Chemical Evolution of a Magmatic System: The Paintbrush Tuff, SW Nevada Volcanic Field

摘要

The chemical and thermal evolution of a single magmatic system is recorded in a series of four ash-flow sheets, the Paintbrush Tuff, that were erupted from the same caldera within a span of 600,000 years. The chemistry of individual glassy pumices, collected from the tops and bottoms of the ash-flow sheets, are used to quantitatively evaluate possible fractionation mechanisms, such as magma mixing and fractional crystallization. The glassy pumices are used because they most nearly approximate the magma in the chamber. All of the chemical variation within the Paintbrush Tuff can be accounted for by fractional crystallization or magma mixing operating alone and/or in conjunction. No other fractionation processes need by invoked. Also, volume estimates based on quantitative modeling reveal that the size of the ash-flow sheets do not reflect the size of their associated reservoirs. (ERA citation 12:050328)