Slab narrowing in the Central Mediterranean: the Calabro-Ionian subduction zone as imaged by high resolution seismic tomography

Abstract

A detailed 3D image of the Calabro-Ionian subduction system in the central Mediterranean was obtained by means of a seismic tomography, exploiting a large dataset of local earthquakes and computing algorithms able to build a dense grid of measure nodes. Results show that the slab is continuous below the southern sector of the Calabro-Peloritan Arc, but the deformation processes developing at its edges are leading to its progressive narrowing, influencing tectonics and magmatism at the surface, and with possible stress concentration in the tip zones. In the southwest, the deformation occurring at a free slab edge lead to propagation of a vertical lithospheric tear in the overriding plate, which extends along a NW-SE fault system (Aeolian-Tindari-Letojanni) up to about 30 km into the Ionian Sea; further southeast, the lithosphere appears only flexed and not broken yet. In the northeast, the slab seems to break progressively, parallel to the trench. Finally, northwest of Mt. Etna, the tomography highlights low VP that can be related to an upwelling of deep mantle material likely flowing laterally through a window opened by the complete slab detachment.

Geometry of the Deep Calabrian Subduction (Central Mediterranean Sea) From Wide‐Angle Seismic Data and 3‐D Gravity Modeling

“…The models show relatively large uncertainties concerning the depth of the interfaces of ±2.5 km for the Moho interface and the top of the oceanic crust. These results are in agreement with the DY‐P4 velocity model and also the tomographic model from Scarfì et al (). Three different lithospheric mantle densities enabled us to reproduce the large‐scale regional observed free‐air gravity anomaly and then to test the three slab depth hypotheses.…”

“…A slab length offset between the originally attached Calabrian and the Kabylides slab might be at the origin of the initiation of a subduction-transform edge propagator (STEP, Govers & Wortel, 2005) fault that then separated these into two slabs ( van Hinsbergen, Mensink, et al, 2014). The modern-day fore-arc STEP fault is thought to be located either at the Alfeo Fault system (Dellong et al, 2018;Gutscher et al, 2016Gutscher et al, , 2017 or at the Ionian Fault system (Polonia et al, 2011;Scarfì et al, 2018) (Figure 2). An earlier proposition that the STEP fault follows the Malta Escarpment, a 3-km-high feature offshore E Sicily (Argnani & Bonazzi, 2005) formed during the Tethyan rifting history of the Ionian Sea (Frizon de Lamotte et al, 2011;Gallais et al, 2011), seems unlikely given the absence of tectonic deformation along the central to southern Malta Escarpment since the Messinian, on the basis of high-resolution seismic profiles shot across the escarpment (Gutscher et al, 2016).…”

“…However from preliminary tests, it is clear that models using one single density for the mantle do not allow to sufficiently fit the data. These last two layers were obtained by extrapolating the tomographic models (Scarfì et al, 2018) and therefore do not have a corresponding velocity in Table S1, which provides only velocities from wide-angle seismic modeling. The difference between the Hyblean and the Tethyan oceanic mantle domains is small and can be explained by several factors, such as mantle composition or thermal state.…”

“…Recent geodetic work provided evidence for toroidal flow around the retreating slab edges of the Calabrian subduction system expressed by counterclockwise rotations at the northern and clockwise rotations at the southern edge of the slab corresponding to movements predicted by STEP faults (Palano et al, ). Recent tomographic studies imaged a trench‐parallel slab break‐off on both sides of the slab, which might be still propagating, narrowing the slab (Barreca et al, , ; Scarfì et al, , ). Horizontal tearing affecting both sides of the slab was proposed to result in a narrowing of the subduction system and enhanced subsidence along the still‐intact segment of the slab (Scarfì et al, ).…”

“…Recent tomographic studies imaged a trench‐parallel slab break‐off on both sides of the slab, which might be still propagating, narrowing the slab (Barreca et al, , ; Scarfì et al, , ). Horizontal tearing affecting both sides of the slab was proposed to result in a narrowing of the subduction system and enhanced subsidence along the still‐intact segment of the slab (Scarfì et al, ). In central Calabria the depth of the slab has been determined by source‐receiver function analysis during a tomographic experiment.…”