Title: Magmatic Phases I
1Magmatic Phases - I
2Basalt Melting Relations Eruption Temps.
3Magmatic Phases - II
4Conceptual Models of Silicate Melts
From Carmichael et al. 1974
5Common 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.
6Specific Volume of Pure Water
Geothermal Gradient
Pure H2O -gt 218 bars 371C
Pure CO2 -gt 73 bars 31C
Critical Point
At magmatic conditions no distinction between
liquid and gas phases. Refer to phase as volatile
fluids if density lt 2 g/cm3.
From Burnham et al., 1969
7Specific Volume of Water vs. Pressure
specific volume 1 / r
0.1 g/cm3
rmagma 2.2 g/cm3
8Magmatic Volatile Reservoirs
PH2O lt Pf
Px Py Pz
Isostatic Lithostatic pressure
9Water Solubility vs. Pressure
Cold-Seal bomb
Pressure medium
Platinum capsule contains melt dissolved
volatiles
To pump to increase pressure
From Moore et al., 1998
10Depolymerization of Silicate Melts
11Speciation of Water in Silicate Melts
H2O O2- 2OH- in melt in
melt
From Silver et al., 1990
12CO2 Solubility in Silicate Melts
aSiO2
13Pressure Effects on Volatile-rich Systems
14Vesiculation Stages
Bubble Nucleation
Froth Saturation
New Nucleii and Growth
Fragmentation
From Sparks (1978)
15Volatiles and Eruptions
16(No Transcript)
17Explosive Eruptions