Electronic environments of ferrous iron in rhyolitic and basaltic glasses at high pressure: Silicate Glasses at High Pressure

Journal Article · Thu Aug 31 00:00:00 EDT 2017 · Journal of Geophysical Research. Solid Earth

DOI:https://doi.org/10.1002/2017JB014363· OSTI ID:1397300

Solomatova, Natalia V. ^[1]; Jackson, Jennifer M. ^[1]; Sturhahn, Wolfgang ^[1]; Rossman, George R. ^[1]; Roskosz, Mathieu ^[2]

---

1. California Inst. of Technology (CalTech), Pasadena, CA (United States)
2. Centre National de la Recherche Scientifique (CNRS), Paris (France)

The physical properties of silicate melts within Earth's mantle affect the chemical and thermal evolution of its interior. Chemistry and coordination environments affect such properties. We have measured the hyperfine parameters of iron-bearing rhyolitic and basaltic glasses up to ~120 GPa and ~100 GPa, respectively, in a neon pressure medium using time domain synchrotron Mössbauer spectroscopy. The spectra for rhyolitic and basaltic glasses are well explained by three high-spin Fe²⁺-like sites with distinct quadrupole splittings. Absence of detectable ferric iron was confirmed with optical absorption spectroscopy. The sites with relatively high and intermediate quadrupole splittings are likely a result of fivefold and sixfold coordination environments of ferrous iron that transition to higher coordination with increasing pressure. The ferrous site with a relatively low quadrupole splitting and isomer shift at low pressures may be related to a fourfold or a second fivefold ferrous iron site, which transitions to higher coordination in basaltic glass, but likely remains in low coordination in rhyolitic glass. These results indicate that iron experiences changes in its coordination environment with increasing pressure without undergoing a high-spin to low-spin transition. We compare our results to the hyperfine parameters of silicate glasses of different compositions. With the assumption that coordination environments in silicate glasses may serve as a good indicator for those in a melt, this study suggests that ferrous iron in chemically complex silicate melts likely exists in a high-spin state throughout most of Earth's mantle.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1397300
• Journal Information: Journal of Geophysical Research. Solid Earth, Journal Name: Journal of Geophysical Research. Solid Earth Journal Issue: 8 Vol. 122; ISSN 2169-9313
• Publisher: American Geophysical Union
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

58 GEOSCIENCES
Mossbauer spectroscopy
coordination environment
ferrous iron
high pressure
silicate glass
silicate melt