The dynamics of forearc - back-arc vertical motion: numerical models and
observations from the Mediterranean
Abstract
The evolution of subduction zones influences the rise and demise of
forearc and back-arc basins on the overriding plate. We conducted 2D
elasto-visco-plastic numerical models of oceanic subduction and
subsequent continental collision which include erosion, sedimentation,
and hydration processes. The models show the evolution of wedge-top and
retro-forearc basins in the continental overriding plate, separated by a
forearc high. These forearc regions are affected by repeated compression
and extension phases. Higher subsidence rates are recorded in the
syncline structure of the retro-forearc basin when the slab dip angle is
higher and the subduction interface is stronger and before the slab
reaches the 660 km upper-lower mantle discontinuity. The 3-4 km negative
residual topographic signal is produced by the gradually steepening
slab, which drags down the overlying upper plate. Extensional back-arc
basins are either formed along inherited crustal or lithospheric weak
zones at large distance from the arc region or are created above the
hydrated mantle wedge originating from arc rifting. Back-arc subsidence
is primarily governed by crustal thinning controlled by slab roll-back.
Onset of collision and continental subduction is linked to the rapid
uplift of the forearc basins; however, the back-arc region records
ongoing extension during the initial phase of soft collision. Finally,
during subsequent hard collision both the forearc and back-arc basins
are ultimately affected by compression. Our modelling results provide
insights into the evolution of Mediterranean subduction zones and
propose that the Western-Eastern Alboran, Paola-Tyrrhenian,
Transylvanian-Pannonian Basins should be considered as genetically
connected forearc –back-arc basins, respectively.