Crystal sizes in evolving silicic magma chambers

Contrasting processes in silicic magma chambers: evidence from very large volume ignimbrites

Very large volume (>1000 km of magma) crystal-rich dacitic ignimbrites that lack pronounced evidence of fractional crystallization or vertical zonation erupt in some continental magmatic arcs (e.g. the Lund Tuff of the Great Basin and the Fish Canyon Tuff of Colorado in western USA). Apparently, their magma chambers were only modestly heterogeneous and not systematically zoned from top to botto...

High silica granites: Terminal porosity and crystal settling in shallow magma chambers

A model for the origin of large silicic magma chambers: precursors of caldera-forming eruptions

The relatively low rates of magma production in island arcs and continental extensional settings require that the volume of silicic magma involved in large catastrophic caldera-forming (CCF) eruptions must accumulate over periods of 105 to 106 years. We address the question of why buoyant and otherwise eruptible highsilica magma should accumulate for long times in shallow chambers rather than e...

Caldera size modulated by the yield stress within a crystal-rich magma reservoir

The largest volcanic eruptions in the geologic record have no analogue in the historical record. These eruptions had global impacts1,2, but are known only through their eruptive products. They have left behind calderas that formed as the surface collapsed when eruption evacuated magma chambers at 5–15 km depths3,4. It is generally assumed that calderas reflect the spatial dimensions of underlyi...

Phase equilibrium constraints on the viscosity of silicic magmas 1. Volcanic-plutonic comparison

By using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced atupper crustal levels is approximately constant a -• 104.5 Pa s, irrespective of their temperature and level of emplacement. Magmas crystallizing as granitic plutons are not water-poor and thus not more viscous than their extrusive equivalents. Instead, comparison between pre-erupt...