Strain and shear types of the Louzidian ductile shear zone in southern Chifeng, Inner Mongolia, China

The Louzidian ductile shear zone at the south of Chifeng strikes NE-SW and dips SE at low-medium- angles. This ductile shear zone is mainly composed of granitic mylonite, which grades structurally upward into a chloritized zone, a microbreccia zone, a brittle fault and a gouge zone. All these zones share similar planar attitudes, but contain different linear attitudes and kinematic indicators. Finite strain measurements were performed on feldspar porphyroclasts using the Fry method. These meas- urements yield Fulin indexes of 1.25―3.30, Lode's parameters of -0.535―-0.112 and strain parameters of 0.41―0.75 for the protomylonite, respectively. These data are plotted within the apparent constric- tional field in Fulin and Hossack diagrams. In contrast, for the mylonite, corresponding parameters are 0.99―1.43, -0.176―-0.004 and 0.63―0.82, respectively, and located in the apparent constrictional field close to the plane strain. The mean kinematic vorticity numbers of the protomylonite and mylonite by using three methods of polar Mohr circle, porphyroclast hyperbolic and oblique foliation, are in the range of 0.67―0.95, suggesting that the ductile shearing is accommodated by general shearing that is dominated by simple shear. Combination of the finite strain and kinematic vorticity indicates that shear type was lengthening shear and resulted in L-tectonite at the initial stage of deformation and the shear type gradually changed into lengthening-thinning shear and produced L-S-tectonite with the uplifting of the shear zone and accumulating of strain. These kinds of shear types only produce a/ab strain facies, so the lineation in the ductile shear zone could not deflect 90° in the progressively deformation.     

Water contents and deformation mechanism in ductile shear zone of middle crust along the Red River fault in southwestern China

Using Fourier transform infrared spectroscopy (FTIR), we measured water contents of quartz and feldspar for four thin sections of felsic mylonite and two thin sections of banded granitic gneiss col- lected from a ductile shear zone of middle crust along the Red Rivers-Ailaoshan active fault. The ab- sorbance spectra and peak position suggest that water in quartz and feldspar of granitic gneiss and felsic mylonite occurs mainly as hydroxyl in crystal defect, but also contains inclusion water and grain boundary water. The water contents of minerals were calculated based on the absorbance spectra. Water content of feldspar in granitic gneiss is 0.05 wt%-0.15 wt%, and that of quartz 0.03 wt%-0.09 wt%. Water content of feldspar ribbon and quartz ribbon in felsic mylonite is 0.095 wt%-0.32 wt%, and those of fine-grained feldspar and quartz are 0.004 wt%-0.052 wt%. These data show that the water content of weakly deformed feldspar and quartz ribbons is much higher than that of strongly deformed fine-grained feldspar and quartz. This suggests that strong shear deformation leads to breakage of the structures of constitutional water, inclusion and grain boundary water in feldspar and quartz, and most of water in minerals of mylonite is released to the upper layer in the crust.     

Extensive normal faulting during exhumation revealed by the spatial variation of phengite K–Ar ages in the Sambagawa metamorphic rocks,central Shikoku,SW Japan

Metamorphic rocks experience change in the mode of deformation from ductile flow to brittle failure during their exhumation. We investigated the spatial variation of phengite K–Ar ages of pelitic schist of the Sambagawa metamorphic rocks (sensu lato) from the Saruta River area, central Shikoku, to evaluate if those ages are disturbed by faults or not. As a result, we found that these ages change by ca 5 my across the two boundaries between the lower‐garnet and albite–biotite, and the albite–biotite and upper‐garnet zones. These spatial changes in phengite K–Ar ages were perhaps caused by truncation of the metamorphic layers by large‐scale normal faulting at D₂ phase under the brittle‐ductile transition conditions (ca 300°C) during exhumation, because an actinolite rock was formed along a fault near the former boundary. Assuming that the horizontal metamorphic layers and a previously estimated exhumation rate of 1 km/my before the D₂ phase, the change of 5 my in phengite K–Ar ages is converted to a displacement of about 10 km along the north‐dipping, low‐angle normal fault documented in the previous study. Phengite ⁴⁰Ar–³⁹Ar ages (ca 85 to 78 Ma) in the actinolite rock could be reasonably comparable to the phengite K–Ar ages of the surrounding non‐faulted pelitic schist, because the K–Ar ages of pelitic schist could have been also reset at temperatures close to the brittle–ductile transition conditions far below the closure temperature for thermal retention of argon in phengite (about 500–600°C).     

Quartz microstructures and deformation conditions in the Hatagawa shear zone, north-eastern Japan

Abstract Meso- and microscale structural analyses were carried out in the Hatagawa shear zone, north-eastern Japan. The shear zone is a sinistral strike–slip ductile shear zone, and has a 1-km wide north-south trending region where quartz mean grain size of approximately 35 μm does not vary significantly. Two types of quartz microstructures, A and B, occur in the western and eastern part of the shear zone, respectively. The lattice preferred orientation (LPO) patterns are characterized by a type I crossed girdle in the samples with the quartz microstructure A, and a Y maximum in the samples with the quartz microstructure B. The microstructures under optical and transmission electron microscopes indicates that the quartz recrystallization occurred predominantly by progressive subgrain rotation in microstructure A, and by both progressive subgrain rotation and grain boundary migration in microstructure B. This suggests different deformation conditions in the western and eastern parts of the shear zone. Quartz LPO patterns, presence of myrmekite, feldspar compositions, and dislocation density also suggest difference in the deformation conditions. The syn-deformation temperature in the western part of the shear zone was lower than that of the eastern part of the shear zone. The stress in the western part of the shear zone was higher than that of the eastern part of the shear zone. The difference in the deformation conditions would affect not only the quartz microstructure, but also the quartz LPO patterns and the presence of myrmekite around K-feldspar porphyroclasts.     

Genesis of the Hongzhen metamorphic core complex and its tectonic implications

The Hongzhen metamorphic core complex is situated in the Yangtze plate to the east of the Dabie oro- genic belt. Its ductile detachment zone in the foot wall overprints on the metamorphic complex of the Proterozoic Dongling Group. The present profile of the ductile shear zone with consistent SW-dipping mineral elongation lineation shows antiform and reversed S-shape from northeast to southwest respectively. Exposure structures, microstructures and quartz C-axis fabric all indicate top-to-SW movement for the ductile shear zone. Recrystallisation types of quartz and feldspar in the mylonites demonstrate that the shear zone was developed under the amphibolite facies condition and at mid-crust levels. The metamorphic core complex formed in the Early Cretaceous with a muscovite plateau age of 124.8±1.2 Ma. Regional NE-SW extension along a SW-dipping, gentle detachment zone was responsible for formation of the core complex. Intrusion of the Hongzhen granite with a biotite plateau age of 124.8±1.2 Ma rendered the ductile shear zone curved, uplifted and final localization of the core complex. The Hongzhen metamorphic core complex suggests that the Early Cretaceous magma- tism in this region took place under the condition of regional extension and the eastern Yangtze plate also experienced lithospheric thinning.     

Fluid inclusion microthermometry for P–T constraints on normal displacement along the Median Tectonic Line in Northern Besshi area,Southwest Japan

The Median Tectonic Line (MTL) is a first‐order tectonic boundary that separates the Sanbagawa and Ryoke metamorphic belts. Documented large‐scale top‐to‐the‐north normal displacements along this fault zone have the potential to contribute to the exhumation of the Sanbagawa high‐pressure metamorphic belt. Fluid inclusion analyses of vein material formed associated with secondary faults within the Sanbagawa belt affected by movement on the MTL show normal movement was initially induced under temperatures greater than around 250°C. Microstructures of quartz and K‐feldspar comprising the vein material suggest a deformation temperature of around 300°C, supporting the results of fluid inclusion analyses and suggesting deformation at depths of around 10 km. The retrograde P–T path of the Sanbagawa metamorphic rocks and the estimated isochore of the fluid inclusions do not intersect. The semi‐ductile structures of surrounding rocks and lack of evidence for hydrothermal metamorphism around the veins imply the temperature of the rocks was similar to that of the fluid. These observations suggest fluid pressure of the veins was lower than lithostatic pressure close to the MTL.     

Crustal structure beneath the Dabie orogenic belt from ambient noise tomography

The Qinling–Dabie–Sulu orogenic belt in east-central China is the largest high and ultrahigh pressure (HP and UHP) metamorphic zone in the world. The Dabie Mountains are the central segment of this orogenic belt between the North China and Yangtze cratons. This work studies the nature of the crustal structure beneath the Dabie orogenic belt to better understand the orogeny. To do that, we apply ambient noise tomography to the Dabie orogenic belt using ambient noise data from 40 stations of the China National Seismic Network (CNSN) between January 2008 and December 2009. We retrieve high signal noise ratio (SNR) Rayleigh waves by cross-correlating ambient noise data between most of the station pairs and then extract phase velocity dispersion measurements from those cross-correlations using a spectral method. Taking those dispersion measurements, we obtain high-resolution phase velocity maps at 8–35 second periods. By inverting Rayleigh wave phase velocity maps, we construct a high-resolution 3D shear velocity model of the crust in the Dabie orogenic belt.The resulting 3D model reveals interesting crustal features related to the orogeny. High shear wave velocities are imaged beneath the HP/UHP metaphoric zones at depths shallower than 9 km, suggesting that HP/UHP metaphoric rocks are primarily concentrated in the upper crust. Underlying the high velocity HP/UHP metamorphic zones, low shear velocities are observed in the middle crust, probably representing ductile shear zones and/or brittle fracture zones developed during the exhumation of the HP/UHP metamorphic rocks. Strong high velocities are present beneath the Northern Dabie complex unit in the middle crust, possibly related to cooling and crystallization of intrusive igneous rocks in the middle crust resulting from the post-collisional lithosphere delamination and subsequent magmatism. A north-dipping Moho is revealed in the eastern Dabie with the deepest Moho appearing beneath the Northern Dabie complex unit, consistent with the model of Triassic northward subduction of the Yangtze Craton beneath the North China Craton.     

Cretaceous-Eocene compression in the central Southern Alps (N Italy) inferred from Ar/Ar dating of pseudotachylytes along regional thrust faults

The integration of structural analyses with ⁴⁰Ar/³⁹Ar dating of fault-related pseudotachylytes provides time constraints for the reconstruction of the Alpine evolution of the central portion of the South Alpine orogenic wedge. In the northern sector of the belt a Variscan basement is stacked southward on the Permian to Mesozoic cover along regional faults (Orobic and Porcile thrusts). Fault zones, slightly postdating a first folding event of Alpine age, experienced a complex evolution through the ductile and brittle deformation regime, showing greenschist facies mylonites overprinted by a penetrative cataclastic deformation. Generation of fault-related pseudotachylyte veins marks the onset of brittle conditions, lasting up to the youngest episodes of fault activity. ⁴⁰Ar/³⁹Ar dating of the pseudotachylyte matrix of 9 samples give two separated age clusters: Late Cretaceous (80–68 Ma) and latest Palaeocene to Middle Eocene (55–43 Ma). These new data provide evidence that the pre-Adamello evolution of the central Southern Alps was characterised by the superposition of different tectonic events accompanying the exhumation of the deepest part of the belt through the brittle–ductile transition. The oldest pseudotachylyte ages demonstrate that south-verging regional thrusting in the central Southern Alps was already active during the Late Cretaceous, concurrently with the development of a synorogenic foredeep basin where the Upper Cretaceous Lombardian Flysch was deposited.     

沂沭断裂带中段基底韧性剪切带

在沂沭断裂带中段的泰山群结晶基底中,存在着一系列北东、北北东走向的左行韧性剪切带。对其中发育糜棱岩的韧性剪切带的结构构造、应变测量、变形岩石的显微构造、显微组构以及长石粒度和含量的变化规律进行了观测分析。讨论了韧性剪切带的变形条件和机制。及其递进发展的趋势。指出基底韧性剪切带是沂沭断裂带元古宙时期断裂活动时在地壳较深层次上形成的构造表象。在此基础上,讨论了地壳不同层次上的断裂变形及断裂岩石的综合分类问题     

High temperatures and inverted metamorphism in the schist of Sierra de Salinas,California

New field and thermobarometric work in the Californian Salinian block clarifies current and pre-Tertiary relationships between the schist of Sierra de Salinas and Cretaceous arc-related granitic rocks. The contact is variably preserved as a brittle fault and high-temperature mylonite zone, the Salinas shear zone, which represents the contact between North America and sediments accreted above the Farallon slab between ∼ 76 Ma and ∼ 70 Ma. Near granulite facies, prograde replacement of hornblende with clinopyroxene is associated with deformation of plutonic rocks at the base of the upper plate. In the lower plate, the schist of Sierra de Salinas, garnet–biotite thermometry indicates decreasing temperatures down-section from at least 714 °C to ∼ 575 °C over an exposed thickness of ∼ 2.5 km, consistent with petrologic evidence of an inverted metamorphic gradient. The measured temperatures are significantly higher than observed at shallow levels above subducting slabs or predicted by 2D computational models assuming low shear stresses. Previous workers have called upon shear heating to explain similar observations in the correlative Pelona schist, an unlikely scenario given the results of recent rock deformation experiments which predict that feldspar–quartz–mica aggregates are far too weak to withstand stresses of ∼ 70 MPa required by the shear heating hypothesis. As an alternative, we propose that high temperatures resulted from conductive heating while the leading edge of the schist traveled ∼ 150 km beneath the recently active Salinian continental arc during the initiation of shallow subduction. Weakening of the schist due to high temperatures helped facilitate the collapse of the Salinian arc as the schist was emplaced. Schist emplacement coincided with loss of lower, mafic portions of the arc, and therefore evolution of the Southern California crust towards a more felsic composition.     

Features and origin time of Mesozoic strike-slip structures in the Yilan-Yitong Fault Zone

The NE-striking Yilan-Yitong Fault Zone(YYFZ) with a length of ca. 900 km is an important major fault zone in northeastern China. Its origin has been a controversial issue for a long time. Detailed field investigation and comprehensive analyses show that strike-slip faults or ductile shear belts exist as the origination structures on the both shoulders of the Cretaceous-Paleogene grabens. These strike-slip structures are dominated by brittle transcurrent faults, and appear as ductile shear belts only in the Weiyuanpu-Yehe and Shulan parts in the south and middle of the fault zone, respectively. The shear belts strike NE-SW and show steep mylonitic foliation and gentle mineral elongation lineation. Outcrop structures, microstructures and quartz c-axis fabrics demonstrate a sinistral shear sense with minor reverse component for the ductile shear belts. The microstructures suggest deformation temperatures of 400–450°C for the Weiyuanpu-Yehe shear belts and 350–400°C for the Shulan shear belt. A series of zircon U-Pb dating results for deformed and undeformed plutons or dikes in the shear belts constrain the strike-slip motion to the time between 160 and 126 Ma. It is further inferred from ages of main geological events in this region that the fault zone originated in the earliest Early Cretaceous. It is suggested therefore that the southern and middle parts of the Tan-Lu Fault Zone, which originated in Middle Triassic, propagated into northeastern China along the sinistral YYFZ under the earliest Early Cretaceous regional compression that is referred to as the Yanshan B event. The earliest Early Cretaceous initiation of the YYFZ results from both the high-speed oblique subduction of the Izanagi Plate and the final closure of the Mongol-Okhotsk Ocean, but the Izanagi Plate subduction played a major dynamic role in the fault zone origin.     

Characteristics of fault rocks and paleo-earthquake source along the Koktokay-Ertai fault zone,Xinjiang,China

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红河断裂带中南段糜棱岩分形特征及主要流变参数的估算

红河断裂带是一条经历了长期构造演化的块间构造变形带,该断裂的西南侧出露一套经韧性剪切形成的糜棱岩。研究区糜棱岩宏观上发育多种变形组构,如构造面理、线理、S-C组构等。微观变形特征有云母鱼、长石碎斑、长石和角闪石压扁拉长、碎斑旋转形成的压力影等;尤其是石英普遍变形,其特征有波状消光、核幔构造、动态重结晶、单颗粒压扁拉长及石英条带等;石英动态重结晶新颗粒尤其发育,重结晶的新颗粒边界具有锯齿状或港湾状等不同的微观特征,这些不同的特征记录了变形时的温压环境和流变速率。石英新颗粒分维几何统计分析表明:研究区石英动态重结晶颗粒边界形态具有自相似性,表现出分形特征。分维数值为1.150～1.180,变形温度大约500℃,同构造变质环境属高绿片岩相-低角闪岩相;初步估算应变速率可能低于10-8.4s-1,根据石英重结晶的粒径估算变形古应力为42.0～58.0MPa     

北京北石城断层带与河防口断层带断层岩石显微构造研究

本文论述了糜棱岩类与碎裂岩类的变形特征,它们各自代表了不同的成因机制,反映了断层带经历过早期韧性剪切和后期脆性破裂的发育历史。根据断层岩石的显微构造特征,估算了断层带发育过程中两个阶段的温度、压力、应变速率、差异应力大小和方位,并讨论了韧性剪切带、地壳中弹塑性过渡带与大陆地震多发层之间的关系     

Geological and mineralogical study of eclogite and glaucophane schists in the Naga Hills Ophiolite,Northeast India

A variety of low‐ to high‐pressure metamorphic assemblages occur in the metabasic rocks and metachert in the Upper Cretaceous–Eocene ophiolite belt of the central part of the Naga Hills, an area in the northern sector of the Indo–Myanmar Ranges in the Indo–Eurasian collision zone. The ophiolite suite includes peridotite tectonite containing garnet lherzolite xenoliths, layered ultramafic–mafic cumulates, metabasic rocks, basaltic lava, volcaniclastics, plagiogranite, and pelagic sediments emplaced as dismembered and imbricated bodies at thrust contacts between moderately metamorphosed accretionary rocks/basement (Nimi Formation/Naga Metamorphics) and marine sediments (Disang Flysch). It is overlain by coarse clastic Paleogene sediments of ophiolite‐derived rocks (Jopi/Phokphur Formation). The metabasic rocks, including high‐grade barroisite/glaucophane‐bearing epidote eclogite and glaucophane schist, and low‐grade greenschist and prehnite–clinochlore schist, are associated with lava flows and ultramafic cumulates at the western thrust contact. Chemically, the metabasites show a low‐K tholeiitic affinity that favors derivation from a depleted mantle source as in the case of mid‐ocean ridge basalt. Thermobarometry indicates peak P–T conditions of about 20 kb and 525°C. Retrogression related to uplift is marked by replacement of barroisite and omphacite by glaucophane followed by secondary actinolite, albite, and chlorite formation. A metabasic lens with an eclogite core surrounded by successive layers of glaucophane schist and greenschist provides field evidence of retrogression and uplift. Presence of S‐C mylonite in garnet lherzolite and ‘mica fish’ in glaucophane schist indicates ductile deformation in the shear zone along which the ophiolite was emplaced.     

三轴压缩下两类砂岩变形破坏的实验研究

本文讨论了围压高达700MPa的条件下,发生实验变形的长石砂岩和石英砂岩的变形模式和变形机制。完整长石砂岩的脆延过渡带在200—400MPa,完整石英砂岩的脆延过渡带在250—350MPa,长石砂岩在600MPa围压以上出现高压脆化现象;两类切口岩石的稳滑粘滑过渡界限分别是200MPa和150MPa。不同的变形模式主要起因于程度不同的碎裂机制。文中还对矿物成分的影响、脆性行为之延伸等有关问题进行了简要讨论     

Phengite K-Ar ages of schists from the Sanbagawa southern marginal belt, central Shikoku, southwest Japan: Influence of detrital mica and deformation on age

Abstract K–Ar age determinations were carried out on phengite separates from pelitic schists collected systematically from the Sanbagawa southern marginal belt and the associated area. The petrography and phengite chemistry by electron probe micro-analyzer (EPMA) revealed the existence of detrital white micas in the schist that have an extremely older age (108 Ma) in comparison with the neighboring schists (88 Ma) without any detrital mica. The ages become gradually older from the north ( ca 78 Ma) to the south ( ca 90 Ma) except for some samples that contain detrital micas and/or have been reactivated thermally by intrusives. The age is interpreted as an exhumation-cooling age that has been controlled by the ductile deformation of the host rocks that have never experienced a culmination temperature higher than 350°C which corresponds to the closure temperature of the K–Ar phengite system. The southward aging of the recorded ages in the extensive chlorite zone of the central Shikoku, from the Dozan river area of the north ( ca 65 Ma) to the study area of the south ( ca 85 Ma) through the Asemi river area ( ca 75 Ma), is explained in terms of increasing exhumation/cooling rates of the host rocks from north to south. The phengite K–Ar ages in the pelitic schists from the Kyomizu tectonic zone, which is classically considered as a remarkable thrusting shear zone, have no significant difference in comparison with that of the neighboring schists. This fact suggests that the latest stage of brittle deformation during exhumation/uplift has not significantly affected the ages of phengite in the schists.     

Metamorphic condition of a regional metamorphic complex in the Omuta district in northern Kyushu,southwest Japan

A high‐temperature (T) metamorphic complex occurs in the Omuta district, northern Kyushu, Japan. Three metamorphic zones are defined based on pelitic mineral assemblage, i.e. chlorite–biotite zone, muscovite–andalusite zone and sillimanite–K‐feldspar zone with ascending metamorphic grade from north to south. Two isograds trend approximately east–west, which is oblique to the boundary between the metamorphic complex and the Tamana Granodiorite located on the southeast. The metamorphic condition of two pelitic rocks that occur in the muscovite–andalusite zone and sillimanite–K‐feldspar zone are estimated as 510 ±30 °C, 300 ±60 MPa and 720 ±30 °C, 620 ±60 MPa, respectively. Thermodynamic consideration reveals that use of the same geothermobarometer enables precise determination of the difference in pressure between the samples as 320 ±10 MPa. This indicates that the pelitic samples were metamorphosed at different depth by 11–12 km that is significantly larger than the geographic distance of 6.8 km between the sample localities. This also suggests that crustal thinning took place after the high‐T metamorphism. The high‐T metamorphic complex is, therefore, not of static contact metamorphism but of dynamic regional metamorphism. The present result combined with petrological and chronological similarities implies that this complex suffered the regional Ryoke metamorphism.     

Metamorphic,deformation, fluids and geological significance of low-temperature retrograde mylonites of Diancangshan metamorphic massif along Ailaoshan-Red River strike-slip fault zone,Yunnan, China

Diancangshan metamorphic massif is one of the four metamorphic massifs developed along the Ailaoshan-Red River strike-slip fault zone, Yunnan, China. It has experienced multi-stage metamorphism and deformation, especially since the late Oligocene it widely suffered high-temperature ductile shear deformation and exhumation of the metamorphic rocks from the deep crust to the shallow surface. Based on the previous research and geological field work, this paper presents a detailed study on deformation and metamorphism, and exhumation of deep metamorphic rocks within the Diancangshan metamorphic massif, especially focusing on the low-temperature overprinted retrogression metamorphism and deformation of mylonitic rocks. With the combinated experimental techniques of optical microscope, electron backscatter diffraction attachmented on field-emission scanning electron microscopy and cathodoluminescence, our contribution reports the microstructure, lattice preferred orientations of the deformed minerals, and the changes of mineral composition phases of the superposition low-temperature retrograde mylonites. All these results indicate that: (1) Diancangshan deep metamorphic rock has experienced early high-temperature left-lateral shear deformation and late extension with rapid exhumation, the low-temperature retrogression metamorphism and deformation overprinted the high-temperature metamorphism, and the high-temperature microstructure and texture are in part or entirely altered by subsequent low-temperature shearing; (2) the superposition of low-temperature deformation-metamorphism occurs at the ductile-brittle transition; and (3) the fluid is quite active during the syn-tectonic shearing overprinted low-temperature deformation and metamorphism. The dynamic recrystallization and/or fractures to micro-fractures result in the strongly fine-grained of the main minerals, and present strain localization in micro-domians, such as micro-shear zones in the mylonites. It is often accompanied by the decrease of rock strength and finally influences the rheology of the whole rock during further deformation and exhumation of the Diancangshan massif.     

The North Cycladic Detachment System

Low-angle normal faults accommodate a large part of continental post-orogenic extension. Besides the intrinsic rheological characteristics of the continental crust that may lead to the formation of shallow-dipping shear zones at the brittle–ductile transition, the role of pre-existing low-angle structures such as large thrusts has been proposed by several authors. We explore this question with the example of the North Cycladic Detachment System (NCDS) that is composed of a series of distinct detachments cropping out on the islands of Andros, Tinos and Mykonos, separating the Cycladic Blueschists in the footwall from the Upper Cycladic Nappe in the hanging wall. We show that these extensional structures are part of a single large-scale structure (more than 200 km along strike) that reactivates the Vardar suture zone. It extends eastward on Ikaria and westward offshore Evia and Thessalia where it probably connects to recent shallow-dipping normal faults evidenced on published seismic reflection profiles. The NCDS started its activity in the Oligocene concommitantly with the Aegean extension, and was still active in the Late Miocene. It has exhumed a series of metamorphic domes from southern Evia to Mykonos below low-angle detachment systems, made of low-angle normal faults and low-angle ductile shear zones. The ductile shear zones and the faults were created with a low dip and they kept the same attitude throughout their exhumation. We identify three main detachments that are part of a continuum of extension on the NCDS : Tinos detachment, Livada detachment and Mykonos detachment. A fourth detachment (Vari detachment) is the reactivation of an Eocene exhumation-related structure. Deformation in the footwall is characterized by intense stretching and flattening. Using the spatial evolution observed along strike from Andros to Mykonos we construct a history of formation of the NCDS starting with the reactivation of former thrusts leading to the exhumation of high-temperature metamorphic domes. The Aegean example shows that reactivation of earlier shallow-dipping discontinuities can play a fundamental role in continental post-orogenic extension.