THE IMPORTANCE OF SUBDUCTION FOR THE MODERN STRESS-FIELD IN THE TYRRHENIAN AREA

The Tyrrhenian sea was formed by lithospheric extension ir. a context of continental convergence between Africa and Eurasia. At present, a c ompilation of strain and stress indicators in this region by Rebai et al. (1992) shows that an extensive regime is still predominant in the Tyrrhenian sea while northern Italy and southern Sicily are undergoing compression. This tectonic configuration is the result of two major c ontributions which act on a very heterogeneous lithosphere: the Africa -Eurasia collision, on the one hand, and the subduction along the Cala brian arc, on the other. The latter is expected to create a 'trench su ction force' on the overriding Tyrrhenian plate. The objective of this paper is to investigate the relative importance of these contribution s using a numerical model developed by P. Bird (1989) based on an impr oved version of the 'thin plate' approach which models lithospheric de formation in an horizontal plane. The results of this model demonstrat e the necessity of considering the forces related to subduction to und erstand the modem stress and strain field. An extrusion mechanism alon e cannot explain present-day observations. The salient features of the current tectonic regime are reproduced by the model which, however, p redicts more limited extension than expected. Further work will be nee ded to find a better tuning of the parameters and ascertain the qualit y of available data.