1. Magmatic Phases - I

2. Basalt Melting Relations & Eruption Temps.

3. Magmatic Phases - II

4. Conceptual Models of Silicate Melts
From Carmichael et al. 1974

5. Common Magmatic Volatile Species
Volatiles are defined as those chemical species that at near atmospheric P and high T appropriate for magmas, exist in a gas or vapor phase.
Common chemical species include: H2O (steam), CO2, H2, HCl, HF, F, Cl, SO2, H2S, CO, CH4, O2, NH3, S2, and noble gases He and Ar. H2O and CO2 dominate!
Most volatile species consist of only six low-atomic weight elements: H, C, O, S, Cl, and F. Small but measurable amounts of these elements can be dissolved in both the coexisting melt and crystalline phases.
Oxygen is the major ion in all three phases in magmatic systems: solid, liquid, and volatile.

6. Specific Volume of Pure Water
Geothermal
Gradient
Pure H2O ->
218 bars; 371°C
Pure CO2 ->
73 bars; 31°C
Critical Point
At magmatic conditions no distinction between liquid and gas phases.
Refer to phase as volatile fluids if density < 2 g/cm3.
From Burnham et al., 1969

7. Specific Volume of Water vs. Pressure
specific volume = 1 / r
0.1 g/cm3
rmagma = 2.2 g/cm3

8. Magmatic Volatile Reservoirs
PH2O < Pf
Px = Py = Pz
Isostatic = Lithostatic pressure

9. Water Solubility vs. Pressure
“Cold-Seal” bomb
Pressure medium
Platinum capsule:
contains melt +
dissolved volatiles
To pump to increase
pressure
From Moore et al., 1998

10. Depolymerization of Silicate Melts

11. Speciation of Water in Silicate Melts
H2O + O2- = 2OH-
in melt in melt
From Silver et al., 1990

12. CO2 Solubility in Silicate Melts
aSiO2

13. Pressure Effects on Volatile-rich Systems

14. Vesiculation Stages Bubble Nucleation Froth Saturation
New Nucleii and Growth
Fragmentation
From: Sparks (1978)

15. Volatiles and Eruptions

17. Explosive Eruptions