1994/04/01 by S. J. MATTHEWS, S. J. Matthews, A. P. JONES +3 · 3 citations
Earth and Planetary Sciences · #Geological and Geochemical Analysis #Geology and Paleoclimatology Research #Mineralogy and Gemology Studies
paper · doi:10.1093/petrology/35.2.401
Lascar Volcano, located in the Central Volcanic Zone of Northern Chile, is a medium-to high-K calc-alkaline stratovolcano. Three stages are recognized in the construction of the edifice, with activity ranging from andesitic fissure eruptions to a large-volume dacitic pumice flow, the Soncor Flow. The eruption products are predominantly two-pyroxene andesites and dacites, with some hornblende dacites occurring in the Soncor Flow. Disequilibrium textures resulting from mixing between mafic and acid end-members are recognized in all the eruption products, and geochemical modelling has been carried out to quantify the effects of magma mixing and fractional crystallization. A model is developed which explains the observed textures by the existence of a continuously fractionating magma chamber which receives periodic influxes of basaltic andesite. Primary anhydrite has been found in the Soncor pyroclastic flow. Anhydrite formation and sulphur dioxide degassing are explained in terms of oxidation and quenching of sulphide-rich mafic magma during mixing with the resident more evolved magmas.