“POLYCYCLIC” VOLCANOES: INFERENCES FROM FACIES ANALYSIS AND INTERNAL ARCHITECTURE OF EL CARRIZAL DIATREME, SALTA GROUP, CRETACEOUS-PALEOGENE RIFT IN NORTHWESTERN ARGENTINA

OLIVIA ARENAS; MARCELO ARNOSIO; EMILCE BUSTOS; WALTER BAEZ

Congreso; Cities on Volcanoes 12; 2024

Maar-diatreme volcanoes, the most abundant volcanic structures on Earth's surface after scoria cones, have traditionally been linked with short-duration eruptions, low volume, and simple, dispersed feeding systems. Recent research has unveiled the complexity of monogenetic volcanism, exemplified by polycyclic maardiatreme volcanoes. These structures result from numerous overlapping eruptive events within a confined area and at different times. The Cretaceous-Paleogene rift in northwestern Argentina provides remarkable records of both effusive and explosive volcanic activity related to the Salta Group. This study aims to contribute to the understanding of maar-diatreme evolution through detailed identification and mapping ofdifferent facies. The research involved analyzing stratigraphic relationships, lithofacies contacts, and internal deposit structures. Several facies were distinguished, including bedded pyroclastic deposits with bomb impacts, and massive and poorly sorted pyroclastic deposits. Bedded pyroclastic deposits represent upper diatreme facies, whereas massive pyroclastic deposits indicate lower diatreme facies. Three units were defined using the Units Bounded by Unconformities (UBSU) concept, representing diatremes with different exposure levels. The study revealed a complex system comprising three coalesced diatremes formed by distinct phreatomagmatic pulses. These findings support the concept that monogenetic volcanoes can be polycyclic, forming intricate structures through multiple separate eruptive events over time. Therefore, investigating the evolution of these ancient volcanoes constitutes a crucial tool to expanding our knowledge of the hazards and risks associated with active monogenetic volcanic fields.