A tale of a lava from its shallow zoned reservoir to surface: the case of Azufre volcano in the context of the Altiplano Puna Magma Body (northern Chile)
Abstract
The Azufre volcano (21°47'S; 68°14'W) is emplaced above the western boundary of the Altiplano Puna Magma Body. The youngest lava of the Azufre volcano (50-331 ka) was selected for detailed studies because of the relevant petrological information that could emerge to understand its reservoir as a potential heat source of the neighboring Cerro Pabellón geothermal system. The studied lava corresponds to an andesite-dacite (61-63 SiO2 wt%) with phenocrysts of plagioclase, amphibole (Group 1), biotite, pyroxenes, quartz, and olivine. The lava also contains aphanitic enclaves (58-60 SiO2 wt%), whose groundmass have the same mineralogy of lava samples groundmass consisting of amphibole microphenocryts (Group 2) and microlites of plagioclase, pyroxenes, and Fe-Ti oxides. Disequilibrium textures are commonly observed in the studied samples such as partially resorbed plagioclase phenocrysts, amphibole breakdown, and reverse zoning in pyroxene and plagioclase phenocrysts. Thermobarometry calculations indicated pressures of ~ 2 kbar for Group 1 amphiboles, temperatures of 905-1097 °C for Mg-rich pyroxene phenocrysts and Ca-rich plagioclase (An ≥ 66), and near-solidus temperatures of 712-788 °C for Group 1 amphibole-plagioclase pairs. Group 1 amphiboles also indicate crystallization from an evolved liquid (63-79 wt% of SiO2). Oxidation conditions of QFM + 0.9-2.5 log units were recorded in amphibole and Fe-Ti oxides. Rhyolite-MELTS models reproduce the composition of the high-temperature phases from a melt composition (andesitic enclave) at similar P-T-fO2. The arrival of new hot andesite magma into a crystal-rich shallow reservoir, thermally and compositionally zoned, would have triggered the studied eruption. Diffusion models in Fe-Ti oxides microlites indicated cooling temperatures of 742-866 °C during the sub-aerial emplacement of the lava.
- Publication:
-
Contributions to Mineralogy and Petrology
- Pub Date:
- August 2023
- DOI:
- 10.1007/s00410-023-02031-x
- Bibcode:
- 2023CoMP..178...52H
- Keywords:
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- Altiplano Puna Volcanic Complex;
- Crystal-mush reservoirs;
- Magma mixing;
- Magmatic enclaves