The effect of pressure on iron compounds and the implications for the earth's mantle and core
Abstract/Contents
- Abstract
- Understanding the high-pressure behavior of iron and its various alloys is a fundamental step in gaining insight into the deep Earth. Iron is the most common transition metal within the mantle and is the primary element in the core. In order to explore the properties of iron compounds and alloys at high pressures, the conditions of the deep Earth were replicated in diamond anvil cells and the resulting changes were monitored by a various suite of synchrotron techniques. X-ray emission spectroscopy was used to monitor the spin state of the polymorphs of iron hydroxides up to 85 GPa. FeOOH has four polymorphs: goethite (alpha - FeOOH), akaganeite (beta - FeOOH), lepidocrocite (gamma - FeOOH), and a high-pressure phase, epsilon - FeOOH. The structural changes of these polymorphs as a function of pressure were examined using X-ray diffraction to generate equations of state for beta - FeOOH and gamma - FeOOH. Comparing the equation of state results for the beta and gamma phases with recently published data on the alpha and epsilon phases, the beta - FeOOH exhibits distinct behavior from the other three polymorphs, as it is significantly less compressible and does not undergo a spin transition. A systematic examination of these iron hydroxide polymorphs as a function of pressure provides insights into the relation between electronic spin transitions and structural transitions in these OH- and Fe3+ bearing phases that may have implications on understanding of the water content of the mantle. We collected a series of phonon excitation spectra using nuclear resonant inelastic x-ray scattering on 57Fe-enriched on various iron alloys, FeO, Fe3C, FeS and those with varying nickel content (Fe0.9Ni0.1, Fe0.8Ni0.2 and Fe0.7Ni0.3) at pressures up to 40 GPa at room temperature. The phonon density of states were used to extract each composition's force constant and - factors in order to evaluate their individual effects on stable iron isotope fractionation. This work explores the effect of various light elements, the role of increasing nickel content and the effect of spin transitions on iron isotope fractionation. It provides insights into the potential records left by core formation during planetary differentiation. Radial X-ray diffraction was used in combination with nuclear resonant inelastic x-ray scattering to determine the bulk strength of two iron-nickel alloys (Fe0.88Ni0.12 and Fe0.8Ni0.2) at pressures up to 70 GPa. The results were then used to extrapolate to inner core pressures and temperature in order to evaluate the strength of the inner core. As shear strength is a measure of a material's resistance to flow, these results support dislocation creep as the dominant deformation mechanism in the Earth's inner core.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2018; ©2018 |
| Publication date | 2018; 2018 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Reagan, Mary Marguerite |
|---|---|
| Degree supervisor | Mao, Wendy (Wendy Li-wen) |
| Thesis advisor | Mao, Wendy (Wendy Li-wen) |
| Thesis advisor | Ewing, Rodney C |
| Thesis advisor | Warren, Jessica (Jessica Mendelsohn) |
| Degree committee member | Ewing, Rodney C |
| Degree committee member | Warren, Jessica (Jessica Mendelsohn) |
| Associated with | Stanford University, Department of Geological and Environmental Sciences. |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Mary Marguerite Reagan. |
|---|---|
| Note | Submitted to the Department of Geological and Environmental Sciences. |
| Thesis | Thesis Ph.D. Stanford University 2018. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2018 by Mary Marguerite Reagan
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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