A Duplex Model for the Eastern Cape Fold Belt? Evidence from the Palaeozoic Witteberg and Bokkeveld Groups (Cape Supergroup), Near Steytlerville, South Africa

The eastern part of the Cape Fold Belt, near Steytlerville, South Africa, reveals a typical pattern of numerous, north-verging thrust faults and associated folds, interpreted as part of a large duplex structure that formed along the southern margin of Gondwana during the Late Palaeozoic. Steeply-dipping fore- and backthrusts occur in the Bokkeveld Group (middle Cape Supergroup), where strata are composed of predominantly argillaceous rocks, whereas in the more arenaceous Witteberg Group (upper Cape Supergroup) there are fewer recognizable and less closely-spaced thrusts. Open style folds characterize areas in which the Bokkeveld Group crops out, but in areas of Witteberg outcrop, folds, especially those adjacent to thrusts, are often overturned.In spite of a general absence of marker horizons, a displacement of at least 500 metres can be inferred for one prominent thrust, the Jackalsbos thrust. This fault, the northernmost in the area investigated, is probably the sole thrust in the duplex structure, linked through southward-dipping imbricates to a projected roof thrust (the Baviaanskloof thrust) cropping out immediately south of the study area.Displacements on imbricates within the duplex are difficult if not impossible to measure, but the net effect is certainly accumulative and incremental. Truncation by a roof thrust and subsequent erosional processes may explain why so few of the many thrusts so far identified in the eastern part of the fold belt can be successfully mapped, and their displacements measured. Normal and strike-slip faults, less common than thrust faults, formed during extensional tectonism related to the breakup of Gondwana, during the Mesozoic.     

Centrifuge modelling of deformation of a multi-layered sequence over a ductile substrate: 1. Style and 4D geometry of active cover folds during layer-parallel shortening

Centrifuge analogue modelling illustrates the progressive development of active folds in multilayers upon a ductile substrate during layer-parallel shortening. Models simulate folding of a mechanically stratified sedimentary sequence upon migmatitic gneisses in a large hot orogen, or upon a thick basal evaporite ± shale sequence in deeper levels of fold belts. The absence of a weak low-viscosity and low-density layer at the interface promotes infolding of the cover sequence and ductile substrate, whereas a planar upper surface to the basal ductile substrate is preserved when it is present. Whilst fold style, wavelength, and deformation of the interface with the ductile substrate differ depending on whether a low-viscosity and low-density layer is present at the base of the cover sequence, there is no marked systematic curvature of fold axes as seen in previous sandbox models for fault-bend or fault propagation folding during bulk shortening. Bulk shortening of a layered sequence with relatively thick individual layers above a ductile substrate promotes a regular and upright train of buckle folds, whereas thinner layers promote a more irregular distribution of buckle folds with variable vergence, style, and amplitude. Buckle folds above a ductile substrate progressively develop during bulk shortening from open and upright, to angular and tight, and may further develop into cuspate structures above relatively weak horizons. Relatively thick weak horizons within the layered sequence during bulk shortening interrupt regular fold patterns up structural section and allow out-of-phase folds to develop above and below the weak horizon.     

The relationship of structures across the Lambian unconformity near Taralga,New South Wales

The structures across the Lambian Unconformity near Taralga show evidence of two, and possibly three, significant episodes of folding. The first, Early to Middle Silurian folding is poorly defined, but may be responsible for initial dips that are reflected in the more complex deformation patterns in the Late Ordovician than in the overlying younger rocks. The second, mid‐Devonian folding produced upright folds trending 10° west of north, and the last, latest Devonian to Early Carboniferous folding produced the meridional Cookbundoon Synclinorium and the regional cleavage. No cleavage was associated with the first two episodes of folding in the area studied. The angular discordance across the Lambian Unconformity caused by mid‐Devonian folding is much greater than in the northeastern Lachlan Fold Belt, and reflects the increasing intensity of mid‐Devonian folding southward. The tight, slightly overturned profile of the Cookbundoon Synclinorium reflects an intensity of latest Devonian to Early Carboniferous folding similar to that found in the northeastern Lachlan Fold Belt, but the intensity of this folding decreases further south.     

Neotectonic morphotructures in the junction zone of the Cape Verde Rise and Cape Verde Abyssal Plain,Central Atlantic

Acoustic profiling carried out with an Edgetech 3300 prophilograph in the junction zone of the Cape Verde Rise, Cape Verde Abyssal Plain, and Grimaldi and Bathymetrists seamounts in the Central Atlantic during Cruise 23 of the R/V Akademik Nikolaj Strakhov allowed us to obtain new data on neotectonic deformations in the ocean and to propose their interpretation. It has been established that neotectonic movements occurred in the discrete manner: blocks of undeformed rocks alternate with linear zones of intense deformation spatially related to paleotransform fracture zones, where anticlines, horsts, diapir-like morphostructures, and grabens were formed. The Cape Verde Ridge is a large horst. Its sedimentary cover is disturbed by thrust (?), reverse, and normal faults, steeply dipping fracture zones, and folds. Three stages of tectonic movements—Oligocene-early Miocene, pre-Quaternary, and Holocene—are recognized. The tectonic deformations occurred largely under near-meridional compression. Extension setting was characteristic of the Cape Verde Ridge and the Carter Rise in the Holocene.     

Role of extensional structures on the location of folds and thrusts during tectonic inversion (northern Iberian Chain,Spain)

The Aguilón Subbasin (NE Spain) was originated daring the Late Jurassic-Early Cretaceous rifting due to the action of large normal faults, probably inherited from Late Variscan fracturing. WNW-ESE normal faults limit two major troughs filled by continental deposits (Valanginian to Early Barremian). NE-SW faults control the location of subsidiary depocenters within these troughs. These basins were weakly inverted during the Tertiary with folds and thrusts striking E-W to WNW-ESE involving the Mesozoic-Tertiary cover with a maximum estimated shortening of about 12 %. Tertiary compression did not produce the total inversion of the Mesozoic basin but extensional structures are responsible for the location of major Tertiary folds. Shortening of the cover during the Tertiary involved both reactivation of some normal faults and development of folds and thrusts nucleated on basement extensional steps. The inversion style depends mainly on the occurrence and geometry of normal faults limiting the basin. Steep normal faults were not reactivated but acted as buttresses to the cover translation. Around these faults, affecting both basement and cover, folds and thrusts were nucleated due to the stress rise in front of major faults. Within the cover, the buttressing against normal faults consists of folding and faulting implying little shortening without development of ceavage or other evidence of internal deformation.     

湖南锡田锡钨多金属矿床成矿构造特征及其找矿意义

锡田矿床内发育近SN向花岗岩穹窿伸展构造、NE向复式褶皱和NE或NEE向走滑伸展构造系统。穹窿构造主要由印支期和燕山期侵入的花岗岩和古生代地层及不连续的环形滑脱断层组成,控制燕山期花岗岩与围岩接触带矽卡岩型矿体的分布;复式褶皱为古生代地层组成的NE向复式向斜,在矿区中部被锡田复式花岗岩体切割。严塘复式向斜与小田复式向斜中的背斜核部,尤其断层叠加的部位常控制一些构造破碎带型钨锡富矿体的分布。NE向或NEE向走滑伸展构造系统包括NE向右行(伸展)走滑断层、NE向或近EW向右行次级的走滑伸展断层、近SN向左行走滑断层和NW向伸展断层,控制了锡田矿区内的不同方向构造蚀变岩型、石英脉型和云英岩脉型锡钨多金属矿床的分布。花岗岩锆石U-Pb、白云母40Ar-39Ar和辉钼矿Re-Os同位素测年表明锡田地区燕山期构造活动、岩浆作用与成矿响应时间非常接近,介于150～160Ma。岩体与地层(灰岩)接触带、岩体中的NEE向断裂带以及被NE向断裂叠加的背斜轴部是重要的成矿区域,可作为下一步矿产勘查工作重要靶区。     

Variable hangingwall palaeotransport during Silurian and Devonian thrusting in the western Lachlan Fold Belt: Missing gold lodes,synchronous Melbourne Trough sedimentation and Grampians Group fold interference

The western margin of the Lachlan Fold Belt contains early ductile and brittle structures that formed during northeast‐southwest and east‐west compression, followed by reactivation related to sinistral wrenching. At Stawell all of these structural features (and the associated gold lodes) are dismembered by a complex array of later northwest‐, north‐ and northeast‐dipping faults. Detailed underground structural analysis has identified northwest‐trending mid‐Devonian thrusts (Tabberabberan) that post‐date Early Devonian plutonism and have a top‐to‐the‐southwest transport. Deformation associated with the initial stages of dismemberment occurred along an earlier array of faults that trend southwest‐northeast (or east‐west) and dip to the northwest (or north). The initial transport of the units in the hangingwall of these fault structures was top‐to‐the‐southeast. ‘Missing’ gold lodes were discovered beneath the Magdala orebody by reconstructing a displacement history that involved a combination of transport vectors (top‐to‐the‐southeast and top‐to‐the‐southwest). Fold interference structures in the adjacent Silurian Grampians Group provide further evidence for at least two almost orthogonal shortening regimes, post the mid‐Silurian. Overprinting relationships, and correlation with synchronous sedimentation in the Melbourne Trough, indicates that the early fault structures are mid‐ to late‐Silurian in age (Ludlow: ca 420–414 Ma). These atypical southeast‐vergent structures have regional extent and separate significant northeast‐southwest shortening that occurred in the mid‐Devonian (‘Tabberabberan orogeny’) and Late Ordovician (‘Benambran orogeny’).     

A tertiary fold and thrust belt in the Valle del Cauca Basin, Colombian Andes

Surface geology and heophysical data, supplemented by regional structural interpretations, indicate that the Valle del Cauca basin and adjacent areas in west-central Colombia form a west-vergent, basement-involved fold and thrust belt. This belt is part of a Cenozoic orogen developed along the west side of the Romeral fault system. Structural analysis and geometrical constraints show that the Mesozoic ophiolitic basement and its Cenozoic sedimentary cover are involved in a “thick-skinned” west-vergent foreland style deformation. The rocks are transported and shortened by deeply rooted thrust faults and stacked in imbricate fashion. The faults have a NE---SW regional trend, are listric in shape, developed as splay faults which are interpreted as joining a common detachment at over 10 km depth. The faults carry Paleogene sedimentary strata and Cretaceous basement rocks westward over Miocene strata of the Valle del Cauca Basin. Fold axes trend parallel or sub parallel to the thrust faults. The folds are westwardly asymmetrical with parallel to kink geometry, and are interpreted to be fault-propagation folds stacked in an imbricate thrust system. Stratigraphic evidence suggests that the Valle del Cauca basin was deformed between Oligocene and upper Miocene time. The kinematic history outlined above is consistent with an oblique convergence between the Panama and South American plates during the Cenozoic.A negative residual Bouguer anomaly of 20–70 mgls in the central part of the Valle del Cauca basin indicates that a substantial volume of low density sedimentary rocks is concealed beneath the thrust sheets exposed at the land surface. The hydrocarbon potential of the Valle del Cauca should be reevaluated in light of the structural interpretations presented in this paper.     

山东鲁西地块断裂构造分布型式与中生代沉积-岩浆-构造演化序列

鲁西地块的断裂构造有两类不同分布型式:一类呈放射状分布, 由陡倾、基底右行韧性剪切带和盖层内复杂力学性质的断裂组成; 另一类呈环绕地块基底核部同心环状分布, 由3个主要盖层伸展拆离带组成, 主滑脱面分别位于古生界盖层与基底间的不整合面、石炭系与奥陶系之间的平行不整合面和中新生代断陷-沉积岩系与新生代火山-沉积物之间的断层。中生代构造变形样式可以分为3个层次:印支期褶皱-逆冲推覆构造、燕山中期NNE轴向的隔槽式箱状褶皱和燕山晚期NW、NNE向共轭正断-走滑断裂。相应地鲁西地块经历了3个成盆期, 即早-中侏罗世、早白垩世和晚白垩世, 这些中生代盆地在空间上的叠置导致了地块内部复杂的盆-山耦合关系。鲁西地块中生代有两个岩浆活动集中时期, 即早侏罗世(约190Ma)和早白垩世(132~110Ma)。综合沉积记录、岩浆活动和构造变形过程, 将鲁西地块中生代构造演化历史划分为6个阶段:晚三叠世挤压变形, 早、中侏罗世弱伸展作用, 中、晚侏罗世挤压变形与地壳增厚作用, 早白垩世大陆裂谷与地壳伸展作用, 早白垩世末期挤压变形与盆地反转事件和晚白垩世区域隆升。这些构造演化阶段和构造事件对研究和理解中生代构造体制和深部岩石圈动力学转换过程具有重要意义。      

Mid‐Devonian movements in the Northeastern Lachlan Fold Belt

Calculations of the angular discordance between the Upper Devonian Lambie/Catombal Groups and underlying Lower Devonian formations at 130 separate locations in six areas in the northeastern Lachlan Fold Belt show that the unconformity is of a low angle except for one locality, near Limekilnes (100°). Fewer than 3% of the calculated angular discordances exceed 30°, and 73%” are less than 20°. Attempts to discover a mid‐Devonian fold direction from the restored orientation of the Lower Devonian beds, after the Upper Devonian beds have been rotated to horizontal, have been unsuccessful. Scatter of the restored bedding poles, either primary, or introduced by deformation or imprecision inherent in the measurement technique, camouflages any consistent mid‐Devonian fold axis.

Although there was demonstrable uplift, tilting, and erosion in the mid‐Devonian, limb dips on any mid‐Devonian folds do not exceed 30°. From consideration of our data, and the interpretation of angular unconformities, we conclude that there is insufficient evidence in the northeastern Lachlan Fold Belt to support an orogenic scheme in which the intense meridional deformation is synchronous with the major mid‐Devonian facies change, and part of a terminal orogeny. Only when the structures above, below and across unconformities have been mapped in some detail, will it be possible to define the nature and extent of any diastrophism that accompanied the formation of the unconformities.     

Northeast-trending folds in the western Skeena Fold Belt,northern Canadian Cordillera: a record of Early Cretaceous sinistral plate convergence

The western portion of the Skeena Fold Belt, northern Canadian Cordillera, contains northeast-trending folds that are highly oblique to northwest-trending folds in the eastern portion of the fold belt, and to most Mesozoic contractional structures in the northern Cordillera. The northeast-trending folds locally interfere with the northwest-trending folds, and one region includes transected folds. Geometric relationships within and between the two fold sets are not easily reconciled by notions of the northeast-trending folds resulting from vertical axis rotation of blocks, influence of basement features, or lateral variations in magnitude of shortening. The northeast-trending folds are inferred to result from sinistral plate convergence early in the history of the fold belt (Early Cretaceous).Northeast-trending folds in the Skeena Fold Belt are the most conspicuous elements of a seldom-studied group of similarly oriented contractional structures, which collectively define a belt at least 1700 km long, within and bordering the Coast Belt. The extent of Early Cretaceous structures potentially related to sinistral convergence supports them having originated in response to the relative plate motion rather than local controls (e.g. indentors). This agrees with relative plate motion studies based on ocean floor reconstructions, which suggest a mid-Cretaceous change from sinistral to dextral convergence.     

SIGNIFICANCE AND CHARACTERISTICS OF OPHIOLITE SUITE IN LAJI SHAN, SOUTHERN QILIAN MOUNTAINS, QINGHAI PROVINCE,CHINA

SIGNIFICANCE AND CHARACTERISTICS OF OPHIOLITE SUITE IN LAJI SHAN, SOUTHERN QILIAN MOUNTAINS, QINGHAI PROVINCE,CHINAthedoctoralprogramofhighereducation (970 49119)     

Tectonic zoning of Wrangel Island,Arctic region

The Northern, Central, and Southern zones are distinguished by stratigraphic, lithologic, and structural features. The Northern Zone is characterized by Upper Silurian–Lower Devonian sedimentary rocks, which are not known in other zones. They have been deformed into near-meridional folds, which formed under settings of near-latitudinal shortening during the Ellesmere phase of deformation. In the Central Zone, mafic and felsic volcanic rocks that had been earlier referred to Carboniferous are actually Neoproterozoic and probably Early Cambrian in age. Together with folded Devonian–Lower Carboniferous rocks, they make up basement of the Central Zone, which is overlain with a angular unconformity by slightly deformed Lower (?) and Middle Carboniferous–Permian rocks. The Southern Zone comprises the Neoproterozoic metamorphic basement and the Devonian–Triassic sedimentary cover. North-vergent fold–thrust structures were formed at the end of the Early Cretaceous during the Chukchi (Late Kimmerian) deformation phase.     

Inversion of two-phase extensional basin systems during subduction of the Paleo-Pacific Plate in the SW Korean Peninsula:Implication for the Mesozoic “Laramide-style” orogeny along East Asian continental margin

During subduction, continental margins experience shortening along with inversion of extensional sedimentary basins. Here we explore a tectonic scenario for the inversion of two-phase extensional basin systems, where the Early-Middle Jurassic intra-arc volcano-sedimentary Oseosan Volcanic Complex was developed on top of the Late Triassic-Early Jurassic post-collisional sequences, namely the Chungnam Basin. The basin shortening was accommodated mostly by contractional faults and related folds. In the basement, regional high-angle reverse faults as well as low-angle thrusts accommodate the overall shortening, and are compatible with those preserved in the cover. This suggests that their spatial and temporal development is strongly dependent on the initial basin geometry and inherited structures.Changes in transport direction observed along the basement-sedimentary cover interface is a characteristic structural feature, reflecting sequential kinematic evolution during basin inversion. Propagation of basement faults also enhanced shortening of the overlying sedimentary cover sequences. We constrain timing of the Late Jurassic-Early Cretaceous(ca. 158-110 Ma) inversion from altered K-feldspar 40 Ar/39 Ar ages in stacked thrust sheets and K-Ar illite ages of fault gouges, along with previously reported geochronological data from the area. This "non-magmatic phase" of the Daebo Orogeny is contemporaneous with the timing of magmatic quiescence across the Korean Peninsula. We propose the role of flat/low-angle subduction of the Paleo-Pacific Plate for the development of the "Laramide-style" basement-involved orogenic event along East Asian continental margin.     

辽南金州隆起区构造变形及流体作用

详细的野外和室内宏观及微观构造分析和有限应变测量结果表明,自中生代以来,本区至少经历了两期变形,即早期的收缩为及后期的伸展反应,收缩应变主要表现为滑脱－－逆冲推覆作用,具有显著的构造层次性,自中、下构造怪次至上支次依次表现为：基底与盖层之间以角闪石及长石碎斑为主的糜棱岩为特征的韧性滑脱剪切罗系之上的逆冲推覆构造;在该构造２剪切主上部盖层中的寒武系,石炭系等逆冲于侏罗系之上的逆冲推覆构造;在该构造变形过程中伴随有强烈的岩浆活动,表明当时的区域热流值较高。伸展应变及同时发生的基底隆升作用,主要表现为基底和盖层中的韧性正剪切带及大量的正断层,基底中大量的NNE向张性白垩纪花岗斑岩脉及区域性的NNE向白垩纪盆地的形成都和本期构造活动相关。辽南地壳基底中大量的沿糜棱面理发育的长英质岩脉表明剪切变形过程中具有局部熔融作用的发生。对长英质岩脉经流体包裹体成分测试表明主要成分为分子水。在野外对长英质脉体的研究表明至少有两期：形成与滑脱作用有关的长英质脉体为含钾长石少、斜长石多、白色;而和伸展应变有关的长英质脉体钾长石含量明显增大,呈红色。两种长英质脉的褶皱变形反映了各自的变形机制。剪切作用过程中发生的动态局部熔融作用,具有自反馈的自组织特征,从而使长英质脉体在糜棱岩中呈现出韵律分布特征。辽南地壳在较短的时间内发生从收缩应变向伸展应变的转化。原因可能为收缩应变导致地壳显著缩短和增厚,并且同期的花岗岩浆的活动表明滑脱作用过程中莫霍面的初始温度较高并且区域热流值亦较高。这种地壳及其热状态的不均衡,导致地壳在较短的时间内发生基底的隆升及相伴随的伸展作用。     

Episodic intraplate deformation of stable continental margins: evidence from Late Neogene and Quaternary marine terraces,Cape Liptrap,Southeastern Australia

The Waratah Fault is a northeast trending, high angle, reverse fault in the Late Paleozoic Lachlan Fold Belt at Cape Liptrap on the Southeastern Australian Coast. It is susceptible to reactivation in the modern intraplate stress field in Southeast Australia and exhibits Late Pliocene to Late Pleistocene reactivation. Radiocarbon, optically stimulated luminescence (OSL), and cosmogenic radionuclide (CRN) dating of marine terraces on Cape Liptrap are used to constrain rates of displacement across the reactivated Waratah Fault. Six marine terraces, numbered Qt₆–Tt₁ (youngest to oldest), are well developed at Cape Liptrap with altitudes ranging from ～1.5 m to ～170 m amsl, respectively. On the lowest terrace, Qt₆, barnacles in wave-cut notches ～1.5 m amsl, yielded a radiocarbon age of 6090–5880 Cal BP, and reflect the local mid-Holocene sea level highstand. Qt₅ yielded four OSL ages from scattered locations around the cape ranging from ～80 ka to ～130 ka. It formed during the Last Interglacial sea level highstand (MIS 5e) at ～125 ka. Inner edge elevations (approximate paleo high tide line) for Qt₅ occur at distinctly different elevations on opposite sides of the Waratah Fault. Offsets of the inner edges across the fault range from 1.3 m to 5.1 m with displacement rates ranging from 0.01 mm/a to 0.04 mm/a. The most extensive terrace, Tt₄, yielded four Early Pleistocene cosmogenic radionuclide (CRN) ages: two apparent burial ages of 0.858 Ma ± 0.16 Ma and 1.25 Ma ± 0.265 Ma, and two apparent exposure ages of 1.071 Ma ± 0.071 Ma (¹⁰Be) and 0.798 Ma ± 0.066 Ma (²⁶Al). Allowing for muonic production effects from insufficient burial depths, the depth corrected CRN burial ages are 1.8 Ma ± 0.56 Ma and 2.52 Ma ± 0.88 Ma, or Late Pliocene. A Late Pliocene age is our preferred age. Offsets of Tt₄ across the Waratah Fault range from a minimum of ～20 m for terrace surface treads to a maximum of ～70 m for terrace bedrock straths. Calculated displacement rates for Tt₄ range from 0.01 mm/a to 0.04 mm/a (using a Late Pliocene age, ～2 Ma), identical to the rates calculated for the Last Interglacial terrace, Qt₅. This indicates that deformation at Cape Liptrap has been ongoing at similar time-averaged rates at least since the Late Pliocene. The upper terraces in the sequence, Tt₃ (～110 m amsl), Tt₂ (～140 m) and Tt₁ (～180 m) are undated, but most likely correlate to sea level highstands in the Neogene. Terraces Tt1–Tt4 show an increasing northward tilt with age.The Waratah Fault forms a prominent structural boundary in the Lachlan Fold Belt discernible from airborne magnetic and bouger gravity anomalies. Seismicity and deformation are episodic. Episodic movement on the Waratah Fault may be coincident with sea level highstands since the Late Pliocene, possibly from increased loading and elevated pore pressure within the fault zone. This suggests that intervals between major seismic events could be on the order of 100 ka.     

Character and kinematics of faults within the turbidite-dominated Lachlan Orogen: implications for tectonic evolution of eastern Australia

Fault zones within turbidite-dominated orogenic systems, typified by the Lachlan Orogen of eastern Australia, are characterised by higher than average strain and intense mica fabrics, transposition foliation and isoclinal folds, poly-deformation with overprinting crenulation cleavages, and steeply to moderately plunging meso- and micro-folds. They have a different character compared to the brittle–ductile fault zones of classic foreland fold-and-thrust belts such as the Appalachians and the Canadian Rocky Mountains. Multiple cleavages and transposition layering record a progressive shear-related deformation history. An intense mica fabric evolves initially during shortening of the overlying sedimentary wedge, but is progressively modified during rotation and emplacement to higher structural levels along the steep parts of inferred listric faults. The deformed wedge outside the fault zones generally undergoes one phase of deformation, shown by a weak to moderately developed slaty cleavage which is parallel to the axial surface of upright, subhorizontally plunging chevron-folds. Other faults within the turbidites of the Lachlan Orogen include the steep zones of ‘ductile’ strike-slip deformation that bound a centrally located, high T/low P metamorphic complex. Characterised by S–C mylonites, these ductile shear zones indicate a southward passage of the metamorphic complex as a crustal wedge, with emplacement to higher structural levels along a leading-edge, ductile thrust-fault. Ar–Ar dating constrains the timing of regional deformation to be mostly Late Ordovician through Silurian across the Lachlan Orogen. Faults in the low grade turbidite sequences record the kinematic evolution of the developing Lachlan Orogen and indicate progressive deformation associated with simultaneous, eastward propagating and migrating deformation fronts in both the western and eastern parts of the fold belt. These deformation fronts are related to ‘accretionary style’ deformation at the leading edges of overriding plates, in an inferred southwest Pacific-type subduction setting from the Late Ordovician to the mid-Devonian, along the former Gondwana margin. The fault zones effectively accommodate and preserve movements within the structurally thickening, migrating and prograding accretionary wedge.     

苏尼特左旗地区海西末——印支期构造活动特征

该文对内蒙古苏尼特左旗地区NNE向褶皱的形态、褶皱成生时承受的轴向载荷、压缩量乃至断裂及韧性剪切带的形态和变形域进行了对比研究,划分了变形序次。在此基础上认为该区存在印支运动的构造形迹,且该形迹是在海西末期形成的构造形迹的基础上,在同一区域构造应力场持续作用下递进变形的产物。      

Basement deformation: tertiary folding and fracturing of the Variscan Bielsa granite (Axial zone,central Pyrenees)

The Bielsa thrust sheet is a south-verging unit of the Axial zone in the central Pyrenees. The Bielsa thrust sheet consists predominantly of a Variscan granite unconformably overlain by a thin cover of Triassic and Cretaceous deposits. During the Eocene–Oligocene, Pyrenean compression, displacement of the Bielsa thrust sheet generated a large-scale south-verging monocline. Low temperature deformation of the Bielsa thrust sheet resulted in the development of: (1) E–W trending, asymmetric folds in the Triassic cover with amplitudes up to 1.5 km; these folds of the cover are related with normal and reverse faults in the granite and with rigid-body block rotations. (2) Pervasive fracturing within the Bielsa granite is also attributed to Pyrenean deformation and is consistent with a NNE to ENE shortening direction; two main, conjugate fault systems are associated with this direction of shortening, as is a subvertical strike-slip system with shallow-plunging slickenside lineations and a moderately dipping fault system with reverse movement; and (3) in addition, we recognise strike-slip and reverse shear bands, associated with sericitisation and brittle deformation of quartz and feldspar in the granite, that enclose Triassic rocks. Basement deformation within the Bielsa thrust sheet can be related to movement of faults developed to accommodate internal deformation of the hanging wall. Several models are proposed to account for this deformation during the southward displacement of the thrust.     

Mechanical aspects of thrust faulting driven by far-field compression and their implications for fold geometry

In this paper we present a mechanical model that intends to captures the kinematical aspects of thrust fault related folds induced by regional-scale far-field contraction. Fold shapes may be the only surface evidence of the geometry of underlying faults, so complex fault interactions are assessed in terms of how they influence fold geometry. We use the finite element method to model the fold and finite deformation frictional contact to model the activation and evolution of slip throughout preexisting faults. From several simulated 2D fault patterns we infer how one may form an anticline similar to that observed at Sheep Mountain Anticline, Wyoming.