The role of trench retreat on the geometry and stress regime in the subduction complexes of the Mediterranean

Abstract

Numerical modelling of the Aegean and Calabrian subductions using geological reconstructions starting 75–80 Myr before the present reproduces the present‐day geometries of the slabs and mantle wedges imaged by seismic tomography. The change from a shallow subduction dip of about 15° from the surface to a depth of 200 km into a dip of 60° below this depth in the Aegean subduction is caused by the south‐west migration of the trench at the velocity of 3 cm/yr, obtained from GPS and geological data. The largest dip of 70° Calabrian subduction is caused by the termination of the active phase of opening of the Tyrrhenian back‐arc basin and by the essentially purely gravitational sinking of the slab, in agreement with the null trench‐migration velocity obtained from GPS data in Calabria. These two different tectonic settings are the ultimate causes of the different styles of seismicity within the two subduction complexes.

Gravity constraints on the dynamics of the crust-mantle system during Calabrian subduction

“…The characteristic dipolar gravity pattern in the arctrench region is shaped by the sinking of light material, belonging to both the overriding and subduction plates. The striking agreement between data and prediction confirms the correctness of the kinematic hypotheses considered in our modelling and firstly proposed in Rizzetto et al (2004). Our comparative analysis supports the hypothesis that the present-day configuration of crust-mantle system below the Calabrian arc results from trench's retreat at a rate of about 3 cm yr −1 , followed by gravitational sinking of the subducted slab in the last 5 Myr.…”

“…Initial and boundary conditions are the same as in Marotta et al (2006), except for the prescribed relative velocity between the two plates during the difference phases of the evolutions of the system. Following Rizzetto et al (2004) and the references therein, we assume an initial convergence phase at a rate of 1 cm yr −1 lasting 60 Myr, followed by a second phase during which the trench retreats at a rate of 3 cm yr −1 . A final phase of 5 Myr, during which a purely gravitational sinking of the subducted slab occurs, is also considered.…”

Arc‐parallel strain in a short rollback‐subduction system: The structural evolution of the Crotone basin (northeastern Calabria, southern Italy)

“…This extension is concentrated in the arc‐perpendicular basins, forming a boudinage of the forearc. This interpretation also implies that subduction has not ended [ Westaway , 1993; Rizzetto et al , 2004; Neri et al , 2009], but has passed the chokepoint.…”

Pacific trench motions controlled by the asymmetric plate configuration

“…The concept of slabs sinking into the mantle more or less vertically, i.e., with a motion vector steeper than the dip of the slab, explained the existence of several subduction‐back‐arc systems without significant plate convergence such as the Mediterranean subduction zones [e.g., Malinverno and Ryan , 1986; Gautier et al , 1999; Faccenna et al , 2001; Faccenna et al , 2004]. In the past years, studies on the dynamics of trench‐normal slab motions have been fuelled by advanced physical models, the possibility to image ductile deformation in the upper mantle through seismic data, and the advent of cheap powerful computers allowing for two‐ and three‐dimensional numerical modeling of subduction processes [ Rizzetto et al , 2004; Funiciello et al , 2004; Gurnis et al , 2004; Enns et al , 2005; Pysklywec and Ishii , 2005; Funiciello et al , 2006; Stegman et al , 2006; Schellart et al , 2007]. Slab retreat is often viewed as resulting from slab pull overpressuring the viscous mantle beneath the subducting plate and thus driving flow around the slab into the domain of the overriding plate.…”