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- All Subjects: cosmochemistry
- All Subjects: Mineralogy
- Creators: Young, Patrick A
Description
The present work covers two distinct microanalytical studies that address issues in planetary materials: (1) Genesis Na and K solar wind (SW) measurements, and (2) the effect of water on high-pressure olivine phase transformations.
NASA’s Genesis mission collected SW samples for terrestrial analysis to create a baseline of solar chemical abundances based on direct measurement of solar material. Traditionally, solar abundances are estimated using spectroscopic or meteoritic data. This study measured bulk SW Na and K in two different Genesis SW collector materials (diamond-like carbon (DlC) and silicon) for comparison with these other solar references. Novel techniques were developed for Genesis DlC analysis. Solar wind Na fluence measurements derived from backside depth profiling are generally lower in DlC than Si, despite the use of internal standards. Nevertheless, relative to Mg, the average SW Na and K abundances measured in Genesis wafers are in agreement with solar photospheric and CI chondrite abundances, and with other SW elements with low first ionization potential (within error). The average Genesis SW Na and K fluences are 1.01e11 (+9e09, -2e10) atoms/cm2 and 5.1e09 (+8e08, -8e08) atoms/cm2, respectively. The errors reflect average systematic errors. Results have implications for (1) SW formation models, (2) cosmochemistry based on solar material rather than photospheric measurements or meteorites, and (3) the accurate measurement of solar wind ion abundances in Genesis collectors, particularly DlC and Si.
Deep focus earthquakes have been attributed to rapid transformation of metastable olivine within the mantle transition zone (MTZ). However, the presence of H2O acts to overcome metastability, promoting phase transformation in olivine, so olivine must be relatively anhydrous (<75 ppmw) to remain metastable to depth. A microtextural analysis of olivine phase transformation products was conducted to test the feasibility for subducting olivine to persist metastably to the MTZ. Transformation (as intracrystalline or rim nucleation) shifts from ringwoodite to ringwoodite-wadsleyite nucleation with decreasing H2O content within olivine grains. To provide accurate predictions for olivine metastability at depth, olivine transformation models must reflect how changing H2O distributions lead to complex changes in strain and reaction rates within different parts of a transforming olivine grain.
NASA’s Genesis mission collected SW samples for terrestrial analysis to create a baseline of solar chemical abundances based on direct measurement of solar material. Traditionally, solar abundances are estimated using spectroscopic or meteoritic data. This study measured bulk SW Na and K in two different Genesis SW collector materials (diamond-like carbon (DlC) and silicon) for comparison with these other solar references. Novel techniques were developed for Genesis DlC analysis. Solar wind Na fluence measurements derived from backside depth profiling are generally lower in DlC than Si, despite the use of internal standards. Nevertheless, relative to Mg, the average SW Na and K abundances measured in Genesis wafers are in agreement with solar photospheric and CI chondrite abundances, and with other SW elements with low first ionization potential (within error). The average Genesis SW Na and K fluences are 1.01e11 (+9e09, -2e10) atoms/cm2 and 5.1e09 (+8e08, -8e08) atoms/cm2, respectively. The errors reflect average systematic errors. Results have implications for (1) SW formation models, (2) cosmochemistry based on solar material rather than photospheric measurements or meteorites, and (3) the accurate measurement of solar wind ion abundances in Genesis collectors, particularly DlC and Si.
Deep focus earthquakes have been attributed to rapid transformation of metastable olivine within the mantle transition zone (MTZ). However, the presence of H2O acts to overcome metastability, promoting phase transformation in olivine, so olivine must be relatively anhydrous (<75 ppmw) to remain metastable to depth. A microtextural analysis of olivine phase transformation products was conducted to test the feasibility for subducting olivine to persist metastably to the MTZ. Transformation (as intracrystalline or rim nucleation) shifts from ringwoodite to ringwoodite-wadsleyite nucleation with decreasing H2O content within olivine grains. To provide accurate predictions for olivine metastability at depth, olivine transformation models must reflect how changing H2O distributions lead to complex changes in strain and reaction rates within different parts of a transforming olivine grain.
ContributorsRieck, Karen Dianne (Author) / Hervig, Richard L (Thesis advisor) / Sharp, Thomas G (Thesis advisor) / Jurewicz, Amy J G (Committee member) / Wadhwa, Meenakshi (Committee member) / Williams, Peter (Committee member) / Young, Patrick A (Committee member) / Arizona State University (Publisher)
Created2015
Description
Meteorites and their components can be used to unravel the history of the early Solar System. Carbonaceous chondrites are meteorites that originated from undifferentiated parent bodies that formed within a few million years of the beginning of the Solar System. These meteorites contain calcium-aluminum-rich inclusions (CAIs), which are the oldest dated solids in the Solar System at ~4.567 billion years old and thus preserve a record of the earliest stage of Solar System formation. The isotopic compositions of CAIs and bulk carbonaceous chondrites can be used to identify the sources of material inherited by the protoplanetary disk, assess the degree of mixing in the disk, and evaluate sample origins and potential genetic relationships between parent bodies. In particular, mass-independent Cr and Ti isotopic compositions have proven to be especially useful for these purposes.
In this work, I first developed new methods for the chemical separation of Cr and Ti, improving the reliability of existing methods to ensure consistent yields and accurate isotopic measurements. I then measured the Cr and Ti isotopic compositions of CAIs from CV and CK chondrites to determine the extent of isotopic heterogeneity in the CAI-forming region and assess the role of CAIs in the preservation of planetary-scale isotopic anomalies. My results show that all measured CAIs originated from a common isotopic reservoir that incorporated material from at least three distinct nucleosynthetic sources and preserved limited isotopic heterogeneity. These results also suggest that planetary-scale isotopic anomalies cannot be attributed solely to the transport of CAIs from one part of the solar nebula to another. I finally measured the Cr and Ti isotopic compositions of bulk CM, CO, and ungrouped chondrites to evaluate the relationship between CM and CO chondrites, which have been suggested to originate from either distinct but related parent bodies or a common compositionally heterogeneous parent body. My results suggest that CM, CO, and related ungrouped chondrites originated from distinct parent bodies that formed from similar precursor materials in nearby formation regions. These results may have implications for asteroid samples returned by the OSIRIS-REx and Hayabusa2 missions.
In this work, I first developed new methods for the chemical separation of Cr and Ti, improving the reliability of existing methods to ensure consistent yields and accurate isotopic measurements. I then measured the Cr and Ti isotopic compositions of CAIs from CV and CK chondrites to determine the extent of isotopic heterogeneity in the CAI-forming region and assess the role of CAIs in the preservation of planetary-scale isotopic anomalies. My results show that all measured CAIs originated from a common isotopic reservoir that incorporated material from at least three distinct nucleosynthetic sources and preserved limited isotopic heterogeneity. These results also suggest that planetary-scale isotopic anomalies cannot be attributed solely to the transport of CAIs from one part of the solar nebula to another. I finally measured the Cr and Ti isotopic compositions of bulk CM, CO, and ungrouped chondrites to evaluate the relationship between CM and CO chondrites, which have been suggested to originate from either distinct but related parent bodies or a common compositionally heterogeneous parent body. My results suggest that CM, CO, and related ungrouped chondrites originated from distinct parent bodies that formed from similar precursor materials in nearby formation regions. These results may have implications for asteroid samples returned by the OSIRIS-REx and Hayabusa2 missions.
ContributorsTorrano, Zachary (Author) / Wadhwa, Meenakshi (Thesis advisor) / Anbar, Ariel D (Committee member) / Schrader, Devin L (Committee member) / Williams, David A. (Committee member) / Young, Patrick A (Committee member) / Arizona State University (Publisher)
Created2020