Geodynamic modelling of lithospheric slab tearing and its topographic response. Application to the Gibraltar Arc

GeoMod 2021 conference , September 19-23, Utrecht, The NetherlandsEarth¿s mantle, has been proposed as a cause of significant surface vertical motions. Although this has been linked to the change implied in the isostatic balance in subduction zones, little is known about the mechanisms and rock properties determining the tear propagation and the uplift-subsidence rates involved. This work aims to explore the link between the tearing of subducted lithospheric slabs and the associated vertical motions. To this purpose, we numerically simulate the process of lithospheric tearing upon continental collision, using the Betic Cordillera as a reference scenario where such tearing-uplift interaction has been proposed for this region. We used 3D thermo-mechanical numerical modelling to investigate the geodynamic parameters affecting the slab-tearing initiation and its lateral propagation, and to quantify the corresponding surface vertical motions. The Betics-inspired model suggests that the obliquity of the continental passive margin (relative to the trench axis) is a major influence on the initiation of slab tearing because it promotes a laterally diachronous continental collision which leads to slab tearing. The model illustrates an east-to-west slab tearing (tearing velocity ~ 37.6¿67.6 cm/yr with the lower-mantle viscosity of up to 1022 Pa·s), which leads to surface uplift signature of 0.5¿1.5 km across the forearc region throughout the tearing process. While the fast slab tearing (< 2 Myr over 600 km wide slab) and the lack of arcuate slab of these models limit a direct comparison with the Western Mediterranean, this approach provides a new insight into the link between slab tearing in the mantle and surface uplift. These experiments yield uplift rates of 0.23¿2.16 mm/yr, as a result of slab tearing, which is compatible with the uplift rate needed to achieve an equilibrium between seaway-uplift and seaway-erosion which could have led to the closure of marine gateways that reduced the water-flow from the Atlantic Ocean into the Mediterranean Sea during the first stage of the Messinian Salinity Crisis