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1.
Abstract Based on a field analysis of slip vectors from Cretaceous and Tertiary rocks and coupled with rift basin analysis in north China, the Cenozoic deformation history of the Tancheng–Lujiang (Tan–Lu) Fault Zone can be divided into three main phases: early Tertiary normal faulting and northwest–southeast extension; Miocene normal faulting and northeast–southwest to north‐northeast–south‐southwest extension; and Quaternary dextral strike–slip faulting and east‐northeast transpression. The early Tertiary extension, which was responsible for rift basin formation in north China, originated from back‐roll mantle convection induced by westward subduction of the Pacific Plate beneath the Asia continent. The Miocene extension occurred possibly in association with the process of the Japan Sea opening. The Quaternary dextral slip was mainly localized along the middle part of the Tan–Lu Fault Zone and resulted from the far‐field effect of the late‐stage India–Eurasia convergence.  相似文献   

2.
The origin of active faults in the Inner zone of the western part of Southwest Japan was explained by a decrease of the minimum principal stress and reactivation of ancient geologic structures. Although the E–W maximum principal stress in Southwest Japan due to the collision of the Southwest and Northeast Japan arcs along the Itoigawa–Shizuoka Tectonic Line is assumed to decrease westward, the density of active strike‐slip faults increases in the western margin of the Southwest Japan Arc (western Chugoku and northern Kyushu) where the subducting Philippine Sea Plate dips steeply. The E–W maximum compressional stress is predominant throughout Southwest Japan, while the N–S minimum principal stress that is presumably caused by coupling between Southwest Japan arc and Philippine Sea Plate decreases due to the weak plate coupling as the plate inclination increases under the western margin of Southwest Japan. The increase of the fault density in the western margin of the arc is attributed to a decrease of the minimum principal stress and consequent increase of shear stress. Low slip rates of the active faults in this region support the view that the westward increase of fault density is not a response to increasing maximum stress. These faults of onshore and offshore lie in three distinct domains defined on the basis of fault strike. They are defined domains I, II, and III which are composed of active faults striking ENE–WSW, NW–SE, and NE–SW, respectively. Faulting in domains I, II, and III is related to Miocene rift basins, Eocene normal faults, and Mesozoic strike‐slip faults, respectively. Although these active faults are strike‐slip faults due to E–W maximum stress, it is unclear whether their fault planes are the same as those of pre‐Quaternary dip‐slip faults.  相似文献   

3.
New paleomagnetic data from shallow-marine sediments of the Ichishi Group suggest a clockwise tectonic rotation of Southwest Japan in the Middle Miocene. Samples have been collected from mud or tuff layers at 17 sites. Stability of remanent magnetization has been examined by using alternating field and thermal demagnetization. The polarity sequence, composed of four normal and seven reversed polarity sites, is correlated to Polarity Epoch 16 (15.2–17.6 Ma), based on micropaleontological assignment of the upper Ichishi Group to Blow's Zone N8. The mean paleomagnetic direction of the 11 sites shows an anomalous declination toward the northeast. This result suggests that Southwest Japan was subjected to a clockwise rotation through 45° since 16 Ma. The clockwise rotation can be explained by the drift of Southwest Japan associated with the spreading of the Japan Sea during the Middle Miocene.  相似文献   

4.
Yong I. Lee 《Island Arc》2008,17(4):458-470
The currently available paleogeographic maps of the East Asia continental margin during the Mesozoic have been recast in the light of recent research results on sediments distributed in Korea and Japan. Both the Korean peninsula and the Inner zone of Southwest Japan exchanged sediment supply during the Middle to Late Mesozoic, suggestive of a close paleogeographic relationship between the two countries at the active continental margin setting. During the latest Middle to earliest Late Jurassic the Mino–Tamba trench was developed along the southeastern Korean peninsula, from which trench‐fill sediments were sourced and to which an accretionary complex was accreted. Lower Cretaceous quartz‐arenite clasts of the Tetori Group in the Hida Marginal Belt of Southwest Japan were derived from pre‐Mesozoic quartz‐arenite strata distributed in the southern central and east central Korean peninsula, suggesting that the Tetori Basin was located close to the central eastern part of the Korean peninsula at the time of deposition of quartz‐arenite clasts, contrary to conventional thought of far distance between the two areas based on paleomagnetic data. During the early Late Cretaceous radiolaria‐bearing chert pebbles and sands in the northern part of the non‐marine Gyeongsang Basin distributed in the southeastern Korean peninsula were derived from the uplifted Mino–Tamba accretionary complex distributed in southwest Japan, suggesting that the Mino–Tamba terrane was land‐connected with the eastern Korean peninsula. These new findings suggest that in contrast to conventional thought, the collage of tectonic blocks in Southwest Japan has assembled in post‐early Late Cretaceous time.  相似文献   

5.
In this work we analyze the tectonic setting of the recent damaging seismic series occurred in the Internal Zones of the eastern Betic Cordillera (SE Spain) and surrounding areas, the tectonic region where took place the 11th May 2011 Mw 5.2 Lorca earthquake. We revisit and make a synthesis of the seven largest and damaging seismic series occurred from 1984 to 2011. We analyze their seismotectonic setting, and their geological sources under the light of recent advances in the knowledge on active faults, neotectonics, seismotectonics and stress regime, with special attention focused on the Lorca Earthquake. These seismic series are characterized by two types of focal mechanisms, produced mainly by two sets of active faults, NNW–SSE to NNE–SSW small (no larger than 20–30 km) extensional faults with some strike slip component, and E–W to NE–SW large strike slip faults (more than 50 km long) with some compressional component (oblique slip faults). The normal fault earthquakes related to the smaller faults are dominant in the interior of large crustal tectonic blocks that are bounded by the large E–W to NE–SW strike-slip faults. The strike slip earthquakes are associated to the reactivation of segments or intersegment regions of the large E–W to NE–SW faults bounding those crustal tectonic blocks. Most of the seismic series studied in this work can be interpreted as part of the background seismicity that occurs within the crustal blocks that are strained under a transpressional regime driven by the major strike slip shear corridors bounding the blocks. The seismotectonic analysis and the phenomenology of the studied series indicate that it is usual the occurrence of damaging compound earthquakes of M  \(\sim \)  5.0 associated with triggering processes driven by coseismic stress transfer. These processes mainly occur in the seismic series generated by NNW–SSE to NNE–SSW faults. These mechanical interaction processes may induce a higher frequency of occurrence of this kind of earthquakes than considered in traditional probabilistic seismic hazard assessments and it should be taken into account in future seismic hazard assessments.  相似文献   

6.
利用断层滑动资料反演构造应力张量从而确定出海原、六盘山断裂带至银川断陷的第四纪两期构造应力场 :早更新世末期以前 ,为北东—南西挤压型构造应力场 ,由此造成该地区断裂活动主要以逆断为主 ;早更新世末期至中更新世以后 ,构造应力场发生了调整 ,主压应力方向由早期的北东—南西改变为北东东—南西西 ,应力结构由挤压型转变为走滑型 ,并导致断裂活动由早期的逆断为主变为走滑为主 ,这种应力场格局一直持续至今。研究区现代构造应力场可划分为 :海原断裂带走滑应力区、六盘山逆断 -走滑混合应力区和银川断陷拉张应力区  相似文献   

7.
A NNW-trending belt of alkaline mafic volcanic fields parallels the Gulf of Mexico from the U.S. border southward to Veracruz state, in eastern Mexico. Previous studies grouped this volcanism into the so-called “Eastern Alkaline Province” (EAP) and suggested that it resulted from Gulf-parallel extensional faulting migrating from north to south from Oligocene to Present. On the basis of new geologic studies, forty-nine unspiked K–Ar and two 40Ar–39Ar ages, we propose a new geodynamic model for the volcanism along the southwestern Gulf of Mexico.We studied in detail four of the six recognized fields of mafic alkaline volcanism in Veracruz state: 1) The lavas flows of Tlanchinol area (7.3–5.7 Ma), 2) the Alamo monogenetic field and Sierra de Tantima (7.6–6.6 Ma), 3) the Poza Rica and Metlatoyuca lava flows (1.6–1.3 Ma) and 4) the Chiconquiaco–Palma Sola area (6.9–3.2 Ma). Other two mafic volcanic fields may represent the continuation of alkaline volcanism to the southeast: the Middle Miocene lavas at Anegada High, offshore port of Veracruz, and the Middle to Late Miocene volcanism at the Los Tuxtlas.The existence of major Neogene extensional faults parallel to the Gulf of Mexico (i.e., ∼N–S to NNW–SSE) proposed in previous works was not confirmed by our geological studies. Elongation of volcanic necks, vent alignment, and faults mapped by subsurface data trend dominantly NE to ENE and NW to NNW. These directions are parallel to transform and normal faults that formed during the Late Jurassic opening of the Gulf of Mexico. Ascent of mafic magmas was likely facilitated and controlled by the existence of these pre-existing basement structures.Coupled with previous studies, our data demonstrate the occurrence of three magmatic episodes in Veracruz: 1) A Middle Miocene (∼15–11 Ma) episode in southern Veracruz (Palma Sola, Anegada, and Los Tuxtlas); 2) A Late Miocene to Early Pliocene (∼7.5–3 Ma) pulse of mafic alkaline volcanism throughout the study region; and 3) A Late Pliocene to Quaternary transitional to calc–alkaline volcanism in southern Veracruz (Palma Sola, Los Tuxtlas). Whereas the first and third episodes may be considered part of the subduction-related Trans-Mexican Volcanic Belt, the second pulse of mafic alkaline volcanism has a more complex origin. The absence of significant extensional faulting precludes a rift origin. We favor a model in which a transient thermal anomaly and melting of the mantle was triggered by the tearing and detachment of part of the subducted slab.  相似文献   

8.
滇西南地区现代构造应力场分析   总被引:36,自引:5,他引:36       下载免费PDF全文
利用断层滑动资料反演构造应力张量的方法,获得滇西南地区20个构造应力张量数据,并通过与由震源机制解资料求解该地区平均应力场结果的对比,获得了研究区现代构造应力场特征:镇源——营盘山断裂以西至龙陵断裂带以南地区,最大主压应力方向为北北东,应力结构以走滑型为主;龙陵断裂带及其以北的局部地区,最大主压应力方向为近南北或北北西,应力结构为走滑型.   相似文献   

9.
王华林  侯珍清 《地震研究》1994,17(1):79-107
昌马断裂带是是青藏高原北部一条活动强烈的左旋走滑断裂带。它表现为重力、航磁、地壳厚度的综合异常梯度带,属于断面陡、切割深的超岩石圈断裂。昌马断裂带由12条长4公里至18公里不等的不连续的主断层和4条次级断层组成,可划分为东、中、西三大段落。断裂的水平位移和滑动速率具有分段性,全新世以来,东、中、西三段的左旋水平滑动速率分别为4.1毫米/年,2.6毫米/年和1.5毫米/年。北东东、北北西和北西西三个方向断层的位移具有分级特征,不同级别的位移具有良好的同步性。全新世以来北东东、北北西和北西西三个方向断层的水平滑动速率分别为4.1毫米/年、3.8毫米/年和2.7毫米/年。白垩纪以来,昌马断裂呈天平式运动,显示了枢纽断裂运动特征,枢纽轴位于断裂中段。昌马地震震源破裂性质及其反映的震源应力场与地震破裂带的破裂性质及其反映的构造应力场不一致。昌马地震震源机制解反映了北北西~南南东挤压,作用应力近于水平的震源应力场;昌马地震破裂带的变形组合反映了东北~南西挤压的构造应力场。昌马地震破裂带长120公里,分为东部正走滑段、中部逆走滑段和西部尾端破裂段,显示了多个水平位移峰值。全新世以来,沿昌马断裂发生了6次强震事件,强震复发  相似文献   

10.
The evidence of east-west compression in northeast Japan has been reported by many investigators on the basis of geodetic, geologic and geomorphic data, but its origin still remains far from understood. In the present study we have proposed a mechanical model of tectonic loading at convergent plate boundary zones, and demonstrated its validity through the numerical simulation of internal stress fields in northeast Japan with realistic 3-D geometry of plate interfaces. At convergent plate boundary zones, in general, a part of plate convergence is consumed by steady slip along plate interfaces, and the remaining part by inelastic deformation (seismic faulting, aseismic faulting, and active folding) of overriding plates. Such a plate boundary process to be called ``partial collision' can be quantitatively described by introducing a collision rate defined as c = 1 − steady slip rate at plate interfaces/plate convergence rate. By this definition, we can simply represent the mechanical process of partial collision, which includes total subduction (c = 0) and total collision (c = 1) as two extreme cases, in terms of steady slip rates at plate interfaces. On the basis of elastic dislocation theory, first, we numerically computed the internal stress fields in northeast Japan produced by the total subduction of the Pacific plate beneath the North American plate, however the computed stress pattern was opposite in sense to observations. Then, we computed the internal stress fields by taking c = 0.1 on average, and succeeded in reproducing the observed east-west compression in northeast Japan. This indicates that the concept of partial collision is essential to understand the mechanism of intraplate tectonic loading.  相似文献   

11.
Abstract In northern Kazakhstan the WNW striking Kokchetav megamélange includes different crustal sequences with high‐pressure/ultrahigh‐pressure (HP/UHP) remnants of their 540–520 Ma subduction metamorphism. Two domains separated by the north‐east trending Chaglinka fault are distinguished. The western domain exhibits NE–SW structures within a single Kumdy–Kol megaunit of diamond‐bearing UHP metasediments and high‐temperature (HT) eclogites. The eastern domain consists of the composite Kulet megaunit with the Kulet UHP unit (coesite‐bearing metasediments, whiteschists and eclogites), the Enbek–Berlyk medium‐pressure (MP) unit (kyanite‐bearing, high‐alumina rocks with interleaved coronitic metagabbro), and ortho‐ and paragneisses with eclogites and amphibolites included. All eclogites in the eastern domain are of the relatively low temperature (LT) type. Sillimanite is common and appears after kyanite in the sheared MP unit. A regional and moderately ESE plunging linear fabric coincides with the fold‐axis of the foliation poles from the eastern domain. Whether this also reflects a regional top to the WNW transport, as inferred from the dextral strike‐slip on steeply to SSW dipping foliation, needs further study. Top to the WNW shear is shown by weakly inclined low pressure (LP) cordierite rocks that flank the eastern domain in the south. Some new 39Ar/40Ar mica cooling ages (519, 521 Ma) from the Kulet UHP micaschists reflect the same early stage evolutionary event as was previously shown for the Kumdy–Kol UHP rocks (515, 517 Ma) in the west. Similar 39Ar/40Ar ages (500, 517 Ma) are recorded by micas and amphibole that outline a top to NNW shear fabric in the non‐subducted Proterozoic basement, north of the megamélange. A 447 Ma overprint of the MP sequences is considered to reflect the strike‐slip deformation with sillimanite and the reworking of an early kyanite‐bearing tectonite. Biotites from the LP cordierite rocks yielded approximately 400 Ma 39Ar/40Ar ages. In case they reflect the WNW shear deformation, the latter is considered to be associated with a regional granite magmatism (420–460 Ma) extending south of the eastern domain. In their present different structural domains the Kulet and Kumdy–Kol UHP units display a similar early stage event. Subsequent LP deformation, which is likely to be associated with regional granite magmatism (420–460 Ma), is assumed to have obliterated any common or uniform early exhumation structure for the whole megamélange. The north‐east structured Kumdy–Kol domain is assumed to have preserved the most information about the early stage exhumation. This domain is at an angle to the regional WNW strike of the megamélange.  相似文献   

12.
为了研究海沟型巨大地震发生机制及其构造动力学特征,详细研究了地震活动与震源机制结果,根据地震俯冲带几何形状及其内应力场区域特征,南海海槽下的俯冲带可划分为两段: 东部的四国-纪伊半岛段和西部的九州段. 东部的菲律宾海板块地震俯冲带呈现出低角度俯冲(10°~22°),且俯冲深度相当浅(60~85km)的特征;而西部九州段的俯冲带为高角度俯冲(40°),且俯冲深度较深(160km). 东、西部俯冲带内部应力场也截然不同. 东部的四国大部分地区和纪伊半岛的俯冲带内表现为俯冲压缩型应力场, 而西部的九州段则为明显的俯冲拉张型应力场. 本文在综合分析了重力异常、GPS、热流量等地球物理观测结果后指出,南海海槽东部, 即四国-纪伊半岛以南的海槽区域, 具有与智利海沟极其相似的地震发生板块构造动力学背景和高应力积累等特征, 属于年轻活动俯冲带的高应力型俯冲. 而西部的九州段,虽然也是海沟型地震活动区, 但不具有大地震发生的构造动力学背景和高应力积累, 不属于年轻活动俯冲带的高应力型俯冲. 俯冲带年龄的不同很可能是造成南海海槽东、西段板块构造动力学以及应力场不同的根本原因之一.  相似文献   

13.
The horizontal movement of the Helan Shan west-piedmont fault is important to determination of the present-day boundary between the Alashan and North China blocks as well as to the exploration of the extent of the northeastward expansion of the Tibetan plateau. Field geological surveys found that this fault cuts the west wing of the Neogene anticline, which right-laterally offset the geological boundary between Ganhegou and Qingshuiying Formations with displacement over 800m. The secondary tensional joints (fissures)intersected with the main faults developed on the Quaternary flood high platform near the fault, of which the acute angles indicate its dextral strike slip. The normal faults developed at the southern end of the Helan Shan west-piedmont fault show that the west wall of this fault moves northward, and the tensional adjustment zone formed at the end of the strike slip fault, which reflects that the horizontal movement of the main fault is dextral strike slip. The dextral dislocation occurred in the gully across the fault during different periods. Therefore, the Helan Shan west-piedmont fault is a dextral strike slip fault rather than a sinistral strike slip fault as previous work suggested. The relationship between the faulting and deformation of Cenozoic strata demonstrates that there were two stages of tectonic deformation near the Helan Shan west-piedmont fault since the late Cenozoic, namely early folding and late faulting. These two tectonic deformations are the result of the northeastward thrust on the Alashan block by the Tibet Plateau. The influence range of Tibetan plateau expansion has arrived in the Helan Shan west-piedmont area in the late Pliocene leading to the dextral strike slip of this fault as well as formation of the current boundary between the Alashan and North China blocks, which is also the youngest front of the Tibetan plateau.  相似文献   

14.
Alternating chert–clastic sequences juxtaposed with limestone blocks, which are units typical of accretionary complexes, constitute the Buruanga peninsula. New lithostratigraphic units are proposed in this study: the Unidos Formation (Jurassic chert sequence), the Saboncogon Formation (Jurassic siliceous mudstone–terrigenous mudstone and quartz‐rich sandstone), the Gibon Formation (Jurassic(?) bedded pelagic limestone), the Libertad Metamorphics (Jurassic–Cretaceous slate, phyllite, and schist) and the Buruanga Formation (Pliocene–Pleistocene reefal limestone). The first three sedimentary sequences in the Buruanga peninsula show close affinity with the ocean plate stratigraphy of the North Palawan terrane in Busuanga Island: Lower–Middle Jurassic chert sequences overlain by Middle–Upper Jurassic clastics, juxtaposed with pelagic limestone. Moreover, the JR5–JR6 (Callovian to Oxfordian) siliceous mudstone of the Saboncogon Formation in the Buruanga peninsula correlates with the JR5–JR6 siliceous mudstone of the Guinlo Formation in the Middle Busuanga Belt. These findings suggest that the Buruanga peninsula may be part of the North Palawan terrane. The rocks of the Buruanga peninsula completely differ from the Middle Miocene basaltic to andesitic pyroclastic and lava flow deposits with reefal limestone and arkosic sandstone of the Antique Range. Thus, the previously suggested boundary between the Palawan microcontinental block and the Philippine Mobile Belt in the central Philippines, which is the suture zone between the Buruanga peninsula and the Antique Range, is confirmed. This boundary is similarly considered as the collision zone between them.  相似文献   

15.
The Atlantic Moroccan Meseta margin is affected by far field recent tectonic stresses. The basement belongs to the variscan orogen and was deformed by hercynian folding and metamorphism followed by a post-Permian erosional stage, producing the flat paleorelief of the region. Tabular Mesozoic and Mio-Plio-Quaternary deposits locally cover the Meseta, which has undergone recent uplift, while north of Rabat the subsidence continues in the Gharb basin, constituting the foreland basin of the Rif Cordillera.The Plio-Quaternary sedimentary cover of the Moroccan Meseta, mainly formed by aeolian and marine terraces deposits, is affected by brittle deformations (joints and small-scale faults) that evidence that this region – considered up to date as stable – is affected by the far field stresses. Striated faults are recognized in the oldest Plio-Quaternary deposits and show strike-slip and normal kinematics, while joints affect up to the most recent sediments.Paleostress may be sorted into extensional, only affecting Rabat sector, and three main compressive groups deforming whole the region: (1) ENE–WSW to ESE–WNW compression; (2) NNW–SSE to NE–SW compression and (3) NNE–SSW compression. These stresses can be attributed mainly to the NW–SE oriented Eurasian-African plate convergence in the western Mediterranean and the escape toward the SW of the Rif Cordillera. Local paleostress deviations may be related to basement fault reactivation. These new results reveal the tectonic instability during Plio-Quaternary of the Moroccan Meseta margin in contrast to the standard passive margins, generally considered stable.  相似文献   

16.
红河断裂带大型右旋走滑运动与伴生构造地貌变形   总被引:19,自引:2,他引:17       下载免费PDF全文
调查研究表明,自中新世以来,红河断裂大规模右旋走滑运动及其伴生构造变形有如下一些主要特征在几何结构上,可将整个红河断裂系分为北、中、南3个变形区。北区东侧为滇西北伸展裂陷区,以轴向NNW,NNE和近SN向3组上新世以来的裂陷型断盆为特征,北段西侧为兰坪—云龙古近纪、新近纪压缩变形区;中段变形以右旋剪切走滑运动为特征,南部断裂东侧有滇东中新世以来的压缩变形,西侧为藤条河中新世拉伸断陷区。上述变形特征反映在构造地貌上为北部盆岭构造、中段线性断谷断盆构造及南部压(张)性盆地变形,其中苍山—洱海一带断裂两侧主夷平面的巨大落差是红河断裂上新世以来断陷正断作用的显著代表。在时空演化上,从古近纪经中新世至上新世,断裂主体活动部位在南段,并呈由南向北的“撕裂”格局,上新世以后至第四纪,尤其是晚第四纪以来,主体活动部位已转移至北段,表现为由N向SE的滑移伸展变形;变形区的范围大小和变形幅度表明红河断裂的东盘地块始终是作为地块相对运动的主动盘  相似文献   

17.
The Chi‐Chi earthquake (MW = 7.6) took place in central western Taiwan in 1999. The earthquake caused reactivation of the Chelungpu Fault and resulted in 100‐km‐long surface ruptures. The fault strikes mostly north–south to NNE–SSW; however, the northern tip of the southern segment of the surface ruptures rotates clockwise to define an east–west trend, then jumps to a shorter NNW‐trending rupture. The largest vertical displacement is recorded in the Shihkang area of the Shihkang–Shangchi Fault Zone, where vertical slips are up to 8–10 m. The Shihkang–Shangchi Fault Zone displays a complex fault pattern as a linkage damage zone between two fault segments with the greatest concentration of faults and fractures. Our new interpretation, based on recent published geometric, kinematic, and geophysical studies on the Chi‐Chi earthquake fault, suggests that the Shihkang–Shangchi Fault Zone is not a simple termination zone, but may be an ‘overstep zone’ or a ‘transfer zone’. Slip analysis along the surface ruptures indicates that they are composed of three fault segments and the amount of slip partly depends on the intersection angle between slip direction and fault strike. Our numerical modeling for the area indicates that Coulomb stress changes are mainly concentrated on tips and bends of the surface ruptures. Slip patterns indicate that the fault propagates toward the northeast. Therefore, this study suggests high potential for future earthquake activity along the unruptured Shangchi segment. Hence, future geohazard studies should focus on the Shangchi segment to evaluate potential earthquakes, determine recurrence intervals, and reduce future earthquake hazards.  相似文献   

18.
The Andaman–Sumatra margin displays a unique set‐up of extensional subduction–accretion complexes, which are the Java Trench, a tectonic (outer arc) prism, a sliver plate, a forearc, oceanic rises, inner‐arc volcanoes, and an extensional back‐arc with active spreading. Existing knowledge is reviewed in this paper, and some new data on the surface and subsurface signatures for operative geotectonics of this margin is analyzed. Subduction‐related deformation along the trench has been operating either continuously or intermittently since the Cretaceous. The oblique subduction has initiated strike–slip motion in the northern Sumatra–Andaman sector, and has formed a sliver plate between the subduction zone and a complex, right‐lateral fault system. The sliver fault, initiated in the Eocene, extended through the outer‐arc ridge offshore from Sumatra, and continued through the Andaman Sea connecting the Sagaing Fault in the north. Dominance of regional plate dynamics over simple subduction‐related accretionary processes led to the development and evolution of sedimentary basins of widely varied tectonic character along this margin. A number of north–south‐trending dismembered ophiolite slices of Cretaceous age, occurring at different structural levels with Eocene trench‐slope sediments, were uplifted and emplaced by a series of east‐dipping thrusts to shape the outer‐arc prism. North–south and east–west strike–slip faults controlled the subsidence, resulting in the development of a forearc basins and record Oligocene to Miocene–Pliocene sedimentation within mixed siliciclastic–carbonate systems. The opening of the Andaman Sea back‐arc occurred in two phases: an early (~11 Ma) stretching and rifting, followed by spreading since 4–5 Ma. The history of inner‐arc volcanic activity in the Andaman region extends to the early Miocene, and since the Miocene arc volcanism has been associated with an evolution from felsic to basaltic composition.  相似文献   

19.
Miocene igneous dikes older and younger than 15 Ma in Southwest Japan are thought to be oriented parallel and perpendicular to the arc, respectively. This difference of orientations was referred to as significant evidence for termination of the opening of the Japan Sea at 15 Ma. The tightest constraint comes from ~60 dikes in the Tajima–Myokensan area, northern Hyogo Prefecture. Here we present orientations of 716 planar intrusive bodies and the directions of 143 meso-scale faults, obtained using the latest stress inversion techniques from the lower to middle Miocene Hokutan Group in the Tajima–Myokensan area. The results contradict the 15 Ma hypothesis for the end of the opening of the Japan Sea. We find that intrusive bodies cannot be separated into two groups by their orientations as reported previously. Rather, the orientations of their poles comprise a horizontal girdle and a vertical cluster. The former indicates NE-SW extensional stress, and the latter NW-SE compression. However, the latter are interpreted as not representative of regional stress, based on common sill intrusions (the formation of which was not influenced by regional stress) in the well-stratified Muraoka Formation resulting in the vertical cluster of pole orientations from which compression was recognized. The results of fault-slip analysis are consistent with the extensional stress. Fission-track and U–Pb ages of zircons were obtained from seven intrusive bodies. These and previously published ages suggest that the area underwent NW-SE extension both before and after 15 Ma. In the main part of Southwest Japan, the weak extension was kept after 16 Ma when intra-arc rifting was terminated. This is consistent with the hypothesis that the Japan Sea continued to open until 13.5 Ma.  相似文献   

20.
Significant advances were made in the last century in the investigations of the Neogene stress history of the NE Japan arc. However, previous studies have failed to fully resolve middle Miocene post‐rift stress conditions owing to their assumption of Andersonian faulting and an inability to determine maximum and intermediate stress axes from dike orientations. We applied the latest methods of paleostress analysis in this study to igneous dikes and mesoscale faults in the Kakunodate area of the NE Japan arc to elucidate post‐rift stress conditions. Stratigraphic constraints and U–Pb dating indicate that the doleritic and dacitic dikes were formed at 16–12 Ma and 15–12 Ma, respectively. Dolerite and dacite dikes yielded NW–SE extensional stresses with intermediate and low stress ratios, respectively. Mesoscale faults in the middle Miocene formations of the studied area indicated similar stresses. We suggest the sluggish deformations resulting in the dike intrusion and faulting in the normal‐faulting stress regime after the termination of intra‐arc rifting at ca. 15 Ma.  相似文献   

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