首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The most important tectonic and magmatic events in the history of ophiolites in the Uralides and the European Variscides occurred almost sinchronously. The rocks of paleooceanic complexes in the both regions have similar paleontological and isotopic ages. The formation of the Ural and Variscan ophiolites is brought into correlation with a wide range of geodynamic settings. The Ural ophiolites mainly correspond to the suprasubduction setting, whereas the Variscan ophiolites are commonly related to rifts and mid-ocean spreading centers of the oceanic crust. The main difference is related to the origin of metamorphic rocks associated with ophiolites. The high-pressure-low-temperature metamorphism of the Ural ophiolites mainly related to the island arc-continent collision, whereas the Barrow-type metamorphism of ophiolites in the European Variscides developed at a higher temperature under medium-low pressure.  相似文献   

2.
Tectonics and plate tectonics model for the Variscan belt of Europe   总被引：2，自引：0，他引：2  
A plate tectonics model is presented to explain the tectonometamorphic characteristics of the European Variscides. After the closing of two oceanic domains by two-sided subduction (500-420 Ma) and obduction (420-380 Ma), collision of the European and African continental plates occurred. We propose that the subsequent complex intracontinental deformation (380-290 Ma) is the result of a double subduction of the continental lithosphere accompanied by crust-mantle décollement. This mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the Variscan Belt. Accounting for this model and for the relationships between the European Variscides and the other Paleozoic peri-Atlantic belts (Caledonides, Appalachian, Mauritanides and Morocco), we infer the relative positions of Africa, America and Europe between the Silurian and the Permian.  相似文献   

3.
The Variscan orogenic collage consists of three subduction-collision systems (Rheno-Hercynian, Saxo-Thuringian and Massif Central-Moldanubian). Devonian to early Carboniferous marine strata are widespread not only in the individual foreland fold and thrust belts, but also in post-tectonic basins within these foreland belts and on the Cadomian crust of peri-Gondwanan microcontinental fragments, which represent the upper plates of the subduction/collision zones. These marine basins preclude high elevations in the respective areas and also in their neighbourhood. Widespread late Carboniferous intra-montane basins with their coal-bearing sequences are likewise incompatible with high and dry plateaus. While narrow belts with high elevations remain possible along active margins within the orogen, comparison of the Variscides with the Himalaya/Tibetan plateau is unfounded. Plausible reasons for the scarcity of high Variscan relief include subduction of oceanic and even continental crust, subduction erosion, orogen-parallel extension and—most important—lithospheric thinning accompanied by high heat flow and magmatism. In many areas, timing and areal array of magmatism and HT metamorphism are not compatible with a model of tectonic thickening and subsequent gravitational collapse. It is suggested, instead, that lithospheric thinning and heating are due to mantle activities caused by the Tethys rift. The lower and middle crust were thermally softened and rendered unfit for stacking and isostatic uplift: in terms of topography, the Variscides represent a failed orogen. The HT regime also explains the abundance of granitoids and HT/LP metamorphic rocks typical of the Variscides. Melting in the HT regime extracted mafic components from Variscan and Cadomian crust as well as from Cadomian metasomatized lithospheric mantle, thus mimicking subduction-related magmatism. The onset of the HT regime at c. 340 Ma may also have triggered the final ascent of HP/UHP felsic metamorphic rocks.  相似文献   

4.
A two-dimensional thermo-mechanical finite element model is used to study the Permo-Carboniferous evolution of Central Europe along a lithosphere-scale transect from the Variscan Internides to the undeformed foreland. The study concentrates on a quantitative evaluation of the processes controlling late-orogenic extension and destruction of the Variscides, particularly the gravitational instability of thickened crust. Modelling results suggest that gravitational forces along cannot reproduce the observed timing and amount of Permo-Carboniferous crustal thinning. Tensile plate-boundary forces are required in addition to gravitation to restore a crustal thickness of approximately 30?km in the Variscan Internides. Stresses as little as 10?MPa result in up to 28% extension and a good fit between observed data and model predictions. It is concluded that the Stephanian to Rotliegend evolution in the vicinity of the modelled traverse resulted not from gravitational forces inherited from Variscan crustal thickening, but was related to a change in orientation of the plate-boundary stresses at the end of the Westphalian.  相似文献   

5.
In the Ligurian Alps, the Barbassiria massif (a Variscan basement unit of the Briançonnais domain) is made up of orthogneisses derived from K‐rich rhyolite protoliths and minor rhyolite dykes. However, on account of subsequent Alpine deformation and a related blueschist facies metamorphic overprint that are pervasive within the Barbassiria Orthogneisses, little evidence of the earlier Variscan metamorphism is preserved. In this study, new U–Pb laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) dating of zircon from the Barbassiria Orthogneisses and dykes was undertaken to unravel the relationships between protolith magmatism and the Variscan metamorphic overprint. The results suggest a protolith age for the Barbassiria Orthogneisses of ~315–320 Ma (i.e., Early/Late Carboniferous), and constrain the age of a subsequent rhyolite dyke emplacement event to 260.2 ± 3.1 Ma (i.e., Late Permian). The Variscan high‐temperature (greenschist–amphibolite facies) metamorphic event that affected the Barbassiria Orthogneisses was likely associated with both tectonic burial and compression during the final stages of the Variscan collision during the Late Carboniferous period. Emplacement of late‐stage rhyolite dykes that cut the Barbassiria Orthogneisses is linked to a diffuse episode of Late Permian rhyolite volcanism that is commonly observed in the Ligurian Alps. The age of this dyke emplacement event followed a ~10–15 Ma Mid‐Permian gap in the volcano‐sedimentary cover sequence of the Ligurian Alps, and represents the post‐orogenic stage in this segment of the Variscides. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

6.
The architecture of the European Variscides has been subdivided by Kossmat (1927) into paleogeographically coherent units which are presently interpreted as former plate fragments. The Mid-German Crystalline Rise (MGCR) separates two fragments (Rhenohercynian and Saxothuringian belts) at the site of an inferred plate boundary and reequilibrated orogenic root. The commonly favoured model interprets the MGCR as the magmatic arc on Saxothuringian crust above a south-dipping subduction zone in Upper Devonian and Carboniferous times. Data from the MGCR, the kinematic evolution of the Mid-European Variscides, and first order volume balancing suggest a reinterpretation of this unit which challenges classical views on the MGCR as well as on the subdivision of Variscan architecture. The MGCR is composed of two rock groups with different tectonic identity. A Lower Carboniferous low pressure-high temperature magmatic arc association on Lower Paleozoic basement rests tectonically on a stack of medium pressuremedium temperature rocks of inferred Rhenohercynian origin. The latter were tectonically accreted to the base of the overriding plate by tectonic underplating. The entire process was controlled by oblique convergence. This led to regional partitioning of the plate kinematic vector into contractional domains (lower Rhenohercynian plate and back-arc area of the upper Saxothuringian plate), bulk heterogeneous plate margin parallel extensional domains (MGCR), and plate margin parallel wrench domains (MGCR boundaries). During this process material was continually transferred from the lower plate to the upper plate, uplifted and exhumed by net crustal extension. The concomitant removal of parts of the former arc and the entire orogenic root necessitates a reappraisal of Variscan architecture and evolution.  相似文献   

7.
Out of a dense network of seismic reflection lines for hydrocarbon exploration in the North-east German Basin, several lines were recorded to 12 s TWT to obtain information about the structure of the crust and the crust-mantle transition. One of these profiles is presented here. This stretches for 110 km in a NNE direction between Neustrelitz and the island of Usedom. It reaches from the External Variscides in the south across the North German Massif into the Rügen-Pomorze Terrane in the Baltic Sea. Below Cenozoic-Mesozoic-Paleozoic cover with clear reflections down to base Zechstein, the reflectivity varies considerably with depth and also laterally. The Paleozoic and Precambrian sediments and basement are generally void of reflections, but the lower crust and the Moho show strong reflections. To the north the reflectivity decreases, and the Moho depth increases to beyond the bottom of the record section at 12 s. There are no direct indications for deep-reaching faults such as the Trans-European Fault in the north. The North German Massif acted as a ramp towards the Variscan Orogeny, similar to the London-Brabant Massif further west.  相似文献   

8.
《Geodinamica Acta》2013,26(3-4):155-164
New structural data pointed out the presence of an older scattered migmatization event (Devonian?, M1) overcome by the well known Variscan migmatization event (Lower-Middle Carboniferous, M2) related to the Late extensional tectonic that affected the High Grade Metamorphic Complex (HGMC) in the Variscan Belt of Sardinia (Italy). The M1 event is only recognizable in the kyanite – amphibole bearing migmatitic gneiss. Both migmatization events (M1 and M2) are characterized by a syn-tectonic non coaxial deformations (D1 and D2 deformational events). D1 shows a top to NW sense of shear while the D2 event a top to NE/SE sense of shear (the shear senses are considered at the present Sardinia – Corsica block position in the Mediterranean sea). The M2+D2 is characterized by a complicate, composite normal shear network; the M1+D1 by inverse shear zones. The M2+D2 is transposed by the late D3 strike slip shear event: the D3 is characterized by strike slip shear zones syn-kinematic to the emplacement of Late Carboniferous granitoids (320 Ma – 300 Ma). Despite the absence of geochronological data about the M1+D1 event, the field relationships suggest, for first time, an older migmatization process (Devonian?) syn-tectonic with the late stage of thickness of the Sardinia Variscan Belt. Similar evolutions are recognized in different segments of the Variscan Belt such as the Massif Central (France) or in the eastern mid-European Variscides.  相似文献   

9.
A characteristic feature of the Moldanubian part of the central European Variscides is late-orogenic high-T/low-P metamorphism. Its past history and the possible reasons for this metamorphism are highlighted by the tectonometamorphic development at the south– eastern margin of the Bohemian massif. During the Variscan orogeny, at ca. 340?Ma, two different crustal segments were juxtaposed by thrusting (the Drosendorf unit on top of the Monotonous unit). This probably marks a collisional event that is widespread in the southeastern Moldanubian zone. The collision was followed by crustal uplift accompanied by strong heating in the lowermost structural unit (Monotonous unit). During the subsequent orogenic collapse, the Moldanubian nappe pile was thrust over parts of the Moravo-Silesian terrane. A late stage of crustal extension under greenschist-facies conditions is linked with pluton emplacement. In general, magmatic underplating as well as delamination of the lithospheric mantle explains the high-T/low-P metamorphism and the large-scale plutonism in the southeastern Moldanubian zone.  相似文献   

10.
The Southern Variscan Front in the Tinerhir area involves Palaeozoic allochthonous units (Ouaklim and Tilouine units) thrust onto the northern edge of the West African Craton during late Carboniferous time. Illite crystallinity data highlight an anchizonal grade for the Ouaklim Unit, and a diagenesis-anchizone transition for the Tilouine Unit during deformation phase D1. The tectonic stack is crosscut by major dextral reverse faults bounding E–W trending domains of dominant shortening deformation (central domain) and strike-slip deformation (northern and southern domains), later segmented by a network of post-Variscan faults. This complex deformation pattern is the result of kinematic partitioning of dextral transpression along the Southern Variscan Front, coeval with the Neovariscan (300–290 Ma) oblique convergence observed at the scale of the whole Moroccan Variscides. Partitioning of dextral transpression described in the Tinerhir area is consistent with dextral wrench faulting along the Tizi n’ Test Fault, and with Appalachian-style south-directed thrusting in the Tinerhir and Bechar-Bou Arfa areas.  相似文献   

11.
《Geodinamica Acta》2013,26(2):115-129
The Variscides of Iberia have a bilateral symmetry with east vergence in the eastern branch and west vergence in the western, on both sides of a Centro-Iberian Zone (CIZ), with predominant steep axial planes. All the structures curve around the Ibero-Armorican Arc (IAA). Unconformities in the sedimentary sequences of Cambrian to Early Ordovician age were ascribed to “Sardic phase” by correlation with similar tectonosedimentary events in Sardinia. Recent studies showed diachronism between these events in Sardinia and Iberia but migration of major geodynamic regime in time may be due to regional variation of major events at plate tectonic scale. We studied in detail two critical areas in the CIZ, the Marão anticline in the NE and the Amêndoa-Carvoeiro synform in the SW. Two unconformities can be put in evidence, as elsewhere in CIZ. A stronger lower unconformity of a Volcano-Sedimentary Complex of Lower Arenig (and Tremadocian?) age on top of a Cambrian clastic sequence with flysch characteristics; and a milder upper unconformity of Armorican Quartzite of Arenig age on both the Volcano-Sedimentary Complex and the Cambrian sequences. The lithostratigraphy of the studied areas is described and correlated with other areas in Iberia. The Volcano-Sedimentary Complex and coeval magmatic bodies with bimodal composition are briefly described. The Sardic event corresponds to folds with steep axial planes at high angles to Variscan structures that produce the penetrative cleavage that cut across the unconformity surfaces. Sardic thrusts are also present and can be explained by thin-skinned compressive tectonics. Sardic folds and thrusts suggest a brief period of transient inversion between a major extensional regime from Cambrian to Devonian. The obliquity of Sardic structures to Variscan compression suggests a component of transpression during the Sardic tectonic event, corresponding to a tectonically enhanced unconformity near the Cambro-Ordovician boundary. The transient Sardic inversion is interpreted in terms of a break-up unconformity related to the migration of an intracratonic rift; in the Ordovician this rift moves into the SW of Ossa Morena Zone (OMZ) and since then become the SW Iberia suture during the Variscan Wilson cycle. This migration induced transient compression and dextral strike-slip in the major boundary between CIZ and OMZ due to presence of incipient primary curvature in this segment of IAA.  相似文献   

12.
The pre-Mesozoic, mainly Variscan metamorphic basement of the Col de Bérard area (Aiguilles Rouges Massif, External domain) consists of paragneisses and micaschists together with various orthogneisses and metabasites. Monazite in metapelites was analysed by the electron microprobe (EMPA-CHIME) age dating method. The monazites in garnet micaschists are dominantly of Variscan age (330–300 Ma). Garnet in these rocks displays well developed growth zonations in Fe–Mg–Ca–Mn and crystallized at maximal temperatures of 670°C/7 kbar to the west and 600°C/7–8 kbar to the east. In consequence the monazite is interpreted to date a slightly pressure-dominated Variscan amphibolite-facies evolution. In mylonitic garnet gneisses, large metamorphic monazite grains of Ordovician–Silurian (~440 Ma) age but also small monazite grains of Variscan (~300 Ma) age were discovered. Garnets in the mylonitic garnet gneisses display high-temperature homogenized Mg-rich profiles in their cores and crystallized near to ~800°C/6 kbar. The Ordovician–Silurian-age monazites can be assigned to a pre-Variscan high-temperature event recorded by the homogenised garnets. These monazite age data confirm Ordovician–Silurian and Devonian–Carboniferous metamorphic cycles which were already reported from other Alpine domains and further regions in the internal Variscides.  相似文献   

13.
The Paleozoic massif of Tichka in the southern part of the Western High Atlas of Morocco constitutes a structural transition between the Meseta and the Anti-Atlas domains. It was affected by a complex network of fractures noticeable at different scales. Using Landsat ETM+ imagery permits detecting the main fracture directions. Various techniques of lineament’s extraction were applied, including the colored compositions, spectral band ratios, and directional filters applied to the principal component analysis. Lineament’s extraction is based on visual interpretation and completed by field observations. The resulted map allows recognizing at least four trending fracture system, with average N-S, NE-SW, E-W, and NW-SE orientations. The surrounding rocks of the granitic massif show a high fracture density. Tectonic indicators show that this massif is initially affected by NW-SE Variscan tectonic extension, followed by NW-SE Variscan compression. This regime is being maintained until the late Variscan period corresponding to the relaxation of the NW-SE major Variscan stress. A clockwise rotation of the latter stress, which became N-S to NNE-SSW, related to the late Variscan deformation, is responsible for reworking preexisting faults.  相似文献   

14.
The terrane concept is understood as an important extension of plate tectonics and is based on the recognition of allochthonous, mobile geological units. The concept is successfully applied to the Variscides with their wide range of collisional belts. It is mainly supported by the dense deep-seismic network of DEKORP, which reveals certain reflectivity patterns and succeeds in mapping old and new deep fault zones between the terranes. Variscan terranes are rooted in the ductile lower crust and seem to consist of continental crust only, partly exclusively of rigid upper crust. Oceanic terranes, on the other hand, are always rooted in the asthenosphere. The development of continental terranes and their boundaries depends strongly on their thermal and rheological history. In the case of post-orogenic collapse with heating and extension of the lower crust, seismic lamellae develop and often truncate former thrust faults.  相似文献   

15.
This study presents the first preliminary U–Pb zircon data on tin-bearing S-type granites from the Gemeric unit of the Western Carpathians (Slovakia). U–Pb single zircon dating controlled by cathodoluminescence suggests crystallization of the Gemeric granites during Permian to Early Triassic (303–241 Ma) time. Post-crystallization, low-temperature metamorphic overprint is reflected by partial Pb loss in zircons. These Gemeric granites are younger than the highly fractionated, S-type, tin- and rare-element-bearing leucogranites in the European Variscides. They may have resulted from partial melting, triggered by increased heat flow from the mantle below the continental crust, and most probably intruded during the post-collisional extension and initial rifting of the Variscan orogenic belt. During Alpine orogeny, the Gemeric granites were affected by a low-temperature deformation and metamorphism.  相似文献   

16.
The Iberian Massif poses a problem of relationships between its northwestern and southern parts. Suture terranes (ophiolites and high-pressure rocks) crop out in NW Iberia but only as allochthonous units, unconnected from their root zone. Sutures cropping out in SW Iberia are discussed in order to relate them to the unknown root of the NW Iberia allochthons. On the other hand, the Moroccan Variscides are very briefly presented with a view to propose their correlation with the Iberian zones. Particularly important is the transition from the Variscides to the Paleoproterozoic basement in Morocco, which is a key argument for palaeogeographic reconstructions.  相似文献   

17.
The Rhine Rift System (RRS) forms part of the European Cenozoic Rift System (ECRIS) and transects the Variscan Orogen, Permo-Carboniferous troughs and Late Permian to Mesozoic thermal sag basins. Crustal and lithospheric thicknesses range in the RRS area between 24–36 km and 50–120 km, respectively. We discuss processes controlling the transformation of the orogenically destabilised Variscan lithosphere into an end-Mesozoic stabilised cratonic lithosphere, as well as its renewed destabilisation during the Cenozoic development of ECRIS. By end-Westphalian times, the major sutures of the Variscan Orogen were associated with 45–60 km deep crustal roots. During the Stephanian-Early Permian, regional exhumation of the Variscides was controlled by their wrench deformation, detachment of subducted lithospheric slabs, asthenospheric upwelling and thermal thinning of the mantle-lithosphere. By late Early Permian times, when asthenospheric temperatures returned to ambient levels, lithospheric thicknesses ranged between 40 km and 80 km, whilst the thickness of the crust was reduced to 28–35 km in response to its regional erosional and local tectonic unroofing and the interaction of mantle-derived melts with its basal parts. Re-equilibration of the lithosphere-asthenosphere system governed the subsidence of Late Permian-Mesozoic thermal sag basins that covered much of the RRS area. By end-Cretaceous times, lithospheric thicknesses had increased to 100–120 km. Paleocene mantle plumes caused renewed thermal weakening of the lithosphere. Starting in the late Eocene, ECRIS evolved in the Pyrenean and Alpine foreland by passive rifting under a collision-related north-directed compressional stress field. Following end-Oligocene consolidation of the Pyrenees, west- and northwest-directed stresses originating in the Alps controlled further development of ECRIS. The RRS remained active until the Present, whilst the southern branch of ECRIS aborted in the early Miocene. Extensional strain across ECRIS amounts to some 7 km. Plume-related thermal thinning of the lithosphere underlies uplift of the Rhenish Massif and Massif Central. Lithospheric folding controlled uplift of the Vosges-Black Forest Arch.  相似文献   

18.
Sixty five per cent of the Paleozoic basement of western and central Europe is hidden by a sedimentary cover and/or sea. This work aims to remove that blanket to detect new structures which could used to build a more comprehensive model of the Variscan orogeny. It is based on the interpretation of various forms of data: (a) published gravity maps corrected for the effects of the crust-mantle boundary topography and light sedimentary basins; (b) aeromagnetic maps; (c) measurements of densities; and (d) induced and remanent magnetizations on rocks from Paleozoic outcrops of the upper Rhenish area. From the northern Bohemian Massif to the eastern Paris Basin, the Saxothuringian is characterized by a 500 km long belt of gravity highs, the most important being the Kraichgau high. Most of the corresponding heavy bodies are buried under a post-early Viséan cover. They are interpreted as relics of Late Proterozoic terranes overlain by an Early to Middle Paleozoic sequence, equivalent to the Bohemian terrane in the Bohemian Massif. The most probable continuation of these dense Bohemian terranes toward the west is the Southern Channel-Northern Brittany Cadomian terrane. The gravity lows are correlated with Variscan granites and pre- and early Variscan metagranites.Gravity and magnetic maps demonstrate large-scale displacement in Devonian-Early Carboniferous times along the parallel and equidistant, NW-SE striking, Vistula, Elbe, Bavarian, Bray and South Armorican dextral wrench faults. In the Vosges-Schwarzwald and Central Massif the faults continue with the east-west striking Lalaye-Lubine-Baden-Baden and Marche faults and with south vergent thrusts. The Bavarian faults shift the Kraichgau terrane by 150 km relative to the Bohemian terrane, whereas the offset of the Northern Brittany Cadomian relative to the Northern Vosges-Kraichgau terranes is estimated at 400 km along the Bray fault. Sinistral wrench faults are the NE-SW striking Sillon Houiller, Rheingraben, Rodl, Vitis and Diendorf faults. The southern Vosges-Schwarzwald Devonian-Dinantian basin is interpreted as a pull-apart basin at the south-easterly extremity of the Bray fault. The Bohemian and Kraichgau body form allochthonous terranes which were thrust over the Saxothuringian crust. Thrusting to the north-west was accompanied by back-thrusting and led to the formation of pop-up structures. Contemporaneous dextral and sinistral wrench faulting resulted in transpressive strain during collision. The zonal structure of the Variscides in the sense of Kossmat (1927) is relevant only to the Rhenohercynian Foreland Belt. Kossmat (1927) already spoke of a Moldanubian Region because it displays no real zonal structure. The Saxothuringian Zone was formed by terrane accretion. Their apparent zonal structure is not a pre-collisional feature, but only the result of accretion and collision.  相似文献   

19.
Geological evidence, supported by biogeographical data and in accord with palaeomagnetic constraints, indicates that “one ocean” models for the Variscides should be discarded, and confirms, instead, the existence of three Gondwana-derived microcontinents which were involved in the Variscan collision: Avalonia, North Armorica (Franconia and Thuringia subdivided by a failed Vesser Rift), and South Armorica (Central Iberia/Armorica/Bohemia), all divided by small oceans. In addition, parts of south-eastern Europe, including Adria and Apulia, are combined here under the new name of Palaeo-Adria, which was also Peri-Gondwanan in the Early Palaeozoic. Oceanic separations were formed by the break-up of the northern Gondwana margin from the Late Cambrian onwards. Most of the oceans or seaways remained narrow, but – much like the Alpine Cenozoic oceans – gave birth to orogenic belts with HP-UHP metamorphism and extensive allochthons: the Saxo-Thuringian Ocean between North and South Armorica and the Galicia-Moldanubian Ocean between South Armorica and Palaeo-Adria. Only the Rheic Ocean between Avalonia and peri-Gondwana was wide enough to be unambiguously recorded by biogeography and palaeomagnetism, and its north-western arm closed before or during the Emsian in Europe. Ridge subduction under the northernmost part of Armorica in the Emsian created the narrow and short-lived Rheno-Hercynian Ocean. It is that ocean (and not the Rheic) whose opening and closure controlled the evolution of the Rheno-Hercynian foldbelt in south-west Iberia, south-west England, Germany, and Moravia (Czech Republic). Devonian magmatism and sedimentation set within belts of Early Variscan deformation and metamorphism are probably strike-slip-related. The first arrival of flysch on the forelands and/or the age of deformation of foreland sequences constrains the sequential closure of the Variscan seaways (Galicia-Moldanubian in the Givetian; Saxo-Thuringian in the Early Famennian; Rheno-Hercynian in the Tournaisian). Additional Mid- to Late Devonian and (partly) Early Carboniferous magmatism and extension in the Rheno-Hercynian, Saxo-Thuringian and Galicia-Moldanubian basins overlapped with Variscan geodynamics as strictly defined. The Early Carboniferous episode was the start of episodic anorogenic heating which lasted until the Permian and probably relates to Tethys rifting.  相似文献   

20.
The latest Carboniferous to lower Permian volcanism of the southern Variscides in Sardinia developed in a regional continental transpressive and subsequent transtensile tectonic regime.Volcanism produced a wide range of intermediate-silicic magmas including medium-to high-K calc-alkaline andesites,dacites,and rhyolites.A thick late Palaeozoic succession is well exposed in the four most representative Sardinian continental basins(Nurra,Perdasdefogu,Escalaplano,and Seui-Seulo),and contains substantial stratigraphic,geochemical,and geochronological evidence of the area's complex geological evolution from the latest Carboniferous to the beginning of the Triassic.Based on major and trace element data and LA-ICP-MS U-Pb zircon dating,it is possible to reconstruct the timing of postVariscan volcanism.This volcanism records active tectonism between the latest Carboniferous and Permian,and post-dates the unroofing and erosion of nappes in this segment of the southern Variscides.In particular,igneous zircon grains from calc-alkaline silicic volcanic rocks yielded ages between299±1 and 288±3 Ma,thereby constraining the development of continental strike-slip faulting from south(Escalaplano Basin)to north(Nurra Basin).Notably,andesites emplaced in medium-grade metamorphic basement(Mt.Cobingius,Ogliastra)show a cluster of older ages at 332±12 Ma.Despite the large uncertainty,this age constrains the onset of igneous activity in the mid-crust.These new radiometric ages constitute:(1)a consistent dataset for different volcanic events;(2)a precise chronostratigraphic constraint which fits well with the biostratigraphic data and(3)insights into the plate reorganization between Laurussia and Gondwana during the late Palaeozoic evolution of the Variscan chain.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号