Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Billy P.Glass, Dept. of Geological Sciences. Includes bibliographical references.

No description available.

No description available.

This study presents a petrographic description and a classification of ordinary chondrite NWA 6514 and aims to establish the first high-precision Pb-Pb age of a single ordinary chondrite chondrule. Furthermore, the distribution of different isotopic Pb signatures among chondritic components will be investigated by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). This study shows that NWA 6514 can be classified as a highly unequilibrated (subtype 3.10) L or LL chondrite that has experienced moderate terrestrial weathering (W2) and a low degree of shock (S2). The LA-ICP-MS measurements suggest that radiogenic Pb signatures have been locally preserved in chondrules. However, the Pb isotopic compositions of leaches from a large chondrule obtained by thermal ionization mass spectrometry show an anomalous distribution that indicates the presence of an exotic Pb component. The best estimate for the chondrule formation age is a model age of the last leach (4566.8 ± 2.6 Myr).

This study presents a petrographic description and a classification of ordinary chondrite NWA 6514 and aims to establish the first high-precision Pb-Pb age of a single ordinary chondrite chondrule. Furthermore, the distribution of different isotopic Pb signatures among chondritic components will be investigated by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). This study shows that NWA 6514 can be classified as a highly unequilibrated (subtype 3.10) L or LL chondrite that has experienced moderate terrestrial weathering (W2) and a low degree of shock (S2). The LA-ICP-MS measurements suggest that radiogenic Pb signatures have been locally preserved in chondrules. However, the Pb isotopic compositions of leaches from a large chondrule obtained by thermal ionization mass spectrometry show an anomalous distribution that indicates the presence of an exotic Pb component. The best estimate for the chondrule formation age is a model age of the last leach (4566.8 ± 2.6 Myr).

Thesis (M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ. 260-267)

Thesis (Ph. D.)--Oregon State University, 1994. / Typescript (photocopy). Includes bibliographical references (leaves 76-83). Also available via the World Wide Web.

No description available.

Asteroid 4 Vesta, the largest differentiated body in the asteroid belt, is a protoplanet, much like those that accreted to form the Earth. Understanding the geology of Vesta furthers understanding of early differentiation processes that occurred on Earth and helps define igneous processes occurring on other differentiated bodies in the early solar system. Howardite, eucrite and diogenite (HED) meteorites, which are thought to have originated from Vesta, can be analyzed to better understand the geology of that asteroid. Here my colleagues and I investigate the petrology and geochemistry of two groups of HEDs. This work is timely, in that the insights gained from these studies can be used to interpret data from the Dawn spacecraft, which has just been placed into orbit around Vesta. In the first four parts of this dissertation we investigate the origin of olivine in diogenites, which are ultramafic cumulates from Vesta. We discover that the majority of these samples are dimict (two-component) breccias, composed of harzburgitic and orthopyroxenitic lithologies. This is contrary to the traditional belief that all diogenites are orthopyroxenites with small amounts of cumulus olivine. Using bulk and in situ trace element chemistries, along with mineral major/minor element compositions, we demonstrate that these two lithologies were likely related through fractional crystallization. We also examine an anomalous achondritic dunite, and use geochemistry and petrology to demonstrate that it is the first recognized dunite belonging to the HED group. This sample likely also fractionated from a melt prior to the fractionation of harzburgitic and orthopyroxenitic diogenites. In the final part of this dissertation, we investigate compositional and textural heterogeneity in a large group of paired howardites, Vestan regolith breccias composed of diogenite and eucrite. We find significant compositional and textural variation within the group, and a preferential distribution of eucritic material in the finer grain sizes. This suggests an immature regolith, and has implications for interpretation of spectral data to be collected by the Dawn orbiter at Vesta.

[Truncated abstract. Please see the pdf version of the abstract for the complete text.] Thirty impact structures of confirmed or possible status are currently identified in Australia. Twenty-two of these structures are confirmed by the presence of meteorite fragments or shock metamorphic features that are diagnostic of meteorite impact. The remainder have an impact origin supported by strong secondary evidence. New impact structures are being discovered in Australia at a rate of about one every year, with geophysics a key tool in the identification of candidate structures for further investigation. It is estimated that between two and five times the current number of impact structures are yet to be discovered on the Australian continent. Past compilations of the geophysical signatures of impact structures, particularly of their potential field responses, have been focused on structures formed in mainly crystalline targets. From these studies the expected gravity response is an overall low due to fracturing of the target rocks, with a local gravity high common over the centre of large complex structures, due to the structural uplift of denser material. An overall demagnetisation of the target rocks by the high shock pressures generated by the impact is also expected, although central magnetic highs may also be produced by remanently magnetised melt or the uplift of magnetic rocks from depth. The geophysical signatures of fifteen Australian impact structures are discussed, including individual case studies on nine structures and a detailed study of the Yallalie structure. Only one of the structures discussed here was formed in crystalline rocks, with a further two in mixed sedimentary / crystalline targets. The other structures that were studied were formed in either Phanerozoic basins or mildly-deformed Proterozoic sedimentary rocks. The potential field responses of these structures show a greater variability than was expected, particularly between structures that were formed in different types of target rock. A positive gravity response is found over four structures formed in clastic sedimentary rocks deposited in a Phanerozoic basin. These anomalies are due to the emplacement of denser rock into the central uplift. A decrease in density due to brecciation is not apparent in this target rock type. Furthermore, it is suggested that by collapsing pore space and removing water, the density of wet sedimentary rocks may be locally increased by impact. Circular magnetic anomalies are found outside the central uplift of six impact structures formed in either Phanerozoic or weakly-metamorphosed Proterozoic sedimentary basins.Four possible sources for these anomalies are proposed; remanently magnetised melt or suevite surrounding the central uplift, creation of new magnetic minerals along internal faults within the crater by post-impact hydrothermal fluids, deformation of a flat-lying magnetic layer within the target stratigraphy, and magnetic (maghemite, heavy minerals) minerals concentrated within the post-impact crater fill. It is not possible to definitively identify an impact crater from geophysical evidence alone. Consequently, candidate structures selected from geophysical data, even those as strongly supported as Silverpit, should not be given equal status to structures that have been proven beyond doubt by diagnostic geological criteria. However, it is proposed that structures that possess several pieces of secondary evidence, such as circular shape, interpretation of characteristic geophysical features and crater morphometry, be reclassified as “provisional” impact structures and be given a status that is between “possible” and “probable”. A global compilation of the natural resources known to be associated with impact structures has been undertaken. Where possible, an economic value is calculated for the total definable resource for each structure. The prospectivity of impact structures for petroleum, mineral or water resources is reconfirmed by this work. Almost 20% of all known terrestrial impact structures are associated with some form of resource that is, or has been, exploited. The most numerous, and generally most valuable, of these resources are hydrocarbon accumulations stored in structural traps or brecciated rocks within, or around, the structure. The structural displacements resulting from crater formation can expose from beneath cover, or preserve from erosion, a pre-existing, or progenetic, mineral deposit. While the massive base-metal deposits of the Sudbury Mining Camp are perhaps the most famous of all impact-related economic resources, they require the preservation of the melt sheet formed by a very large (>150 km diameter) impact structure. The Sudbury mineralisation is probably unique on the Earth, but may be a valid target for metal exploration on other planets. Other types of natural resource include surface or ground water, deposits of chemical or organic-rich sedimentary material, hydrothermal ores and industrial diamonds.