A Pliocene-Quaternary compressional basin in the Interandean Depression, Central Ecuador

Resumen

T h e segment of the Interandean Depression of Ecuador between Ambato and Quito is characterized by an uppermost Pliocene-Quaternary basin, which is located between two N-S trending reverse basement faults: the Victoria Fault t o the west, and the Pisayambo Fault to the east. T h e clear evidence of E-W shortening for the early Pleistocene (between 1.85 and 1.21 Ma) favours a compressional basin interpretation. The morphology (river deviations, landslides, folded and flexure structures) demonstrates continuous shortening during the late Quaternary. T h e late Pliocene-Quaternary shortening reached 3400 f 600 m with a rate of 1.4 f 0.3 m m yr-'. T h e E-W shortening is kinematically consistent with the current right-lateral reverse motion along the NE-SW trending Pallatanga Fault. T h e Quito-Ambato zone appears t o act as a N-S restraining bend in a system of large right-lateral strike-slip faults. T h e compressive deformation. which affects the Interandean Depression during the Pliocene is apparently coeval t o the beginning subduction of very young oceanic lithosphere north of the Gulf of Guayaquil. The relatively buoyant new crust may have significantly increased the mechanical coupling in the subduction zone from Pliocene t o Present.