Blossoming of the Pleistocene volcanism in the Ecuadorian Andes: a review based on new and recent geochronological data

The Ecuadorian arc is composed of an unusually high number of volcanoes organized as along-arc alignments and across-arc clusters, over a relatively small area. Although several geochronological studies were carried out in the past three decades, the eruptive history of the central zone of the arc remained poorly documented, preventing the analyses of volcanism initiation of the whole arc. In this study, we present new K-Ar ages obtained from this central area, referred as the Quito segment. These results were then included in an updated comprehensive geochronological database including about 250 ages, allowing us to describe, at the arc scale, the spatial and temporal development of Quaternary volcanic activity in Ecuador. About eighty Quaternary volcanoes are identified in the Ecuadorian Andes, amounting to 45 volcanic complexes with radiometric ages and/or identified as active or potentially active. The volcanic arc developed in three stages marked by increases in the total number of active volcanoes. During the oldest Plio-Early Pleistocene stage, the documented volcanic activity was mostly concentrated in the Eastern Cordillera of the Quito segment, with minor effusive eruptions in the southern Back-Arc. Since ~ 1.4 Ma, the activity spread to the surroundings of the Quito segment and new edifices also appeared in the Western Cordillera and the Inter-Andean Valley. Towards the end of this intermediate stage (i.e., ~ 800 ka), volcanism occurred in isolated areas to the north and south of the Inter-Andean Valley. Finally, the late and current stage was characterized by a remarkable increase in volcanic activity since ~ 600 ka. Approximately 50 volcanoes were active during this stage. The spatial distribution of the Ecuadorian arc volcanism seems to be guided by deep mechanisms and old crustal tectonic structures from the Western Cordillera, whereas the neotectonics seem to influence the development of stratovolcanoes. In addition, we note that the spatial and temporal evolution of volcanism highlights the influence of the Carnegie Ridge and the thermal regime anomaly of the young Nazca crust on the increase of volcanic activity in Ecuador.