Volatiles and Redox in Mercury and Chondritic Parent Bodies: Insights from Experiments and Laboratory Analyses of Meteorites

Anzures, Brendan Anthony

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Year:: 2021
Contributor:: Anzures, Brendan Anthony (creator); Parman, Stephen (Advisor); Milliken, Ralph (Advisor); Evans, Alexander (Reader); Huber, Christian (Reader); Boesenberg, Joseph (Reader); McCoy, Timothy (Reader); Brown University. Department of Earth, Environmental, and Planetary Sciences (sponsor)
Genre:: theses
Subject:: Spectroscopy; Geochemistry; Water; Planetary science; Petrology; Mercury (Planet); Chondrites (Meteorites); Achondrites; Sulfur; X-ray absorption near edge structure; Secondary ion mass spectrometry; Electron probe microanalysis; Thermogravimetry; Reflectance spectroscopy
Extent:: xix, 292 p.

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Abstract:: Redox strongly affects the amount and species of volatile elements (S, C, F, Cl, H) stable in magmas that exert primary controls on the origin and early evolution of planets. In very reduced planetary interiors relevant for the planet Mercury as well as parent bodies of meteorite groups enstatite chondrites and aubrites, sulfur as S2- is the primary magmatic volatile. Under oxidizing conditions typical of outer solar system planetary bodies, hydrogen split between H2O and OH is the primary geologic volatile of interest. This dissertation includes a diverse set of projects that quantify volatiles in planetary materials (both meteorites and high-pressure, high-temperature experiments) to understand chemical processes at depth and at the surface. Chapter 1 developed new S K-edge XANES spectroscopy standards (Anzures et al., 2020, AmMin), while Chapter 2 applied these new standard spectra as a sensitive probe of S speciation in reduced silicate melts (Anzures et al., 2020, GCA). Chapters 2 and 3 quantified the combined effects of oxygen fugacity (fO2), pressure, temperature, and composition on S speciation, and found that oxygen fugacity exerts the main control on whether FeS (fO2 > IW-2), CaS (IW-2 > fO2 > IW-4), or MgS (fO2 < IW-4) is the dominant sulfide species in silicate melt. These changes in S speciation have substantial impacts on both the chemical and physical properties of the melts that have led to Mercury’s distinct evolution. Chapter 5 developed a novel S-in-enstatite oxybarometer to calculate the fO2 of individual enstatite grains in a suite of reduced meteorites, finding evidence for variable reduction of silicates that were slightly more oxidized than co-existing metal. Chapter 4 focused on understanding how assumptions of planetary surface grain size affect quantitative estimates of water with applications for current missions Hayabusa2 and OSIRIS-REx. Results showed that as particle size decreases, a variety of reflectance spectral parameters related to OH/H2O absorption strength increase in value. Thus, if particle size in not properly accounted for on rubble-pile hydrous asteroids, interpretations of reflectance spectra may lead to underestimates of water content of as much as 6 wt.% in materials that typically have 10-20 wt.% water.
Notes:: Thesis (Ph. D.)--Brown University, 2021

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Citation

Anzures, Brendan Anthony, "Volatiles and Redox in Mercury and Chondritic Parent Bodies: Insights from Experiments and Laboratory Analyses of Meteorites" (2021). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library. https://repository.library.brown.edu/studio/item/bdr:edpubym9/

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Earth, Environmental and Planetary Sciences Theses and Dissertations

Theses and Dissertations for the Earth, Environmental and Planetary Sciences department.
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