-l cm cm. cm Nu-n. g DHT111 DHT112 km Loc. Kp Kp Kp Kp KpI Kc-Sr Kc-Sr km. g DHT113 km Loc. Nl a Kc-Sr cm

6 cm cm. cm cm cm Spfa-. g DHT201 DHT202 Loc. f Ma-f Ma-f m Ma-f Ma-j Ma-i Ma-h Ma-g km g DHT203 Loc. Ds-Oh Ds-Oh cm cm. g BETA ANALYTIC DHT DHT AMS RCYBP AD C Stuiver et al. Talma and Vogel DHT, ybp DHT,, ybp DHT DHT DHT DHT C C Ma-b ybp GaK- Ma-c, ybp GaK- Ma-e, ybp, ybp a Ma-f, ybp GaK-, ybp GaK- Ma-k, ybp Gak- Ma-l, ybp GaK- Katsui et al.,, ybp a Ma-d, ybp DHT Ma-e, ybp DHT Ma-f, ybp DHT, ybp DHT Ma-j, ybp DHT Ma-k, ybp DHT Ma-l, ybp DHT C C Ma-f Ma-l Ma-d Cal BC, Ma-e Cal BC, Ma-f DHT DHT Cal BC, Ma-j DHT Ma-j Ma-f DHT Cal BC,

7 AMS = Rad = a = b = [ ] = Bata. Table 2. Results of radiocarbon dating for the pyroclastic deposits around Kutcharo and Mashu calderas. AMS = accelerator mass spectrometry method; Rad = radiometric method (β-counting); a = charred material within the deposit; b = charred material in the underlying soil; [ ] = Beta number.

8 Ml-a Ng Ng. ka DHT Ng Ma-l Ml-a Cal BC, Cal BC, Fig. 3 Distribution of the calendar ages for the ejecta from Mashu caldera. See Table 2 for the details of ages. DHT DHT DHT Ma-j Ma-j Ma-f Ma-l Ml-a KpII/III KpI KpII/III Aso- KP, +, -, ybp (GaK- ) C Kigoshi, AMS KpI AMS, ybp,, ybp, ybp C Fairbanks et al. KpI ka Nu-g Nu-h b,, ybp AMS C Nu-h DHT Ds-Oh Spfa- Ds-Oh AMS, ybp ka Spfa-.. ka

Fig. 4 Stratigraphic relationship between the ejecta of Kutcharo and Mashu calderas. Black arrows and dotted lines show pyroclastic flow deposits and foreign tephra layers. Fairbanks et al.

9 Fig. 4 Stratigraphic relationship between the ejecta of Kutcharo and Mashu calderas. Black arrows and dotted lines show pyroclastic flow deposits and foreign tephra layers. Fairbanks et al. ( ) Table 3. Calendar ages for the radiocarbon ages from the Nakashumbetsu Tephra Formation. The ages were converted by the calibration program by Fairbanks et al. (2005) on their web page ( C KpI C, ybp KpIV km. Cal BC, km

10 MD - - Fairbanks, R.G., Mortlock, R.A., Chiu, T.-C., Cao, L., Kaplan, A., Guilderson, T.P., Fairbanks, T.W., Bloom, A.L., Grootes, P.M. and Nadeau, M.-J. ( ) Radiocarbon calibration curve spanning to, years BP based on paired Th/ U/ U and C dates on pristine corals. Quaternary Sci. Rev.,, -. - no. - p p. p Katsui, Y., Ando, S. and Inaba, K. ( ) Formation and magmatic evolution of Mashu volcano, East Hokkaido, Japan. J. Fac. Sci. Hokkaido Univ.,, -. Kigoshi, K. ( ) Gakushuin Natural Radiocarbon Measurements VI. Radiocarbon,, V -P p. no. - a p. b C C Stuiver, M., Reimer, P.J., Bard, E., et al. ( ) INTCAL Radiocarbon Age Calibration,, - cal BP. Radiocarbon,, no ) C C p. -. Talma, A.S. and Vogel, J.C. ( ) A simplified approach to calibrating C dates. Radiocarbon,, -. no. -.

地質調査研究報告/Bulletin of the Geological Survey of Japan

地質調査研究報告/Bulletin of the Geological Survey of Japan Shun Nakano, Akira Takada, Yoshihiro Ishizuka, Yusuke Suzuki, Tatsuro Chiba, Ken-ichi Arai, Makoto Kobayashi and Yasuhisa Tajima (2007) Eruption ages of younger-stage lava flows and olderstage pyroclastic