Structural evolution of the southern Ecuadorian forearc in the Santa Elena Peninsula region
Résumé
The southern Ecuadorian forearc system is related to the subduction of the oceanic Farallon/Nazca Plate beneath
the continental South American Plate since the Late Cretaceous, and currently evolves with the dynamic of a
tectonic block called North Andean Sliver. To explore the structural architecture and processes controlling the
Upper Cretaceous-Cenozoic growth of the forearc, we built a ~143 km-long onshore-offshore crustal-scale crosssection
in the Santa Elena Peninsula region using seismic reflection profiles and well and field data. The structure
of the Santa Elena Peninsula forearc system is controlled by imbrication of Upper Cretaceous-Palaeocene oceanic
basement and Cenozoic sedimentary units, and underplating of distal Cenozoic sequences stacked at the trench
zone. This led to the progressive construction of an accretionary wedge through time. The forearc substratum is
mainly formed by the Upper Cretaceous-Palaeocene basement developed during the docking of oceanic terranes.
It is later deformed by NW-trending landward-dipping, normal to strike-slip faults during the Middle Eocene, and
renewed compression by inversion of inherited faults from the Oligocene onwards. Recent deformation consists
in N-trending oceanward-dipping normal faults in the frontal slope domain and fault-controlled uplift of marine
terraces along the coastal area. Therefore, the Upper Cretaceous to present-day structural evolution of the Santa
Elena Peninsula forearc is controlled by the long-lasting subduction dynamics and structural inheritance of the
upper plate.