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1.
The surface geology of central England and Belgium obscures a large ‘basement’ massif with a complex history and stronger crust and lithosphere than surrounding regions. The nucleus was forged by subduction-related magmatism at the Gondwana margin in Ediacaran time. Partitioning into a platform, in the English Midlands, and a basin stretching to Belgium, in the east, was already evident in Cambrian/earliest Ordovician time. The accretion of the Monian Composite Terrane during the Penobscotian deformation phase preceded late Tremadocian rifting, and Floian separation, of the Avalonia Terrane from the Gondwana margin. Late Ordovician magmatism in a belt from the Lake District to Belgium records subduction beneath Avalonia of part of the Tornquist Sea. This ‘Western Pacific-style’ oceanic basin closed in latest Ordovician time, uniting Avalonia and Baltica. Closure of the Iapetus Ocean in early Silurian time was soon followed by closure of the Rheic Ocean, recorded by subduction along the southern margin of the massif. The causes of late Caledonian deformation are poorly understood and controversial. Partitioned behaviour of the massif persisted into late Palaeozoic time. Late Devonian and Carboniferous sequences show strong onlap onto the massif, which was little affected by crustal extension. Compressional deformation during the Variscan Orogeny also appears slight, and was focussed in the west where a wedge-shaped mountain foreland uplift was driven by orogenic indentation, splitting the massif from the Welsh Massif along the reactivated Malvern Line. Permian to Mesozoic sequences exhibit persistent but variable degrees of onlap onto the massif.  相似文献   

2.
易明初 《地球学报》1989,11(1):9-19
本文论述了法国中央高原及毗邻地区的新生代地层、地貌、构造形迹和火山活动等所反映的新构造活动类型及特征,综合分析了中央高原的隆升和构造应力场的演变。提出了高原强烈抬升时期为中更新世以来的观点,以及新生代各时期高原主要经受南北向挤压作用,其间辅以东西和北西—南东方向挤压作用的新认识。  相似文献   

3.
《Geodinamica Acta》1999,12(1):11-24
Located in the central part of the Betic Cordilleras, the large carbonate Sierra Gorda Massif provides an example of a west-Mediterranean karstic aquifer. In spite of a complex polyphased tectonic history, the fracturing presents, from aerial views and at outcrop scale a quite organised geometry. Four fracture directions are found over the massif: N000-010, N050-070, N090-100 and N140-170. The statistical and geostatistical approach allows the characteristics (lengths, orientations) and the spatial structure for each fracture set to be determined. The NOOO-010 and N140-170 sets are grouped in packets whereas the two other sets are grouped in bands. The microtectonic study describes the evolution of the massif in the geodynamic context of this part of Mediterranea, distinguishing three recent stages of brittle tectonic activity in the massif: a WNW-ESE Middle Miocene compression, then a NNW-SSE to NW-SE compression with a poorly wrenching regime, and finally a probably pre-Quaternary N-S radial distension. This last stage is essential for the karstification of the massif and groundwater circulation. From the combined analysis of fracture network geometry and palaeostresses a multiple porosity model in agreement with hydrological observations made inside the massif can be proposed: in particular, the hectometric N090-100 (and N050-070) fractures which are essential for the network connectivity, and have a major drainage role at aquifer scale, while the N000-010 and N140-170 ones have a more local drainage role. This extensive tardy regime, which is for the first time described separately from the internal zones of the Cordilleras, must be considered as a significant phenomenon on a regional scale, and henceforth integrated in future geodynamic schemes of this part of Mediterranea.  相似文献   

4.
《Geodinamica Acta》2013,26(4):157-163
The Terena Formation is located in the central part of the Ossa-Morena Zone (OMZ) and outcrops in the core of a latter (D3) first order syncline. This Formation is a Lower Devonian flysch and shows an unusual “Z” shape, with a central sector trending nearly N-S, and the tips trending NW-SE. This central sector is crossed by the cleavage (NW-SE) showing an apparent dextral (clockwise) transection pattern, anomalous and opposite to the regional widespread sinistral (anti-clockwise) transpression. The same sector with cartographic dextral transection, shows at outcrop scale, mesoscopic folds with a sinistral transection. During the Lower Devonian a N-S trending basin was developed as an effect of an early tectonic deformation phase. This trough was filled with turbidites and its elongated geometry determined the shape of the main syncline. We propose that the dextral transection pattern, at cartographic scale, result from the superposition of the NW-SE upright S3 cleavage on this major regional structure controlled by a sedimentary trough. The mesoscopic folds, observed on the upper levels of the sedimentary sequence were not influenced by the topographic anisotropy of the basin, and therefore they developed a left transection, according to the regional deformation mechanisms.

The “Z” shape of the syncline could be explained as a consequence of two major tectonic shear zones situated along the north and south boundaries of the OMZ, respectively the Tomar-Badajoz-Cordoba Shear Zone and the South Iberian Suture, lined by the Beja-Acebuches Ophiolitic Complex. Both shear zones have a sinistral transpressive character and were active during late Variscan tectonic events.  相似文献   

5.
The discrimination between distinct remote compressions and multiple local stress deviations within a single compressive stress field has been carried out in the central-eastern Iberian Chain, by using structural criteria, computing palaeostress directions, identifying and ‘filtering’ stress deviations, and analysing time relationships. A probabilistic analysis based on a systematic comparison of real and expected frequencies of coexistence of two compressions is applied by means of the χ 2 Test. This allows us to identify those tectonic compressions that behave as independent events from the probabilistic point of view. The results suggest that among five initially defined compression directions only three can be considered as representative of distinct (although partially superposed) externally applied intraplate stress fields: Iberian s.l. (NE-SW), Betic s.l. (NW-SE), and Pyrenean (N-S to NNE-SSW).  相似文献   

6.
Abstract

A review of data on the Lys-Caillaouas massif leads to a re-interpretation of its Variscan structural evolution. During a first phase of N-S shortening upright folds with steep axial plane foliations were formed. Subsequent regional metamorphism was followed by porphyroblast rotation and formation of gently dipping crenulation cleavages. During this event a N-closing recumbent fold at the scale of the massif developed, with relatively undeformed first phase foliations in the upper limb (suprastrucfure) and highly deformed and transposed foliations in the lower limb (infrastructure). This recumbent fold is argued to result from temperature induced gravity collapse of a crustal block previously having subvertical planes of anisotropy.  相似文献   

7.
张岳桥  施炜  廖昌珍  胡博 《地质学报》2006,80(5):639-647
基于对鄂尔多斯盆地西南缘构造带、中央断裂、东缘边界带和东北部地区的断裂几何特征、运动学及其活动期次的野外观察和测量,并根据断层面上滑动矢量的叠加关系和区域构造演化历史,确定了鄂尔多斯盆地周边地带晚中生代构造主应力方向、应力体制及其转换序列,提出了4阶段构造演化模式和引张-挤压交替转换过程。早中侏罗世,盆地处于引张应力环境,引张方向为N-S至NNE-SSW向。中侏罗世晚期至晚侏罗世,构造应力场转换为挤压体制,盆地周缘遭受近W-E、NW-SE、NE-SW等多向挤压应力作用。早白垩世,盆地构造应力场转换为引张应力体制,引张应力方向为近W-E、NW-SE和NE-SW向。早白垩世晚期至晚白垩世,盆地应力体制再次发生转换,从前期的引张应力体制转换为NW-SE向挤压应力体制。晚中生代构造应力体制转换和应力场方向变化不仅记录了不同板块之间汇聚产生的远程效应,同时记录了盆地深部构造-热活动事件,并对盆地原型进行了一定的改造。  相似文献   

8.
Abstract

Located in the central part of the Betic Cordilleras, the large carbonate Sierra Gorda Massif provides an example of a west-Mediterranean karstic aquifer. In spite of a complex polyphased tectonic history, the fracturing presents, from aerial views and at outcrop scale a quite organised geometry. Four fracture directions are found over the massif. N000—010, NOS0-070, N090–100 and N140–170. The statistical and geostatistical approach allows the characteristics (lengths, orientations) and the spatial structure for each fracture set to be determined. The N000–010 and N140–170 sets are grouped in packets whereas the two other sets are grouped in bands. The microtectonic study describes the evolution of the massif in the geodynamic context of this part of Mediterranea, distin guishing three recent stages of brittle tectonic activity in t e massif: a WNW-ESE Middle Miocene compression, then a NNW-SSE to NW-SE compression with a poorly wrenching regime, and finally a probably pre-Quaternary N-S radial distension. This last stage is essential for the karstification of the massif and groundwater circulation. From the combined analysis of fracture network geometry and palaeostresses a multiple porosity model in agreement with hydrological observations made inside the massif can be proposed: in particular, the hectometric N090–100 (and N050–070) fractures which are essential for the network connectivity, and have a major drainage role at aquifer scale, while the N000–010 and N140- 170 ones have a more local drainage role. This extensive tardy regime, which is for the first time described separately from the internal zones of the Cordilleras, must be considered as a significant phenomenon on a regional scale, and henceforth integrated in future geodynamic schemes of this part of Mediterranea. © Elsevier, Paris  相似文献   

9.
Among the Middle Penninic basements of the Internal NW-Alps, the Ruitor massif shows the best preserved remnants of pre-Permian metamorphic rocks. Their Barrovian-type mineral associations are somewhat masked by the greenschist to blueschist Alpine metamorphism of Tertiary age. Four Ruitor gneisses have been analysed, showing geochemical characters of granitoids from orogenic zones. Zircon morphology also suggests magmatic protoliths and a crustal source; some of the morphological zircon types suggest anatectic granites. The first U-Pb ages on zircon for this massif have been obtained concurrently through conventional multigrain and ion microprobe dating. Two metavolcanic rocks at 471LJ and 468ᆪ Ma could be slightly older than the porphyritic augen gneisses at 465ᆟ and 460lj Ma. Regional data from the other Internal basement massifs suggest that the Variscan event is poorly recorded, except in Ruitor-type units. Ruitor and Sapey gneisses belonged to the same unit (Nappe des Pontis), which was affected by a 480-450-Ma event including volcanism and anatexis and ended with a late calc-alkaline granite emplacement at 460-450 Ma. The distribution of Variscan basement units roughly parallels Alpine zonation.  相似文献   

10.
库车坳陷脆性构造序列及其对构造古应力的指示   总被引：3，自引：0，他引：3  
在对野外脆性构造(主要是节理和断层) 大量观测的基础上, 根据它们与应力的关系, 讨论了库车坳陷白垩纪末期以来的古构造应力时空变化.结果表明, 在库车坳陷脆性构造中, 早期隆升作用形成的主要发育在中生界的NEE-SWW向系统节理被晚期同构造期的在中生界与上第三系均发育的NNW-SSE向和NW-SE向节理切割并改造, 这是对区域上构造应力场在进入新近纪时从弱伸展变化到强烈挤压这一过程的响应.基于断层滑动分析的古应力反演结果显示, 此时盆山边界处以近N-S向伸展应力状态占主导, 而坳陷内部则表现为近N-S向和NW-SE向挤压应力状态.说明在进入新近纪后, 最大主应力(σ1) 方向从垂向变成水平, 应力场发生了转变.此后的天山快速垂向隆升是库车坳陷北缘和内部应力状态存在差异的原因.   相似文献   

11.
The discrimination between distinct remote compressions and multiple local stress deviations within a single compressive stress field has been carried out in the central-eastern Iberian Chain, by using structural criteria, computing palaeostress directions, identifying and ‘filtering’ stress deviations, and analysing time relationships. A probabilistic analysis based on a systematic comparison of real and expected frequencies of coexistence of two compressions is applied by means of the χ 2 Test. This allows us to identify those tectonic compressions that behave as independent events from the probabilistic point of view. The results suggest that among five initially defined compression directions only three can be considered as representative of distinct (although partially superposed) externally applied intraplate stress fields: Iberian s.l. (NE-SW), Betic s.l. (NW-SE), and Pyrenean (N-S to NNE-SSW).  相似文献   

12.
Abstract

Detailed structural analysis in the southwestern part of the Variscan Sehwarzwald Massif (SW Germany) indicates polyphase, synmetamorphic deformation in ductile shear zones. The tectono-melainnrphir evolution is characterized by orogenic crustal shortening and subsequent late- orogenic crustal extension in Carboniferous times. Convergence is responsible for an KSK trending, north dipping thrust zone with intense deformation in orthogneissic S-C type mylonites Superposed on schistose and folded metasediments presumably lower Carboniferous in age. Southeastward thrust-’“g parallel to pervasive stretching lineation, similar to the pre-dominant oblique convergent structures ill the central part of the massif, is related to crustal stacking. Relations of early granite intrusions with the outlasting retrograde tectonics Point to a Lower Carboniferous (Late-Visean) age of shortening.

Subsequent crustal extension is indicated by a broad N-S trending and west dipping ductile shear zone within high grade meetamorphic (I1T7LP) gneisses. Retrograde stretching lineatone marked by sillimanite to chlorite anr consistent with a top-to-the-west shearing on the western flank of a large progressively warping domai structure. Intensely sheared and boudinaged granitic rocks are syn-tectonic and seal the age of extension at about 325 Ma (Lower/ Upper Carboniferous boundary). During progressively cataclastic stages of tectonic denudation the still active detachment controlled formation of an adjacent late Paleozoic (Stephano-Pcrniian) continental basin supersedding high-grade gneiss. As elsewhere in the Varisean belt, the late extensional process in the tectono-”“‘tainorphie evolution of the southern Sehwarzwald is related rapid uplift, exhumation and thinning by a gravitational collaps of a previously thickened crust.  相似文献   

13.
New seamless onshore to offshore bedrock (1:10 k scale) mapping for the Lyme Bay area is used to resolve the westward termination of the Purbeck–Wight Fault Zone (PWFZ) structure, comprising one of the most prominent, long-lived (Variscan–Cimmerian–Alpine) structural lineaments in the southern UK. The study area lies south of the Variscan Frontal Thrust and overlays the basement Variscide Rhenohercynian Zone, in a region of dominant E-W tectonic fabric and a secondary conjugate NW-SE/NE-SW fabric. The PWFZ comprises one of the E-W major structures, with a typical history including Permian to early Cretaceous growth movement (relating to basement Variscan Thrust reactivation) followed by significant Alpine (Helvetic) inversion. Previous interpretations of the PWFZ have been limited by the low resolution (1:250 k scale) of the available offshore BGS mapping, and our study fills this gap. We describe a significant change in structural style of the fault zone from east to west. In the Weymouth Bay area, previous studies demonstrate the development of focussed strain associated with the PWFZ, accompanied by distributed strain, N-S fault development, and potential basement uplift in its hangingwall. In the Lyme Bay area to the west, faulting is dominantly E-W, with N-S faulting absent. Comparison of the newly mapped faulting networks to gravity data suggests a spatial relationship between this faulting variation and basement variability and uplift.  相似文献   

14.
Native gold, in association with tetrahedrite, bournonite, bismuthian jamesonite, antimonian bismuth, chalcopyrite, sphalerite, gersdorffite, galena, covelline, yarrowite and acanthite occurs in a NW-SE trending quartz carbonate vein which cuts folded Lower Devonian slates of the Meadfoot Group. The locality, 2.5 km north of the village of Loddiswell, lies in a belt of Devonian thrust and nappe terrain with a roughly E-W trend. The host-rocks are muddy turbiditic sediments interbedded with spilitic lavas, keratophyres and tuffs, together with intrusive dolerites (greenstones) which were deformed together during the Variscan orogeny. The deposit was worked briefly in the nineteenth century but little ore was raised and it is doubtful whether any gold was recovered. Analysis of samples collected in the present study revealed gold values of 5-10 ppm and silver values of 1000-2000 ppm. The relationship between gold-antimony mineralization, the basic igneous rocks in the nappe sequence, and their intersection by a series of major NW-SE fracture zones is discussed in the context of the regional metallogenic evolution of SW England. The mineralization is considered to be the result of fluid extraction during shear movements on the NW-SE structures and shows features in common with mesothermal gold-bearing sulphide veins in other Palaeozoic provinces.  相似文献   

15.
In the context of the present study the structural pattern in the Western Thessaly Basin (Greece) has been examined, based on structural data collected from the entire study area that were further correlated to the hydrographic network. The structural pattern of the area was revealed from tectonic analysis. Additionally, the topography, stratigraphy and sedimentology of the study area were taken into account. GIS techniques were used to map the spatial distribution of the geological and tectonic features on the topographic relief of the area. The oldest structures are contractional in nature, deformed by normal faulting related to the extensional episodes initiated in Serravallian times. It is inferred that the orientation of the stress field in the area has changed several times: the N-S stress field which was dominant during Late Serravallian times changed to NW-SE (Messinian-Zanclian) up to E-W in Zanclian and subsequently to roughly NNW-SSE (in late Piacencian). The NE-SW stress that was dominant in Pleistocene became N-S in later times. In addition, some changes in orientation are also indicated for the transitional periods of the pre-mentioned extensional episodes, possibly related to local events, or as a block-related deformation. The development of the 7th order streams is probably related to the N-S extensional faulting initiated in Pliocene times, while the dominant direction of the 6th, 5th and 4th order streams is possibly connected with the presence of the NNE-SSW and NW-SE extensional faults. Finally, the lower order streams are probably related to the most recent E-W striking normal faults.  相似文献   

16.
《Geodinamica Acta》2013,26(3-4):197-211
This work deals with the magnetic susceptibility and its anisotropy (AMS) in the Variscan Millares pluton in the Central Pyrenees. The zonation of low-field magnetic susceptibility is consistent with the concentric arrangement of rock-types, with more basic compositions at the external areas. Magnetic foliations defined from AMS strike NE-SW and dip gently towards the NW. Magnetic foliations are mainly perpendicular and oblique to the elongation of the pluton in map view (NW-SE) and show a concentric pattern at the central part, where the more acid rocks crop out. Magnetic lineations are scattered between NW-SE and NE-SW and plunge shallowly to the N. In map view magnetic lineations are distributed in domains normal to the elongation of the pluton. The contours of P' (degree of magnetic anisotropy) are oriented NE-SW and bands of oblate and prolate ellipsoids alternate perpendicular to the elongation of the pluton in map view. P' is between 1.009 and 1.055 in 93% of the specimens. Such low values are currently recorded in granites having magmatic fabrics and for which the anisotropy is mainly carried by biotite. The attitude of the magnetic foliation and the magnetic lineation, the geometry of the pluton, and their relationship with the host-rock structure suggest an intrusion contemporary with a transpressional regime, syntectonic with the late stages of the Variscan orogeny.  相似文献   

17.
The south-eastern part of the European Variscan belt forms a zone composed of several crystalline segments: the External Crystalline Massifs of the western Alps, the Maures-Tanneron massif, also Corsica and Sardinia, which are mutually displaced due to the Alpine deformation of the European Paleozoic lithosphere. All these crystalline fragments record similar structural, metamorphic, geochronological and magmatic histories during Paleozoic times. In particular, the Late Carboniferous period (～320–300 Ma) is characterized by crustal-scale folding associated with strike-slip faulting and intracontinental basin formation. In this transpressive context, dome structures exhume partially-molten crust in convergent setting, which is in contradiction with generally accepted models of late orogenic collapse of the Variscan belt. It is suggested that this particular transpressive–obliquely convergent template, exemplified by tectonometamorphic evolution of the Maures-Tanneron massif, is valid for the whole eastern European Variscan margin.  相似文献   

18.
The study of intraplate tectonics is crucial for understanding the deformation within plates, far from active plate boundaries and associated stress transmission to the plate interiors. This paper examines the tectonic evolution of the Variscan basement at the western margin of the Cenozoic Duero basin. Located east of the Vilariça Fault System in NW Iberia, this intraplate zone is a relatively flat but elevated area with an intense NNE-SSW trending fault system and associated moderate seismicity. Although the area has played an important role in the Duero basin configuration, its Alpine to present-day tectonic evolution has not been well constrained. In order to characterize the successive paleostress fields, 1428 pairs of fault-striae were measured at 56 sites and two focal mechanisms were used. Stress inversion methods have been applied to analyze paleostress regimes. Results show the existence of three dominant maximum horizontal stress (Shmax) trends: N-S, NE-SW and E-W. Relative and absolute dating of the activated faults for each Shmax shows that the clearly predominant N-S paleostress field in the zone has been active since the Oligocene up to the present day; while a NE-SW stress field is found to have been active during the Cretaceous and an older E-W paleostress field was active in the earlier Alpine cycle (Late Triassic).  相似文献   

19.
The Cenozoic paleostress state of the Earth’s crust at the southwestern flank of the Baikal Rift System (Tunka system of basins) is reconstructed. With allowance for known facts about the geologic history of the Tunka system of basins, the evolution of the stress field and its formation conditions are established by comparison of the obtained reconstructions, including the dated stress fields, with the Pleistocene-Holocene deformations in active fault zones and the present-day stress state (seismotectonic deformations calculated from the focal mechanisms of earthquakes). The opening of basins in the NW-SE direction was proceeding in the transtensional regime from the Oligocene to the late Miocene or early Pliocene. At the early-late Pliocene boundary, this process was followed by the transpressional regime with compression in the NW direction. In the late Pliocene, the situation at the southwestern flank changed drastically. Since that time, deformation has occurred in the transpressional regime and the compression axis has been oriented in the NE direction. The alternative models of the evolution of the Tunka system of basins—oblique extension, the transform fracture zone, or a pull-apart system—are considered. Both models are combined in the framework of the suggested stress-field reconstruction. The oblique extension (transtension) was related to the early stages of evolution, whereas a possibility of forming pull-apart basin was existent at the late stages.  相似文献   

20.
Abstract

The Cadomian Dyje Batholith, in the foot–wall of the Variscan Moravian nappe pile, has been involved in Variscan ductile deformation. The Cadomian Brunovistulian rocks were obliquely underthrusted during Carboniferous dextral transpression.

Strain intensity is inversely proportional to the distance from the contact of the Variscan thrust front. The microstructures of deformed granodiorites and quartz–diorites show a characteristic zonality marked by relatively high temperature flow in the west (550–580 °C) characterized by dynamic recrystallization of feldspars and grain boundary migration recrystallization of quartz. The size of quartz grains decreases with decreasing strain towards the east. At the easternmost part of the autochthonous Dyje massif, fracturing of feldspar and subgrain rotation recrystallization of quartz predominate. Flow stress estimates calculated from recrystallized quartz grain size show a regional increase of stress intensity from the highly strained margin towards the less deformed core of the Dyje massif. This microstructural zonation is oblique with respect to the major thrust boundary and corresponds roughly to metamorphic isogrades. The microstructural zonation reflects underthrusting of the Brunovistulian domain below the Moldanubian nappe.

The main ductile tectonic event D1 is followed by a retrogressive brittle–ductile and brittle deformation D2. D2 results in the development of shear zones and faults superimposed on the D1 mylonite fabric. D2 is related to extension oblique to the D1 fabric, associated with detachment and the westward movement of the Moravian nappes. © Elsevier, Paris  相似文献   

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