A. Chiodi

Polycyclic scoria cones of the Antofagasta de la Sierra basin, Southern Puna plateau, Argentina

Abstract Despite a number of published papers focusing on the geodynamic implications of the recent Southern Puna mafic magmatism, there have been fewer studies of the volcanology and stratigraphy of this outstanding volcanism. This paper presents a detailed map of two well-preserved Quaternary scoria cones showing their complex stratigraphy. Complementary morphometric, morpho-structural, petrographic and geochemical data were used to reconstruct the evolution of both volcanoes. The occurrence of more than one eruption at each volcano was inferred by the recognition of temporal hiatuses using morpho-stratigraphic criteria. The polycyclic nature of both scoria cones could be related to a combination of a high input magma in response to lithospheric delamination, a favourable regional stress field and the interaction of rising magma with pre-existing faults. The youngest eruptions in both volcanoes were complex, with shifts in the eruptive style from violent strombolian to hawaiian/strombolian phases, and probably lasted for a few years. The explosive activity was accompanied by the emission of lava flows from lateral vents. Phreatomagmatic activity was triggered during the waning stages of the eruptions. The occurrence of more than one eruption in a single scoria cone and the changes in the eruptive style during long-lasting eruptions are important topics for volcanic hazard assessment in the Southern Puna.