Magmatic differentiation at La Poruña scoria cone, Central Andes, northern Chile: Evidence for assimilation during turbulent ascent processes, and genetic links with mafic eruptions at adjacent San Pedro volcano

Features That Favor the Prediction of the Emplacement Location of Maar Volcanoes: A Case Study in the Central Andes, Northern Chile

“…The small-volume scale of monogenetic volcanoes enables preservation of the petrological features of the magmatic systems [13]. Juvenile material of monogenetic volcanoes is considered a "window to the mantle" allowing an insight into the processes that produce their magmas, (e.g., [105][106][107][108][109][110]), whereas the lithic content of these monogenetic systems could be considered as a "window to the crust and to the substrate" (e.g., [111][112][113][114][115]). In both senses, monogenetic volcanoes provide a unique opportunity to study the details of volcanic processes from the magmatic source to the surface.…”

“…These textural features correspond mainly to disequilibrium textures and indicate decompression, rapid cooling, and a relatively high magma ascent rate (e.g., [116][117][118]). On the other hand, the survival of quartz xenocrysts and country rocks fragments suggest a relatively short contact time of magma-country rock interaction, indicating a low degree of assimilation and any significant pausing of the magma within the CVZ thick crust (e.g., [108,109,119]). In addition, the occurrence of amphibole breakdown/reaction rim width with skeletal and sieve textures within the xenoliths suggest that a fine-scale magma mixing/mingling would have taken place during the magma ascent in the shallow crust at depths of 4-8 km and temperatures of 880-920 • C [120][121][122] which is concordant with the shallow magma reservoirs reported and suggested for the Altiplano-Puna area [67,[123][124][125].…”

“…This magmatic process is consistent with fine-grained textures, skeletal textures, xenoliths, and quartz xenocrysts found in the rock samples. ATA process has been suggested for Cerro Overo maar [54] and other centers in the Altiplano-Puna Volcanic Complex (e.g., [108,109,[135][136][137]). This assimilation during the turbulent ascent process cannot be strongly supported for Cerro Tujle maar, Tilocálar Sur maar, and the other volcanoes of the Tilocálar monogenetic field due to the little amount of isotopic data available.…”

Constraining the sub-arc, parental magma composition for the giant Altiplano-Puna Volcanic Complex, northern Chile

“…La Poruña is composed of pyroclastic material and an extensive basaltic-andesite to andesite lava flow that extends up to 8 km to the south-west of the main vent, whereas San Pedro is a composite stratovolcano formed by two superimposed coalescent cones 21 . The entire La Poruña volcano represents a monogenetic, relatively small to medium volume and short-lived singular eruption, whose magmatic evolution has been described as a two-stage evolutionary process involving minor assimilation and fractionation, followed by selective assimilation during turbulent ascent 22 . In contrast, San Pedro is a >100 km 2 andesitic-to-dacitic volcanic field, with a long-lived (from ca.…”

“…Olivine-and pyroxene-phyric lava and scoria are ubiquitous at La Poruña, San Pedro, Paniri, La Poruñita, Palpana and Chela and vary from basaltic-andesite to andesite in composition, with whole-rock elemental and Sr and Nd isotope compositions that range from e.g., SiO 2 = 54.6 to 62.9 wt%, MgO = 1.6 to 6.1 wt%, Sr = 389 to 885 ppm, Cr = 5 to 625 ppm, 87 Sr/ 86 Sr = 0.705541(10) to 0.707656 (10), and 143 Nd/ 144 Nd = 0.512337(12) to 0.512513(50) (see 12,22,23 ). Recent work on these volcanoes utilised whole-rock elemental and Sr and Nd isotope data to construct an evolutionary model, in which limited magmatic differentiation occurred at mid-upper crustal levels 12,22 . Lavas of these selected volcanoes may thus represent the composition of parental magmas feeding volcanism within the Altiplano-Puna Volcanic Complex, as the magmas feeding these mafic eruptions largely escaped assimilation of APMB felsic melts during ascent 12 .…”