This study focuses on the construction and evolution through time of volcanic edifices located in the southern part of the Ecuadorian arc, with the objective to contribute to a better understanding of the interactions between magmatism, slab geometry and the activity of tectonic faults. Our new groundmass K-Ar ages obtained for a dozen volcanoes from the southern Quaternary arc are rather young, without ages older than 800 ka, and highlight an increasing volcanic activity between 300 and 100 ka. These new temporal constraints suggest that a southward migration of the Ecuadorian arc occurred during the last 600 ka. We interpret this evolution as the result of major and recent geodynamic reorganization in Ecuador related to the activation of lithospheric faults and to the flexure of the slab at depth, following the inland prolongation of the Grijalva fracture zone. Both phenomena could have been induced by the oblique subduction of the Nazca plate towards the convex margin of the South American continent, and the coupling of these two plates along the Wadati-Benioff zone, progressively intensified by the Carnegie ridge subduction. Southward migration of the slab flexure at depth could have changed pressure and temperature conditions, favoring the partial melting of the mantle wedge and magma genesis, thereby inducing a southward migration of the Ecuadorian arc volcanoes. These results contribute therefore to a better knowledge of the current arc dynamics in the Northern Andes, and provide insights into the use of geochronological data applied to volcanic rocks for studies of past tectonic activity in Ecuador.