GNGTS 2021 - Atti del 39° Convegno Nazionale

133 GNGTS 2021 S essione 1.3 THE RECENT DYNAMICS OF THE CENTRAL MEDITERRANEAN CONSTRAINED BY COUPLED GEODYNAMIC-SEISMOLOGICAL MODELLING R. Lo Bue, M. Faccenda, J. Yang Dipartimento di Geoscienze, Università degli Studi di Padova, Italy The Central Mediterranean region in the Tertiary was characterized by intermittent pha- ses of subduction and collision, the opening of back-arc extensional basins (i.e., Liguro-Pro- vençal, Alboran, and Tyrrhenian basins) and episodes of slab lateral tearing, segmentation and break-off that led to the currently complex geological setting. Although the shallow tectonic evolution of the region has been relatively well constrained by abundant geological data, the mechanisms that generated the present-day surface and deep slab geometry remain unclear. Among the aspects of the geodynamic history that have not yet been fully clarified there are (i) the development and evolution of the episodes of slab tearing and segmentation along the western Adria and northern Africa plate margins, and (ii) the links between mantle dynamics and plate surface and deep kinematics. The latter can be estimated by measuring seismic ani- sotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrin- sically anisotropic minerals. Seismic anisotropy is widespread in the Mediterranean and it shows an intricate pattern that likely has some relations with the recent (20-30 Myr) behavior of subducting slabs. The extrapo- lation of the mantle flow from seismic anisotropy is neither simple nor always warranted, espe- cially at subduction zones where complex and non-steady-state 3D flow patterns may establish. A promising approach, which helps reducing the number of plausible models that can explain a given anisotropy dataset, is to compare seismic measurements with predictions of numerical flow models (Long et al.,2007). Recently, Faccenda and Capitanio (2012, 2013) have extended this methodology to account for the non-steady state evolution typical of many subduction zo- nes, yielding mantle fabrics that are physically consistent with the deformation history. In this study, we apply a similar modelling approach to the Central Mediterranean convergent margin. We investigate the subduction evolution of the Central Mediterranean region during the last ~20-30 Myr through numerical modelling. The modelling focuses on the reconstruction of the mantle flow history beneath the region and its relation to the present-day anisotropy patterns. Specifically, the method combines macro-scale geodynamic modelling of the Mediterranean subduction system with micro-scale simulations of strain-induced upper mantle fabrics and sei- smological synthetics. 3D petrological-thermo-mechanical numerical models have been carried out using the viscoplastic code I3MG (Gerya, 2019), to compute the LPO and the synthetic SKS splitting we use a modified version of D-REX (Kaminski et al., 2004) and the softwares package FSTRACK (Becker, 2006), respectively. The subduction models were designed and calibrated according to paleogeographic-tectonic reconstructions of 30 Ma (Lucente and Speranza, 2001; van Hinsbergen et al., 2014) and seismo- logical observations from the Mediterranean region available in the literature. We test different initial configurations in order to optimize the fit between predicted and observed slabs position and obtain a final model configuration resembling the present-day surface and deeper structu- res. The initial numerical models (Fig. 1) consist of a subducting oceanic plate which represents the Ionian Ocean, two lateral continental blocks corresponding to the Adria and Africa plates, and an overriding plate that corresponds to the Iberia, Sardinia-Corsica and European plates. To initiate subduction self-consistently, a wide slab is located from Gibraltar to Corsica dipping 40° and extending down to 300 km in the upper mantle. In some models the Adria plate structure, located in the current Apenninic area, is characterized by the presence of a stiffer continental promontory in its central portion and of a thin continental lithosphere in the Umbria-Marche