Abstract

The Tilocalar 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 Tilocalar Norte lava, the El Mani dome, the Tilocalar Sur small-lava shield, and the Tilocalar Sur maar, respectively, and were formed between 460 +/- 50 ka to 1 Ma ago along the north-south-striking Tilomonte ridge that underlies the Tucucaro 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 Mani, under a dominantly compressional tectonic setting. The Tilocalar 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 Tilocalar Norte lavas have an intermediate composition (mostly andesite, 62.02 wt.% SiO2) 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 x 10(7) m(3). The El Mani lava dome is small (covering 750 m(2) area and consisting of 1.06 x 10(3) m(3) DRE volume) that presents mingled mafic (63.89 wt.% SiO2) and felsic (73.73 wt.% SiO2) products of the original magma source, related to shallow crustal melts. The Tilocalar 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 km(2) and consisting of 7.75 x 10(5) m(3) DRE volume. In contrast, the lavas are characterized by an andesitic composition (57.64 wt.% SiO2), 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 km(2) with 9.15 x 10(7) m(3) DRE volume. Tilocalar 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 Tilocalar 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. (C) 2021 Elsevier B.V. All rights reserved.