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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Shock Effects and Mineral Assemblages in the Genomict Eucrite Northwest Africa 8677

Description
Shock effects in meteorites provide important insights into impacts on their parent bodies. Eucrites are among the Howardite-Eucrite-Diogenite (HED) class of achondrites that likely originate from the intact, differentiated asteroid Vesta. Brecciated eucrites provide a record of the impact processes that occurred after the crustal formation of the parent body.…

Shock effects in meteorites provide important insights into impacts on their parent bodies. Eucrites are among the Howardite-Eucrite-Diogenite (HED) class of achondrites that likely originate from the intact, differentiated asteroid Vesta. Brecciated eucrites provide a record of the impact processes that occurred after the crustal formation of the parent body. Radiometric dating of HEDs has shown that they were affected by resetting events at 3.4 – 4.1 and 4.48 Ga. Therefore, shock effects in HEDs are windows into ancient impacts on asteroids early in solar system history. Northwest Africa (NWA) 8677 is a genomict eucrite with lithologies that are texturally different, but compositionally similar. The clasts in the breccia include strongly shocked (S5) gabbroic fragments and weakly shocked (S3) basaltic clasts. Coesite, a high-pressure polymorph of quartz, is preserved in the core of a large (~250 μm) silica grain, indicating the gabbro was strongly shocked. A large thermal overprint from the surrounding melt resulted in the transformation of coesite to low-pressure silica phases of quartz and cristobalite on the rims of this grain. The shock melt, interstitial to the breccia fragments, exhibits well-developed quench textures and contains a low-pressure mineral assemblage of plagioclase and pyroxene, implying that crystallization occurred after pressure release. The heterogeneity in shock features between the gabbroic and basaltic lithologies suggests that NWA 8677 experienced a variable impact history, which included at least two impact events. An initial impact strongly shocked and brecciated the gabbro and ejected both onto the regolith of the parent body where a more weakly shocked basalt was incorporated. A second impact produced the interstitial melt between the breccia matrix. The temperature of this shock melt remained high after pressure release, resulting in crystallization of a low-pressure assemblage of pyroxene and feldspar, as well as the transformation of quartz + cristobalite rims on coesite
ContributorsMarquardt, Madeline Claire (Co-author) / Sharp, Thomas (Co-author, Thesis director) / Fudge, Crystylynda (Co-author) / Irving, Tony (Co-author) / Barboni, Melanie (Committee member) / Desch, Steve (Committee member) / School of Earth and Space Exploration (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
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Tissintite-II and Other High Pressure/Temperature Minerals in Lunar Meteorite NWA 13967

Description

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…

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.
ContributorsKroemer, Christian (Author) / Wadhwa, Meenakshi (Thesis director) / Wittmann, Axel (Committee member) / Sharp, Thomas (Committee member) / Barrett, The Honors College (Contributor) / School of Human Evolution & Social Change (Contributor) / Historical, Philosophical & Religious Studies, Sch (Contributor) / School of Earth and Space Exploration (Contributor)
Created2022-05