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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Chemical Reduction of Silicates by Meteorite Impacts and Lightning Strikes

Sheffer, Abigail Anne January 2007 (has links)
A suite of lightning strike glasses and unmelted starting materials has been studied by electron microscope and Mossbauer spectroscopy to determine Fe oxidation states. Nine of eleven samples are reduced compared to the starting materials; four of the glasses contain Fe0. Only one sample contained evidence of reduction by carbon, and the results support the reduction of Fe as intrinsic to the rapid, high temperature processing during lightning strikes.A thermodynamic modeling code is used to model the formation of moldavite tektites and the reduction of Fe from sediments around the Ries crater. During isentropic cooling from a strong shock, Fe3+ is reduced to Fe2+ at all modeled conditions. The best matches to an average moldavite composition and the compositions of the Bohemian and Bohemian:Radomilice sub-strewn fields occur with a mixture of surface and subsurface sands along a 4500 J/kg-K isentropic cooling path, consistent with an asteroid impact. The Lusatian and Moravian sub-strewn fields are better represented by starting materials of entirely surface sands, consistent with the uppermost layers of surface material having traveled the farthest from the impact.The thermodynamic code is also used to investigate the formation of lunar regolith agglutinates and reduction of Fe to Fe0. Forming Fe0 requires assuming Fe0 is miscible in silicate liquid at elevated temperatures and pressures. When Fe0 is included in the liquid solution, it is stable at modeled conditions. Simple separation of liquid from vapor is not sufficient to reproduce agglutinate glass. When the vapor phase is allowed to partially redeposit and some Fe0 is directly condensed from vapor, the resulting liquid better reproduces mare agglutinate glasses. This model cannot reproduce highland agglutinate glass, because the Al concentration remains too high in the liquid. The best match to mare glass is produced using the <10 µm fraction of the mare soil along the 8000 J/kg-K cooling isentrope at 100 bars, 4370 K with 95% vapor redeposition and 50% of the Fe(g) directly condensed as Fe0. The reduced fulgurite samples and the results of the impact models suggest that Fe reduction is intrinsic to the rapid, high temperature processing of silicates.
42

Petrographic investigation of selected samples from drill cores Eyreville A and Eyreville B Chesapeake Bay impact structure, Virginia /

Glidewell, Jennifer Lynn. King, David T. January 2008 (has links) (PDF)
Thesis (M.S.)--Auburn University, 2008. / Abstract. Includes bibliographical references (p. 113-121).
43

Geology and lithology of the early Palaeozoic marine impact structures Kärdla and Neugrund (Estonia) /

Suuroja, Kalle-Mart, January 2008 (has links)
Thesis (doctoral)--University of Tartu, 2008. / Vita. Includes bibliographical references.
44

Application of Isoleucine Epimerization to Assess Terrestrial Contamination and Constrain the Duration and Effects of Aqueous Alteration of Carbonaceous Chondrite Meteorites

January 2014 (has links)
abstract: Carbonaceous chondrites (CCs) present a unique opportunity for learning about the earliest organic chemistry that took place in our Solar System. The complex and diverse suite of meteoritic organic material is the result of multiple settings and physicochemical processes, including aqueous and thermal alteration. Though meteorites often inform origin-of-life discussions because they could have seeded early Earth with significant amounts of water and pre-biotic, organic material, their record of abiotic, aqueous, and organic geochemistry is of interest as well. 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. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2014
45

Hydrogen Isotopic Systematics of Nominally Anhydrous Phases in Martian Meteorites

January 2015 (has links)
abstract: Hydrogen isotope compositions of the martian atmosphere and crustal materials can provide unique insights into the hydrological and geological evolution of Mars. While the present-day deuterium-to-hydrogen ratio (D/H) of the Mars atmosphere is well constrained (~6 times that of terrestrial ocean water), that of its deep silicate interior (specifically, the mantle) is less so. In fact, the hydrogen isotope composition of the primordial martian mantle is of great interest since it has implications for the origin and abundance of water on that planet. Martian meteorites could provide key constraints in this regard, since they crystallized from melts originating from the martian mantle and contain phases that potentially record the evolution of the H2O content and isotopic composition of the interior of the planet over time. Examined here are the hydrogen isotopic compositions of Nominally Anhydrous Phases (NAPs) in eight martian meteorites (five shergottites and three nakhlites) using Secondary Ion Mass Spectrometry (SIMS). This study presents a total of 113 individual analyses of H2O contents and hydrogen isotopic compositions of NAPs in the shergottites Zagami, Los Angeles, QUE 94201, SaU 005, and Tissint, and the nakhlites Nakhla, Lafayette, and Yamato 000593. The hydrogen isotopic variation between and within meteorites may be due to one or more processes including: interaction with the martian atmosphere, magmatic degassing, subsolidus alteration (including shock), and/or terrestrial contamination. Taking into consideration the effects of these processes, the hydrogen isotope composition of the martian mantle may be similar to that of the Earth. Additionally, this study calculated upper limits on the H2O contents of the shergottite and nakhlite parent melts based on the measured minimum H2O abundances in their maskelynites and pyroxenes, respectively. These calculations, along with some petrogenetic assumptions based on previous studies, were subsequently used to infer the H2O contents of the mantle source reservoirs of the depleted shergottites (200-700 ppm) and the nakhlites (10-100 ppm). This suggests that mantle source of the nakhlites is systematically drier than that of the depleted shergottites, and the upper mantle of Mars may have preserved significant heterogeneity in its H2O content. Additionally, this range of H2O contents is not dissimilar to the range observed for the Earth’s upper mantle. / Dissertation/Thesis / Masters Thesis Geological Sciences 2015
46

Early Solar System to Deep Mantle: The Geochemistry of Planetary Systems

January 2014 (has links)
abstract: The origin of the solar system and formation of planets such as Earth are among the most fascinating, outstanding scientific problems. From theoretical models to natural observations, it is possible to infer a general way of how the solar system evolved from the gravitational collapse of the molecular cloud to accretion and differentiation of planetary-sized bodies. This dissertation attempts to place additional constraints on the source, distribution, and evolution of chemical variability in the early solar system, Mars, and Earth. A new method was developed for the measurement of titanium isotopes in calcium-aluminum-rich inclusions (CAIs) by laser ablation multi-collector inductively coupled plasma mass spectrometry. The isotopic compositions of 17 Allende CAIs define a narrow range with clearly resolved excesses in 46Ti and 50Ti and suggests that "normal" CAIs formed from a relatively uniform reservoir. Petrologic and isotopic analysis of a new FUN (Fractionated and Unknown Nuclear effects) CAI suggests that normal and FUN CAIs condensed in similar environments, but subsequently evolved under vastly different conditions. Volatiles may have influenced the formation and evolution of basaltic magmas on Mars. Light lithophile element (LLE) and fluorine (F) concentrations and isotopic compositions of pyroxene determined in situ in several Martian meteorites suggests that the primary magmatic signature of LLE and F zonation in Shergottite pyroxene has been disturbed by post-crystallization diffusive equilibration. Using relevant crystal-melt partition coefficients the F contents for Martian meteorite parental melts are ~910 and ~220 ppm. Estimates of the F content in the Shergottite and Nakhlite source regions are similar to that of mid-ocean ridge basalts (MORB) and ocean island basalts (OIB), respectively, here on Earth. Noble gas systematics of OIBs relative to MORBs, suggests OIBs preferentially sample a primordial reservoir located within Earth's mantle. Geodynamic calculations were performed to investigate the time-dependent rate of material entrained into plumes from these primordial reservoirs. These models predict melts rising to the surface will contain variable proportions of primordial material. The results demonstrate that although high 3He/4He ratios may mandate a mantle plume that samples a primordial reservoir, more MORB-like 3He/4He ratios in OIBs do not preclude a deep plume source. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2014
47

Le flux de météorites sur Terre : apport de la mesure de multiples nucléides cosmogéniques, et collectes en milieu désertique / The flux of meteorites on Earth : Contribution of measuring the concentration of multiple cosmogenic nuclides, and collections in arid areas

Hützler, Aurore 30 January 2015 (has links)
Le flux de météorites vers la Terre peut être déterminé en observant des bolides, ou en étudiant des collections de météorites. Pour estimer l’intensité et la composition du flux, nous avons collecté et classifié une collection de 213 météorites issues du désert de l’Atacama (Chili). Nous avons développé un protocole chimique afin d’extraire des nucléides cosmogéniques de chondrites ordinaires. La fraction métallique est d’abord séparée de la météorite. Les échantillons sont ensuite dissouts dans l’acide, et les éléments utiles sont extraits et purifiés grâce à des résines échangeuses d’ions et des précipitations contrôlées. Après la mesure par SMA, les concentrations de nucléides cosmogéniques nous permettent de calculer l’âge terrestre, le rayon pré-atmosphérique et la profondeur dans le météoroide, en utilisant l'approche développée par Leya & Masarik (2009). En combinant le nombre de météorites par unité de surface et les spectres d’âge terrestre, nous pouvons déterminer un flux de 218 météorites>10g/Ma/km2 sur une période de 700 ka avec la méthode 41Ca.Dans le cadre d’une collaboration avec l’Université de Bern (Suisse), nous avons aussi mesuré les concentrations en gaz rares dans certaines de ces météorites. Les concentrations en gaz rares et en nucléides radiogéniques ont ensuite été étudiées avec le modèle développé par Ammon et al. (2009), afin de déterminer le temps d’exposition dans l’espace, l’âge terrestre, le rayon pré-atmosphérique et la profondeur dans le météoroide. / Meteorite flux to the Earth can be determined using observations of fireballs or studying meteorites collections. To estimate the intensity and the composition of the flux, we collected and classified a 213 samples collection from the Atacama desert (Chile). We developed a mathematical model to help pairing of meteorites, and hence get a reliable number of falls per unit of surface. A chemical procedure to extract the cosmogenic nuclides 10Be, 26Al, 36Cl and 41Ca from ordinary chondrites was developed. The metallic fraction was extracted from the bulk meteorite. Samples were dissolved into acid and the elements of interest were extracted and purified using ion-exchange resins and pH controlled precipitation. After measurements using the Accelerator Mass Spectrometry (AMS) technique, the cosmogenic nuclides concentrations enable us to calculate terrestrial age, pre-atmospheric radius and shielding depth, using the Leya & Masarik (2009) model. Combining the number of meteorites per km2 and the terrestrial ages spectrum, we determine a flux of 218 meteorites > 10g/Ma/km2 over 700 ka with the 41Ca calculation method. Applying the same procedure as described above, we studied a selection of iron meteorites in which noble gases (He, Ne and Ar isotopes) concentrations were measured in collaboration with the University of Bern (Switzerland). Stable and radiogenic nuclides concentration results were then used according to the Ammon et al. (2009) model to determine Cosmic Ray Exposure (CRE) ages, terrestrial ages, pre-atmospheric radii and shielding depths.
48

New Insights Into the Petrogenesis of Lunar Basaltic Breccia Meteorites from the Dominion Range (DOM) 18543

Schweitzer, Alex Ross 19 July 2023 (has links)
No description available.
49

The Gatun structure [electronic resource] : a geological assessment of a newly recognized impact structure near Lake Gatun in the Republic of Panama / by Livio Leonardo Tornabene.

Tornabene, Livio Leonardo. January 2002 (has links)
Title from PDF of title page. / Document formatted into pages; contains 558 pages. / Original thesis submitted in HTML and can be accessed at http://www.lib.usf.edu/ETD-db/theses/available/etd-10122001-142859/unrestricted/frame.html / td.pdf / Thesis (M.S.)--University of South Florida, 2002. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: The Gatun Structure, (Latitude N 09° 05&softsign; 58.1", Longitude W 79° 47&softsign; 21.8", situated in the triple-canopy rainforest 10 km to the WSW of the Gamboa and about 2 km south of the Isle of Barbacoas, Republic de Panama), is a partially inundated, quasi-concentric surface feature 2.2 - 3km in diameter, which appears in aerial photographs and in radar imagery as an arcuate chain of islands with a raised center. Although the structure has been heavily weathered and altered, it has retained morphology consistent with complex craters: an elevated circular central uplift 500-600 m in diameter and 50m high, and arcuate boundary ridges (a rim structure?) ranging from 50-100 meters high. Within the central peak, highly altered and fractured siltstone of the Gatuncillo (?) formation (Eocene) (+-) older rocks are uplifted and exposed through surrounding calcareous units of the Caimito formation (Oligocene) and the Las Cascadas formation (Miocene), the major target rocks in the region. / ABSTRACT: Lithologies in the structure include highly fractured siliciclastic rocks (siltstone, sandstones and greywackes), limestones with anomalous spherical glass inclusions, both black and white hypocrystalline glasses (possible melt rocks), lithic fragmental breccias, and melt-bearing breccias (possible impact melt breccias and suevites), some of which contain flow banding and evidence for selective melting of minerals. Three types of spherules (glass, fluid-drop and lithic), a pyroxene-quartz "necklace" disequilibrium structure (coronas), plagioclase feldspars exhibiting mosaicism and partially amorphization, possible liquid immiscibility between melts of calcite and felpspathic glass, as well as decomposition of titanomagnite or ulvospinel, are all petrographic indicators of a hypervelocity impact event. / ABSTRACT: The structure is crosscut by numerous dikes of unshocked basalt and basaltic andesite related to volcanism along the Panamanian segment of the Central American arc to the south. However, the lithologies of the Gatun Structure are chemically inconsistent with the regional volcanic rocks and the unshocked volcanic rocks that crosscut the structure. The lack of an igneous relationship between the Gatun structure and the explosive volcanism of Panamanian arc the presence of classical shock lithologies within the site, and the occurrence of spherules, maskelynite and other disequilibrium shock features in the rocks, an impact origin is our preferred interpretation for the Gatun structure. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.
50

Origin and evolution of ureilite vein metal - Fe, Ni, Co and Ni-isotope systematics of ureilite vein metal and ureilite silicates

Gabriel, Aron David 30 October 2009 (has links)
No description available.

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