Earth
and Space Sciences Faculty |
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Victor
Kress |
Areas of Interest:
Experimental Petrology, Geochemistry
Research Groups:
Petrology/Mineralogy/Geochemistry
Volcanology
Education:
Ph.D. in Geology : University
of California at Berkeley, 1990.
. . . Thesis: Experiments in Silicate Liquids: Redox State and Sound Speeds.
M.S. in Geology : State
University of New York at Stony Brook, 1986.
. . . Thesis: Iron-Manganese Exchange in Coexisting Garnet and Ilmenite.
B.S. in Geology : University of California at Santa Cruz, 1981.
Current Research:
Passive Degassing
in High-Sulfur Volcanoes
The goal of this project is to improve our understanding of the volcanic mechanism
for non-explosive, passive degassing at high-gas-flux volcanoes. We hypothesize
that "excess" gas emission at passively degassing volcanoes may be
explained by circulation of magma in the volcanic conduit at both mafic and
silicic subduction zone volcanoes. We are focussing on two contrasting volcanoes,
Popocatépetl (Mexico) and Villarrica (Chile). Popocatépetl has
been passively degassing enormous quantities of SO2 vapor for the last 5 years
despite very limited magma production. Villarrica has had an actively degassing
lava lake perched in its summit crater for the last 15 years. High rates of
heat and gas transfer associated with conduit circulation may be responsible
for the observed phenomena at Popocatépetl and Villarrica.
We are pursuing the solution to this problem along two complementary tracks. We are employing geochemical analysis of rock samples from Popocatépetl and Villarrica to help us define pre-eruptive conditions in the magma chamber (e.g. temperature and pressure) and quantify the composition and size of the volcanic gas source. We are also pursuing multi-phase, fluid-dynamic computer modeling of magma circulation in the conduit. This computer modeling allows us to explore conditions under which conduit convection can be a viable mechanism for generating the observed volatile output at the two study volcanoes. A field campaign at Villarrica will make COSPEC measurements of SO2 flux, directly sample gas from summit fumaroles, and collect rock samples from representative explosive and effusive eruptions.
Results of this study will shed light on mechanisms for degassing and heat transfer in explosive and non-explosive volcanic systems. The research will give a more complete understanding of processes at work in the plumbing systems of passively degassing high-gas-flux volcanoes.
Thermodynamics
of Sulfur in Magmatic Systems
Sulfide liquids are found in virtually all igneous environments on Earth, where
they occur as immiscible melts in magmatic silicate melts. The density of sulfide
liquids is ~40% greater than silicate liquids creating a tremendous impetus
to segregation of these liquids from their host silicate and consequent modification
of Ni, Cu, Fe and other chalcophile trace elements. It is by this mechanism
that sulfide liquids participated in one of the most significant events in the
chemical evolution of Earth and the other terrestrial planets; the segregation
of a liquid core. Sulfide liquids are major players in the redox balance in
igneous systems. They are major contributors to aerosol emissions of SO2 from
volcanoes such as Pinatubo and Popocatpetl (Kress, 1997b). This volcanic SO2
is believed to exert an important effect on global climate and the ozone layer.
Despite the tremendous importance of these sulfide liquids in igneous systems, remarkably little is known about their chemistry and saturation conditions. Work is presently under way in my laboratory to derive a thermodynamic model for sulfide liquids of geologically relevant compositions at one atmosphere, and integrate this into the thermodynamic model for igneous systems of Ghiorso and Sack (1995). Volume and compressibility data will be obtained in coming years allowing one-atmosphere results to be extrapolated to higher pressure. We are presently performing density measurements in sulfide liquids which will contribute to our understanding of segregation of sulfide liquids from their igneous host in ore bodies and in differentiating planetary bodies. Work is also underway to obtain direct measurements of sulfide-liquid solubility in silicates at elevated pressures and temperatures.
My thermodynamic model for the sulfide-liquid phase will eventually be extended to address problems of trace element partitioning. Results will be applied to address redox and trace-element evolution of magmatic systems as well as larger issues of planetary evolution.
Viscoelastic properties of volatile-bearing melts at high pressure
The effects of H2O and CO2 on the bulk moduli of silicate liquids are currently poorly known. These are the only major melt components whose effects on the compression properties of melts have not been explored.
I am presently laying the groundwork for a project designed to address this problem. I will examine ultrasonic viscoelastic properties in silicate melts at pressures up to 1 GPa using new internally heated pressure vessel facilities at the University of Washington. By performing ultrasonic interferometry experiments at pressures where the solubility of H2O is significant, the effect of this important component on the compression properties of the melt can be determined quantitatively.
The pressure dependence of viscosity has been determined in only a few silicate liquid compositions. Using the high-pressure ultrasonic device described above I intend to examine the pressure dependence of viscosity. This will be done via an in-situ determination of the ultrasonic relaxation frequency at temperature and pressure. This procedure will also allow us to refine our knowledge of the effect of volatile components and pressure on the viscosity of silicate melts.
Spectroscopic
studies of iron in silicate liquids
I am in the process of examining the effect of the Mössbauer recoil-free
fraction for ferric and ferrous iron using the cryostatic Mössbauer device
at the Geophysical laboratory. This effect has not been well studied in silicate
liquids, though it has significant potential implications in the interpretation
of Mössbauer-derived redox and structural data.
In-situ Raman spectroscopy combined with Mössbauer spectroscopy should help to establish the validity of the hypothesis that ferric and ferrous iron associate in the melt to a species of roughly spinel stoichiometry (KRESS and CARMICHAEL, 1989, 1991).
Selected Publications:
KRESS V.C. (1999b) Thermochemistry
of sulfide liquids III. Ni-bearing liquids at 1 bar. (in prep.)
KRESS V.C. (1999a) Thermochemistry of sulfide liquids II. Associated solution model for sulfide liquids in the system O-S-Fe. Contributions to Mineralogy and Petrology. (in press).
KRESS V.C. (1997b) Magma mixing as a source for Pinatubo sulfur. Nature. 389:591-593.
KRESS V.C. (1997a) Thermochemistry of sulfide liquids I: The system Fe-S-O at 1 bar. Contributions to Mineralogy and Petrology. 127:176-186.
KRESS V.C. AND GHIORSO M.S. (1994) Multicomponent diffusion in basaltic melts. Geochimica et Cosmochimica Acta. 59:313-324.
KRESS V.C. AND GHIORSO M.S. (1993) Multicomponent diffusion in MgO-Al2O3-SiO2 and CaO-MgO-Al2O3-SiO2 melts. Geochimica et Cosmochimica Acta. 57:4453-4466.
KRESS V.C. AND CARMICHAEL I.S.E. (1991) The compressibility of silicate liquids containing Fe2O3 and the effect of composition, temperature, oxygen fugacity and pressure on their redox states. Contributions to Mineralogy and Petrology. 108:82-92.
KRESS V.C. AND CARMICHAEL I.S.E. (1989) The lime-iron-silicate melt system: Redox and volume systematics. Geochimica et Cosmochimica Acta. 53:2883-2892.
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