Progress Summary The goal of this research project is to measure the oxidation state and spin state of iron in mantle silicate phases, i.e., perovskite, post-perovskite, and amorphous phase. The spin and oxidation states of iron in mantle silicates have significant implications for the dynamics and chemical differentiation in the lower mantle. We collaborate with Dr. Morgan at University of Wisconsin to combine our experimental results with their theoretical results. We have conducted Nuclear Forward Scattering (NFS) and X-ray Emission Spectroscopy (XES) measurements at the Advanced Photon Source. The combination of these two complementary synchrotron techniques allows us to determine the spin and oxidation states of iron unambiguously. In silicate glass, which we used as an analog for mantle melt, we found that Fe2+ undergoes a gradual spin transition, starting from 10 GPa and never reaches a complete low spin state up to the pressure expected at the core-mantle boundary. The diverse Fe-O coordination environments in disordered system results in the gradual spin transition. This new result may provide important insights on the density crossover and iron partitioning between silicates and melts in the deep mantle. This result was submitted to Geophysical Research Letters for publication. We have conducted a series of synchrotron X-ray spectroscopy measurements on mantle perovskite and post-perovskite with realistic amount of Al. A key improvement we made over the previous study is that we regulate the redox state of the sample in the laser heated diamond-anvil cell. We also used two different starting materials, crystalline and amorphous, investigating the effects of kinetics on the oxidation state of iron in the silicates in the laser-heated diamond-anvil cell experiments. In this new experiment, we have also conducted measurements on the recovered samples, which allows us to determine the oxidation state more accurately.
|Effective start/end date||10/1/12 → 8/31/15|
- National Science Foundation (NSF): $69,447.00