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  • 1
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    Evidence for a serpentinized plate interface favouring continental subduction (2020)
    Nature P. G.
    Details
    Publication Date: 2020-05-19
    Description: The dynamics of continental subduction is largely controlled by the rheological properties of rocks involved along the subduction channel. Serpentinites have low viscosity at geological strain rates. However, compelling geophysical evidence of a serpentinite channel during continental subduction is still lacking. Here we show that anomalously low shear-wave seismic velocities are found beneath the Western Alps, along the plate interface between the European slab and the overlying Adriatic mantle. We propose that these seismic velocities indicate the stacked remnants of a weak fossilised serpentinite channel, which includes both slivers of abyssal serpentinite formed at the ocean floor and mantle-wedge serpentinite formed by fluid release from the subducting slab. Our results suggest that this serpentinized plate interface may have favoured the subduction of continental crust into the upper mantle and the formation/exhumation of ultra-high pressure metamorphic rocks, providing new constraints to develop the conceptual and quantitative understanding of continental-subduction dynamics.
    Description: This research was supported by NSFC (grant nos. 41888101, 91755000, and 41625016), CAS program (GJHZ1776), Agence Nationale de la Recherche (contract ANR-15-CE31-0015), and Labex OSUG@2020 (Investissement d’Avenir, ANR-10-LABX-56). T.B. is funded by the European Union’s Horizon 2020 research and innovation program (grant no. 716542). This is contribution 1484 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au). This work was supported by resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia.
    Description: Published
    Description: id 2171
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Lithosphere reology ; serpentinites ; subduction ; Western Alps ; exhumation ; 04.01. Earth Interior ; 04.07. Tectonophysics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Seismotectonics at the Transition Between Opposite‐Dipping Slabs (Western Alpine Region) (2021)
    Wiley Agu
    Details
    Publication Date: 2023-11-16
    Description: We analyze a fully reprocessed data set of ~9,000 seismic events recorded in the western Alpine region during the past 30 yr, in order to understand how convergence between Africa and Eurasia is presently accommodated at the transition between the opposite‐dipping Alpine and Apenninic slabs. We confirm that seismicity in the Internal Zone of the Western Alps is clustered along two different arcs (Briançonnais and Piedmont arcs), clearly outlined by events in the 0–12 km depth range. The Piedmont Arc is best outlined by events in the 12–30 km depth range, forming a narrow belt that matches the shape and location of the Ivrea gravity anomaly. In the Internal Zone, σ3, is oblique to the orogen trend. Although the mountain range is spreading gravitationally at a shallow level, spreading occurs intermittently with other earthquakes that are more directly related to plate interactions. Strike‐slip solutions are predominant for events of magnitude Ml 〉 4, and reverse solutions are dominant along the Piedmont Arc for events of magnitude Ml 〈 4. Nodal planes have dominant NNW‐SSE and ENE‐WSW orientations that are common to major faults mapped in the study area. Integration with available tectonic and geodynamic constraints indicates that lithology distribution in the subduction wedge, orientation of major faults within and outside the subduction zone, and the exhumation of mantle rocks at shallow depth concurrently determine a complex seismotectonic scenario that may be expected in other subduction zones worldwide.
    Description: Published
    Description: e2020TC006086
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Seismotectonics ; Adria-Europa plate boundary ; opposite-dipping slabs ; exhumed mantle wedge ; tectonic inheritance ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Receiver function mapping of the mantle transition zone beneath the Western Alps: New constraints on slab subduction and mantle upwelling (2023)
    Elsevier
    Details
    Publication Date: 2023-01-17
    Description: To better constrain the deep structure and dynamics of the Western Alps, we studied the mantle transition zone (MTZ) structure using P-wave receiver functions (RFs). We obtained a total of 24904 RFs from 1182 events collected by 307 stations in the Western Alps. To illustrate the influence of the heterogeneity on the upper mantle velocity, we used both IASP91 and three-dimensional (3-D) velocity models to perform RF time-to-depth migration. We documented an MTZ thickening of about 40 km under the Western Alps and most of the Po Plain due to the uplift associated with the 410-km discontinuity and the depression associated with the 660-km discontinuity. Based upon the close spatial connection between the thickened MTZ and the location of the subducted slabs, we proposed that the thick MTZ was due to the subduction of the Alpine slab through the upper MTZ and the presence of remnants of subducted oceanic lithosphere in the MTZ. The uplift associated with the 410-km discontinuity provided independent evidence of the subduction depth of the Western Alps slab. In the Alpine foreland in eastern France, we observed localized arc-shaped thinning of the MTZ caused by a 12 km depression of the 410-km discontinuity, which has not been previously reported. This depression indicated a temperature increase of 120 K in the upper MTZ, and we proposed that it was caused by a small-scale mantle upwelling. Hardly any uplift of the 660 km discontinuity was observed, suggesting that the thermal anomaly was unlikely to be the result of a mantle plume. We observed that the thinning area of the MTZ corresponded to the area with the highest uplift rate in the Western Alps, which may have indicated that the temperature increase caused by the mantle upwelling contributed to the topographic uplift.
    Description: Published
    Description: 117267
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: receiver function, mantle transition, slab subduction ; Receiver function for the Western Alps ; 04.07. Tectonophysics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    A seismotectonic picture of the inner southern Western Alps based on the analysis of anomalously deep earthquakes (2018)
    Details
    Publication Date: 2022-06-09
    Description: The anomalously deep seismicity beneath the Western Po Plain is here analyzed to shed light on the complex and still poorly understood tectonic configuration of the internal side of the Western Alps area. The original dataset, including 590 earthquakes deeper than 20 km recorded during the last 25 years, has been accurately relocated with HypoDD using both catalog and cross-correlation differential times. We found that the distribution of seismic events faithfully mirrors the presence of two distinct tectonic domains (axial belt domains 1 and 2), originally belonging to the Paleogene Alpine wedge and now anomalously juxtaposed beneath the sedimentary infill of the Western Po Plain. Shallow, low-magnitude earthquakes (b20 km depth) are concentrated in domain 1, and are possibly triggered by the isostatic reequilibration of the accretionary wedge. Earthquakes between 25 and 75 km depth, instead, define a NNW–SSE linear cluster along the boundary between domains 1 and 2, and mark an apparent plane steeply dipping to the ENE. We propose that this plane may represent a major tectonic boundary of Neogene age, here referred to as the Rivoli–Marene deep fault. Focal mechanisms along the Rivoli–Marene deep fault are invariably transpressional, and suggest ongoing left-lateral motion in agreement with available plate motion constraints. The normal throw inferred from surface geology data (N8 km), and accommodated in correspondence of the fault, could be linked to its Neogene activity, coeval with the northward translation of the retreating Adriatic slab
    Description: Published
    Description: 190-199
    Description: 1T. Deformazione crostale attiva
    Description: JCR Journal
    Keywords: 04.07. Tectonophysics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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