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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
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• 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
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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
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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)
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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
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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
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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
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Basal I-type
tonalite
Qtz + pl + opx + hbl
+ bt
Basal S-type
tonalite
Qtz + pl + opx +
grt + bt
Mafic granulite
Metased. granulite
Contrastingsources
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Middle ‘I-type’ Middle ‘I-type’ tonalitetonalite
Centre of body
Assimilation of metasedimentary rock at the
periphery
Margin of body
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Middle hbl-bt tonalite
Upper bt-hbl granite
Basal opx-hbltonalite
I-type zircons
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I-type samples #1
BASAL I-TYPE TONALITE (Niikappu)
Data at 2
Concordia diagram Average Pb/U age
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I-type samples #2
MIDDLE I-TYPE TONALITE (Satsunai)
Data at 2Data at 2
Concordia diagram Average Pb/U age
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I-type samples #3
UPPER I-TYPE GRANITE (Nupinai)
Data at 2
Concordia diagram Average Pb/U age
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Basal S-type zircons
53 Ma
42 Ma19 Ma
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Basal S-types
Grt-opx tonalites - Pankenushi & Niikappu
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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
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Middle S-types
Ms-bt-crd tonalites - Satsunai & Pipairo
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Upper S-type
Biotite granite - Nissho
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Grt-opx granulite
Grt-opx-crd granulite
21 Ma
19 Ma
18 Ma
54 Ma
Metased. granulites
19 Ma
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Metased. granulites
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S-type vs granulite zircons
S-type rims = magmaticGranulite rims = metamc
50 Ma zircons in S-typesderived from metas. protolith
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Mafic rocks
Mafic granulite(MORB-like meta-basalt)
2-px gabbro(MORB-like)
Magmatic zircons igneous crystallisation ages
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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)
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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?
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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
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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
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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
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4
6
8
H
f (t)
2
10
12
14
16
20 30 40 50 6010
Age (Ma)
Hf isotope evolution
18
20
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4
6
8
H
f (t)
2
10
12
14
16
20 30 40 50 6010
Age (Ma)
Hf isotope evolution
18
20
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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?