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Volcano sector collapses are catastrophic events that can mobilize huge volumes of material and cause changes in the magmatic plumbing system, leading to variations in growth rate and/or composition. Dating pre-historic volcanic debris avalanche deposits is challenging. Geological materials directly recording avalanche formation and amenable to radiometric dating are rare, and, in the case of Holocene events, the applicable radiometric dating techniques are scarce. Socompa volcano suffered the largest collapse event in the Central Volcanic Zone of the Andes, producing one of Earth's most spectacular and best-preserved volcano avalanche deposits. We apply multiple dating techniques to unravel the timing of Socompa's collapse and gain insights into its pre- and post-collapse eruptive history. The age of the collapse event is constrained by a 14C age of 6,200–6,400 BP of a paleosol buried by the avalanche, and by a post-collapse lava flow dated at 5.91 ± 0.43 ka by zircon double-dating. Bayesian age sequence modeling integrating these ages determines that the collapse occurred at 6.18 - 0.64 + 0.28 ka. Four zircon eruption dates and one unspiked K–Ar age between 69.2 ± 6.0 and 22.1 ± 1.9 ka constrain the age of the youngest stage of activity before the collapse. The ages, together with paleosurface modeling and volume calculations, allow estimating growth rates for the young pre-collapse and post-collapse stages of ~ 0.2–0.3 km3/kyr and ~ 0.5–2 km3/kyr, respectively, indicating a significant increase in activity after the collapse event. The collapse may have triggered a new growth phase or accelerated an ongoing one and was likely associated with a Plinian eruption that produced widespread pumice fallout. The pre- and post-collapse lavas have similar compositions and zircon crystallization age distributions, suggesting that the same or a similar magma reservoir was tapped before and after the collapse. Thus, huge collapses such as Socompa's event can promote increased volcanic activity as a consequence of the unloading effect, but the overall plumbing system may not be affected enough to show significant variations in erupted compositions, at least transiently. Our results highlight the efficacy of the zircon double-dating method for dating very young felsic lavas and for constraining the age of debris avalanche deposits. This is particularly relevant in the Andean Central Volcanic Zone and other regions with arid climates, where organic material is rare and hence 14C dating is often unfeasible. Furthermore, the post-collapse zircon eruption age of 5.91 ± 0.43 ka is the youngest radiometric age yet obtained for a lava flow in the southern Central Volcanic Zone, highlighting the youth of volcanic activity at Socompa, and confirming its status as a Holocene active volcano. [ABSTRACT FROM AUTHOR]

Monogenetic volcanoes are small-volume landforms (< 1 km3) which can develop complex eruption histories. Their genesis may include variations in their primary magma sources and petrogenetic evolution, eruption styles transitions, changes in their emplacement conditions. The Central Andes (Northern Chile) contains >900 small-volume volcanoes, most of which lack a detailed knowledge of their eruption histories due to the limited volcanological studies available. In this paper, we present a detailed volcanostratigraphic, morphometric and petrologic study are used to reconstruct the geology and eruptive history of Cerro Negro volcano. It is a Pleistocene pyroclastic cone which stands out from all monogenetic volcanoes of this region due to its larger size (~1 km3) and location along the axis of the orogen. The activity of Cerro Negro began with a phreatomagmatic phase that produced breccias and a lithic-rich tuff, followed by magmatic activity with lava fountaining and Strombolian styles. This latter magmatic phase produced short lava flows, but mostly spatter agglutination and tephra fallout layers. The composition of erupted materials spans from calk-alkaline basaltic andesite to dacite. The least evolved magmas of Cerro Negro are derived from mantle wedge's partial melts without significant crustal assimilation. However, changes in the composition through the eruption suggest crystal fractionation and shallow magma storage, followed by mixing and crustal contamination during the late stage of the eruption. The absence of significant repose period between the deposition of the distinct products and their total volume together with the observed compositional variations imply that Cerro Negro represents a large volume polycyclic monogenetic volcano. These results are important to understand the mafic magma evolution in thickened crusts and the eruptive styles of long-lasting monogenetic eruptions. • Cerro Negro (CNV) is a c. 1 km3 (bulk volume) Pleistocene pyroclastic cone; it classifies as a large monogenetic volcano • CNV erupted in successive phreatomagmatic, lava fountaining and Strombolian phases; the eruption may have lasted years • CNV magmas were calk-alkaline (55.1 to 66.5 wt% SiO 2) and became more silicic as the eruption progressed • Magmas sourced from metasomatized spinel peridotite; polymagmatism involving fractionation, crustal assimilation and mixing [ABSTRACT FROM AUTHOR]

The Tilocálar volcanic complex comprises four monogenetic volcanoes located at the southeastern edge of the Salar de Atacama Basin, northern Chile. These monogenetic volcanic centers are the Tilocálar Norte lava, the El Maní dome, the Tilocálar Sur small–lava shield, and the Tilocálar Sur maar, respectively, and were formed between 460 ± 50 ka to < 1 Ma ago along the north–south-striking Tilomonte ridge that underlies the Tucúcaro Ignimbrite (3.2 ± 0.3 Ma). Their formation is the result of an intermediate magma rising to the surface during a local transtensional regime, which is observed at El Maní, under a dominantly compressional tectonic setting. The Tilocálar monogenetic centers provide a rare opportunity to examine the variability from individual and small–volume magma batches to the development of a monogenetic volcanic field. These volcanoes and the control on their eruption styles were studied by geological mapping and stratigraphic considerations, morphometric analysis, textural studies (density and vesicularity), petrographic observations, and geochemical analyzes. The Tilocálar Norte lavas have an intermediate composition (mostly andesite, 62.02 wt.% SiO 2) that reach a maximum distance of 3.9 km to the north and 1.2 km to the southwest from their vent, with a dense–rock equivalent (DRE) volume of 8.73×107 m3. The El Maní lava dome is small (covering 750 m2 area and consisting of 1.06×103 m3 DRE volume) that presents mingled mafic (63.89 wt.% SiO 2) and felsic (73.73 wt.% SiO 2) products of the original magma source, related to shallow crustal melts. The Tilocálar Sur small lava–shield is characterized by a pyroclastic fall deposit and lavas. The pyroclastic fall deposit is characterized by agglutinated andesite scoria–spatter fall units, covering 2.81 km2 and consisting of 7.75×105 m3 DRE volume. In contrast, the lavas are characterized by an andesitic composition (57.64 wt.% SiO 2), which is 1.8 km in length to the northwest and 1.4 km to the east of their source. These lavas cover an area of 3.78 km2 with 9.15×107 m3 DRE volume. Tilocálar Sur maar crater has an elliptical shape in map view (363 m diameter east–west and 288 m diameter north–south), surrounded by individual conglomerates, sandstones, granitoids, and tuff fragments that lie on the present–day surface around the crater rim. The Tilocálar volcanic complex is interpreted as a small monogenetic volcanic field that shows an eruption history defined by a spectrum of eruptive processes determined by internal and external parameters at any given time from the four independent volcanic centers. • Four monogenetic centers are characterized as the Tilocálar monogenetic volcanic field. • Magmatic effusive, magmatic explosive, and phreatomagmatic activity is evidenced. • The Monturaqui-Negrillar-Tilopozo aquifer is associated with the Tilocálar Sur maar. • The El Maní dome with flow–mingled textures indicates a local transtensive regime. • A local transtensive regime is proposed for the Tilocálar volcanoes emplacement. [ABSTRACT FROM AUTHOR]