Timing of Quaternary volcanism and its relationship with tectonics in the central segment of the Ecuadorian Andes

The unusually high number of volcanoes in the Ecuadorian Arc, located in the deformation zone of the continental North Andean Sliver, coincides with the projection of the major oceanic structures observed in the Nazca Plate, such as the Carnegie Ridge and the Grijalva fracture zone. Although the relationship between this tectonic setting and volcanism has been widely discussed in the literature, their temporal relationship has not been thoroughly investigated due to the lack of geochronological data. We present here 20 new KAr and 2 40Ar/39Ar ages obtained for 7 volcanoes of the central segment of the Ecuadorian arc, which together with previous data show that volcanism in this area started at ∼1.3 Ma. A notable increase in volcanic activity occurred since ∼0.6 Ma, when the formation of a dozen volcanoes occurred in a relatively small area of the central segment. While this arrangement of volcanoes, here referred to as a “volcanic cluster”, appears to be controlled by crustal tectonic structures, the order of onset of these volcanoes and their eruptive activity does not show clear migration patterns over time. However, the presence of older volcanoes in the north of the central segment suggests a possible southward extension of volcanism between ∼1.3 and ∼ 0.6 Ma. Finally, based on the cumulative bulk volumes calculated for the volcanic edifices over time, we infer that the magmatic productivity rate has been roughly constant during the last ∼550 kyr in this area.