Evolution of the Manabí forearc basin in Ecuador: from the accretion of oceanic allochthonous terranes to the uplift of the Andes and Coastal Cordilleras

National audience; Along the Ecuadorian convergent margin, the onshore Manabí sedimentary forearcbasin is bounded to the east by the foothills of the Andes, while to the north and west, itis limited by the Canandé and Jama fault systems. The fault systems limit basementblocks resulting from the fragmentation of an oceanic plateau topped by island arcs,which were accreted against the continental margin during the Late Cretaceous toEocene times. From the interpretation of 2D seismic reflection profiles we identify thesyn- and post-accretionary tectonic phases recorded in the Manabí basin area. Werecognize 9 seismic units (S1 to S9) above the acoustic basement (Ub) separated by 9unconformities (U1 to U9), which were dated by the correlation with the Ricaurte-1well and regional stratigraphy.Seismic units S1-S2 (Late Cretaceous to Eocene) onlap irregular basement topographyinterpreted as inheritance of eroded island arcs prior to accretion. S1 is deformedby low angle NE-dipping thrust faults, which were sealed by regional unconformity U1.This unconformity is tentatively dated ~75 Ma and correlated with an early stage ofcollision. Then, E-dipping reverse faults were developed in the foothills of the Andesand are associated to an erosional and sedimentary hiatus (U2, Early-Middle Eocene),marking the last stage of accretion. The development of the modern forearc basin ismarked by S3 deposition (Oligocene), which extends beyond the current edges of thebasin. Then the overlying S4 depocenter (Early Miocene) migrated eastward as a resultof the higher subsidence and depositional rates associated to the orogenic buildingeffects of the Andean reliefs. An extensional stage is evidenced by a fan shape of S5(17.8 -15.9 Ma) against the Jama fault. After U5 (top dated 15.9 Ma) and up to U8 (~5Ma), a sedimentary platform was built by NW sedimentary progradation, thus markinga remarkable change in the mode of basin filling. The Coastal Cordillera uplifts during aPliocene compressional stage (post S8) marked by a antiform development along theJama fault system, and the uplift of the footwall block of the Canandé fault.Synchronously, Santo Domingo fan developed at the foot of the Andes causing theeastward down flexing of flat erosional surface U9. This stage coincides with the arrivalin subduction of the Carnegie ridge.