Summary Geological and geophysical constraints to reconstruct the evolution of the Central Mediterranean subduction zone are presented. Geological observations such as upper plate stratigraphy, HP–LT metamorphic assemblages, foredeep/trench stratigraphy, arc volcanism and the back‐arc extension process are used to define the infant stage of the subduction zone and its latest, back‐arc phase. Based on this data set, the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross‐sections from the northern Apennines and from Calabria to the Gulf of Lyon can be derived. Further, the reconstruction is used to unravel the main evolutionary trends of the subduction process. Results of this analysis indicate that (1) subduction in the Central Mediterranean is as old as 80 Myr, (2) the slab descended slowly into the mantle during the first 20–30 Myr (subduction speeds were probably less than 1 cm year− 1), (3) subduction accelerated afterwards, producing arc volcanism and back‐arc extension and (4) the slab reached the 660 km transition zone after 60–70 Myr. This time‐dependent scenario, where a slow initiation is followed by a roughly exponential increase in the subduction speed, can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull. Finally, the third stage is controlled by the interaction between the slab and the 660 km transition zone. In the southern region, this results in an important re‐shaping of the slab and intermittent pulses of back‐arc extension. In the northern region, the decrease in the trench retreat can be explained by the entrance of light continental material at the trench.

Abstract. In this paper we present P wave tomographic images of the mantle beneath Italy obtained by inverting -6000 teleseismic P and PKP wave arrival times, accurately repicked, recorded in the time period 1988-1994 by the stations of the National Seismic Network of the Istituto Nazionale di Geofisica. We pay great attention in the data selection and picking procedure of seismic phases to obtain a very high quality data set. The data were inverted with the well-established Aki-Christofferson-Husebye tomographic technique; different reference models and residuals computation have been tried to verify the stability of the results. The high quality of the repicked arrival times allows us to enhance the definition of the deep structures beneath both the Alps and the Apennines, looking for their lateral and vertical continuity down to 800 km depth. The main finding of this study is a continuous high-velocity body located between 250 and 670 km depth beneath the entire Apenninic system dipping toward the Tyrrhenian area, which continues upward segmented in two main anomalies in the northern Apenninic and the Calabrian Arcs. We interpret this high-velocity feature as the subducted oceanic lithosphere between the Eurasian and African plates, dipping down to the upper-lower mantle boundary beneath the Tyrrhenian Sea. The retrieved images of the lithosphere subducting beneath Apennines are reliable in terms of thickness (about 80-90 km) and P wave velocity contrast (2-4% higher than the normal mantle). Furthermore, our tomographic images, which focus on the deep geometry and continuity of the velocity structures, provide new keys to understanding the geodynamic evolution of the Italian region. The segmentation of the high-velocity slab upward suggests a complex evolution of the arctrench system and the initially continuous subduction of the Ionian-Adriatic plate progressively developed in subordinate arcs, probably due to lateral heterogeneity of the subducting lithosphere.

[1] Tectonic activity in convergent plate boundaries commonly involves backward migration (rollback) of narrow subducting slabs and segmentation of subduction zones through slab tearing. Here we investigate this process in the Italian region by integrating seismic tomography data with spatiotemporal analysis of magmatic rocks and kinematic reconstructions. Seismic tomography results show gaps within the subducting lithosphere, which are interpreted as deep (100-500 km) subvertical tear faults. The development of such tear faults is consistent with proposed kinematic reconstructions, in which different rates of subduction rollback affected different parts of the subduction zone. We further suggest a possible link between the development of tear faults and the occurrence of regional magmatic activity with transitional geochemical signatures between arc type and OIB type, associated with slab tearing and slab breakoff. We conclude that lithosphericscale tear faults play a fundamental role in the destruction of subduction zones. As such, they should be incorporated into reconstructions of ancient convergent margins, where tear faults are possibly represented by continental lineaments linked with magmatism and mineralization. Citation: Rosenbaum, G., M. Gasparon, F. P. Lucente, A. Peccerillo, and M. S. Miller (2008), Kinematics of slab tear faults during subduction segmentation and implications for Italian magmatism, Tectonics, 27, TC2008,

Abruzzi region (central Italy) producing vast damage in the L'Aquila town and surroundings. In this paper we present the location and geometry of the fault system as obtained by the analysis of main shock and aftershocks recorded by permanent and temporary networks. The distribution of aftershocks, 712 selected events with M L ! 2.3 and 20 with M L ! 4.0, defines a complex, 40 km long, NW trending extensional structure. The main shock fault segment extends for 15-18 km and dips at 45°to the SW, between 10 and 2 km depth. The extent of aftershocks coincides with the surface trace of the Paganica fault, a poorly known normal fault that, after the event, has been quoted to accommodate the extension of the area. We observe a migration of seismicity to the north on an echelon fault that can rupture in future large earthquakes.

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