Indiana University-Purdue University Indianapolis (IUPUI) / The objectives of this study are, generally, to analyze and understand internal processes that produce melts in an oceanic-continental subduction setting; and, specifically, to understand the assembly of a Cretaceous magmatic arc pluton (Palms pluton), including the timing of melt emplacement(s) and melt evolution from the source. SiO2 concentrations vary from ~ 69-76 % by weight. Whole rock trace element concentrations vary up to 7 times. Zircon analysis shows a minimum age difference in the pluton of 3 my, if considering the uncertainties of the oldest and youngest samples. According to the model made from the HEAT program, this is approximately six times longer than the estimated crystallization time of one batch of melt with the same physical properties as the Palms pluton. Two distinct sources, perceived from chemical analysis of premagmatic zircons, are found throughout the pluton. REE compositional patterns show a hybridization of Proterozoic and Mesozoic sources in some, but not all, Palms pluton granites. This data suggests that the pluton formed from multiple intrusions and the Proterozoic source remained relatively consistent throughout the pluton’s assembly with few additions of younger Mesozoic source material.

Mid-ocean ridge hydrothermal systems are known to extend to deep levels of the oceanic crust, including the plutonic section, but little is known about the timing and nature of fluid-rock interactions at these levels. To investigate the temporal and spatial characteristics of hydrothermal alteration in the lower crust, this study investigates a suite of hydrothermally altered (<5 to >20% hydrous alteration) gabbroic rocks recovered from the Hess Deep Rift, where 1.2 Ma fast-spreading East Pacific Rise crust is well-exposed. These samples were altered to amphibole-dominated assemblages with chlorite-rich samples occurring in a restricted region of the field area. Hornfels, indicative of reheated, previously altered rocks, are clustered in the central part of the field area. The entire sample suite has elevated 87Sr/86Sr (mean: 0.70257±0.00007 (2σ), n=16) with respect to fresh rock (0.7024). Bulk rock 87Sr/86Sr is strongly correlated with percentage of hydrous alteration and weakly correlated with bulk rock Sr content. The distribution of Sr in igneous and metamorphic minerals suggests that greenshist-facies alteration assemblages (chlorite, actinolitic amphibole, albitic plagioclase) lose Sr to the fluid while amphibolite-facies secondary assemblages (secondary hornblende, anorthitic plagioclase) take up Sr. The temperature-dependent mobilization of Sr in hydrothermal systems has implications for the 87Sr/86Sr and ultimately fluid/rock ratio calculations based on the assessed 87Sr/86Sr systematics. Considering Sr behaviour, minimum fluid/rock ratios of ~1 were calculated for the plutonic section. Due to the large uncertainty regarding fluid Sr composition at depth and the sensitivity of fluid/rock ratio calculations on this parameter, a model combining the sheeted dike complex and the plutonic section to one hydrothermal system is introduced, yielding a fluid/rock ratio of 0.5. This value may be more realistic since the fluid composition entering and exiting the sheeted dike complex is better constrained. The regional distribution of hornfelsed material with elevated 87Sr/86Sr suggests that fluid ingress into the upper plutonics at Hess Deep occurred on-axis in a dynamic interface of a vertically migrating axial magma chamber (AMC) and the base of the hydrothermal system. / Graduate

Aim of this study was to describe capillary water and vapor transport in shallow subsurface of Hrubá Skála sandstone in the Bohemian Paradise. I have quantified permeability of Hrubá Skála sandstone for water vapor using "wet cup" method and also capillary water absorption of sandstone drill cores. I have found out general rules of evaporation and rate of evaporation from several sandstone outcrops in real microclimate. Important part of my work was to determine whether surface crust plays some role in studied parameters. Based on my results, permeability of different types of sandstones for water vapor does not vary significantly and surface crust has no effect on rate of water vapor diffusion. Rate of capillary water absorption is reduced by surface crust. Hrubá Skála sandstone is classified as medium or highly absorbing material. I have proved that evaporation from porous medium can be approximated by exponential function. Rate of evaporation is strongly controlled by climatic conditions, especially by relative humidity. Powered by TCPDF (www.tcpdf.org)

Sous le Chili central et l’ouest de l'Argentine (29°-35°S), la plaque océanique Nazca, en subduction sous la plaque continentale Amérique du Sud, change radicalement de géométrie : inclinée à 30°, puis horizontale, engendrée par la subduction de la chaine de volcans de Juan Fernandez. Le but de mon étude est d'évaluer, la variation de nature et de propriétés physiques de la lithosphère chevauchante entre ces deux régions afin de mieux comprendre (1) sa structure profonde et (2) les liens entre les déformations observées en surface et en profondeur. Pour répondre à cette thématique, j’utilise une approche originale couplant la sismologie, la thermométrie, et la pétrologie. Je montre ainsi des images 3-D de tomographie sismique les plus complètes de cette région par rapport aux études précédentes, qui intègrent (1) de nombreuses données sismiques provenant de plusieurs catalogues, (2) un réseau de stations sismiques plus dense permettant de mieux imager la zone de subduction. J’apporte la preuve que la plaque en subduction se déshydrate dans deux régions distinctes : (1) le coin mantellique, et (2) le long de la ride subduite avant que celle-ci ne replonge plus profondément dans le manteau. La croûte continentale au-dessus du flat slab possède des propriétés sismiques très hétérogènes en relation avec des structures de déformation profondes et des domaines géologiques spécifiques. La croûte chevauchante d’avant-arc, au-dessus du flat slab, est décrite par des propriétés sismiques inhabituelles, liées à la géométrie particulière du slab en profondeur, et/ou liées aux effets du séisme de 1997 de Punitaqui (Mw 7.1). Mes résultats, confirmant les études antérieures, montrent que : - le bloc Cuyania situé plus à l’est, dans la zone d’arrière-arc est plus mafique et contient une croûte inférieure éclogitisée ; quant à, la croûte continentale inférieure sous l’arc Andin, est épaisse et non-éclogitisée, décrivant surement le bloc felsique de Chilenia. / Beneath central Chile and western Argentina, the oceanic Nazca slab drastically changes geometry from horizontal to dipping at an angle of 30°, and correlates with the subduction of the Juan Fernandez seamount ridge. The aim of our study is to assess, using a thermo-petrological-seismological approach, the differences of the overriding lithosphere between these two regions, in order to better understand the deep structure of the continental lithosphere above the flat slab, and the links between the deformations at the surface and at depth. We show the most complete regional 3-D seismic tomography images of this region, whereby, in comparison to previous studies, we use (1) a much larger seismic dataset compiled from several short-term seismic catalogs, (2) a much denser seismic station network which enables us to resolve better the subduction zone. We show significant seismic differences between the flat and normal subduction zones. As expected, the flat slab region is impacted by colder temperatures, and therefore by faster seismic velocities and more intense seismic activity, compared to the normal slab region. We show evidence that the flat slab dehydrates within the mantle wedge, but also along the subducting ridge prior to re-subducting. The forearc crust above the flat slab is described by unusual seismic properties, correlated to the slab geometry at depth, and/or, to the aftershock effects of the 1997 Mw 7.1 Punitaqui earthquake which occurred two years before the recording of our events. The continental crust above the flat slab has very heterogeneous seismic properties which correlate with important deformation structures and geological terranes at the surface. We confirm previous studies that have shown that the thick lower crust of the present day Andean arc is non-eclogitized and maybe representing the felsic Chilenia terrane, whereas to the east, the Cuyania terrane in the backarc is more mafic and contains an eclogitized lower crust.

Pour la première fois, une étude par spectroscopie infrarouge à transformée de Fourrier et par microsonde ionique des minéraux majeurs de la croûte inférieure et des péridotites mantelliques a été entreprise afin de mieux caractériser les mécanismes d’incorporation et les teneurs en eau de ces minéraux nominalement anhydres, et de déterminer leurs compostions isotopiques en H, O, et Li pour retracer les échanges latéraux et horizontaux de l’eau dans la lithosphère continentale profonde. Les résultats montrent que: (1) Les minéraux nominalement anhydres, comme les pyroxènes et plagioclase, dans les granulites de la croûte inférieure contiennent de l’eau en trace essentiellement sous forme hydroxyles et accessoirement sous forme moléculaire, avec des concentrations (exprimées en poids H2O) allant de 200 à 2330 ppm pour les clinopyroxènes, de 60 à 1875 ppm pour les orthopyroxènes, de 65 à 900 ppm pour les plagioclases. Les teneurs calculées pour chaque roche totale d’après sa composition minéralogique et la teneur en eau des minéraux varient de 155 à 1100 ppm. (2) Les teneurs en H2O des minéraux majeurs et en roche totale de la croûte continentale inférieure sont manifestement plus élevées que celles du manteau lithosphérique sous-jacent, suggérant des variations verticales de la quantité d’H2O dans la lithosphère continentale profonde. Un tel contraste peut affecter de façon notable le comportement rhéologique de la lithosphère continentale. (3) Les rapports isotopiques de l’oxygène des pyroxènes étudiés, et probablement les roches totales, exprimés en [delta]18OSMOW , vont de ~ 4,5 à 12,5‰. Ceci indique la contribution de matériaux recyclés de la croûte continentale durant la pétrogenèse des échantillons ayant un TM18O élevé. (4) Les minéraux de la granulites sont caractérisés par des valeurs de élevées TMD, avec des valeurs de -80~-10‰ exprimées en [delta]DSMOW; les minéraux sont le plus souvent en équilibre les uns avec les autres lorsque l’on considère leurs compositions isotopiques moyennes. (5) Les compositions isotopiques du Lithium mesurée dans les minéraux de nos échantillons de granulites, exprimées en [delta]7Li par rapport à Lsvec, varient de -13 à +4.7 ‰. Ces valeurs sont donc pour la plus part inférieures à celles mesurées sur les MORB (2 – 6‰). La dispersion des valeurs reflètent l’hétérogénéité de la source des granulites, et les valeurs bassent resultent probablement de la perte par diffusion de Li pendant la mise en place des liquides silicatées provenant du manteau dans la croûte inférieure. (6) La grande hétérogénéité des teneurs en eau et en Lithium, et des compositions isotopiques de H-O-Li indique l’absence de circulation de fluide pervasive au travers de la croûte inférieure, qui aurait pour effet de supprimer les hétérogénéités à petite échelle et de les diminuer fortement à grande échelle / For the first time, systematic investigations of water content and H-O-Li isotopic compositions of minerals in lower crustal granulites, as well as water content of minerals in mantle peridotites, from eastern China have been carried out by Fourier transform infrared spectrometer and ion microprobe. The results show that: (1) Nominally anhydrous minerals, such as pyroxenes and plagioclase, in the lower crust generally contain trace amounts of structural water, with their content (H2O by wt.) varying from 200 to 2330 ppm for clinopyroxene, 60 to 1875 ppm for orthopyroxene, 65 to 900 ppm for plagioclase and 155 to 1100 ppm for the estimated bulk compositions. (2) Water contents of minerals in lower crustal granulites from eastern China, and their bulk values, are significantly higher than those in the underlying upper mantle, implying vertical heterogeneities of water distribution in the deep continental lithosphere; the contrast in water content even affect the rheological strength of the lithosphere. (3) The O-isotopic compositions of pyroxenes in the lower crustal granulites from eastern China are highly variable between different localities (~ 4.5 to 12.5‰, expressed in [delta]18OSMOW values), indicating variable influences from recycled crustal materials on their protoliths. (4) The H-isotopic compositions of granulite minerals from eastern China, are mostly in the range of -80 to -10‰ expressed in [delta]DSMOW values, and these minerals are usually in equilibrium with their [delta]D values. The relatively high [delta]D of granulite minerals may be related with degassing loss of H during the genesis of granulites. (5) The Li-isotopic compositions of granulite minerals from eastern China are usually in the range of -13 to 4.7‰, mostly lower than those of MORB (2-6‰). They reflect the source heterogeneity and are probably results of high-T Li diffusion during the intrusion of their original melts into the preexisting lower crust. (6) The large dispersion of Li and water contents and of H-O-Li isotopic results indicate the absence of any pervasive fluids in the lower crust

La formation de la croute continentale est une des conséquences majeures de la différenciation de la Terre. Les avancées récentes dans la compréhension de ce phénomène résultent de l’amélioration des techniques analytiques permettant la mesure in situ des compositions isotopiques en U-Pb-Hf-O de grains de zircon, minéral abondant dans les roches crustales. Cette étude reconstitue l’histoire du segment de croute affleurant dans l’est du Massif Central français (MCF), portion de la chaine Varisque d’Europe de l’Ouest, dans le but d’évaluer les limites d’utilisation des zircons pour retracer l’évolution crustale. L’origine et la signification géodynamique des principales unités lithologiques du MCF ont été étudiées en combinant les approches classiques de la pétrologie avec des données isotopiques U-Pb-Hf-O acquises sur zircon. Deux incohérences majeures existent entre nos résultats et les conclusions tirées de l’étude des zircons considérés hors de leur contexte pétrologique, approche généralement suivie pour analyser l’évolution crustale. Les âges modèles calculés à partir des données Hf suggèrent une importante croissance crustale au Mésoproterozoique dans le MCF, en contradiction avec le fait que 60% de la croute locale soit d’âge Néoproterozoïque. De plus, 5 à 10% de la croute du MCF a été formée durant l’orogènese Varisque sans que cela ne soit enregistré par le zircon. Dans les deux cas, ces incohérences résultent du caractère hybride des signatures isotopiques portées par les zircons. Celles-ci ne peuvent être correctement détectées et interprétées qu’en disposant de données pétrologiques complémentaires sur les roches contenant les grains analysés / The formation of the continental crust is a major consequence of Earth differentiation. Understanding how the crust formed and evolved through time is paramount to locate the vast mineral deposits hosted therein and address its influence on the global climate, ultimately affecting the development of terrestrial life. Recent advances on the topic of continental crust evolution benefited from improvements of analytical techniques enabling in situ measurements of U-Pb- Hf-O isotope compositions in zircon, a widespread accessory mineral of continental igneous rocks. The time constrains derived from the U-Pb chronometer coupled with the petrogenetic information retrieved from Hf-O isotope signatures are currently used to unravel the diversity and succession of magmatic events affecting the continental crust at the regional and global scales. This study reconstructs the evolutionary path followed by the crust segment today exposed in the eastern part of the French Massif Central (FMC), a portion of the Variscan belt of Western Europe, with the aim to investigate the potential flaws of the zircon record of crust evolution. In this scope, the origin and geodynamic significance of the constituent FMC lithological units are tackled by combining conventional petrological observations with zircon U-Pb-Hf-O isotope data. The results obtained following this integrated approach are then confronted to the conclusions that would have been drawn solely from zircon isotopic signatures, taken out of their petrological context, as is commonly performed in studies investigating crust evolution. The oldest rocks of the FMC correspond to Ediacaran (590_550 Ma) meta-sediments deposited in back-arc basins along the northern Gondwana margin. Such basins were fed by a mixed detritus originating from the adjacent Cadomian magmatic arc and a distal Gondwana source, presumably the Sahara Metacraton. Partial melting of these meta-sediments at the Ediacaran/Cambrian boundary led to voluminous S-type granitic magmatism, pinpointing a first major crust reworking event in the FMC. The origin of anatexis likely stems from the transient thickening of the hot, back-arc crust caused by the flattening of the Cadomian subduction. Subordinate melting of the depleted backarc mantle at that time is also documented. During the Lower Paleozoic, rifting of the northern Gondwana provoked coeval crust and (limited) mantle melting. Mantle-derived igneous rocks show markedly diverse trace element and isotopic signatures, consistent with a very heterogeneous mantle source pervasively modi_ed by the Cadomian subduction. Finally, the Variscan collision resulted in crustal melting as evidenced by the emplacement of S-type granites and the formation of migmatite domes, the spatial distribution of which being partly controlled by the crustal architecture inherited from pre-orogenic events. Synchronous intrusion of mafic mantle-derived magmas and their differentiates testify for Variscan post-collisional new continental crust production in the FMC. Two major inconsistencies exist between these results and the zircon record. First, zircon Hf model ages would point to substantial Mesoproterozoic crust formation in the FMC whereas more than 60% of the crust is actually Neoproterozoic in age. Second, new additions to the continental crust volume during the Variscan orogeny are not recorded even though 5 to 10% of the exposed crust formed at that time. The origin of both discrepancies inherently lies in the mixed isotopic signature carried by many zircon grains. Such equivocal information can only be detected when additional petrological constrains on the zircon host rocks are available and provide guidance in interpreting the zircon record of crust evolution

Le travail de thèse reporté dans ce manuscrit se focalise sur la reconnaissance ainsi que l'expression des processus de différenciation crustale à l'Archéen. Cet éon représente à lui tout seul 1/3 des temps géologiques, et se caractérise notamment par des lithologies diagnostiques, ainsi que des contextes géodynamiques complexes. La majorité des études sont portées sur l’investigation des phases alumineuses qui permettent de contraindre précisément les événements métamorphiques au-cours d’une géodynamique d’épaississement crustal. Toutefois, ces phases alumineuses représentent rarement plus de 10% des terrains archéens, alors qu’ils sont faits à plus de 75% de gneiss orthodérivés. L'étude qui suit est une caractérisation du complexe de gneiss gris composite de la marge Nord du craton archéen du Kaapvaal en Afrique du Sud. Les résultats produits durant cette investigation ont amené à plusieurs conclusions importantes au regard de la géodynamique archéenne. L'étude isotopique U-Pb/Lu-Hf sur zircon couplée à des analyses pétro-métamorphiques montre que la construction d’un complexe de gneiss gris composite correspond à une géodynamique prolongée dans le temps, accomplie au-travers de processus de différenciations crustales internes à la Zone accrétée, 1.e. le bloc crustal évolue en système thermodynamiquement fermé. Les complexes de gneiss gris ne sont que modérément étudiés toutefois, les informations contenues dans ces lithologies apparaissent complémentaires avec celles obtenues par les études métamorphiques sur les lithologies alumineuses. Il est donc nécessaire d'approfondir ce type d’investigations afin de mieux contraindre les modèles géodynamiques archéens / The PhD work presented in this manuscript focuses on the recognition and the manifestation of Archean crustal differentiation processes. The Archean eon which represents 1/3 of the geological record is featured by both lithologies unrecognized in younger eons and cryptic geodynamics. Most of investigations concentrate on the characterisation of aluminium-rich lithologies that allow an accurate determination of the pressure-temperature evolution underwent by crustal materials during crustal thickening geodynamics. However, aluminium-rich lithologies - mainly represented by metasediments - account for only 10% on average of Archean terranes whereas orthoderived gneisses - which also testify for crustal differentiation processes - form around 75% of these terranes. The following contribution depicts an Archean composite grey gneiss complex located at the northern edge of the Kaapvaal craton is South Africa. Results carried out during this PhD study have major consequences on Archean geodynamics. The zircon U-Pb/Lu-Hf isotope Investigation coupled with strong petro-metamorphic observations show that composite grey gneiss complexes may be built over a protracted time span, achieved through self-refinement of crustal materials, i.e. the crustal block evolved in a thermodynamically closed system. Grey gneiss compiexes are only moderately investigated even though information enclosed in these lithologies is complementary with those from aluminium-rich rocks. Therefore, deeper investigations of these geological objects must be a central scope in order to improve the knowledge of the Archean eon and appears necessary for the building of even more realistic geotectonic models

First distinguished from other sedimentary successions in 1928, the Entrada Sandstone has been the subject of numerous studies. The western extent of the formation was initially described as laterally continuous "earthy" red beds, and categorized as sub- to supratidal marine-influenced sediments. Recent workers have reexamined the sedimentary facies hosted by the Entrada Sandstone, and findings suggest purely terrestrial depositional environments. Several outcrops of the upper Entrada hosted peculiar sedimentary features, including undulatory and convex-upward, parallel-laminated bedforms, reminiscent of hummocky cross-stratification- unexpected features in a terrestrial environment. The purpose of this study was to collect detailed outcrop measurements of these and other facies present in the upper Entrada Sandstone and to place them in context within a regional sedimentary system. Measured section data was analyzed and divided into sixteen primary facies based on textures, features, bedforms, grain size, and other characteristics. Surfaces were also noted and described. Each facies and surface was recognized to have developed under specific depositional or flow conditions, including eolian, paleosol, and fluvial subcritical, critical, supercritical, and waning flow. Primary facies were grouped into observed and interpreted facies associations. A depositional environment was then assigned to each facies association. These environments included sabkha, overbank splay/paleosol, distal terminal splay, and hyper-distal terminal splay. Ancient analogs were found in the Blomidon, Skagerrak, and Ormskirk Formations, which have been described as dryland fluvial systems that terminated onto saline mudflats (sabkhas). Modern analogs were found in the central Australian continent, in the form of fluvial terminal splays in ephemeral Lakes Eyre and Frome. The sedimentary system of the upper Entrada Sandstone of the San Rafael Swell is interpreted as an interfingering fluvial terminal splay and inland sabkha system. These are marked by a wide array of sedimentary structures representing stark extremes, from hyperarid to flash flooding conditions. During arid conditions, the only source of water was evaporative pumping of a high water table. During the rare occasions when surface water flowed through the system, flash flooding events produced the highest stage of supercritical flow described in geological literature. The succession of these facies reveals allogenic and autogenic processes active at the time of deposition, including episodes of tectonic uplift and fluvial avulsions.

This thesis is a compendium of three papers related to the magnetotelluric (MT) method and its application to the characterization of lithospheric-scale geoelectrical structures. The thesis begins with an Introduction where the motivation and the aims are presented as well as the geological context of the Pyrenees, the previous geophysical studies and the used data set. The Introduction also contains a description of the MT method with basic concepts useful to understand the MT analysis developed in the three papers. Then the three papers, which are the main part of the thesis, are exposed. After the papers, there is a Discussion where the results are commented and compared, extending some of the ideas proposed in the articles and including a new geoelectrical crustal model of the Western Pyrenees. Then there are the Conclusions and proposals of future works related to the MT sites acquired in the Pyrenees and the proposed method for processing MT data. At the end of the thesis there are the references of the cited works and an annex containing a copy of the two published papers and a copy of the submitted manuscript of the third paper. The first published paper determines the geoelectrical structures below the Central Pyrenees using new BBMT and LMT data acquired close to the ECORS-Pyrenees deep seismic profile. The aim of this study has been to improve the results obtained by Ledo (1996) and Pous et al. (1995a), taking advantage of the progress occurred in the last fifteen years associated with the MT method and the acquisition of MT data. The most important improvements that have been achieved are the better definition of the top of the electrical resistivity structure associated with the Iberian subducted lower crust (IBSLC) and the determination of the lithosphere-asthenosphere boundary (LAB) below the Iberian and the European plates close to the collision zone. Complementary, an analysis of the geological properties of the lower-crust and the dehydration point of the muscovite and biotite rocks provides more arguments in favour of the hypothesis of partial melting to explain the geophysical observations associated with the IBSLC. In the second paper the MT method has been applied to characterize the geoelectrical structures below the West-Central Pyrenees in a new MT profile across the Pyrenean mountain range. This new MT profile is 130 km long and is composed by twenty BBMT sites acquired in 2010, seven of them also with LMT data. Results have been compared with the ones obtained in the Central Pyrenees characterizing the main geoelectrical variations between the two MT profiles. An analysis of the thermal re-equilibration of the IBSLC has been developed completing the analysis of the previous paper about the presence or absence of partial melting in the IBSLC. This analysis corroborates partial melting as the best explanation for the low electrical resistivity values of the IBSLC. The LAB below the West-Central Pyrenees has been determined not only below the Iberian and the European plates, as in the Central Pyrenees, but also below the collision zone. Additionally, an unexpected geoelectrical structure completely buried below the Ebro basin has been associated with a Variscan boundary. In the third paper a new method is proposed for processing MT data. The proposed method uses the horizontal magnetic fields recorded at a neighbouring site to process the MT data of a local site from inter-station tensor relationships. Results obtained in the experiments validate the method. A parameter has been defined in order to determine, in each specific study for each used period, if the proposed method can be applied. / Aquesta tesi es composa de tres articles relacionats amb el mètode Magnetotelluric (MT) i la seva aplicació a la caracterització d’estructures geoelèctriques de la litosfera. La tesi comença amb una introducció on es presenten les motivacions d’aquesta i els objectius plantejats, així com el context geològic dels Pirineus, els estudis previs que s’han realitzat i les dades fetes servir pel desenvolupament de la tesis. La introducció conté també una descripció del mètode MT amb l’objectiu d’ajudar a entendre l’anàlisi que es desenvolupa en els articles. Tot seguit s’exposen els tres articles, es discuteixen els resultats obtinguts i s’exposen les conclusions a les que s’ha arribat. El primer article mostra les estructures geoelèctriques sota el Pirineu Central. L’objectiu d’aquest estudi ha estat millorar els resultats de Ledo (1996) i Pous et al. (1995a), aplicant els progressos que hi ha hagut en el camp de la MT en els darrers quinze anys. Els nous resultats han permès caracteritzar millor la zona de fusió parcial associada amb la subducció de l’escorça Ibèrica Inferior (IBSLC) i el límit litosfera astenosfera (LAB). De forma complementaria, s’ha dut a terme un anàlisi de les propietats de l’escorça inferior que ha permès aportar més arguments a favor de la hipòtesis de la fusió parcial. En el segon article el mètode MT s’ha fet servir per caracteritzar les estructures geoelèctriques sota el Pirineu Occidental-Central en un nou perfil de MT. En aquest estudi també s’han observat estructures geoelèctriques associades amb la fusió parcial de la IBSLC i amb el LAB. Sota la conca de l’Ebre s’ha observat per primer cop una anomalia geoelèctrica que s’ha associat amb la presència d’un límit Hercinià. Els resultats han estat comparats amb els del Pirineu Central per tal de caracteritzar l’evolució de les principals estructures geoelèctriques al llarg de la serralada. En el tercer article s’ha proposat un nou mètode per processar dades MT. Aquest mètode utilitza els camps magnètics horitzontals enregistrats en una estació veïna per processar les dades de la zona d’estudi únicament a partir de relacions tensorials entre estacions. Els experiments duts a terme corroboren la validesa del mètode.

<p>Severe accidents in a Light Water Reactor (LWR) have been a subject of the research for the last three decades. The research in this area aims to further understanding of the inherent physical phenomena and reduce the uncertainties surrounding their quantification, with the ultimate goal of developing models that can be applied to safety analysis of nuclear reactors. The research is also focusing on evaluation of the proposed accident management schemes for mitigating the consequences of such accidents.</p><p>During a hypothetical severe accident, whatever the scenario, there is likelihood that the core material will be relocated and accumulated in the lower plenum in the form of a debris bed or a melt pool. Physical phenomena involved in a severe accident progression are complex. The interactions of core debris or melt with the reactor structures depend very much on the debris bed or melt pool thermal hydraulics. That is why predictions of heat transfer during melt pool formation in the reactor lower head are important for the safety assessment.</p><p>The main purpose of the present study is to advance a method for describing turbulent natural convection heat transfer of a melt pool, and to develop a computational platform for cost-effective, sufficiently-accurate numerical simulations and analyses of Core Melt-Structure-Water Interactions in the LWR lower head during a postulated severe core-melting accident.</p><p>Given the insights gained from Computational Fluid Dynamics (CFD) simulations, a physics-based model and computationally-efficient tools are developed for multi-dimensional simulations of transient thermal-hydraulic phenomena in the lower plenum of a Boiling Water Reactor (BWR) during the late phase of an in-vessel core melt progression. A model is developed for the core debris bed heat up and formation of a melt pool in the lower head of the reactor vessel, and implemented in a commercial CFD code. To describe the natural convection heat transfer inside the volumetrically decay-heated melt pool, we advanced the Effective Convectivity Conductivity Model (ECCM), which was previously developed and implemented in the MVITA code. In the present study, natural convection heat transfer is accounted for by only the Effective Convectivity Model (ECM). The heat transport and interactions are represented through an energy-conservation formulation. The ECM then enables simulations of heat transfer of a high Rayleigh melt pool in 3D large dimension geometry.</p><p>In order to describe the phase-change heat transfer associated with core debris, a temperature-based enthalpy formulation is employed in the ECM (the phase-change ECM or so called the PECM). The PECM is capable to represent possible convection heat transfer in a mushy zone. The simple approach of the PECM method allows implementing different models of the fluid velocity in a mushy zone for a non-eutectic mixture. The developed models are validated by a dual approach, i.e., against the existing experimental data and the CFD simulation results.</p><p>The ECM and PECM methods are applied to predict thermal loads to the vessel wall and Control Rod Guide Tubes (CRGTs) during core debris heat up and melting in the BWR lower plenum. Applying the ECM and PECM to simulations of reactor-scale melt pool heat transfer, the results of the ECM and PECM calculations show an apparent effectiveness of the developed methods that enables simulations of long term accident transients. It is also found that during severe accident progression, the cooling by water flowing inside the CRGTs plays a very important role in reducing the thermal load on the reactor vessel wall. The results of the CFD, ECM and PECM simulations suggest a potential of the CRGT cooling as an effective mitigative measure during a severe accident progression.</p>