Zircon U-Pb Zircon U-Pb (& Lu-Hf) (& Lu-Hf) isotope geochronology of isotope geochronology of

the the Hidaka Metamorphic Belt, Hidaka Metamorphic Belt,

Hokkaido, NE JapanHokkaido, NE Japan

Tony KEMP, Toshiaki Tony KEMP, Toshiaki

SHIMURASHIMURADepartment of Geology, Niigata Department of Geology, Niigata

UniversityUniversity

• Tomokazu Hokada, Daniel DunkleyNational Institute for Polar Research, Tokyo, Japan

• Richard HintonEdinburgh Ion Microprobe Facility, Edinburgh University, UK

• Chris HawkesworthDepartment of Earth Sciences, University of Bristol, UK

CollaboratorsCollaborators

Micro-chronology of Micro-chronology of zirconzircon

U-Pb isotopesU-Pb isotopes

Crystallisation Crystallisation ageage

Lu-Hf isotopesLu-Hf isotopes

Source ageSource age

Ion Ion microprobemicroprobe

LaserLaserAblationAblation

42°N

143°E

43°N

143°E

0 10 20 30

km

Hokkaido

Cape Erimo

Hidaka Metamorphic Belt

Poroshiri Ophiolite

upper metamorphic rocks

lower metamorphic rocks

upper granitoid

middle tonalite

lower tonalite

basal tonalite

gabbro & diorite

peridotite

Geological Map of the Hidaka Metamorphic Belt

Hidaka Metamorphic Hidaka Metamorphic BeltBelt

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

Hidaka Metamorphic Hidaka Metamorphic BeltBelt

Idealised succession of the

metamorphic and igneous

rocks in the ‘Hidaka Crust’

(modified from Komatsu et al. 1986)

1. What is the temporal framework?

2. Magmatic

differentiation

mechanisms? Crustal evolutionary

processes in arcs

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 (??)

Previous age studies

42°N

143°E

43°N

143°E

0 10 20 30

km

Hokkaido

Cape Erimo

Hidaka Metamorphic Belt

Poroshiri Ophiolite

upper metamorphic rocks

lower metamorphic rocks

upper granitoid

middle tonalite

lower tonalite

basal tonalite

gabbro & diorite

peridotite

Geological Map of the Hidaka Metamorphic Belt

Pankenushi2-Px Gabbro

NiikappuBasal S-type tonaliteBasal I-type tonaliteLower S-type tonalite

PankenushiBasal S-type tonalite& Enclave

SatsunaiMiddle S-type tonaliteMiddle I-type tonalite

NisshoUpper S-type granite

NupinaiUpper I-type granite

HorobetsuGrt-Opx granuliteOpx-Crd-Ged granuliteOpx mafic granulite

HoromanMafic layer in peridotite

PipairoMiddle S-type tonalite

Sample localities

Basal I-type

tonalite

Qtz + pl + opx + hbl

+ bt

Basal S-type

tonalite

Qtz + pl + opx +

grt + bt

Mafic granulite

Metased. granulite

Contrastingsources

Middle ‘I-type’ Middle ‘I-type’ tonalitetonalite

Centre of body

Assimilation of metasedimentary rock at the

periphery

Margin of body

Middle hbl-bt tonalite

Upper bt-hbl granite

Basal opx-hbltonalite

I-type zircons

I-type samples #1

BASAL I-TYPE TONALITE (Niikappu)

Data at 2

Concordia diagram Average Pb/U age

I-type samples #2

MIDDLE I-TYPE TONALITE (Satsunai)

Data at 2Data at 2

Concordia diagram Average Pb/U age

I-type samples #3

UPPER I-TYPE GRANITE (Nupinai)

Data at 2

Concordia diagram Average Pb/U age

Basal S-type zircons

53 Ma

42 Ma19 Ma

Basal S-types

Grt-opx tonalites - Pankenushi & Niikappu

Pipairo crd tonalite

Satsunai ms tonalite

71 Ma

All ca. 37 Ma

53 Ma

37 Ma

38 Ma

52 Ma

46 Ma37 Ma

38 Ma 112

Middle S-types

Ms-bt-crd tonalites - Satsunai & Pipairo

Upper S-type

Biotite granite - Nissho

Grt-opx granulite

Grt-opx-crd granulite

21 Ma

19 Ma

18 Ma

54 Ma

Metased. granulites

19 Ma

Metased. granulites

S-type vs granulite zircons

S-type rims = magmaticGranulite rims = metamc

50 Ma zircons in S-typesderived from metas. protolith

Mafic rocks

Mafic granulite(MORB-like meta-basalt)

2-px gabbro(MORB-like)

Magmatic zircons igneous crystallisation ages

Summary of U-Pb Ages

Two magmatic pulses in the Hidaka Belt

• ca. 19 Ma (early Miocene)

crystallisation of MORB-like gabbros granulite facies MM and partial melting generation of S-type magmas

emplacement of I-type magmas at all crustal levels mid-crustal anatexis/assimilation

• ca. 37 Ma (late Eocene)

Lu-Hf isotopes in zircon

- 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)

Why?

2

4

6

8

H

f (t)

0

10

12

14

16

0.04 0.06 0.08 0.10 0.120.02 0.14

Yb / Hf

Lu-Hf isotopes in zircon

zrc crystallisation

Depleted mantle +16

crustal contamination

Mantle input

2

4

6

8

H

f (t)

0

10

12

14

16

0.04 0.06 0.08 0.10 0.120.02 0.14

zrc crystallisation

Depleted mantle +16

crustal contamination

Lu-Hf isotopes in zircon

Yb / Hf

2

4

6

8

H

f (t)

0

10

12

14

16

0.04 0.06 0.08 0.10 0.120.02 0.14

zrc crystallisation

Depleted mantle +16

crustal contamination

Lu-Hf isotopes in zircon

Yb / Hf

4

6

8

H

f (t)

2

10

12

14

16

20 30 40 50 6010

Age (Ma)

Hf isotope evolution

18

20

4

6

8

H

f (t)

2

10

12

14

16

20 30 40 50 6010

Age (Ma)

Hf isotope evolution

18

20

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?