Iron-bearing Oxides, Silicate Glasses and Carbonates at Lower Mantle Pressures

Iron is the fourth most abundant element in Earth’s mantle and it affects geophysically observable properties, such as the density, sound velocities, viscosity and transport properties of mantle phases. Additionally, the concentration of iron in minerals and melts of the lower mantle dictates their structure and stability. Thus, understanding the effect of iron is important to interpret seismically observable complexities and understand their effect on processes in the deep Earth. In this thesis, I use experimental and theoretical methods to improve our understanding of the high-pressure behavior of iron-bearing periclase (“ferropericlase”), silicate glasses and carbonates. Ferropericlase is thought to represent a significant fraction of Earth’s lower mantle, and may explain the slow compressional and shear sound velocities of ultra-low velocity zones at the core-mantle boundary. To understand the effect of iron concentration on the (Mg,Fe)O solid solution, the equation of state and hyperfine parameters of (Mg,Fe)O with 48 mol% FeO were measured using X-ray powder diffraction and time-domain Mössbauer spectroscopy, respectively, and the spin crossover behavior was compared to that of (Mg,Fe)O with 10 to 60 mol% FeO. I find that iron-rich ferropericlase at core-mantle boundary pressures likely contains a significant fraction of high-spin iron, contributing a positive buoyancy to promote topographic relief of ultra-low velocity zones in the lowermost mantle. Some ultra-low velocity zones, particularly those at the base of the central parts of large low shear velocity provinces, may be best explained by the presence of iron-bearing silicate melts. The behavior of iron in silicate melts is poorly understood, but may be approximated by iron-bearing silicate glasses. I measured the hyperfine parameters of iron-bearing rhyolitic glass up to ~120 GPa and basaltic glasses up to ~90 GPa using time-domain Mössbauer spectroscopy. Iron within these glasses experiences changes in coordination environment with increasing pressure without undergoing a high-spin to low-spin transition. Thus, ferrous iron in chemically–complex silicate melts likely exists in a high-spin state throughout most of Earth’s mantle. Decomposition of carbonates may be responsible for creating silicate melts within the lower mantle by lowering the melting temperature of surrounding rock. Identifying and characterizing the stability of carbonate phases is therefore a necessary step towards understanding the transport and storage of carbon in Earth’s interior. Dolomite is one of the major mineral forms in which carbon is subducted into the Earth’s mantle. Although iron-free dolomite is expected to break down upon compression into single-cation carbonates, high-pressure polymorphs of iron-bearing dolomite may resist decomposition. Using a genetic algorithm that predicts crystal structures (USPEX), I have found a monoclinic phase with space group C2/c that has a lower energy than all previously reported dolomite structures at pressures above 15 GPa, and the substitution of iron for magnesium stabilizes monoclinic dolomite with respect to decomposition at certain pressures of the lower mantle. In this thesis, I demonstrate that iron undergoes a spin transition in (Mg,Fe)O, (Mg,Fe)CO3 and Ca(Mg,Fe)(CO3)2, while iron in basaltic and silicate glasses likely does not experience a spin transition up to lowermost mantle pressures. Additionally, I find that the amount of iron in (Mg,Fe)O and Ca(Mg,Fe)(CO3)2 dictates the dynamic and thermodynamic stabilities of those phases within Earth’s lower mantle.</p

Internet platforms as alternative sources of information during the Russian-Ukrainian war

The deployment of Russian military aggression in Ukraine actualized the search for additional sources of information about hostilities. The war has shown that the official pro-Kremlin media is spreading outright propaganda. So, the demand for independent and operational information about the situation at the front has led to the emergence of individual observers who use available platforms for their activities. The purpose of the article is to analyze Internet platforms as alternative sources of information about the Russian-Ukrainian war. The research used methods of analysis and synthesis, prognostic method, content analysis. The results trace the peculiarities of the use of digital platforms as sources of information about Russian aggression. The main attention is paid to the peculiarities of work in social networks Facebook and Twitter (we are talking about the channels Hromadske.ua, InformNapalm),&nbsp;messengers (Telegram pages of the Center for countering disinformation at the NSDC, InformNapalm, DeepState). Attention is also drawn to independent OSINT researchers, whose reports made it possible to detect war crimes committed by the Russian army during the occupation of certain areas of Ukrainian territory. The conclusions emphasize the importance of further research into this vector, as independent groups of analysts actively use Internet platforms for work

Equation of State, Structure, and Transport Properties of Iron Hydride Melts at Planetary Interior Conditions

Iron hydrides are a potentially dominant component of the metallic cores of planets, primarily because of hydrogen's ubiquity in the universe and affinity for iron. Using ab initio molecular dynamics, we examine iron hydrides with 0.1, 0.33, 0.5, and 0.6&nbsp;mol fraction hydrogen up to 100&nbsp;GPa between 3,000 and 5,000&nbsp;K to describe how hydrogen content affects the melt structure, hydrogen speciation, equation of state (EOS), atomic diffusivity, and melt viscosity. We find that the addition of hydrogen decreases the average Fe–Fe coordination number and lengthens Fe–Fe bonds, while Fe–H coordination number increases. The pair distribution function of hydrogen at low pressure indicates the presence of molecular hydrogen. By tracking chemical speciation, we show that the amount of molecular hydrogen increases and the number of iron in Hx≥1Fey≥0 clusters decreases as the hydrogen concentration increases. We parameterize a pressure, volume, temperature, and composition EOS and show that the molar volume and Grüneisen parameter of the melts decrease while the compressibility and thermal expansivity increase as a function of hydrogen concentration. We find that hydrogen acts as a lubricant in the melts as the iron and hydrogen become more diffusive and the melts become more inviscid as the hydrogen concentration increases. We estimate 2.7&nbsp;wt% hydrogen in the Martian core and 0.49–1.1&nbsp;wt% hydrogen in Earth's outer core based on comparisons to seismic models, with the assumption that the cores are pure liquid iron-hydrogen alloy, and we compare the small exoplanet population with mass-radius curves of iron hydride planets

Electronic environments of ferrous iron in rhyolitic and basaltic glasses at high pressure

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 Fe^(2+)-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

A Synchrotron Mössbauer Spectroscopy Study of a Hydrated Iron-Sulfate at High Pressures

Szomolnokite is a monohydrated ferrous iron sulfate mineral, FeSO₄·H₂O, where the ferrous iron atoms are in octahedral coordination with four corners shared with SO4 and two with H₂O groups. While somewhat rare on Earth, szomolnokite has been detected on the surface of Mars along with several other hydrated sulfates and is suggested to occur near the surface of Venus. Previous measurements have characterized the local environment of the iron atoms in szomolnokite using Mössbauer spectroscopy at a range of temperatures and 1 bar. Our study represents a step towards understanding the electronic environment of iron in szomolnokite under compression at 300 K. Using a hydrostatic helium pressure-transmitting medium, we explored the pressure dependence of iron’s site-specific behavior in a synthetic szomolnokite powdered sample up to 95 GPa with time-domain synchrotron Mössbauer spectroscopy. At 1 bar, the Mössbauer spectrum is well described by two Fe²⁺-like sites and no ferric iron, consistent with select conventional Mössbauer spectra evaluations. At pressures below 19 GPa, steep gradients in the hyperfine parameters are most likely due to a structural phase transition. At 19 GPa, a fourth site is required to explain the time spectrum with increasing fractions of a low quadrupole splitting site, which could indicate the onset of another transition. Above 19 GPa we present three different models, including those with a high- to low-spin transition, that provide reasonable scenarios of electronic environment changes of the iron in szomolnokite with pressure. We summarize the complex range of Fe²⁺ spin transition characteristics at high-pressures by comparing szomolnokite with previous studies on ferrous-iron bearing phases

Carbon Speciation and Solubility in Silicate Melts

To improve our understanding of the Earth's global carbon cycle, it is critical to characterize the distribution and storage mechanisms of carbon in silicate melts. Presently, the carbon budget of the deep Earth is not well constrained and is highly model-dependent. In silicate melts of the uppermost mantle, carbon exists predominantly as molecular carbon dioxide and carbonate, whereas at greater depths, carbon forms complex polymerized species. The concentration and speciation of carbon in silicate melts is intimately linked to the melt's composition and affects its physical and dynamic properties. Here we review the results of experiments and calculations on the solubility and speciation of carbon in silicate melts as a function of pressure, temperature, composition, polymerization, water concentration, and oxygen fugacity

Bioassay of Redioactive Pollution of the Peter the Great Bay (Sea of japan) Through Macrophytes

Pacific Georgrphical InstitutePromoting Environmental Pesearch in Pan-Japan Sea Area : Young Researchers\u27 Network, Schedule: March 8-10,2006,Kanazawa Excel Hotel Tokyu, Japan, Organized by: Kanazawa University 21st-Century COE Program, Environmental Monitoring and Prediction of Long- & Short- Term Dynamics of Pan-Japan Sea Area ; IICRC(Ishikawa International Cooperation Research Centre), Sponsors : Japan Sea Research ; UNU-IAS(United Nations University Institute of Advanced Studies)+Ishikawa Prefecture Government ; City of Kanazaw

Electronic environments of ferrous iron in rhyolitic and basaltic glasses at high pressure

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 Fe^(2+)-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