The Dynamics of Forearc – Back‐Arc Basin Subsidence: Numerical Models and Observations From Mediterranean Subduction Zones

Abstract

The subsidence history of forearc and back‐arc basins reflects the relationship between subduction kinematics, mantle dynamics, magmatism, crustal tectonics, and surface processes. The distinct contributions of these processes to the topography variations of active margins during subduction initiation, oceanic subduction, and collision are less understood. We ran 2D elasto‐visco‐plastic numerical models including surface and hydration processes. The models show the evolution of wedge‐top and retro‐forearc basins on the continental overriding plate, separated by a forearc high. They are affected by repeated compression and extension phases. Compression‐induced subsidence is recorded in the syncline structure of the retro‐forearc basin from the onset of subduction. The 2–4 km upper plate negative residual topography is produced by the gradually steepening slab, which drags down the upper plate. Trench retreat leads to slab unbending and decreasing slab dip angle that leads to upper plate trench‐ward tilting. Back‐arc basins are either formed along inherited weak zones at a large distance from the arc or are created above the hydrated mantle wedge originating from arc rifting. Back‐arc subsidence is primarily governed by crustal thinning that is controlled by slab roll‐back and supported by the underlying mantle convection. High subduction and mantle convection velocities result in large wavelength negative dynamic topography. Collision and continental subduction are linked to the uplift of the forearc basins; however, the back‐arc records ongoing extension during a soft collision. During the hard collision, both the forearc and back‐arc basins are ultimately affected by the compression. Our modeling results provide insights into the evolution of Mediterranean subduction zones.

Back-arc basins: A global view from geophysical synthesis and analysis

“…The evolution of the Southern Tyrrhenian back-arc basin, conventionally ascribed to slab roll-back and possibly promoted by the upper mantle flow (e.g. Doglioni, 1991;Panza et al, 2007;Carminati et al, 2012;Balázs et al, 2022) (Fig. 2c), was complicated by the collision of the African and the Eurasian Plates (Doglioni et al, 1997(Doglioni et al, , 2009.…”

“…There seems to be little consensus on the extent of isostatic equilibrium in various marine back-arc basins. A large amplitude of free-air gravity anomalies implies a disturbed isostatic equilibrium in most of the backarc basins with many geophysical studies advocating an importance of dynamic topography (Martínez et al, 1999;Abers et al, 2002;Conder and Wiens, 2007;Kneller and van Keken, 2008;Long and Wirth, 2013;Magni, 2019;Balázs et al, 2022). Other studies (smaller in number) favour the isostatic equilibrium (Horváth et al, 1981;Tontini et al, 2007;Molnar et al, 2015), and gravity modeling based on the isostatic principle is still often used to infer the BABs crustal thickness (Tirel et al, 2004;Liu et al, 2016).…”

“…The effect of mantle melting on anomalous bathymetry in back-arc basin settings has been extensively analyzed in geochemical studies (Woodhead et al, 1993;Taylor, 1995;Taylor and Martinez, 2003;Kelley et al, 2006;Mibe et al, 2011;Li et al, 2022), geophysical studies (Cross and Pilger, 1982;Sdrolias and Mueller, 2006;Kneller and van Keken, 2008;Long and Wirth, 2013;Balázs et al, 2022), and numerical simulations (Billen and Gurnis, 2001;Gerya and Yuen, 2003;Syracuse et al, 2010;Lee and Wada, 2017;Magni, 2019). Nonetheless, the density structure of the BABs mantle remains speculative.…”

The Effect of Magma Poor and Magma Rich Rifted Margins on Continental Collision Dynamics

“…However, some models of continental collision completely ignore the presence of rifted margins by modeling an abrupt transition from continent to ocean (e.g., Magni et al., 2012; van Hunen & Allen, 2011). Other subduction models do incorporate a gradual transition from continent to ocean, but they do not discriminate between magma‐poor and magma‐rich margins nor discuss in details the effect that this transition has on subduction zone processes, such as topography, delamination and slab detachment (e.g., Balazs et al., 2022; Boonma et al., 2023; Duretz et al., 2011; Duretz et al., 2014; Duretz & Gerya, 2013; Erdős et al., 2022; Francois et al., 2014; Ueda et al., 2012). Importantly, the geometries and physical properties of rifted margins can be much more complex than a gradual transition (Kjøll, Galland, et al., 2019; Williams et al., 2019), and this complexity will be reflected in the subduction dynamics, suggesting the need to consider it in modeling studies.…”

Lithospheric Structure of the Circum‐Pannonian Region Imaged by S‐To‐P Receiver Functions

“…The pre‐rift orogenic crust and lithosphere were derived from the Alpine collisional zone and underwent Miocene thinning governed by the Carpathians slab roll‐back. This retreating subduction and subsequent collision resulted in coeval contraction in the Carpathians and extension in the Pannonian back‐arc (Balázs et al., 2022; Harangi & Lenkey, 2007; Horváth et al., 2015; Mațenco et al., 2016). Most previous studies focused on the sedimentary infill, thermal and subsidence evolution (Balázs et al., 2021; Lenkey, 1999), fault geometries (Bada et al., 2007; Fodor et al., 2021; Koroknai et al., 2020; Tari et al., 1999), volcanism (e.g., Harangi et al., 2006), Moho discontinuity (Bielik et al., 2006; Horváth et al., 2015) and the internal crustal structure (Kalmár et al., 2021) beneath the wider study area.…”