Calabrian Arc present-day regional deformation in the surroundings of the Block model versus thermomechanical model: new insights on the Geological Society, London, Special Publications

A finite-element thermomechanical model is used to analyse present-day crustal deformation in the surroundings of the Calabrian Arc. The major structural complexities of the Tyrrhenian area are taken into account, along with the rheological properties of the rocks resulting from a thermal analysis. A comparison between the results obtained from a model composed of three wide rheologically uniform blocks and those obtained from the thermomechanical model allows us to better constrain the geophysical assumptions and shed light on the roles of the different active mechanisms acting in the Tyrrhenian. Our comparative analysis enlightens the crucial role played by lateral rheological heterogeneities when deformation is analysed at short wavelengths of a few hundred kilometres of the Tyrrhenian, driving the observed diffuse SW–NE extension within the regional context of active Africa–Eurasia convergence. Furthermore, a x analysis based on comparisons with GPS data confirms the hypothesis that a significant part of the Africa–Eurasia convergence is absorbed through the Calabrian subduction. Present-day crustal deformation in the Tyrrhenian is the result of a complex interplay of various dynamic processes acting at both local (e.g. faults processes) and regional scales (e.g. Africa–Eurasia convergence and Calabrian subduction). A great variability in thermal regime, surface heat flow (Pollack et al. 1993; Artemieva & Mooney 2001; Artemieva 2006) and crustal thickness (Bassin et al. 2000; Tesauro et al. 2008) also characterizes the central Mediterranean and the Italian Peninsula, inducing horizontal heterogeneities in the rheology through the Tyrrhenian area. The combination of the different tectonic mechanisms and the rheological heterogeneities generates an enigmatic regional deformation pattern in which areas subjected to extension, such as the Tyrrhenian and Provencal basins, are embedded in areas subjected to compression and strong crustal thickening, such as the Alps and the Appennine. New advanced GPS (Global Positioning System) techniques and long geodetic time series make it possible to monitor this deformation with more accuracy at different length and timescales. In addition, geodetic data better constrain the geophysical forward modelling (e.g. Jiménez-Munt et al. 2003; Marotta et al. 2004; Negredo et al. 2004; Wang & Zheng-Ren 2006) used to test different geodynamic hypotheses in the area that were originally constrained using the geological global models NUVEL-1 or NUVEL-1A (DeMets et al. 1994; DeMets & Dixon 1999). The inadequacy of global models NUVEL-1 and NUVEL-1A in reproducing present-day relative plate motion has been widely demonstrated by several recent geodetic and numerical studies (among others, Sella et al. 2002; Fernandes et al. 2003; Nocquet & Calais 2003; Kremer et al. 2003; Marotta & Sabadini 2008). In Marotta & Sabadini’s (2008) comparative analysis, the authors show that the geodetically constrained tectonic models in the Tyrrhenian area predict a regional deformation that is in better agreement with the observed deformation compared to models constrained with geological data. However, one major limitation of Marotta and From: SPALLA, M. I. , MAROTTA, A. M. & GOSSO, G. (eds) Advances in Interpretation of Geological Processes: Refinement of Multi-scale Data and Integration in Numerical Modelling. Geological Society, London, Special Publications, 332, 129–147. DOI: 10.1144/SP332.9 0305-8719/10/$15.00 # The Geological Society of London 2010. Sabadini’s model is the lack of an appropriate coupling between the rheological properties of the lithosphere and the regional thermal field. One main advancement characterizes the present tectonic analysis with respect to Marotta & Sabadini (2008). This approach accounts for three wide rheological uniform units: the stiff East Europe platform (light grey in Fig. 1a); the European plate (intermediate grey in Fig. 1a); and the soft Mediterranean domain (dark grey in Fig. 1a). Marotta et al. (2004) show that a rheological averaged block model can reproduce the observed deformation at the long wavelengths ranging from several hundred to thousands of kilometres. However, when deformation is analysed at the shorter wavelengths of a few hundred kilometres, a deeper knowledge of lithosphere rheology is needed. Within a more localized analysis focused on the Tyrrhenian, Marotta & Sabadini (2008) showed, for example, that a further rheological differentiation between the Tyrrhenian and the Adria microplate (either as an unique block or subdivided into two blocks) is needed to predict at least part of the extensional component of the strain-rate tensor observed within the Tyrrhenian. To improve this analysis a detailed thermal analysis is performed in the present study with the aim of evaluating a rheological structure of the lithosphere, relative to the Mediterranean, that is more realistic than that in Marotta & Sabadini (2008). The results of the present analysis will be discussed in comparison to the models of Marotta et al. (2004) and Marotta & Sabadini (2008), referred to as the ‘block model’ for the remainder of this paper.