Filtering by
- All Subjects: Meteorites
- Creators: School of Earth and Space Exploration
- Creators: Shock, Everett L
CC materials previously resided on asteroidal parent bodies, relic planetesimals of Solar System formation which never accreted enough material to develop long-lived, large-scale geological processes. These bodies were large enough, however, to experience some degree of heating due to the decay of radiogenic isotopes, and the meteorite record suggests the existence of 100-150 parent bodies which experienced varying degrees of thermal and aqueous alteration for the first several 10 Myr of Solar System history.
The first chapter of this dissertation reviews literature addressing aqueous alteration as an essential participant in parent body geochemistry, organic synthesis, or both (though papers which address both are rare). The second chapter is a published organic analysis of the soluble organic material of Bells, an unclassified type 2 chondrite. Analytical approaches to assess terrestrial contamination of meteorite samples are also reviewed in the first chapter to allow introduction in chapter 3 of kinetic modeling which rules out certain cases of contamination and constrains the timing of thermal and aqueous alteration. This is the first known application of isoleucine epimerization for either of these purposes. Chapter 4 is a kinetic study of D-allo-isoleucine epimerization to establish its behavior in systems with large, relative abundances of alloisoleucine to isoleucine. Previous epimerization studies for paleontological or geological purposes began with L-isoleucine, the only protein amino acid of the four isoleucine stereoisomers.
Kinetic model calculations using isoleucine stereoisomer abundances from 7 CR chondrites constrain the total duration of the amino acids' residence in the aqueous phase. The comparatively short timescales produced by the presented modeling elicit hypotheses for protection or transport of the amino acids within the CR parent body.
Lunar meteorites are created when an asteroid impacts the Moon. In such events, the lunar surface, known as regolith, can experience extreme pressures and temperature conditions. Some of this regolith material can be ejected from the Moon and enter interplanetary space where it can be captured by Earth's gravity. Even after falling to Earth, the minerals of lunar meteorites preserve the history and conditions of lunar impact processes. One such mineral that has gained attention recently is tissintite due to its relatively specific temperature and pressure formation conditions. The lunar meteorite NWA 13967 and its mineral assemblage provided an opportunity for comparison to other lunar meteorites (Zhang et al. 2021). Based on its mineralogy and petrography, NWA 13967 likely experienced peak pressures of 18 to 24 GPa and peak temperatures above 2000℃, as indicated by the presence of intergranular melt, vesicles, and corundum. The occurrence of tissintite-II and coesite suggest crystallization during cooling and decompression, while other high pressure minerals likely back-transformed to lower pressure polymorphs.