The Apparent Polar Wander Path For the North China Block Since the Jurassic   总被引：7，自引：0，他引：7  

Zhong Zheng  Masaru Kono  Hideo Tsunakawa  Gaku Kimura  Qingyun Wei  Xiangyuan Zhu  Tianyao Hao 《Geophysical Journal International》1991,104(1):29-40

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A deep section of accretionary complex: Susunai Complex in Sakhalin Island, Northwest Pacific Margin     

Gaku  Kimura Masayuki  Sakakibara Hisashi  Ofuka Hideo  Ishizuka Sumio  Miyashita Makoto  Okamura Olex A.  Melinikov Vilera  Lushchenko 《Island Arc》1992,1(1):166-175

Abstract A deep section of accretionary complex, the metamorphosed Susunai Complex, is observed on Sakhalin Is., Russia. High pressure part of pumpellyite-actinolite facies metavolcanics, metacherts and metapelites are well exposed and constitute a tectonic pile preserving primary structures related to underplating of the oceanic crust. Three stages of deformation, D₁ through D₃, suggest successive deformation during subduction, underplating and exhumation of the complex. Oceanic material in the complex is more abundant than other well documented ancient accretionary complexes (e.g. the Shimanto Belt in southwest Japan and the Ghost Rocks Formation in Alaska), which were shallowly underplated. At Susunai, deep down-stepping of a décollément has scraped off the upper part of the oceanic crust, primarily the pillowed basalt horizon. This down-stepping results from crustal weakening as overpressured water is released from the fractured oceanic crust during metamorphism.  相似文献   

Origin of the early Cenozoic belt boundary thrust and Izanagi–Pacific ridge subduction in the western Pacific margin     

Gaku Kimura  Yujin Kitamura  Asuka Yamaguchi  Jun Kameda  Yoshitaka Hashimoto  Mari Hamahashi 《Island Arc》2019,28(5)

The belt boundary thrust within the Cretaceous–Neogene accretionary complex of the Shimanto Belt, southwestern Japan, extends for more than ~ 1 000 km along the Japanese islands. A common understanding of the origin of the thrust is that it is an out of sequence thrust as a result of continuous accretion since the late Cretaceous and there is a kinematic reason for its maintaining a critically tapered wedge. The timing of the accretion gap and thrusting, however, coincides with the collision of the Paleocene–early Eocene Izanagi–Pacific spreading ridges with the trench along the western Pacific margin, which has been recently re‐hypothesized as younger than the previous assumption with respect to the Kula‐Pacific ridge subduction during the late Cretaceous. The ridge subduction hypothesis provides a consistent explanation for the cessation of magmatic activity along the continental margin and the presence of an unconformity in the forearc basin. This is not only the case in southwestern Japan, but also along the more northern Asian margin in Hokkaido, Sakhalin, and Sikhote‐Alin. This Paleocene–early Eocene ridge subduction hypothesis is also consistent with recently acquired tomographic images beneath the Asian continent. The timing of the Izanagi–Pacific ridge subduction along the western Pacific margin allows for a revision of the classic hypothesis of a great reorganization of the Pacific Plate motion between ~ 47 Ma and 42 Ma, illustrated by the bend in the Hawaii–Emperor chain, because of the change in subduction torque balance and the Oligocene–Miocene back arc spreading after the ridge subduction in the western Pacific margin.  相似文献   

Rejuvenated extension of the Philippine Sea plate and its effect on subduction dynamics in the Nankai Trough     

Gaku Kimura  Yasuyuki Nakamura  Kazuya Shiraishi  Gou Fujie  Shuichi Kodaira  Asuka Yamaguchi  Rina Fukuchi  Yoshitaka Hashimoto 《Island Arc》2021,30(1):e12402

The Nankai Trough, Japan, is a subduction zone characterized by the recurrence of disastrous earthquakes and tsunamis. Slow earthquakes and associated tremor also occur intermittently and locally in the Nankai Trough and the causal relationship between slow earthquakes and large earthquakes is important to understanding subduction zone dynamics. The Nankai Trough off Muroto, Shikoku Island, near the southeast margin of the rupture segment of the 1946 Nankai earthquake, is one of three regions where slow earthquakes and tremor cluster in the Nankai Trough. On the Philippine Sea plate, the rifting of the central domain of the Shikoku Basin was aborted at ~15 Ma and underthrust the Nankai forearc off Muroto. Here, the Tosa-Bae seamount and other high-relief features, which are northern extension of the Kinan Seamount chain, have collided with and indented the forearc wedge. In this study, we analyzed seismic reflection profiles around the deformation front of accretionary wedge and stratigraphically correlated them to drilling sites off Muroto. Our results show that the previously aborted horst-and-graben structures, which were formed around the spreading center of the Shikoku Basin at ~15 Ma, were rejuvenated locally at ~6 Ma and more regionally at ~3.3 Ma and have remained active since. The reactivated normal faulting has enhanced seafloor roughness and appears to affect the locations of slow earthquakes and tremors. Rejuvenated normal faulting is not limited to areas near the Nankai Trough, and extends more than 200 km into the Shikoku Basin to the south. This extension might be due to extensional forces applied to the Philippine Sea plate, which appear to be driven by slab-pull in the Ryukyu and Philippine trenches along the western margin of the Philippine Sea plate.  相似文献   

Crustal structure and tectonics of the Hidaka Collision Zone, Hokkaido (Japan), revealed by vibroseis seismic reflection and gravity surveys     

Kazunori Arita  Takashi Ikawa  Tanio Ito  Akihiko Yamamoto  Matsuhiko Saito  Yasunori Nishida  Hideyuki Satoh  Gaku Kimura  Teruo Watanabe  Takeshi Ikawa  Toru Kuroda 《Tectonophysics》1998,290(3-4):197-210

This study is the first integrated geological and geophysical investigation of the Hidaka Collision Zone in southern Central Hokkaido, Japan, which shows complex collision tectonics with a westward vergence. The Hidaka Collision Zone consists of the Idon'nappu Belt (IB), the Poroshiri Ophiolite Belt (POB) and the Hidaka Metamorphic Belt (HMB) with the Hidaka Belt from west to east. The POB (metamorphosed ophiolites) is overthrust by the HMB (steeply eastward-dipping palaeo-arc crust) along the Hidaka Main Thrust (HMT), and in turn, thrusts over the Idon'nappu Belt (melanges) along the Hidaka Western Thrust (HWT). Seismic reflection and gravity surveys along a 20-km-long traverse across the southern Hidaka Mountains revealed hitherto unknown crustal structures of the collision zone such as listric thrusts, back thrusts, frontal thrust-and-fold structures, and duplex structures. The main findings are as follows. (1) The HMT, which dips steeply at the surface, is a listric fault dipping gently at a depth of 7 km beneath the eastern end of the HMB, and cutting across the lithological boundaries and schistosity of the Hidaka metamorphic rocks. (2) A second reflector is detected 1 km below the HMT reflector. The intervening part between these two reflectors is inferred to be the POB, which is only little exposed at the surface. This inference is supported by the high positive Bouguer anomalies along the Hidaka Mountains. (3) The shallow portion of the IB at the front of the collision zone has a number of NNE-dipping reflectors, indicative of imbricated fold-and-thrust structures. (4) Subhorizontal reflectors at a depth of 14 km are recognized intermittently at both sides of the seismic profile. These reflectors may correspond to the velocity boundary (5.9–6.6 km/s) previously obtained from seismic refraction profiling in the northern Hidaka Mountains. (5) These crustal structures as well as the back thrust found in the eastern end of the traverse represent characteristics of collisional tectonics resulting from the two collisional events since the Early Tertiary.  相似文献   

Physical property anisotropy of foliated fault rocks: Study from the Nobeoka Thrust,Shimanto Belt,southwest Japan          下载免费PDF全文

Mari Hamahashi  Wataru Tanikawa  Yohei Hamada  Yoshitaka Hashimoto  Saneatsu Saito  Gaku Kimura 《Island Arc》2018,27(5)

To investigate the physical property anisotropies of foliated fault rocks in subduction zones, the hanging wall phyllites and footwall cataclasites exhumed along the Nobeoka Thrust, a fossilized out‐of‐sequence‐thrust in the Shimanto Belt, Japan, was focused. Discrete physical property (electric resistivity, P‐ and S‐wave velocities, and porosity) measurements were conducted employing geologic coordinates (depth‐parallel direction, strike direction, and maximum dip direction of foliation), using the core samples obtained from the Nobeoka Thrust Drilling Project and compared the data to borehole geophysical logs. A higher sample P‐wave velocity (Vp), lower S‐wave velocity (Vs), higher Vp/Vs, and lower sample porosity and resistivity compared to the logs, are inferred to have been caused by the larger sampling scale of the logs and lower fluid saturation of the borehole. The phyllites and cataclasites exhibited substantial vertical and horizontal anisotropy of Vp (0.4–17.3 % and 2.7–13.8 %, respectively), Vs (0.5–56 % and 7.7–43 %, respectively), and resistivity (0.9–119 % and 2.0–65.9 %, respectively). The physical property anisotropies are primarily affected by the dip angles of foliation. The fault rocks that have gentler dip angles exhibit a higher Vp in the strike and maximum dip direction and a lower Vp in the depth‐parallel direction. In contrast, the fault rocks that have steeply dipping structures show a higher Vp in the strike and depth‐parallel directions with a lower velocity in the maximum dip direction. Resistivity anisotropy show a trend opposite to that of the Vp in relation to the dip angles. Our results show lower Vp anisotropy than those obtained in previous studies, which measured wave speeds perpendicular or parallel to foliation under confining pressure. This study highlights the significance of dip angles on vertical properties in geophysical surveys across foliated fault rocks.  相似文献   

Acoustic properties of deformed rocks in the Nobeoka thrust,in the Shimanto Belt,Kyushu, Southwest Japan          下载免费PDF全文

Yoshitaka Hashimoto  Shogo Abe  Hiroki Tano  Gaku Kimura  Asuka Yamaguchi  Rina Fukuchi  Jun Kameda  Yohei Hamada  Yujin Kitamura  Koichiro Fujimoto  Mio Eida 《Island Arc》2017,26(4)

Laboratory measurements for compressional and shear wave velocities (Vp and Vs, respectively) and porosity were conducted with core samples from the Nobeoka Thrust Drilling Project (NOBELL) under controlled effective pressure (5–65 MPa at 5 MPa intervals) and wet conditions. Samples were classified according to deformation texture as phyllite, foliated cataclasite, or non‐foliated cataclasite. Measured values of Vp, Vs, and porosity are within a range of 5.17–5.57 km/s, 2.60–2.71 km/s, and 2.75–3.10 %, respectively, for phyllite; 4.89–5.23 km/s, 2.46–2.57 km/s, and 3.58–4.53 %, respectively, for foliated cataclasite; and 4.90–5.32 km/s, 2.51–2.63 km/s, and 3.79–4.60 %, respectively, for non‐foliated cataclasite, which are all consistent with the previous laboratory experiments conducted with outcrop samples under dry conditions. However, our results also indicate higher Vp and Vs and lower porosity than those measured by the previous studies that adopted the wire‐line logging methods. The variations in Vp, Vs, and porosity are controlled by deformation structure and are greater for phyllite and foliated cataclasite than for non‐foliated cataclasite.  相似文献   

Three‐dimensional texture of natural pseudotachylyte: Pseudotachylyte formation mechanism in hydrous accretionary complex          下载免费PDF全文

Yohei Hamada  Gaku Kimura  Jun Kameda  Asuka Yamaguchi  Mari Hamahashi  Rina Fukuchi  Yujin Kitamura  Shin'ya Okamoto 《Island Arc》2018,27(2)

Melt‐origin pseudotachylyte is the most reliable seismogenic fault rock. It is commonly believed that pseudotachylyte generation is rare in the plate subduction zone where interstitial fluids are abundant and can trigger dynamic fault‐weakening mechanisms such as thermal pressurization. Some recent studies, however, have discovered pseudotachylyte‐bearing faults in exhumed ancient accretionary complexes, indicating that frictional melting also occurrs during earthquakes in subduction zones. To clarify the pseudotachylyte generation mechanism and the variation of slip behavior in the plate subduction zone, a pseudotachylyte found in the exhumed fossil accretionary complex (the Shimanto Belt, Nobeoka, Japan) was re‐focused and microscopic and three‐dimensional observations of the pseudotachylyte‐bearing fault were performed based on optical, electron, and X‐ray microscope images. Based on the patterns contained in the fragment, the pseudotachylyte is divided into four domains, although no clear domain boundaries or layering structures are not found. Three‐dimensional observation also suggests that the pseudotachylyte were fragmented or isolated by cataclasite or carbonate breccia. The pseudotachylyte was rather injected into the surrounding carbonate breccia, which is composed of angular fragments of the host rock and a matrix of tiny crystalline carbonate. The pseudotachylyte volume was extracted from the X‐ray microscope image and the heat abundance consumed by the pseudotachylyte generation was estimated at 2.18 MJ/m², which can be supplied during a slip of approximately 0.5 m. These observations and calculations, together with the results of the previous investigations, suggest hydrofracturing and rapid carbonate precipitation that preceded or accompanied the frictional melting. Dynamic hydrofracturing during a slip can be caused by rapid fluid pressurization, and can induce abrupt decrease in fluid pressure while drastically enhancing the shear strength of the shear zone. Consequently, frictional heating would be reactivated and generate the pseudotachylyte. These deformation processes can explain pseudotachylyte generation in hydrous faults with the impermeable wall rock.  相似文献   

Temporal stress variations along a seismogenic megasplay fault in the subduction zone: An example from the Nobeoka Thrust,southwestern Japan          下载免费PDF全文

Ryoji Kawasaki  Yoshitaka Hashimoto  Makoto Otsubo  Asuka Yamaguchi  Yujin Kitamura  Jun Kameda  Yohei Hamada  Rina Fukuchi  Gaku Kimura 《Island Arc》2017,26(3)

The Nobeoka Thrust, an ancient megasplay fault in the Shimanto Belt, southwestern Japan, contains fault rocks from the seismogenic zone, providing an accessible analog of active megasplay faults in deep subduction settings. In this study, the paleostress along the Nobeoka Thrust was analyzed using multiple inversion techniques, including k‐means clustering of fault datasets acquired from drillcores that intersected the thrust. The six resultant stress orientation clusters can be divided into two general groups: stress solutions with north–south‐trending σ₁ axes, and those with east–west‐trending σ₁ axes. These groups are characterized by the temporal changes for the orientations of the σ₁ and σ₃ principal stress axes that involve alternation between horizontal and vertical. The findings are probably due to a change in stress state before and after earthquakes that occurred on the fault; similar changes have been observed in active tectonic settings, such as the 2011 Tohoku‐Oki earthquake (Japan).  相似文献   

Variations in stress and driving pore fluid pressure ratio using vein orientations along megasplay faults : Example from the Nobeoka Thrust,Southwest Japan          下载免费PDF全文

Makoto Otsubo  Ayumu Miyakawa  Ryoji Kawasaki  Katsushi Sato  Asuka Yamaguchi  Gaku Kimura 《Island Arc》2016,25(6):421-432

The Nobeoka Thrust of Southwest Japan is an on‐land example of an ancient megasplay fault that provides an excellent record of deformation and fluid flow at seismogenic depths. The present study reports: (i) temporal stress changes for the seismogenic period of the Nobeoka Thrust; and (ii) spatial heterogeneities in driving pressure ratios P* obtained from mineral veins around the Nobeoka Thrust fault zone. Many quartz veins that filled mode I cracks can be observed in the hanging wall and footwall of the thrust. Inversion for stress orientation suggests that normal faulting dominated in both the hanging wall and footwall, with similar stress axis orientations in both. The orientation of σ₃ for the estimated stress regime is parallel to the slip direction of the Nobeoka Thrust. The detected normal‐faulting‐type stress regimes likely resulted from post‐seismic stress buildup after megathrust earthquakes. The hanging wall of the Nobeoka Thrust has smaller P* values than the footwall. Two possible explanations are proposed for the observed spatial variations in the driving pore fluid pressure ratio, P*: spatial variations in pore fluid pressure P_f are directly responsible for P* variations, or P* variations are controlled by differences in mechanical properties between the hanging wall and footwall.  相似文献