Origin of a double forearc basin: The example of the Tumaco - Manglares basin, Northestern Southamerica

The subsidence and uplift history of the forearc system of southwestern Colombia and northern Ecuador margin is complex and reveals several stages of deformation. The sequential stratigraphy of the forearc area shows the development of three megasequences (M1 to M3). The basal megasequence corresponds to the basement of the forearc, which was formed at the end of the Mesozoic and at the beginning of the Cenozoic and accreted against the Northwestern part of South America related to the accretion of the Late Cretaceous – Paleoceneoceanic plateau. This accretion occurred in a transpressional regime. The second megasequence is composed by deep water sediments, recording the transition between transpressional to compressional stages of the margin from the Late Eocene to the Middle Miocene. The third megasequence is characterized by shallow water sediments strongly constrained by the compressional stage of the margin and the uplift activity of the structural highs since the Late Miocene up to present. The structural geometry of the margin is characterized by basement thrusts that deformed the forearc crust. Westward, the forearc zone -according to the support of the overriding plate -is divided into mantle wedge and lower plate domains. The margin evolution suggests that the subducting plate geodynamical changes affect strongly the interplate coupling and mantle wedge and produce changes in the subsidence or uplift through the double forearc basin systems.