Magmatic Phases - I

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