1,721,057 research outputs found
How deep can we find the traces of Alpine subduction?
No full textSlab-like seismic velocity heterogeneities below the
Alpine chain, interpreted as subducted lithosphere, are
imaged by tomographic studies down to only about 300 km
depth. A non-negligible discrepancy therefore exists
between tomographic and geological data, the latter
indicating at least 500 km of Tertiary convergence at
trench. Yet a recently published tomographic study detects a
pronounced high velocity anomaly at the bottom of the
upper mantle right below the Alpine area. Combining
tomographic images of the mantle, geological findings and
plate system kinematics, we investigate how the presence of
this feature in the transition zone below the Alps can be
traced back to the Tertiary Alpine subduction and possibly
explain the observed discrepancy. We propose that a part of
the fast velocity body now residing just above the 660 km
discontinuity once belonged to the Alpine slab, torn off by
an event occurred at about 30–35 Ma.PublishedL066053.3. Geodinamica e struttura dell'interno della TerraJCR Journalreserve
Plume-related magmatism in collision zones: examples from the Tertiary-Quaternary magmatism in Italy.
No full textFrom late Cretaceous to present time, an extensive magmatic activity developed both in Europe and northern Africa, showing a progressive transition with time from calc-alkaline to Na-rich alkaline features in areas tightly connected with subduction systems (Morocco, Algeria, Tunisia, Spain, Italy), while Na-rich basalts and basanites, with minor tholeiitic volcanics, occur at extensional tectonic settings, both associated or not to orogenic dynamics (Valencia trough, Pannonian, Alboran, Tyrrhenian, and Aegean basins, Pantelleria-Etna-Iblean area, Veneto Province, Cenozoic Rift System). The widespread alkaline magmatism in the European and circum Mediterranean area shows a uniform HIMU-DMM type signature which has been recently ascribed to a mantle contamination episode triggered by the rise of the Central Atlantic Plume (CAP) head since Cretaceous time (Piromallo et al., 2008).
The occurrence of a HIMU-DMM component within lavas originated in collision environments such as the Veneto Volcanic Province in NE Alps (related to the Tertiary convergence of Europe and Africa plates) or the Roman Magmatic Province (related to the Cenozoic Adria subduction) might be explained in terms of slab breakoff (Macera et al., 2008; Gasperini et al., 2002). Evidence for slab breakoff in these areas comes from seismic tomography (Piromallo and Faccenna, 2004) and geophysical modeling consisting in evaluating the time evolution of buoyancy of oceanic and continental lithosphere during subduction with both constant and time-varying convergence rates (Macera et al., 2008). If the subducted slab intercepts a hot mantle diapir rising from the frayed plume head, the corresponding part of the slab is heated and therefore softened. The softening effect is enhanced if the slab includes continental material. The combination of changes in negative buoyancy caused by continental subduction, and softening of a part of the slab caused by slab-plume interaction, may act as a regulator for the time of slab breakoff and consequently for the time and type variations of magmatism in the overriding lithosphere above a subduction zone. In the Alpine region, we assume that the plume material interacted with the subducting slab causing its heating, softening, and finally its detachment. Ensuing upwelling of plume material through the resulting plate window is supposed to be the responsible for partial melting in the lithospheric mantle wedge and/or decompression melting of the ascending plume material.
Plume-related volcanism in subduction zones is possible either before the subducted slab intercepts plume head material , or after slab breakoff. The above considerations provide a framework for the occurrence of plume-related and calc-alkaline magmatism in the southeastern Alps and probably in other similar tectonic settings such as the Central Europe Magmatic Province. The heat released by the hot mantle component to the overriding mantle wedge contributed to its partial melting and production of calc-alkaline mafic magmas. The latter additionally favored the genesis of calc-alkaline felsic magmas through partial melting of the lower crust by underplating. A quantitative approach based on mixing calculations on Sr-Nd and Pb isotopes support these hypotheses
Subduction age and stress state control on seismicity in the NW Pacific subducting plate
Full text linkIntermediate depth (70–300 km) and deep (> 300 km) earthquakes have always been puzzling Earth scientists: their occurrence is a paradox, since the ductile behavior of rocks and the high confining pressure with increasing depths would theoretically preclude brittle failure and frictional sliding. The mechanisms proposed to explain deep earthquakes, mainly depending on the subducting plate age and stress state, are generally expressed by single parameters, unsuitable to comprehensively account for differences among distinct subduction zones or within the same slab. We analyze the Kurile and Izu–Bonin intraslab seismicity and detail the Gutenberg–Richter b-value along the subducted planes, interpreting its variation in terms of stress state, analogously to what usually done for shallow earthquakes. We demonstrate that, despite the slabs different properties (e.g., lithospheric age, stress state, dehydration rate), in both cases deep earthquakes are restricted to depths characterized by equal age from subduction initiation and are driven by stress regimes affected by the persistence of the metastable olivine wedge
Reply to the comment by G. Capponi et al. on “Subduction polarity reversal at the junction between the Western Alps and the Northern Apennines, Italy”, by G. Vignaroli et al. (Tectonophysics, 2008, 450, 34–50)
No full textConstraints on mantle flow in subduction system as inferred from petrological features of magmas and mantle xenoliths
No full text
Imaging the Mediterranean upper mantle by p- wave travel time tomography
No full textTravel times of P-waves in the Euro-Mediterranean region show strong and consistent lateral variations, which can be associated to structural heterogeneity in the underlying crust and mantle. We analyze regional and tele- seismic data from the International Seismological Centre data base to construct a three-dimensional velocity model of the upper mantle. We parameterize the model by a 3D grid of nodes -with approximately 50 km spacing -with a linear interpolation law, which constitutes a three-dimensional continuous representation of P-wave velocity. We construct summary travel time residuals between pairs of cells of the Earth's surface, both inside our study area and -with a broader spacing -on the whole globe. We account for lower mantle heterogeneity outside the modeled region by using empirical corrections to teleseismic travel times. The tomo- graphic images show generai agreement with other seismological studies of this area, with apparently higher detail attained in some locations. The signature of past and present lithospheric subduction, connected to Euro- African convergence, is a prominent feature. Active subduction under the Tyrrhenian and Hellenic arcs is clearly imaged as high-velocity bodies spanning the whole upper mantle. A clear variation of the lithospheric structure beneath the Northem and Southern Apennines is observed, with the boundary running in correspon- dence of the Ortona-Roccamonfina tectonic lineament. The western section of the Alps appears to have better developed roots than the eastern, possibly reflecting à difference in past subduction of the Tethyan lithosphere and subsequent continental collision.JCR Journalope
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