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Palaeogene deformations of the forearc zone of south Ecuador in relation to the geodynamic evolution

Abstract:

The coastal zone of Ecuador is constituted by terranes of oceanic origin accreted to the continental margin and supporting three successive island arcs. Collision occurred during latest Palaeocene-earliest Eocene, with an east-dipping tectonic contact. This was followed by the creation of forearc basins in an extensional regime (≈ middle Eocene). The basins were deformed and became emergent during a second compressional event of late Eocene age. The latter deformed the former tectonic contact which becomes locally west-dippoing. These tectonic events coincide with important changes in the rate and/or direction of convergence, expressed by jumps of magmatic arcs. Creation of the forearc basins, considered as a consequence of tectonic erosion of the continental margin, seems to follow compressional crisis. We propose that tectonic erosion is favoured by the compressional crisis, and that the subsidence of the forearc tones occurs after the release of the compressional stress.