GNGTS 2021 - Atti del 39° Convegno Nazionale

139 GNGTS 2021 S essione 1.3 METAMORPHIC AND DEFORMATION PATTERNS PRODUCED DURING AN OCEANIC SUBDUCTION: INSIGHTS FROM 2D NUMERICAL MODELS A. Regorda 1 , M.I. Spalla 1 , M. Roda 1 , J.-M. Lardeaux 2 , A.M. Marotta 1 1 Dipartimento di Scienze della Terra ’A. Desio’, Universita degli Studi di Milano, Milano, Italy 2 UMR Géoazur, Université Nice Sophia-Antipolis, Sophia-Antipolis, France We analyzed the distribution of pressure and temperature (P-T) conditions in different re- gions of a subduction complex by means of a 2D numerical model that simulates the evolution of an oceanic subduction until the continental collision. Regions with P-T conditions characteristic of different metamorphic facies have been explored to verify if subduction velocity can influence their distribution throughout the numerical simulation. Distribution patterns of strain rates and development of coronitic, tectonitic and mylonitic fabrics have also been investigated to analyze under which metamorphic facies conditions they can be developed easier. Our results show that different domains characterized by contrasting metamorphic condi- tions can be simultaneously recorded in different regions of the subduction complex, in agree- ment with the commonly observed coexistence of contrasted P-T conditions in orogenic belts, but in contrast with the widespread idea that different metamorphic series are representative of peculiar geodynamic scenarios. In particular, we recognized three domains characterized by contrasted Pressure/Temperature (P/T) ratios: (i) a first domain in the upper plate characterized by low to intermediate P/T ratios; (ii) a second domain located in the external part of the mantle wedge characterized by high P/T ratios; and (iii) a third domain in the internal portion of the mantle wedge characterized by high P/T ratios. In addition, we observed that metamorphic facies traditionally associated with continental collisional complexes can be also associated with ocea- nic subductions characterized by high velocities (5 and 8 cm/yr). We also verified that mylonitic fabrics can develop more frequently in metamorphic facies characterized by high P/T ratios, while coronitic fabric can be better preserved in metamorphic facies with low-to-medium P/T ratios. Corresponding author: alessandro.regorda@unimi.it