**2. Geological background**

The CVZ is located between 14°S (Quimsachata, Peru) and 28°S (Ojos del Salado, Chile) of the Andean Cordillera, including southern Peru, northern Chile, southwestern Bolivia, and northwestern Argentina (**Figure 1a** and **b**). This volcanic zone is a highly elevated region, reaching a width of 350–400 km at much of it over 4000 m a.s.l., constituting the Western Cordillera and Altiplano-Puna physiographic provinces (**Figure 1c**). It is the second-highest altitude plateau in the world in size (after Tibetan Plateau of Central Asia) [36] built on a thickened continental crust that attains a maximum thickness of ~70 km [37]. The crustal thickening and high elevation of the CVZ are related to the crustal shortening [38], sub-crustal magmatism [39], delamination of eclogitic lower crust and lithosphere [40], and climatically controlled low erosion rates with limited sedimentation on the subduction trench [41]. In addition, this crustal thickness is the reason for the magma composition features that characterize the rocks that make up the CVZ as residual garnet during differentiation, crustal contamination,

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a short period from hours to decades. Monogenetic centers can build several volcanic landforms in response to their relationship with different environmental settings [6]. They can be produced by different eruptive styles (e.g., Hawaiian, Strombolian, violent Strombolian, phreatomagmatic, Surtseyan, and effusive activity) that are determined by internal- and external- factors [7], and evidencing several magmatic processes (e.g., fractionation, mixing, contamination) [5]. Therefore, each monogenetic volcanic system is different depending on many factors (mentioned above). For this reason, current efforts around the world focus on understanding monogenetic volcanism in different scenarios, in order to provide a better understanding of this variability and to provide tools to estimate possible scenarios of future eruption [8]. The Central Volcanic Zone (CVZ) of the Andes and particularly northern Chile (18–28°S) (**Figure 1**), is an excellent natural laboratory to study monogenetic systems of changing magma compositions in time and space related to the evolution of an active continental margin, and a ~ 70 km thick orogenic crust [12]. Despite this,

*a) Map showing the location of the Northern, Central, Southern, and Austral Volcanic Zones (NVZ, CVZ, SVZ, and AVZ, respectively) of the Andes defined by Thorpe and Francis [9] (modified from [10]). b) Location map of the CVZ (modified from [10]) showing the central active polygenetic volcanoes [11]. c) Map of northern Chile showing the major morpho-tectonic units of the Central Andes (modified from [12]).*

**250**

**Figure 1.**

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melting-assimilation-storage-homogenization (MASH), and assimilation by depletion of heavy rare earth elements (HREE) in volcanic rocks [28].

The magmatic activity of the CVZ has been continuous from the Upper Oligocene to the present day [42]. The basement is mainly comprised by i) Paleozoic, Mesozoic, and Miocene-Oligocene continental volcanic and sedimentary rocks; ii) Paleozoic and Mesozoic marine sedimentary rocks; iii) Precambrian and Paleozoic metamorphic rocks; and iv) Paleozoic, Mesozoic, and Paleocene intrusive rocks ([43] and references therein).

The Central Andes is known as the home of "andesitic" magmatism [36]; nevertheless, lava and pyroclastic rocks of dacitic, rhyolitic, and occasionally basaltic andesite and basaltic composition volcanic rocks also occur in the CVZ, building calderas, extensive ignimbrite sequences, stratovolcanoes and monogenetic volcanoes [44].
