Effect of the chemical composition of the crust on the metamorphic evolution of orogenic wedges

Petrological data provide a good record of the thermal structure of deeply eroded orogens, and, in principle, might be used to relate the metamorphic structure of an orogen to its deformational history. In this paper, we present two‐dimensional thermal modelling of various subduction models taking into account varying wedge geometry as well as variation of density and topography with metamorphic reactions. The models clearly show that rock type accreted in the wedge has important effects on the thermal regime of orogenic wedges. The thermal regime is dominated by radiogenic heat production. Material having high radioactive heat production, like the granodioritic upper crust, produces high temperature metamorphism (amphibolitic conditions). Material with low radioactive heat production results in low temperature metamorphism of greenschist or blueschist types depending on the thickness of the wedge. Application of this model to seemingly unrelated areas of the Central Alps (Lepontine Dome, Grisons) and Eastern Alps (Tauern Window) explains the coexistence and succession of distinct Barrovian and blueschist facies metamorphic conditions as the result of a single, continuous tectonic process in which the main difference is the composition of the incoming material in the orogenic wedge. Accretion of the European upper continental crust in the Lepontine and Tauern Domes produces Barrovian type metamorphism while accretion of oceanic sediments results in blueschist facies metamorphism in the Valaisan domain.     

中国西北部造山带中几个古生代俯冲增生楔的识别与确认

中国西北部涉及古亚洲和特提斯两大构造域,造山带结构复杂,成矿地质条件优越.为推进地质找矿突破行动计划,中国地质调查局在各成矿(造山)带部署了一批1:5万、1:25万区域地质调查与基础地质综合研究项目,取得了一批新发现、新进展,有效提升了对各成矿带成矿地质条件的认知程度,尤其是在阿尔泰南缘、南天山、南昆仑等地识别并确认出规模可观的、成矿作用优越的板块俯冲增生楔,是造山带中的增生造山亚带,是寻找斑岩型铜、构造蚀变岩型金及多金属矿的最有利区带."增生造山带"的构造、岩浆活动及空间展布等的确认,为地质找矿突破提供了强有力的技术支撑.     

Failure in accretionary wedges with the maximum strength theorem: numerical algorithm and 2D validation

The objective is to capture the 3D spatial variation in the failure mode occurring in accretionary wedges and their analog experiments in the laboratory from the sole knowledge of the material strength and the structure geometry. The proposed methodology relies on the maximum strength theorem which is inherited from the kinematic approach of the classical limit analysis. It selects the optimum virtual velocity field which minimizes the tectonic force. These velocity fields are constructed by interpolation thanks to the spatial discretization conducted with ten-noded tetrahedra in 3D and six-noded triangles in 2D. The resulting, discrete optimization problem is first presented emphasizing the dual formalism found most appropriate in the presence of nonlinear strength criteria, such as the Drucker–Prager criterion used in all reported examples. The numerical scheme is first applied to a perfectly triangular 2D wedge. It is known that failure occurs to the back for topographic slope smaller than and to the front for slope larger than a critical slope, defining subcritical and supercritical slope stability conditions, respectively. The failure mode is characterized by the activation of a ramp, its conjugate back thrust, and the partial or complete activation of the décollement. It is shown that the critical slope is captured precisely by the proposed numerical scheme, the ramp, and the back thrust corresponding to regions of localized virtual strain. The influence of the back-wall friction on this critical slope is explored. It is found that the failure mechanism reduces to a thrust rooting at the base of the back wall and the absence of back thrust, for small enough values of the friction angle. This influence is well explained by the Mohr construction and further validated with experimental results with sand, considered as an analog material. 3D applications of the same methodology are presented in a companion paper.     

Late structural evolution in an accretionary wedge: insights from the Voltri Massif (Ligurian Alps,Italy)

The Voltri Massif underwent a polyphasic tectono-metamorphic evolution that records both the Alpine and part of the Apennine deformation events. So this is a key-area to investigate the relationships between Alpine and Apennine deformation events.

This paper focus on the upper crustal deformations (UCD) that characterize the last stages of the tectonics of the Voltri Massif. In the Voltri Massif UCD are characterized by the superpositions of ductile, brittle-ductile and brittle structures that can be attributed to three main tectonic events (from D3 to D5). The oldest UCD event (D3) developed folds and reverse shear zones under ductile to brittle-ductile conditions. Main compressive NW-SE oriented regime characterized D3 event. Brittle-ductile to brittle reverse shear zones and important strike-slip/transpressive systems overprinted D3 structures. This D4 event was significant at the regional scale and occurred under main transpressive, NE-SW oriented, regime. The latest normal and transtensional brittle structures, that formed during UCD D5 event, locally reactivated the older structures.     

Elastic behaviour and structural evolution of topaz at high pressure

The elastic behaviour and the high-pressure structural evolution of a natural topaz, Al_2.00Si_1.05O_4.00(OH_0.26F_1.75), have been investigated by means of in situ single-crystal X-ray diffraction up to 10.55(5) GPa. No phase transition has been observed within the pressure range investigated. Unit-cell volume data were fitted with a third-order Birch-Murnaghan Equation of State (III-BM-EoS). The III-BM-EoS parameters, simultaneously refined using the data weighted by the uncertainties in P and V, are: V ₀=345.57(7) ų, K _T0=164(2) GPa and K′=2.9(4). The axial-EoS parameters are: a ₀=4.6634(3) Å, K _T0(a)=152(2) GPa, K′(a)=2.8(4) for the a-axis; b ₀=8.8349(5) Å, K _T0(b)=224(3) GPa, K′(b)=2.6(6) for the b-axis; c ₀=8.3875(7) Å, K _T0(c)=137(2) GPa, K′(c)=2.9(4) for the c-axis. The magnitude and the orientation of the principal Lagrangian unit-strain ellipsoid were determined. At P−P ₀=10.55 GPa, the ratios ε₁:ε₂:ε₃ are 1.00:1.42:1.56 (with ε₁||b, ε₂||a, ε₃||c and |ε₃| > |ε₂| > |ε₁|). Four structural refinements, performed at 0.0001, 3.14(5), 5.79(5) and 8.39(5) GPa describe the structural evolution in terms of polyhedral distortions.     

构造变形对海相页岩储层渗透率演化的影响

与北美不同,中国南方海相页岩层经历了多期构造改造,页岩储层物性受构造变形作用的影响较大。为了研究构造变形对南方海相页岩储层渗透率的影响特征和机理,以雪峰山西侧地区五峰-龙马溪组页岩为研究对象,利用气体脉冲衰减法、压汞法和扫描电子显微镜等手段对不同变形页岩样品的渗透率、孔隙结构及孔隙形貌特征进行了测试分析,探讨构造变形页岩的渗透率演化特征及其对孔隙结构演化的响应机理。测试结果显示,强烈构造变形页岩的渗透性较原生页岩和弱变形页岩的渗透性显著提高,强变形页岩样品的渗透率在0.2 mD和2.69 mD之间,比未变形和弱变形页岩样品的渗透率(在1.5×10-4 mD和1.7×10-3 mD之间)高三个数量级,表明强构造变形作用对页岩渗透率具有显著促进作用;同时,不同有效压力条件下页岩渗透率的演化特征显示,强变形页岩气体渗透率的压力敏感性比原生页岩和弱变形页岩显著降低。构造变形条件下页岩孔隙结构与渗透率相关性的进一步分析认为,强变形页岩的孔隙结构变化特别是大孔和裂隙的发育,是促进其渗透率增加的主要原因。这些研究结果表明,伴随强烈的构造变形,南方海相页岩易形成大孔和微裂隙发育的孔隙结构特征,有助于强变形页岩层渗透性的显著提高。构造变形页岩渗透率的提高有利于地质条件下气体的运移,一方面,将有利于页岩气往构造高点的迁移和富集从而形成游离气型或外源型页岩气甜点;另一方面,也可能导致页岩气在盖层条件不佳和断裂发育区的散失。      

CO2地质封存中储层流体压力演化规律的解析模型

为使解析模型可以更加科学准确地描述储层中多相流体的迁移机制与压力演化规律,提高解析计算与分析的精度。首先将储层中的流场划分为3个区域,然后根据渗流体积守恒方程反演储层中两相流体混合渗流区的各相流体饱和度,进而将总流度直接引入到达西公式中得到了一个适用于两相流的广义达西公式,据此推导出了一个更为精确的表征储层流体压力演化规律的解析模型。最后,通过案例分析,将该解析模型的计算结果与既有文献的显式积分解及TOUGH2/ECO2N的数值解进行对比,验证了该模型的可靠性及相比于既有文献的显式积分解在计算精度方面的优越性。此外,计算结果也表明,该解析模型虽然是在稳态流的假定条件下得到的,但对于实际储层流体压力演化的全过程均具有很强的表征能力,这主要归因于该模型可科学准确地确定饱和度,因此,可以在工程中推广应用。     

The sedimentological evolution of a Lower Palaeozoic accretionary fore-arc in the Southern Uplands of Scotland

Thick turbidites accumulated along the northern margin of the Iapetus Ocean in Britain from mid-Ordovician to late Silurian times. Recent plate tectonic reconstructions hold that, during subduction, packets of these sediments, together with the underlying pelagic facies and thin portions of the uppermost ocean crust, were stripped from the descending plate and accreted to the inner trench wall on the Laurentian (North American) continental margin. The resulting accretionary prism is represented today by the Ordovician and Silurian rocks of the Southern Uplands of Scotland and the Longford-Down massif of Ireland. In these areas major reverse faults separate tracts of steeply dipping greywackes and mudstones with minor amounts of cherts and basalts. These tracts are up to several kilometres wide; their constituent beds face predominantly to the northwest, away from the site of the ancient ocean, while becoming progressively younger in each major fault slice towards the Iapetus suture in the southeast. From the stratigraphic sequences in these fault slices the sedimentary history of a portion of the Iapetus Ocean, and the British sector of its northern margin, can be reconstructed. In the Southern Uplands the earliest turbidites (mid- and late-Ordovician) are preserved in the northernmost fault slices. Regional facies trends, and vertical facies analysis, suggest that they accumulated in a trench dominated by a series of relatively small lower trench slope-derived fans. Pelagic sediments of the same age are found in the fault slices to the south, suggesting that the Ordovician turbidites were confined to the trench. During the lower and middle Llandovery, volcaniclastic trench turbidites were separated from quartz-rich ocean-floor turbidites (represented in the southern fault slices) by an elongate rise, on which pelagic deposits accumulated. This is interpreted as the outer trench high. In late Llandovery times the rise was overwhelmed, and thick laterally derived quartzose turbidites blanketed both the trench and the ocean floor. Sedimentation was strongly influenced by the evolution of the accretionary prism. By Llandovery times a trench slope break had emerged, supplying sediment both south to the trench and north to an upper slope basin in the Midland Valley of Scotland. In this basin early Silurian turbidites were followed by shallow-water and terrestrial sediments. Most of the sediment was derived from the emergent trench slope break: the volcanic arc and the Grampian orogenic belt to the north provided little or no detritus. Throughout the Ordovician and Silurian, sediment in the trench and on the ocean floor was derived from the volcanic arc, from the lower trench slope/trench slope break, from a degrading plutonic/metamorphic terrain (the Grampian Orogen), and locally by a minor amount of submarine sliding from carbonate-capped volcanic seamounts. Progressive elevation of the trench slope break in Silurian (and perhaps late Ordovician) times indicates that sediment from the arc-orogen hinterland must have bypassed the upper slope in the unexposed section of the margin to the northeast of the Southern Uplands, and travelled into the area axially along the trench floor.     

Growth of accretionary wedges and pulsed ophiolitic mélange formation by successive subduction of trench‐parallel volcanic elevations

Fault‐bounded coherent belts alternating with belts of mélanges are common in accretionary wedges and are usually interpreted as a result of imbrication along subduction zone megathrusts. Using the Neoproterozoic/early Cambrian Blovice accretionary complex (BAC), Bohemian Massif, as a case example, we present a new model for the origin of alternating belts through the repetition of several cycles of (1) offscraping and deformation of trench‐fill sediments to form the coherent units, interrupted by (2) arrival and subduction of linear, trench‐parallel volcanic elevations. The latter process leads to an increase in the wedge taper, triggering mass‐wasting and formation of olistostromes. At the same time, ophiolitic mélanges form by disruption of an upper part of the volcanic ridge and incorporation of the disrupted ocean‐floor succession into the olistostromes. Specifically, the BAC represents a complete section across an accretionary wedge and records three such major pulses of ophiolitic mélange formation through subduction of an outboard back‐arc basin.     

孔隙水压力对锯齿状结构面剪切蠕变特性的影响

为探究孔隙水压对岩体结构面剪切蠕变特性的影响,自主研制了结构面一体化制作模具和多功能剪切流变仪,开展了孔隙水压力下锯齿状结构面的剪切蠕变试验,分析了孔隙水压对结构面蠕变变形、蠕变速率和长期强度的影响。试验结果表明：不同孔隙水压力下的结构面先后经历了瞬时变形阶段、减速蠕变阶段和稳定蠕变阶段,并且孔隙水压力的增大促进了结构面非线性特征的发展;随着孔隙水压力的增大,结构面瞬时位移、蠕变位移和稳态蠕变速率逐渐增大,而蠕变时长、破坏应力和长期强度均呈现明显降低的趋势。根据试验结果,考虑孔隙水压力对模型参数的影响,将蠕变模型中的瞬时剪切模量、黏性剪切模量以及黏性系数替换为孔隙水压力的函数,构建了能够反映孔隙水压力影响的结构面蠕变模型,并对模型参数进行辨识,将试验曲线和理论模型曲线进行对比,验证了模型的正确性和适用性。研究成果对富水区岩体长期稳定性分析提供一定的理论指导。     

P-T evolution of metapelites from the Bajgan complex in the Makran accretionary prism,south eastern Iran

The Bajgan Complex, one of the basement constituents of the arc massif in Iranian Makran forms a rugged, deeply incised terrain. The complex consists of pelitic schists with minor psammitic and basic schists, calc silicate rocks, amphibolites, marbles, metavolcanosediments, mafic and felsic intrusives as well as ultramafic rocks. Metapelitic rocks show an amphibolite facies regional metamorphism and contain garnet, biotite, white mica, quartz, albite ± rutile ± apatite. Thermobarometry of garnet schist yields pressure of more than 9 kbar and temperatures between 560 and 675 °C. The geothermal gradient obtained for the peak of regional metamorphism is 19 °C/km, corresponding to a depth of ca. 31 km. Replacement of garnet by chlorite and epidote suggest greenschist facies metamorphism due to a decrease in temperature and pressure through exhumation and retrograde metamorphism (370–450 °C and 3–6 kbar). The metapelitic rocks followed a ‘clockwise’ P–T path during metamorphism, consistent with thermal decline following tectonic thickening. The formation of medium-pressure metamorphic rocks is related to presence of active subduction of the Neotethys Oceanic lithosphere beneath Eurasia in the Makran.     

依—舒地堑方正断陷古近系构造演化与沉积相带展布特征

方正断陷由南向北划分为南部斜坡、南部凹陷、中部凸起、北部凹陷和北部斜坡共5个二级构造单元。古近系是方正断陷形成、发育、演化的主要阶段,乌云组和新安村组沉积时期为强烈断陷期,达连河组沉积时期为持续断陷期,宝泉岭组一段沉积时期为断凹转化期,宝泉岭组二段沉积时期为断陷萎缩期。乌云—新安村组和宝二段沉积时期,盆地总体构成了水系发育的扇三角洲-滨浅湖沉积体系;达连河组和宝一段沉积时期,盆地总体构成了横向水系发育的扇三角洲-半深湖沉积体系。从乌云—新安村组到宝泉岭组二段,沉积中心由北到南再到北,湖泊面积由小变大再到小,湖泊水体由浅变深再变浅。     

Early Tertiary fluid flow and pressure–temperature conditions in the Shimanto accretionary complex of south-west Japan: constraints from fluid inclusions

The pressure and temperature history of the Tertiary Shimanto belt of south-west Japan has been elucidated by analysing fluids trapped in quartz crystals which grew syn-kinematically along late-stage brittle faults. The samples come from three areas that span the Paleogene exposures on the Muroto Peninsula of Shikoku Island. Applying microthermometric and laser Raman microsampling techniques to coeval water-rich and carbonic fluid inclusions, we have constrained the pressure and temperature conditions that accompanied a widespread and kinematically distinct phase of deformation. The results suggest elevated geothermal gradients during late-stage deformation, conditions that are in disaccord with previous plate reconstructions that have depicted old, thermally mature Pacific crust subducting beneath Eurasia during the early to middle Tertiary. These conditions can most easily be accounted for by including an additional plate boundary in the western Pacific during Paleogene time. Plate reconstructions that include the Kula plate in this region are therefore consistent with our findings. In addition, our results provide clues to the conditions that likely accompany seismogenic deformation at active convergent plate boundaries.     

Stratal disruption and development of mélange, Western Newfoundland: effect of high fluid pressure in an accretionary terrain during ophiolite emplacement

The Bay of Islands Ophiolite was emplaced onto the continental margin of North America during the mid-Ordovician Taconic orogeny, when tectonic slices of continental margin sediments were accreted to the moving allochthon. Tectonic slices grade into and are surrounded by mélange. Early fracture in sandstones formed without grain breakage and allowed penetration of liquid petroleum along fracture planes. Other fractures involved cataclastic flow and were sometimes re-activated during formation of later pressure solution cleavage. Shear-fracture and extension-fracture boudinage affect competent strata; extensional veins cut cement in limestone beds and are filled by shale, quartz, calcite and bitumen. Folds also formed, at a time when siltstone and sandstone were at least partially lithified. Mélange matrix shows abundant shear and extension fractures in a variety of orientations.Coaxial extension responsible for disruption of bedding can be explained by a brittle accretionary wedge model in which high fluid pressures resulted from tectonic dewatering of shales. Surface slope decreased as fluid pressure rose beneath the ophiolite, causing horizontal extension of the wedge. After escape of excess water the surface slope steepened again as renewed stacking occurred.     

新疆东天山晚古生代地壳增生和成矿作用

地壳增生和成矿作用是矿床学研究的前沿领域;东天山作为中亚造山带的重要组成部分,在晚古生代地壳演化过程中经历了板块俯冲、碰撞造山大规模走滑剪切和后造山演化阶段,在每个构造演化阶段都伴随有地壳增生和大量有用金属元素的堆积。按照地壳增生和成矿作用关系,研究区晚古生代主要有如下几种矿床类型:1)晚泥盆世—早石炭世增生前形成的Cu-Mo-Au-Ag矿床;2)早石炭世增生前形成的Fe-Cu-Pb-Zn矿床;3)晚石炭世—早二叠世增生后形成的造山型Cu-Ni-PGE矿床;4)晚石炭世—早二叠世增生后形成的造山型Au-Cu矿床。上述矿床在形成过程中既有地壳的水平增生,也有地壳的垂向增生作用,已经构成了我国重要的内生金属矿床富集区。     

Metallogeny,structural evolution,post-mineral cover distribution and exploration in concealed areas of the northern Chilean Andes

Mineral exploration of prospective areas concealed by extensive post-mineralization cover is growing, being very complex and expensive. The projection of rich and giant Paleocene to early Oligocene porphyry-Cu-Mo belts in northernmost Chilean Andes (17.5–19.5°S) has major exploration potential, but only a few minor deposits have been reported to date, due to the fact that the area is largely covered by post-mineral strata. We integrate the Cenozoic stratigraphic, structural and metallogenic evolution of this sector, in order to identify the most promising regions related to lesser post-mineral cover and the projection of different metallogenic belts. The Paleocene to early Eocene metallogenic belt extends along the Precordillera, with ca. 30 km wide, and includes porphyry-Cu prospects and small Cu (±Mo-Au-Ag) vein and breccia-pipe deposits. Geochronological data indicate an age of 55.5 Ma for an intrusion related to one deposit and ages from 69.5 to 54.5 Ma for hydrothermal alteration in one porphyry-Cu prospect and largest known Cu deposits. The middle Eocene to early Oligocene porphyry belt, in the Western Cordillera farther east, is associated with 46–44 Ma intrusions. It is estimated to be 40-km wide, but is largely concealed by thick post-mineral cover. The youngest Miocene to early Pliocene metallogenic belt, also in the Western Cordillera, is well-exposed and includes Au-Ag epithermal and polymetallic veins and manto-type deposits.The Oligocene-Holocene cover consists of a succession of continental sedimentary and volcanic rocks that overall increase in thickness from 0 to 5000 m, from west to east. These strata are subhorizontal in the west and folded-faulted towards the east. Miocene gentle anticlines and monocline flexures extend along strike for 30–60 km in the Precordillera and were generated by propagation of high-angle east-dipping blind reverse faults with at least 300–900 m of Oligocene bedrock offset. The thickness of cover exceeds 2000 m in the eastern Central Depression, whereas it is generally less than 1000 m in the Precordillera along the Paleocene to early Eocene porphyry-Cu belt and it can reach locally up to 5000 m in the Western Cordillera, above the middle Eocene to early Oligocene belt.In the studied Andean segment, the Miocene to early Pliocene metallogenic belt is superimposed on the Paleocene to Oligocene belts in a 40–50 km wide zone. This overlap may be explained by an accentuated migration of the magmatic front, from east to west, since ca. 25 Ma, as a consequence of subduction slab steepening after a period of magmatic lull and flat subduction from ca. 30–35 to 25 Ma. The identified areas of lesser cover thickness are prone to exploration for concealed deposits, especially along the projection of major porphyry-Cu-Mo belts.     

Polyphase structural evolution of the southwestern Argentine Precordillera

The western and southwestern parts of the Argentine Precordillera display complex geometries which are not consistent with those of a typical high-level fold-and-thrust belt. They are the result of a polyphase structural evolution which spans the Early Paleozoic to Late Tertiary period. After an Early Paleozoic folding and shearing event under a greenschist facies metamorphism, uplift, erosion, and deposition of Late Carboniferous to Early Permian clastics were accompanied by extensional faulting. This was followed by a Permian folding and faulting event which led to a partial inversion of the Late Carboniferous-Early Permian graben fill. Permian to Triassic crustal extension was combined with block faulting and the deposition of a thick volcanic sequence. The subsequent Late Tertiary crustal shortening partly reactivated older fault lines. Excluding folds, a few thrusts, and reverse faults, the crustal shortening within the older blocks was accommodated by a dominant sinistral strike-slip faulting under a W-E compressive regime. Above a major décollement, the entire sequence of faulted and folded blocks was carried from west to east towards its present position. The regional situation indicates that this southern part of the orogen was transferred further to the east with respect to the central thin-skinned parts. The movements are interpreted to be related to an important thrust fault which obliquely cuts through the fold-and-thrust belt.     

The structural evolution of the Paleozoic of the Pyrenees

Five deformationphases occurring on a regional scale have been found in the Paleozoic sequence of the Pyrenees. The first phase was responsible for the development of large concentric folds in the southern and northern borders of the axial zone. The second or main phase has lead to the differentiation in suprastructure and infrastructure. Folds have E-W axes and are accompanied by cleavage or schistosity. The next phase has N-S axes and its occurrence is restricted to the infrastructure. The third cleavage phase is a conjugate system with vertical NW and NE striking axial planes of folds. Like the N-S phase it indicates E-W compression. The fourth cleavage phase has again an E-W direction like the main phase. The intrusion of the granites can be related to this structural history. A final phase consists of tilting and fanning of the cleavage of the suprastructure, accompanied by the formation of knickzones.

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Zusammenfassung Im Paläozoikum der Pyrenäen konnten fünf verschiedene Deformationsphasen über große Gebiete hinweg festgestellt werden. Die erste hat im Süden und Norden der Axialzone sehr große N-S bis NE-SW gerichtete Biegefalten verursacht. Die zweite, aber erste Schieferurigsphase ist in dem epizonalen Schiefergebirge oder Oberbau und in dem meso- bis katazonalen Unterbau verschiedenartig entwickelt. In beiden Fällen streichen jedoch die Faltenachsen E-W, und es liegt eine N-S-Einengung vor. Die folgende Phase ist auf die metamorphen Gebiete beschränkt und wird von N-S gerichteten Falten mit flacher Schieferung begleitet. Die dritte Schieferungsphase besteht aus zwei gleichzeitigen Scherfaltensystemen in NW- und NE-Richtung. Sie weist wie die vorhergehende Phase auf eine Einengung in E-W-Richtung hin. Die vierte Phase hat E-W gerichtete Falten mit Schieferung hervorgerufen und ist wie die Hauptphase eine N-S-Zusarnmenstauung. Die Intrusion der Granite kann in diese tektonische Entwicklung eingeordnet werden. Während einer späten Phase sind die Schieferungsflächen zu einem großen Fächer verstellt worden. Das Auftreten von Knickzonen ist mit diesem Auseinanderfallen der Schieferung verbunden.

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Résumé Dans le Paléozoique des Pyrénées cinq phases de déformation peuvent être reconnues. La première phase a formé des plis concentriques sans schistosité et se trouve près de la bordure nord et sud de la zone axiale. Les quatre phases suivantes sont accompagnées d'une schistosité. La phase principale a causé une différentiation entre supra- et infrastructure, tous les deux avec des plis E-W. La deuxième phase synschisteuse ne se trouve que dans l'infra-structure et est caractérisée par des plis N-S. Une phase suivante consiste d'une système conjugée de plis avec direction des plans axiaux des plis NW et NE. La dernière phase a produit des plis E-W. L'intrusion des granites peut être datée dans cet histoire tectonique. Une phase tardive a causé la formation d'un gros structure en éventail des plans de clivage du suprastructure.

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