120 MPa and for 930-960 C up to 150 MPa. We are working to provide additional constraints on the system with analyses of natural crystal phases and H2O-undersaturated experiments. Hopefully, this work will appear soon in Journal of Geophysical Research, with a companion article to follow addressing theoretical aspects of crystal nucleation and growth processes. Black represents pits or vesicles, dark gray is glass, light gray is plagioclase, and oxides and Fe-Mg minerals are white. These conditions resulted in high nucleation rate and high plagioclase growth rate.
Crystals have extremely high aspect ratios and thready forms.
Note the blockier, skeletal and cellular forms of the plagioclase crystals. The timing and extent of pre-eruptive magma degassing influences the explosivity of volcanic eruptions. Because decompression and devolatilization of magmas during ascent destabilizes hydrous minerals and drives crystallization of anhydrous phases, crystal textures may record the degassing history of erupted magmas. Laboratory experiments were conducted to study the temporal evolution of the kinetics of feldspar nucleation and growth resulting from isothermal decompression. Feldspar nucleation and growth kinetics are strongly dependent on the degree of feldspar supersaturation, S, and therefore pressure, P. Crystal nucleation rate, J, and growth rate, G, conform to the classical bell-shaped curves observed in cooling experiments and predicted by theory.