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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 Negros de Aras monogenetic volcanic field in the Central Volcanic Zone of the Andes displays the highest concentration of scoria cones in northern Chile (0.23 per km2). It contains 66 vents, 22 of which are emission points of lava flows without an associated recognizable volcanic edifice, whereas 44 are typical scoria cones. Most vents are associated with basaltic andesite and andesite lava flows of up to 4.6 km in length. A few scoria cones show signs of either initial or final phreatomagmatic eruptions recorded in their pyroclastic successions. A geomorphological, morphometric, and spatial distribution analysis of the scoria cones of this volcanic field was carried out with the purpose of identifying the factors and processes that governed their emplacement, growth, and final morphology. The morphometric analysis was performed on 16 well-delimited scoria cones applying the MORVOLC algorithm using the TanDEM-X 12 m resolution digital elevation model. Analysis of the distribution and elongation of the craters of the scoria cones defines four alignments inferred to be related to the local and regional structural elements of the area. Volcanic activity seems to have been related to a N-S fault system with an E-W maximum stress orientation, favoring magma ascent and scoria cone emplacement following inherited fractures in these preferential orientations. The scoria cones show a wide range of morphologies and morphometries that can be related to different syn - and post-eruptive processes. Cones with large craters and high crater width / basal width ratios show clear evidence of phreatomagmatic eruptions (within their pyroclastic successions), whereas horseshoe-type cones are related to cone breaching or coeval lava flow effusion, and more pristine (i.e., relatively younger) cones are generally steeper. • First morphometric analysis of scoria cones in northern Chile. • Negros de Aras volcanic field contains 66 volcanic centers (44 scoria cones and 22 vents). • A local extensive regime and inherited N-S structures determined the spatial distribution of the scoria cones. • The MORVOLC algorithm with a TanDEM-X 12 m spatial resolution was used for calculating morphometric parameters. [ABSTRACT FROM AUTHOR]

Effusion rate is the instantaneous lava flow output by a vent. It is one of the most important factors that govern the emplacement and dynamics of lava flows and can be determined by direct measurements or estimated through modeling. The Negros de Aras monogenetic volcanic field, located in the Central Volcanic Zone of the Andes, is the largest volcanic field in northern Chile. It is situated north of the active Socompa volcano and south of the Salar de Atacama basin, consisting of scoria cones and lava flows. Here, we estimate the effusion rates of three overlapping and representative solidified lava flows from this volcanic field applying an iterative procedure using the Q-LavHA GIS plugin, where the effusion rate is treated as an unknown parameter and the solution is reached by comparing the simulated results with the real extension of the flows. The pre-eruptive surface was reconstructed using the 12 m resolution TanDEM-X digital elevation model. Other required input parameters for the modeling (e.g., channel ratio, viscosity, temperature) were estimated through geomorphometric, petrographic, and geochemical analysis. The estimated effusion rates vary between 14 and 113 m3/s, comparable with rates measured elsewhere. The method was validated by applying it to two directly measured (Nyamuragira 2006; Mount Etna 2001) and one calculated effusion rate (Lentiscal 2450 BP, Canary Islands). The estimated effusion rates gave an average underestimation of 10%. Considering this percentage of adjustment, the effusion rates for the three studied lava flows from the Negros de Aras monogenetic volcanic field vary from 15 m3/s to 124 m3/s. Our results provide valuable information for mitigating volcanic risk in the event of future lava flow eruptions, which could affect nearby villages and mining operations. • Estimation of effusion rate of cooled lava flows in the Negros de Aras monogenetic volcanic field. • Estimation of effusion rate using the lava flow simulation software Q-LavHA GIS. • Lava flows morphotypes vary from 'a'ā type to blocky type. • The pre-eruptive surface was modeled using the TanDEM-X 12 m spatial resolution digital elevation model. [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]

A detailed study on the mineralogy and chemistry of fumarolic deposits with a focus on metals and metalloids is presented. Two active volcanoes in northern Chile, Guallatiri and Lastarria, are characterised by vigorous and persistent fumarolic activity and the formation of zoned fumarolic deposits. Twelve minerals were identified in the studied deposits by X-ray diffraction: anhydrite, barite, gypsum, rhomboclase, orpiment, pyrite, galena, cristobalite, quartz, magnetite, sassolite, and native sulphur. Chemical analyses revealed the presence of 30 chemical elements, including metals and metalloids such as As, Hg, Pb, Sb, Te, and Tl. Backscattered-electron imaging revealed four types of rock textures in the fumarolic deposits: i) massive and poorly vesiculated, ii) highly vesiculated, iii) clastic-like, and iv) flow-like. Micro-chemical analyses showed the presence of cinnabar nataliyamalikite and unidentified mineral assemblages of As S, Te S, Pb S, Hg S, Tl I, and Tl-I-Pb compositions. Based on colour, outlet gas temperature, mineralogy, and chemistry, four distinct zones of fumarolic deposits are identified. (1) Grey zone: sulphide and silicate dominant with minor native elements, high concentrations of Pb and As, and a clastic-like texture (gas outlet temperature > 265 °C). (2) Red zone: sulphide and silicate dominant with minor oxides and native elements, small As, Pb, Tl, I, and Te minerals, and predominance of a flow-like texture (200–280 °C). (3) Yellow-orange zone: dominated by native sulphur and minor borates and sulphur with small As-, Sb-, Hg-, and I-containing minerals, massive and vesiculated texture (80–200 °C). (4) Yellow-white zone: formed by native sulphur, minor borates and As-rich zones, usually displaying a vesiculated texture (<100 °C). • Mineralogy and chemistry of fumarolic deposits of Guallatiri and Lastarria volcanoes are investigated. • Native sulphur is the most common mineral in fumarolic deposits. • Rare As S, Te S, Pb S, Hg S, Tl I, and Tl-I-Pb mineral assemblages were found. • A detailed description of northern Chilean fumarolic deposits is provided. [ABSTRACT FROM AUTHOR]