Abstract
The Sanbagawa belt sensu lato in Japan is one of the world's classical high-pressure (HP) metamorphic belts and has long been considered to be a coherent HP belt of the Cretaceous age. However, recent progress in detrital zircon geochronology together with the accumulation of abundant phengites K-Ar (Ar-Ar) ages revealed that the belt is comprised of two petrotectonic belts-Sanbagawa sensu stricto HP belt and Shimanto HP belt. These two belts have distinctly different ages of peak metamorphism and different P-T conditions of metamorphism. The Sanbagawa schists sensu stricto were metamorphosed in the conditions of the pumpellyite-actinolite facies through the epidote-blueschist to epidote-amphibolite facies and up to the eclogite facies during a prograde stage in a subduction zone at 120-115. Ma. Phengite K-Ar geochronology revealed that the subsequent exhumation after the peak metamorphism took placed in a manner that the higher-grade rocks exhumed more rapidly in comparison with the lower-grade rocks; this is supported by a positive correlation between age and apparent metamorphic gradient that have formed during the post-metamorphic peak hydration/recrystallization. Moreover, the schists have experienced intense ductile deformation and long-term exhumation; it took longer than 31. m.y. to reset the phengite K-Ar system. In contrast, the Shimanto HP schists were metamorphosed in the epidote-blueschist/greenschist transitional facies to the epidote-amphibolite facies and have experienced a short-term deformation for less than 13. m.y. This short deformation formed a negative correlation between K-Ar age and apparent metamorphic gradient. These two contrasting age-temperature relationships suggest different exhumation processes between the two HP belts, most likely due to a change in subducting oceanic plates in the Cretaceous along the paleo-Japanese convergent margin.
| Original language | English |
|---|---|
| Pages (from-to) | 1075-1090 |
| Number of pages | 16 |
| Journal | Journal of Asian Earth Sciences |
| Volume | 42 |
| Issue number | 6 |
| DOIs | |
| Publication status | Published - Nov 11 2011 |
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Keywords
- Argon depletion
- Exhumation process
- Phengite K-Ar ages
- Sanbagawa metamorphic belt
- Shimanto metamorphic belt
ASJC Scopus subject areas
- Earth-Surface Processes
- Geology
Cite this
Evolution of the Sanbagawa and Shimanto high-pressure belts in SW Japan : Insights from K-Ar (Ar-Ar) geochronology. / Itaya, Tetsumaru; Tsujimori, Tatsuki; Liou, Juhn G.
In: Journal of Asian Earth Sciences, Vol. 42, No. 6, 11.11.2011, p. 1075-1090.Research output: Contribution to journal › Article
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TY - JOUR
T1 - Evolution of the Sanbagawa and Shimanto high-pressure belts in SW Japan
T2 - Insights from K-Ar (Ar-Ar) geochronology
AU - Itaya, Tetsumaru
AU - Tsujimori, Tatsuki
AU - Liou, Juhn G.
PY - 2011/11/11
Y1 - 2011/11/11
N2 - The Sanbagawa belt sensu lato in Japan is one of the world's classical high-pressure (HP) metamorphic belts and has long been considered to be a coherent HP belt of the Cretaceous age. However, recent progress in detrital zircon geochronology together with the accumulation of abundant phengites K-Ar (Ar-Ar) ages revealed that the belt is comprised of two petrotectonic belts-Sanbagawa sensu stricto HP belt and Shimanto HP belt. These two belts have distinctly different ages of peak metamorphism and different P-T conditions of metamorphism. The Sanbagawa schists sensu stricto were metamorphosed in the conditions of the pumpellyite-actinolite facies through the epidote-blueschist to epidote-amphibolite facies and up to the eclogite facies during a prograde stage in a subduction zone at 120-115. Ma. Phengite K-Ar geochronology revealed that the subsequent exhumation after the peak metamorphism took placed in a manner that the higher-grade rocks exhumed more rapidly in comparison with the lower-grade rocks; this is supported by a positive correlation between age and apparent metamorphic gradient that have formed during the post-metamorphic peak hydration/recrystallization. Moreover, the schists have experienced intense ductile deformation and long-term exhumation; it took longer than 31. m.y. to reset the phengite K-Ar system. In contrast, the Shimanto HP schists were metamorphosed in the epidote-blueschist/greenschist transitional facies to the epidote-amphibolite facies and have experienced a short-term deformation for less than 13. m.y. This short deformation formed a negative correlation between K-Ar age and apparent metamorphic gradient. These two contrasting age-temperature relationships suggest different exhumation processes between the two HP belts, most likely due to a change in subducting oceanic plates in the Cretaceous along the paleo-Japanese convergent margin.
AB - The Sanbagawa belt sensu lato in Japan is one of the world's classical high-pressure (HP) metamorphic belts and has long been considered to be a coherent HP belt of the Cretaceous age. However, recent progress in detrital zircon geochronology together with the accumulation of abundant phengites K-Ar (Ar-Ar) ages revealed that the belt is comprised of two petrotectonic belts-Sanbagawa sensu stricto HP belt and Shimanto HP belt. These two belts have distinctly different ages of peak metamorphism and different P-T conditions of metamorphism. The Sanbagawa schists sensu stricto were metamorphosed in the conditions of the pumpellyite-actinolite facies through the epidote-blueschist to epidote-amphibolite facies and up to the eclogite facies during a prograde stage in a subduction zone at 120-115. Ma. Phengite K-Ar geochronology revealed that the subsequent exhumation after the peak metamorphism took placed in a manner that the higher-grade rocks exhumed more rapidly in comparison with the lower-grade rocks; this is supported by a positive correlation between age and apparent metamorphic gradient that have formed during the post-metamorphic peak hydration/recrystallization. Moreover, the schists have experienced intense ductile deformation and long-term exhumation; it took longer than 31. m.y. to reset the phengite K-Ar system. In contrast, the Shimanto HP schists were metamorphosed in the epidote-blueschist/greenschist transitional facies to the epidote-amphibolite facies and have experienced a short-term deformation for less than 13. m.y. This short deformation formed a negative correlation between K-Ar age and apparent metamorphic gradient. These two contrasting age-temperature relationships suggest different exhumation processes between the two HP belts, most likely due to a change in subducting oceanic plates in the Cretaceous along the paleo-Japanese convergent margin.
KW - Argon depletion
KW - Exhumation process
KW - Phengite K-Ar ages
KW - Sanbagawa metamorphic belt
KW - Shimanto metamorphic belt
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UR - http://www.scopus.com/inward/citedby.url?scp=80051992828&partnerID=8YFLogxK
U2 - 10.1016/j.jseaes.2011.06.012
DO - 10.1016/j.jseaes.2011.06.012
M3 - Article
VL - 42
SP - 1075
EP - 1090
JO - Journal of Asian Earth Sciences
JF - Journal of Asian Earth Sciences
SN - 1367-9120
IS - 6
ER -