The thermal history of the Earth, from planetary accretion and core differentiation up to the present time, is of paramount importance for understanding our planet. The thermal evolution of the core and the mantle dictate the generation of the Earth's internal magnetic field and its evolution through time. In this dissertation, I study scenarios for the thermal and magnetic evolution of the Earth, using numerical simulations for mantle convection and implementing recent geochemical models for the mantle and core. The conditions for which a magnetic field can be generated in the Earth's core are studied using parameterized models for energy and entropy. The model devised in this project couples the results of the numerical simulations with the parameterized models for the core, to produce a global thermal and magnetic history, with feed-back between events happening in the mantle and the core.<p> The dissertation presents an analysis of the scenarios that can be constructed from implementing new constraints into the thermal models for the mantle and core and emphasizes the most relevant scenarios which can be applied to the Earth's evolution, consistent with physical parameters, and geochemical and magnetic constraints known to date. In addition, I discuss the relevance of some of the scenarios which appear incompatible with the Earth's evolution, but are reminiscent of the evolution of other terrestrial bodies.<p> The results of this work show that the most successful scenarios for the thermal and magnetic evolution require the presence of small amounts of core internal heating in the form of radioactive potassium, or a slightly increased concentration of radioactive elements at the base of the mantle, due to isolated, if the base of the mantle is less mobile and acts as a thermal insulator between the core and the overlying convective mantle primordial reservoirs. Successful scenarios are also obtained if the base of the mantle is less mobile and acts as a thermal insulator between the core and the overlying convective mantle. If the base of the mantle is less mobile and acts as a thermal insulator between the core and the overlying convective mantle.

The thermal history of the Earth, from planetary accretion and core differentiation up to the present time, is of paramount importance for understanding our planet. The thermal evolution of the core and the mantle dictate the generation of the Earth's internal magnetic field and its evolution through time. In this dissertation, I study scenarios for the thermal and magnetic evolution of the Earth, using numerical simulations for mantle convection and implementing recent geochemical models for the mantle and core. The conditions for which a magnetic field can be generated in the Earth's core are studied using parameterized models for energy and entropy. The model devised in this project couples the results of the numerical simulations with the parameterized models for the core, to produce a global thermal and magnetic history, with feed-back between events happening in the mantle and the core.<p> The dissertation presents an analysis of the scenarios that can be constructed from implementing new constraints into the thermal models for the mantle and core and emphasizes the most relevant scenarios which can be applied to the Earth's evolution, consistent with physical parameters, and geochemical and magnetic constraints known to date. In addition, I discuss the relevance of some of the scenarios which appear incompatible with the Earth's evolution, but are reminiscent of the evolution of other terrestrial bodies.<p> The results of this work show that the most successful scenarios for the thermal and magnetic evolution require the presence of small amounts of core internal heating in the form of radioactive potassium, or a slightly increased concentration of radioactive elements at the base of the mantle, due to isolated, if the base of the mantle is less mobile and acts as a thermal insulator between the core and the overlying convective mantle primordial reservoirs. Successful scenarios are also obtained if the base of the mantle is less mobile and acts as a thermal insulator between the core and the overlying convective mantle. If the base of the mantle is less mobile and acts as a thermal insulator between the core and the overlying convective mantle.

To understand the fluid temperature and pressure during the Ouachita orogeny, we used isotopic analysis of syntectonic veins and adjacent host material, quartz-calcite oxygen isotope thermometry and fluid inclusion analysis. The veins were at or near isotopic equilibrium with their host rocks; neither the host nor veins has been isotopically reset. The average isotopic variation in (delta18)O between vein and host is 2.4 plus/minus 1.7% and 0.7 plus/minus 1.7% for quartz and calcite, respectively. The temperature of vein formation from quartz-calcite oxygen isotope thermometry is about 210-430 degrees C. Although this is a large range, the temperature does not vary systematically in the exposed Ordovician through Mississippian rocks. The lack of isotopic difference between host and vein suggests that the host oxygen determined that of the veins. This in turn suggests that the fluid in the rocks did not change regionally. The vitrinite reflectance/temperature of the host rocks increases with restored stratigraphic depth more than that calculated with the quartz-calcite thermometer in veins. Fluid inclusion analysis in vein quartz constrains homogenization temperatures to be from 106-285 degrees C. Isochores from fluid inclusion analyses were constrained using quartz-calcite thermometry and vitrinite reflectance temperatures to calculate vein formation pressures of 0.3?4.7 kbars. These pressures correspond to vein formation depths up to 19 km, assuming an unduplicated stratigraphic section. Using burial curves and a reasonable range of geothermal gradients, vein formation ages are between 300 to 315 Ma, i.e., Early to Middle Pennsylvanian.

As características das matérias-primas particuladas como tamanho, forma, área específica, entre outras, determinam não somente o desempenho final de um produto, mas também o processo de sua fabricação. Neste sentido, matérias-primas sintéticas são produzidas por meio de conversões químicas que têm como finalidade o controle da reprodutibilidade de características. Esta tese tem como objetivo o estudo de precursores sintetizados com matérias-primas nacionais de elevada pureza, quanto à área específica (AE), estrutura cristalina e morfologia das fases formadas durante as transformações térmicas de alguns hidróxidos (gibsita e pseudoboemita), sais (acetato e formato) e sulfatos duplos (de amônio e de sódio) de alumínio. As amostras sintetizadas e aquecidas foram caracterizadas por DRX, MEV, BET e análise térmica (TG, DTA e DSC), a fim de que fossem observadas as variações nas características das fases formadas. Observou-se que todos os precursores, à exceção do \"sulfato-Na\", evoluem termicamente resultando como produto final somente a a-alumina. No caso particular do \"sulfato-Na\", em que se apresenta resultados preliminares, verifica-se a formação, além da a- alumina, de B-alumina. Os hidróxidos e os sais de alumínio passam por uma seqüência de aluminas de transição que exibem valores de área específica elevados. Com relação à pseudoboemita, além da caracterização proposta no trabalho, foi estudada a influência do método de secagem e do tempo de envelhecimento da pseudoboemita nas características dos materiais sintetizados. Verificou-se que o método de secagem pode influenciar as temperaturas de transformações de fases das aluminas. Precursores secos por nebulização podem formar a fase a concomitantemente com a fase 0, o que não ocorre com os materiais secos ao ar. Já o tempo de envelhecimento influenciou no tamanho final das fibrilas de pseudoboemita. Tanto o método de secagem quanto o tempo de maturação afetam de forma determinante a organização das fibrilas que, por sua vez, estabelecem a distribuição de poros nos materiais produzidos. / Features of powdered raw materials like size, morphology, specific area, determine the product performance, besides the fabrication process product. In this direction, the synthetic raw materials are produced by means of chemical conversion to control the characteristics reprodutibility. This thesis has as objective the study of precursor\'s synthesized with national raw materials of raised pureness, by the study if the specific area (AE), crystalline structure and morphology of the phases formed during thermal transformation of some hydroxides as (aluminum hydroxides- gibbsite and pseudoboehmite; aluminum salts - acetate and formate and aluminum sulphates - sodium and amonium) produzed by high pure nacional raw materials. The sythetized and heated samples are examined by DRX, MEV, BET and thermal analysis (TG, DTA e DSC) to verify the characteristics variations in the formed phases. It\'s can be seen that every thermal treated precursors evolve to a-alumina. In the particular case of \"Na-sulfate\", the preliminary results present also B-alumina. The hydroxides and salts pass by a sequence of alumina transition, that show high specific area. In the case of pseudoboehmite, was also studied the influence of dried method and the aging of aqueous aluminum hydroxide gels in the characteristic of synthesized materials. It verified that the dried method can influence the temperature of the alumina phase\'s transitions. Dried precursors by spray drier can form the phase a and 0 together, this not occur with the others. The aging can influence in the pseudoboehmite microfibrils size. The dried method and the aging influence the organization microfibrils, and this one determines the pore distribution from the produced materials.

<div>Fused deposition modeling (FDM) represents one of the most common techniques for rapid proto-typing in additive manufacturing (AM). This work applies image based thermography to monitor the FDM process in-situ. The nozzle temperature, print speed and print orientation were adjusted during the fabrication process of each specimen.</div><div>Experimental and numerical analysis were performed on the fabricated specimens. The combination of the layer wise temperature profile plot and temporal plot provide insights</div><div>for specimens fabricated in x, y and z-axis orientation. For the x-axis orientation build possessing 35 layers, Specimens B16 and B7 printed with nozzle temperature of 225 ➦C and</div><div>235 ➦C respectively, and at printing speed of 60 mm/s and 100 mm/s respectively with the former possessing the highest modulus, yield strength, and ultimate tensile strength. For the y-axis orientation build possessing 59 layers, Specimens B23, B14 and B8 printed with nozzle temperature of 215°C, 225°C and 235°C respectively, and at printing speed of 80 mm/s, 80 mm/s and 60 mm/s respectively with the former possessing the highest modulus and yield strength, while the latter the highest ultimate tensile strength. For the z-axis orientation build possessing 1256 layers, Specimens B6, B24 and B9 printed with nozzle temperature of 235°C, 235°C and 235°C respectively, and at printing speed of 80 mm/s, 80 mm/s and 60 mm/s respectively with the former possessing the highest modulus and ultimate tensile strength, while B24 had the highest yield strength and B9 the lowest modulus, yield strength and ultimate tensile strength. The results show that the prints oriented in the y-axis orientation perform relatively better than prints in the x-axis and z-axis orientation.</div>

Cette étude vise à décrire le rôle de l’héritage et de la segmentation associés au rifting pour la réactivation ainsi qu’à étudier l’importance de l’asymétrie tectonique sur l’évolution thermique syn-rift, en utilisant le système pyrénéo-cantabrique comme laboratoire naturel. L’étude de la jonction entre les segments pyrénéen et cantabrique infirme l’hypothèse d’une faille transformante de Pampelune et met en évidence une zone d’accommodation où les segments de rifts se propagent au nord et au sud des massifs basques, associée à une direction d’extension nord-sud. Lors de la convergence, cette segmentation et le niveau de découplage associé aux évaporites triasiques contrôlent fortement la réactivation ainsi que l’architecture orogénique locale. Enfin, cette étude démontre que l’asymétrie lors de l’hyper-étirement est associée à une évolution thermique asymétrique et diachrone, et souligne l’importance de l’évolution tectonique pour l’architecture thermique. / This study aims to describe the role of rift-inheritance and segmentation for reactivation and to investigate the influence of asymmetric rifting on the syn-rift thermal evolution, using the Pyrenean-Cantabrian system as a natural laboratory. The study of the Pyrenean-Cantabrian junction discards the existence of a Pamplona transform fault between the two rift segments and argues for an accommodation zone where rift segments overlap north and south of the Basque massifs in relation with north-south direction of extension. During convergence, rift segmentation and the Triassic evaporite decoupling horizon controlled the reactivation and the local orogenic architecture. Finally, this study shows that asymmetric hyperextension is associated with asymmetric and diachronous thermal evolution, and highlights the importance of understanding the tectonic evolution to define the thermal architecture.

In der vorliegenden Arbeit werden Methoden der Erdsystemanalyse auf die Untersuchung der Habitabilität terrestrischer Exoplaneten angewandt. Mit Hilfe eines parametrisierten Konvektionsmodells für die Erde wird die thermische Evolution von terrestrischen Planeten berechnet. Bei zunehmender Leuchtkraft des Zentralsterns wird über den globalen Karbonat-Silikat-Kreislauf das planetare Klima stabilisiert. Für eine photosynthetisch-aktive Biosphäre, die in einem bestimmten Temperaturbereich bei hinreichender CO2-Konzentration existieren kann, wird eine Überlebenspanne abgeschätzt. Der Abstandsbereich um einen Stern, in dem eine solche Biosphäre produktiv ist, wird als photosynthetisch-aktive habitable Zone (pHZ) definiert und berechnet. Der Zeitpunkt, zu dem die pHZ in einem extrasolaren Planetensystem endgültig verschwindet, ist die maximale Lebenspanne der Biosphäre. Für Supererden, massereiche terrestrische Planeten, ist sie umso länger, je massereicher der Planet ist und umso kürzer, je mehr er mit Kontinenten bedeckt ist. Für Supererden, die keine ausgeprägten Wasser- oder Landwelten sind, skaliert die maximale Lebenspanne mit der Planetenmasse mit einem Exponenten von 0,14. Um K- und M-Sterne ist die Überlebensspanne einer Biosphäre auf einem Planeten immer durch die maximale Lebensspanne bestimmt und nicht durch das Ende der Hauptreihenentwicklung des Zentralsterns limitiert. Das pHZ-Konzept wird auf das extrasolare Planetensystem Gliese 581 angewandt. Danach könnte die 8-Erdmassen-Supererde Gliese 581d habitabel sein. Basierend auf dem vorgestellten pHZ-Konzept wird erstmals die von Ward und Brownlee 1999 aufgestellte Rare-Earth-Hypothese für die Milchstraße quantifiziert. Diese Hypothese besagt, dass komplexes Leben im Universum vermutlich sehr selten ist, wohingegen primitives Leben weit verbreitet sein könnte. Unterschiedliche Temperatur- und CO2-Toleranzen sowie ein unterschiedlicher Einfluss auf die Verwitterung für komplexe und primitive Lebensformen führt zu unterschiedlichen Grenzen der pHZ und zu einer unterschiedlichen Abschätzung für die Anzahl der Planeten, die mit den entsprechenden Lebensformen besiedelt sein könnten. Dabei ergibt sich, dass komplex besiedelte Planeten heute etwa 100-mal seltener sein müssten als primitiv besiedelte. / In this thesis methods of Earth system analysis are applied to the investigation of the habitability of terrestrial exoplanets. With the help of parameterized convection models for the Earth the thermal evolution of terrestrial planets is calculated. Under increasing central star luminosity the global carbonate-silicate cycle stabilizes the planetary climate. The life span of a photosynthetic-active biosphere existing in a certain temperature interval under adequate CO2 concentration is estimated. The range of orbital distances within which such a biosphere is productive is defined as the photosynthetic-active habitable zone (pHZ) and is calculated. The maximum life span of the biosphere is the point in time when the pHZ of an extrasolar planetary system finally disappears. For super-Earths, i.e. massive terrestrial planets, it is as longer as more massive the planet is and as shorter as more the planet is covered with continents. For super-Earths, which are not pronounced land or water worlds, the maximum life span scales with the planetary mass with an exponent of 0.14. The life span of the biosphere on a planet around K- or M-stars is always determined by the maximum life span and not limited by the end of the main-sequence evolution of the central star. The pHZ approach is applied to the extrasolar planetary system Gliese 581. Accordingly the super-Earth of 8 Earth masses Gliese 581d could be habitable. Based on the presented pHZ concept the Rare Earth Hypothesis established by Ward and Brownlee 1999 is quantified for the Milky Way. This hypothesis claims that complex life may be very rare in the Universe while primitive life is likely common and widespread. Different temperature and CO2 tolerances as well as a different influence on weathering of complex and primitive life forms result different boundaries of the pHZ and a different estimate of the number of planets potentially harboring these different life forms. It arises that planets with complex life might be 100 times rarer than primitive life bearing planets.

The thermal histories of terrestrial planets are investigated using two parameterized mantle convection models for either Earth like planets and planets with no active plate tectonics. Using parameterized models of mantle convection, we performed computer simulations of planetary cooling and volatile cycling. The models estimate the amount of volatile in mantle reservoir, and calculate the outgassing and regassing rates. A linear model of volatile concentration-dependent is assumed for the activation energy of the solid-state creep in the mantle. The kinematic viscosity of the mantle is thus dynamically affected by the activation energy through a variable concentration in volatile. Mantle temperature and heat flux is calculated using a model derived from classic thermal boundary layer theory of a single layered mantle with temperature dependent viscosity. The rate of volatile exchanged between mantle and surface is calculated by balancing the amount of volatiles degassed in the atmosphere by volcanic and spreading related processes and the amount of volatiles recycled back in the mantle by the subduction process. In the cases that lack plate tectonics, the degassing efficiency is dramatically reduced and the regassing process is absent. The degassing effect is dependent on average spreading rate of tectonic plates and on the amount of volatile in the melt extract in the transition zone between mantle and upper boundary laver. The regassing effect is dependent on the subduction rate and on the amount of volatile present on a hydrated layer on top of the subducting slab. The degassing and regassing parameters are all related to the intensity of the convection in the mantle and to the surface temperature of the planet, and they are regulated by the amount of volatiles in reservoir. Comparative study with the previous models display significant differences and improve the versatility of the model. The optimum efficiency factors found are in the range of 0.01-0.06 for degassing/regassing processes, in agreement with more recent estimates. An important effect of the volatile cycling process is a general negative feedback effect that results in a general trend to adjust the mantle volatile content in time to a value set by the energy balance in the system. As a result, the initial amount of volatile in the mantle is rendered irrelevant for late stage of thermal evolution. In the case of no plate tectonics, the opposite effect takes place: initial volatilization plays an important role through entire evolution. The implications of mantle convection on the stability of the lithosphere were investigated further using the thermal history calculations and numeric simulations. They point to the conclusion that mantle convection induced stress levels increase from the past to the present fact that leads to a greater potential of craton deformation. The main consequence of this trend is that sections of continental lithosphere that have remained stable since the Archean and Proterozoic are becoming progressively more prone to instability in the geologically modem era. After the volatiles are degassed from the mantle, they are cycled through the atmosphere. The interact with the climate influencing the surface temperature, and further controlling the mantle convection. Using a grey radiative-convective model for the atmosphere, we analyzed the feedback relationships between volatiles, especially water, and surface temperature. We showed that large amount of water degassed during a hot, possible melt ocean phase after the planet formation could conserve large amount of water in atmosphere and maintain the surface temperature at moderate level.

The thermal evolution of pyroclastic density currents (PDCs) is the result of entrainment of ambient air, particle concentration, and initial eruptive temperature, which all impact PDC dynamics and their hazards, such as runout distance. The associated hazards and opaqueness of PDCs make it impossible for in-situ entrainment efficiencies or concentration measurements that would provide critical information on the thermal evolution and physical processes of PDCs. The thermal evolution of explosive eruptive events such as volcanic plumes and pyroclastic density currents (PDCs) is reflected in the textures of the material they deposit. A multiscale model is developed to evaluate how the rinds of breadcrust bombs can be used as a unique thermometer to examine the thermal evolution of PDCs. The multiscale, integrated model examines how bubble growth, pyroclast cooling, and dynamics of PDC and projectile pyroclasts form unique pyroclast morphology. Rind development is examined as a function of transport regime (PDC and projectile), transport properties (initial current temperature and current density), and pyroclast properties (initial water content and radius). The model reveals that: 1) rinds of projectile pyroclasts are in general thicker and less vesicular than those of PDC pyroclasts; 2) as the initial current temperature decreases due to initial air entrainment, the rinds on PDC pyroclasts progressively increase in thickness; and 3) rind thickness increases with decreasing water concentration and decreasing clast radius. Therefore, the modeled pyroclast’s morphology is dependent not only on initial water concentration but also on the cooling rate, which is determined by the transport regime. The developed secondary thermal proxy is then applied to the 2006 PDCs from the Tungurahua eruption to constrain the entrainment efficiency and thermal evolution of PDCs. A three-dimensional multiphase Eulerian-Eulerian-Lagrangian (EEL) model is coupled to topography and field data such as paleomagnetic data and rind thicknesses of collected pyroclasts to study the entrainment efficiency and thus the thermal history of PDCs at Tungurahua volcano, Ecuador. The modeled results that are constrained with observations and thermal proxies demonstrate that 1) efficient entrainment of air to the upper portion of the current allows for rapid cooling, 2) the channelized pyroclastic density currents may have developed a stable bed load region that was inefficient at cooling and 3) the PDCs had temperatures of 600-800K in the bed load region but the upper portion of the currents cooled down to ambient temperatures. The results have shown that PDCs can be heterogeneous in particle concentration, temperature, and dynamics and match observations of PDCs down a volcano and the thermal proxies. Lastly, the entrainment efficiencies of PDCs increases with increasing PDC temperature and entrainment varies spatially and temporally. Therefore, the assumption of a well-mixed current with a single entrainment coefficient cannot fully solve the thermal evolution and dynamics of the PDC.

An analytic boundary layer model for thermal convection with a finite-strength plate and depth-dependent viscosity is developed. The model includes a specific energy balance for the lithosphere and accounts for coupling between the plate and underlying mantle. Multiple solutions are possible with three solution branches representing three distinct modes of thermal convection. One branch corresponds to the classic boundary layer solution for active lid plate tectonics while two new branches represent solutions for sluggish lid convection. The model is compared to numerical simulations with highly temperature dependent viscosity and is able to predict both the type of convection (active, sluggish, or stagnant lid) as well as the presence of single and multiple solution regimes. The existence of multiple solutions suggests that the mode of planetary convection may be history dependent. The dependence of mantle viscosity on temperature and water concentration is found to introduce a strong dynamic feedback with plate tectonics. A dimensionless parameter is defined to quantitatively evaluate the relative strength of this feedback and demonstrates that water and heat transport may be equally important in controlling present-day platemantle dynamics for the Earth. A simple parameterized evolution model illustrates the feedback and agrees well with our analytic results. This suggests that a simple relationship may exist between the rate of change of water concentration and the rate of change of temperature in the mantle. This study concludes by investigating the possibility of a magnetic field dynamo in early solar system planetesimals. The thermal evolution of planetesimals is modeled by considering melting, core formation, and the onset of mantle convection and then employing thermal boundary layer theory for stagnant lid convection (if possible) to determine the cooling rate of the body. We assess the presence, strength and duration of a dynamo for a range of planetesimal sizes and other parameters. We find that a minimum radius of O(500) km is required for a thermally driven dynamo of duration O(10) My. The dependence of the results on model parameters is made explicit through the derivation of an analytic solution. / Earth and Planetary Sciences