Theses and Dissertations
This collection includes both ASU Theses and Dissertations, submitted by graduate students, and the Barrett, Honors College theses submitted by undergraduate students.
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Description
Meteorites provide an opportunity to reconstruct the history of the SolarSystem. Differentiated meteorites, also called achondrites, are the result of melting
and differentiation processes on their parent body. Stable isotopic compositions of
differentiated meteorites and their components have added to the understanding of
physical parameters, such as temperature, pressure, and redox conditions relevant
to differentiation processes on planetesimals and planets in the early Solar System.
In particular, Fe and Si isotopes have proven to be useful in advancing the
understanding of physical and chemical processes during planetary accretion and
subsequent evolution.
In this work, I developed a new method to simultaneously purify Fe and Si
from a single aliquot of sample while ensuring consistently high yields and accurate
and precise isotopic measurements. I then measured the Fe isotope compositions
and Si contents of metals from aubrite meteorites to infer the structure and thermal
evolution of their asteroidal parent body. Thereafter, I determined the combined Si
and Fe isotope compositions of aubrite metals and the Horse Creek iron meteorite,
and compared the magnitude of Si and Fe isotope fractionation factors between
metal and silicates for both enstatite chondrites and aubrites to estimate the effect of
high-temperature core formation that occurred on the aubrite parent body. I
additionally assessed whether correlated Si and Fe isotope systematics can be used
to trace core formation and partial melting processes for the aubrite parent body,
angrite parent body, Mars, Vesta, Moon, and Earth. Finally, I measured the combined
Fe and Si isotope composition of a variety of ungrouped achondrites and brachinites
that record different degrees of differentiation under different redox conditions to
evaluate the role of differentiation and oxygen fugacity in controlling their Fe and Si
isotope compositions. Taken together, this comprehensive dataset reveals the
thermal evolution of the aubrite parent body, provides insights into the factors controlling the Fe and Si isotope compositions of various planetary materials, and
helps constrain the bulk starting composition of planets and planetesimals.
ContributorsRay, Soumya (Author) / Wadhwa, Meenakshi (Thesis advisor) / Garvie, Laurence (Committee member) / Till, Christy (Committee member) / Hervig, Richard (Committee member) / Schrader, Devin (Committee member) / Arizona State University (Publisher)
Created2021
Description
This study explores how bulk composition and oxygen fugacity (fO2) affect the partitioning of sulfur between the molten mantle and core of an early planetesimal. The model can be used to determine the range of potential sulfur concentrations in the asteroid (16) Psyche, which is the target of the National Aeronautics and Space Administration/Arizona State University Psyche Mission. This mission will be our visit to an M-type asteroid, thought to be dominantly metallic.
The model looks at how oxygen fugacity (fO2), bulk composition, temperature, and pressure affect sulfur partitioning in planetesimals using experimentally derived equations from previous studies. In this model, the bulk chemistry and oxygen fugacity of the parent body is controlled by changing the starting material, using ordinary chondrites (H, L, LL) and carbonaceous chondrites (CM, CI, CO, CK, CV). The temperature of the planetesimal is changed from 1523 K to 1873 K, the silicate mobilization and total melting temperatures, respectively; and pressure from 0.1 to 20 GPa, the core mantle boundary pressures of Vesta and Mars, respectively.
The final sulfur content of a differentiated planetesimal core is strongly dependent on the bulk composition of the original parent body. In all modeled cores, the sulfur content is above 5 weight percent sulfur; this is the point at which the least amount of other light elements is needed to form an immiscible sulfide liquid in a molten core. Early planetesimal cores likely formed an immiscible sulfide liquid, a eutectic sulfide liquid, or potentially were composed of mostly troilite, FeS.
The model looks at how oxygen fugacity (fO2), bulk composition, temperature, and pressure affect sulfur partitioning in planetesimals using experimentally derived equations from previous studies. In this model, the bulk chemistry and oxygen fugacity of the parent body is controlled by changing the starting material, using ordinary chondrites (H, L, LL) and carbonaceous chondrites (CM, CI, CO, CK, CV). The temperature of the planetesimal is changed from 1523 K to 1873 K, the silicate mobilization and total melting temperatures, respectively; and pressure from 0.1 to 20 GPa, the core mantle boundary pressures of Vesta and Mars, respectively.
The final sulfur content of a differentiated planetesimal core is strongly dependent on the bulk composition of the original parent body. In all modeled cores, the sulfur content is above 5 weight percent sulfur; this is the point at which the least amount of other light elements is needed to form an immiscible sulfide liquid in a molten core. Early planetesimal cores likely formed an immiscible sulfide liquid, a eutectic sulfide liquid, or potentially were composed of mostly troilite, FeS.
ContributorsBercovici, Hannah La'ia (Author) / Elkins-Tanton, Linda T. (Thesis advisor) / Garvie, Laurence (Committee member) / Wadhwa, Meenakshi (Committee member) / Arizona State University (Publisher)
Created2020