Amphibole recycling and polybaric crystallization in rhyolitic lava domes from melt inclusion geochemistry at Cerro La Torta, Altiplano-Puna Volcanic Complex

La Torta is a rhyolitic lava dome located in the El Tatio volcanic complex, Regi ' on de Antofagasta (northern Chile), to the west of the Cerros de Tocorpuri volcanoes. La Torta is considered to be an important part of the central zone of the Altiplano Puna Magma Body (APMB) based on chemical and petrological signatures that distinguish it from other highly silicic volcanic systems in the area (i.e., Chao dacite). The petrological and geochemical characteristics, along with parental composition and magma evolution, were determined by analyzing amphibole and plagioclase-hosted melt inclusions using electron microprobe (EMP) and laser ablation ICP-MS (LA-ICP-MS). Our results show that La Torta dome was formed from a rhyolitic Ca-and K-rich, calc-alkaline magma, with an average SiO2 content of 76.8 wt % and H2O content of about 5.4 wt %, which was emplaced in the upper continental crust between 3.9 and 7.6 km below the paleosurface. The parental source of La Torta dome was a highly hydrous mush of andesitic composition, with plagioclase + amphibole +/- quartz +/- pyroxene crystal assemblage.Heating by an influx of magmas ascending from deeper sources to upper crustal depths (i.e., Altiplano-Puna Magma Body) caused the partial melting of amphibole and pyroxene in the source, evidenced by amphibole dissolution textures, enriching the melt in Cr, Ni, HFSE and HREE. As the system starts to cool and ascend, new amphibole crystallized from this mush, trapping the enriched residual melt as enriched melt inclusions in its cores, along with crystallization of biotite and plagioclase. We refer to this process as amphibole recycling. At the same time, the new melt drags the plagioclase and quartz inherited from the parental mush, forming the magma that emplaced at shallower levels in the crust to eventually erupt as La Torta.

Automated summary

La Torta is an important rhyolitic lava dome located in northern Chile. It stands out from other volcanic systems in the area due to its unique petrological and geochemical characteristics. The dome was formed from a rhyolitic magma with high contents of calcium and potassium, and its parental source was a highly hydrous mush of andesitic composition. The process of heating and ascent of the magma caused partial melting of amphibole and pyroxene, leading to the formation of enriched melt inclusions. New amphibole crystallized and trapped the enriched melt, while plagioclase and quartz inherited from the parental mush also became part of the magma that eventually erupted as La Torta.