华北克拉通东部地块和大别—苏鲁造山带印支期褶皱-逆冲构造与动力学背景

大别-苏鲁造山带不同岩片(块)经历了不同的褶皱变形.榴辉岩块(或透镜体)和硬玉石英岩片经历了高压-超高压背景下的两幕褶皱变形之后,在区域性第一幕变形期间主要发生透镜化为主,后期与围岩共同经历紧闭同斜第二幕褶皱.而其它岩片主要经历了现今野外可见的区域性三幕褶皱,其中区域性第一幕褶皱为片内残留褶皱,在斜长角闪岩透镜体中多见,宏观规律不明.区域性第二幕褶皱在露头尺度多见,轴面为折劈理,局部强烈置换成片理化带(复合片理或第二期片理),恢复第三幕褶皱改造作用后,揭示出各种岩片中的各级尺度的第二幕褶皱都为轴面北西倾南东倒、轴迹走向为NNE向的紧闭不对称褶皱,不对称性一致反映其指向与各种岩片向南东的逆冲运动有关.第三幕褶皱为以片理或折劈理为变形面的宽缓褶皱,轴迹走向NWW,枢纽向西倾伏.韧性剪切带为非透入性构造,分早晚两期,早期为韧性逆冲,新县穹隆以南,运动学标志指示向北逆冲,错切第二幕褶皱,结合新县穹隆北部向南的逆冲特征,反映这些韧性逆冲断层多数为第二幕大型褶皱翼部的次级逆冲断层;晚期为韧性滑脱带,其发育局限于几个岩性差异较大的接触带,带内伸展型折劈理发育,并对挤压构造样式有重要的改造作用.华北克拉通东部地块是华北克拉通的重要组成,其盖层古生界和三叠系在印支运动期间经历了一幕宽缓褶皱作用,其轴迹方向主体也为NWW向.这一褶皱构造明显在变形时间、变形样式和展布方向上都和大别-苏鲁造山带中的第三幕褶皱非常一致,说明它们具有动力学上的必然联系.同时,研究表明在华北克拉通东部地块中没有经历大别-苏鲁造山带中区域性第一、第二幕褶皱变形的记录,故本文认为印支期这两幕变形主要发生在华北板块东南缘的边界上,并没有波及到板内,而且从东向西高压-超高压岩石剥露具有穿时性.只有当华北板块和华南板块在第二幕变形之后构成了统一块体后,第三幕变形才波及华北板内.     

Crustal thickening and attenuation as revealed by regional fold interference patterns: Ciudad Rodrigo basement area (Salamanca,Spain)

The structure of the Ciudad Rodrigo area (Iberian Massif, Central Iberian Zone) has been revisited in order to integrate new geological data with recent models of the evolution of the Iberian Massif. Detailed mapping of fold structures along with a compilation of field data have been used to constrain the geometry and relative timing of ductile deformation events in this section of the hinterland of the Variscan belt. The structural evolution shows, in the first place, the development of a regional train of overturned folds with associated axial planar foliation (D₁). Towards the lower structural levels, the deflection of the fold limbs and a subhorizontal crenulation cleavage depict the upper structural boundary of a superimposed low angle shear zone (D₂), which extends at least to the deepest parts of the basement exposed in the study area. The amplification and rotation of D₁ folds about a horizontal axis also occurred within this shear zone. The flat-lying character of the D₂ structures accounts for the attenuation of the previously thickened crust, which developed following gravity gradients during thermal re-equilibration. Subsequent deformation led to the formation of two orthogonal sets of upright folds (D₃), representing a new shift between crustal thinning and crustal thickening in the region.     

Syn-orogenic extension in the Peloritani Alpine Thrust Belt (NE Sicily,Italy): Evidence from the Alì Unit

Structural and petrological analyses on the Alì Unit, in the Peloritani Thrust Belt, document the first evidence for Alpine exhumation associated with syn-orogenic extension in this part of the Calabria-Peloritani Arc. The Alì Unit displays ductile structures occurred during three Alpine deformation phases (D_a1, D_a2, D_a3). D_a1 and D_a3 developed in a contractional context, whereas D_a2 was generated in an extensional regime. The present-day tectonic contact between the Alì Unit and the overlying Mandanici Unit is interpreted as a low-angle extensional detachment responsible for the metamorphic break between the two units. Structural overprinting relationships indicate that the development of D_a2 structures and related tectonic exhumation occurred during syn-convergence extension, and were followed by further nappe stacking in the Peloritani Belt. To cite this article: R. Somma et al., C. R. Geoscience 337 (2005).     

Tectonics of the Lepontine Alps: ductile thrusting and folding in the deepest tectonic levels of the Central Alps

The Lepontine dome represents a unique region in the arc of the Central and Western Alps, where complex fold structures of upper amphibolite facies grade of the deepest stage of the orogenic belt are exposed in a tectonic half-window. The NW-verging Mont Blanc, Aar und Gotthard basement folds and the Lower Penninic gneiss nappes of the Central Alps were formed by ductile detachment of the upper European crust during its Late Eocene–Early Oligocene SE-directed underthrust below the upper Penninic and Austroalpine thrusts and the Adriatic plate. Four underthrust zones are distinguished in the NW-verging stack of Alpine fold nappes and thrusts: the Canavese, Piemont, Valais and Adula zones. Up to three schistosities S1–S3, folds F1–F3 and a stretching lineation XI with top-to-NW shear indicators were developed in the F1–F3 fold nappes. Spectacular F4 transverse folds, the SW-verging Verzasca, Maggia, Ziccher, Alpe Bosa and Wandfluhhorn anticlines and synclines overprint the Alpine nappe stack. Their formation under amphibolite facies grade was related to late ductile folding of the southern nappe roots during dextral displacement of the Adriatic indenter. The transverse folding F4 was followed since 30 Ma by the pull-apart exhumation and erosion of the Lepontine dome. This occurred coevally with the formation of the dextral ductile Simplon shear zone, the S-verging backfolding F5 and the formation of the southern steep belt. Exhumation continued after 18 Ma with movement on the brittle Rhone-Simplon detachment, accompanied by the N-, NW- and W-directed Helvetic and Dauphiné thrusts. The dextral shear is dated by the 29–25 Ma crustal-derived aplite and pegmatite intrusions in the southern steep belt. The cooling by uplift and erosion of the Tertiary migmatites of the Bellinzona region occurred between 22 and 18 Ma followed by the exhumation of the Toce dome on the brittle Rhone–Simplon fault since 18 Ma.     

Phanerozoic polyorogenic deformation in southern Jiuling Massif,northern South China block: Constraints from structural analysis and geochronology

The structure of the Jiuling Massif has been investigated in order to delineate the polyorogenic deformation and discuss its geodynamic evolution and orogenic mechanisms. Detailed structural analysis indicates that the D₁ event is characterized by top-to-the NNW ductile shearing with pervasive foliation, and mineral and stretching lineation developed in the entire region. Compared with the D₁ deformation, D₂ structures are localized in ductile shear zones with subvertical foliation and subhorizontal E–W trending lineation, indicating a dextral ductile shearing. The D₃ event, marked by folds and thrusts mainly in a brittle domain, modified the D₁ structures by asymmetrical folds. The dominant D₄ structures are gravitational folds and normal faults, corresponding to a later extension. Our new geochronological data suggest that the D₁ event occurred between 465 and 380 Ma with D₂ dextral shearing at the end of this Early Paleozoic orogen, and the D₃ event has been constrained at 245–215 Ma. The final uplift of the Jiuling Massif by the D₄ event can be correlated with the Late Mesozoic extension across the eastern South China block. Along with previous studies in the South China block, the structural pattern of the Jiuling Massif elucidates the influence of the Early Paleozoic and Early Mesozoic intracontinental belts triggered by repeated reactivation of the Jiangshan–Shaoxing Fault. Combined with deformation to the south, the Early Paleozoic belt shows a positive flower pattern, with opposing kinematics, rooted in the Jiangshan–Shaoxing Fault. During the Early Mesozoic, a general intracontinental belt was developed with uniform kinematics in both the Jiuling Massif and the Xuefengshan Belt, possibly resulted from the far-field effect of the Triassic NW-directed Paleo-Pacific subduction.     

Foreland- and hinterland-verging structures in fold-and-thrust belt: an example from the Variscan foreland of Sardinia

In the Variscan foreland of SW-Sardinia (Western Mediterranean sea), close to the leading edge of the nappe zone, nappe emplacement caused folding and repetition of stratigraphic successions, km-scale offset of stratigraphic boundaries and an extensive brittle-ductile shear zone. Thrusts assumed a significant role, accommodating a progressive change of shortening direction and forming complicated thrust triangle zones. During thrust emplacement of the nappes, strong penetrative deformation affected rocks beneath the basal thrust of the nappe stack and produced coeval structures with both foreland-directed and hinterland-directed (backthrusting) shear sense. Cross-cutting and overprinting relationships clearly show that the shortening direction changed progressively from N–S to E–W, producing in sequence: (1) E–W trending open folds contemporaneous with early nappe emplacement in the nearby nappe zone; (2) recumbent, quasi-isoclinal folds with axial plane foliation and widespread, “top-towards-the-SW”, penetrative shearing; (3) N–S trending folds with axial plane foliation, contemporaneous with late nappe emplacement; (4) backthrusts and related asymmetrical folds developed during the final stages of shortening, postdating foreland-verging structures. Structures at (3) and (4) occurred during the same tectonic transport “top-towards-the-E” of the nappe zone over the foreland. The several generations of folds, thrusts, and foliations with different orientations developed, result in a complex finite structural architecture, not completely explicable by the theoretical model proposed up to date.     

Deformation history of the Hengshan–Wutai–Fuping Complexes: Implications for the evolution of the Trans-North China Orogen

The Trans-North China Orogen separates the North China Craton into two small continental blocks: the Eastern and Western Blocks. As one of the largest exposure in the central part of the orogen, the Hengshan–Wutai–Fuping Complexes consist of four lithotectonic units: the Wutai, Hengshan and Fuping Complexes and the Hutuo Group. The Hengshan Complex contains high pressure mafic granulites and retrograded eclogites. Structural analysis indicates that most of the rocks in these complexes underwent three distinct episodes of folding (D₁ to D₃) and two stages of ductile thrust shearing (STZ₁ between D₁ and D₂ and STZ₂ after D₃). The D₁ deformation formed penetrative axial planar foliations (S₁), mineral stretching lineations (L₁), and rarely-preserved small isoclinal folds (F₁) in the Hengshan and Fuping Complexes. In the Wutai Complex, however, large-scale F₁ recumbent folds with SW-vergence are displayed by sedimentary compositional layers. Penetrative transposition resulted in stacking of thrust sheets which are separated by ductile shear zones (STZ₁). The kinematic indicators of STZ₁ in the Hengshan and Wutai Complexes show top-to-the-S230°W thrusting likely related to northeastward, oblique pre-collisional subduction. D₁ resulted in crustal thickening with resultant prograde peak metamorphism. The Hutuo Group did not undergo the D₁ deformation, either because sedimentation was coeval with the D₁ deformation or because it was at a high structural level and was not influenced directly by the early deformation. The D₂ deformation produced NW-verging asymmetric and recumbent folds. The D₂ deformation is interpreted to have resulted from collision between the Eastern and Western Blocks of the North China Craton. In the Hutuo Group and the Fuping Complex, the development of ESE-verging asymmetric tight folds is associated with D₂. The structural pattern resulting from superimposition of D₁ and D₂ is a composite synform in the Hengshan–Wutai–Fuping Complexes. All four lithotectonic units were superposed during the later D₃ deformation. The D₃ deformation developed NW-trending open upright folds. Ongoing collision led to development of transpressional ductile shearing (STZ₂), forming the transpressional Zhujiafang dextral ductile shear zone between the northern Hengshan Complex and the southern Hengshan Complex, and generating the sinistral Longquanguan ductile shear zone between the Fuping Complex and the Wutai Complex, respectively. The STZ₁ and D₂ deformation were possibly responsible for fast syn-collisional exhumation of the high pressure mafic granulites and retrograded eclogites. The structural patterns and elucidation of the deformation history of the Hengshan–Wutai–Fuping Complexes places important constraints on the tectonic model suggesting that an oceanic lithosphere between the Eastern and Western Blocks underwent northeastward-directed oblique subduction beneath the western margin of the Eastern Block, and that the final closure of this ocean led to collision between the two blocks to form the coherent basement of the North China Craton.     

On the relationship between kilometer-scale sheath folds, ductile thrusts and minor structures in the basal high-pressure units of the Cabo Ortegal complex (NW Spain)

Large sheath folds in the basal high-pressure nappes of the Cabo Ortegal complex are described and a kinematic interpretation provided. The principal penetrative and map structures relate to regional D2 deformation, which produced foliations (S2) bearing mineral and stretching lineations (L2) and several types of folds (a-type, sheath-like and ‘folded folds’). The latter structures are subparallel to the trend of the orogen. Their attitude suggests that the units involved shared a common tectonic evolution during progressive ductile deformation of an anisotropic medium. Reconstruction of major geological structures was accomplished through projection of map-scale features onto the ductile flow plane and the plane perpendicular to the ductile flow direction. The structures reconstructed illustrate their development in the deeper structural levels of an orogenic channel subjected to high-pressure metamorphism during the early phases of the Hercynian orogeny in NW Iberia. We argue that orogen-normal tectonic displacements (of up to a few hundreds of kilometers) represent the minor components of the transpression with possibly thousands of kilometers along-strike dextral displacement between the intervening plates (during subduction/collision).     

Structural analyses of the crystalline rocks between Dirang and Tawang,West Kameng district,Arunachal Himalaya

In Kameng Valley of Arunachal Pradesh, the crystalline rocks of Se La Group of Higher Himalaya are thrust over the Lesser Himalayan rocks of Dirang Formation, Bomdila Group along the Main Central Thrust and exhibit well preserved structures on macro- to microscopic scales. Detailed analysis of structures reveals that the rocks of the area have suffered four phases of deformation D₁, D₂, D₃ and D₄. These structures have been grouped into (i) early structures (ii) structures related to progressive ductile thrusting and (iii) late structures. The early structures which developed before thrusting formed during D₁ and D₂ phases of deformation, synchronous to F₁ and F₂ phases of folding respectively. The structures related to progressive ductile shearing developed during D₃ phase of deformation, when the emplacement of the crystalline rocks took place over the rocks of Dirang Formation along the Main Central Thrust. Different asymmetric structures/kinematic indicators developed during this ductile/brittle-ductile regime suggest top-to-SSW sense of movement of the crystalline rocks of the area. D₄ is attributed to brittle deformation. Based on satellite data two new thrusts, i.e. Tawang and Se La thrusts have been identified parallel to Main Central Thrust, which are suggestive of imbricate thrusting. Strain analysis from the quartz grains of the gneissic rocks reveals constriction type of strain ellipsoid where k value is higher near the MCT, gradually decreases towards the north. Further, the dynamic analysis carried out on the mesoscopic ductile and brittle-ductile shear zones suggest a NNE-SSW horizontal compression corresponding to the direction of northward movement of Indian Plate.     

库鲁克塔格赛马山一带中元古界构造变形研究

通过构造解析的研究，确定赛马山地区中元古代所发生的阿尔金运动共有三幕变形，第一幕发生在长城纪早期，为EW向伸展机制下中部构造相的大规模顺层滑脱韧性变形，形成了赛马西山顺层滑脱韧性变形带，具超塑性流动变形特征和多层结构样式，第二幕发生在长城纪末，为主期变形，在NS向挤压机制下，在浅部构造相形成了EW向紧闭褶皱（局部倒转褶皱），并卷入早期的顺层滑脱韧性变形带，褶皱后期，由于应力的集聚，在浅表层次下，沿兴地塔格群内岩层软弱面发生剪切而形成了滑脱面，产生由南向北的逆冲，形成了具叠瓦扇结构的永红山飞来峰构，第三幕，蓟县纪末由于SN向强烈挤压后出现“松驰”引张而产生EW向挤压应力，形成NS向开阔褶皱，叠加于主期褶皱之上，形成了赛马西山－永红山穹盆构造。     

Hot metamorphic core complex in a cold foreland

The Montagne Noire forms the southernmost part of the French Massif Central. Carboniferous flysch sediments and very low-grade metamorphic imprint testify to a very external position in the orogen. Sedimentation of synorogenic clastic sediments continued up to the Viséan/Namurian boundary (≤320 Ma). Subsequently, the Palaeozoic sedimentary pile underwent recumbent folding and grossly southward thrusting. An extensional window exposes a hot core of Carboniferous HT/LP gneisses, migmatites and granites (Zone Axiale), which was uplifted from under the nappe pile. After the emplacement of the nappes on the Zone Axiale (Variscan D₁), all structural levels shared the same tectonic evolution: D₂ (extension and exhumation), D₃ (refolding) and post-D₃ dextral transtension. HT/LP-metamorphism in the crystalline rocks probably started before and continued after the emplacement of the nappes. Peak metamorphic temperatures were attained during a post-nappe thermal increment (M₂). M₂ occurred during ENE-directed bilateral extension, which exhumed the Zone Axiale and its frame as a ductile horst structure, flanked to the ENE by a Stephanian intra-montane basin. Map patterns and mesoscopic structures reveal that extension in ENE occurred simultaneously with NNW-oriented shortening. Combination of these D₂ effects defines a bulk prolate strain in a “pinched pull-apart” setting. Ductile D₂ deformation during M₂ dominates the structural record. In wide parts of the nappes on the southern flank of the Zone Axiale, D₁ is only represented by the inverted position of bedding (overturned limbs of recumbent D₁ folds) and by refolded D₁ folds. U–Pb monazite and zircon ages and K–Ar muscovite ages are in accord with Ar–Ar data from the literature. HT/LP metamorphism and granitoid intrusion commenced already at ≥330 Ma and continued until 297 Ma, and probably in a separate pulse in post-Stephanian time. Metamorphic ages older than c. 300 Ma are not compatible with the classical model of thermal relaxation after stacking, since they either pre-date or too closely post-date the end of flysch sedimentation. We therefore propose that migmatization and granite melt generation were independent from crustal thickening and caused, instead, by the repeated intrusion of melts into a crustal-scale strike-slip shear zone. Advective heating continued in a pull-apart setting whose activity outlasted the emplacement of the Variscan nappe pile. The shear-zone model is confirmed by similar orogen-parallel extensional windows with HT/LP metamorphism and granitoid intrusion in neighbouring areas, whose location is independent from their position in the orogen. We propose that heat transfer from the mantle occurred in dextral strike-slip shear zones controlled by the westward propagating rift of the Palaeotethys ocean, which helped to destroy the Variscan orogen.     

秦岭南缘大巴山褶皱－冲断推覆构造的特征

秦岭造山带南缘的大巴山巨型逆冲推覆构造主要是在秦岭造山带板块俯冲碰撞造山与中、新生代以来陆内造山过程中长期复合作用形成的。详细的室内外构造研究表明,巴山逆冲推覆构造可以巴山弧形断裂带为界划分为北大巴山逆冲推覆构造和南大巴山逆冲推覆构造。北大巴山自北而南依次由安康－武当推覆体、紫阳－平利推覆体、高桥－镇坪推覆体和高滩推覆体逆冲叠置而成。南大巴山则以镇巴－阳日断裂为界,分为北部的前陆冲断褶皱带和南部的前陆褶皱带。北大巴山主要是印支期碰撞造山作用和燕山期陆内逆冲推覆作用叠加改造的结果,南大巴山则主要是燕山期递进变形过程中的产物。构造变形北强南弱,北以冲断褶皱变形为特征,南以皱褶作用为主;北部褶皱紧闭复杂,向南渐变为宽缓的薄皮构造。逆冲作用在时序上具有由北向南扩展传递的特点。     

Progressive deformation and the rotation of contemporary fold axes in the Ballybofey Nappe,north-west Ireland

Internal regions of orogenic belts may be characterized by an alignment of fold axes with mineral elongation lineations. This relationship is commonly interpreted as representing progressive tightening and rotation towards the shear direction of early buckle folds, the hinges of which were initiated orthogonal to this direction. Detailed structural analysis of lower amphibolite facies Dalradian metasediments of the Ballybofey (fold) Nappe, north-west Ireland, shows that an intense S₃ schistosity is developed axial planar to mesoscopic and minor F₃ folds. In areas of low D₃ strain, F₃ fold axes plunge gently towards the north-east, whereas in regions of greater strain plunges are towards the south-east subparallel to the constant mineral lineation. Minor folds which initiated at angles of 70–80° from the mineral lineation subsequently rotated towards the shear direction in a consistent clockwise sense. Progressive and variable non-coaxial deformation oblique to the original mean F₃ orientation has resulted in a unimodal distribution pattern of fold axes. Analysis of the angular rotation of fold axes enables estimates of the bulk shear strain to be evaluated and models of progressive deformation to be assessed.     

Structural analysis and implicit 3D modelling of high-grade host rocks to the Venetia kimberlite diatremes,Central Zone,Limpopo Belt,South Africa

The Beit Bridge Complex of the Central Zone (CZ) of the Limpopo Belt hosts the 519 ± 6 Ma Venetia kimberlite diatremes. Deformed shelf- or platform-type supracrustal sequences include the Mount Dowe, Malala Drift and Gumbu Groups, comprising quartzofeldspathic units, biotite-bearing gneiss, quartzite, metapelite, metacalcsilicate and ortho- and para-amphibolite. Previous studies define tectonometamorphic events at 3.3–3.1 Ga, 2.7–2.5 Ga and 2.04 Ga. Detailed structural mapping over 10 years highlights four deformation events at Venetia. Rules-based implicit 3D modelling in Leapfrog Geo™ provides an unprecedented insight into CZ ductile deformation and sheath folding. D₁ juxtaposed gneisses against metasediments. D₂ produced a pervasive axial planar foliation (S₂) to isoclinal F₂ folds. Sheared lithological contacts and S₂ were refolded into regional, open, predominantly southward-verging, E–W trending F₃ folds. Intrusion of a hornblendite protolith occurred at high angles to incipient S₂. Constrictional-prolate D₄ shows moderately NE-plunging azimuths defined by elongated hornblendite lenses, andalusite crystals in metapelite, crenulations in fuchsitic quartzite and sheath folding. D₄ overlaps with a: 1) 2.03–2.01 Ga regional M₃ metamorphic overprint; b) transpressional deformation at 2.2–1.9 Ga and c) 2.03 Ga transpressional, dextral shearing and thrusting around the CZ and d) formation of the Avoca, Bellavue and Baklykraal sheath folds and parallel lineations.     

Tectonic observations in the northern Saih Hatat,Sultanate of Oman

The Saih Hatat region, in northeastern Oman, is characterized by a large tectonic window, tectonically overlain during the upper Cretaceous by nappes composed of sedimentary rocks from the Mesozoic Hawasina ocean and the Samail ophiolite. In this window, the autochthonous sedimentary cover of the eastern Arabian Platform from the Late Neoproterozoic to the Cenomanian is well exposed. The oldest of these strata, the Hatat schists, were deformed into a NE-facing fold nappe during the upper Cretaceous. Within the overturned and thrusted lower limb of that fold nappe, we identified three small windows exposing stratigraphically younger Hiyam carbonates and Ordovician sandstone. The structural inventory of the windows and the surrounding area indicates three major tectonic phases. The first deformation led to NNE-SSW trending fold structures which probably formed simultaneously with the major fold nappe of the Hatat schists, followed by the extreme attenuation and thrusting of the lower limb of the fold nappe. The second phase was a gentle folding of the thrust with N-S oriented fold axes and third deformation phase that formed WNW-ESE oriented open folds. The windows are situated in the intersection of anticline axes of these two superposed fold generations and represent a mini basin-and-dome structure with an extension of just 1 km?×?1 km.     

Oligocene–Miocene thrusting in central Aegean: insights from the Cycladic island of Amorgos

In the central Aegean, the Cycladic island of Amorgos consists of two high‐pressure (HP) units, the marble‐rich Amorgos unit, which is correlated to the Mesozoic ‘cover’ sequence of the Menderes Massif, and the Cycladic Blueschist unit. New structural data show that the deformation history of the Amorgos HP‐rocks was principally governed by early Oligocene (or late Eocene)–early Miocene ductile to brittle thrusting (D₁–D₃) followed by middle–late Miocene oblique contractional movements (D₄–D₅). The D₁ phase caused syn‐blueschist‐facies ductile thrusting of the Cycladic Blueschist unit over the Amorgos unit, with ambiguous kinematics. Progressive deformation under continuous NW–SE compression produced a sequence of imbricate NW‐directed thrusts (D_2/3) characterized by a stratification of fault‐related rocks, with mylonitic zones (D₂) giving way downwards to cataclastic zones (D₃). Ductile D₂ thrusting synchronous to greenschist‐facies retrogression, was accompanied by mega‐sheath folding during constrictional and general shear deformation. Brittle D₃ thrusting was associated with NW‐verging F₃ folds trending at a high‐angle to the transport direction. Orthogonal contraction gave way to transpression during which the compression orientation changed from NW–SE (D₄) to NE–SW (D₅). Back‐arc related NW–SE pure extension (D₆) seems to have been established in post‐late Miocene times and related high‐angle normal faulting affected HP‐rocks only after they had already reached the uppermost crustal levels. Oligocene–early Miocene deformation history is interpreted to indicate syn‐compressional exhumation of HP‐rocks possibly in an extrusion wedge. In this case, Amorgos HP‐rocks should have occupied the base of the extrusion wedge. Copyright © 2011 John Wiley & Sons, Ltd.     

造山带逆冲推覆构造研究的主要新进展

造山带逆冲推覆构造研究是造山带研究中最为重要的课题之一。造山带外带即前陆褶皱冲断带(主要发育盖层冲断推覆体,一般遵循薄皮构造变形规则)与造山带内带(主要是基底褶皱推覆体,呈现厚皮构造变形规律)结晶逆冲推覆构造的几何学、运动学特征存在较大差异,二者形成机制也不相同,但其间仍有紧密的联系。近20年来造山带逆冲推覆构造研究的主要新进展为:①前陆褶皱冲断带逆冲断层及其相关褶皱的几何学特征分析已趋定量化,对其组合类型与演化时序有了更全面的认识,且对前陆褶皱冲断带的发展演化模式取得了新的共识,即遵循临界库仑楔模式;②平衡剖面技术在前陆褶皱冲断带的应用已从二维平衡与复原演进到三维平衡与复原,且日渐计算机化;③对造山带内带结晶基底逆冲推覆构造的主要类型(C型与F型逆冲岩席)及其特征已有较深的理解;④对前陆褶皱冲断带与结晶基底逆冲构造的相互关系及其形成演化模式有了新认识。目前造山带逆冲推覆构造研究过程中存在的主要问题为:①造山带内带结晶逆冲推覆构造的研究比较薄弱;②造山带晚期走滑构造及伸展构造的叠加与改造使得造山带内结晶逆冲推覆构造更为复杂化,致使其研究难度加大;③全面、精细的造山带深部地球物理资料较缺乏;④造山带内结晶逆冲岩席变形变质历史与超高压变质岩的形成机制及折返过程之间的关系尚未揭示清楚。在今后研究过程中应加强对上述问题的深入研究。     

Discrete proterozoic structural terranes associated with low-P, high-T metamorphism, Anmatjira Range, Arunta Inlier, central Australia: tectonic implications

Structural overprinting relationships indicate that two discrete terranes, Mt. Stafford and Weldon, occur in the Anmatjira Range, northern Arunta Inlier, central Australia. In the Mt. Stafford terrane, early recumbent structures associated with D_1a,_1b deformation are restricted to areas of granulite facies metamorphism and are overprinted by upright, km-scale folds F_1c), which extend into areas of lower metamorphic grade. Structural relationships are simple in the low—grade rocks, but complex and variable in higher grade equivalents. The three deformation events in the Mt. Stafford terrane constitute the first tectonic cycle (D₁-D₂) deformation in the Weldon terrane comprises the second tectonic cycle. The earliest foliation (S_2a) was largely obliterated by the dominant reclined to recumbent mylonitic foliation (S_2b), produced during progressive non-coaxial deformation, with local sheath folds and W- to SW-directed thrusts. Locally, (D_2d) tectonites have been rotated by N—S-trending, upright (F_2c) folds, but the regional upright fold event (F_2d), also evident in the adjacent Reynolds Range, rotated earlier surfaces into shallow-plunging, NW—SE-trending folds that dominate the regional outcrop pattern.The terranes can be separated on structural, metamorphic and isotopic criteria. A high-strain D₂ mylonite zone, produced during W- to SW-directed thrusting, separates the Weldon and Mt. Stafford terranes. 1820 Ma megacrystic granites in the Mt. Stafford terrane intruded high-grade metamorphic rocks that had undergone D_1a and D_1b deformation, but in turn were deformed by S_1c, which provides a minimum age limit for the first structural—metamorphic event. 1760 Ma charnockites in the Weldon terrane were emplaced post-D_2a, and metamorphosed under granulite facies conditions during D_2b, constraining the second tectonic cycle to this period.Each terrane is associated with low-P, high-T metamorphism, characterized by anticlockwise P—T—t paths, with the thermal peaks occurring before or very early in the tectonic cycle. These relations are not compatible with continental-style collision, nor with extensional tectonics as the deformation was compressional. The preferred model involves thickening of previously thinned lithosphere, at a stage significantly after (>50 Ma) the early extensional event. Compression was driven by external forces such as plate convergence, but deformation was largely confined to and around composite granitoid sheets in the mid-crust. The sheets comprise up to 80% of the terranes and induced low-P, high-T metamorphism, including migmatization, thereby markedly reducing the yield strength and accelerating deformation of the country rocks. Mid-crustal ductile shearing and reclined to recumbent folding resulted, followed by upright folding that extended beyond the thermal anomaly. Thus, thermal softening induced by heat-focusing is capable of generating discrete structural terranes characterized by subhorizontal ductile shear in the mid-crust, localized around large granitoid intrusions.     

Does the Manning Orocline exist? New structural evidence from the inner hinge of the Manning Orocline (eastern Australia)

The map-view structure of the southern New England Orogen in the eastern Gondwanan margin is characterised by four tight orogenic-scale curvatures: Texas, Coffs-Harbour, Manning and Nambucca oroclines. Here we focus on the geometry of the Manning Orocline and examine whether the inner-arc area of the oroclinal structure is expressed within the accretionary wedge rocks of the Tablelands Complex. Our observations from the Tablelands Complex (Armidale–Walcha area) show that rocks were subjected to penetrative deformation (D₁), which resulted in a regional slaty cleavage (S₁) and related isoclinal folds. This was followed by subsequent deformation (D₂) associated with minor gentle folds. In a larger scale, the steeply dipping S₁ structural fabric shows a continuous map-view curvature, thus defining a macroscopic fold structure. We interpret this macroscopic fold as the expression of the Manning Orocline within the accretionary wedge complex. This interpretation is consistent with the contorted spatial distribution of other tectonic elements (serpentinite belt, forearc basin terranes and early Permian granitoids), which independently define the structure of the Manning Orocline. Our new structural data support the existence of the Manning Orocline and the quadruple oroclinal geometry of the whole southern New England Orogen. The origin of these oroclines is attributed to multiple stages of bending, possibly associated with an earlier phase of curvature during slab rollback (in the early Permian), followed by a subsequent (middle-late Permian) episode of contractional deformation that tightened the oroclinal structure.