The diffusion of water in dacitic and andesitic melts was investigated at temperatures of 1458 to 1858 K and pressures between 0.5 and 1.5 GPa using the diffusion couple technique. Pairs of nominally dry glasses and hydrous glasses containing between 1.5 and 6.3 wt.% dissolved H2O were heated for 60 to 480 s in a piston cylinder apparatus. Concentration profiles of hydrous species (OH groups an...

Diffusion couple experiments with wet half (up to 4.6 wt%) and dry half were carried out at 789–1,516 K and 0.47–1.42 GPa to investigate water diffusion in a peralkaline rhyolitic melt with major oxide concentrations matching Mount Changbai rhyolite. Combining data from this work and a related study, total water diffusivity in peralkaline rhyolitic melt can be expressed as:

We have obtained new shock-wave equation of state (EOS) and release adiabat data for rhyolite. These data are combined with those of Swegle (1989, 1990) to give an experimental Hugoniot which is described by Us=2.53(±0.08)+3.393(±0.37)up for up<0.48 km s−1 , Us=3.85(±0.05)+0.65(±0.03)up for 0.48≤up<2.29 km s−1 , Us=1.52(±0.08)+1.67(±0.02)up for 2.29≤up<4.37 km s−1 , and Us=3.40(±034)+ 1.24(±0.0...

Inclusions of quenched mafic magma occur in a 21 Ma rhyolite lava and precursory non-welded tuff that form the Spor Mountain Formation in west-central Utah. The mafic inclusions are not lithic inclusions; no comparable volcanic unit was present at the surface when the Spor Mountain Formation erupted. Mineral and bulk compositions preclude liquid immiscibility. The mafic inclusions show clear mo...

Two fundamentally different types of silicic volcanic rocks formed during the Cenozoic of the western Cordillera of the United States. Large volumes of dacite and rhyolite, mostly ignimbrites, erupted in the Oligocene in what is now the Great Basin and contrast with rhyolites erupted along the Snake River Plain during the Late Cenozoic. The Great Basin dacites and rhyolites are generally calc-a...

New analytical and experimental data constrain the storage and equilibration conditions of the magmas erupted in 1912 from Novarupta in the 20th century’s largest volcanic event. Phase relations at H2O+CO2 fluid saturation were determined for an andesite (58.7 wt% SiO2) and a dacite (67.7 wt%) from the compositional extremes of intermediate magmas erupted. The phase assemblages, matrix melt com...