Phreatomagmatic and phreatic eruptions in locally extensive settings of Southern Central Andes: The Tocomar Volcanic Centre (24°10′S–66°34′W), Argentina

Two Pleistocene eruptions are studied, linked to an increment in the tectonic activity of an extensive system related to Calama–Olacapato–El Toro Fault (COT Fault). The first one, consisting of dense pyroclastic flows and pyroclastic surges interbedded with fall deposits, was caused by a phreatoplinian eruption. The second one, consisting of a succession of pyroclastic surges, derived from a phreatic eruption. Both eruption vents have been located in en echelon normal faults with an NNE trend, and conjugated to strike faults following an NNW trend. In both episodes pyroclastic deposits and ballistic blocks follow an E–SSE trend, the direction to which the fault planes and topographical slope lean. The obsidianic deposit filling the first eruption vent has the same trend and dip as the main fault plane and provides (preliminary) evidences of syntectonic emplacement. On the other hand, pyroclastic surge deposits linked to the second episode offer evidences of syndepositional faulting with listric growth faults. It is concluded that this local horizontal area linked to the COT fault was intensely active during the Pleistocene and triggered both eruptions.