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1.
Abstract Paleostress fields of the Late Paleozoic to Early Mesozoic Pyeongan Supergroup that is distributed along the northeastern part of the Ogcheon Belt in South Korea were investigated using the calcite strain gauge (CSG) technique. Combining the results of this study with those of other studies investigating the relationship between twin strain, twin density and width, which are used as indicators of deformation conditions in the natural low-temperature deformation of limestone, it was estimated that calcite twins in the study area were probably formed at temperatures lower than 170°C. From two samples, two different principal paleostress directions were inferred from calcite twins, while only one direction was inferred from two other samples. This result suggests that deformation occurred during two or more different tectonic events in the Pyeongan Supergroup during the Mesozoic era. The maximum shortening axis was oriented in two directions, northeast–southwest and northwest–southeast, respectively, which coincide well with the paleostress directions inferred from the stress inversion for many fault sets. Combining the results of the paleostress analysis from this and other studies, we hypothesize that the directions of the maximum shortening axis in the Pyeongan Supergroup changed from northeast–southwest during the pre-Daebo orogeny period (Late Triassic period) to northwest–southeast during the syn-Daebo orogeny period (Early Jurassic to Early Cretaceous period) in the Mesozoic era. 相似文献
2.
Abstract Paleostress of the Joseon Supergroup in the northeastern part of the Ogcheon Belt, South Korea, is reconstructed in the Jecheon–Danyang area with the help of calcite twinning. In the study area, the average twin thickness and intensity increase with the total twin strain increase. From the appearance of twins, the average twin thickness and intensity, and the total twin strain, it is estimated that calcite twins were produced under temperatures lower than 200°C. The maximum shortening axis in the study area changes orientation from northeast–southwest to NNW–SSE or northwest–southeast, and finally to north–south. We suggest these three distinct stages with different orientations of the maximum shortening axis can be correlated with: (i) the Paleozoic to Early Jurassic Songrim orogeny; (ii) the Early Jurassic to Late Jurassic Daebo orogeny; and (iii) the Cretaceous Bulgugsa orogeny. 相似文献
3.
Kantaro Fujioka Wataru Tokunaga Hisayoshi Yokose Junzo Kasahara Toshinori Sato Ryo Miura Teruaki Ishii 《Island Arc》2005,14(4):616-622
Abstract The Hahajima Seamount, located at the junction between the Izu–Bonin and Mariana forearc slopes, is a notable rectangular shape and consists of various kinds of rocks. An elaborated bathymetric swath mapping with geophysical measurements and dredge hauls showed the Hahajima Seamount is cut by two predominating lineaments, northeast–southwest and northwest–southeast. These lineaments are of faults based on the topographic cross-sections and a 3-D view (whale's eye view). The former lineament is parallel to the transform faults of the Parece Vela Basin, whereas the latter is parallel to the nearby transform fault on the subducting Pacific Plate. The rocks constituting the seamount are ultramafic rocks (mostly harzburgite), boninite, basalt, andesite, gabbro, breccia and sedimentary rocks, which characterize an island arc and an ocean basin. Gravity measurement and seismic reflection survey offer neither a definite gravity anomaly at the seamount nor definite internal structures beneath the seamount. A northwest–southeast-trending fault and small-scale serpentine flows were observed during submersible dives at the Hahajima Seamount. The rectangular shape, size of the seamount, various kinds of rocks and geophysical measurements strongly suggest that the Hahajima Seamount is not a simple serpentine seamount controlled by various tectonic movements, as previously believed, but a tectonic block. 相似文献
4.
Abstract Upper Paleozoic to Mesozoic sedimentary sequences of chert (Liminangcong Formation), clastics (Guinlo Formation) and a number of limestone units (Coron Formation, Minilog Formation and Malajon Limestone) constitute the accretionary complex of the North Palawan block, Philippines. Based on chert-to-clastic transitions from different stratigraphic sequences around the Calamian Islands, three accretionary belts are delineated: the Northern Busuanga Belt (NBB), the Middle Busuanga Belt (MBB) and the Southern Busuanga Belt (SBB). The accretion events of these belts along the East Asian accretionary complex, indicated by their sedimentary transitions, began with the Middle Jurassic NBB accretion, followed by the Late Jurassic MBB accretion and the Early Cretaceous SBB accretion. Several limestone blocks that formed over the seamounts became juxtaposed with chert–clastic sequences during accretion. During the Late Cretaceous, accretion-subduction along the East Asian margin subsided bringing tectonic stability to the region. The seafloor spreading during the mid-Oligocene disconnected the entire North Palawan block from the Asian mainland and then migrated southward. The collision between the North Palawan block and the Philippine Island Arc system in the middle Miocene generated a megafold structure in the Calamian Islands as a result of the clockwise turn of the accretionary belts in the eastern Calamian from originally northeast–southwest to northwest–southeast. 相似文献
5.
6.
Abstract Numerous Neogene/Quaternary marl outcrops of the submarine Antique Ridge and southern Negros accretionary complexes (Sulu Sea, Philippines) were formed by an oversteepen-ing of the slope by the collision with the Cagayan Ridge and Cuyo Platform and also by erosion.
The outcrops exhibit distinct joint systems that were developed under compressional stress parallel to an east-northeast subduction of the southeast Sulu Basin complex under the Panay-Negros Fore-Arc and Arc Complexes during the Late Miocene/earliest Pliocene. Typical bc-(longitudinal) joints following the axial trend of the subduction zone, hkO (diagonal) shear joints, and ac-(transverse) joints were formed. The regional stress in south-southeast, which has changed to northeast since the Early Pliocene, has caused an uplift of the accretionary complexes and a clockwise rotation of the subduction/collision zone axis of the Antique Ridge complex from a more northern direction to NNE. Consequently the pre-existing joint system has also rotated for 10° to 20°. A strike-slip motion parallel to this axis as a consequence of the NE collision may have been accommodated within the accretionary complex by the bc-joints.
Some bedding-plane parallel white veins or layers may be related to calcium carbonate precipitation via oxidation of methane which was probably carried by migrating fluids along shear zones.
Downslope, sediment transport as well as trench-parallel sediment transport in southerly directions is still going on, indicating active tectonic oversteepening of the slopes of the accretionary complexes as well as flowing water, possibly of intermediate water from the Northwest Sulu Basin into the Southeast Sulu Basin via the Panay Canyon. 相似文献
The outcrops exhibit distinct joint systems that were developed under compressional stress parallel to an east-northeast subduction of the southeast Sulu Basin complex under the Panay-Negros Fore-Arc and Arc Complexes during the Late Miocene/earliest Pliocene. Typical bc-(longitudinal) joints following the axial trend of the subduction zone, hkO (diagonal) shear joints, and ac-(transverse) joints were formed. The regional stress in south-southeast, which has changed to northeast since the Early Pliocene, has caused an uplift of the accretionary complexes and a clockwise rotation of the subduction/collision zone axis of the Antique Ridge complex from a more northern direction to NNE. Consequently the pre-existing joint system has also rotated for 10° to 20°. A strike-slip motion parallel to this axis as a consequence of the NE collision may have been accommodated within the accretionary complex by the bc-joints.
Some bedding-plane parallel white veins or layers may be related to calcium carbonate precipitation via oxidation of methane which was probably carried by migrating fluids along shear zones.
Downslope, sediment transport as well as trench-parallel sediment transport in southerly directions is still going on, indicating active tectonic oversteepening of the slopes of the accretionary complexes as well as flowing water, possibly of intermediate water from the Northwest Sulu Basin into the Southeast Sulu Basin via the Panay Canyon. 相似文献
7.
A magnetic anomaly map of the northern part of the Philippine Sea plate shows two conspicuous north–south rows of long-wavelength anomalies over the Izu–Ogasawara (Bonin) arc, which are slightly oblique to the present volcanic front. These anomalies are enhanced on reduced-to-pole and upward-continued anomaly maps. The east row is associated with frontal arc highs (the Shinkurose Ridge), and the west row is accompanied by the Nishi-Shichito Ridge. Another belt of long-wavelength anomalies very similar to the former two occurs over the Kyushu–Palau Ridge. To explain the similarity of the magnetic anomalies, it is proposed that after the spreading of the Shikoku Basin separated the Izu–Ogasawara arc from the Kyushu–Palau Ridge, another rifting event occurred in the Miocene, which divided the Izu–Ogasawara arc into the Nishi-Shichito and Shinkurose ridges. The occurrence of Miocene rifting has also been suggested from the geology of the collision zone of the Izu–Ogasawara arc against the Southwest Japan arc: the Misaka terrain yields peculiar volcanic rocks suggesting back-arc rifting at ～ 15 Ma. The magnetic anomaly belts over the Izu–Ogasawara arc do not extend south beyond the Sofugan Tectonic Line, suggesting a difference in tectonic history between the northern and southern parts of the Izu–Ogasawara arc. It is estimated that the Miocene extension was directed northeast–southwest, utilizing normal faults originally formed during Oligocene rifting. The direction is close to the final stage of the Shikoku Basin spreading. On a gravity anomaly relief map, northeast–southwest lineaments can be recognized in the Shikoku Basin as well as over the Nishi-Shichito Ridge. We thus consider that lines of structural weakness connected transform faults of the Shikoku Basin spreading system and the transfer faults of the Miocene Izu–Ogasawara arc rifting. Volcanism on the Nishi-Shichito Ridge has continued along the lines of weakness, which could have caused the en echelon arrangement of the volcanoes. 相似文献
8.
S. A. Kovachev I. P. Kuzin L. I. Lobkovskii 《Izvestiya Physics of the Solid Earth》2009,45(9):777-793
The results of detailed seismological observations with bottom seismographs in the Central Kurile segment in August-September,
2006 are discussed. The system of six bottom seismographs was placed on the island slope of the Kurile deep-sea trench southeast
of Urup Island and southwest of the Bussol Strait. Over 230 earthquakes with M
LH = 0.5–5.5 were registered in the area with a radius of 150 km around the center of the observation system at depths up to
300 km during 16 days. Records of 80 earthquakes with hypocenters in the earth crust (h = 0–30 km) beneath the island slope of the Kurile deep-sea trench were first obtained by bottom seismographs. These data
are inconsistent with previous concepts of aseismicity of this zone. The discovery of the unique morphological structure of
the Benioff zone beneath the central Kurile Arc represents the most important result of detailed seismological observations.
The zone consists of an inner seismoactive subzone, which is located beneath the island slope of the arc at depths of 15–210
km, being characterized by an angle of incline of 50° under the latter and crosses the ocean bottom approximately 80 km away
from the trench axis, and outer low-activity subzone. The latter is traceable beyond the trench almost parallel to the inner
zone beginning from a depth of 50 km below the sea bottom up to a depth of approximately 300 km. Due to the slightly lower
incline (∼45°) of the outer subzone, both subzones gradually converge downward. The integral thickness of the Benioff zone
varies from 150 km in its upper part to 125 km at depths of 210–260 km. The medium sandwiched between these subzones is practically
aseismic. The reality of this defined structure is confirmed by the distribution of aftershocks of the earthquake that occurred
on November 15, 2006 (M = 8.3). These seismic events served as foreshocks for the subsequent strong earthquake of January 13, 2007 (M = 8.1) with the hypocenter located beyond the trench under the ocean bottom. Such a structure of this zone within the central
Kurile Arc segment is unique, having no analogues either in the flanks of the Kurile-Kamchatka Arc or other arcs. The results
of detailed seismological observations obtained two months before the first of the catastrophic Central Kurile earthquakes
appeared to be typical for the period of foreshocks (the lower seismic activity of the Simushir block, which hosted the hypocenter
of the earthquake that occurred on November 15, 2006, particularly at depths of 0–50 km, the gentler incline of the recurrence
plot, and other features). 相似文献
9.
Measurements of the seafloor deformation under ocean waves (compliance) reveal an asymmetric lower crustal partial melt zone (shear velocity less than 1.8 km/s) beneath the East Pacific Rise axis between 9° and 10°N. At 9°48′N, the zone is less than 8 km wide and is centered beneath the rise axis. The zone shifts west of the rise axis as the rise approaches the westward-stepping 9°N overlapping spreading center discontinuity and is anomalously wide at the northern tip of the discontinuity. The ratio of the compliance determined shear velocity to the compressional velocities (estimated by seismic tomography) suggests that the melt is well-connected in high-aspect ratio cracks rather than in isolated sills. The shear and compressional velocities indicate less than 18% melt in the lower crust on average. The compliance measurements also reveal a separate lower crustal partial melt zone 10 km east of the rise axis at 9°48′N and isolated melt bodies near the Moho beneath four of the 39 measurement sites (three on-axis and one off-axis). The offset of the central melt zone from the rise axis correlates strongly with the offset of the overlying axial melt lens and the inferred center of mantle melting, but its shape appears to be controlled by crustal processes. 相似文献
10.
Fault configuration produced by initial arc rifting in the Parece Vela Basin as deduced from seismic reflection data 总被引：1，自引：0，他引：1
Mikiya Yamashita Tetsuro Tsuru Narumi Takahashi Kaoru Takizawa Yoshiyuki Kaneda Kantaro Fujioka Keita Koda 《Island Arc》2007,16(3):338-347
Abstract The Parece Vela Basin (PVB), which is a currently inactive back-arc basin of the Philippine Sea Plate, was formed by separation between the Izu-Ogasawara Arc (IOA) and the Kyushu-Palau Ridge (KPR). Elucidating the marks of the past back-arc opening and rifting is important for investigation of its crustal structure. To image its fault configurations and crustal deformation, pre-stack depth migration to multichannel seismic reflection was applied and data obtained by the Japan Agency for Marine-Earth Science and Technology and Metal Mining Agency of Japan and Japan National Oil Corporation (Japan Oil, Gas and Metals National Corporation). Salient results for the pre-stack depth-migrated sections are: (i) deep reflectors exist around the eastern margin of KPR and at the western margin of IOA down to 8 km depth; and (ii) normal fault zones distributed at the eastern margin of the KPR (Fault zone A) and the western margin of the IOA (Fault zone B) have a total displacement of greater than 500 m associated with synrift sediments. Additional normal faults (Fault zone C) exist 20 km east of the Fault zone B. They are covered with sediment, which indicates deposition of recent volcanic products in the IOA. According to those results: (i) the fault displacement of more than 500 m with respect to initial rifting was approximately asymmetric at 25 Ma based on PSDM profiles; and (ii) the faults had reactivated after 23 Ma, based on the age of deformed sediments obtained from past ocean drillings. The age of the base sediments corresponds to those of spreading and rotation after rifting in the PVB. Fault zone C is covered with thick and not deformed volcanogenic sediments from the IOA, which suggests that the fault is inactive. 相似文献
11.
Abstract Neotectonic crustal deformation in central Japan near a triple-junction of plates is investigated on the basis of paleomagnetic data. The progressive thermal demagnetization test isolated characteristic remanent magnetization from 18 sites of the early Quaternary Eboshidake volcanic rocks erupted around the termination of active strike-slip faults. The site-mean directions show considerably large scatter in declinations, and easterly deflection in average (Dm = −161.7°). On the basis of inclination statistics, measured inclinations (Im = −48.9°, δI = 6.6°) are concordant with an expected value from latitude of the study area. Because the sampling was planned to cover a wide stratigraphic range and eliminate the effect of geomagnetic secular variation, an easterly deflection is attributed to clockwise rotation around vertical axis. Together with previous paleomagnetic data, the present study indicates that clockwise-rotated areas in central Japan are aligned on a northeast–southwest recent shear zone delineated through geodetic survey. Deflection and scatter of paleomagnetic declinations of the Eboshidake volcanic rocks are much greater than those extrapolated from a recent strain rate, and might be explained by complicated motion anticipated at fault terminations and/or enhanced crustal rotation under elevated temperatures around a Quaternary volcanic province. 相似文献
12.
Abstract To determine how local geological events contributed to the evolution of accretionary complexes and eventual exposure of rocks with different structural levels, geochronological mapping was carried out using fission track (FT) analysis at the Kii Peninsula, southwest Japan. At this site, the original zonal structure of Cretaceous accretionary complexes parallel to the subduction zone is disturbed by the northward projection of the Shimanto accretionary complex. Twenty-six zircon FT ages were obtained from an area of ∼12 km in an east–west direction and ∼15 km in a north–south direction, and classified into three groups: (i) ages ∼15 Ma (range ∼10–20 Ma), which are distributed along the northwest–southeast valley; (ii) ages of ∼50 Ma in the northwest of the study area; and (iii) ages older than those in Groups 1 and 2. Based on results from eight zircon FT length distributions, the Miocene ages appear to be the result of spatial variations in heat influx and cooling after the regional exhumation of the area, as recorded by FT ages of ∼50 Ma. 相似文献
13.
本研究拾取了中国数字测震台网固定台站记录的2008-2016年2级以上地震事件中的27233条高质量Pn到时资料,反演得到了郯庐断裂带及其邻区上地幔顶部Pn波速度和各向异性结构模型.结果显示,研究区上地幔顶部Pn波速度结构存在强烈的横向不均匀性,速度异常形态与区域地质构造较为吻合.太行山造山带、鲁西隆起、大别造山带、苏鲁褶皱带、胶辽隆起和华北盆地南端等隆起区表现为低波速异常,而黄海北、南部盆地、渤海湾和华北盆地北部等凹陷区均为高波速异常.壳内强震主要发生在Pn低波速异常和高低波速异常的横向过渡地带,说明强震的发生与上地幔结构的横向变化之间存在有一定关联.郯庐断裂带两侧Pn波速度以郯城地震为界其东北侧和西南侧分别分布有与断裂带近平行的低波速异常条带,而西北侧和东南侧分别分布有高波速异常条带,各向异性快波方向近乎沿断裂带走向,可能由于上地幔热物质沿郯庐断裂带上涌形成低速异常后断裂带发生左旋平移运动所致.华北盆地内上地幔顶部Pn波速度结构和各向异性的明显变化,反映华北克拉通破坏过程中经历了地幔热物质上涌、莫霍面隆升以及岩石圈拆沉等复杂构造变形. 相似文献
14.
Japan Sea: a pull-apart basin? 总被引：1，自引：0，他引：1
Recent field work in the Hokkaido Central Belt and marine geology studies along the eastern margin of Japan Sea in addition to previously published data lead us to propose a new model of opening of the Japan Sea. The synthesis of both on-land and offshore structural data gives new constraints about the structural evolution of the system. The rhombohedral shape of the Japan Basin and the particular tectonic behaviour of the margins on both east and west sides can be explained by an early Eo-Oligocene rifting of a pull-apart basin accommodated along two large right-lateral shear zones, east of Korea and west of northeast Japan and Sakhalin. It is followed, during Upper Oligocene/Lower Miocene, by the main opening of the Japan Basin as a mega pull-apart. Then a back-arc spreading probably related to the subduction process, induced the creation of the Yamato and Tsushima Basins at the end of Lower Miocene and in Middle Miocene. Clockwise rotation of southwest Japan larger than 20° or major bending of Honshu mainland deduced from paleomagnetic studies is unlikely at this time. Since 1 or 2 My B.P. to Present, compression prevails along the eastern margin of the Japan Sea. The generation of marginal basins as pull-apart basins along intracontinental strike-slip faults is a mechanism which has been proposed by other authors concerning the South China Sea, the question then is whether the fragmentation of the Asiatic continent is an intracontinental deformation related process as proposed here or a subduction related one. 相似文献
15.
The 1963 great Kurile earthquake was an underthrust earthquake occurred in the Kurile?CKamchatka subduction zone. The slip distribution of the 1963 earthquake was estimated using 21 tsunami waveforms recorded at tide gauges along the Pacific and Okhotsk Sea coasts. The extended rupture area was divided into 24 subfaults, and the slip on each subfault was determined by the tsunami waveform inversion. The result shows that the largest slip amount of 2.8?m was found at the shallow part and intermediate depth of the rupture area. Large slip amounts were found at the shallow part of the rupture area. The total seismic moment was estimated to be 3.9?×?1021?Nm (Mw 8.3). The 2006 Kurile earthquake occurred right next to the location of the 1963 earthquake, and no seismic gap exists between the source areas of the 1963 and 2006 earthquakes. 相似文献
16.
K–Ar ages of the Cenozoic basaltic rocks from the Far East region of Russia (comprising Sikhote-Alin and Sakhalin) are determined to obtain constraints on the tectono-magmatic evolution of the Eurasian margin by comparison with the Japanese Islands, Northeast China, and the formation of the back-arc basin. In the early Tertiary stage (54–26 Ma), the northwestward subduction of the Pacific Plate produced the active continental margin volcanism of Sikhote-Alin and Sakhalin, whereas the rift-type volcanism of Northeast China, inland part of the continent began to develop under a northeast–southwest-trending deep fault system. In the early Neogene (24–17 Ma), a large number of subduction-related volcanic rocks were erupted in connection with the Japan Sea opening. After an inactive interval of the volcanism ∼ 20–13 Ma ago, the late Neogene (12–5 Ma) volcanism of Sikhote-Alin and Sakhalin became distinct from those of the preceding stages and indicated within-plate geochemical features similar to those of Northeast China, in contrast to the Japan Arc which produces island arc volcanism. During the Japan Sea opening, the northeastern Eurasian margin detached and became a continental island arc system, and an integral part of continental eastern Asia comprising Sikhote-Alin, Sakhalin and Northeast China, and the Japan Arc with a back-arc basin. The convergence between the Eurasian Plate, the Pacific Plate and the Indian Plate may have contributed to the Cenozoic tectono-magmatism of the northeastern Eurasian continent. 相似文献
17.
We investigated the upper mantle anelastic structure beneath the northern Philippine Sea region, including the Izu-Bonin subduction zone and the Shikoku Basin. We used regional waveform data from 69 events in the Pacific and the Philippine Sea slabs, recorded on F-net and J-array network broadband stations in western Japan. Using the S–P phase pair method, we obtained differential attenuation factors, δt*, which represent the relative whole path Q. We conducted a tomographic inversion using 978 δt* values to invert for a fine-scale (50–100 km) three-dimensional anelastic structure.
The results shows two high-Q regions (QP>1000) which are consistent with the locations of the Pacific and the Philippine Sea slabs. Also there is a low-Q (QP110) area extending to the deeper parts (350–400 km) of the model just beneath the old spreading center and the Kinan Seamount Chain in the Shikoku Basin. A small depth dependence of the laterally averaged QP was found, with values of 266 (0–250 km), 301 (250–400 km), and 413 (400–500 km). 相似文献
18.
The aseismic Willaumez-Manus Rise on the Bismarck Sea floor separates the Manus Basin from the New Guinea Basin. The rise does not appear to be an extinct spreading axis, or a remnant arc, but may be the result of excess magmatism possibly related to an inferred mantle hot spot beneath St. Andrew Strait. A preferred interpretation is that the rise is the raised edge of the New Guinea Basin, formed in response to a thermal anomaly beneath the extensional Manus Basin which formed later than the New Guinea Basin. 相似文献
19.
通过地震分布及地震机制解所反映的日本海-鄂霍次克海俯冲带的形态及应力状态,研究了俯冲带深部形变及650km间断面的穿透问题.日本海Benioff带较直,连续性较好;鄂霍次克海Benioff带弯度稍大,220-320km深度之间地震很少.两俯冲带在浅部及深部地震密集,100-200km深度之间有双地震层.应力状态随深度变化,200km深度以下P,T轴方向相对集中,P轴接近俯冲方向,在约100-200km深度附近,P,T轴均接近俯冲方向.观测和理论地震图拟合分析表明,地震断层面走向接近俯冲带走向,断裂的结果使俯冲带在深部倾角变小. 相似文献
20.
Global tectonics and the plate motion obtained from the ITRF97 station velocity vectors 总被引：2，自引：0，他引：2
~~Global tectonics and the plate motion obtained from the ITRF97 station velocity vectors@马宗晋
@任金卫
@张进~~ 相似文献