Rifting and subsidence following lithospheric removal in continental back arcs

It has been suggested that post-orogenic lithospheric removal in continental back arcs promotes extension and surface subsidence. However, the surface response of this process and its primary difference from "classical" back-arc opening have remained uncertain. Here, the back-arc extension process with varying continental mantle lithosphere thickness and thermal heterogeneities is studied by using thermomechanical subduction experiments. The experiments illustrate that models with only slab retreat result in minor surface subsidence and extension in the back-arc region. Alternatively, there is notable extension due to the slab retreat and a localized high-temperature zone in the back arc with uniform lithospheric thickness. Models with advecting mantle (after lithospheric removal) in the extending back arc predict rifting (stretching factor β > 2) and surface subsidence (>1.5 km) in the center of the basin. The results of this work suggest that lithospheric removal may be an important trigger for continental back-arc development rather than slab retreat alone causing lithospheric extension and subsidence. The findings help explain rift formation and subsidence in the Aegean Sea-west Anatolia, and possibly other Mediterranean back arcs, such as the Alboran Sea and the Pannonian Basin.