Every year staff members of the USGS are called upon to respond to and assess unrest at active volcanoes in the U.S. or internationally, and responses typically include measurements of the amounts and types of gases being released over time and with changing styles of unrest. Such efforts continue to improve the precision and breadth of volcanic gas data, but often the question remains: What do these signals mean for the processes happening in upper crustal magma reservoirs and sub-volcanic conduits? This shortcoming stems to a large degree from the limited understanding of the combined solubilities of sulfur species with H2O and CO2 at the oxidized conditions of most subduction zone magmas.
This opportunity would address that deficiency by developing and executing a series of high temperature, moderate-to-high pressure laboratory experiments to determine the solubilities of S-species mixed with H2O and CO2 in one or more subduction-related compositions, and then integrating those and literature results to develop a mixed-volatile solubility model. The experimental portion of the effort would be conducted in the Volcano Science Center’s Magma Dynamics Lab, Menlo Park, California. The Mendenhall Fellow would then use those results and the published solubility literature to develop an integrated H2O-CO2-S solubility model, the comprehensiveness of which would depend on the breadth of experimental results. Components of the model could include the ability to calculate gas composition from melt composition, and vice versa, at specified pressures, temperatures, and oxidation states, and possibly the ability to calculate changes in exsolved gas composition along different magma ascent paths, both in an open and a closed system (gas escapes versus stays with melt), and the effects of gas fluxing at various proportions and with a range of influx compositions through a static magma column. Ideally, the model would be accessible as a software application, in addition to being released in one or more scientific publications.
The Magma Dynamics Lab contains end-loaded piston-cylinder presses (2) calibrated at pressures of 2.8 GPa down to 400 MPa, rapid-quench MHZ/ZHM/TZM-type gas-pressurized vessels capable of pressures up to about 250 MPa, an atmospheric-pressure gas-mixing furnace, and classical water-pressurized cold-seal vessels (10), along with supporting laboratory equipment, chemicals, and noble metal stocks. The USGS, Menlo Park, has acquired and is in the process of installing a 5-spectrometer JEOL field-emission electron-microprobe, operates a TESCAN scanning electron microscope (SEM) with dual large-area energy-dispersive X-ray spectroscopy (EDS) spectrometers and supporting elemental mapping software, a Fourier Transform Infrared Spectroscopy (FTIR) laboratory for analysis of dissolved H2O and CO2, and a laboratory for chemical analyses of volcanic gas samples. The nearby SLAC Stanford Synchrotron Radiation Lightsource (SSRL) beamline 6-2 has been used to detect and map sulfur speciation in natural materials by the XANES method, and could be employed in this project, depending on the interests of the Mendenhall Fellow.
Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.
Proposed Duty Station: Menlo Park, CA or Moffett Field, CA
Areas of PhD: Igneous petrology or volcanic gas geochemistry with experience in high temperature/pressure experiments, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).
Qualifications: Applicants must meet the qualifications for: Research Geologist
(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)
Human Resources Office Contact: Beverly Ledbetter, 916-278-9396, bledbetter@usgs.gov
