Lateral discontinuity of the Apennines-Calabria subduction zone in Southern Italy: the tearing of the Calabrian slab and its relation to mantle wedge seismic structure.

Piana Agostinetti N.

IV - Geofisica e fisica dell'ambiente
Aula 32C-1 - Giovedì 20 h 16:30 - 19:00
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The vast majority of the world mountain ranges develops where convergent continental and/or oceanic tectonic plates collide, i.e. gravitational-stable rocks clash together (the so-called collisional orogeny), or where one heavier plate is subducted beneath a lighter plate, and sinks in the Earth's mantle (the so-called subduction orogeny). The Apennines-Calabria mountain chain is a well-studied subduction orogen, where along-strike variations in the subduction system have been documented and broadly mimic the heterogeneity in the sinking Apenninic-Calabrian slab. The nature of the lithospheric materials subducted at the trench, i.e. where the two plates separate, changed in time, determining a variety of subduction styles along the Apennines. The rock density is the key-factor influencing the subduction process, where lighter materials composing the continental margins offer a stronger resistance to subduction with respect to heavier rocks forming the oceanic plates. Gravity-driven differential stress within the subducting plate can lead to slab deformation, tearing and disruption. This process is well documented along the Apennines, where different stages of slab tearing have been suggested. We focus on the transition between Southern Apennines (SA) and the Calabrian arc (CA), where the Calabrian slab is teared off the Apenninic slab. While the SA developed from the crustal wedge of the subduction of continental margin (i.e. the subduction of a continental shelf), the CA is a widely-recognized, classical subduction of an oceanic plate (i.e. the former Tethys ocean). The differences in the two subduction regimes are striking (i.e. SA subduction is almost stopped, while CA subduction is still active), and they are likely responsible for strong heterogeneity in the mantle wedge, i.e. the portion of upper mantle comprised in between the overriding and subducting plates Here, we use a teleseismic receiver function, i.e. the analysis of the P-to-s converted phases from the seismic interfaces, to investigate the mantle wedge and the subducted plate along the Tyrrhenian coast, from the southern edge of the SA orogens to the central portion of the CA. We apply a method for harmonic decomposition of the RF data-set, to retrieve both isotropic and anisotropic properties of the mantle wedge materials, where the former are related to the nature of the slab and the latter are linked to the asthenospheric the mantle flow driven by slab rollback.Preliminary results highlight the presence of a lateral discontinuity in the mantle wedge structure at the boundary between SA and CA. Both thickness and intensity of anisotropy within the mantle wedge change dramatically there, while the direction of the symmetry axis of the anisotropic materials keeps a coherent trench-normal pattern, likely related to the mantle flow in front of a retreating slab. Moreover, our study helps define the topography of the plate boundary beneath Calabria, at about 60 km, in an area where independent measurements are still lacking.

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