Influence of oxygen fugacity on the viscosity of CO2-, H2O-, and halogen-bearing basaltic melts

• Applicant: Professorin Dr. Sharon Webb
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 271760878

The viscosity of mid-ocean ridge basalt (MORB) as a function of CO2-content, oxygen fugacity, water content and halogen content will be determined across the entire viscosity range (10^0 to 10^12 Pa s) using falling-sphere and micropenetration techniques. As MORB rises from the magma chamber to form sub-aqueous pillow lavas, it degasses and loses some of its water, CO2, and halogen content. At the same time the oxygen fugacity experienced by the magma changes. Depending upon how fast the magma rises, the chemical condition of the magma may or may not be in equilibrium with the surrounding conditions. There are very few studies of the rheology of melts at the correct oxygen fugacity conditions. Here, the major theme is to determine viscosity at the redox conditions of the Earth, and to determine the effects of changing redox on viscosity. The volatiles we have chosen to investigate range from the often studied effects of water, to the less studied effects of halogens to the essentially unknown effects of CO2 on viscosity. Our preliminary study on the effect of CO2 shows that it decreases the viscosity of the melt. This observation is contrary to that found in a previous study (Morizet et al., 2007) in which CO2 was found to have no effect on the glass transition temperature of an iron-free phonolite melt.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Burkhard Schmidt