Geometry and Kinematics of the Afogados da Ingazeira Shear Zone,Northeast Brazil

Numerous transcurrent NE-SW, mainly sinistral, and E-W dextral-trending shear zones transect Borborema Province, northeastern Brazil. The most important kinematic event involving those shear zones reflects deformation related to the Brasiliano (Pan-African) tectonic cycle. The Afogados da Ingazeira shear zone (AISZ) is probably the most important of the NE-SW-trending lineaments, having continuity for over 250 km. Field work associated with petrographic studies (including quartz c-axis patterns), conducted in an area encompassing the north-central part of this shear zone, indicate that sinistral transcurrent deformation was responsible for the main banding/foliation (C-S) observed in the rocks. Mineral assemblages and microstructural features are suggestive of a deformational history starting under low- to medium-amphibolite facies (thermal peak conditions) and decreasing until greenschist facies.     

Tectonic Evolution of the Lufilian Arc (Central Africa Copper Belt) During Neoproterozoic Pan African Orogenesis

The Lufilian arc of Central Africa (also called Katangan belt or Copperbelt) is a zone of low to highgrade metasedimentary (and subsidiary igneous) rocks of Neoproterozoic age hosting highgrade CuCoU and PbZn mineralizations. The Lufilian arc is located between the Congo and Kalahari cratons and defines a structure which is convex to the north. Three major phases of deformation characterize the construction of the Lufilian arc. The first phase (D1) called the “Kolwezian phase” developed folds and thrust sheets with a northward transport direction. D1 deformation occurred in the Lufilian arc between ca. 800 and 710 Ma, with a peak in the range 790–750 Ma. It is here correlated with the main deformation in the Zambezi belt. Southward-verging folds with the same trends as the D₁ structures were previously linked to a second tectonic event named Kundelunguian phase of the Lufilian orogeny. We show in this paper that they are backfolds developed during D1 along Katangan ramps and especially along the Kibaran foreland. The second phase (D2) of the Lufilian orogeny is the “Monwezi phase” including several large leftlateral strikeslip faults which have been activated successively. During this deformation phase, the eastern block of the belt rotated clockwise, giving the present day NWSE trend of D1 structures in this part of the Lufilian arc, and generating its convex geometry. The Mwembeshi dislocation, the major transcurrent shear zone separating the Zambezi and Lufilian arc, was mostly active during the D2 deformation phase. D2 deformation occurred between ca. 690 and 540 Ma. Such a long time interval is attributed to the migration of strikeslip faults developed sequentially from south to north, and probably to a slow convergence velocity during the collision between the Congo and Kalahari cratons. The third phase (D3) of the Lufilian orogeny is a late event called the “Chilatembo phase”, marked by structures transverse to the trends of the Lufilian arc. This deformation and the post-D_2′ uppermost Kundelungu sequence (Ks3 Plateaux Group), are younger than 540 Ma and probably early Paleozoic.     

新疆中天山北缘胜利达坂韧性剪切带

胜利达坂韧性剪切带沿中天山构造带北缘呈近EW向展布,为一条由一系列糜棱岩带、强片理化带及典型韧性变形显微构造所组成的强应变带。根据变形强度和原岩类型可划分出不同的构造带。显微构造的运动学和动力学分析表明,剪切带经历了早期的由南向北的斜冲推覆剪切及晚期的近水平右行走滑剪切。剪切带内发生了强烈的硅化、碳酸盐化、黄铁矿化、绢云母化和绿泥石化等蚀变,它们与金矿成矿作用关系密切。     

Archaean greenstone belts: A structaral test of tectonic hypothesis

Tectonic hypotheses for Archaean greenstone belts are tested against structural data from the Agnew belt, Western Australia. This belt shows the following critical features:

1. (1) A sialic infrastructure, formed by semi-concordant tonalitic intrusions, was present before tectonism began.

2. (2) An early deformation formed recumbent folds and a flat-lying schistosity; a second deformation formed major upright folds and steep ductile shear zones that outline the present tectonic belt. Neither deformation caused major disruptions in the stratigraphy. Both were accompanied by metamorph ism under upper greenschist to amphibolite facies conditions and low pressure.

3. (3) The belt is bounded on either side by tonalitic gneiss of unknown age, emplaced along steep shear zones.

Comparison with Phanerozoic orogenic belts representing a subduction complex, a collisional suture zone, and a collapsed marginal basin, indicates that the belt was not formed in any of these plate-tectonic environments.The second deformation in the belt resulted from regional crustal distortion, accomplished by right-lateral ductile wrenching along major N- to NNW-trending shear zones. Associated en-echelon buckle folding formed large granite-cored anticlines and tight synclines. The detailed structural pattern is not consistent with a diapiric origin for these folds. The ductile wrench faults may have been related to mantle flow patterns in a manner analogous to modern transform faults.     

A new tectonic model for the Cameroon Line,Central Africa

The Cameroon Line, a major geological feature in Central Africa, has been considered successively as a series of horsts and grabens, a continental rift and a mega-shear zone. It is marked out by about 60 anorogenic complexes and a dozen volcanic centres, all of which have alkaline affinity.Remote sensing allows us recognition of the main lineament trends: N70°, N-S, N135° and E-W, while autocorrelation analysis reveals a major fault zone striking N30° in western Cameroon and N15° in the northern region. A mega left-lateral shear zone is the model that best accounts for the fracture pattern and associated features such as linear and circular structures alignment of subvolcanic complexes, syntectonic leucogranites marking out older shear zones and vein dykes. The N70° Adamawa fault zone, a Pan-African fracture reworked during Albian-Aptian times, is the only shear zone of continental scale that could have initiated “en echelon” mega-tension gashes within the Cameroon Line during a Cainozoic left-lateral transcurrent movement.     

The origin of strain patterns resulting from contemporaneous deformation and metamorphism in the Sambagawa metamorphic belt

Abstract The magnitudes of plastic strains of 104 metacherts were determined from the deformed shape of initially spherical radiolarians in the Sambagawa high- P type metamorphic belt of Western Shikoku, Japan. The strain magnitude increases with increasing metamorphic temperature from several per cent to 250%. The a₂/a₃ ratio of strain ellipsoids in the higher metamorphic grades decreases with increasing metamorphic grade while the a₁/a₂ ratio increases rapidly. The long axis of the strain ellipsoid for every grade is nearly parallel to the length of the metamorphic belt, suggesting that the flow direction of the synmetamorphic deformation was uniform along the belt. A map of strain zones within the Sambagawa high- P type metamorphic belt reveals that the metamorphic belt underwent a progressive bulk inhomogeneous shear deformation and that the high-grade zones represent a deep-seated boundary shear zone on the accretionary wedge between a subducting oceanic plate and the immobile rigid continental plate.     

中天山北缘大型右旋走滑韧剪带研究

中天山北缘是一个近 EW向的大型右旋走滑韧剪带。宏、微观构造尺度的运动学研究表明 ,该带经历过至少二期韧性变形作用。第一期为从南向北的逆冲推覆韧剪变形 ,时代为中—晚志留世 ,以米什沟剖面为代表 ,对应于早古生代洋壳从北向南俯冲及稍后吐哈陆块朝中天山岛弧的碰撞事件。第二期为沿 EW方向的右旋走滑韧性变形 ,其构造形迹广泛分布于中天山北缘带各个地段 ;北天山石炭纪火山岩已卷入该期构造活动 ,走滑时代为晚石炭世—早二叠世 ,对应于晚石炭世塔里木与西伯利亚两大板块碰撞造山诱发的陆内变形、走滑剪切。走滑带中新生白云母 4 0 Ar/39Ar年龄为 ( 2 69± 5) Ma。剪切面理、拉伸线理、矿物韧剪构造、石英 C轴组构提供了构造运动学证据 ;地层不整合及同位素测年值提供了变形时间证据。二叠纪以后的构造事件也影响到中天山北缘带 ,但只有脆性变形形迹 ,无韧性剪切。最后对本区古生代构造演化进行了讨论     

Transposition of structures in the Neoproterozoic Kaoko Belt (NW Namibia) and their absolute timing

Three structural profiles across the Coastal Terrane, the Boundary Igneous Complex and the Orogen Core have been studied in the Kaoko Belt of northwestern Namibia. The oldest known Si fabric is inherited from an older tectono-metamorphic event. It occurs in the Coastal Terrane only and the extent of its reworking increases from south to north. The S1 foliation reactivates or folds Si fabric in the Coastal Terrane and appears as an early planar fabric in granitoids of the Boundary Igneous Complex and migmatites of the Orogen Core domain. Superimposed subvertical S2 fabric corresponds to axial plane cleavage of upright close to isoclinal folds and the extent of its development also increases from south to north. Active migration of partial melt during S2 development in the Orogen Core dates the onset of this deformation at ~550?Ma. Distribution of F2 fold axes and L2 stretching lineations suggests pure shear?Cdominated deformation associated with development of N?CS trending S2 cleavage preserved in the central profile, followed by sinistral simple shear?Cdominated deformation on newly developed NW?CSE trending pervasive cleavage in the northern part of the area. Such spatial variation in the deformation record is attributed to the irregular shape of the Congo Craton indenter that is reflected by heterogeneous development of the S2 cleavage front in the Coastal Terrane and the Boundary Igneous Complex. Common orientation of L1 and L2 stretching lineations and solid-state reworking on both S1 and S2 planes suggest single event of sinistral transpression since 550?Ma with strain partitioning into domains of oblique thrusting (reactivated S1) and transcurrent sinistral shearing (S2 and S3). Such succession of deformation structures suggests that major subvertical shear zones in the Kaoko Belt do not correspond to early crustal discontinuities, but rather reflect late strain localization during cooling.     

Evidence of 1.7- to 1.8-Ga Collisional Arc in the Kaoko Belt, NW Namibia

Detailed structural and isotopic analyses in the Hoanib and Ugab River Valleys indicate the existence of an exotic 1.7- to 1.8-Ga terrane in the Pan-African Kaoko Belt. This crustal block, called as Mudorib Complex, is imbricated between autochthonous and para-autochthonous rocks of Congo Craton, Kaoko Basin, and Western Kaoko Batholith units during the main tectono-thermal phase of Kaoko Belt collision around 580?Ma, involving the Rio de La Plata, Congo and Kahalari paleoplates. This terrain is positioned between the 1.9-Ga Pruwes Complex units of SW edge of the Congo Craton and the 0.58- to 0.55-Ga Amspoort Suite granitoids of the Western Kaoko Batholith. It is coincident with a regional positive aeromagnetic anomaly trending from NNW in the Ugab region to the Namibia-Angola border. Internally, Mudorib Complex consists in 1.73- to 1.81-Ga tonalitic?Ctrondhjemitic?Cdioritic?Cgranodioritic sequence of gneisses associated with cogenetic gabbroic and anothositic-gneisses in the core zone of this Pan-African structure. Field relationship and U?CPb zircon and Sm?CNd whole-rock isotope data combined with geochemical information suggest the existence of two rock associations in the Mudorib Complex, namely late Paleoproterozoic tonalitic?Ctrondhjemitic?Cdioritic-gneisses with island-arc affinity and tholeiitic metabasites of juvenile origin, showing Nd model age of 1.73?C2.17?Ga and ??Nd(t) of ?2.05?C+4.3. This 1.8- to 1.7-Ga complex is also intruded by granitic dykes formed at 1.49?C1.50?Ga with Nd model age of 1.75?C2.34?Ga during stable tectonic conditions. In addition to widespread Pan-African tectono-metamorphic events, a secondary metamorphic event of ~1.3?Ga is also recognized in the Mudorib rocks, which may be associated with accretion process of the complex to the Paleoproterozoic to Archean nucleus of the Kaoko Belt in the Hoanib River Valley.     

Deformation partitioning during transpression in response to Early Devonian oblique convergence,northern Appalachian orogen,USA

Transpressive deformation was distributed heterogeneously within the Central Maine belt shear zone system, which formed in response to Early Devonian oblique convergence during the Acadian orogeny in the northern Appalachians. ‘Straight’ belts are characterized by tight folds, S>L fabrics and sub-parallel form lines, and asymmetric structures that together indicate dextral–SE-side-up kinematics. In contrast, intervening zones between ‘straight’ belts are characterized by open folds and L≫S fabrics. Within both types of zone, metasedimentary rocks have fabrics defined by the same minerals at the same metamorphic grade, including a penetrative, moderately to steeply NE-plunging mineral lineation. Thus, we interpret accumulation of plastic deformation and regional metamorphic (re-) crystallization to have been synchronous across the Central Maine belt shear zone system. Discordance between inclusion trails in regionally developed porphyroblasts of garnet and staurolite and matrix fabrics in ‘straight’ belt rocks records shortening by tightening of folds and greater reorientation of matrix fabrics with respect to porphyroblasts. Kinematic partitioning of flow was responsible for the contrasting states of finite deformation recorded in the Central Maine belt shear zone system. Perturbations in the flow were caused by serially developed thrust-ramp anticlines in the stratigraphic succession immediately above the Avalon-like basement, at which décollement of the shear zone system was initially rooted. General shear deformation at the ramps involved strain softening with an enhanced component of noncoaxial flow. In contrast, deformation during extrusion in the intervening zones involved strain hardening with a greater component of coaxial flow. Part of the thickening stratigraphic succession exceeded T_solidus, reflected by the occurrence of migmatites and granites. The latter were partly sourced from the underlying Avalon-like basement that was involved in the deformation and melting.     

The geology of the Taparko gold deposit, Birimian greenstone belt, Burkina Faso, West Africa

The Taparko gold deposit, located in the eastern branch of the Proterozoic Birimian Bouroum-Yalogo greenstone belt (Burkina Faso) consists of a network of quartz veins developed in a N 170° trending shear zone (250 m wide, 4 km long) superimposed on the regional Birimian structural pattern. The quartz vein network is composed of: (a) a dominant array of quartz veins (type 1), parallel to the shear zone and comprising strongly deformed dark quartz exhibiting foliation, layering, ribbon, tension gashes, etc.; (b) oblique and subparallel related veins (type 2) of gray to white weakly deformed quartz crosscutting the dominant quartz veins resulting in breccia structures; and (c) shallow dipping veins (type 3), cross-cutting veins types 1 and 2 and filled by undeformed white buck structure quartz. Cross-cutting relationships and different quartz types in different veins and within individual veins imply a concomitant filling of the veins during the progressive deformation. Initial sinistral transcurrent shearing evolved with time to sinistral reverse shearing. Metallic minerals occur only in type 1 and 2 veins and were deposited in two stages, with native gold being related to second stage sulfides. Gold (and chalcopyrite) precipitated preferentially upon the surfaces of fractured pyrite grains in low-pressure sites (pressure shadow zones) around and/or within the sulfide grains (along subsequently annealed fractures). The formation of the South Taparko deposit can be divided into a succession of events: (a) during the first event, N 170°-directed sinistral transcurrent shearing resulted in a N 20° mylonitic foliation and fractured rock which allowed H₂O-, CO₂- and SiO₂-rich fluids to circulate and deposit quartz with buck texture; (b) during the second event, type 1 quartz was strongly deformed and type 2 veins formed with sigmoidal shapes as viewed on a horizontal plane; and (c) during the third event, the sinistral transcurrent shearing evolved to sinistral reverse shearing and the deformation style evolved correspondingly from ductile to brittle-ductile. During the last phase of deformation gold nucleated and deposited in low-pressure zones. Received: 9 July 1997 / Accepted: 23 March 1998     

A Large-Scale Palaeozoic Dextral Ductile Strike-Slip Zone:the Aqqikkudug-Weiya Zone along the Northern Margin of the Central Tianshan Belt,Xinjiang,NW China

The nearly E-W-trending Aqqikkudug-Weiya zone, more than 1000 km long and about 30 km wide, is an important segment in the Central Asian tectonic framework. It is distributed along the northern margin of the Central Tianshan belt in Xinjiang, NW China and is composed of mylonitized Early Palaeozoic greywacke, volcanic rocks, ophiolitic blocks as a mélange complex, HP/LT-type bleuschist blocks and mylonitized Neoproterozoic schist, gneiss and orthogneiss. Nearly vertical mylonitic foliation and sub-horizontal stretching lineation define its strike-slip feature; various kinematic indicators, such as asymmetric folds, non-coaxial asymmetric macro- to micro-structures and C-axis fabrics of quartz grains of mylonites, suggest that it is a dextral strike-slip ductile shear zone oriented in a nearly E-W direction characterized by "flower" strusture with thrusting or extruding across the zone toward the two sides and upright folds with gently plunging hinges. The Aqqikkudug-Weiya zone experienced at least two stages of ductile shear tectonic evolution: Early Palaeozoic north vergent thrusting ductile shear and Late Carboniferous-Early Permian strike-slip deformation. The strike-slip ductile shear likely took place during Late Palaeozoic time, dated at 269(5 Ma by the40Ar/39Ar analysis on neo-muscovites. The strike-slip deformation was followed by the Hercynian violent S-type granitic magmatism. Geodynamical analysis suggests that the large-scale dextral strike-slip ductile shearing is likely the result of intracontinental adjustment deformation after the collision of the Siberian continental plate towards the northern margin of the Tarim continental plate during the Late Carboniferous. The Himalayan tectonism locally deformed the zone, marked by final uplift, brittle layer-slip and step-type thrust faults, transcurrent faults and E-W-elongated Mesozoic-Cenozoic basins.     

Structural and Chronological Evidence for the India-Eurasia Collision of the Early Paleocene in the Eastern Himalayan Syntaxis, Namjagbarwa

The eastern Himalayan syntaxis in Namjagbarwa is a high-grade metamorphic terrain formed by the India-Eurasia collision and northward indentation of the Indian continent into Asia. Right- and left-lateral slip zones were formed by the indentation on the eastern and western boundaries of the syntaxis respectively. The Dongjug-Mainling fault zone is the main shear zone on the western boundary. This fault zone is a left-lateral slip belt with a large component of thrusting. The kinematics of the fault is consistent with the shortening within the syntaxis, and the slipping history along it represents the indenting process of the syntaxis. The Ar-Ar chronological study shows that the age of the early deformation in the Dongjug-Mainling fault zone ranges from 62 to 59 Ma. This evidences that the India-Eurasia collision occurred in the early Paleocene in the eastern Himalayan syntaxis.     

Thrusting and transpressional shearing in the Pan-African nappe southwest El-Sibai core complex,Central Eastern Desert,Egypt

The Wadi El-Shush area in the Central Eastern Desert (CED) of Egypt is occupied by the Sibai core complex and its surrounding Pan-African nappe complex. The sequence of metamorphic and structural events in the Sibai core complex and the enveloping Pan-African nappe can be summarized as follows: (1) high temperature metamorphism associated with partial melting of amphibolites and development of gneissic and migmatitic rocks, (2) between 740 and 660 Ma, oblique island arc accretion resulted in Pan-African nappe emplacement and the intrusion of syn-tectonic gneissic tonalite at about 680 ± 10 Ma. The NNW–SSE shortening associated with oblique island arc accretion produced low angle NNW-directed thrusts and open folds in volcaniclastic metasediments, schists and isolated serpentinite masses (Pan-African nappe) and created NNE-trending recumbent folds in syn-tectonic granites. The NNW–SSE shortening has produced imbricate structures and thrust duplexes in the Pan-African nappe, (3) NE-ward thrusting which deformed the Pan-African nappe into SW-dipping imbricate slices. The ENE–WSW compression event has created NE-directed thrusts, folded the NNW-directed thrusts and produced NW-trending major and minor folds in the Pan-African nappe. Prograde metamorphism (480–525 °C at 2–4.5 kbar) was synchronous with thrusting events, (4) retrograde metamorphism during sinistral shearing along NNW- to NW-striking strike-slip shear zones (660–580 Ma), marking the external boundaries of the Sibai core complex and related to the Najd Fault System. Sinistral shearing has produced steeply dipping mylonitic foliation and open plunging folds in the NNW- and NE-ward thrust planes. Presence of retrograde metamorphism supports the slow exhumation of Sibai core complex under brittle–ductile low temperature conditions. Arc-accretion caused thrusting, imbrication and crustal thickening, whereas gravitational collapse of a compressed and thickened lithosphere initiated the sinistral movement along transcurrent shear zones and low angle normal ductile shear zones and consequently, development and exhumation of Sibai core complex.     

Aseismic deformation in the Alps: GPS vs. seismic strain quantification

Neotectonics of the Western and Central Alps is characterized by ongoing widespread extension in the highest zones of the chain and transcurrent/compressive tectonics at the external limits of the belt. The overall geodetically measured deformations also indicate extension across the Western Alps. There is a good qualitative coherency between seismotectonic and geodetic approaches. Here we attempt to quantify the seismic part of the deformation. The seismic strain is compared to the deformation derived from geodesy. In sub‐areas of homogeneous seismic stress/strain, we computed the total seismic moment tensor and related strain tensor. This study provides new quantitative elements about the ongoing geodynamic processes in the alpine belt. The important discrepancies obtained between seismic strains and geodetically‐measured deformations raise the issue of aseismic deformation in the Alps, which could be related to elastic loading, creeping and/or a slower ductile‐style deformation.     

The transpressional connection between Dom Feliciano and Kaoko Belts at 580�C550?Ma

A new U?CPb SHRIMP age of 551?±?4?Ma on a mylonitic porphyry that intruded into the Sierra Ballena Shear Zone (Southernmost Dom Feliciano Belt, Uruguay) and a review of relevant published data make possible a more refined correlation and reconstruction of Brasiliano/Pan-African transpressional events. Paleogeographic reconstruction, kinematics and timing of events indicate a connection between the shear systems of the Dom Feliciano and Kaoko Belts at 580?C550?Ma. Sinistral transpression recorded in shear zones accommodates deformation subsequent to collision between the Congo and Río de la Plata Cratons. The correlation is strengthened by the similarity of magmatic and metamorphic ages in the Coastal Terrane of the Kaoko Belt and the Punta del Este Terrane of the Dom Feliciano Belt. This post-collisional sinistral transpression brought these units near to their final position in Gondwana and explains the different evolution at 550?C530?Ma. While in the Kaoko Belt, an extensional episode resulted in exhumation as a consequence of collision in the Damara Belt, in the Dom Feliciano Belt, sinistral transpression occurred associated with the closure of the southern Adamastor Ocean due to Kalahari-Río de la Plata collision.     

Deciphering polymetamorphic episodes in high-grade metamorphic orogens: Constraints from PbSL, Sm/Nd and Lu/Hf garnet dating of low- to high-grade metasedimentary rocks from the Kaoko belt (Namibia)

Three dating techniques for metamorphic minerals using the Sm–Nd, Lu–Hf and Pb isotope systems are combined and interpreted in context with detailed petrologic data from crustal segments in NW Namibia. The combination of isochron ages using these different approaches is a valuable tool to testify for the validity of metamorphic mineral dating. Here, PbSL, Lu–Hf and Sm–Nd garnet ages obtained on low- to medium-grade metasedimentary rocks from the Central Kaoko Zone of the Neoproterozoic Kaoko belt (NW Namibia) indicate that these samples were metamorphosed at around 550–560 Ma. On the other hand, granulite facies metasedimentary rocks from the Western Kaoko Zone underwent two phases of high-grade metamorphism, one at ca. 660–625 Ma and another at ca. 550 Ma providing substantial evidence that the 660–625 Ma-event was indeed a major tectonothermal episode in the Kaoko belt. Our age data suggest that interpreting metamorphic ages by applying a single dating method only is not reliable enough when studying complex metamorphic systems. However, a combination of all three dating techniques used here provides a reliable basis for geochronological age interpretation.     

Progressive shortening axis rotation recorded by Variscan synkinematic granites : example of the South Armorican shear zone in the Vendée (France)

The Variscan continental collision is expressed by large shear zones in Western Europe. The synthesis of granite ages, related to different deformation fields in the Vendée area, suggests a geodynamic model for the tectonic evolution of this part of the Variscan belt between 370 Ma – 320 Ma. After the first step of the continental collision, leading to high temperature and anatexis at 375-360 Ma, the south-eastern part of the Armorican massif underwent large dextral shearing along N110-N125 trending shear zones, related to a bulk NNW-SSE shortening direction, up to early Visean time. Large-scale displacements progressively decreased at around 345-340Ma. During middle Visean time, the shortening axis direction rotated towards a NNE-SSW position implying changes in the regional deformation field. The occurrence of N70-N100 sinistral and N110-N130 dextral conjugate shear zones within leucogranites are related to that epoch. Finally, a new dextral shear zone system, trending N130-N150 along the Parthenay shear zone, occurs during late Visean time. This progressive middle Visean change of shortening direction probably corresponds to a major change in the Iberian plate motion and indentation during the Mississipian collision.     

天山东段推覆构造研究

本文概括性总结了天山东段大型推覆构造的基本特征。根据地质证据和同位素年龄,东天山存在早古生代末,晚古生代晚期和新生代三期推覆构造;根据推覆构造分布规律及构造背景,在平面上划分为五大推覆带、9个大型韧剪带;根据出露岩石的矿物变形相将东天山推覆构造划分为深、中深和浅三个深度层次;通过韧剪变形组构的观察分析,确定了多期韧性变形性质与运动方向。糜棱岩中超微构造、古应力及小构造变形缩短率测量统计,证明东天山推覆变形具有显著的地壳缩短增厚作用。新生代板块碰撞导致本区中新生代盆地基底向造山带A型俯冲,造山带向盆地推覆,其结果就构成了今日看到的镶嵌状盆地-山脉构造地貌景观。     

Transpression

Transpression is considered as a wrench or transcurrent shear accompanied by horizontal shortening across, and vertical lengthening along, the shear plane. A model for the strain in transpression is derived, from which the shape and orientation of the finite strain ellipsoid, and the stretch and rotation of lines can be determined. Shortening across the zone of transpression leads to oblate finite strain ellipsoids (k<1).By considering the superposition of small increments of strain various model deformation paths are computed. These are used to interpret the development of structures, such as en-échelon folds, in transpression zones. The incremental strain ellipsoid allows prediction of the orientation of the principal stresses and hence brittle structures within such zones. The model is also applied to bends and terminations of shear zones and used to interpret the observed patterns of folds and fractures in these.