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Cerro Tujle is an isolated Quaternary maar located 21 km south-east of the Salar de Atacama basin. It is situated at 3,554 m a.s.l., on the top of the Cordón de Tujle ridge forming a north-south striking morphological element in the Central Volcanic Zone of the Andes, in northern Chile. The material erupted at Cerro Tujle lies over the Tucúcaro Ignimbrite (3.2 ± 0.3 Ma), covering the whole area. The origin of the magma source, as well as the evolution and control of the volcanic eruptive styles, were determined by fieldwork, stratigraphic, morphometric, textural (density and vesicularity), petrographic, and geochemical analyses. The Cerro Tujle maar features an elliptical crater (333 × 279 m wide in east-west and north-south directions, respectively) surrounded by lava flow and tephra deposits. The total Dense Rock Equivalent volume of the products was calculated in 1.53 × 105 m3, and mainly correspond to andesites (58.62–59.80 wt% of SiO 2). The lava flow can be categorized in at least two types: i) brown-red and green-to-gray andesites located on the north-northwestern flank of the crater, and ii) black andesites with felsic rock clasts distributed around the crater underlying the other lavas. In contrast, the pyroclastic deposit displays breccias of juvenile pyroclasts with xenoliths of rhyolitic composition. These felsic clasts suggest magma assimilation with a shallow magma reservoir during a relatively fast ascent of the magma. This is evidenced by disequilibrium textures in mineral levels, such as reaction rim, and skeletal and sieve textures of the phenocrysts. The field evidence and results of the different analyses suggest a change in the eruptive style from effusive to explosive. This transition is associated with a decrease of the magma flux and a withdrawal of magma below the groundwater table, which has produced a phreatomagmatic eruption by magma-water interaction. • The field relationships between lava flow emission and pyroclastic surge deposit. • Changing eruptive styles in intermediate volcanism. • The hydromagmatic explosive eruptions are not uncommon in the Altiplano-Puna region, northern Chile. [ABSTRACT FROM AUTHOR]

El País is a monogenetic lava flow field located 16 km southeast of Peine town in the Altiplano-Puna area, Antofagasta region, Chile. El País is a monogenetic lava flow field located 16 km southeast of Peine town in the Altiplano-Puna area, Antofagasta region, Chile. El País is composed by lava flows of small-to-moderate volumes, which are fed from individual point sources unassociated with a central volcano of large-volume (stratovolcano) typical of the Andean arc. This lava flow field was emplaced in an area dominated by thin-skinned deformation under a compressive tectonic regime, where multiple volcanic centers (monogenetic and polygenetic volcanoes) have been developed. The volumetric and chemical evolutions were determined by fieldwork, stratigraphic, morphometric, textural (density and vesicularity), petrographic, and geochemical analyses. El País can be divided into three principal mafic lava flows such as Northern-, Main-, and Western-lava flows, which display an E-W orientation. Besides, at least eight ephemeral vents were identified as small erosion remnants of lava emitting point-sources. The identified vents are principally aligned in an ENE-WSW direction, east of the Main lava flow. It is inferred that El País was emplaced near-simultaneously above two ignimbrite sheets: Tucúcaro Ignimbrite (3.2 Ma) and Patao Ignimbrite (3.1 Ma). Stratigraphically, the Main lava flow has a surface texture with strong similarities to an ʻaʻā lava flow, composed of three unique layers well distinguishable in the field such as i) Basal, ii) Top auto-breccia, composed of sub-angular scoriaceous and dense clasts in an oxidized matrix, and iii) A single core between both auto-breccias, composed of dense lavas, exhibiting multiple cooling jointing, such as vertical to platy jointing. The advanced stage of erosion since the formation of El País is evidenced by the poorly preserved lava flows (flat morphology), upper auto-breccia layer, and the presence of large sub-angular blocks of lava (vesicular and dense) along the axis of the lava flows. The eruptive products are geochemically basaltic andesite (Main lava flow and ephemeral vents) and andesite (specifically in the Northern lava flow), making the lava flow field one of the most mafic in the broader region. The lava presents a glomeroporphyric texture, showing at least three different glomerocrysts: i) Plagioclase + clinopyroxene having reabsorption boundaries, ii) Clinopyroxene with reabsorption boundaries, and iii) Plagioclase with sieve-texture. The groundmass is principally composed of glass, plagioclase microlites with a low orientation preference, and opaque minerals (magnetite). This study helps understand the development of dispersed-monogenetic-volcanism (e.g., Tilocálar complex and Cerro Tujle maar), and its relationship with neighboring polygenetic volcanism (e.g., Toloncha stratovolcano) in the Central Volcanic Zone of the Andes, northern Chile. • Different vent location during effusive eruption in lava flow field context. • Ascent rate of basic and intermediate volcanism related with deep source and low magma supply. • Erosion process in dessert climate. [ABSTRACT FROM AUTHOR]