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Zircon U-Pb (& Lu-Hf) isotope geochronology of the Hidaka Metamorphic Belt, Hokkaido, NE Japan

Zircon U-Pb (& Lu-Hf) isotope geochronology of the Hidaka Metamorphic Belt, Hokkaido, NE Japan. Tony KEMP, Toshiaki SHIMURA Department of Geology, Niigata University. Collaborators. Tomokazu Hokada, Daniel Dunkley National Institute for Polar Research, Tokyo, Japan Richard Hinton

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Zircon U-Pb (& Lu-Hf) isotope geochronology of the Hidaka Metamorphic Belt, Hokkaido, NE Japan

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  1. Zircon U-Pb (& Lu-Hf) isotope geochronology of the Hidaka Metamorphic Belt, Hokkaido, NE Japan Tony KEMP, Toshiaki SHIMURA Department of Geology, Niigata University

  2. Collaborators • Tomokazu Hokada, Daniel Dunkley National Institute for Polar Research, Tokyo, Japan • Richard Hinton Edinburgh Ion Microprobe Facility, Edinburgh University, UK • Chris Hawkesworth Department of Earth Sciences, University of Bristol, UK

  3. Micro-chronology of zircon Lu-Hf isotopes U-Pb isotopes Ion microprobe LaserAblation Crystallisation age Source age

  4. Hidaka Metamorphic Belt ‘an exposed crustal slab derived from an immature island arc’ (Komatsu et al. 1986; Osanai et al. 1991)

  5. Hidaka Metamorphic Belt Idealised succession of the metamorphic and igneous rocks in the ‘Hidaka Crust’ (modified from Komatsu et al. 1986) • What is the temporal framework? • Magmatic differentiation mechanisms? • Crustal evolutionary processes in arcs

  6. Previous age studies Most K-Ar and Rb-Sr mineral ages cluster around 40-28 Ma and 20-15 Ma • Owada et al 1991 : peak metamorphism and anatexis at 56 ± 6.1 Ma (WR Rb-Sr isochron) • Usuki et al 2002 : granulite facies metamorphism at 23-18 Ma (SHRIMP U-Pb on thin zircon rims) • Maeda et al. 1990: Gabbro-diorite-granite K-Ar WR ages of 19.6-17 Ma. Cooling/exhumation ages (??)

  7. Nissho Upper S-type granite Sample localities Pankenushi 2-Px Gabbro Pankenushi Basal S-type tonalite & Enclave Pipairo Middle S-type tonalite Niikappu Basal S-type tonalite Basal I-type tonalite Lower S-type tonalite Satsunai Middle S-type tonalite Middle I-type tonalite Horobetsu Grt-Opx granulite Opx-Crd-Ged granulite Opx mafic granulite Nupinai Upper I-type granite Horoman Mafic layer in peridotite

  8. Basal I-type tonalite Qtz + pl + opx + hbl + bt Basal S-type tonalite Qtz + pl + opx + grt + bt Contrastingsources Mafic granulite Metased. granulite

  9. Middle ‘I-type’ tonalite Centre of body Margin of body Assimilation of metasedimentary rock at the periphery

  10. I-type zircons Upper bt-hbl granite Middle hbl-bt tonalite Basal opx-hbl tonalite

  11. I-type samples #1 Concordia diagram Average Pb/U age Data at 2 BASAL I-TYPE TONALITE (Niikappu)

  12. I-type samples #2 Concordia diagram Average Pb/U age Data at 2 Data at 2 MIDDLE I-TYPE TONALITE (Satsunai)

  13. I-type samples #3 Concordia diagram Average Pb/U age Data at 2 UPPER I-TYPE GRANITE (Nupinai)

  14. Basal S-type zircons 19 Ma 42 Ma 53 Ma

  15. Basal S-types Grt-opx tonalites - Pankenushi & Niikappu

  16. Satsunai ms tonalite Pipairo crd tonalite 71 Ma 37 Ma 52 Ma All ca. 37 Ma 53 Ma 37 Ma 46 Ma 38 Ma 112 38 Ma

  17. Middle S-types Ms-bt-crd tonalites - Satsunai & Pipairo

  18. Upper S-type Biotite granite - Nissho

  19. Metased. granulites Grt-opx-crd granulite Grt-opx granulite 18 Ma 19 Ma 19 Ma 21 Ma 54 Ma

  20. Metased. granulites

  21. S-type vs granulite zircons S-type rims = magmatic Granulite rims = metamc 50 Ma zircons in S-types derived from metas. protolith

  22. Mafic rocks Mafic granulite (MORB-like meta-basalt) 2-px gabbro (MORB-like) Magmatic zircons • igneous crystallisation ages

  23. Summary of U-Pb Ages Two magmatic pulses in the Hidaka Belt • ca. 37 Ma (late Eocene) • emplacement of I-type magmas at all crustal levels • mid-crustal anatexis/assimilation • ca. 19 Ma (early Miocene) • crystallisation of MORB-like gabbros • granulite facies MM and partial melting • generation of S-type magmas

  24. Lu-Hf isotopes in zircon Why? - zircon has low Lu/Hf (< 0.001) • preserve initial 176Hf/177Hf of magma - robust, high Hf content (~1%) • impervious to isotopic disturbance - zoning in 176Hf/177Hf • source rocks, magmatic evolution (e.g. Griffin et al. 2002 Lithos 61, 237-239)

  25. Lu-Hf isotopes in zircon 16 Depleted mantle +16 Mantle input 14 12 zrc crystallisation 10 Hf (t) 8 6 crustal contamination 4 2 0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 Yb / Hf

  26. Lu-Hf isotopes in zircon 16 Depleted mantle +16 14 12 zrc crystallisation 10 Hf (t) 8 6 4 crustal contamination 2 0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 Yb / Hf

  27. Lu-Hf isotopes in zircon 16 Depleted mantle +16 14 12 zrc crystallisation 10 Hf (t) 8 6 4 crustal contamination 2 0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 Yb / Hf

  28. Hf isotope evolution 20 18 16 14 Hf (t) 12 10 8 6 4 2 10 20 30 40 50 60 Age (Ma)

  29. Hf isotope evolution 20 18 16 14 Hf (t) 12 10 8 6 4 2 10 20 30 40 50 60 Age (Ma)

  30. Conclusions Hidaka magmatic arc was assembled episodically • 37 Ma- I-type (?arc) magmatism - juvenile crustal growth • 19 Ma - S-type magmatism & granulite formation - recycling of older crustal materials driven by mafic magma under-plating What were the tectonic controls?

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