1,721,076 research outputs found
The fingerprints of intra-continental deformation in central Europe as evisaged by the synergic use of predicting modelling and geodetic data
No full textThe large scale crustal deformation geodetically observed in Europe is the result of a complex interplay of different geodynamic forces, such as the Africa-Eurasia plates' convergence, the mid-Atlantic spreading and the post-glacial rebound. Each force has a different impact on the deformation in Europe, with tectonic forces playing the major role in the southernmost part of continental Europe, between the Alpine front and the southern border of Fennoscandia, while the post-glacial rebound mainly affects the deformation at high latitudes, north of Potsdam. The lateral rheological heterogeneities also have a crucial role in stiffening the propagation of tectonic deformation throughout northern Europe. When Global Positioning System data are used to constrain predictive geophysical modelling, they reveal their crucial role in distinguishing different geodynamic processes responsible for the observed deformation. A comparison between predicted tectonic deformation and geodetic data demonstrates, in fact, that tectonic forces and post-glacial rebound must be simultaneously taken into account for a correct interpretation of the deformation in northern and central Europe measured by geodetic techniques
The role of mantle hydration in continental crust recycling in the wedge region
No full textIn orogenic belts high pressure–low temperature (HP–LT) metamorphism can widely affect units derived from both the oceanic and the continental lithosphere. In order to verify whether high P/T (pressure/temperature) ratios recorded in the continental lithosphere can result from tectonic erosion, ablative subduction and recycling in the mantle wedge, we implemented a 2D numerical model to simulate oceanic subduction beneath a continent. Particular attention is paid to the role played by mantle hydration within the continental crust recycled in the wedge region. A comparison between hydrated and non-hydrated models highlights that hydration is fundamental in allowing the recycling of crustal material at shallow depths (≤150 km for a convergence rate of 1 cm year−1), making the uprising and exhumation of buried crustal material during active subduction possible. The recycled crustal material can originate from any crustal level. The Tmax and Pmax distributions within the final marker configuration show that crustal recycling induces the coupling of volumes that reached different depths during their paths in the corner flow. To verify the reliability of this model we compare predictions with natural geological data from the Austroalpine Sesia–Lanzo Zone (SLZ), the largest eclogite-facies crustal fragment of early Alpine age and whose Alpine tectonic evolution has been interpreted as compatible with a cycle of burial at depth and exhumation during active subduction of the oceanic lithosphere. The relationships between natural P–T estimates and predicted P–T values show that the simulated geodynamic scenario generates a thermal regime coherent with that affecting the subducted continental crust of the SLZ, which may have been stable for a long time during Alpine subduction, allowing the SLZ rocks to accomplish their burial and exhumation path under an active subduction regime
P-T evolutions vs numerical modelling to understand the transition from Paleozoic to early-Mesozoic tectonics in the Alps
No full textThe geodynamic significance of the transition between the Variscan collision metamorphism and the HT Permo-Triassic metamorphism: a numerical modelling
No full text
P-T evolution vs numerical modelling : a key to unravel the Paleozoic to early-Mesozoic tectonic evolution of the Alpine area
No full textThe pre-Alpine continental crust of the Alps preserves Permian-Triassic magmatic and high-temperature (HT) metamorphic evolutions, which overprinted records of Variscan subduction and collision-related metamorphism. The occurrence of numerous Variscan eclogites in the pre-Alpine continental crust, presently belonging to different structural domains, indicates that part of the Variscan suture zone occurs in the Alpine belt. The late Variscan evolution took place from 340 to 300 Ma, and therefore the igneous and metamorphic signatures up to Upper Carboniferous may represent the record of the late orogenic evolution. On the contrary, different authors interpreted the HT metamorphism associated with gabbro to granite intrusions younger than 290 Ma as the effect of Permian-Triassic late-orogenic collapse or continental rifting. The goal of this study is to reduce the ambiguity about the geodynamic significance of the Permian-Triassic HT metamorphism and igneous activity in the Alpine continental crust, with the support of numerical modelling of: ocean subduction, continental collision, lithospheric detachment and subsequent gravitational thermal relaxation. Comparison of the model predictions with structural and petrologic data has driven the successive model refinements to improve the fit. The best fit model predictions show a rather good agreement with natural data (coincidence of age, P-T values and rock compositional affinity) up to late-Variscan times. The poor agreement during the Permian-Triassic evolution suggests that, with respect to the thermal state established during the post-collisional gravitational evolution, an additional positive heat anomaly is necessary to induce the thermal state indicated by natural P-T estimates
Africa-Eurasia kinematics control of long wavelength tectonic deformation in the central Mediterranean
No full textWe use a spherical thin sheet geophysical model to study the regional deformation pattern in the CentralMediterranean and compare model predictions with the deformation resulting from newITRF2005 data, in terms of both amplitude and direction of the strain rate eigenvectors. We quantify the effects of the choice of a specific data set in defining the boundary conditions for Africa–Eurasia convergence in a predictive model that spreads the information resulting from a discrete data set over a continuum, such as the geodetic one. The fairly good agreement between geodetic and modelled patterns shows that, within the study area, the deformation predicted by tectonic models based on ITRF2005 boundary conditions (b.c.) for Africa–Eurasia relative motion differs from that predicted by models based on Deos2k b.c., only on long distances from the Africa–Eurasia boundary. Geodetically retrieved SSE–NNW compression and SSW–
NNE extension are well reproduced by the eigenvectors of the strain-rate tensor in the central Mediterranean and Italian peninsula, with eigenvalues generally slightly underestimating the observed ones, resulting in a global strain-rate of the order of a few nanostrain yr−1. The effects of viscosity contrasts across the model domain are assessed in terms of their impact on
baseline variations and strain rates
Tectonic versus glacial isostatic adjustment deformation in Europe
No full textTectonic deformation induced by the Alpine collision and Glacial Isostatic Adjustment (GIA) in Europe are modelled by means of a finite element scheme and viscoelastic normal modes techniques in order to compare the resulting deformation patterns with the ITRF2000 (International Terrestrial Reference Frame) geodetic dataset. Due to the Alpine collision and to the flow from the equatorial mantle to the deglaciated regions in the northern hemisphere, both tectonics and GIA contribute to the observed widespread shortening, with tectonics playing a major role in the southern part of the modelled domain, from Potsdam to the Alpine front, and GIA affecting the shortening in proximity of the region subject to post glacial rebound. Since the stiff Baltic Shield causes a counterclockwise rotation of the collision velocity away from the shield itself and the GIA induced velocities are directed outward from the deglaciated region, both tectonics and GIA contribute to the observed east-west baseline extension of 0.8-1.1 mm/yr at the latitude of ONSA
Permian-Triassic high thermal regime in the Alps : result of Late Variscan collapse or continental rifting? Validation by numerical modeling
No full textThe Permian-Triassic igneous activity, associated with regional scale deformation developed under high-temperature/low-pressure (HT-LP) metamorphic conditions and widely recorded in the pre-Alpine crust of the European Alps, can result from late orogenic collapse of a collisional belt or from lithospheric thinning leading to a continental rifting process. In order to reduce this ambiguity, we use a two-dimensional finite element model to give new insights on the sequence of mechanisms operating during active ocean-continent convergence, followed by continental collision and pure gravitational evolution and on the regional geodynamic interpretation of the Paleozoic-Mesozoic evolution of the Alpine area. The modeling predictions are compared with the PT climax conditions of Variscan and Permian-Triassic metamorphism affecting the continental crust of the Helvetic to Southalpine domains. The good agreement between model predictions and natural data realized for the early to Neovariscan evolution indicates that during Paleozoic, the pre-Alpine crust of the Alps was part of an active ocean-continent convergence margin and an intracontinental suture zone. Furthermore, modeling results support the interpretation envisaging a Permian-Triassic lithospheric extension as responsible for the HT metamorphism and related intense igneous activity. This evolution was precursor of the Mesozoic oceanization, during which the tectonic units, coupled and accreted during the Variscan subduction and collision, were separated to form the two passive European and Adriatic continental margins
- …
