Crustal structure of the Hidaka collision zone and its foreland fold-and-thrust belt, Hokkaido, Japan.

谷生, 伊藤

doi:10.3720/japt.65.103

Cited by 33 publications

(38 citation statements)

References 5 publications

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“…Reports of a similar structural configuration were the result of numerous seismic reflection studies that were mentioned in the introduction and described in the compilation by Ito []. These studies revealed a clear eastward dip of the western (Japan) block underneath the eastern (Kuril) block, which correlates with a system of thrust faults in the Hidaka Belt (Figure ).…”

Section: Discussionmentioning

confidence: 99%

“…A particular behavior of reflectors in the lower crust may indicate the delamination of the lower mantle material and its possible descent to the mantle wedge. In particular, Ito [] stated that “the upper half of the lithosphere (upper crust + upper portion of the lower crust) thrusts westward on the northeast Japan arc, whereas the lower half (lower portion of the lower crust + upper mantle) descends down.” Similar conclusions follow from another reflection seismic study by Tsumura et al . [], who proposed that “the Hidaka Collision Zone represents an active model for continental growth by arc accretion with delamination of lower arc crust.” This concept is also supported by geological observations indicating the peak metamorphic grades exposed in the Hidaka Belt [ Osanai et al ., ].…”

Section: Discussionmentioning

confidence: 99%

“…In addition to earthquake tomography, active source studies have also been performed on Hokkaido since the 1970s. Several seismic profiles were shot mostly in the mountain area of Hidaka, and the collected refraction and reflection data were used to construct detailed images of the upper crust that generally extended down to a depth of 20 km and in few cases extended down 40 km [e.g., Moriya et al ., ; Iwasaki et al ., , ; Tsumura et al ., ; Ito , , and references herein]. In the same area, Arita et al .…”

Section: Introductionmentioning

confidence: 99%

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Anisotropic tomography of Hokkaido reveals delamination‐induced flow above a subducting slab

et al. 2015

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We present a new 3-D anisotropic seismic model for the crust and upper mantle beneath Hokkaido (Japan) based on tomographic inversion of P and S arrival times from a regional seismic database. The P model is parameterized with three parameters at each point that describe the azimuthal anisotropy; the S model is represented isotropically. The isotropic P and S velocity anomalies match nearly perfectly. In the crust, they show a prominent linear anomaly in central Hokkaido along the Kamuikotan and Hidaka Belts, which represents the area of eastward underthrusting of the Japan Block underneath the Kuril fore arc. We interpret the high-velocity anomaly beneath the Hidaka zone as being delaminated mafic crust and entrained mantle lithosphere, which developed due to crustal shortening in the collision zone. One of our vertical sections shows a very unusual configuration for a subduction zone: a low-velocity slab is overlain by a high-velocity body in the mantle wedge. We propose that the high-velocity delaminated material sinking along the slab surface prevents the escape of fluids and melts from the upper part of the slab, where they are generated due to phase transitions. As a result, a large portion of the fluids is entrained downward and lowers the seismic velocities in the slab. The azimuthal anisotropy in the crust clearly corresponds to the major tectonic units and delineates the major suture zones. In the mantle, the anisotropy has a fan-shaped configuration and most likely represents the deviating of flows starting in southern Hokkaido and splitting into three directions. The western and eastern flows proceed toward the two volcanic groups on Hokkaido, and they may carry with them additional material to trigger the characteristic caldera-forming eruptions in these groups.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Anisotropic tomography of Hokkaido reveals delamination‐induced flow above a subducting slab

et al. 2015

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“…mid-Miocene when the style of faulting changed from strike-slip to thrusting, inferred to be the result of early Kuril arc collision, which is still ongoing (Ito, 2000;Kato et al, 2004). At a minimum, it seems wise to remove any later contractional deformation before attempting to reconstruct the kinematics at the northern end of the back-arc during opening.…”

Section: Accepted Manuscriptmentioning

confidence: 96%

Evolution of the Sea of Japan back-arc and some unsolved issues

2017

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“…High temperature metamorphic rocks of Tertiary age are exposed and include materials from the upper and lower crust (e.g., Shimura et al, 2004). Ito (2000) and Iwasaki et al (2004) suggested this region is characterized by delamination of the lower crust, with partial exhumation of the lower crust, and partial subduction along the Pacific slab. The combination of inferences from local geology and tomographic imaging suggests that the presence of subducted fore-arc materials cause thermal shielding of the slab to greater depths than elsewhere.…”

Section: Seismicity and Thermal Structure At The Trench Junctionmentioning

confidence: 99%

Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

2012

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Abstract. The cause of intermediate-depth (> 40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, which include dehydration embrittlement, shear instabilities and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The wellinstrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediatedepth seismicity occurs. This study combines new finite element models that predict the dynamics and thermal structure of the Japan subduction system with a high-precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths > 80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between the thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models that take into account the seismically imaged modified upper mantle structure in this region fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by timedependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediatedepth seismicity.

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Crustal structure of the Hidaka collision zone and its foreland fold-and-thrust belt, Hokkaido, Japan.

Abstract: Crustal structure of the Hidaka collision zone and its foreland fold-and-thrust belt, Hokkaido, Japan

Cited by 33 publications

References 5 publications

Anisotropic tomography of Hokkaido reveals delamination‐induced flow above a subducting slab

Anisotropic tomography of Hokkaido reveals delamination‐induced flow above a subducting slab

Evolution of the Sea of Japan back-arc and some unsolved issues

Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

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