Jour. Geol. Soc. Japan, Vol. 116, No. 10, p , October 2010 U-Pb FT LA-ICP-MS U-Pb Zircon U-Pb and fission-track ages of

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1 Jour. Geol. Soc. Japan, Vol. 116, No. 10, p , October 2010 U-Pb FT LA-ICP-MS U-Pb Zircon U-Pb and fission-track ages of granitic rocks from the Nojima Fault and its vicinity: A new horizon for the LA-ICP-MS U-Pb dating method Hisatoshi Ito, Akihiro Tamura, Tomoaki Morishita and Shoji Arai Geosphere Science Sector, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko, Chiba , Japan Frontier Science Organization, Kanazawa Univ., Kakuma, Kanazawa, Ishikawa , Japan Department of Earth Sciences, Kanazawa Univ., Kakuma, Kanazawa, Ishikawa , Japan Corresponding author; H. Ito, ito_hisa@criepi.denken.or.jp Abstract Zircon U-Pb dating by laser ablation-inductively coupled plasma-mass spectrometry LA-ICP-MS and zircon fission-track FT dating were performed on granitic rocks from the Nojima Fault and its vicinity on northern Awaji Island, Hyogo Prefecture, Japan. The analyses yielded zircon FT ages of - Ma, which are in agreement with previously reported zircon FT ages. Zircon U-Pb U- Pb ages of - Ma were also determined. By combining these results with existing radiometric age data, we estimated the entire cooling history of the granitic basement on northern Awaji Island, spanning the period from the time of intrusion to the present. U-Pb ages were determined from zircons that were prepared for FT dating. Moreover, U-Pb ages were corrected based on analyses of Fish Canyon Tuff zircons as a standard material. As a result, a precise and accurate age of.. Ma was obtained for the Buluk Member Tuff. This result demonstrates that the effect of common Pb is minimal even when analyzing zircons that are chemically etched, and that the Fish Canyon Tuff, which is a well-known age standard for FT dating, can be used as a standard for U-Pb dating. Many previous studies have reported on zircon FT analyses performed throughout the world. The method applied in the present study should pave the way for adding information on the crystallization age of the studied rocks by analyzing the zircons prepared previously for FT dating. Keywords: U-Pb dating, LA-ICP-MS, fission-track dating, zircon, Nojima Fault 1995 FT Murakami and Tagami, 2004 FT Yamada et al., 2007 U-Th Watanabe et al., 2008 FT Ito, 2004 U-Th /He, 2006 Ito 2004 U-Pb FT U-Pb FT Laser Ablation Inductively Coupled Plasma Mass Spectrometry LA-ICP-MS U-Pb U-Th /He FT LA- ICP-MS U-Pb CThe Geological Society of Japan km, 1991, 1990, 1981;, Fig U-Pb kg

116 10 U-Pb FT 545 block 1 FT 51.6 2.3 Ma U-Pb Fig.. Topographic map showing sampling localities on northern Awaji Island, along with zircon U-Pb and zircon FT ages Ma obtained in this study.

2 U-Pb FT 545 block 1 FT Ma U-Pb Fig.. Topographic map showing sampling localities on northern Awaji Island, along with zircon U-Pb and zircon FT ages Ma obtained in this study. UPb: zircon 238 U- 206 Pb age, FT: zircon fissiontrack age. Geology is after Mizuno et al µm SPT PFA : 1 cm 1 cm 1 mm 10 µm FT NaOH-KOH JRR-3 PN-2 20 FT FT Hurford, 1990 ED1: Gleadow, 1981 FT STAge Dumitru, 1993, 1999 FT Table Ma FT Murakami and Tagami Ma Yamada et al Ma FT Uplifted U-Pb LA-ICP-MS Table nm He He Ar ICP-MS 50 µm U-Pb 238 U- 206 Pb Fish Canyon Tuff Schmitz and Bowring, U-Pb FT PFA common Pb U-Pb U-Pb Fish Canyon Tuff Buluk Member Tuff Hurford and Watkins, 1987 U-Pb U-Pb Table 3 Fig T σt 1 1 st T 1 N 206 N 238 N 206 N Pb 238 U : cps Fish Canyon Tuff σt Schmitz and Bowring 2001 Fish Canyon Tuff Ma Fish Canyon Tuff Ma st st 2 T w T w 28.5 T w σt w Fish Canyon Tuff Fish Canyon Tuff Buluk Member Tuff Ma Table 3 Fig. 2Buluk Member Tuff Ma Hurford and Watkins, 1987

3 Table. Results of zircon fission-track dating of granitic rocks from the Nojima Fault and its vicinity. U-Pb common Pb common Pb Pb common Pb common Pb 204 Pb ICP-MS 204 Pb 204 Hg 204 Pb 204 Hg 204 Hg 202 Hg 204 Pb 100 cps common Pb Buluk Member Tuff 204 Pb 40 cps Table 3, Fig Pb common Pb U-Pb U-Pb Fig Ma 204 Pb 175 cps common Pb 202 Hg 204 Pb 204 Hg Pb 206 Pb radiogenic Pb loss common Pb Pb common Pb Pb Davis et al Table. LA-ICP-MS operating conditions at Kanazawa University, Japan. common Pb Pb Pb α Fish Canyon Tuff Buluk Member Tuff common Pb Pb Ma Ma common Pb common Pb

4 U-Pb FT 547 Table. LA-ICP-MS analytical results.

5 Fig.. Grain-by-grain U-Pb ages a and corresponding 204 Pb and 202 Hg values b. Sample numbers correspond to those in Table Fish Canyon Tuff U Pb Fish Canyon Tuff 206 Pb/ 238 U Table 3 : : U Pb 20

6 U-Pb FT 549 Table. Radiometric ages determined for granitic rocks from the Nojima Fault and its vicinity. FT apatite ages are from Ito 2004, and the U-Th /He apatite age is from Ito LA-ICP-MS U- Pb Table 4 Table 4 FT Uplifted block 1 4 FT FT FT FT FT FT 240 : Hurford, : Naeser, 1981 FT FT FT FT FT Uplifted block 3 U-Pb U-Th /He K-Ar, 1992 Fig. 3 Ito, 2004;, 2006 U-Pb 100 Fig.. Inferred cooling curve for an uplifted block of granite on northern Awaji Island. Horizontal bars represent the error 2σ. All the ages except for K-Ar are from Uplifted block 3 Table 4. K- Ar ages are from Takahashi The adopted closure temperatures are as follows: U-Pb zircon 1000 from Mezger and Krogstad 1997, K-Ar hornblende 500 from Harrison 1981, K-Ar biotite 320 from Harrison et al. 1985, FT zircon 240 from Hurford 1986, FT apatite 100 from Naeser 1981, and U-Th /He apatite 70 from Farley LA-ICP-MS U-Pb FT Fish Canyon Tuff U-Pb U-Pb a mm cm b Pb/U c, Slama et al., 2008 Fish Canyon Tuff a b FT Fish Canyon Tuff U-Pb FT U-Pb common Pb

7 Buluk Member Tuff U-Pb FT FT LA-ICP-MS U-Pb FT FT U-Pb U-Pb FT 1 FT Ma FT U-Pb common Pb Ma 2 U-Pb LA-ICP-MS 238 U- 206 Pb FT FT Fish Canyon Tuff U-Pb Buluk Member Tuff U-Pb FT FT FT FT FT Tubingen Istvan Dunkl Trackkey version 4.0.c Davis, D. W., Williams, I. S. and Krogh, T. E., 2003, Historical development of zircon geochronology. In Hanchar, J. M. and Hoskin, P. W. O., eds., Zircon, Rev. Mineral. Geochem.,, Dumitru, T. A., 1993, A new computer-automated microscope stage system for fission-track analysis. Nucl. Tracks Radiat. Meas.,, Farley, K. A., 2002, U-Th /He dating: techniques, calibrations, and applications. In Porcelli, P. D., Ballentine, C. J. and Wieler, R. eds., Noble Gases in Geochemistry and Cosmochemistry, Rev. Mineral. Geochem.,, Galbraith, R. F., 1981, On statistical models for fission track counts. Math. Geol.,, Gleadow, A. J. W., 1981, Fission-track dating methods: What are the real alternatives?. Nucl. Tracks,, Green, P. F., 1981, A new look at statistics in fission track dating. Nucl. Tracks,, Harrison, T. M., 1981, Diffusion of 40 Ar in hornblende. Contrib. Mineral. Petrol.,, Harrison, T. M., Duncan, I. and McDougall, I., 1985, Diffusion of 40 Ar in biotite: Temperature, pressure and compositional effects. Geochim. Cosmochim. Acta,, Hurford, A. J., 1986, Cooling and uplift patterns in the Lepontine Alps South Central Switzerland and an age of vertical movement on the Insubric fault line. Contrib. Mineral. Petrol.,, Hurford, A. J., 1990, Standardization of fission track dating calibration: Recommendation by the Fission Track Working Group of the I. U. G. S. Subcommission on Geochronology. Chem. Geol. Isot. Geosci. Sect.,, Hurford, A. J. and Watkins, R. T., 1987, Fission-track age of the tuffs of the Buluk Member, Bakate formation, Northern Kenya: a suitable fissiontrack age standard. Chem. Geol. Isot. Geosci. Sect.,, Ito, H., 1999, FT FT STAge Chikyu Monthly, extra ed., no. 26, Ito, H., 2004, Apatite fission-track dating of fault-related rocks along the Nojima and Kusumoto faults and its tectonic significance. Geophys. Res. Lett.,, L21610, doi: /2004GL Ito, H., 2006, Central Res. Inst. Electric Power Industry Rep. : N05060, 18p Ito, H., Kurahashi, K., Tamura, A., Chida, T., Arai, S. and Morishita, T., 2009, LA-ICP-MS FT U-Pb Nd-YAG Fission Track Newsl.,, Ito, H. and Taniguchi, T., 2002, Fission Track Newsl.,, The Research Group for Active Faults, ed., 1991, Active Faults in Japan, New Edition-distribution map and the related materials- Univ. Tokyo Press, 363p Mezger, K. and Krogstad, E. J., 1997, Interpretation of discordant U-Pb zircon ages: an evaluation. Jour. Metam. Geol.,, Mizuno, K., Hattori, H., Sangawa, A. and Takahashi, Y., 1990, 5 1 Geology of the Akashi District. Quadrangle Series, scale 1: 50000, Geol. Surv. Japan, 90p Murakami, M. and Tagami, T., 2004, Dating pseudotachylyte of the Nojima fault using the zircon fission-track method. Geophys. Res. Lett.,, L12604, doi: /2004GL Naeser, C. W., 1981, The fading of fission-tracks in the geological environment: Data from deep drill holes. Nucl. Tracks Radiation. Meas.,, Oka, Y. and Sangawa, A., 1981, Jour. Geogr.,, Schmitz, M. D. and Bowring, S. A., 2001, U-Pb zircon and titanite systematics of the Fish Canyon Tuff: an assessment of high-precision U-Pb geochronology and its application to young volcanic rocks. Geochim. Cosmochim. Acta,, Slama, J., Kosler, J., Condon, D. J., Crowley, J. L., Gerdes, A., Hanchar, J. M., Horstwood, M. S. A., Morris, G. A., Nasdala, L., Norberg, N., Schaltegger, U., Schoene, B., Tubrett, M. N. and Whitehouse, M. J., 2008,

8 U-Pb FT 551 Plesovice zircon-a new natural reference material for U-Pb and Hf isotopic microanalysis. Chem. Geol,, Takahashi, Y., 1992, K-Ar Jour. Min. Petr. Econ. Geol./Ganko,, Watanabe, Y., Nakai, S. and Lin, A., 2008, Attempt to determine U-Th dating of calcite veins in the Nojima fault zone, Japan. Geochem. Jour.,, Yamada, R., Matsuda, T. and Omura, K., 2007, Apatite and zircon fissiontrack dating from the Hirabayashi-NIED borehole, Nojima Fault, Japan: Evidence for anomalous heating in fracture zones. Tectonophysics,, English translation from the original written in Japanese U-Pb FT LA-ICP-MS U-Pb Ito, H., Tamura, A., Morishita, T. and Arai, S., 2010, Zircon U-Pb and fission-track ages of granitic rocks from the Nojima Fault and its vicinity: A new horizon for the LA-ICP-MS U-Pb dating method. Jour. Geol. Soc. Japan,, FT LA-ICP-MS U-Pb Ma FT Ma U-Pb 238 U- 206 Pb U-Pb FT Fish Canyon Tuff U-Pb Buluk Member Tuff U-Pb Ma FT FT

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