Early Oligocene top-to- the-west motion along the Sashu fault, a low-angle oblique thrust of the Paleo-Median Tectonic Line, east Kyushu, Japan

聡, 山北; 谷生, 伊藤; 秀実, 田中; 弘樹, 渡辺

doi:10.5575/geosoc.101.978

Cited by 23 publications

(17 citation statements)

References 3 publications

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“…Similar IC behavior near a fault core was reported, for instance, from the Matapedia fault in Canada (Duba and Williams-Jones, 1983), the Sashiu fault in Southwest Japan (Yamakita et al 1995), and the Akaishi Tectonic Line in central Japan . Tanaka et al (1995) argued that IC values increase toward the fault because muscovite crystals are buckled, fractured, and comminuted into finer grain sizes or replaced by fine crystals via hydrothermal alteration and the recrystallization of micaceous clay minerals.…”

Section: Factors Controlling Illite Crystallinity Within Fault Zonesupporting

confidence: 74%

Changes in illite crystallinity within an ancient tectonic boundary thrust caused by thermal, mechanical, and hydrothermal effects: an example from the Nobeoka Thrust, southwest Japan

Fukuchi

Fujimoto

Kameda

et al. 2014

Earth, Planets and Space

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Illite crystallinity (IC), the full width at half maximum of the illite (001) peak in clay-fraction X-ray diffraction (XRD), is a common geothermometer widely applied to various tectonic settings. Paleotemperature estimation using IC presents methodological ambiguity because IC is not only affected by background temperature but also by mechanical, hydrothermal, and surface weathering effects. To clarify the influences of these effects on IC in the fault zone, we analyzed the IC and the illite 001 peak intensity of continuous borehole core samples from the Nobeoka Thrust, a fossilized tectonic boundary thrust in the Shimanto Belt, the Cretaceous-Paleogene Shimanto accretionary complex in southwest Japan. We also carried out grinding experiments on borehole core samples and sericite standard samples as starting materials and investigated the effect of mechanical comminution on the IC and illite peak intensity of the experimental products. We observed the following: (1) the paleotemperatures of the hanging wall and footwall of the Nobeoka Thrust are estimated to be 288°C to 299°C and 198°C to 249°C, respectively, which are approximately 20°C to 30°C lower than their previously reported temperatures estimated by vitrinite reflectance; (2) the fault core of the Nobeoka Thrust does not exhibit IC decrease; (3) the correlation of IC and illite peak intensity in the hanging wall damage zone were well reproduced by the grinding experiment, suggesting that the effect of mechanical comminution increases toward the fault core and; (4) the abrupt increase in IC value accompanied by high illite peak intensity is explained by hydrothermal alterations including plagioclase breakdown and the formation of white micas. Our results indicate that IC has potential for quantifying the effects of mechanical comminution and hydrothermal alteration within a fault zone.

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Section: Factors Controlling Illite Crystallinity Within Fault Zonesupporting

confidence: 74%

Changes in illite crystallinity within an ancient tectonic boundary thrust caused by thermal, mechanical, and hydrothermal effects: an example from the Nobeoka Thrust, southwest Japan

Fukuchi

Fujimoto

Kameda

et al. 2014

Earth, Planets and Space

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“…As already noted by Yusa et al (1992), Yamakita et al (1995) and Ito et al (1996), the Beppu graben is in the hanging wall of the MTL, which was reactivated as a normal fault in Plio-Quaternary times. Reverse motion along the MTL near Beppu dates back to the Oligocene or earlier (Yamakita et al 1995). Normal faults also developed in the vicinity of the NTL (Fig.…”

Section: Accommodation Of Extension Through Reactivation Of Thrust Famentioning

confidence: 59%

“…Outside the graben, pre-Miocene basement rocks are locally exposed, whereas, inside the graben, they have subsided to about 3000 m below the surface, as shown by Bouguer gravity anomaly, seismic reflection profiling and drilling. Based on seismic reflection profiles, Yusa et al (1992), Yamakita et al (1995) and Ito et al (1996) interpreted the Beppu graben as a half-graben developed above the northwarddipping MTL reactivated as a master detachment fault during Plio-Quaternary times (Fig. 8).…”

Section: Beppu Regionmentioning

confidence: 99%

Transtensional deformation at the junction between the Okinawa trough back-arc basin and the SW Japan island arc

Fabbri

Monié²,

Fournier

2004

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The Okinawa trough is a back-arc basin currently forming above the subducting Philippine Sea plate by crustal stretching of the Eurasia lithosphere. Existing geophysical investigations have revealed that the northern part of the Okinawa trough consists of a series of en echelon left-stepping grabens or half-grabens, some of which were formed in Miocene times and are presently inactive. In the Kyushu island, three major zones of extensional deformation are recognized. They are characterized by 20-40 km long sediment-filled basins lying on the hanging-wall side of N60 ~ to N80~ north-or NW-dipping normal faults. These basins display an en echelon left-stepping arrangement. The ages of faulted rocks, the ages of graben-filling sediments and radiometric ages newly obtained on pseudotachylites associated with normal faulting indicate that extension started at 13 Ma at the southern end of Kyushu and migrated northwards in the middle part of Kyushu (Beppu Bay), where it is still active today.The continentward-dipping, listric geometry inferred in depth for the fault systems is consistent with that of faults imaged by existing seismic profiles obtained off-shore in the Okinawa trough and across the Beppu Bay. The spatial association between Miocene or younger normal faults and pre-Miocene regional low-angle thrust faults suggests the possibility of a reactivation of some of the thrust faults as low-angle detachment faults merging in depth into a mid-crustal partial attachment zone.

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“…These ages are similar to the 60-70 Ma ages obtained by the K-Ar dating of biotite from Ryoke mylonitic granites (Shibata & Takagi 1988). K-Ar datings performed on clay minerals from MTLrelated gouges yielded ages between 58 and 10 Ma (Takagi & Shibata 1992;Yamakita et al 1995). Apatite fission track ages systematically decrease towards the MTL from about 55 Ma (at >5 km from the fault zone) to 9-13 Ma closest to the fault zone (Tagami et al 1988).…”

Section: Southern Boundary Of the Western Chugoku Fault Systemmentioning

confidence: 97%

Distributed strike-slip faulting, block rotation and possible intracrustal vertical decoupling in the convergent zone of SW Japan

Fabbri

Iwamura

Matsunaga³

et al. 2004

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Between the Median Tectonic Line (MTL) and the Japan Sea, the western Chugoku region of SW Japan is cut by a series of N45~ first-order faults and oblique (N60~176 second-order faults. This fault network, probably formed during Late Cretaceous-Palaeocene times (70-60Ma), defines a regional block structure. PrePlio-Quaternary kinematical indicators suggest left-lateral motion along the first-order faults and right-lateral motion along some of the second-order faults. Geomorphological evidence and earthquake focal mechanisms indicate that Plio-Quaternary slip senses are opposite to Pre-Plio-Quatemary ones.The overall fault pattern is geometrically and kinematically similar to patterns obtained by experimental modelling of simple shear deformation distributed at the base of a brittle layer analogue over its entire width. This similarity suggests the possibility of a midcrustal, flat-lying partial attachment zone which could have controlled the formation of the western Chugoku fault network in Cretaceous to Palaeocene times. The zone, presently inactive, could correspond to the 'proto-MTL', a low-angle fault recently imaged by seismic reflection studies and whose trace approximately coincides with the present-day MTL. Reactivation of the system occurred twice after its formation: firstly in Miocene times, during the opening of the Japan Sea and concomitant clockwise rotation of the entire SW Japan arc; and secondly in Late Pliocene to Quaternary times, after a shift of the relative direction of convergence between the Philippine and Eurasia plates. Unlike the first reactivation, the second reactivation led to an inversion of the sense of slip along the faults.Wrench tectonics can be localized along a single strike-slip fault but can also be diffuse and encompass large areas whose widths can exceed several tens or hundreds of kilometres (e.g. Moore 1979). Diffuse wrench zones are composed of crustal blocks and slivers delimited by vertical faults. The mechanism of internal deformation of diffuse wrench zones typically involves vertical-axis rotations of blocks and concomitant strike-slip along the block-bounding faults, the so-called 'bookshelf' mechanism of Mandl (1987). Examples of analyses of internal deformation of diffuse wrench zones are numerous and often rely on palaeomagnetic investigations (Luyendyk et al.

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Early Oligocene top-to- the-west motion along the Sashu fault, a low-angle oblique thrust of the Paleo-Median Tectonic Line, east Kyushu, Japan

Cited by 23 publications

References 3 publications

Changes in illite crystallinity within an ancient tectonic boundary thrust caused by thermal, mechanical, and hydrothermal effects: an example from the Nobeoka Thrust, southwest Japan

Changes in illite crystallinity within an ancient tectonic boundary thrust caused by thermal, mechanical, and hydrothermal effects: an example from the Nobeoka Thrust, southwest Japan

Transtensional deformation at the junction between the Okinawa trough back-arc basin and the SW Japan island arc

Distributed strike-slip faulting, block rotation and possible intracrustal vertical decoupling in the convergent zone of SW Japan

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