Fault gouges and their K-Ar ages from the Akaishi Tectonic Line, central Japan

Tanaka, Hidemi; Saka, Yukiyasu; Abe, Takeshi; Kohama, Syunsuke; Itaya, Tetsumaru

doi:10.5575/geosoc.98.39

Cited by 5 publications

(3 citation statements)

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“…For K‐Ar dates of illite from the Akaishi Tectonic Line, the circles are shaded in grey. The references cited are *1 (Okada, ), *2 (Takagi et al, ), *3 (Takeshita, ), *4 (Yamakita et al, ), *5 (Takagi & Shibata, modified after Shibata & Takagi, , Shibata & Uchiumi, , Shibata & Takagi, ; Shibata et al, , and Takagi et al, , ), *6 (Miyata et al, ), *7 (Miyata, ), *8 (Tanaka et al, ), *9 (Tanaka & Hara, ), *10 (Hara et al, , ), *11(Tanaka et al, ), *12 (Takagi et al, ), *13 (e.g., Takeshita et al, ), *14 (Narita et al, ), *15 (e.g., Noda & Sato, ; Seike et al, ), *16 (Ichikawa, ), *17 (e.g., Otofuji & Matsuda, ), *18 (e.g., Itaya & Takasugi, ), *19 (Seton et al, ), the plate velocity and azimuth data were created using GPlates software (www.gplates.org), *20 (Whittaker et al, ), *21 (Famin et al, , the extension period extended to the age of 37 to 31 Ma of Kobe Group (Ozaki et al, ), *22 (Takeshita et al, ).…”

Section: Discussionmentioning

confidence: 99%

Kinematic Analyses and Radiometric Dating of the Large‐Scale Paleogene Two‐Phase Faulting Along the Median Tectonic Line, Southwest Japan

Kubota

Takeshita

Yagi³

et al. 2020

Tectonics

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The Median Tectonic Line (MTL) in Southwest Japan, a major east-west trending arc-parallel fault, has been defined as the boundary fault between the Cretaceous Sambagawa metamorphic rocks and the Ryoke granitic and metamorphic rocks, which are unconformably covered by the Upper Cretaceous Izumi Group. Based on the detailed fieldwork and microstructural studies of fault rocks, we reconstruct the kinematic history along the MTL during the Paleogene, which can be divided into the Ichinokawa and pre-Tobe phases. While the Ichinokawa phase is defined by large-scale, top-to-the-north normal faulting, the pre-Tobe phase is represented by large-scale, high-angle right-stepping en échelon faults almost parallel to the MTL in the Upper Cretaceous Izumi Group. We found that left-handed en échelon folds have developed along the right-stepping faults, which contain 25-60 m wide cataclasite and fault gouge. Both map scale en échelon folds and microstructures (e.g., composite planar structures) in the fault rocks suggest that they were formed by sinistral-reverse faulting with top-to-the-SW kinematics. Furthermore, based on the new K-Ar age dating of authigenic illite from the fault gouge along the MTL and right-stepping faults, it can be concluded that the MTL was activated in two discrete stages at approximately 59 Ma (Ichinokawa phase) and 47-46 Ma (pre-Tobe phase). Based on these results, we reappraise the kinematic framework of the MTL in the Paleogene, which can be interpreted as the record of the movements of the subducting oceanic plate relative to the continental plate.

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Section: Discussionmentioning

confidence: 99%

Kinematic Analyses and Radiometric Dating of the Large‐Scale Paleogene Two‐Phase Faulting Along the Median Tectonic Line, Southwest Japan

Kubota

Takeshita

Yagi³

et al. 2020

Tectonics

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“…1980), *7 (Miyata 1990), *8 (Takagi & Shibata 1992 modified after Shibata & Takagi 1988; Takagi et al . 1991; Tanaka et al . 1992), *9 (Tanaka & Hara 1990), *10 (Tanaka et al .…”

Section: Geological Settingmentioning

confidence: 99%

“…1 for these areas). References cited are: *1 (Okada 1972), *2 , *3 (Takeshita 1993), *4 (Yamakita et al 1995), *5 modified after Shibata et al 1989), *6 (Miyata et al 1980), *7 (Miyata 1990), *8 modified after Shibata & Takagi 1988Takagi et al 1991;Tanaka et al 1992), *9 (Tanaka & Hara 1990), *10 (Tanaka et al 1992), *11 (e.g. Takeshita et al 2000), *12 (Narita et al 1999), *13 (e.g.…”

Section: Izumi Groupmentioning

confidence: 99%

Paleocene large‐scale normal faulting along the Median Tectonic Line, western Shikoku, Japan

Kubota¹,

Takeshita

2007

Island Arc

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The Median Tectonic Line (MTL) in southwest Japan, a major east-westtrending arc-parallel fault, has been defined as the boundary fault between the Cretaceous Sambagawa metamorphic rocks and Ryoke granitic and metamorphic rocks, which are unconformably covered by the Upper Cretaceous Izumi Group. The juxtaposition by faulting occurred after the deposition of the Izumi Group. Based on detailed fieldwork and previous studies, the authors reconstruct the kinematic history along the MTL during the Paleogene period, which has not been fully understood before. It is noted that although the strata of the Izumi Group along the MTL dip gently, east-west-trending north-vergent folds with the wavelength of~300 m commonly develop up to 2 km north from the MTL. Along the MTL, a disturbed zone of the Izumi Group up to 400 m thick, defined by the development of boudinage structures with the transverse boudin axis dipping nearly parallel to the MTL, occurs. Furthermore, east-west-trending north-vergent folds with the wavelength of 1-5 m develop within the distance up to 60 m from the MTL. The disturbed zone with the map-scale north-vergent folds along the MTL, strongly suggests that they formed due to normal faulting with a top-to-the-north sense along the MTL. Considering that the normal faulting is associated with the final exhumation of the Sambagawa metamorphic rocks, and its juxtaposition against the Izumi Group at depth, this perhaps occurred before the denudation of the Sambagawa metamorphic rocks indicated by the deposition of the Lower Eocene Hiwada-toge Formation. Dynamic equilibrium between crustal thickening at depth (underplating) and extension at shallow level is a plausible explanation for the normal faulting because the arc-normal extension suggests gravity as the driving force.

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Timing of the cataclastic deformation along the Akaishi Tectonic Line, central Japan

Tanaka

Uehara

Itaya

1995

Contrib Mineral Petrol

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Fault gouges and their K-Ar ages from the Akaishi Tectonic Line, central Japan

Cited by 5 publications

References 0 publications

Kinematic Analyses and Radiometric Dating of the Large‐Scale Paleogene Two‐Phase Faulting Along the Median Tectonic Line, Southwest Japan

Kinematic Analyses and Radiometric Dating of the Large‐Scale Paleogene Two‐Phase Faulting Along the Median Tectonic Line, Southwest Japan

Paleocene large‐scale normal faulting along the Median Tectonic Line, western Shikoku, Japan

Timing of the cataclastic deformation along the Akaishi Tectonic Line, central Japan

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