Tectonic interpretation of a 3D seismic model of the Eastern Alps (original) (raw)
2006
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Abstract
Neogene extensional processes. Some terranes (e.g. Tisza, Saxothuringian) can be delineated by their distinct middle crust. In some areas (e.g. Vienna basin) deep sediments are not isostatically compensated by shallow Moho but by lower crust with high velocity and density.
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Tectonophysics
The crustal structure of the Eastern Alps and adjacent tectonic units investigated in this work sheds new light on the relationship of surface geology to geodynamic processes operating at depth. Of particular interest are the nature of a previously proposed Moho gap south and east of the Tauern Window, the plate tectonic affinity of the steeply dipping Eastern Alpine slab, and the relationship of the Alps to the Neogene sedimentary basins and the Bohemian Massif. To address these questions, we use various seismological approaches based on converted waves from the temporary passive experiment EASI (Eastern Alpine Seismic Investigation), a complementary experiment of the AlpArray project. The EASI is a densely spaced, 540 km long seismic network along 13.3°E we operated for more than a year. The uppermost-crustal structures in and near the Alps exhibit dipping layers and/ or tilted anisotropy that correlate well with surface geology observations. The Moho, despite its variable appearance, is clearly identified along most of the swath. The Variscan lithospheric blocks beneath the Bohemian Massif are imaged with sub-vertical boundaries. Beneath the Eastern Alps, the shape of the Moho is consistent with bi-vergent orogenic thickening, with a steeper and deeper-reaching Adriatic plate plunging northwards beneath the European plate in the north. At the junction of these plates at depth, around the previously proposed Moho gap, the root of the Eastern Alps is a broad trough characterized by a zone of low velocity-gradient that is up to 20 km thick, transitioning between crust and mantle. Our receiver-function results corroborate earlier lithosphere-upper mantle seismic tomography images, and highlight the Adriatic affinity of the Eastern Alpine slab. The zigzag deployment pattern of stations in the EASI experiment also allows distinction of short-wavelength variations perpendicular to the profile, both within the shallow and the deep crust. This underlines the importance of applying 3D imaging in complex geodynamic systems.
The Swiss Alps and their peripheral foreland basin: Stratigraphic response to deep crustal processes
Tectonics, 2002
This paper gives a synoptic view of the Cenozoic evolution of the Swiss Alps and their northern foreland basin. In this orogen, deep crustal processes (subduction, nappe stacking, underplating, and exhumation) are intimately linked with surface processes (surface uplift, erosion, basin formation, and basin-axis migration). Within the foreland basin the spatial pattern of subsidence and alluvial fan construction suggests that an increase in flexure of the foreland plate and the creation of relief in the orogen migrated from east to west in the course of collision. In the orogen itself, crustal thickening involved lower crust of the Adriatic margin in the east and the European margin in the west. Exhumation of upper crustal units occurred earlier in the east as compared with the west. An Adriatic mantle wedge (the Ivrea body) and its associated wedge of lower crustal material are identified as an extra lithospheric load which contributed to downward flexure of the European plate. As a result of enhanced subsidence of the foreland plate, relief was generated presumably in order to adjust to critical taper geometry. It appears, therefore, that the westward motion of the Adriatic wedge ultimately caused the contemporaneous westward propagation of the location of enhanced rates of alluvial fan construction. Coeval strike-slip and N-S convergence juxtaposed the Adriatic wedge sequentially to different European upper crustal units which resulted in different styles of crustal structure and evolution along strike within the orogen.
Geological Society, London, Special Publications, 2008
The Austroalpine basement underwent a multistage Precambrian to Tertiary evolution. Meta-magmatic rocks occur in pre-Early Ordovician and post-Early Ordovician units. Protolith zircon ages and whole-rock trace element data define two magmatic evolution lines. An older trend with Th/Yb typical of subduction-related metamorphism, started by 590 Ma N-MORB-type and 550–530 Ma volcanic arc basalt-type basic suites which mainly involved depleted mantle sources, and was continued by mainly crustal-source 470–450 Ma acid magmatic suites. A presumably younger evolution by tholeiitic MORB-type and 430 Ma alkaline within-plate basalt-type suites is characterized by an intraplate mantle metasomatism and multicomponent sources. These magmatic trends can be related to a Neoproterozoic to Ordovician active margin and a subsequent Palaeo-Tethys passive margin along the north-Gondwanan periphery. During Variscan collision, the Austroalpine basement underwent multiphase deformation and metamorphism. ...
Plate tectonics in the Eastern Alps
Earth and Planetary Science Letters, 1975
The weight of the geological evidence, which includes the recognition of a late Cretaceous paired metamorphic belt, suggests that a southward dipping subduction zone existed in the Eastern Alps. On this basis a new plate tectonic model is presented for the post-Palaeozoic evolution of that orogen.
Crustal structure of the Eastern Alps and Bohemian Massif along longitude 13.3°E
2018
The crustal structure of the Eastern Alps and adjacent tectonic units investigated in this work sheds new light on the relationship of surface geology to geodynamic processes operating at depth. Of particular interest are the nature of a previously proposed Moho gap south and east of the Tauern Window, the plate tectonic affinity of the steeply dipping Eastern Alpine slab, and the relationship of the Alps to the Neogene sedimentary basins and the Bohemian Massif. To address these questions, we use various seismological approaches based on converted waves from the temporary passive experiment EASI (Eastern Alpine Seismic Investigation), a complementary experiment of the AlpArray project. The EASI is a densely spaced, 540 km long seismic network along 13.3°E we operated for more than a year. The uppermost-crustal structures in and near the Alps exhibit dipping layers and/or tilted anisotropy that correlate well with surface geology observations. The Moho, despite its variable appearan...
How to interpret upper mantle structure under the Eastern Alps?
Recent controlled source seismic investigations, supplemented by potential field studies, have substantially improved our knowledge about the lithospheric structure of the Eastern Alps. Crustal structures due to collision and escape tectonics were imaged and an improved Moho map revealed the fragmentation of the mantle lithosphere into three blocks, the European plate (EU), the Adriatic micro-plate (AD), and a newly interpreted Pannonian domain (PA) comprising the mantle lithosphere below ALCAPA, Tisza, and the Dinarides. The EU, AD, and PA blocks compose a triple junction near the southeastern border of the Tauern window. Images of the upper mantle supplied by seismic tomography provide a better understanding of plate tectonic processes. These studies identified a slab below the EU-AD plate boundary, with its eastern termination near the triple junction. We interpret the European lithospheric mantle to be connected to this slab (East Alpine slab, EAS), and thus, identify it as form...
Subduction and obduction processes in the Swiss Alps
Tectonophysics, 1998
The significance of the Briançonnais domain in the Alpine orogen is reviewed in the light of data concerning its collision with the active Adriatic margin and the passive Helvetic margin. The Briançonnais which formerly belonged to the Iberian plate, was located on the northern margin of the Alpine Tethys (Liguro-Piémont ocean) since its opening in the early-Middle Jurassic. Together with the Iberian plate the Briançonnais terrane was separated from the European plate in the Late Jurassic-Early Cretaceous, following the northern Atlantic, Bay of Biscay, Valais ocean opening. This was accompanied by the onset of subduction along the northern margin of Adria and the closure of the Alpine Tethys. Stratigraphic and metamorphic data regarding this subduction and the geohistory of the Briançonnais allows the scenario of subduction-obduction processes during the Late Cretaceous-early Tertiary in the eastern and western Alps to be specified. HP-LT metamorphism record a long-lasting history of oceanic subduction-accretion, followed in the Middle Eocene by the incorporation of the Briançonnais as an exotic terrane into the accretionary prism. Middle to Late Eocene cooling ages of the Briançonnais basement and the presence of pelagic, anorogenic sedimentation lasting until the Middle Eocene on the Briançonnais preclude any sort of collision before that time between this domain and the active Adria margin or the Helvetic margin. This is confirmed by plate reconstructions constrained by magnetic anomalies in the Atlantic domain. Only a small percentage of the former Briançonnais domain was obducted, most of the crust and lithospheric roots were subducted. This applies also to domains formerly belonging to the southern Alpine Tethys margin (Austroalpine-inner Carpathian domain). It is proposed that there was a single Palaeogene subduction zone responsible for the Alpine orogen formation (from northern Spain to the East Carpathians), with the exception of a short-lived Late Cretaceous partial closure of the Valais ocean. Subduction in the western Tethyan domain originated during the closure of the Meliata ocean during the Jurassic incorporating the Austroalpine-Carpathian domain as terranes during the Cretaceous. The subduction zone propagated into the northern margin of Adria and then to the northern margin of the Iberian plate, where it gave birth to the Pyrenean-Provençal orogenic belt. This implies the absence of a separated Cretaceous subduction zone within the Austro-Carpathian Penninic ocean. Collision of Iberia with Europe forced the subduction to jump to the SE margin of Iberia in the Eocene, creating the Apenninic orogenic wedge and inverting the vergence of subduction from south-to north-directed.
Earth-Science Reviews, 2010
A new reconstruction of Alpine Tethys combines plate-kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution, from sea-floor spreading through subduction to collision in the Alps. Unlike previous models, which relate the fate of Alpine Tethys solely to relative motions of Africa, Iberia and Europe during opening of the Atlantic, our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record. The motions of these microplates (Adria, Iberia, Alcapia, Alkapecia, and Tiszia) relative to both Africa and Europe during Late Cretaceous to Cenozoic time involved the subduction of remnant Tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces: (1) 131-84 Ma intra-oceanic subduction of the Ligurian part of Alpine Tethys attached to Iberia coincided with Eo-alpine orogenesis in the Alcapia microplate, north of Africa. These events were triggered primarily by foundering of the older (170-131 Ma) Neotethyan subduction slab along the NE margin of the composite African-Adriatic plate; subduction was linked by a sinistral transform system to E-W opening of the Valais part of Alpine Tethys; (2) 84-35 Ma subduction of primarily the Piemont and Valais parts of Alpine Tethys which were then attached to the European plate beneath the overriding African and later Adriatic plates. NW translation of Adria with respect to Africa was accommodated primarily by slow widening of the Ionian Sea; (3) 35 Ma-Recent rollback subduction of the Ligurian part of Alpine Tethys coincided with Western Alpine orogenesis and involved the formation of the Gibraltar and Calabrian arcs. Rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable, retreating Adriatic and African slabs during slow convergence of Africa and Europe. The upper European-Iberian plate stretched to accommodate this slab retreat in a very mobile fashion, while the continental core of the Adriatic microplate acted as a rigid indenter within the Alpine collisional zone. The subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the Alps and Apennines, as well as beneath parts of the Pannonian Basin, the Adriatic Sea, the Ligurian Sea, and the Western Mediterranean. The predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10-30%, indicating that parts of slabs may be superposed within the mantle transition zone and/or that some of this subducted lithosphere became seismically transparent.
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Crustal structure and active tectonics in the Eastern Alps
Tectonics, 2010
During the last decade, a series of controlled source seismic experiments brought new insight into the crustal and lithospheric structure of the Eastern Alps and their adjacent tectonic provinces. A fragmentation of the lithosphere into three blocks, Europe (EU), Adria (AD), and the new Pannonian fragment (PA), was interpreted and a triple junction was inferred. The goal of this study has been to relate these deep crustal structures to active tectonics. We used elastic plate modeling to reconsider the Moho fragmentation. We interpret subduction of EU below AD and PA from north to south and underthusting of AD mantle below PA from southwest to northeast. The Moho fragmentation correlates well with major upper crustal structures and is supported by gravity, seismic, and geodetic data. An analysis of crustal thickening suggests that active convergence is associated with continued thrusting and lateral extrusion in the central Eastern Alps and thickening of the Adriatic indenter under the Southern Alps. According to the velocity relations at the triple junction, PA moves relative to EU and AD along ENE and SE striking faults, mainly by strike slip. An eastward directed extensional component is compensated by the lateral extrusion of the central Eastern Alps. The Periadriatic (Insubric) line east of the triple junction and the mid-Hungarian fault zone have relatively recently lost their role as first-order active structures. We favor the idea that the Pannonian fragment and the TISZA block merged to a "soft" microplate surrounded by the Eastern and Southern Alpine, Carpathian, and Dinaric orogens.
Geophysical-geological transect and tectonic evolution of the Swiss-Italian Alps
Tectonics, 1996
A complete Alpine cross section integrates numerous seismic reflection and refraction profiles, across and along strike, with published and new field data. The deepest parts of the profile are constrained by geophysical data only, while structural features at intermediate levels are largely depicted according to the results of three-dimensional models making use of seismic and field geological data. The geometry of the highest structural levels is constrained by classical along-strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units. Because the transect is placed close to the western erosional margin of the Austroalpine nappes of the Eastern Alps, it contains all the major tectonic units of the Alps. A model for the tectonic evolution along the transect is proposed in the form of scaled and area-balanced profile sketches. Shortening within the Austroalpine nappes is testimony of a separate Cretaceous-age orogenic event.
Geological Society, London, Special Publications, 2009
When continental rifting does not develop on a stable continental lithosphere, geodynamic interpretation of igneous and metamorphic records, as well as structural and sedimentary imprints of rifting-related lithospheric extension, can be highly ambiguous since different mechanisms can be responsible for regional HT-LP metamorphism. This is the case of the European Alps, where the exposure of Variscan structural and metamorphic imprints within the present-day Alpine structural domains indicates that before the Pangaea break-up, the continental lithosphere was thermally and mechanically perturbed by Variscan subduction and collision. To reduce this ambiguity, we use finite-element techniques to implement numerical geodynamic models for analysing the effects of active extension during the Permian-Triassic period (from 300 to 220 Ma), overprinting a previous history of Variscan subduction-collision up to 300 Ma. The lithosphere is compositionally stratified in crust and mantle and its rheological behaviour is that of an incompressible viscous fluid controlled by a power law. Model predictions of lithospheric thermal state and strain localization are compared with metamorphic data, time interval of plutonic and volcanic activity and coeval onset of sedimentary environments. Our analysis confirms that the integrated use of geological data and numerical modelling is a valuable key for inferring the preorogenic rifting evolution of a fossil passive margin. In the specific case of the European Alps, we show that a relative high rate of active extension is required, associated for example with a far extensional field, to achieve the fit with the maximal number of tectonic units. Furthermore, in this case only, thermal conditions allowing partial melting of the crust accompanying gabbroic intrusions and HT-LP metamorphism are generated. The concordant set of geological events that took place from Permian to Triassic times in the natural Alpine case is justified by the model and is coherent with the progression of lithospheric thinning, later evolving into the appearance of oceanic crust.
Tectonic significance of Cenozoic exhumation and foreland basin evolution in the Western Alps
Tectonics, 2016
The Alps are the archetypical collisional orogenic system on Earth, and yet our understanding of processes controlling topographic growth in the Cenozoic remains incomplete. Whereas ideas and models on the Alps are abundant, data from the foreland basin record able to constrain the timing of erosion and sedimentation, mechanisms of basin accommodation and basin deformation are sparse. We combine seismic stratigraphy, micropaleontology, white mica 40 Ar/ 39 Ar, detrital zircon (U-Th)/He and apatite fission track thermochronology to Oligocene-Pliocene samples from the retrowedge foreland basin (Saluzzo Basin in Italy) and to Oligocene-Miocene sedimentary rocks from the prowedge foreland basin (Bârreme Basin in France) of the Western Alps. Our new data show that exhumation in the Oligocene-Miocene was nonuniform across the Western Alps. Topographic growth was underway since the Oligocene and exhumation was concentrated on the proside of the orogenic system. Rapid and episodic early Miocene exhumation of the Western Alps was concentrated instead on the retroside of the orogen and correlates with a major unconformity in the proximal retroforeland basin. A phase of orogenic construction is recorded by exhumation of the proximal proforeland in both the Central and Western Alps at circa 16 Ma. This is associated with high sedimentation rates, and by inference erosion rates, and suggests that an increase in accretionary flux associated with the dynamics of subduction of Europe under Adria controlled orogenic expansion in the Miocene.
Stephan Mueller Special Publication Series, 2001
Present-day tectonics of the Eastern Alps are characterized by strike-slip faulting regime in a complex transition zone between the European, the Pannonian and the Adriatic stress provinces. Evidence can be found for vertical as well as horizontal stress decoupling within the orogen due to a thermally and mechanically weakened crust. Differential vertical uplift derived from repeated precise levellings relative to the reference point in the Bohemian massif is observed in western Austria including the Tauern Window and subsidence in the Vienna basin and in the Styrian basin. We relate this behaviour of vertical motions to the effects of isostatic response to active plate convergence and strain partitioning as well as to rebound in response to Quaternary deglaciation and ice-induced erosion.
Deep structure of the Alps—what do we really know?
Physics of the Earth and Planetary Interiors, 1993
In the last five decades the deep structure of the Alps has been probed by every geophysical method applicable, and the resulting amount of data is unmatched for any other orogen. In this study, an attempt is made to review the data and the proposed structural models with the aim of separating the certain from the probable and from the speculative information. This can be achieved by first reviewing the theoretical resolving power and ambiguity of the applied interpretation methods and then analysing the proposed models. The methods reviewed are inversion of surface wave data, teleseismic and local earthquake seismic tomography, near-vertical reflection seismology, wide-angle reflection and refraction seismology, and gravity modelling. All information about the Moho rated as certain is combined to give a Moho map of the Alpine area. The information rated as certain and probable, and additional qualitative arguments, are used to discuss a crustal model of the Western and Central Alps represented by two cross-sections. Major structural elements in this crustal model are a thick overthrust Penninic nappe system, wedging at mid-to lower-crustal levels, a discontinuous Moho and strong variations along the strike of the orogen. Whereas the structures of the European upper crust and of the Penninic nappe system are well constrained, only few and isolated lower-crustal structural elements are rated as certain. Finally, the shape of the lower lithosphere in the Alps is discussed by review and comparison of the results from surface-wave, teleseismic travel-time residual and tomographic studies. Qualitative arguments suggest the existence of a lithospheric root or slab beneath the Alps. Probable tomographic information suggests a south-vergent European lithospheric slab beneath the Southern Alps and the Po Plain. Despite the considerable number of studies aimed at resolving the deepest part of Alpine orogeny, the available quantitative information on the sub-Moho structure cannot be rated as certain.