CONICET | Buscador de Institutos y Recursos Humanos

The Plio-Pleistocene Llancanelo Volcanic Field (LVF) is located in the south-eastern region of the province ofMendoza, Argentina. This wide back-arc lava plateau, with hundreds of monogenetic pyroclastic cones, covers animportant area behind the active Andean volcanic arc. Here we focus on the northern LVF, particularly in Las Bombas(LB) volcano. LB volcano is an eroded but still recognizable scoria cone located in a circular depression surrounded bya basaltic lava flow, suggesting that LB volcano was there when the lava flow field formed and therefore the lava flowengulfed it completely. While this explanation seems reasonable, the common presence of similar landforms in thispart of the field justifies the need to establish correctly the stratigraphic relationship between lava flow fields and thesecircular features on it. The principal aim of this work is to investigate LB volcano 3D subsurface architecture by meansof geophysical methods. We carried out a paleomagnetic study and detailed topographic, magnetic and gravimetricland surveys. A circular relative negative complete Bouguer anomaly was detected beneath LB scoria cone. Thenegative anomaly indicates the existence of a mass deficit. This deficit would be related to the presence of fracturezones below LB volcano cone due to sudden degassing of younger magma beneath it or to a single phreaticexplosion. Magnetic anomalies of normal and reverse polarity point to the occurrence of two different episodes ofvolcanic activity. Paleomagnetic results further constrained the chronologic order of the genetic processes, suggestingthat LB scoria cone is younger than the sorrouding basaltic lava flow field. Our results provide new and detailedinformation about LB volcano subsurface architecture

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