Brittle normal faulting in the highest-grade Sambagawa metamorphic rocks of central Shikoku, southwest Japan: Indication of the exhumation into the upper crustal level

El-Fakharani, Abdelhamid; Takeshita, Toru

doi:10.1016/j.jseaes.2008.02.001

Cited by 18 publications

(20 citation statements)

References 66 publications

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“…These microstructures were formed during the final exhumation into upper crustal levels at the frictional-viscous transition conditions, which was called D 2 phase in the previous studies (Osozawa and Publis, 2007;El-Fakharani and Takeshita, 2008).…”

Section: Introductionmentioning

confidence: 93%

“…2) the Ojoin mélange zone. Both Fukunari and Wallis (2007) and El-Fakharani and Takeshita (2008) analyzed the fault systems in this area, and concluded that most of these are low-angle normal faults dipping NNW, which can be correlated with those in the Asemi river area (Takeshita and Yagi, 2004). Although the metamorphic layers (D 1 foliation) are clearly cut by these normal faults, these are significantly dragged, indicating the semi-brittle nature of the faulting (Fig.…”

Section: Post-d 1 Deformations In the Niihama Area And Sample Localitiesmentioning

confidence: 99%

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Coupled micro-faulting and pressure solution creep overprinted on quartz schist deformed by intracrystalline plasticity during exhumation of the Sambagawa metamorphic rocks, southwest Japan

Takeshita

El-Fakharani

2013

Journal of Structural Geology

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In the Sambagawa schist, southwest Japan, while ductile deformation pervasively occurred at D 1 phase during exhumation, low-angle normal faulting was locally intensive at D 2 phase under the conditions of frictional-viscous transition of quartz (c. 300 o C) during further exhumation into the upper crustal level. Accordingly, the formation of D 2 shear bands was overprinted on type I crossed girdle quartz c-axis fabrics and microstructures formed by intracrystalline plasticity at D 1 phase in some quartz schists. The quartz c-axis fabrics became weak and finally random with increasing shear, accompanied by the decreasing degree of undulation of recrystallized quartz grain boundaries, which resulted from the increasing portion of straight grain boundaries coinciding with the interfaces between newly precipitated quartz and mica. We interpreted these facts as caused by increasing activity of pressure solution: the quartz grains were dissolved mostly at platy quartz-mica interface, and precipitated with random orientation and pinned by mica, thus having led to the obliteration of existing quartz c-axis fabrics. In the sheared quartz schist, the strength became reduced by the enhanced pressure solution creep not only due to the reduction of diffusion path length caused by increasing number of shear bands, but also to enhanced dissolution at the interphase boundaries.

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Section: Introductionmentioning

confidence: 93%

Section: Post-d 1 Deformations In the Niihama Area And Sample Localitiesmentioning

confidence: 99%

Coupled micro-faulting and pressure solution creep overprinted on quartz schist deformed by intracrystalline plasticity during exhumation of the Sambagawa metamorphic rocks, southwest Japan

Takeshita

El-Fakharani

2013

Journal of Structural Geology

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“…In particular, when exhuming rocks are further elevated to upper crustal level across the depth of brittle‐ductile transition, pervasive brittle faulting seems to occur (e.g. Foster & Lister ; Sedlock ; El‐Fakharani & Takeshita ; Takeshita & El‐Fakharani ).…”

Section: Introductionmentioning

confidence: 99%

“…) during D 1 phase. However, both Osozawa and Pavlis () and El‐Fakharani and Takeshita () have recently argued that D 2 large‐scale E–W trending and north‐dipping normal faulting also played an important role in final exhumation into the brittle region and formation of map‐scale structures in addition to the D 1 ductile deformation. In order to test whether or not E–W trending map‐scale normal faults in fact exist in the N–S cross section of the Sambgawa metamorphic rocks, we conducted phengite K–Ar dating of pelitic schist collected along N–S routes in the Saruta River area, where the map‐scale normal faults were inferred to exist (Yagi & Takeshita ; Takeshita & Yagi ).…”

Section: Introductionmentioning

confidence: 99%

Extensive normal faulting during exhumation revealed by the spatial variation of phengite K–Ar ages in the Sambagawa metamorphic rocks, central Shikoku, SW Japan

Takeshita

Yagi²,

Gouzu³

et al. 2015

Island Arc

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Metamorphic rocks experience change in the mode of deformation from ductile flow to brittle failure during their exhumation. We investigated the spatial variation of phengite K-Ar ages of pelitic schist of the Sambagawa metamorphic rocks (sensu lato) from the Saruta River area, central Shikoku, to evaluate if those ages are disturbed by faults or not. As a result, we found that these ages change by ca 5 my across the two boundaries between the lower-garnet and albite-biotite, and the albite-biotite and uppergarnet zones. These spatial changes in phengite K-Ar ages were perhaps caused by truncation of the metamorphic layers by large-scale normal faulting at D 2 phase under the brittle-ductile transition conditions (ca 300°C) during exhumation, because an actinolite rock was formed along a fault near the former boundary. Assuming that the horizontal metamorphic layers and a previously estimated exhumation rate of 1 km/my before the D 2 phase, the change of 5 my in phengite K-Ar ages is converted to a displacement of about 10 km along the north-dipping, low-angle normal fault documented in the previous study. Phengite 40 Ar-39 Ar ages (ca 85 to 78 Ma) in the actinolite rock could be reasonably comparable to the phengite K-Ar ages of the surrounding non-faulted pelitic schist, because the K-Ar ages of pelitic schist could have been also reset at temperatures close to the brittle-ductile transition conditions far below the closure temperature for thermal retention of argon in phengite (about 500-600°C).

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“…1b, Nakajima, 1982Banno, 1998Nakajima et al 1977Nakajima 1982 Sakaguchi Goto et al, 2007B Nakajima 1982-Fig. 1b Enami et al 1994 300-360 5.5-6.5 kb D1 D2 D3 , , 1977 ;Faure, 1983 ;Wallis, 1990, Hara et al, 1992D1 D2 , , 1977Faure, 1983 D2 Osozawa andPavlis, 2007 ;El-Fakharani andTakeshita, 2008 D3 -D3 Banno et al, 1978 ;Hara et al, 1992Hara et al, 1980 Higashino, 1990). Sample localities A and B are shown by small arrows.…”

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confidence: 99%

Fission-track zircon ages of psammitic schist from the chlorite zone of the Sambagawa metamorphic belt, central Shikoku, Japan:

Takeshita¹,

Hasebe²,

Nomura³

2011

Jour. Geol. Soc. Japan

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We analyzed the fission-track (FT) thermochronology of zircon in two samples of psammitic schist from the chlorite zone of the Sambagawa metamorphic belt, central Shikoku, Japan. The samples were collected from the lower-grade part of the chlorite zone (pumpellyite-actinolite facies). Detrital zircons from a single locality along the Asemi River are completely annealed, yielding FT ages of .. Ma ( σ, grains), and those from a single locality along the Dozan River are also completely annealed, yielding FT ages of .. Ma ( σ, grains). Although both samples were collected from within the chlorite zone, the two FT zircon ages are different, possibly because they represent the timing of peak metamorphism in the former sample, and a D thermal event (post peak-metamorphism) in the latter sample.

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Brittle normal faulting in the highest-grade Sambagawa metamorphic rocks of central Shikoku, southwest Japan: Indication of the exhumation into the upper crustal level

Cited by 18 publications

References 66 publications

Coupled micro-faulting and pressure solution creep overprinted on quartz schist deformed by intracrystalline plasticity during exhumation of the Sambagawa metamorphic rocks, southwest Japan

Coupled micro-faulting and pressure solution creep overprinted on quartz schist deformed by intracrystalline plasticity during exhumation of the Sambagawa metamorphic rocks, southwest Japan

Extensive normal faulting during exhumation revealed by the spatial variation of phengite K–Ar ages in the Sambagawa metamorphic rocks, central Shikoku, SW Japan

Fission-track zircon ages of psammitic schist from the chlorite zone of the Sambagawa metamorphic belt, central Shikoku, Japan:

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