Styles of zoning in central Andean ignimbrites - Insights into magma chamber processes

Data are presented showing that calc-alkaline high-K ignimbrites from the Altiplano-Puna Volcanic Complex of the Central Volcanic Zone of the Andes, showing a variety of compositional zonations. The characteristics of the juvenile material from the zoned and heterogenous ignimbrites suggest that crystallization of the observed phenocrysts occurred in prezoned magma chambers consisting of two or more layers. It is suggested that the width/height ratio of a magma chamber plays a critical role in the control of the style of zonation that may develop in a closed magma chamber.