Pit crater and pit crater chains associated to the volcano Arsia Mons on Mars have been mapped to analyse their spatial pattern and to conclude about their formation. For the mapping, high resolution satellite data gathered during the Mars Express mission were used. The spatial distribution of the pit craters was then compared with typical patterns of magmatic sheet intrusions within volcanoes as they are known from Earth. The results show that the pattern of the mapped pit craters and pit crater chains are in good agreement with these sheet intrusions and are therefore likely related to Martian sheet intrusions. / Kollapskratrar och kraterkedjor relaterade till vulkanen Arsia Mons på Mars har karterats för att analysera deras spatiala mönster och för att komma till slutsatser för deras tillblivelse. Högupplösta satellitbilder tagna av Mars Express-sonden har använts för karteringen. Fördelningen av de karterade kraterkedjorna jämfördes med typiska fördelningar av magmatiska gångbergarter från vulkaner på jorden. Resultaten visar att fördelningen av kollapskratrar och kraterkedjor överensstämmer enligt förväntningarna och påvisar en relation mellan kollapskratrar och magmatiska gångbergarter på Mars.

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Wellbore seismic measurements were recorded in the Lake Bosumtwi impact structure, Ghana, in 2004. A full range of petrophysical measurements were also performed in the laboratory on core samples from the same boreholes. The Vertical Seismic Profile shows low velocities for both P and S waves in the hardrock basement of the crater. Although we were expected to locate fractures within the rock, no upgoing waves were detected. Density and porosity measurements on the core samples indicate higher than normal porosity in the impact damaged rocks. Mercury porosimetry and SEM analysis characterized the pores as impact induced microcracks. These microcracks are most likely the reason for the low velocities observed on the seismic profiles, the in situ sonic logs, and the seismic velocity measurements on the core samples. Furthermore our laboratory P and S velocities measurements indicate a strong heterogeneity within the impactites. / Geophysics

Thesis (M.S.)-Oregon State University, 1978. / Includes bibliographical referenes (leaves 151-162). Also available via the Internet.

Thesis (M.S.)--Oregon State University. / Includes bibliographical references (leaves 77-78). Also available on the World Wide Web.

abstract: Both volcanism and impact cratering produce ejecta and associated deposits incorporating a molten rock component. While the heat sources are different (exogenous vs. endogenous), the end results are landforms with similar morphologies including ponds and flows of impact melt and lava around the central crater. Ejecta from both impact and volcanic craters can also include a high percentage of melted rock. Using Lunar Reconnaissance Orbiter Camera Narrow Angle Camera (LROC NAC) images, crucial details of these landforms are finally revealed, suggesting a much more dynamic Moon than is generally appreciated. Impact melt ponds and flows at craters as small as several hundred meters in diameter provide empirical evidence of abundant melting during the impact cratering process (much more than was previously thought), and this melt is mobile on the lunar surface for a significant time before solidifying. Enhanced melt deposit occurrences in the lunar highlands (compared to the mare) suggest that porosity, target composition, and pre-existing topography influence melt production and distribution. Comparatively deep impact craters formed in young melt deposits connote a relatively rapid evolution of materials on the lunar surface. On the other end of the spectrum, volcanic eruptions have produced the vast, plains-style mare basalts. However, little was previously known about the details of small-area eruptions and proximal volcanic deposits due to a lack of resolution. High-resolution images reveal key insights into small volcanic cones (0.5-3 km in diameter) that resemble terrestrial cinder cones. The cones comprise inter-layered materials, spatter deposits, and lava flow breaches. The widespread occurrence of the cones in most nearside mare suggests that basaltic eruptions occur from multiple sources in each basin and/or that rootless eruptions are relatively common. Morphologies of small-area volcanic deposits indicate diversity in eruption behavior of lunar basaltic eruptions driven by magmatic volatiles. Finally, models of polar volatile behavior during impact-heating suggest that chemical alteration of minerals in the presence of liquid water is one possible outcome that was previously not thought possible on the Moon. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2016

abstract: Impact craters are ubiquitous throughout the Solar System, formed by one of the principal processes responsible for surface modification of terrestrial planets and solid bodies (i.e., asteroids, icy moons). The impact cratering process is well studied, particularly on the Moon and Mercury, where the results remain uncomplicated by atmospheric effects, plate tectonics, or interactions with water and ices. Crater measurements, used to determine relative and absolute ages for geologic units by relating the cumulative crater frequency per unit area to radiometrically-determined ages from returned samples, are sensitive to the solar incidence angle of images used for counts. Earlier work is quantitatively improved by investigating this important effect and showing that absolute model ages are most accurately determined using images with incidence angles between 65&deg; and 80&deg;, and equilibrium crater diameter estimates are most accurate at ~80&deg; incidence angle. A statistical method is developed using crater size-frequencies to distinguish lunar mare age units in the absence of spectral differences. Applied to the Moon, the resulting areal crater densities confidently identify expansive units with >300&ndash;500 my age differences, distinguish non-obvious secondaries, and determine that an area >1&times;104 km2 provides statistically robust crater measurements. This areal crater density method is also applied to the spectrally-homogeneous volcanic northern smooth plains (NSP) on Mercury. Although crater counts and observations of embayed craters indicate that the NSP experienced at least two resurfacing episodes, no observable age units are observed using areal crater density measurements, so smooth plains emplacement occurred over a relatively short timescale (<500 my). For the first time, the distribution of impact melt on Mercury and the Moon are compared at high resolution. Mercurian craters with diameters &ge;30 km have a greater areal extent of interior melt deposits than similarly sized lunar craters, a result consistent with melt-generation model predictions. The effects of shaking on compositional sorting within a granular regolith are experimentally tested, demonstrating the possibility of mechanical segregation of particles in the lunar regolith. These results provide at least one explanation toward understanding the inconsistencies between lunar remote sensing datasets and are important for future spacecraft sample return missions. / Dissertation/Thesis / Ph.D. Geological Sciences 2013

Araguainha é a maior e mais bem exposta cratera complexa da América do Sul, formada em sedimentos horizontais da Bacia do Paraná. Sua portentosa estrutura com aproximados 40 km de diâmetro e 25 km de cavidade transiente revela um contraste negativo de densidade e susceptibilidade magnética na região do soerguimento central. Esta feição permite inferir um limite de propriedade física entre o Núcleo Central Soerguido (NCS) e o Embasamento Granítico Soerguido (EGS), que por sua vez apresenta baixa razão de Koenigsberger. A caracterização geofísica de Araguainha é sustentada por modelamento 2,5D com base em informações gravimétricas, aeromagnéticas e magnéticas terrestres, o que permite classificá-la como uma estrutura concêntrica e simétrica, com profundidade média do embasamento a 1,0 km, exceto para a borda sul, que apresenta soerguimento mais acentuado. A interface embasamento/sedimento é seccionada por pares espelhados de falhas radiais que surgem no estágio de modificação da cratera. Estas estruturas rúpteis conferem as maiores profundidades à região da bacia anelar e promovem constricção dos sedimentos com tensão horizontal radial. A observação e interpretação destas deformações permitem caracterizar Araguainha como uma estrutura de impacto de domínio rúptil-dúctil. / Araguainha is the largest and the best-exposed complex crater of South America, formed in horizontal sediments of the Paraná Basin. Its portentous structure with 40 km in diameter and 25 km of transient cavity reveals a negative contrast of density and magnetic susceptibility in the central uplift. That feature allows to infer a limit of physical property between the uplifted central core and the uplifted granite basement, which shows a low Konigsberger?s ratio. The geophysical characterization of Araguainha is sustained by 2,5D modeling with gravity, aeromagnetic, and ground magnetic information and It allows to classify it as a concentric, symmetrical structure, with average basement depth of 1.0 km, except in the southern rim, that shows a bigger uplift. The basement/sediment interface is cut by specular pairs of radial faults that appears in the modification stage of the crater. These brittle structures are responsible for the biggest depths in the annular basin region, and they promote a sediment constriction with horizontal radial tension. The observation and interpretation of these deformations allow to characterize Araguainha as an impact brittle-ductile domain structure.

Orientadores: Carlos Roberto de Souza Filho, Cristiano de Carvalho Lana / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-23T13:22:26Z (GMT). No. of bitstreams: 1 Silva_Dailto_D.pdf: 6673922 bytes, checksum: ad586d69e4694b3e81cab5a383dfef3f (MD5) Previous issue date: 2013 / Resumo: A pesquisa foi realizada na cratera de impacto de meteorito de Araguainha (Goiás / Mato Grosso, Brasil) e compreendeu três desenvolvimentos científicos principais. O primeiro engloba a petrografia e geoquímica de rochas graníticas parcialmente fundidas do núcleo da cratera de impacto. Foi possível separar, por petrografia e posicionamento geográfico, os litotipos do granito preservado (GP) dos litotipos de fusão (granito parcialmente fundido (GPF), veios de fusão (VF) e capa de fusão (CF)). Contudo, estes litotipos apresentam características geoquímicas muito semelhantes para elementos maiores, menores, traços e terras raras. O diagrama que se mostrou o melhor discriminante entre os litotipos de fusão e os granitos preservados foi o Th/U x TiO2, que indica enriquecimento relativo na razão Th/U nos granitos. O granito preservado é também rico em quartzo e apresenta empobrecimento em elementos como Ti, Zr, Ce, Y, Eu, Nb e elementos terras raras. Essas características permitem postular uma possível influência hidrotermal na geração dos litotipos de fusão. O segundo desenvolvimento aborda a mobilidade dos elementos traço e geração de fusões félsicas na crosta terrestre durante o impacto de meteoritos e implicações para a evolução da crosta Hadeana. Nesse caso, o processo de acresção crustal por impacto pode ser um mecanismo complementar, capaz de explicar uma importante modificação da crosta terrestre Hadeana ocorrida entre 3.9-4.5 Ga. O terceiro desenvolvimento trata dos efeitos do impacto na indução de fusão incongruente da crosta da Terra, tendo como base a fusão da biotita. O estudo mostrou que a biotita pré-impacto é distinta daquela pós-impacto, com texturas, estrutura e quimismo contrastantes. Demonstrou-se que até 9% do granito de Araguainha é produto de cristalização a partir da quebra da biotita. A biotita funde incongruentemente durante o processo de impacto, produzindo uma fusão aluminosa, que preenche bolsões e rede de fraturas nas rochas. Impactos do tamanho de Araguainha ou maiores são capazes de gerar volumes substanciais de fundidos aluminosos na crosta / Abstract: The focus of this PhD thesis is on granitic targets impacted by meteorites and felsic melting generation in the crust during impacts. Key features of the Araguainha impact crater (Goiás / Mato Grosso, Brazil) were employed as a control. Field, petrographic and analytical data collected in the study area were grouped into three, central scientific developments. The first comprises the petrography and geochemistry of partially melted granitic rocks observed in the core of the Araguainha crater. The work shows that it is possible to separate, by petrography and geographical positioning, preserved granite rocks from melt rock types, such as the partially melted granite (GPF), the melted veins (VF), and the melted caps (CF). These rock types have very similar geochemical characteristics regarding major, minor, trace and rare earth elements. However, melt rock types are readily discriminated from preserved granites in Th/U x TiO2 scatergrams; granites show relative enrichment in the ratio Th/U. Another noteworthy feature is that the preserved granite rich in quartz is depleted in Ti, Zr, Ce, Y, I, Nb and REE, indicating a possible influence of hydrothermal systems in the formation of melt products. The second development provides clues on the mobility of trace elements and generation of felsic melts in the crust during the meteorite impact, and implications for the evolution of the Hadean crust. It is argued that process of crustal accretion by impacts may have been one of the mechanisms that can explain important modification of the Earth's crust during the Hadean (3.9-4.5 Ga). The third development deals with the effects of shock-induced incongruent melting within Earth's crust, using the case of biotite melting. It was demonstrated that pre-impact and pos-impact biotites found in Araguainha show distinct textures, structures and chemistry. Results show that up to 9% of Araguainha granite is a product of magma crystallization from breakdown of biotite. The biotite melts incongruently during the impact process, producing an aluminous fusion, which fulfills pockets and fracture networks of the rocks. Impacts of the size of Araguainha or larger seem to be capable of generating substantial amounts of aluminous melt in the crust / Doutorado / Geologia e Recursos Naturais / Doutor em Ciências

Title: Impact crater relaxation throughout the Solar System Author: Martin Kihoulou Department: Department of Geophysics Supervisor: RNDr. Klára Kalousová, Ph.D., Department of Geophysics Abstract: In this thesis, we study the viscous relaxation of an impact-deformed icy shell of a dwarf planet Pluto. Motivation for this work is the position of Sputnik Planitia, a 1000 km wide, nitrogen-filled elliptic basin, which is located very close to Pluto-Charon tidal axis. Given this unlikely position on Pluto's sur- face, it was suggested that the basin was formed elsewhere and the whole body reoriented afterwards. For the reorientation to occur, the basin has to generate a positive gravity anomaly for which a combination of impact-related subsurface ocean uplift, ejecta blanket and accumulation of nitrogen ice was suggested. How- ever, to maintain the orientation towards the minimum principal axis of inertia until today, the ocean uplift must be present on timescales of billions of years, which may be achieved due to an insulating layer of high viscosity clathrates at the ice/ocean interface. We solve Pluto's ice shell evolution by the finite element method in 2D spherical axisymmetric geometry with an evolving free surface and assuming a viscous rheology. Our results show that the thermal effect of the im- pact...