AMS record of brittle dilation,viscous-stretching and gravity-driven magma ascent in area of magma-rich crustal extension (Vosges Mts., NE France)

Orogenic compression-related fabrics (~340–335 Ma) were reworked during regional extensional deformation (~328–325 Ma) in a large anatectic crustal domain of the Central Vosges (NE France). The extension was first accommodated by brittle dilation affecting vertically anisotropic high-grade rocks associated with emplacement of subvertical granitic sheets. The AMS fabric of granitoids is consistent with highly partitioned transtensional deformation marked by alternations of flat and steep foliations and development of orthogonal lineations. This deformation passes to top-to-the-southwest ductile shearing expressed in southerly migmatitic middle crust. The AMS fabric revealed moderately west-dipping foliations bearing subhorizontal NNW–SSE-trending lineations and predominantly plane strain to prolate shapes. This fabric pattern is interpreted as a viscous response of stretched partially molten crust during continuous ductile extension. Vertical ascent of voluminous granites and stoping of the upper crust occurs further south. This gravity ascent triggered by extension leads to development of south-dipping AMS foliations, south-plunging lineations and oblate fabrics in various crustal granites. Vertical shortening related to ascent of these (~325 Ma) granitoids and persistent N–S stretching is responsible for reworking and remelting of originally vertical compression-related fabric in roof supracrustal granites (~340 Ma) and development of highly prolate fabrics in these rocks. This work shows that the finite shape of AMS fabric ellipsoid is highly sensitive to both strain regime and superpositions of orthogonal deformation events.     

The transition from brittle to ductile deformation in the Sambagawa metamorphic belt, Japan

The dominant deformation mechanism during the Sambagawa metamorphism changes from brittle to ductile with increasing metamorphic temperature. The magnitude of plastic strains inferred from the shapes of deformed radiolaria in metachert increases sharply across the boundary between the epidote-pumpellyite-actinolite zone and the epidote-actinolite zone. The synmetamorphic crack density of metachert is an indicator of the contemporaneous brittle strain of rocks, and it decreases sharply as the grade reaches the epidote-actinolite zone. Hence, the ratio of the ductile strain to the brittle strain of metachert decreases rapidly across the transition to the epidote-actinolite zone of the Sambagawa metamorphic belt.
The sharp change of the ductile strain magnitude also takes place at the epidote-actinolite grade in the Shimanto metamorphic belt of Japan, an example of the intermediate pressure facies series of metamorphism. It is concluded that the transition from brittle to ductile deformation takes place at about 300-400°C. and is independent of pressure of metamorphism.     

Deformation path concepts in strain analysis: Applications for study of ductile shear zones

The internal fabric of a deformed rock represents the state of finite strain. In some special cases the fabrics also record the strain history of the deformed body. These special cases can profitably be utilized to compare the predictions of dynamic models and strain paths in natural deformations. In this contribution, the concept of deformation path in the study of ductile shear zones has been demonstrated.     

辽南金州拆离断层带中花岗质岩石的变形:显微构造、组构与年代学分析

花岗岩(脉)在中下地壳韧性剪切带中普遍发育,如何正确鉴别剪切带中剪切前、剪切期及剪切后花岗岩(脉)以及正确理解剪切过程中构造变形与岩浆作用之间的关系一直是一个重要课题。本文以辽南金州拆离断层带为研究对象,选取中部地壳伸展作用过程中具有不同变形表现的花岗岩(脉)开展宏观-微观构造观察、石英EBSD组构分析及锆石LA-ICP-MS年代学测试等工作,从而进一步丰富构造-岩浆关系判别准则。剪切前花岗岩(脉)多变形强烈且具有后期固态变形叠加在早期高温岩浆组构之上的特点,而剪切期的花岗岩由于侵位的时间不同,岩石的变形程度也会不同。剪切晚期侵入的岩脉遭受了较弱的晶内塑性变形,而剪切早期的岩脉可以显示岩浆流动或结晶后高温至中温固态变形。从组构特点上看,剪切前和剪切期花岗质岩石石英c轴组构大多表现为中高温组构叠加有低温组构的特点。剪切后的花岗质岩石仅发生微弱的晶内变形或未变形而显示低温或无规律的组构特征。对五个典型的样品进行年代学测试,其结果符合相应的期次划分类型。应用宏观构造、显微构造与组构分析,结合年代学测试综合分析,对于辽南变质核杂岩构造-岩浆活动性进行了精细划分,包括134~130Ma初始伸展阶段,130~115Ma峰期伸展与强烈岩浆活动阶段,以及115Ma前后伸展作用结束。     

Partial melting and melt segregation in footwall units within the contact aureole of the Sudbury Igneous Complex (North and East Ranges,Sudbury structure), with implications for their relationship to footwall Cu–Ni–PGE mineralization

We performed detailed field and drill core mapping of partial melting features and felsic rocks (footwall granophyres, FWGRs) representing segregated and crystallized partial melts within the contact aureole of the Sudbury Igneous Complex (SIC) in the 1.85 Ga Sudbury impact structure. Our results, derived from mapping within the North (Windy Lake, Foy, Wisner areas) and East Ranges (Skynner, Frost areas) of the structure, reveal that partial melting was widespread in both felsic and mafic footwall units up to distances of 500 m from the basal contact of the SIC. Texturally and mineralogically, significant differences exist between rocks formed by partial melting within and between localities. In general, however, melt bodies are dominated by different quartz-feldspar intergrowths (e.g. granophyric, graphic) and miarolitic cavities up to 5 cm in diameter. Major and trace element compositions of Wisner and Frost FWGRs imply that they crystallized from melts dominantly derived from partial melting of felsic Levack Gneiss and Cartier granitoid rocks, as well as from gabbroic rocks only at Frost. These results accord with our observations on in situ partial melting features and crystallized melt of microscopic scale in both felsic and mafic rocks. We conclude that partial melting occurred at a pressure of 1.5 ± 0.5 kbar and at temperatures up to 750°C in the Wisner area and up to 900°C in the Frost and Windy Lake areas. Segregations of partial melt into veins and dikes are present in all localities, and were promoted by deformation of the Sudbury structure in the Penokean orogeny as indicated by dominant strike directions. Whereas veins and dikes reflect brittle conditions during melt migration, sheared melt pods in the Sudbury breccia matrix indicate ductile conditions during their crystallization. Our results suggest a close genetic association of partial melting, melt segregation, and hydrothermal processes responsible for remobilization of Cu–Ni–PGE sulphides into and within the SIC footwall.     

Construction of crossed girdles by superposing four subfabrics,each with a single maximum

Commonly, basal glide is the predominant deformation mechanism of quartz in tectonites. Therefore, local deformation is probably mostly progressive simple shear rotating the sheared domains as well as deforming them. If a tectonite body is constrained to be deformed irrotationally and approximately homogeneously throughout, it is necessarily traversed by closely spaced material surfaces that are approximately plane and orthogonal originally, and stay so through time. These surfaces act as internal boundaries and enforce cancellation of the rigid-body rotations of, in the general case, four distinct families of domains, with slip planes and directions mutually mirror-symmetric. The overall symmetry of the fabric is orthorhombic, with the mirror planes coinciding with the principal planes of strain. Certain grains with basal planes in favorable orientation for one of the four ideal simple shears could initiate the deformation, and because of the need for compatibility, entrain neighboring grains into a similar strain, making the surroundings of an initiating grain a shear zone. Compatibility also requires thec-axes of grains in a domain to be rotated progressively toward the direction of maximum shortening. If the original orientation of crystallographic axes was random, domains of one family thus acquire a fabric with a single maximum, and the four resulting fabrics with single maxima combine to form crossed-girdle patterns. Depending on the orientation of the average shear planes and slip directions in the four families, the crossed girdles can be of different types; most fabric types that have been observed in quartz tectonites can be obtained by superposition. Crossed-girdle fabrics with low symmetry result from non-coaxial strain histories.     

太行山中北段褶皱构造序列

太行山中北段中－深变质岩区的褶皱构造变形复杂，不同期次间叠加改造强烈，构造置换作用明显，作者采用变质岩区构造解析方法，在观察，测量，分析了大量构造面，线组构的基础上，划分出５期褶皱构造，建立了本区的构造变形序列，并认为构造变形经历了从强塑性变表到韧脆性变形的演化过程，反映出地壳从纵向增厚作用转变为变质核杂岩隆升的演化过程。     

华北克拉通基底花岗质片麻岩变形和流变学研究——以辽西寺儿堡地区为例

辽西寺儿堡镇新太古代花岗质片麻岩内发育的宏观、微观构造变形特征表明该地区曾遭受了强烈的韧性变形改造。花岗质岩石变形程度在初糜棱岩–糜棱岩之间,岩石经历了SWW向左行剪切作用改造。岩石中石英有限应变测量判别结果表明,构造岩类型为L-S型,为平面应变。岩石的剪应变平均值为1.43,运动学涡度值为0.788~0.829,指示岩石形成于以简单剪切为主的一般剪切变形中。此外,石英颗粒以亚颗粒旋转重结晶和颗粒边界迁移重结晶作用为主,长石颗粒塑性拉长,部分发生膨凸式重结晶作用;石英组构特征(EBSD)揭示石英以中–高温柱面滑移为主;石英颗粒边界具有明显的分形特征,分形维数值为1.151~1.201,指示了中高温变形条件。综合石英、长石的变形行为、石英组构特征以及分形法Kruhl温度计的判别结果,推断辽西寺儿堡镇新太古代花岗质片麻岩经历过480~600℃的中高温变形,其同构造变质相为高绿片岩相-低角闪岩相。花岗质岩石的古差异应力为10.62~12.21 MPa,估算的应变速率为10~(–11.67)~10~(–13.34) s~(–1),即缓慢的变形,可能记录早期中高温、低应变速率的韧性变形过程,反映华北克拉通基底中下部地壳变形特征。     

The Sudbury Structure (Ontario,Canada): a tectonically deformed multi-ring impact basin

The occurrence of shock metamorphic features substantiates an impact origin for the 1.85 Ga old Sudbury Structure, but this has not been universally accepted. Recent improvements in knowledge of large-scale impact processes, combined with new petrographic, geochemical, geophysical (LITHOPROBE) and structural data, allow the Sudbury Structure to be interpreted as a multi-ring impact structure. The structure consists of the following lithologies: Sudbury Breccia —dike breccias occurring up to 80 km from the Sudbury Igneous Complex (SIC); Footwall rocks and Footwall Breccia — brecciated, shocked crater floor materials, in part thermally metamorphosed by the overlying SIC; Sublayer and Offset Dikes, Main Mass of the SIC and Basal Member of the Onaping Formation (OF) — geochemically heterogeneous coherent impact melt complex ranging from inclusion-rich basal unit through a dominantly inclusion-free to a capping inclusion-rich impact melt rock; Grey Member of OF — melt-rich impact breccia (suevite); Green Member of OF — thin layer of fall back ejecta; Black Member of OF — reworked and redeposited breccia material; Onwatin and Chelmsford Formations — post-impact sediments. Observational and analytical data support an integrated step-by-step impact model for the genesis of these units. Analysis of the present spatial distribution of various impact-related lithologies and shock metamorphic effects result in an estimated original rim-to-rim diameter of the final crater of 200 or even 280 km for the Sudbury Structure, prior to tectonic thrusting and deformation during the Penokean orogeny.     

Kinematic analysis of mélange fabrics: examples and applications from the McHugh Complex, Kenai Peninsula, Alaska

Permian to Cretaceous mélange of the McHugh Complex on the Kenai Peninsula, south-central Alaska includes blocks and belts of graywacke, argillite, limestone, chert, basalt, gabbro, and ultramafic rocks, intruded by a variety of igneous rocks. An oceanic plate stratigraphy is repeated hundreds of times across the map area, but most structures at the outcrop scale extend lithological layering. Strong rheological units occur as blocks within a matrix that flowed around the competent blocks during deformation, forming broken formation and mélange. Deformation was noncoaxial, and disruption of primary layering was a consequence of general strain driven by plate convergence in a relatively narrow zone between the overriding accretionary wedge and the downgoing, generally thinly sedimented oceanic plate. Soft-sediment deformation processes do not appear to have played a major role in the formation of the mélange. A model for deformation at the toe of the wedge is proposed in which layers oriented at low angles to σ₁ are contracted in both the brittle and ductile regimes, layers at 30–45° to σ₁ are extended in the brittle regime and contracted in the ductile regime, and layers at angles greater than 45° to σ₁ are extended in both the brittle and ductile regimes. Imbrication in thrust duplexes occurs at deeper levels within the wedge. Many structures within mélange of the McHugh Complex are asymmetric and record kinematic information consistent with the inferred structural setting in an accretionary wedge. A displacement field for the McHugh Complex on the lower Kenai Peninsula includes three belts: an inboard belt of Late Triassic rocks records west-to-east-directed slip of hanging walls, a central belt of predominantly Early Jurassic rocks records north–south directed displacements, and Early Cretaceous rocks in an outboard belt preserve southwest–northeast directed slip vectors. Although precise ages of accretion are unknown, slip directions are compatible with inferred plate motions during the general time frame of accretion of the McHugh Complex. The slip vectors are interpreted to preserve the convergence directions between the overriding and underriding plates, which became more oblique with time. They are not considered indicative of strain partitioning into belts of orogen-parallel and orogen-perpendicular displacements, because the kinematic data are derived from the earliest preserved structures, whereas fabrics related to strain partitioning would be expected to be superimposed on earlier accretion-related fabrics.     

Small-scale ductile shear zones as transposed rheologically weak domains: A numerical modeling investigation and practical application

We test the hypothesis that small ductile shear zones are developed from initial rheologically weak domains. We regard weak domains as ellipsoidal inhomogeneities and apply Eshelby's formalism extended for power-law viscous materials to investigate the kinematics and finite strain evolution of the partitioned flow fields in weak domains. We show that, under an imposed bulk flow field, weak domains, regardless of their initial shapes and orientations, deform into zone-like features at relatively small bulk strains and the deformation paths inside weak domains have all characteristics expected in ductile shear zones. We apply our model to the Cap de Creus area Spain, where abundant small ductile shear zones exist. To relate the fabrics inside these shear zones with the regional deformation, we take a multi-scale approach. We assume that the area contained many weak domains which were randomly shaped and oriented initially and were deformed into shear zones eventually in response to the regional flow. We constrain the regional flow field by the fabric patterns across the area and compute numerically the partitioned flow fields in individual weak domains. The latter are related to fabrics inside shear zones. Our model reproduces first-order features of field-observed fabrics. Although the deformation path of each shear zone was close to simple shearing, the deformation of the whole belt was not. Our approach also resolves the strain compatibility problem for a finite-sized shear zone embedded in a far less deformed country rock.     

新疆东天山觉罗塔格韧性挤压带基本特征及动力学意义

新疆觉罗塔格韧性挤压带发育于吐哈地块和中天山地块之间石炭系东西向火山-沉积建造中,由一组走向东西、产状陡立的透入性片理组成。眼球状结构、平行带状结构和菱形网状结构是韧性挤压带不同构造区亚带的排布格式,它们相对变形带主界面而言具有很好的对称性。片理构造、拉伸线理构造、同生褶皱构造、布丁构造、压力影构造、碎斑构造、粒内面理构造、位错构造和矿物光轴优选定向等韧性构造形迹发育,这些不同尺度的韧性变形构造形迹的组构都具以片理面为对称面而呈现出对称的特征。韧性挤压带横分为3个亚带,3个亚带岩石形变相变和应力应变等方面都呈横向对称状分布。“奶油饼”结构是韧性挤压带的应变结构。该韧性挤压带成因于南北两侧吐哈地块和中天山地块的南北向水平共轴挤压作用,形成于255Ma至280Ma(早二叠世),压扁机制是该韧性变形带的变形机制,它的力学性质表明该韧性变形带不应属于南北两大板块之间的俯冲-剪切带,其成因可能与板块孤后盆地的对称开合有关。     

塔里木盆地北缘兴地断裂构造变形特征

兴地断裂发生在中元古代末期，使中元古巨厚的沉积岩发生了强烈褶皱和隆起，并伴有大量岩浆侵入和区域变质作用。在兴地断裂形成的同时，发生了第一期构造变形，其特点以韧性变形为主，由三个变形幕构成，形成了本区主要构造骨架；晚元古代本区进入晋宁期发展阶段，团结的塔里木地台基底局部裂开，形成一系列近东西向的断陷盆地，发生了第二期变形，形成以塑性变形为主的板劈理和千枚理为其特征。该期变形结束了塔里木基底发展，进入了稳定盖层沉积发展阶段；进入早古生代，兴地断裂控制了该时期的沉积作用，之后发生第三期变形，以脆性变形为主，形成一系列碎裂岩和脆性变形组构，使兴地断裂形成几十米乃至上百米宽的破碎带，从而改造了早期的糜棱岩；至中、新生代，兴地断裂再次活动，形成断裂两侧南升北降的扭动形迹。通过对兴地断裂的深入探讨，笔者认为：该断裂具有线性特征明显，活动时间漫长，构造变形复杂，是塔里木盆地北缘规模巨大的复活大断裂。     

江苏东海CCSD主孔超高压变形与折返变形的叠加关系

位于苏鲁超高压变质地体南部的中国大陆科学钻探工程（CCSD）主孔岩石经历了超高压变形及多期折返变形。第一期折返变形为伸展折返变形,榴辉岩发生角闪岩相退变质作用,没有新生面理或线理的发育,基本保留了超高压阶段的S-L组构,并有显示熔融体特征的强退变榴辉岩发育。第二期折返变形为SEE-NWW向挤压折返变形,超高压变形期形成的不同岩石类型在本期变形中表现出不同的叠加变形现象,榴辉岩类岩石早期形成的S倾面理主体部分转为SEE倾,但拉伸线理产状与超高压变形期的近SN走向基本一致,反映早期面理沿NNE轴向的重褶作用,局部又被向SEE缓倾的韧性剪切带切割;而片麻岩类岩石在超高压变形期形成的S-L组构的主体部分已被新生成的总体向SEE缓倾的S-L组构置换,反映早期面理不仅重褶,而且大部分再度发生韧性剪切变形,具SEE向NWW的逆冲剪切指向,矿物普遍重新定向。第三期折返变形发育具NWW向SEE正滑剪切指向的韧性剪切带,并伴随大量“Z”型褶皱构造的发育。第四期折返变形以NWW向SEE正滑的张性或张扭性脆性断裂活动为主。探讨了苏鲁超高压变质地体折返变形的力学机制及CCSD主孔岩石面理变化的形成机制。     

辉绿岩脆-塑性变形转化的高温高压实验研究

以天然叶腊石为传压介质, 在温度800~100 0℃、围压0.6~1.0 GPa和应变速率10-4~10-5 s-1条件下, 对Maryland辉绿岩的脆性-塑性转化进行了实验研究.实验结果表明, 在10-4~10-5 s-1应变速率和固定围压1.0 GPa条件下, 当温度低于800℃时, 岩石变形为典型脆性破裂; 温度高于1000℃时岩石变形以准稳态蠕变为主; 温度在800~950℃之间, 岩石变形从脆性破裂向准塑性流动转化.温度变化对岩石脆-塑性转化影响敏感度高于压力变化对变形的敏感度.显微构造观察显示, 辉绿岩脆-塑性转化以稀疏弥漫状共轭塑性流动网络为特征.      

Structural and metamorphic evolution of the Moornambool Metamorphic Complex,western Lachlan Fold Belt,southeastern Australia

The wedge‐shaped Moornambool Metamorphic Complex is bounded by the Coongee Fault to the east and the Moyston Fault to the west. This complex was juxtaposed between stable Delamerian crust to the west and the eastward migrating deformation that occurred in the western Lachlan Fold Belt during the Ordovician and Silurian. The complex comprises Cambrian turbidites and mafic volcanics and is subdivided into a lower greenschist eastern zone and a higher grade amphibolite facies western zone, with sub‐greenschist rocks occurring on either side of the complex. The boundary between the two zones is defined by steeply dipping L‐S tectonites of the Mt Ararat ductile high‐strain zone. Deformation reflects marked structural thickening that produced garnet‐bearing amphibolites followed by exhumation via ductile shearing and brittle faulting. Pressure‐temperature estimates on garnet‐bearing amphibolites in the western zone suggest metamorphic pressures of ～0.7–0.8 GPa and temperatures of ～540–590°C. Metamorphic grade variations suggest that between 15 and 20 km of vertical offset occurs across the east‐dipping Moyston Fault. Bounding fault structures show evidence for early ductile deformation followed by later brittle deformation/reactivation. Ductile deformation within the complex is initially marked by early bedding‐parallel cleavages. Later deformation produced tight to isoclinal D₂ folds and steeply dipping ductile high‐strain zones. The S₂ foliation is the dominant fabric in the complex and is shallowly west‐dipping to flat‐lying in the western zone and steeply west‐dipping in the eastern zone. Peak metamorphism is pre‐ to syn‐D₂. Later ductile deformation reoriented the S₂ foliation, produced S₃ crenulation cleavages across both zones and localised S₄ fabrics. The transition to brittle deformation is defined by the development of east‐ and west‐dipping reverse faults that produce a neutral vergence and not the predominant east‐vergent transport observed throughout the rest of the western Lachlan Fold Belt. Later north‐dipping thrusts overprint these fault structures. The majority of fault transport along ductile and brittle structures occurred prior to the intrusion of the Early Devonian Ararat Granodiorite. Late west‐ and east‐dipping faults represent the final stages of major brittle deformation: these are post plutonism.     

构造叠加弱应变沉积岩地区的磁组构研究——以川西北盆地为例

磁组构是一种灵敏的应变指示计。单一方向应力作用下,在平行层缩短的初始阶段,磁线理与地层走向是一致的。然而,在构造叠加背景下弱变形的沉积岩地区,另一个（多个）不同方向的应力使得已经产生定向排列的磁性矿物发生旋转,表现为磁线理和与地层走向斜交。川西北盆地在新生代是一个典型的构造叠加区域,来自龙门山和米仓山的变形在此相互作用。本文在川西北盆地分3条剖面在18个采样点中采集了172个样品进行了磁组构研究。研究区内观察到3种弱变形的磁组构类型：沉积磁组构、初始变形磁组构和铅笔状磁组构。由于应变的叠加,由盆地内部向造山带前缘没有出现应变由弱到强的变化趋势,同时磁线理的方向也不一致。由盆地向造山带,来自米仓山的变形逐渐增强,磁线理从与地层走向一致转变成与地层走向斜交。     

Strain path partitioning within thrust sheets: microstructural and petrofabric evidence from the Moine Thrust zone at Loch Eriboll,northwest Scotland

Quartz c axis fabrics and microstructures have been investigated within a suite of quartzites collected from the Loch Eriboll area of the Moine Thrust zone and are used to interpret the detailed processes involved in fabric evolution. The intensity of quartz c axis fabrics is directly proportional to the calculated strain magnitude. A correlation is also established between the pattern of c axis fabrics and the calculated strain symmetry.Two kinematic domains are recognized within one of the studied thrust sheets which outcrops immediately beneath the Moine Thrust. Within the upper and central levels of the thrust sheet coaxial deformation is indicated by conjugate, mutually interfering shear bands, globular low strain detrital quartz grains whose c axes are aligned sub-parallel to the principal finite shortening direction (Z) and quartz c axis fabrics which are symmetric (both in terms of skeletal outline and intensity distribution) with respect to mylonitic foliation and lineation. Non-coaxial deformation is indicated within the more intensely deformed and recrystallized quartzites located near the base of the thrust sheet by single sets of shear bands and c axis fabrics which are asymmetric with respect to foliation and lineation.Tectonic models offering possible explanations for the presence of kinematic (strain path) domains within thrust sheets are considered.     

Magnetic susceptibility anisotropy as a strain indicator in the sudbury basin, Ontario

The magnetic susceptibility anisotropy of 181 samples from the Chelmsford Formation, the Onaping Formation and the norite of the Sudbury Basin has been measured. Magnetic foliation planes are almost exactly parallel to the planar structural elements (slaty cleavage and foliation) that are axial planar to the Basin. Magnetic lineations, where present, are parallel to linear structural elements (mineral elongation lineations). The shapes of the susceptibility ellipsoids of individual samples and the grouping of their principal axes are used to classify each site according to one of nine possible anisotropy types. In the Chelmsford Formation there is dominantly one anisotropy type, but several are present in the norite. At each site there is a variation in shape of the anisotropy ellipsoids, which can be interpreted using magnetic susceptibility axial ratio plots analogous to the deformation plots used by structural geologists. Using this technique the measured anisotropy patterns are interpreted in terms of progressive modification of original predeformation magnetic fabrics by various types of strain. In the norite the shape of the susceptibility ellipsoid and the anisotropy type vary systematically with distance from the Grenville Front.     

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.