The dynamics of back-arc extension: an experimental approach to the opening of the Tyrrhenian Sea

Abstract

The E-W-opening Tyrrhenian Sea developed after the Cretaceous-Palaeogene Alpine collision, nearly perpendicular to the motion of the African plate, as a back-arc of the Adria-Ionian westward subduction. Three driving mechanisms have been proposed to explain the dynamic evolution of the Tyrrhenian-Apennine system: ( 1 ) the northward indentation of the African plate; (2) the retreating subduction of the Adria-Ionian lithosphere; and (3) the gravitational collapse of the Alpine post-collisional wedge. In order to define the relative contribution of each of these mechanisms in the Neogene dynamic of the Tyrrhenian-Apennine system, we performed 3-D laboratory experiments, in which we simulated a retreating subduction process in a compressional regime oriented perpendicularly to the direction of subduction; in this framework we also tested the influence of the gravitational collapse of the overriding plate. Experiments were constructed using dry sand and silicone putties to simulate brittle upper crust and ductile lower crust/upper mantle, respectively; these layers floated on a highdensity, low-viscosity glucose syrup which simulated the asthenosphere. The main conclusion of our experiments is that large-scale continental extension, similar to that observed in the Tyrrhenian area, could be reproduced perpendicular to the shortening direction induced by the indentation of the African plate; in this framework, extensional processes are indeed possible if the trench retreat velocity is higher than the rate of shortening induced by the advancing African plate. Our experimental results indicate that this high trench retreat velocity could be explained by the coexistence of the gravitational collapse of the post-Alpine wedge with a slab-pull process, linked to the retreating subduction of the Adria-Ionian plate. While the first mechanism is predominant in the Northern Tyrrhenian area, the second one seems to be important in the latest stage of extension and oceanic accretion of the Southern Tyrrhenian area.

Subduction or delamination beneath the Apennines? Evidence from regional tomography

“…It was first proposed by Malinverno and Ryan (1986) that the loop-shaped boundary, leading to back-arc extension in the Tyrrhenian sea (Spadini et al, 1995), was formed due to strongly curved subduction occurring in the narrow zone in front of the Apennines. However, such a strong bending of the subducting plate appears to be mechanically not plausible, as was shown by analogue experiments by Faccenna et al (1996). Alternatively, Faccenna et al (2004) have proposed that the complex boundary shape in the Apennines region was formed due to the initial evolution of the western Mediterranean subduction zone (WMSZ) followed by trench retreat and back-arc extension.…”

New insights into the onset and evolution of the central Apennine extensional intermontane basins based on the tectonically active L’Aquila Basin (central Italy)

“…15) could indicate a partial decoupling of processes responsible for the migration of shortening and extension toward the foreland. These processes include (1) convergence and rollback of the subducting plate, responsible for the migration of the compressional front toward the foreland (e.g., Doglioni et al, 1997;Funiciello et al, 1999;Faccenna et al, 2001;Carminati and Doglioni, 2012), and (2) mantle upwelling, responsible for the development of the hinterland extensional domain, the uplift of the compressional tectonic wedge, and intermontane extensional basin formation (e.g., Dewey, 1988;Doglioni, 1995;Faccenna et al, 1996;Cavinato and DeCelles, 1999;D'Agostino et al, 2001;Fig. 16).…”

“…XX/XX as a lithospheric response of the upper plate to the rollback of the subducting Adria plate (Dewey, 1988;Faccenna et al, 1996Faccenna et al, , 2001Funiciello et al, 1999;Carminati and Doglioni, 2012), led to the continental rupture and oceanization of the Tyrrhenian area. Moreover, it enhanced the orogenic collapse of the Apennine tectonic wedge (Dewey, 1988), defining the onset of the second stage of intermontane basins in the Apennines.…”

Nonlinear P‐wave tomography of subducted lithosphere beneath central‐southern Apennines (Italy)

“…One of the most intriguing tectonic scenario in peninsular Italy is related to the subduction of lithosphere beneath central-southern Apennines, which is supposed to occur as a result of the eastward migration of the Adriatic-Ionian lithosphere after the continental collision between the European and Adria-African plates (Faccenna et al, 1996; and references therein). Indeed, the complex, almost continuous sub- final goal to better constrain the geometry of the subducted lithosphere.…”