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1.
It is commonly accepted that collisional orogens involve the reactivation of former rifted margins. While it remains debated how rift inheritance can be identified and how it controls the architecture of orogens this case study analyses the importance of rift-inheritance during reactivation of a passive margin. The study analyses complex, non-layer cake rift structures within the well-exposed Err and Platta nappes (SE Switzerland), representing the former distal Adriatic margin of the Alpine Tethys. Diagnostic criteria for rift inheritance include: (1) typical fault rocks with a mantle derived fluid signature, and (2) tectono-sedimentary breccias made of reworked exhumed basement and grading upwards into late syn- and post-rift sediments. Based on the study of “recognisable” features, a methodology is etablished, which enables to (1) map rift-related detachment faults and (2) to analyse their role during reactivation and formation of a thrust stack. First, second and third order thrust systems are defined. First order thrust systems juxtapose different rift domains (proximal, necking, and distal). Second order systems are dominantly made up of basement sheets sampling the former footwall of an extensional detachment fault. Third order systems mainly consist of the former hanging wall of an extensional detachment fault. A major result of this study is that thrust faults commonly reactivate former extensional detachment faults, especially in the exhumed mantle domain (Platta nappe), while in the hyperextended domain (Err nappe) reactivation of rift-inherited structures is more complex and often incomplete. The results of this study may help to better identify remnants of former distal margins and to define and analyse their complex stacking patterns observed in many internal parts of collisional orogens.  相似文献   

2.
The Liaonan metamorphic core complex (mcc) has a three-layer structure and is constituted by five parts, i.e. a detachment fault zone, an allochthonous upper plate and an supradetachment basin above the fault zone, and highly metamorphosed rocks and intrusive rocks in the lower plate. The allochthonous upper plate is mainly of Neoproterozoic and Paleozoic rocks weakly deformed and metamorphosed in pre-Indosinan stage. Above these rocks is a small-scale supradetachment basin of Cretaceous sedimentary and volcanic rocks. The lower plate is dominated by Archean TTG gneisses with minor amount of supracrustal rocks. The Archean rocks are intruded by late Mesozoic synkinematic monzogranitic and granitic plutons. Different types of fault rocks, providing clues to the evolution of the detachment fault zone, are well-preserved in the fault zone, e.g. mylonitic gneiss, mylonites, brecciated mylonites, microbreccias and pseudotachylites. Lineations in lower plate granitic intrusions have consistent orientation that indicate uniform top-to-NW shearing along the main detachment fault zone. This also provides evidence for the synkinematic characteristics of the granitic plutons in the lower plate. Structural analysis of the different parts in the mcc and isotopic dating of plutonic rocks from the lower plate and mylonitic rocks from detachment fault zone suggest that exhumation of the mcc started with regional crustal extension due to crustal block rotation and tangential shearing. The extension triggered magma formation, upwelling and emplacement. This event ended with appearance of pseudotachylite and fault gauges formed at the uppermost crustal level. U-Pb dating of single zircon grains from granitic rocks in the lower plate gives an age of 130±5 Ma, and biotite grains from the mam detachment fault zone have 40Ar-39Ar ages of 108-119 Ma. Several aspects may provide constraints for the exhumation of the Liaonan mcc. These include regional extensional setting, cover/basement contact, temporal and spatial coupling of extension and magmatism, basin development and evolution of fault tectonites along detachment fault zone. We propose that the exhumation of the Liaonan mcc resulted from regional extension and thinning of crust or lithosphere in eastern North China, and accompanied with synkinematic intrusion of granitic plutons, formation of detachment fault zone, uplifting and exhumation of lower-plate rocks, and appearance of supradetachment basin.  相似文献   

3.
The major structure accommodating orogen-parallel extension in the Eastern Alps is inferred to be the Brenner Fault, which forms the western boundary of the Tauern Window. The estimated amount of extension along this fault varies from a minimum of 10–20 km to a maximum of >70 km. All investigations that have attempted to constrain this amount of extension have calculated the fault plane parallel displacement required to restore the difference in structural level between footwall and hanging wall as constrained by geobarometry. However, these calculations neglected the component of exhumation of the footwall resulting from folding and erosion. Therefore, the total amount of extensional displacement was systematically overestimated. In the present study, we project a tectonic marker surface from the footwall and hanging wall of the Brenner Fault onto a N–S-striking cross section. This marker surface, which is the base of the Patscherkofel unit in the footwall and the base of the Ötztal basement in the hanging wall, is inferred to have occupied the same structural level in the hanging wall and footwall of the Brenner Fault before its activity. Therefore, the difference in height between the marker projected from the footwall and from the hanging wall is a measure of the vertical offset across the Brenner Fault. This construction shows that the vertical offset of the marker horizon on both sides of the Brenner Fault varies strongly and continuously along strike of the Brenner Fault, attaining a maximum value of 15 km at the hinge of the folded footwall (Tauern Dome). The along-strike change of vertical offset is explained by large-scale upright folding of the footwall that did not affect the hanging wall of the Brenner Fault. Therefore, the difference in vertical offset of 10 km between the area of the Brenner Pass and the area immediately south of Innsbruck corresponds to the shortening (upright folding) component of exhumation of the footwall. The remaining 5 km of vertical offset must be attributed to extensional deformation. The Brenner Fault itself is barely folded, its dip varies between 20 and 70°, and it crosscuts the upright folds of the western Tauern Window. Given the offset of 5 km, the dip of the fault constrains the extensional displacement to be between 2 and 14 km. We conclude that the Tauern Window was exhumed primarily by folding and erosion, not by extensional unroofing.  相似文献   

4.
In the eastern part of the Strandja Massif constituting the east end of the Rhodope Massif, the amphibolite facies basement rocks intruded by Permian metagranites are juxtaposed against the greenschist facies cover metasediments of Triassic-Middle Jurassic protolith age. The distinct metamorphic break between the basement and cover rocks requires a missing metamorphic section. The boundary between the two groups of rocks is a ductile to brittle extensional shear zone with kinematic indicators exhibiting a top to the E/NE shear sense. Footwall rocks are cut by weakly metamorphosed and foliated granite bodies which are clearly distinguished from the Permian metagranites by their degree of deformation, cross-cutting relations and syn-tectonic/kinematic character. Also, hangingwall rocks were intruded by unmetamorphosed and weakly foliated leucogranites. 40Ar/39Ar data indicate that the ductile deformation from 156.5 to 143.2 Ma (Middle Oxfordian-Earliest Berriasian) developed during the syn-tectonic plutonism in the footwall. Deformation, and gradual/slower cooling-exhumation survived until to 123 Ma (Barremian). The mylonitic and brittle deformation in the detachment zone developed during Oxfordian-Earliest Berriasian time (155.7–142.6 Ma) and Early Valanginian-Aptian time (136–118.7 Ma), respectively. Our new field mapping and first 40Ar/39Ar ages demonstrate the existence of an extensional core complex of Late Jurassic-Early Cretaceous age not previously described in the Rhodope/Strandja massifs.  相似文献   

5.
ABSTRACT

The late Mesozoic tectonics of the North China Craton (NCC) and its adjacent regions were characterized by a general lithospheric extension and remarked by extensional dome structures, such as the metamorphic core complexes, syn-tectonic plutons, rolling-hinge structures, and widespreadgraben/half graben basins. According to our own field observations, laboratory work, and previous results of other groups, from north to south, five extensional domains have been delineated, namely Transbaikalia–Mongol–Okhotsk, western part of NCC, eastern part of NCC and Korea, Qinling–Dabie and its neighbouring, and the interior of South China Block, respectively. As the largest crustal scale extensional tectonic realm in the world, these domains are featured by a NW–SE extensional direction with strong extensional exhumation of middle to lower crust rocks to the surface along detachment faults. Geochronological work on these ductile detachment faults constrain a narrow activity period around 130 Ma except several extensive structures along the Tan–Lu fault, which documents a relative longer extensional period. The foundering of the lower part of the lithosphere could be a possible mechanism of this continent-scale extensional tectonics. This geodynamic model could help us to enhance the knowledge of the time, scale, and mechanism of the NCC destruction from the view of structural analysis.  相似文献   

6.
《Geodinamica Acta》2013,26(5):267-282
The interaction of distinct geologic processes involved during late orogenic extensional exhumation history of the metamorphic units in the Eastern Rhodope is refined by new and reviewing 40Ar/39Ar geochronological and structural data. Minerals with different closure temperatures from metamorphic rocks investigated in this study are combined with those from magmatic and ore-forming hydrothermal rocks in two late stage metamorphic domes – the Kesebir-Kardamos and the Biala reka-Kehros domes. The 38-37 Ma muscovite and biotite cooling ages below 350°-300°C characterize basement metamorphic rocks that typified core of the Kesebir-Kardamos dome, constraining their exhumation at shallow crustal levels in the footwall of detachment. These ages are interpreted as reflecting last stage of ductile activity on shear zone below detachment, which continued to operate under low-temperature conditions within the semi-ductile to brittle field. They are close to and overlap with existing cooling ages in southern Bulgaria and northern Greece, indicating supportively that the basement rocks regionally cooled between 42-36 Ma below temperatures 350°-300°C. The spatial distribution of ages shows a southward gradual increase up structural section, suggesting an asymmetrical mode of extension, cooling and exhumation from south to the north at latitude of the Kesebir-Kardamos dome. The slightly younger 36.5-35 Ma crystallization ages of adularia in altered rocks from the ore deposits in the immediate hanging-wall of detachments are attributed to brittle deformation on high-angle normal faults, which further contributed to upper crustal extension, and thus constraining the time when alteration took place and deformation continued at brittle crustal levels. Silicic dykes yielded ages between 32-33 Ma, typically coinciding with the main phase of Palaeogene magmatic activity, which started in Eastern Rhodope region in Late Eocene (Priabonian) times. The 40Ar/39Ar plateau ages from the above distinct rock types span time interval lasting approximately ca. 6 Ma. Consequently, our geochronologic results consistently indicate that extensional tectonics and related exhumation and doming, epithermal mineralizations and volcanic activity are closely spaced in time. These new 40Ar/39Ar age results further contribute to temporal constraints on the timing of tectonic, relative to ore-forming and magmatic events, suggesting in addition that all above mentioned processes interfered during the late orogenic extensional collapse in the Eastern Rhodope region.  相似文献   

7.
松辽盆地变质核杂岩和伸展断陷的构造特征及成因   总被引：18，自引：3，他引：15  
文中讨论了松辽盆地北部中央基底隆起变质核杂岩和徐家围子伸展断陷的构造特征、成因和演化 ,重点讨论了下列问题 :( 1)中央基底隆起变质核杂岩具有科迪勒拉变质核杂岩的许多特征 ;( 2 )识别出组成中央基底隆起变质核杂岩的多层次、低角度韧性拆离体系 ,它们是使中地壳的中深变质岩层抽拉至上地壳的主要原因 ;( 3)穹窿状火山岩台地于晚侏罗世 ( 145.7±6.2 )Ma形成 ,受顶部拆离断层控制的伸展断陷于早白垩世 ( 133～ 12 0Ma)形成 ,而邻近顶部拆离断层的糜棱岩年龄为 ( 12 6.7± 1.54)Ma。这表明变质核杂岩的形成始于晚侏罗世。早白垩世递进的伸展构造与变质核杂岩较深部的部分上拱至地表相伴生 ,推测该变质核杂岩的上拱和剥露、火山岩台地和伸展断陷盆地的形成可能是由伊泽奈奇和亚洲板块陆陆碰撞后的地幔拆沉作用、地幔的岩浆底侵作用以及伸展垮塌作用联合造成的。  相似文献   

8.
The Penola Trough is an intensely faulted northwest – southeast-trending half-graben structure. It is bound to the south by the major listric Hungerford/Kalangadoo Fault system. Several large prominent faults observed in the Penola Trough show offset of basement at depth. These basement-rooted faults have exerted significant controls on the geometry of smaller intra-rift faults throughout the entire structural history of the area. Faulting of the basement was initiated during the initial rift event of the Late Jurassic – Early Cretaceous. Faulting first propagated through a pre-existing basement fabric oblique to the north – south extension direction prevalent during this time. This resulted in the formation of the Hungerford/Kalangadoo and St George Faults with a northwest – southeast and north-northeast – south-southwest trend, respectively. A series of east – west-trending basement faults subsequently initiated perpendicular to the north – south extension direction as extensional strain increased in magnitude. Significant displacement along these basement-rooted faults throughout the initial rift event was associated with the formation of a complex set of intra-rift faults. These intra-rift faults exhibit a broadly east – west orientation consistent with the interpreted north – south extensional direction. However, this east – west orientation locally deviates to a more northwest – southeast direction near the oblique-trending St George Fault, attributed to stress perturbation effects. Many of the intra-rift faults die out prior to the end of the Early Cretaceous initial rift event while displacement on basement faults continued throughout. Faulting activity during the Late Cretaceous post-rift fault event was almost exclusively localised onto basement faults, despite a significant change in extension direction to northeast – southwest. A high-density, en échelon array of northwest – southeast-trending fault segments formed directly above the St George Fault and the large east – west-trending basement faults contemporaneously reactivated. Seismic variance data show that post-rift fault segments that are hard-linked to the St George Fault at depth have propagated through near-surface units. Non-basement-linked post-rift fault segments that lie away from the St George basement have not. This suggests that recent fault activity has continued to occur preferentially along basement faults up to relatively recent times, which has significant implications for fault seal integrity in the area. This is empirically validated by our structural analysis of fault-dependent hydrocarbon traps in the area, which shows that partially breached or breached hydrocarbon columns are associated with basement faults, whereas unbreached hydrocarbon columns are not.  相似文献   

9.
The article describes the characteristics of the Yagan metamorphic core complex, especially the associated detachment fault and various extensional structures in its footwall. The age of the complex is discussed in some detail as well. The basic features of the Yagan metamorphic complex (Jurassic in age) are similar to those of the metamorphic core complex (Tertiary in age) in the Cordilleran area; they are as follows: (a) mylonitic gneisses in the footwall, (b) chloritized sheared mylonitic rocks, (c) pseudotachylites and flinty cataclasites or microbreccias, (d) unmetamorphosed or epimetamorphic rocks in the hanging wall with a layer of fault gouges or incohesive fault breccia next to the detachment fault. In contrast to its Cordilleran counterpart, however, there are many extensional faults with different styles (from dactile low-angle normal faults through brittle-ductile to brittle high-angle normal faults)in the footwall.  相似文献   

10.
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11.
《Gondwana Research》2014,26(4):1469-1483
China's largest gold resource is located in the highly endowed northwestern part of the Jiaodong gold province. Most gold deposits in this area are associated with the NE- to NNE-trending shear zones on the margins of the 130–126 Ma Guojialing granite. These deposits collectively formed at ca. 120 ± 5 Ma during rapid uplift of the granite. The Dayingezhuang deposit is a large (> 120 t Au) orogenic gold deposit in the same area, but located along the eastern margin of the Late Jurassic Linglong Metamorphic Core Complex. New 40Ar/39Ar geochronology on hydrothermal sericite and muscovite from the Dayingezhuang deposit indicate the gold event is related to evolution of the core complex at 130 ± 4 Ma and is the earliest important gold event that is well-documented in the province. The Dayingezhuang deposit occurs along the Linglong detachment fault, which defines the eastern edge of the ca. 160–150 Ma Linglong granite–granodiorite massif. The anatectic rocks of the massif were rapidly uplifted, at rates of at least 1 km/m.y. from depths of 25–30 km, to form the metamorphic core complex. The detachment fault, with Precambrian metamorphic basement rocks in the hangingwall and the Linglong granitoids and migmatites in the footwall, is characterized by early mylonitization and a local brittle overprinting in the footwall. Gold is associated with quartz–sericite–pyrite–K-feldspar altered footwall cataclasites at the southernmost area of the brittle deformation along the detachment fault. Our results indicate that there were two successive, yet distinct gold-forming tectonic episodes in northwestern Jiaodong. One event first reactivated the detachment fault along the edge of the Linglong massif between 134 and 126 Ma, and then a second reactivated the shears along the margins of the Guojialing granite. Both events may relate to a component of northwest compression after a middle Early Cretaceous shift from regional NW–SE extension to a NE–SW extensional regime.  相似文献   

12.
Gneiss domes involving the South Tibetan Detachment System provide evidence for crustal extension simultaneous with shortening. The Nielaxiongbo gneiss dome is composed of a metamorphic complex of granitic gneiss, amphibolite, and migmatite; a ductilely deformed middle crustal layer of staurolite- or garnet-bearing schist; and a cover sequence of weakly metamorphosed Triassic and Lower Cretaceous strata. The middle crust ductilely deformed layer is separated from both the basement complex and the cover sequence by lower and upper detachments, respectively, with a smaller detachment fault occurring within the ductilely deformed layer. Leucogranites crosscut the basement complex, the lower detachment, and the middle crustal layer, but do not intrude the upper detachment or the cover sequence. Three deformational fabrics are recognized: a N–S compressional fabric (D1) in the cover sequence, a north- and south-directed extensional fabric (D2) in the upper detachment and lower tectonic units, and a deformation (D3) related to the leucogranite intrusion. SHRIMP zircon U–Pb dating yielded a metamorphic age of ～514 million years for the amphibolite and a crystallization age of ～20 million years for the leucogranite. Hornblende from the amphibolite has an 40Ar/39Ar age of 18 ± 0.3 million years, whereas muscovites from the schist and leucogranite yielded 40Ar/39Ar ages between 13.5 ± 0.2 and 13.0 ± 0.2 million years. These results suggest that the basement was consolidated at ～510 Ma and then exhumed during extension and silicic plutonism at ～20 Ma. Continuing exhumation led to cooling through the 500°C Ar closure temperature in hornblende at ～18 Ma to the 350°C Ar closure temperature in muscovite at ～13 Ma. The middle crustal ductilely deformed layer within gneiss domes of southern Tibet defines a southward-extruding ductile channel, marked by leucogranites emplaced into migmatites and amphibolites. We propose a model involving thinned upper crust for the initial extension of the Tibetan Plateau in the early Miocene.  相似文献   

13.
In this paper, a scenario for the early evolution of the Jurassic oceanic Liguria-Piemonte basin is sketched. For this purpose, four selected examples of ophiolite sequences from the Northern Apennines and Corsica are described and analyzed. In the External Ligurian units (Northern Apennines), the ocean–continent transition of the Adria plate was characterized by a basement made up of subcontinental mantle and lower continental crust, covered by extensional allochthons of upper crust. Both, the basement rocks and the extensional allochthons are cut by basaltic dikes and covered by basalts and pelagic deposits. The conjugate ocean–continent transition of the Corsica margin, represented by the Balagne nappe (Corsica), was composed of mantle peridotites and gabbros covered by basaltic flows and minor breccias, that in addition include continent-derived clasts. By contrast, the innermost (i.e., closest to the ocean) preserved area observed in the Internal Ligurian (Northern Apennines) and Inzecca (Corsica) units consists of former morphological highs of mantle peridotites and gabbros, bordered by small basins where the basement is covered by a volcano-sedimentary complex, characterized by ophiolitic breccias and cherts interlayered with basaltic flows. The overall picture resulting from our reconstructions suggests an asymmetric architecture for the Liguria-Piemonte basin with a central area bounded by two different transition zones toward the continental margins. This architecture can be interpreted as the result of a rifting process whose development includes a final stage characterized by passive, asymmetric extension of the lithosphere along an east-dipping detachment fault system.  相似文献   

14.
Abstract The article describes the characteristics of the Yagan metamorphic core complex, especially the associated detachment fault and various extensional structures in its footwall. The age of the complex is discussed in some detail as well. The basic features of the Yagan metamorphic complex (Jurassic in age) are similar to those of the metamorphic core complex (Tertiary in age) in the Cordilleran area; they are as follows: (a) mylonitic gneisses in the footwall, (b) chloritized sheared mylonitic rocks, (c) pseudotachylites and flinty cataclasites or microbreccias, (d) unmetamorphosed or epimetamorphic rocks in the hanging wall with a layer of fault gouges or incohesive fault breccia next to the detachment fault. In contrast to its Cordilleran counterpart, however, there are many extensional faults with different styles (from dactile low-angle normal faults through brittle — ductile to brittle high — angle normal faults) in the footwall.  相似文献   

15.
湘东茶陵地区老山坳剪切带特征及其与湘东钨矿的关系   总被引：3，自引：2，他引：1  
湘东茶陵地区老山坳剪切带及其与湘东钨矿的关系是长期以来备受关注且颇具争议的问题。其争议主要表现为:(1)老山坳剪切带(断层)的性质(逆断层、正断层,还是走滑断层)及其发育机理;(2)老山坳剪切带对湘东钨矿的成矿是促进作用还是破坏作用。本文对老山坳剪切带以及湘东钨矿进行了系统地观察和测量,采用宏观、微观构造研究和矿脉统计相结合的方法进行了综合分析。结果表明,老山坳剪切带的活动主要分为两期:早期主要表现为向SE方向的伸展拆离作用,且可能与晚侏罗世八团岩体侵位密切相关,形成了透入性的强烈脆、韧性变形,特别是在糜棱岩中,由于高压流体的作用造成了一系列同期节理(R和R’节理)发育,为石英脉型钨锡矿床的形成提供了条件;后期,大致在晚白垩世及之后老山坳剪切带表现为向NW方向的逆冲作用,致使上盘(主动盘)的钨锡矿脉被推至浅部。因此,我们认为晚侏罗世八团岩体的侵位作用与老山坳剪切带的伸展拆离作用共同控制了湘东钨矿的形成。韧性剪切带中,由于高压流体作用引起局部应变速率增加,同时降低岩石强度而发生脆性破裂(如T节理,R和R’节理),而且按照破裂准则发生和扩展,该过程为成矿元素析出成矿提供了条件,这可能是剪切带成矿的重要方式之一。  相似文献   

16.
Apatite fission-track (AFT) dating applied to uplifted Variscan basement blocks of the Bavarian Forest is employed to unravel the low-temperature history of this segment of the Bohemian Massif. Twenty samples were dated and confined track lengths of four samples were measured. Most samples define Cretaceous APT ages between 110 and 82 Ma (Albian to Campanian) and three samples give older ~148–140 Ma (Jurassic–Cretaceous boundary) ages. No discernible regional age variations exist between the areas north-east and south-west of the Pfahl shear zone, but >500 m post-Jurassic and post-Cretaceous vertical offsets along this and other faults can be inferred from elevation profile analyses. The AFT ages clearly postdate the Variscan exhumation history of the Bavarian Forest. Thermal modeling reveals that the ages are best explained by a slight reheating of the basement rocks to temperatures within the apatite partial annealing zone during the middle and late Jurassic and/or by late Cretaceous marine transgression causing burial heating, which affected marginal low-lying areas of the Bohemian Massif and the Bavarian Forest. Late Jurassic period was followed by enhanced cooling through the 120–60 °C temperature interval during the subsequent exhumation phase for which denudation rates of ~100 m myr?1 were calculated. On a regional scale, Jurassic–Cretaceous AFT ages are ubiquitous in marginal structural blocks of the Bohemian Massif and seem to reflect the exhumation of these zones more distinctly compared to central parts.  相似文献   

17.
青藏高原北缘阿尔金东段中生代南北向伸展作用   总被引：7，自引：2，他引：5  
青藏高原北缘的阿尔金山脉东段发育了延伸大于300 km、东西走向的拉配泉断裂,为南倾的正断层,局部倾角可以低至30°以下。断层中段表现为30~50 m厚的韧性剪切带,发育有较好的糜棱岩组构和矿物伸展线理;东段和西段以碎裂变形为特征。断裂带内运动学标志,如不对称香肠构造、不对称褶皱和次级脆性和韧性断裂,都指示了上盘向南的正滑移剪切方式。两方面证据控制了拉配泉断裂的活动时代。首先,拉配泉断裂上盘局部产出早-中侏罗世沉积地层。侏罗系地层中的砾石,特别是其中的含叠层石硅质灰岩和紫色石英岩,可以与断裂下盘的岩石相对比。早-中侏罗世地层可能为拉配泉断裂之上的伸展盆地沉积。其次,拉配泉断裂下盘岩石的40Ar/39Ar热年代学分析给出2个明显的冷却事件。较老的事件出现在约220~187 Ma之间的三叠纪末期至侏罗纪早期,而年轻的事件出现在早白垩世的晚期(约100 Ma).约220~187 Ma之间的冷却年龄在拉配泉断裂下盘岩石中普遍存在,代表了拉配泉断裂正断作用的主要阶段。约100 Ma时,断裂东段的正断作用再次活动,该事件可能被南倾的恰什坎正断层运动所叠加而增强,并与拉配泉断裂的东段合并。这2条断裂具有共同的上盘向南的正滑移运动方式。青藏高原和东亚其它地区的中生代伸展作用可以归结为特提斯洋向北和太平洋向西俯冲形成的弧后伸展作用。   相似文献   

18.
The western Daqingshan area, located in the eastern Yinshan belt, is dominated by the southern Daqingshan fold-and-thrust system and the northern Shiguai basin. Based on detailed structural investigations, stratigraphic controls, and geochronology, a three-stage tectonic evolution is proposed for the western Daqingshan area during the Jurassic. The discovery of syndepositional normal faults in the Early–Middle Jurassic sequences suggests that an N–S extensional regime (ca. 200–170 Ma) characterized the first deformational stage, which controlled the initial formation of the Shiguai basin. Subsequently, the relatively expansive rift basin was dissected by the initial development of the Daqingshan fold-and-thrust system that was associated with a N–S compressional regime (ca. 170–160 Ma). This phase of deformation involved the Lower–Middle Jurassic synrift sediments into a series of E–W-trending compressional structures, and controlled the deposition of Late–Middle Jurassic Changhangou growth strata ahead of the deformation front. Finally, the progression of Daqingshan fold-and-thrust system was dominated by NW–SE compression (ca. 160–145 Ma), which converted the previous E–W-trending compressional structures into a stepped geometry marked by several NE-trending oblique footwall ramps, and resulted in the depocentre of the Late Jurassic Daqingshan synorogenic conglomerate migrating markedly northeastwards. The driving mechanisms for these three palaeostress fields are considered as asthenosphere upwelling following Permian–Triassic collisional orogenesis, closure of the Mongol–Okhotsk Ocean, and NW-directed subduction of the Palaeo-Pacific plate, respectively.  相似文献   

19.
We demonstrate that Pliocene to Early Quaternary sedimentary formations in Baja California Sur (Mexico) were deposited syn-tectonically over a major detachment associated with the exhumation of Mesozoic crust. The detachment dips to the ENE and is associated with E–W stretching. This large extensional structure strikes almost parallel to the general trend of the Gulf of California and extension is oblique to the East-Pacific seafloor-spreading direction. Crustal-scale stretching in this area was still active after the beginning of seafloor spreading c.  3.6 Ma ago. The detachment is capped by Late Pleistocene–Holocene alluvial sediments the deposition of which seems to be partly syn-tectonic and controlled by minor stretching subparallel to the present-day North American–Pacific kinematic vector. We discuss the implications of our observations on strain partitioning during opening of the California Gulf as well as on the structure of the Gulf of California margin.  相似文献   

20.
Analysis of the Gachsar structural sub-zone has been carried out to constrain structural evolution of the central Alborz range situated in the central Alpine Himalayan orogenic system. The sub-zone bounded by the northward-dipping Kandovan Fault to the north and the southward-dipping Taleghan Fault to the south is transversely cut by several sinistral faults. The Kandovan Fault that controls development of the Eocene rocks in its footwall from the Paleozoic–Mesozoic units in the fault hanging wall is interpreted as an inverted basin-bounding fault. Structural evidences include the presence of a thin-skinned imbricate thrust system propagated from a detachment zone that acts as a footwall shortcut thrust, development of large synclines in the fault footwall as well as back thrusts and pop-up structures on the fault hanging wall. Kinematics of the inverted Kandovan Fault and its accompanying structures constrain the N–S shortening direction proposed for the Alborz range until Late Miocene. The transverse sinistral faults that are in acute angle of 15° to a major magnetic lineament, which represents a basement fault, are interpreted to develop as synthetic Riedel shears on the cover sequences during reactivation of the basement fault. This overprinting of the transverse faults on the earlier inverted extensional fault occurs since the Late Miocene when the south Caspian basin block attained a SSW movement relative to the central Iran. Therefore, recent deformation in the range is a result of the basement transverse-fault reactivation.  相似文献   

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