Nucleosynthetic zinc isotope variations in meteorites
File(s)
Author(s)
Martins Pimentel, Rayssa
Type
Thesis
Abstract
Nucleosynthetic isotope anomalies have been extensively used as tracers to identify Earth’s building blocks among other Solar System materials. However, while such anomalies have been well characterized for refractory elements, studies attempting to identify anomalies of volatile elements – many of which are essential for life – have found them to be undetectable with available precision levels, or of ambiguous origin, leaving the sources of terrestrial volatiles unconstrained. The present study focuses on characterizing the mass-independent isotope compositions of the moderately volatile element Zn in meteorites with the purpose of identifying anomalies, establishing their origin, and using them to constrain the sources of Earth’s Zn.
The mass-independent Zn isotope compositions of twenty-seven meteorites were determined and found to be compatible with the predicted isotopic yields of two types of supernovae. Other mechanisms that can induce isotope fractionation were considered but reasonably discarded, making a nucleosynthetic origin the most likely explanation for the anomalies. The results were used in a series of mass balance mixing models intended to determine which of the available Solar System materials could have contributed to Earth’s Zn budget. The models suggest that carbonaceous materials, which formed at much greater heliocentric distances than Earth, supplied nearly half of its Zn, with the remaining fraction originating from more locally sourced non-carbonaceous materials.
Further constraints provided by meteorite and terrestrial elemental, nucleosynthetic and mass-dependent isotope compositions of elements other than Zn were employed in additional models that attempted to constrain not only the mass, but also the volatile contributions of Earth’s precursor materials. The results suggest that Earth accreted mainly (~60% of its mass) from highly volatile depleted differentiated non-carbonaceous bodies, with most of its volatile content being supplied by undifferentiated planetesimals. The addition of primitive material may therefore be necessary to establish the volatile content of terrestrial planets.
The mass-independent Zn isotope compositions of twenty-seven meteorites were determined and found to be compatible with the predicted isotopic yields of two types of supernovae. Other mechanisms that can induce isotope fractionation were considered but reasonably discarded, making a nucleosynthetic origin the most likely explanation for the anomalies. The results were used in a series of mass balance mixing models intended to determine which of the available Solar System materials could have contributed to Earth’s Zn budget. The models suggest that carbonaceous materials, which formed at much greater heliocentric distances than Earth, supplied nearly half of its Zn, with the remaining fraction originating from more locally sourced non-carbonaceous materials.
Further constraints provided by meteorite and terrestrial elemental, nucleosynthetic and mass-dependent isotope compositions of elements other than Zn were employed in additional models that attempted to constrain not only the mass, but also the volatile contributions of Earth’s precursor materials. The results suggest that Earth accreted mainly (~60% of its mass) from highly volatile depleted differentiated non-carbonaceous bodies, with most of its volatile content being supplied by undifferentiated planetesimals. The addition of primitive material may therefore be necessary to establish the volatile content of terrestrial planets.
Version
Open Access
Date Issued
2023-10-28
Date Awarded
2024-02-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Rehkämper, Mark
Sponsor
Imperial College London
Publisher Department
Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)