Thesis (Ph. D.)--Oregon Graduate Center, 1978.

In the process of deformation of a solid at low strain rates, the rate of atomic migration in the crystal lattice is a critical factor. Experiments designed to measure the diffusion coefficient of Fe in olivine were unsuccessful. It is theoretically shown that at temperatures greater than one-half of the melting temperature the diffusion coefficient of Mg in olivine silicate is an exponential function of temperature and pressure. [formula omitted] The results also indicate that at T > .5Tm and at nonhydrostatic stresses <500 bars the experimentally determined steady state creep of the upper mantle rocks dunite and peridotite may be governed by movement of dislocations. It is shown that the rate limiting parameter in the creep-equation is probably the ionic diffusion coefficient in the olivine silicate structure. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Les études géologiques des régions volcaniques de Mars ont clairement montré la diversité et la complexité du volcanisme martien avec des structures aux morphologies variées, témoins de son évolution volcanique et magmatique. Une meilleure compréhension de ce volcanisme nécessite toutefois une connaissance plus précise de la composition minéralogique de ces régions. Cette composition est en effet très dépendante des conditions internes de la planète et de son évolution. Dans ce travail de thèse je me suis donc intéressée à l’évolution volcanique et interne de Mars à partir d’une étude de la minéralogie obtenue grâce à l’imageur hyperspectral OMEGA/Mars Express. Le jeu de données OMEGA a permis la cartographie à l’échelle globale et avec une résolution kilométrique des principaux minéraux mafiques (pyroxènes et olivines), et des phases ferriques, incluant les oxydes ferriques nanophases, qui permettent de jauger l’état d’oxydation de la surface et de tracer la présence de poussière. Leurs distributions spatiales confirment la composition basaltique des terrains de l’hémisphère sud et de certaines régions sombres des plaines du nord ainsi que la nature nanophasée des oxydes ferriques présents dans la poussière martienne. Ces cartes représentent des produits complets et finaux qui sont mis à la disposition de la communauté. En complément de cette analyse globale, la distribution de l’olivine à la surface de Mars a fait l’objet d’une étude locale plus détaillée mettant en évidence plusieurs aspects du volcanisme et du magmatisme martien. Des laves hespériennes enrichies en olivine ayant rempli des dizaines de cratères et de dépressions de l’hémisphère sud ont été identifiées. De l’olivine a également été identifiée dans les plaines du nord associée à du matériau excavé par des cratères (<20 km) et à des affleurements étendus suggérant que ces plaines du nord soient également en partie recouvertes de ces laves. Ces observations peuvent s’expliquer par un évènement planétaire de volcanisme fissural durant le début de l’Hespérien. Ceci indique également que la couche supérieure de sédiment présente dans les plaines du nord est peu épaisse et d’origine volcanique. Cet enrichissement en olivine des laves hespériennes, à l’opposé des terrains noachiens dépourvus de signatures, pose la question d’une évolution des conditions internes de la planète entre ces deux périodes, et/ou d’une altération importante des terrains noachiens. De l’olivine associée à des éjectas de grands cratères (>20 km) dans les plaines du nord, ainsi qu’à des buttes dans l’hémisphère sud suggère que la croûte noachienne/primitive enfouie soit enrichie en olivine au moins en certains endroits. Enfin, de l’olivine associée à des buttes sur les terrasses des bassins d’Argyre et d’Hellas, interprétées comme étant des éjectas de manteau, indique que le manteau martien a subi un overturn à la suite de sa cristallisation. La dernière étape de mon travail a consisté à identifier les régions sources de certaines météorites martiennes en recherchant la similarité de leurs signatures spectrales dans l’infrarouge proche avec celle de la surface de Mars. Un des résultats majeurs de cette étude est que les shergottites basaltiques Los Angeles et Shergotty ont des signatures spectrales similaires à celles des grands massifs volcaniques hespériens tels que Syrtis Major, Thaumasia et Hespéria Planum. Une telle analogie est en accord avec un âge ancien pour ces météorites. / Geologic studies of martian volcanic regions have demonstrated the diversity and complexity of the martian volcanism through various morphologies, witnesses of the volcanic and magmatic evolution of this planet. A better understanding of this volcanism nevertheless requires a better knowledge of the mineralogical composition of these regions. This composition highly depends on the internal conditions of the planet and its evolution. In my PhD thesis, I focused on the internal and volcanic evolutions of Mars from a study of the mineralogy obtained with the visible near-infrared imaging spectrometer OMEGA / Mars Express. The OMEGA dataset has allowed the mapping of key anhydrous mineral of the martian surface at a global scale with a kilometer spatial resolution. These minerals are major mafic minerals (pyroxene and olivine), and ferric phases, including nanophase ferric oxides. Their spatial distributions confirm the basaltic composition of the southern hemisphere and the low albedo regions of the northern plains, as well as the nanophase nature of ferric oxides present in the martian dust. These global maps represent complete and final products and are available for the community. In addition to this global analysis, the global distribution of olivine on the surface of Mars was the subject of a more detailed local study highlighting several aspects of the martian volcanism and magmatism. Hesperian olivine enriched lavas that have filled dozens of craters and depressions in the southern hemisphere were identified. Olivine was also identified in the northern plains associated with material excavated by craters (<20 km) and with extended outcrops, suggesting that the northern plains were also partly filled with these lavas. These observations can be explained by a planetary event of olivine enriched fissural volcanism during the early Hesperian. They also indicate that the upper layer of sediment present in the northern plains is very fine (<100m) and of volcanic origin. This olivine enrichment of hesperian lavas, unlike olivine-depleted noachian terrains, questions the variation of internal conditions of the planet between these two periods, and/or significant alteration of the noachian terrains. Olivine associated with large crater ejectas (> 20 km) in the northern plains, and buttes in the southern hemisphere suggests that the buried noachian/primitive crust was olivine enriched in some locations. Finally, olivine found in buttes on terraces of Argyre and Hellas basins, interpreted as mantle ejectas, indicates that the martian mantle have experienced an overturn after its crystallization. The last chapter of my work was to identify the source regions of Martian meteorites by looking for some similarity in their spectral signatures in the near infrared with those of the martian surface. A major outcome of this study is that the basaltic shergottites Shergotty and Los Angeles have spectral signatures similar to those of the hesperian volcanic massifs such as Syrtis Major, Hesperia Planum and Thaumasia Planum. Such an analogy is consistent with an old age for these meteorites.

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Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Undergraduate honors paper--Mount Holyoke College, 2006. Program in Geochemistry. / Includes bibliographical references (leaves 84-89).

Mantle xenoliths have been used to interpret the magnetic characteristics of the lithospheric mantle because their rapid rate of ascent to the surface does not allow enough time for alteration. Studies of mantle xenoliths have suggested that magnetite in the mantle contributes to long wave length magnetic anomalies over areas of suppressed geothermal gradients (cratons, forearcs). Magnetite will only form in oxidizing conditions. This leads to a debate if mantle xenoliths become altered through oxidation to form magnetite in the mantle before ascent, during ascent (decompression), or after ascent at the surface. Natural and experimental occurrences of magnetite forming as inclusions or dislocations in fosterite from Fe-impurities suggest that oxidation of olivine is a mechanism for magnetite formation in the mantle. To test this, high olivine samples were placed into a furnace at 600C and 900C in free air at 1bar of pressure, removing samples at different time increments ranging from 0.2 to 625 hours. These temperatures were used because they represent mantle like temperatures in oxidizing conditions. After oxidation, samples from the 900C experiment show evidence for magnetite/hematite formation after only 0.2 hours and the amount of Fe-oxide formation increases with time. Samples from the 600C experiment show significant alteration and Fe-oxide formation after 125 hours. These results suggest that it is possible for magnetite to form from the Fe in the fayalite component of fosterite in the mantle from oxidizing event such as metasomatism.