Join us Thursday mornings throughout October for seminars on the theme of redox controls on planetary processes.
Dan Frost of Bayreuth Geoinstitut will kick the series off with a presentation entitled, "The redox state of the lower mantle."
There is reason to believe that while iron is dominantly in the 2+ state in the upper mantle, in the lower mantle it is distributed more evenly between 2+, 3+, and metallic states. Loss of metallic iron from the lower mantle to the core may have raised the redox state of the mantle as a whole after the end of core formation, thus allowing the degassing of an early carbon dioxide-rich atmosphere. In addition, however, ferric iron components in the dominant lower mantle mineral bridgmanite are likely to have decisive effects on transport properties. A number of studies performed in the diamond anvil cell have questioned whether metallic iron may be in equilibrium with bridgmanite throughout the entire lower mantle. Using the results of high pressure and temperature experiments, where the oxygen fugacity was either controlled or measured, we have derived a thermodynamic model to describe the compositions of lower mantle minerals as a function of redox state, composition, and pressure. We show that at least some previous experimental results from the laser-heated diamond anvil cell can be brought into agreement with this model, once the effects of oxygen fugacity are considered. The results imply that metallic iron should be present throughout much of the lower mantle. Further experiments indicate that a magma ocean at lower mantle conditions may have also been in equilibrium with metallic iron whilst containing ferric iron contents that are consistent with the present-day mantle.
Our weekly seminars are primarily designed for a scientific audience and have limited space, so we aren't advertising the Zoom links publicly. That said, all are welcome to join, email epl-info@carnegiescience.edu for information on how to attend.
EPL staff will receive a Zoom link prior to this event via email.