Evolution of the Sanbagawa and Shimanto high-pressure belts in SW Japan: Insights from K–Ar (Ar–Ar) geochronology

Itaya, Tetsumaru; Tsujimori, Tatsuki; Liou, J. G.

doi:10.1016/j.jseaes.2011.06.012

Cited by 61 publications

(64 citation statements)

References 109 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The white micas of the augen-gneiss and the micaschists have therefore experienced ductile deformation during exhumation. This ductile deformation could have enhanced argon release, with large amount of radiogenic argon, as already documented in previous phengite K-Ar (Ar-Ar) geochronological studies of HP-UHP metamorphic rocks (Itaya et al, 2011;Gouzu et al, 2016).…”

Section: Discussionsupporting

confidence: 60%

Preliminary report on the excess argon bearing K–feldspar from metagranite in the Brossasco–Isasca UHP Unit of Dora–Maira Massif, Italy

Itaya¹,

Yagi²,

Gouzu³

et al. 2017

Journal of Mineralogical and Petrological Sciences

Self Cite

View full text Add to dashboard Cite

The metagranite, that still preserves the igneous structure, is composed mainly of K-feldspar, plagioclase, quartz, biotite, white mica and accessory ilmenite. Quartz, K-feldspar, plagioclase and biotite preserve the original igneous shape, but are either re-equilibrated or replaced by new phases. Quartz occurs as fine-grained granoblastic aggregate, statically derived from inversion of coesite. Plagioclase is now composed of a finegrained mineral aggregate including albite, zoisite, phengite, titanite and apatite. Biotite is surrounded and partly replaced by fine-grained white mica.K-Ar analyses of K-feldspar from the metagranite were carried out, giving 42.6 ± 0.9 Ma. This age, significantly older than the SHRIMP zircon U-Pb age (35.4 ± 1.0 Ma) previously estimated for the metamorphic peak of the Brossasco-Isasca UHP unit, is apparent due to inherited excess argon (~3.4%) from the host lithologies. This inherited excess argon is interpreted as related to the fact that K-feldspar has trapped the excess argon wave generated by the argon release from micas (that have large amount of radiogenic argon) during exhumation and cooling of the host lithologies.

show abstract

Section: Discussionsupporting

confidence: 60%

Preliminary report on the excess argon bearing K–feldspar from metagranite in the Brossasco–Isasca UHP Unit of Dora–Maira Massif, Italy

Itaya¹,

Yagi²,

Gouzu³

et al. 2017

Journal of Mineralogical and Petrological Sciences

Self Cite

View full text Add to dashboard Cite

show abstract

“…White micas K-Ar age data of the two metapelites and a pillow basalt from the Hakoishi and Tobiishi sub-units, respectively rocks (Saito et al, 2005). Our new result and the previous K-Ar ages were all obtained from white mica separates extracted from the metamorphic rocks of which peak P-T conditions are significantly lower than the closure temperature of the K-Ar white mica system (~500°C: e.g., Itaya et al, 2011), so there is a fear that the obtained ages could be inherited from older detrital/protolith white micas.…”

Section: Discussionsupporting

confidence: 43%

White mica K–Ar ages from lawsonite–blueschist facies Hakoishi sub–unit and from prehnite–pumpellyite facies Tobiishi sub–unit of the Kurosegawa belt, Kyushu, Japan

Sato

Hirajima

Kamimura³

et al. 2014

Journal of Mineralogical and Petrological Sciences

View full text Add to dashboard Cite

White mica K-Ar age dating was carried out for metapelites in the Hakoishi sub-unit and a meta-pillow basalt in the Tobiishi sub-unit of the Kurosegawa belt (Kamimura et al., 2012), Yatsushiro district, Kyushu, Japan. The Hakoishi sub-unit suffered the lawsonite-blueschist facies metamorphism with peak conditions of 0.7-0.9 GPa and <300°C. Phengite separate with K content of 5.323 wt% from OD 28 gives 299.0 ± 6.1 Ma and those with K content of 1.222 wt% and 2.142 from OD 113 give 280.2 ± 5.8 Ma and 245.3 ± 5.1 Ma, respectively. The Tobiishi sub-unit suffered the prehnite-pumpellyite facies metamorphism with the peak conditions round <0.4 GPa and <350°C. White mica named as alumino-celadonite with a composition range of Si from 3.79 to 3.94 and Fe 3+ from 0.30 to 0.48 for Oxygen = 11 basis is developed in amygdules of meta-pillow basalts, closely associated with pumpellyite and chlorite. Alumino-celadonite separates obtained from pillow basalt, SOD01-B, vary K content from 5.601 to 2.343 wt% and give K-Ar ages from 181 to 173 Ma. The peak P-T conditions of the all studied samples were much lower than the closure temperature of Ar in white micas, so those data can be interpreted as the peak metamorphic timing of each sub-unit, i.e., the existence of both late Paleozoic (299-245 Ma) lawsonite blueschist facies metamorphic rocks and Mesozoic (181-173 Ma) prehnitepumpellyite facies metamorphic rocks are newly identified from the Kurosegawa belt in Kyushu, although Mesozoic epidote-blueschist facies metamorphic rocks have been reported in the relevant area. Obtained metamorphic ages and grade from the Hakoishi and Tobiishi sub-units are almost similar with those of the Osayama area in the Renge belt (Tsujimori and Itaya, 1999) and of the Katsuyama area in the Suo belt of the Inner Zone of Southwest Japan, respectively (Hashimoto, 1968;Nishimura, 1998). These data support the Inner Zone origin of the Kurosegawa belt proposed by Isozaki and Itaya (1991).

show abstract

“…This ductile deformation could have enhanced argon release from white micas with radiogenic argon, as already documented in previous phengite K-Ar (Ar-Ar) geochronological studies of HP-UHP metamorphic rocks (cf. Itaya et al, 2011;Gouzu et al, 2016). The studied biotite crys- Ar K ratios of biotite crystals from DM1517 and DM1540 by the laser step-heating analyses.…”

Section: Possible Source Of Eaw In the Dora-maira Massifmentioning

confidence: 99%

Laser step–heating <sup>40</sup>Ar/<sup>39</sup>Ar analyses of biotites from meta–granites in the UHP Brossasco–Isasca Unit of Dora–Maira Massif, Italy

Itaya¹,

Hyodo

Imayama

et al. 2018

Journal of Mineralogical and Petrological Sciences

Self Cite

View full text Add to dashboard Cite

Two undeformed metagranite samples were collected from the UHP Brossasco-Isasca Unit (BIU) of Dora-Maira Massif, Italy to carry out the laser step-heating 40 Ar/ 39 Ar analyses of individual biotite crystals. The metagranites occur as undeformed domains (m-to ten of meters in size) within strongly deformed augen-gneiss. They still preserve their medium-to coarse-grained igneous texture and are composed mainly of K-feldspar, plagioclase pseudomorph, quartz, and biotite that preserve their original igneous shape but are either re-equilibrated or replaced by new phases.Three biotite crystals from the first sample have similar age spectra showing 400 to 300 Ma, except for the first fraction (500-1500 Ma). On the contrary, the age spectra of five biotite crystals from the second sample are significantly different; these biotites show saddle shape 40 Ar/ 39 Ar age spectra, except for one crystal. The oldest fractions have ages (800 to 1300 Ma) three to four times older than that of the granite protolith (which is late Permian). This extremely high intensity of excess argon could be due to an 'Excess-Argon Wave' (EAW) phenomenon, occurred during the quick exhumation of the BIU, combined with the extremely short ductile deformation history. The observed variation of the biotite age spectra may reflect the different trapping processes of EAW and/or localized source of EAW.

show abstract

Evolution of the Sanbagawa and Shimanto high-pressure belts in SW Japan: Insights from K–Ar (Ar–Ar) geochronology

Cited by 61 publications

References 109 publications

Preliminary report on the excess argon bearing K–feldspar from metagranite in the Brossasco–Isasca UHP Unit of Dora–Maira Massif, Italy

Preliminary report on the excess argon bearing K–feldspar from metagranite in the Brossasco–Isasca UHP Unit of Dora–Maira Massif, Italy

White mica K–Ar ages from lawsonite–blueschist facies Hakoishi sub–unit and from prehnite–pumpellyite facies Tobiishi sub–unit of the Kurosegawa belt, Kyushu, Japan

Laser step–heating <sup>40</sup>Ar/<sup>39</sup>Ar analyses of biotites from meta–granites in the UHP Brossasco–Isasca Unit of Dora–Maira Massif, Italy

Contact Info

Product

Resources

About