PALEOGENE DEFORMATIONS OF THE FORE-ARC ZONE OF SOUTH ECUADOR IN RELATION TO THE GEODYNAMIC EVOLUTION

The coastal zone of Ecuador is constituted by terranes of oceanic orig in accreted to the continental margin and supporting three successive island arcs. Collision occurred during latest Palaeocene-earliest Eoce ne, with an east-dipping tectonic contact. This was followed by the cr eation of forearc basins in an extensional regime (approximate to midd le Eocene). The basins were deformed and became emergent during a seco nd compressional event of late Eocene age. The latter deformed the for mer tectonic contact which becomes locally west-dipping.These tectonic events coincide with important changes in the rate and/or direction o f convergence, expressed by jumps of magmatic arcs. Creation of the fo rearc basins, considered as a consequence of tectonic erosion of the c ontinental margin, seems to follow compressional crisis. We propose th at tectonic erosion is favoured by the compressional crisis, and that the subsequent subsidence of the forearc zones occurs after the releas e of the compressional stress.