A K-Ar Investigation of the Chichibu Quartz Diorite and Some Discussions on Its Cooling History.

K-Ar age studies in the Ashigawa and the southern part of the Tokuwa granodioritic bodies, which consist of the southern part of the Kofu plutonic complex, revealed that they formed between 12 and 9 Ma. Quite a narrow range of ages obtained from the Ashigawa southernmost part of the Tokuwa pluton implies that they cooled rapidly. The southern part of the Tokuwa pluton, as a whole, shows a systematic age distribution with a decrease in age to the north. Compilation of currently available plutonic ages in the South Fossa Magna suggests that the plutonic activities occurred three times in this region. Episodic activity like this could be argued in relation to the tectonic development of this region.

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K‐Ar dating studies of Ashigawa and Tokuwa granodiorite bodies and plutonic geochronology in the South Fossa Magna, central Japan

Salto

Kato

Sugi

1997

Island Arc

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Miocene intra‐arc bending at an arc‐arc collision zone, central Japan

Takahashi¹,

Saito²

1997

Island Arc

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Recent paleomagnetic studies are reviewed in an effort to clarify the relationship between the intra-arc deformation of central Japan and the collision tectonics of the Izu-Bonin Arc. The cusp structure of the pre-Neogene terranes of central Japan, called the Kanto Syntaxis, suggests a collisional origin with the Izu-Bonin Arc. The paleomagnetic results and newly obtained radiometric ages of the Kanto Mountains revealed the Miocene rotational history of the east wing of the Kanto Syntaxis. More than 90" clockwise rotation of the Kanto Mountains took place after deposition of the Miocene Chichibu Basin (planktonic foraminifera1 zone of N.8: 16.6-15.2 Ma). After synthesizing the paleomagnetic data of the Japanese Islands and collision tectonics of central Japan, it appears that approximately a half rotation (40-50") probably occurred at ca 15Ma in association with the rapid rotation of Southwest Japan. The remainder (5040") continued until 6 Ma, resulting in the sharp bent structure of the pre-Neogene accretionary complexes (Kanto Syntaxis). The latter rotation seems t o have been caused by the collision of the Izu-Bonin Arc on the northwestward migrating Philippine Sea Plate.

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Geochemical characteristics of Miocene Fe-Cu–Pb–Zn granitoids associated mineralization in the Chichibu skarn deposit (central Japan): evidence for magmatic fluids generation coexisting with granitic melt

Ishiyama

Miyata

Shibata

et al. 2011

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In this work we study mechanisms and timing of magmatic fluid generation during magma emplacement. Our focus is the Miocene calc-alkaline granitic rocks from the Chichibu mining area, in Japan. The granitoids consist of northern and southern Bodies and of the Daikoku Altered stocks. Cathodoluminescence observation of quartz phenocrysts from the northern body point towards magmatic resorption, which is thought to be caused by mixing between a more differentiated and a more primitive magma. The coexistence of vapour-rich two-phase and halite-bearing polyphase fluid inclusions in a single quartz crystal from the northern Body supports the possibility of pressure decrease during magma emplacement. The magmatic fluids that originated the Chichibu deposit are thought to have been generated by pressure release, related to magmatic differentiation when the SiO2-content reaches about 65 wt%. As a result, heavy metals, such as copper, gold and arsenic, coexisting with the silicate melt, were transported into the sedimentary strata through degassing of magmatic fluids. A later major fault system caused the intercalation between heavy-metal-free limestone and orebodies, as a secondary skarn-building process took place in the dominant limestone area.

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A K-Ar Investigation of the Chichibu Quartz Diorite and Some Discussions on Its Cooling History.

Cited by 4 publications

References 8 publications

K‐Ar dating studies of Ashigawa and Tokuwa granodiorite bodies and plutonic geochronology in the South Fossa Magna, central Japan

K‐Ar dating studies of Ashigawa and Tokuwa granodiorite bodies and plutonic geochronology in the South Fossa Magna, central Japan

Miocene intra‐arc bending at an arc‐arc collision zone, central Japan

Geochemical characteristics of Miocene Fe-Cu–Pb–Zn granitoids associated mineralization in the Chichibu skarn deposit (central Japan): evidence for magmatic fluids generation coexisting with granitic melt

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