Subduction Zones Interaction Around the Adria Microplate and the Origin of the Apenninic Arc

Abstract

The study of slab-slab interactions has come to the front of geodynamics researches to explain geological and geophysical observations from tectonically complex areas. Here we aim to better understand the geodynamics of the Central Mediterranean, where the Adria plate subducts on its two opposite sides. Additionally, the slab below the Central South Apennines has been progressively breaking off during the last 3 Myr. The role of a slab window in a single slab or in an outward dipping double-sided subduction system is addressed by analog models at the scale of the upper mantle, realized using glucose syrup and silicone putty, to model the interaction between the Earth's mantle and the lithosphere. Our results show that the presence of a slab window modifies the pattern of mantle circulation, as well as the trench geometry and kinematics. In particular, the opening of the slab window induces the formation of two arcs flanking the window, while the mantle flows through it and turns toward the arcs, creating a small-scale toroidal flow. The effect of a slab window is more pronounced on double subduction systems, as the outflow through the window is amplified, while internal deformation is induced in the plate by the opposite slab pull force. These experimental results suggest that the origin of the Apenninic and the Calabrian arcs is the result of the formation of a slab window, providing a new interpretation of the surface deformation and the SKS shear wave splitting pattern of the Adria microplate. Plain Language SummaryThe Adria microplate in the Central Mediterranean is an important part of the tectonic puzzle between the converging Africa and Eurasia plates. The heavy lithosphere sinks into the underlying mantle on two sides of the Adria plate, under the Apennines in the west and under the Dinarides in the east. During the most recent few millions of years, the lithosphere started to detach from the surface in the Central South Apennines while sinking into the mantle. This opened a slab window, an additional escape route for the mantle, which is squeezed by the two subducting lithospheres. We scaled down and simplified this setting in order to model and investigate the role of the dual subduction and the opening slab window in the evolution of the Central Mediterranean by means of analog models. Our results show that the two opposite subduction zones have a regional tectonics effect via the complex subduction-induced mantle circulation. Furthermore, the detaching lithosphere modifies the geometry of the subduction zone, which results in a double-arc geometry resembling the Northern Apennines and Calabria.

Mantle flow below the central and greater Alpine region: insights from SKS anisotropy analysis at AlpArray and permanent stations

“…4b) and thus do not support this hypothesis; on the contrary, here it is possible to assume that the supra European slab space is large enough to host the eastward mantle flow coming from beneath the Apennines (Fig. 8), which is in agreement also with previous possible flow scenarios (Király et al, 2018, and references therein).…”

Deriving a New Crustal Model of Northern Adria: The Northern Adria Crust (NAC) Model

“…It is worth noting that their boundary between AD and EU is further north than ours. If confirmed by other data, this would imply two oppositely dipping subduction zones (Király et al, 2018) and should lead to a re-analysis of the other datasets. The fragmentation of the Moho, leading to our MO2 model, was suggested based on the analysis of the seismic data of the CELEBRATION andALP 2002 experiments (Behm et al, 2007) and supported by the elastic plate modeling of Brückl et al (2010), gravimetric, geodetic, and seismicity pieces of evidence (Brückl, 2011).…”

The Slab Puzzle of the Alpine‐Mediterranean Region: Insights From a New, High‐Resolution, Shear Wave Velocity Model of the Upper Mantle

“…The counterclockwise rotation of Africa since the Cretaceous is a key indicator for the larger amount of subducted oceanic lithosphere in the east compared to the west. At present, the eastern and western Mediterranean are separated by the about 300 km wide, continental remnant of the Adriatic microplate that, on its general northwestward path (e.g., Platt & Vissers, 1989), has been colliding with Eurasia to form the Alps, the Dinarides, and northern Hellenides (Figure 1; Carminati & Doglioni, 2012; Handy et al., 2015; Király et al., 2018; Rosenbaum & Lister, 2004; van Hinsbergen et al., 2019).…”