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1.
Zircon and apatite fission track ages were determined on granulites dredged along the Bay of Biscay margins. A sample from Ortegal Spur (Iberia margin) yielded 725 ± 67 Ma (zircon). A sample from Le Danois Bank (Iberia margin) yielded 284 ± 58 Ma (zircon), indicating post‐Variscan cooling. Apatite from this sample gave 52 ± 2 Ma, interpreted as final cooling after ‘Pyrenean’ thrust imbrication. Two other samples from Le Danois Bank have Early Cretaceous apatite ages (138 ± 7 and 120 ± 8 Ma), interpreted to result from exhumation during rifting. Finally, a granulite from Goban Spur (Armorican margin) gave 212 ± 10 Ma (apatite), coinciding with a precursory rifting phase. Together with published radiometric results, these data indicate a Precambrian high‐grade terrane at the site of the current margins. The distribution of the granulites on the seafloor reflects tectonic and erosional processes related to (a) Mesozoic rifting and (b) Early Tertiary incipient subduction of the Bay of Biscay beneath Iberia.  相似文献   

2.
The evolution of the European Cenozoic Rift System (ECRIS) and the Alpine orogen is discussed on the base of a set of palaeotectonic maps and two retro-deformed lithospheric transects which extend across the Western and Central Alps and the Massif Central and the Rhenish Massif, respectively.During the Paleocene, compressional stresses exerted on continental Europe by the evolving Alps and Pyrenees caused lithospheric buckling and basin inversion up to 1700 km to the north of the Alpine and Pyrenean deformation fronts. This deformation was accompanied by the injection of melilite dykes, reflecting a plume-related increase in the temperature of the asthenosphere beneath the European foreland. At the Paleocene–Eocene transition, compressional stresses relaxed in the Alpine foreland, whereas collisional interaction of the Pyrenees with their foreland persisted. In the Alps, major Eocene north-directed lithospheric shortening was followed by mid-Eocene slab- and thrust-loaded subsidence of the Dauphinois and Helvetic shelves. During the late Eocene, north-directed compressional intraplate stresses originating in the Alpine and Pyrenean collision zones built up and activated ECRIS.At the Eocene–Oligocene transition, the subducted Central Alpine slab was detached, whereas the West-Alpine slab remained attached to the lithosphere. Subsequently, the Alpine orogenic wedge converged northwestward with its foreland. The Oligocene main rifting phase of ECRIS was controlled by north-directed compressional stresses originating in the Pyrenean and Alpine collision zones.Following early Miocene termination of crustal shortening in the Pyrenees and opening of the oceanic Provençal Basin, the evolution of ECRIS was exclusively controlled by west- and northwest-directed compressional stresses emanating from the Alps during imbrication of their external massifs. Whereas the grabens of the Massif Central and the Rhône Valley became inactive during the early Miocene, the Rhine Rift System remained active until the present. Lithospheric folding controlled mid-Miocene and Pliocene uplift of the Vosges-Black Forest Arch. Progressive uplift of the Rhenish Massif and Massif Central is mainly attributed to plume-related thermal thinning of the mantle-lithosphere.ECRIS evolved by passive rifting in response to the build-up of Pyrenean and Alpine collision-related compressional intraplate stresses. Mantle-plume-type upwelling of the asthenosphere caused thermal weakening of the foreland lithosphere, rendering it prone to deformation.  相似文献   

3.
R.L.M. Vissers  P.Th. Meijer 《Earth》2012,110(1-4):93-110
Following on paleomagnetic studies in the sixties showing ~ 35° counterclockwise rotation of Iberia during the Mesozoic, two classes of scenarios have been proposed for the motion history of Iberia which are currently competing. One class infers convergence in the Pyrenees in response to a scissor-type opening of the Bay of Biscay, described by a pole of rotation for Iberia with respect to Europe located within the Bay. The other class of scenarios assumes extensional or transtensional motions in the Pyrenees, compatible with opening of the Bay of Biscay described by a pole of rotation located in northern France. Although plate-kinematic studies over the last decade increasingly support the scissor-type model, geological studies in the Pyrenees have accumulated arguments in favour of an extensional or transtensional regime in the Pyrenean realm.We perform a detailed plate-kinematic analysis of the Late Jurassic and Cretaceous motion history of Iberia and surrounding plates with respect to Europe. A total of six sea-floor reconstructions in combination with paleomagnetic studies onland allow to recognize four distinct stages. (1) Early rifting and ultraslow spreading since the Kimmeridgean led to the development of an oceanic Neotethys domain north of Iberia. (2) This was followed by ~ 35° CCW rotation of Iberia during the Aptian, kinematically linked to progressive opening of the Bay of Biscay. (3) Motions in the Bay became stagnant during the Albian till Santonian, followed by the latest stages of spreading in the Bay, and (4) onset of largely Tertiary continental collision between Iberia and Europe eventually leading to the present day structure of the belt.Our analysis confirms the results of previous studies indicating that extensional or transtensional motions in the Pyrenean realm during opening of the Bay of Biscay and concurrent rotation of Iberia are incompatible with plate-kinematic reconstructions based on sea-floor anomalies. This invites a reappraisal of the geological data. Convergence in the Pyrenean realm during opening of the Bay and rotation of Iberia was accommodated by up to 300 km of subduction of mantle-dominated ocean floor exhumed during the late Jurassic and early Cretaceous. The stagnant stage in the progressive opening of the Bay indicates that convergence in the Pyrenean realm virtually came to a halt during the Albian. We hypothesize that the lithosphere previously subducted during Aptian convergence became gravitationally unstable, leading to asthenospheric upwelling and consequent magmatism and high temperature metamorphism in the overlying European margin now exposed in the North Pyrenean Zone. Aside from these magmatic and thermal effects, an enhanced gravitational potential energy of the remaining lithosphere column underlain by shallow asthenosphere may have led to a stress state allowing belt-parallel extensional deformation. Such a detachment scenario, inspired by plate-kinematic results, may provide an alternative to explain many of the geological data commonly quoted to infer a transtensional or extensional tectonic regime in the Pyrenees during the rotation of Iberia.  相似文献   

4.
H. Laubscher 《地学学报》1990,2(6):645-652
Gravity surveys of the past century established that mountains have roots, seismic refraction lines shot in the second half of this century confirmed the downbulge of the Moho under the Alps, and recent reflection traverses provided new details on the behaviour of crustal layers in the deep part of the Alps. However, geophysical data are ambiguous geologically. For models of the root in terms of rock distribution to be tectonophysically acceptable, they must be the retrodeformable result of kinematic sequence that fits the geological surface data. For a cross-section through the Swiss Alps based on refraction data and somewhat modified by the recent reflection traverses, a kinematic model compatible with large-scale geological data may be obtained by the superposition of three Neogene phases with alternating vergence. Although Alpine collision is largely dextrally compressive in the central Alps, the N-S component may be discussed in a cross-section. Particularly puzzling geophysical features include a high-velocity body in the middle crust and the disappearance of the layered foreland crust in the root. In order to account for these phenomena, it is proposed that the crustal root is interpreted as the result of complex reshuffling of middle and lower crustal masses as well as large-scale phase transformations. The mid-crustal highvelocity body is interpreted as a delaminated section of the lower crust of the Adria plate that was wedged into the middle crust of the Alps in the middle Miocene. The disappearance of the foreland lower crust is attributed to eclogitization attendant on the subduction of continental crust. Material balance estimates suggest that during Alpine collision large volumes of continental crust have disappeared through subduction.  相似文献   

5.
The structure of the Hercynian collision zone in the southeast of the Armorican Massif is illustrated by a 70-km long deep seismic profile acquired in September 2000. The profile images a previously unknown south-dipping thrust that brought the Champtoceaux Domain on top of the Central Armorican Domain during Carboniferous times. Dextral strike-slip motions along the South Armorican Shear Zone, which is downward cut by the thrust zone, are partly coeval with northward thrusting. A major discontinuity, hidden by the thrust front, is also imaged in the lower crust between the Champtoceaux area and the Central Armorican Domain. These new data lead to a structural and kinematic re-interpretation of this part of the Hercynian collision zone. To cite this article: A. Bitri et al., C. R. Geoscience 335 (2003).  相似文献   

6.
The interpretation of DSS (deep seismic soundings) profiles in Central and Eastern Alps is recalled in the paper and the models of the lower crust and Moho proposed several years ago are compared to the results of the TRANSALP seismic reflection profile. This evaluation highlights a good agreement as far as the geometry of the deep crustal structure is concerned. Therefore, the reliability of the interpretative models, previously exclusively based on DSS profiles, becomes improved. The deep structure beneath the whole Alpine range is examined reconsidering the map of the Moho boundary and the structural model already proposed for the central-eastern sector. Five main interpretative transects are put side by side, starting from the Western Alps and moving eastwards to the Swiss–Lombardian Central Alps (“European Geotraverse”), to the cross section from southern Bavaria to the Euganei Hills, to the TRANSALP profile, and finally to the easternmost profile available so far (southern Bavaria–Trieste). The comparison outlines lateral variations of the deep crustal structure as well as a sharp contrast between the Adria and the European lower crust and Moho. The transition from the Adria plate to the Dinaric domain remains, up to now, undefined.  相似文献   

7.
《Geodinamica Acta》2000,13(2-3):103-117
Intermediate orthogranulites were collected on the western flank of the Galicia bank during the Galinaute II cruise in 1995. The petrography of these rocks reveals two types of granulites. The first type is hydrous granulites with K-feldspar + plagioclase + quartz + orthopyroxene + hornblende + garnet + biotite + opaque + zircon + apatite assemblage. Both hornblende and orthopyroxene define a weak foliation plane. A late deformation event is expressed by some fractures cross-cutting the foliation. The second is anhydrous granulites with K-feldspar + plagioclase + quartz + orthopyroxene + clinopyroxene + opaque + zircon + apatite assemblage. The rocks display a granoblastic texture and are affected by brittle deformation as testified by the development of numerous microfractures. The P–T conditions (7 ± 1 Kbar, 750 ± 50 °C) calculated from two representative samples demonstrate that the rocks equilibrated under granulite facies conditions. Ar-Ar dating gives Precambrian ages ranging between ca. 2500–2000 Ma for the amphibole from the hydrous granulite and 1600–1500 Ma for the core of the K-feldspar from the anhydrous and hydrous granulites. A younger age of 900 Ma is obtained from the recrystallized rims of the K-feldspar from the two samples. These data indicate that the granulitic rocks in the Galicia Bank had already been exhumed and cooled below ca. 140–400 °C (blocking T° for K-feldspar) in Precambrian times (900 Ma). Given the very well preserved granulitic minerals assemblage of the rocks, the granulites behaved as competent and metastable boudins during their exhumation. The granulitic samples were previously interpreted as fragments of the lower continental crust sampled by the main detachment fault during Cretaceous rifting, but they were part of an upper continental crust from the Precambrian. Geochronological data and petrological assemblages suggest that the granulite blocks in the Galicia Bank probably were derived from the North Armorican Domain (northern part of France) where a Precambrian terrain outcrops. The opening of the Bay of Biscay could be responsible for the scattering of the Precambrian terrain and may explain the presence of the granulitic blocks on both sides of the Bay of Biscay. During the subduction of Europe below the Iberian peninsula the granulite blocks were transported southward and incorporated into a Cretaceous conglomerate forming the accrecionary prism on the Northern Iberia Margin. The granulite facies blocks found on the Galicia Bank represent another example of Gondwanian relics supporting the idea that the West European plate belonged to the West African craton during the Proterozoic.  相似文献   

8.
Abstract

Intermediate orthogranulites were collected on the western flank of the Galicia bank during the Galinaute II cruise in 1995. The petrography of these rocks reveals two types of granulites. The first type is hydrous granulites with K-feldspar + plagioclase + quartz + orthopyroxene + hornblende + garnet + biotite + opaque + zircon + apatite assemblage. Both hornblende and orthopyroxene define a weak foliation plane. A late deformation event is expressed by some fractures cross-cutting the foliation. The second is anhydrous granulites with K-feldspar + plagioclase + quartz + orthopyroxene + clinopyroxene + opaque + zircon + apatite assemblage. The rocks display a granoblastic texture and are affected by brittle deformation as testified by the development of numerous microfractures. The P-T conditions (7 ± 1 Kbar, 750 ± 50 °C) calculated from two representative samples demonstrate that the rocks equilibrated under granulite facies conditions. Ar-Ar dating gives Precambrian ages ranging between ca. 2500–2000 Ma for the amphibole from the hydrous granulite and 1600–1500 Ma for the core of the K-feldspar from the anhydrous and hydrous granulites. A younger age of 900 Ma is obtained from the recrystallized rims of the K-feldspar from the two samples. These data indicate that the granulitic rocks in the Galicia Bank had already been exhumed and cooled below ca. 140–400 °C (blocking T° for K-feldspar) in Precambrian times (900 Ma). Given the very well preserved granulitic minerals assemblage of the rocks, the granulites behaved as competent and metastable boudins during their exhumation. The granulitic samples were previously interpreted as fragments of the lower continental crust sampled by the main detachment fault during Cretaceous rifting, but they were part of an upper continental crust from the Precambrian. Geochronological data and petrological assemblages suggest that the granulite blocks in the Galicia Bank probably were derived from the North Armorican Domain (northern part of France) where a Precambrian terrain outcrops. The opening of the Bay of Biscay could be responsible for the scattering of the Precambrian terrain and may explain the presence of the granulitic blocks on both sides of the Bay of Biscay. During the subduction of Europe below the Iberian peninsula the granulite blocks were transported southward and incorporated into a Cretaceous conglomerate forming the accrecionary prism on the Northern Iberia Margin. The granulite facies blocks found on the Galicia Bank represent another example of Gondwanian relics supporting the idea that the West European plate belonged to the West African craton during the Proterozoic. © 2000 Éditions scientifiques et médicales Elsevier SAS  相似文献   

9.
《Geodinamica Acta》2013,26(1):21-35
We present and discuss the Late Cretaceous evolution of the Southeast France Basin (SEFB) owing to the Pyrenean and Alpine belts. The available geological data (isopachs maps, boreholes and field data) were integrated in 3D GeoModeller software to build a 3D model of the geometry of the Cenomanian to Campanian sedimentary series of the Late Cretaceous period. Maps, 3D block diagrams and cross-sections extracted from the 3D model reveal a significant eastward marine regression during the Late Cretaceous with an average velocity of 0.5 to 1 cm per year. According to the location of the Late Cretaceous depocenters, two sub-basins are recognized in the SEFB and correspond to “en-échelon” synclines filled by syn-buckling sediments. These events are related to the sub-meridian “Pyrenean-Provence” crustal shortening. During Campanian time, the deepening and the tilting of the SEFB are interpreted as a consequence of the subduction of the Alpine Tethys. The Late Cretaceous SEFB is the prolongation on the European foreland of the Alpine subduction trench.  相似文献   

10.
The eastern margin of the Variscan belt in Europe comprises plate boundaries between continental blocks and terranes formed during different tectonic events. The crustal structure of that complicated area was studied using the data of the international refraction experiments CELEBRATION 2000 and ALP 2002. The seismic data were acquired along SW–NE oriented refraction and wide-angle reflection profiles CEL10 and ALP04 starting in the Eastern Alps, passing through the Moravo-Silesian zone of the Bohemian Massif and the Fore-Sudetic Monocline, and terminating in the TESZ in Poland. The data were interpreted by seismic tomographic inversion and by 2-D trial-and-error forward modelling of the P waves. Velocity models determine different types of the crust–mantle transition, reflecting variable crustal thickness and delimiting contacts of tectonic units in depth. In the Alpine area, few km thick LVZ with the Vp of 5.1 km s− 1 dipping to the SW and outcropping at the surface represents the Molasse and Helvetic Flysch sediments overthrust by the Northern Calcareous Alps with higher velocities. In the Bohemian Massif, lower velocities in the range of 5.0–5.6 km s− 1 down to a depth of 5 km might represent the SE termination of the Elbe Fault Zone. The Fore-Sudetic Monocline and the TESZ are covered by sediments with the velocities in the range of 3.6–5.5 km s− 1 to the maximum depth of 15 km beneath the Mid-Polish Trough. The Moho in the Eastern Alps is dipping to the SW reaching the depth of 43–45 km. The lower crust at the eastern margin of the Bohemian Massif is characterized by elevated velocities and high Vp gradient, which seems to be a characteristic feature of the Moravo-Silesian. Slightly different properties in the Moravian and Silesian units might be attributed to varying distances of the profile from the Moldanubian Thrust front as well as a different type of contact of the Brunia with the Moldanubian and its northern root sector. The Moho beneath the Fore-Sudetic Monocline is the most pronounced and is interpreted as the first-order discontinuity at a depth of 30 km.  相似文献   

11.
The present comment disproves the tectonic model of a late Devonian/early Carboniferous Tibetan-style collisional plateau in the Teplá-Barrandean (TB) part of the Bohemian Massif, which later collapsed by thermal weakening of the underlying crust. Contrary to this model, the TB neither reveals major crustal thickening nor uplift and erosion, and eastern continuations of the TB were, during the relevant time-span, areas of open marine sedimentation. Late Devonian/early Carboniferous marine sediments widespread also in the Armorican and Central Massifs of France testify to low topography in central parts of the Variscan orogen. Notional traces of a Permo-Carboniferous ice cap on the French Massif Central do not support the plateau model, because they are questionable and much younger than the inferred plateau stage of the TB. The relative uplift of high-grade metamorphic rocks to the NW and the SE of the TB is not due to sinking of an elevated TB, but, instead, to the hydraulic and buoyant expulsion of HP material from the Saxo-Thuringian and Moldanubian subduction channels. The rise of lower-grade HT rocks along the southwestern margin of the Bohemian Massif was effected by late Carboniferous transpression. The high temperature and the resulting low viscosity of the rising materials were probably not caused by Variscan mantle delamination, but relate to lithospheric thinning and heating at the tip of the westward propagating Tethys Rift.  相似文献   

12.
We constructed a geological map, a 3D model and cross-sections, carried out a structural analysis, determined the stress fields and tectonic transport vectors, restored a cross section and performed a subsidence analysis to unravel the kinematic evolution of the NE emerged portion of the Asturian Basin (NW Iberian Peninsula), where Jurassic rocks crop out. The major folds run NW-SE, normal faults exhibit three dominant orientations: NW-SE, NE-SW and E-W, and thrusts display E-W strikes. After Upper Triassic-Lower Jurassic thermal subsidence, Middle Jurassic doming occurred, accompanied by normal faulting, high heat flow and basin uplift, followed by Upper Jurassic high-rate basin subsidence. Another extensional event, possibly during Late Jurassic-Early Cretaceous, caused an increment in the normal faults displacement. A contractional event, probably of Cenozoic age, led to selective and irregularly distributed buttressing and fault reactivation as reverse or strike-slip faults, and folding and/or offset of some previous faults by new generation folds and thrusts. The Middle Jurassic event could be a precursor of the Bay of Biscay and North Atlantic opening that occurred from Late Jurassic to Early Cretaceous, whereas the Cenozoic event would be responsible for the Pyrenean and Cantabrian ranges and the partial closure of the Bay of Biscay.  相似文献   

13.
The Pirin-Pangaion Structural Zone occupies the south-western part of the Rhodope Massif. It consists of Proterozoic amphibolite facies metamorphic rocks of the Rhodopian Supergroup, and granitoids of Hercynian, Late Cretaceous and Palaeogene age. The pre-Hercynian structure of the zone is dominated by an interference pattern of three superimposed fold generations of NE-SW and NW-SE trends. These structures are cut by Hercynian granitoids, and the entire complex is affected by late Hercynian or early Alpine conical folds. The zone was overthrusted by the Ogražden and Kroussia Units (Serbo-Macedonian ‘Massif’) along the north-east vergent Mid-Cretaceous Strimon overthrust, and by the Central Rhodope Zone of the Rhodope Massif, along the south-west vergent Meso-Rhodopean Overthrust. With this thrusting event, the Pirin-Pangaion Structural Zone was brought together with the Serbo-Macedonian ‘Massif’ and the Central Rhodope Zone to form the Late Cretaceous Morava-Rhodope Zone, which acted as a ‘plateau’ along the southern edge of the Eurasian plate. Late Cretaceous granitoid magma of crustal origin intruded this zone, whereas north of it the Srednogorie volcanic island arc was the site of igneous activity with magmas originating in the upper mantle. The West Thrace Zone developed as a Palaeocene to Oligocene depression superimposed over the older basement obliquely to the southern periphery of the Rhodope Massif. In the Late Eocene and Early Oligocene, this depression represented a volcanic island arc with mantle-derived basic to intermediate magmas; contemporaneous granitoid magmas formed through crustal melting in the thickened crust of the Rhodope Massif (Pirin and Pangaion Units included). Early Miocene thrusting was most intense in the Pangaion Unit, and was followed by Late Miocene to Quaternary extension.  相似文献   

14.
The researches carried out on the recent dyke activity in the south-western Tyrol have revealed a widespread “andesitic” magmatism in the austroalpine realm. The magmatic activity developed at least in two distinct phases; but in this paper we are only concerned with the unmetamorphosed dykes which are younger than the alpine folding. The existence of a calc-alkaline magmatism mainly of the intermediate type, and the occurrence of garnet as the first mineral on the liquidus, imply a very deep origin of such a magmatism, which agrees with the geodynamic models, providing the subduction of oceanic crust recently hypothesized for the Alpine evolution. Regarding the age of dyke activity, very recent radiometric results (K/Ar) testify for the first time in the Alps an “andesitic” magmatism from Upper Cretaceous to Tertiary and suggest both continuous or separate subductive processes from the Upper Cretaceous onwards.  相似文献   

15.
P. Giese  C. Morelli  L. Steinmetz   《Tectonophysics》1973,20(1-4):367-379
During the past two decades deep seismic sounding measurements have been carried out in western and southern Europe, mainly using the refraction method. These investigations were performed partly on a national basis but as well within international cooperative programs under the sponsorship of the European Seismological Commission.

In France, a systematic study has been executed to determine the main feature of deep structures under the Central Massif and the Paris Basin. In the Forez and Margeride regions, the sub-crustal velocity is lower (7.2 km/sec) than the normal value (8.0 km/sec) observed in the adjacent areas.

The central and southern part of Western Germany is covered by an extensive network of refraction profiles. The crustal thickness varies, similarly to France, from 25 to 35 km. A great amount of deep reflection data was obtained by commercial and special reflection work. The crust beneath the Rhinegraben area shows the typical “rift system” structure with a low subcrustal velocity (7.4–7.7 km/sec).

Very intensive refraction work has been carried out in the Alpine area. The maximum crustal thickness found near the axis of the negative gravity anomaly is about 55–60 km. Furthermore, a clear lowvelocity layer at a depth between 10 and 30 km has been detected. A key position with regard to the geotectonic structure of the Alps is held by the zone of Ivrea characterized by a pronounced gravity high. From the refraction work it may be concluded that there material of the lower crust and the upper mantle (7.2–7.5 km/sec) is overlying a layer of extremely low velocity (5.0 km/sec) which is interpreted as sialic crust.

Three years ago, a systematic study of crustal structure of the Italian peninsula has been started. Reversed profiles were observed on Sicily, in Calabria, and in Puglia. On Sicily, the structure is very complicated; the crust of the western part looks like a transition between a continental and oceanic structure whereas the eastern side shows a continental-type crust. In Calabria and Puglia, the crustal thickness has been determined to be about 25–35 km.  相似文献   


16.
C. Bois 《地学学报》1992,4(1):99-108
Deep seismic reflection images from a set of profiles shot in Western Europe have been reviewed and compared, and tentative conclusions have been proposed concerning the evolution of the layered lower crust and the Moho. The disappearance of Variscan mountain roots is related to the set-up of a new Moho at a typical 30-km depth and the creation of seismic layering in the lower crust. Deep seismic profiles suggest that these processes resulted, at least in part, from magmatic intrusion, partial crustal melting and metamorphism of deep crustal rocks into eclogite. On the other hand, the layered lower crust is greatly attenuated beneath Cretaceous basins and Tertiary rifts in relation to prominent Moho upwellings. The unusual amplitude of the Moho reflection and the presence of anomalously high seismic velocities in the lowermost crust beneath the Tertiary rifts suggest that the Moho and part of the layering are comparatively young features related to interactions between crust and mantle. Beneath Triassic-Jurassic basins, the layered lower crust was not affected by the subsidence of the basement, with the whole crustal thinning being entirely concentrated in the upper crust. This indicates that the layered lower crust and the Moho were formed or restored during or after the main rifting phase. Seismic data reveal constraints on the processes that affect the crust-mantle transition and seem to restore the Moho to its typical depth after any mechanical deformation of the lithosphere.  相似文献   

17.
The Pyrenees is a young mountain belt formed as part of the larger Alpine collision zone. This excursion explores the development of the Pyrenean Mountain Belt in southern France, from its early extensional phase in the mid‐Cretaceous and subsequent collisional phase, through its uplift and erosion in the Late Cretaceous and again in the Eocene, which led to the development of the Aquitaine‐Languedoc foreland basin. One of the complexities of the Pyrenean Belt is that thrusting, uplift and erosion during the Pyrenean orogeny exposed older Variscan basement rocks in the central core of the mountains, rocks which were metamorphosed during an earlier event in the late Carboniferous. Thus, this orogenic belt also tells the story of an earlier collision between Laurussia in the north and Gondwana in the south at c. 300 Ma, prior to the onset of the Pyrenean events at c. 100 Ma. Here we seek to unravel these two separate orogenic stories.  相似文献   

18.
A three-dimensional gravity modelling of the Carpatho-Pannonian region was carried out to get a better image of the Moho boundary and the most prominent intra-crustal density heterogeneities. At first, only the major density boundaries were considered: the bottom of the Tertiary basin fill, the Moho discontinuity and the lithosphere to asthenosphere boundary. Density contrasts were represented by relative densities. The improved density model shows a transitional unit of high density at the base of the crust along the Teisseyre-Tornquist Zone. In the Western Carpathians, an extensive, relatively low-density unit was inferred in mid-crustal levels. The border zone between the Southern Carpathians and the Transylvanian basin is characterized by a sharp, step-like contact of the two crustal units. The Moho configuration reveals important information on the tectonic evolution of the region. Zones of continental collision are represented by thick Moho roots (Eastern Alps, Eastern Carpathians). Transpressional orogenic segments, however, are different: in the Western Carpathians, the Moho is a flat surface; in the Dinarides, a medium Moho root is observed; the Southern Carpathians are characterized by a thick crustal root. The differences are explained with the presence or absence of “subductible” oceanic crust along the Carpathians during the extrusion of Pannonian blocks.  相似文献   

19.
Several E-W profiles of Bouguer anomalies across the Precambrian basement were inverted by applying a linearized inversion procedure in the spectral domain and using a simplified two-layer model with a crust-upper mantle interface of constant density contrast. From these inverted profiles, a contour map of Moho topography has been constructed which covers the area of exposed Precambrian basement in the eastern and central parts of the island. Such imaging of the Moho depth in particular exhibits a N20°E-trending zone of substantially thinned crust along the axis of the island. This parallels the east coast margin which resulted from the northward motion of India relative to Madagascar in the Upper Cretaceous. From combined analysis of geological, tectonic and metamorphic observations, this prominent crustal feature in the Precambrian basement of Madagascar is interpreted as the relic of continental lithospheric extension and thinning possibly related to Panafrican collapse tectonics on the eastern edge of the Mozambique belt. This extensional feature would have been reactivated only in part during the rifting and dislocation stages of the Madagascar and India continental blocks as evidenced by an axis of Cretaceous volcanism emphasized by the Ankaratra and Itasy massifs. Final separation nevertheless occurred further east, at the site of the east coast margin.  相似文献   

20.
Tectonic map and overall architecture of the Alpine orogen   总被引：9，自引：0，他引：9  
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