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1.
《International Geology Review》2012,54(14):1803-1821
ABSTRACT

In the Central Anatolia, the style of neotectonic regime governing the region has been a controversial issue. A tectonic study was carried out in order to contribute to this issue and better understand the neotectonic stress distribution and style of deformation in the west-southwest of the Konya region. From Middle Miocene to Recent time, Konya region was part of the Central Anatolia extensional province. The present-day topography in the west-southwestern part of Konya is characterized by alternating elongate grabens and horsts trending E-W and NW-SE. The grabens were developed upon low-grade metamorphic rocks of Palaeozoic and Mesozoic ages and ophiolite slabs of possibly Late Cretaceous age. The evolutionary history of grabens is episodic as evidenced by two graben infills; older and younger graben infills separated by an angular unconformity. The older infill consists of fluviolacustrine sequence intercalated with calc-alkaline lavas and pyroclastic rocks. This infill is folded; thrust faulted and Middle Miocene-Early Pliocene in age. The younger and undeformed basin fill comprises mainly of Plio-Quaternary conglomerates, sandstone-mudstone alternations of alluvial fan and recent basin floor deposits. Three major tectonic phases were differentiated based on the detailed mapping, morphological features and kinematic analysis. Approximately N-S trending extension began in the Middle Miocene-Early Pliocene in the region with the formation of E-W and NW-SE-trending grabens. Following NE-SW-directed compression which deformed the older basin fill deposits by folding and thrusting, a second period of ENE-WSW-trending extension began in the late Pliocene and continued to the present. The west-southwestern margin of the Konya depression is bounded by the Konya Fault Zone. It is an oblique-slip normal fault with a minor dextral strike-slip component and exhibits well-preserved fault slickensides and slickenlines. Recent seismicity and fault-related morphological features reveal that the Konya Fault Zone is an active neotectonic structure.  相似文献   

2.
The study area is the Van earthquake region. It is located in the western section of the East Anatolian–Iranian plateau outside and to the east of the Karlıova triple junction. Based on the tectonic periods, the rock units exposed in the study area are classified into two common categories. These are the Pre-Late Pliocene paleotectonic units and the Plio-Quaternary neotectonic units. The Paleotectonic units are composed of the Yüksekova Complex of Campanian–Maastrichtian age and the Kırkgeçit Formation of Oligo-Miocene age. The paleotectonic units are intensely deformed (folded, thrust to reverse faulted and converted into an imbricate stack). The neotectonic units are composed of fluvio-lacustrine sedimentary facies with volcanic interclations. It is full of soft-sedimentary structures such as deltaic structure, slump fold, sand dikes to sills and normal to reverse types of growth faults which imply to a sedimentation accompanied by both a volcanic activity and active tectonics. Originally the Paleotectonic units are overlain with an angular unconformity by the nearly flat-lying neotectonic units. This angular unconformity and the big difference in the deformational patterns of both categories of rock units indicate an inversion in tectonic regime in Late Pliocene. The new tectonic regime is the strike-slip faulting-dominated neotectonic regime. It is governed by an approximately N–S-directed compression, and composed of NW- to NE-trending strike-slip faults, N–S trending oblique-slip normal faults to fissures and the E–W trending thrust to reverse faults. Most of thrust to reverse faults are inherited from the Pre-Late Pliocene paleotectonic regime. Some of them have reactivated and led to the occurrence of large and devastative earthquakes. The last devastative seismic event is the 23 October 2011 Tabanlı (Van) earthquake of Mw = 7.2 that caused 644 deaths and moderate to heavy damage of ¼ of structures (28,532) in Van earthquake region. The source of the Tabanlı earthquake is the Everek erosional reverse fault. In addition the Tabanlı earthquake is the largest seismic event occurred till now in Turkey. It was followed by a series (over 6000) of small-sized aftershocks and severeal moderate-sized indepentent earthquakes of reverse, normal and strike-slip faulting origin. Both the field and new seismic data strongly reveal that the prominent tectonic regime in the East Anatolian plateau is the strike-slip neotectonic regime, not the tensional tectonic regime as has been reported in some previous works. The strike-slip faulting and related deformation are confined into the upper shallowing part (up to 40 km) of the crust, whilst the extensional deformations are the subcrustal processes and being taking place in a squashy zone at the depths of approximately 40–60 km.  相似文献   

3.
《Geodinamica Acta》2001,14(1-3):45-55
Field studies on the Neogene successions in south of İzmir reveal that subsequent Neogene continental basins were developed in the region. Initially a vast lake basin was formed during the Early–Middle Miocene period. The lacustrine sediments underwent an approximately N–S shortening deformation to the end of Middle Miocene. A small portion of the basin fill was later trapped within the N–S-trending, fault-bounded graben basin, the Çubukludağ graben, opened during the Late Miocene. Oblique-slip normal faults with minor sinistral displacement are formed possibly under N–S extensional regime, and controlled the sediment deposition. Following this the region suffered a phase of denudation which produced a regionwide erosional surface suggesting that the extension interrupted to the end of Late Miocene–Early Pliocene period. After this event the E–W-trending major grabens and horsts of western Anatolia began to form. The graben bounding faults cut across the Upper Miocene–Pliocene lacustrine sediments and fragmented the erosional surface. The Çubukludağ graben began to work as a cross graben between the E–W grabens, since that period.  相似文献   

4.
《International Geology Review》2012,54(12):1401-1418
The Neogene–Quaternary succession in the Kütahya region is of importance in the neotectonic evolution of western Anatolia because the strata contain clear evidence of compression and extension. During the early-middle Miocene, N–S compression/transpression as well as NE–SW- and NW–SE-oriented oblique conjugate faults formed. NE–SW-oriented horsts and grabens developed, controlled by the dominant NE–SW faults. The Seyitömer and Sabuncup?nar grabens were filled primarily by terrestrial clastic sedimentary and volcanic rocks. At the end of the middle Miocene, the graben fill was locally folded and reverse faulted, reflecting reactivation of compression. Between the late Miocene and the middle Pliocene, the region underwent erosion and lacustrine sediments accumulated in topographic lows. Between the middle and late Pliocene, compression in the region was again reactivated and basal units were thrust over the pre-upper Pliocene units. The late Plio-Quaternary marked the onset of N–S extension and development of the NW–SE-oriented Kütahya Graben, co-genetic equivalents of which are common throughout western Anatolia. This study indicates that tectonic evolution of western Anatolia involved multiple stages of contraction and extension.  相似文献   

5.
The kinematic analysis of fault-slip data obtained from lower Pliocene and Pleistocene deposits indicates two successive extensional events in the southeastern end of the Gediz graben. The late Pliocene N-S extensional phase was followed by a NNE-SSW extension in the Pleistocene. This change in extension direction from N-S to NNE-SSW is indicated by slip vectors on active fault planes and historic fault offsets. This younger extensional event is still active, as suggested by recent seismic activity and focal mechanisms of earthquakes in the region. The slip regime has important implications for the Neogene tectonic evolution of western Anatolia.  相似文献   

6.
《Geodinamica Acta》2001,14(1-3):177-195
The east Anatolian plateau and the Lesser Caucasus are characterised and shaped by three major structures: (1) NW- and NE-trending dextral to sinistral active strike-slip faults, (2) N-S to NNW-trending fissures and /or Plio-Quaternary volcanoes, and (3) a 5-km thick, undeformed Plio-Quaternary continental volcano-sedimentary sequence accumulated in various strike-slip basins. In contrast to the situation in the east Anatolian plateau and the Lesser Caucasus, the Transcaucasus and the Great Caucasus are characterised by WNW-trending active thrust to reverse faults, folds, and 6-km thick, undeformed (except for the fault-bounded basin margins) continuous Oligocene-Quaternary molassic sequence accumulated in actively developing ramp basins. Hence, the neotectonic regime in the Great Caucasus and the Transcaucasus is compressional–contractional, and Oligocene-Quaternary in age; whereas it is compressional–extensional, and Plio-Quaternary in age in the east Anatolian plateau and the Lesser Caucasus.Middle and Upper Miocene volcano-sedimentary sequences are folded and thrust-to-reverse-faulted as a result of compressional–contractional tectonic regime accompanied by mostly calc-alkaline volcanic activity, whereas Middle Pliocene-Quaternary sequences, which rest with angular unconformity on the pre-Middle Pliocene rocks, are nearly flat-lying and dominated by strike-slip faulting accompanied by mostly alkali volcanic activity implying an inversion in tectonic regime. The strike-slip faults cut and displace dykes, reverse to thrust faults and fold axes of Late Miocene age up to maximum 7 km: hence these faults are younger than Late Miocene, i.e., these formed after Late Miocene. Therefore, the time period between late Serravalian (∼ 12 Ma) continent–continent collision of Arabian and Eurasian plates and the late Early Pliocene inversion in both the tectonic regime, basin type and deformation pattern (from folding and thrusting to strike-slip faulting) is here termed as the Transitional period.Orientation patterns of various neotectonic structures and focal mechanism solutions of recent earthquakes that occurred in the east Anatolian plateau and the Caucasus fit well with the N–S directed intracontinental convergence between the Arabian plate in the south and the Eurasian plate in the north lasting since Late Miocene or Early Pliocene in places.  相似文献   

7.
Dextral-slip in the Nyainqentangiha region of Tibet resulted in oblique underthrusting and granite generation in the Early to Middle Miocene, but by the end of the epoch uplift and extensional faulting dominated. The east-west dextral-slip Gangdise fault system merges eastward into the northeast-trending, southeast-dipping Nyainqentangiha thrust system that swings eastward farther north into the dextral-slip North Damxung shear zone and Jiali faults. These faults were took shape by the Early Miocene, and the large Nyainqentangiha granitic batholith formed along the thrust system in 18.3-11.0 Ma as the western block drove under the eastern one. The dextral-slip movement ended at -11 Ma and the batholith rose, as marked by gravitational shearing at 8.6-8.3 Ma, and a new fault system developed. Northwest-trending dextral-slip faults formed to the northwest of the raisen batholith, whereas the northeast-trending South Damxung thrust faults with some sinistral-slip formed to the southeast. The latter are replaced farther to the east by the west-northwest-trending Lhunzhub thrust faults with dextral-slip. This relatively local uplift that left adjacent Eocene and Miocene deposits preserved was followed by a regional uplift and the initiation of a system of generally north-south grabens in the Late Miocene at -6.5 Ma. The regional uplift of the southern Tibetan Plateau thus appears to have occurred between 8.3 Ma and 6.5 Ma. The Gulu, Damxung-Yangbajain and Angan graben systems that pass east of the Nyainqentangiha Mountains are locally controlled by the earlier northeast-trending faults. These grabens dominate the subsequent tectonic movement and are still very active as northwest-trending dextral-slip faults northwest of the mountains. The Miocene is a time of great tectonic change that ushered in the modern tectonic regime.  相似文献   

8.
Abstract

Field studies on the Neogene successions in south of ?zmir reveal that subsequent Neogene continental basins were developed in the region. Initially a vast lake basin was formed during the early-Middle Miocene period. The lacustrine sediments underwent an approximately N-S shortening deformation to the end of Middle Miocene. A small portion of the basin fill was later trapped within the N-S-trending, fault-bounded graben basin, the Çubukluda? graben, opened during the Late Miocene. Oblique-slip normal faults with minor sinistral displacement are formed possibly under N–S extensional regime, and controlled the sediment deposition. Following this the region suffered a phase of denudation which produced a regionwide erosional surface suggesting that the extension interrupted to the end of Late Miocene–Early Pliocene period. After this event the E–W-trending major grabens and horsts of western Anatolia began to form. The graben bounding faults cut across the Upper Miocene–Pliocene lacustrine sediments and fragmented the erosional surface. The Çubukluda? graben began to work as a cross garden between the E–W grabens, since that period. © 2001 Éditions scientifiques et médicales Elsevier SAS  相似文献   

9.
Abstract

The east Anatolian plateau and the Lesser Caucasus are characterised and shaped by three major structures: (1) NW- and NE-trending dextral to sinistral active strike-slip faults, (2) N-S to NNW-trending fissures and /or Plio-Quatemary volcanoes, and (3) a 5-km thick, undeformed Plio-Quatemary continental volcanosedimentary sequence accumulated in various strike-slip basins. In contrast to the situation in the east Anatolian plateau and the Lesser Caucasus, the Transcaucasus and the Great Caucasus are characterised by WNW-trending active thrust to reverse faults, folds, and 6-km thick, undeformed (except for the fault-bounded basin margins) continuous Oligocene-Quaternary molassic sequence accumulated in actively developing ramp basins. Hence, the neotectonic regime in the Great Caucasus and the Transcaucasus is compressional-contractional, and Oligocene-Quaternary in age; whereas it is compressional-extensional, and Plio-Quatemary in age in the east Anatolian plateau and the Lesser Caucasus.

Middle and Upper Miocene volcano-sedimentary sequences are folded and thrust-to-reverse-faulted as a result of compressional- contractional tectonic regime accompanied by mostly calc-alkaline volcanic activity, whereas Middle Pliocene-Quaternary sequences, which rest with angular unconformity on the pre-Middle Pliocene rocks, are nearly flat-lying and dominated by strike-slip faulting accompanied by mostly alkali volcanic activity implying an inversion in tectonic regime. The strike-slip faults cut and displace dykes, reverse to thrust faults and fold axes of Late Miocene age up to maximum 7 km: hence these faults are younger than Late Miocene, i.e., these formed after Late Miocene. Therefore, the time period between late Serravalian (~ 12 Ma) continent-continent collision of Arabian and Eurasian plates and the late Early Pliocene inversion in both the tectonic regime, basin type and deformation pattern (from folding and thrusting to strike-slip faulting) is here termed as the Transitional period.

Orientation patterns of various neotectonic structures and focal mechanism solutions of recent earthquakes that occurred in the east Anatolian plateau and the Caucasus fit well with the N-S directed intracontinental convergence between the Arabian plate in the south and the Eurasian plate in the north lasting since Late Miocene or Early Pliocene in places. © 2001 Éditions scientifiques et médicales Elsevier SAS  相似文献   

10.
In southeastern Turkey, the NE-trending Antakya Graben forms an asymmetric depression filled by Pliocene marine siliciclastic sediment, Pleistocene to Recent fluvial terrace sediment, and alluvium. Along the Mediterranean coast of the graben, marine terrace deposits sit at different elevations ranging from 2 to 180 m above present sea level, with ages ranging from MIS 2 to 11. A multisegmented, dominantly sinistral fault lying along the graben may connect the Cyprus Arc in the west to the Amik Triple Junction on the Dead Sea Fault (DSF) in the east. Normal faults, which are younger than the sinistral ones, bound the graben’s southeastern margin. The westward escape of the continental ?skenderun Block, delimited by sinistral fault segments belonging to the DSF in the east and the Eastern Anatolian Fault in the north caused the development of a sinistral transtensional tectonic regime, which has opened the Antakya Graben since the Pliocene. In the later stages of this opening, normal faults developed along the southeastern margin that caused the graben to tilt to the southwest, leading to differential uplift of Mediterranean coastal terraces. Most of these normal faults remain active. In addition to these tectonic movements, Pleistocene sea level changes in the Mediterranean affected the geomorphological evolution of the area.  相似文献   

11.
The main exhumation of the Menderes massif, western Turkey, occurred along an originally N‐dipping Datça–Kale main breakaway fault that controlled depositions in the Kale and the Gökova basins during the Oligocene – Early Miocene interval. The isostatically controlled upward bending of the main breakaway fault brings the lower plate rocks to the surface. In the Early Miocene, E–W‐trending N‐ and S‐dipping graben‐bounding faults fragmented the exhumed, dome‐shaped massif. The development of half grabens by rolling master fault hinges has allowed further exhumation of the central Menderes massif. After the Pliocene, high‐angle normal faults cut all of the previous structures. This model suggests that the Menderes massif is a single large metamorphic core complex that has experienced a two‐stage exhumation process.  相似文献   

12.
《Geodinamica Acta》2013,26(3-4):167-208
The Denizli graben-horst system (DGHS) is located at the eastern-southeastern converging tips of three well-identified major grabens, the Gediz, the Küçük Menderes and the Büyük Menderes grabens, in the west Anatolian extensional province. It forms a structural link between these grabens and the other three NE-NW-trending grabens—the Çivril, the Ac?göl and the Burdur grabens—comprising the western limb of the Isparta Angle. Therefore, the DGHS has a critical role in the evolutionary history of continental extension and its eastward continuation in southwestern Turkey, including western Anatolia, west-central Anatolia, and the Isparta Angle. The DGHS is a 7-28-km wide, 62-km long, actively growing and very young rift developed upon metamorphic rocks of both the Menderes Massif and the Lycian nappes, and their Oligocene-Lower Miocene cover sequence. It consists of one incipient major graben, one modern major graben, two sub-grabens and two intervening sub-horsts evolved on the four palaeotectonic blocks. Therefore, the DGHS displays different trends along its length, namely, NW, E-W, NE and again E-W.

The DGHS has evolved episodically rather than continuously. This is indicated by a series of evidence: (1) it contains two graben infills, the ancient graben infill and the modern graben infill, separated by an intervening angular unconformity; (2) the ancient graben infill consists of two Middle Miocene-Middle Pliocene sequences of 660 m thickness accumulated in a fluvio-lacustrine depositional setting under the control of first NNW-SSE- and later NNE-SSW-directed extension (first-stage extension), and deformed (folded and strike-slip faulted) by a NNE-SSW- to ENE-WSW-directed phase of compression in the latest Middle Pliocene, whereas the modern graben infill consists of 350-m thick, undeformed (except for local areas against the margin-bounding active faults), nearly flat-lying fanapron deposits and travertines of Plio-Quaternary age; (3) the ancient graben infill is confined not only to the interior of the graben but is also exposed well outside and farther away from the graben, whereas the modern graben infill is restricted to only the interior of the graben. These lines of evidence imply an episodic, two-stage extensional evolutionary history interrupted by an intervening compressional episode for the DGHS.

Both the southern and northern margin-bounding faults of the DGHS are oblique-slip normal faults with minor right- and/or left-lateral strike-slip components. They are mapped and classified into six categories, and named the Babada?, Honaz, A?a??da?dere, Küçükmal?da?, Pamukkale and Kaleköy fault zones, and composed of 0.5-36-km long fault segments linked by a number of relay ramps. Total throw amounts accumulated on both the northern and southern margin-bounding faults are 1,050 m and 2,080 m, respectively. In addition, the maximum width of the DGHS and the thickness of the crust beneath it are more or less same (~ 28 km). The total of these values indicate a vertical slip rate of 0.15-0.14 mm/year and averaging 7% extension for the asymmetrical DGHS.

The master faults of the Babada?, Honaz, Küçükmal?da?, Pamukkale and Kaleköy fault zones are still active and have a potential seismicity with magnitudes 6 or higher. This is indicated by both the historical (1703 and 1717 seismic events) to recent (1965, 1976, 2000 seismic events) earthquakes sourced from margin-bounding faults and some diagnostic morphotectonic features, such as deflected drainage system, degraded alluvial fans with apices adjacent to fault traces, back-tilting of fault-bounded blocks, and actively growing travertine occurrences. The kinematic analyses of main fault-slip-plane data, Upper Quaternary fissure ridges and focal-mechanism solutions of some destructive earthquakes clearly indicate that the current continental extension (second-stage extension) by normal faulting in the DGHS continues in a (mean) 026° to 034° (NNE-SSW) direction.

Detailed and recent field geological mapping, stratigraphy of the Miocene-Quaternary basins, palaeostress analysis of fault populations and main margin-bounding faults of these basins, extensional gashes to fissures, and focal-mechanism solutions of destructive earth-quakes that have occurred in last century strongly indicate that extension is not unidirectional and confined only to western Anatolia, but also continues farther east across the Isparta Angle and west-central Anatolia, up to the Salt Lake fault zone in the east and the inönü-Eski?ehir fault zone in the north-northeast. Therefore, the term “southwest Turkey extensional province” is proposed in lieu of the term “west Anatolian extensional province”.  相似文献   

13.
基于塔里木盆地中央隆起区的地震剖面以及钻井等资料,研究了中央隆起区寒武纪的构造特征及演化。从震旦纪开始,塔里木盆地进入了区域伸展的构造背景,早-中寒武世继承震旦纪的构造格局,发育一系列的箕状断陷,控制了中央隆起区小范围内地层的发育与沉积相带的展布。半地堑的分布范围与塔里木盆地的磁异常区相一致,说明半地堑的形成受基底隐伏断裂影响。早-中寒武世之后以挤压-挠曲作用为主,对箕状断洼起到重塑的作用。结合中央隆起区寒武系的基本成藏条件,指出了中央隆起区有利的油气领域,主要包括:构造圈闭领域、隆起高部位、古城墟隆起的上寒武统以及断洼沉积的岩性地层圈闭。  相似文献   

14.
太行山隆起南段新构造变形过程研究   总被引：9，自引：0，他引：9  
基于TM遥感影像解译和断裂滑动矢量资料的野外观测,结合年轻地质体热同位素和放射性同位素年代学测试结果分析,重点描述了太行山隆起南段构造地貌特征,划分了新构造变形阶段,确定了新构造应力场及其转换历史。研究表明,新近纪以来,太行山南段经历了两期重要的引张变形时期。中新世中晚期,伴随华北地区广泛的基性火山喷溢活动,太行山南段受近NE-SW向引张应力作用,构造变形集中在南段东缘和南缘断裂带上。上新世至早更新世时期,强烈的NW-SE向地壳引张导致太行山隆起南段夷平地貌的解体和地堑盆地的形成。自中晚更新世以来,太行山南缘断裂带成为新构造变形的主要边界带。断面滑动矢量分析和山前年轻冲积扇体和小冲沟沿断裂错移特征分析,表明太行山南缘断裂带是一条斜张左旋走滑边界断裂带,引张方向为NW-SE至NNW-SSE.从区域大地构造角度,中新世中国东部NE-SW向拉伸作用与东部太平洋板块向西俯仲导致的弧后扩张动力过程有关;而上新世以来新构造变形是与青藏高原快速隆升及其向东构造挤出作用有关。   相似文献   

15.
现有各种资料都说明,"汾渭地堑"实际上包含着分别从始新世和上新世开始发生的3个相互斜列,向西南收敛,向东北撒开的独立地堑。3个地堑分别是由3个背斜轴部的纵向张断裂发育而成的,3个背斜是祁吕贺山字型构造体系弧顶东侧的组分。据此,对该区地震、现今地裂缝、地热异常、地下水量和水质,以及某些地方性疾病的分布等,都给予了合理的地质解释。   相似文献   

16.
Dextral-slip in the Nyainqêntanglha region of Tibet resulted in oblique underthrusting and granite generation in the Early to Middle Miocene, but by the end of the epoch uplift and extensional faulting dominated. The east-west dextral-slip Gangdise fault system merges eastward into the north into the dextral-slip North Damxung shear zone and Jiali faults. These faults were took shape system in 18.3-11.0 Ma as the western block drove under the eastern one. The dextral-slip movement ended at ～11 Ma and the batholith rose, as marked by gravitational shearing at 8.6-8.3 Ma, and a new fault system developed. Northwest-trending dextral-slip faults formed to the northwest of the raisen batholith, whereas the northeast-trending South Damxung thrust faults with some sinistral-slip formed to the southeast. The latter are replaced farther to the east by the west-northwest-trending Miocene deposits preserved was followed by a regional uplift and the initiation of a system of generally north-south grabens in the Late Miocene at ～6.5 Ma. The regional uplift of the southern Tibetan Plateau thus appears to have occurred between 8.3 Ma and 6.5 Ma. The Gulu, Damxungcontrolled by the earlier northeast-trending faults. These grabens dominate the subsequent tectonic movement and are still very active as northwest-trending dextral-slip faults northwest of the mountains. The Miocene is a time of great tectonic change that ushered in the modern tectonic regime.  相似文献   

17.
南沙海区礼乐盆地沉积地层与构造特征分析   总被引：4，自引：1，他引：3  
通过对地震剖面、钻井及拖网采样资料的分析,认为礼乐盆地发育有海相的中、新生代地层,存在晚白垩世与晚渐新世两个区域性不整合面,将沉积层分为三套构造层:下构造层较厚,为中生代地层,表现为翘倾断块和宽缓背斜两种构造样式;中构造层较薄甚至局部缺失,为古新世-早渐新世充填的张裂期沉积,表现为半地堑构造样式;上构造层为晚渐新统至第四系沉积,充填区域沉降期海相地层,地层较为平稳。在中构造层沉积过程中发育多排NE向控洼断裂,断裂倾向NW,形成多个半地堑,控制了新生代早期的沉积充填,同时也表现出礼乐盆地在新生代早期受明显的张裂作用。通过对各构造层的构造、沉积特征分析,认为礼乐盆地经历了挤压、拉张、漂移、区域沉降四个构造演化阶段,是一个以中生代地层为主的叠合盆地。  相似文献   

18.
青藏高原中部第四纪左旋剪切变形的地表地质证据   总被引：7，自引：5，他引：2  
在青藏铁路的格尔木—拉萨段进行的活动断裂调查发现,在沱沱河—五道梁之间宽约150km的地段内发育了多条由北西西向次级断层左列分布构成的北西西向和北西向左旋张扭性断裂带,在断裂带之间则发育"S"型的北东向裂陷盆地和雁列分布的菱形裂陷盆地,盆地边界断裂也为左旋张扭性质。上述断裂带和裂陷带主要形成于第四纪,它们构成了宽约150km的不均匀的左旋简单剪切变形域,该变形域的整体活动性较弱,属于弱的不均匀剪切变形域。但其中的二道沟断陷盆地是个例外,该盆地边界断裂的垂直活动速率约为0 5mm/a,左旋活动速率介于0 8～1 0mm/a之间。而在整个左旋剪切变形带累计的左旋走滑速率不会超过6mm/a,它们所调节的昆仑山与唐古拉山之间的地壳南北缩短量也可能仅占总缩短量的15%～30%。上述弱剪切变形域与强烈左旋走滑的昆仑断裂系共同构成了高原中部的左旋剪切变形带,它们在印度板块与欧亚板块强烈碰撞的构造动力学背景下,起着调节青藏高原南北向缩短的重要作用。  相似文献   

19.
The results of focal mechanisms determination for the recent seismic activity (earthquakes of 1951, 1955, 1987, 1988, and 1998) in the passive continental margin of Egypt may shed some light on the local stress field in this area. Moreover, studying the source mechanism of these events provides an opportunity to understand the structural style of the passive margin of Egypt, as well as the tectonic setting beside its variation in space and time. This study reveals that there are two types of tectonic regimes which caused these mechanisms. The first is a tensional regime, represented by NW oblique (normal-dextral) faults and the second is a compressive one represented by E–W to ENE (reverse-sinstral) faults. These fault trends probably indicate rejuvenation of inherited E–W Mesozoic and NW Oligo-Miocene faults.  相似文献   

20.
A few cases of occurrence of normal aftershocks after strike slip earthquakes in compressive regime have been reported in the literature. Occurrence of such aftershocks is intriguing as they occurred despite the apparent stabilizing influence of compressive plate tectonic stresses on the normal faults. To investigate the occurrence processes of such earthquakes, we calculate change in static stress on optimally oriented normal and reverse faults in the dilational and compressional step over zones, respectively, due to slip on a vertical strike slip fault under compressive regime. We find that change in static stress is much more pronounced on normal faults as compared to that on reverse faults, for all values of fault friction. Change in static stress on reverse fault is marginally positive only when the fault friction is low, whereas for normal faults it is positive for all values of fault friction, and is maximum for high fault friction. We suggest that strike slip faulting in compressive regime creates a localized tensile environment in the dilational step over zone, which causes normal faulting in that region. The aftershocks on such normal faults are considered to have occurred as an almost instantaneous response of stress transfer due to strike slip motion.  相似文献   

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