Les expériences ont été menées pour déterminer les propriétés électriques des verres et liquides silicatés du Vésuve et du Kilauea par spectroscopie d’impédance. Une étude méthodologique des mesures à deux et quatre électrodes a amélioré la qualité des mesures électriques. Les mesures ont été faites entre 400 et 1400°C, 0.1 et 400MPa et pour des fugacités en oxygène de 10-8 à 0.2 bar. La conductivité électrique croît avec la température, les teneurs en eau et sodium et lorsque pression et fO2 diminuent. Des lois d’Arrhénius ont été déterminées dans les verres et liquides pour étudier les propriétés de transport. Des énergies d’activation de 60 à 150kJ/mol et un volume d’activation de 20cm3/mol ont été calculés. Une méthode semiempirique a été déduite pour estimer la conductivité d’une large gamme de melts. Une application géophysique de nos résultats a consisté en un modèle direct de la conductivité du Vésuve. Les fonctions de transfert s’expliquent par la seule présence d’une saumure. Sa forte conductivité rend la détection d’un corps magmatique profond difficile. Cependant, nos simulations ont démontré que les données géophysiques actuelles sont en accord avec un réservoir de magma cristallisé ou du magma plus chaud interconnecté dans l’encaissant carbonaté. Une application géochimique a consisté au suivi en temps réel des cinétiques redox dans des basaltes, en utilisant la dépendance au temps de la conductivité suite à un changement de fO2. L’évolution de la conductivité au cours du temps, liée à la mobilité du sodium, est identique à celle du ratio fer ferrique/fer ferreux du melt. La réduction sous CO-CO2 et l’oxydation à l’air sont limitées par la diffusion, mais pas l’oxydation sous CO2, probablement à cause de réactions à l’interface gaz/melt. Les valeurs calculées élevées de diffusivité et d’énergie d’activation ont été expliquées par des mécanismes redox impliquant une coopération entre flux d’alcalins, de cations divalents et d’oxygène. / Experiments were conducted to determine the electrical properties of silicate glasses and liquids from Mt Vesuvius and Kilauea volcanoes using impedance spectroscopy. A methodological study of the two and four electrode measurements improved the quality of the electrical measurements. Measurements were performed between 400 and 1400°C, from 0.1 to 400MPa and for oxygen fugacities ranging from 10-8 to 0.2 bar. The electrical conductivity increases with increasing temperature, water content, sodium content and with decreasing pressure and fO2. Arrhenius laws were determined for glasses and liquids to investigate the transport properties. Activation energies from 60 to 150kJ/mol and an activation volume of 20cm3/mol were calculated. A semi-empirical method was deduced to estimate the conductivity of a wide range of melts. A geophysical application of our results consisted in the forward modelling of the conductivity of Mt Vesuvius. Transfer functions are explained by the only presence of a brine. Its high conductivity makes difficult the detection of a deeper magmatic body. Still, our simulations demonstrated that present geophysical data are compatible with a crystallized magma reservoir or a hotter magma interconnected in the surrounding carbonates. A geochemical application consisted in the monitoring in real-time of redox kinetics in basaltic liquids, using the time-dependence of electrical conductivity following fO2 step changes. The evolution of the conductivity with time, related to sodium mobility, is identical to that of the ferric/ferrous ratio of the melt. Reduction under CO-CO2 and oxidation in air are diffusion-limited, while oxidations under CO2 are not, probably due to gas/melt interface reactions. High calculated diffusivities and activation energies have been explained by redox mechanisms involving cooperative alkali, divalent cation and oxygen fluxes.

Long-wavelength magnetic anomalies (LWMA) are broad scale magnetic fields that are usually observed at satellite altitudes. The origin of these fields have been assumed to be solely from the crust, disregarding possible contributions from the upper mantle. Using data from magnetic mantle xenoliths, the possible mantle contribution to LWMA was investigated for different regions including Siberian craton, Kamchatka subduction zone fore-arc, Hawaii hotspot, and French Massif Central plume. To do this, a MATLAB-based forward-modeling of magnetic anomalies from tectonic regions with different upper mantle geotherms and magnetized mantle geometries was developed. This model incorporated the increase in Curie temperature of magnetite with pressure, the current geotherms of the specific regions, and the statistical distributions of magnetic data from xenoliths in the specific regions. A Monte-Carlo method of random selection of values and repeated calculations was utilized in constraining the range of potential mantle contributions to satellite-observable LWMA. The Siberian craton shows the highest possible contribution to satellite magnetic anomalies with amplitudes ranging from 2 nT to 9 nT, with a wavelength equivalent to the long-axis of the craton. The Hawaii hotspot region displays a significant contribution of its upper mantle to satellite measured magnetic anomalies with an amplitude of the order of 2 nT, while the Massif Central plume regions shows an insignificant contribution of its upper mantle to satellite magnetic anomalies with potential total magnetic anomaly amplitude of 0.07 nT. Finally, the mantle portion of Kamchatka subduction zone shows a sizeable contribution to magnetic anomalies measurable at satellite altitude with an amplitude up to 1.3 nT. These results when compared with lithospheric total field intensity model derived from SWARM satellite data, show that the upper mantle can contribute significantly to LWMA depending on (a) the average remanent magnetization in xenoliths from such regions, (b) the thickness of magnetized mantle, and (c) the size of the region under consideration.

Les systèmes sédimentaires carbonatés forment à la fois des archives géologiques uniques des changements globaux-locaux des enveloppes externes de la Terre et renferment plus de 75 % des réserves d'hydrocarbure conventionnelles. Ils sont complexes et très difficiles à comprendre et à prédire. Cette complexité à toutes les échelles spatio-temporelles rend nécessaire l'intégration de méthodes naturalistes et quantitatives pour les étudier. La modélisation numérique basée processus permet de réduire les incertitudes des prédictions des propriétés des réservoirs carbonatés.Le manuscrit présente une méthode de modélisation itérative des systèmes carbonatés de la stratigraphie à la sismique en intégrant la diagenèse. Cette approche est basée sur le couplage de plusieurs outils numériques et par une démarche de travail combinant la sédimentologie, la diagenèse, la physique des roches et la simulation sismique.L’approche de modélisation développée permet ainsi d’intégrer un grand nombre de données multi-échelles et multidisciplinaire au sein d’un modèle facilement partageable entre toutes les disciplines en géosciences. L’intégration de ces nombreuses données est facilitée par un continuum du modèle entre les différentes échelles d’espace et de temps (du bassin au réservoir). La sismique synthétique ainsi obtenue n’est pas une simple convolution géométrique, elle intègre les propriétés sédimentologiques et diagénétiques, permettant une analyse de la signification stratigraphique des réflecteurs sismiques. Cette approche innovante intègre les méthodes naturalistes et quantitatives nécessaires à la compréhension et à la prédiction des systèmes carbonatés. / Carbonate sedimentary systems record both global and local geological changes of the outer envelope of the Earth and contain more than 75% of conventional hydrocarbon reserves. These carbonate systems show a great complexity at every spatial and temporal scales. To increase our ability to understand and predict such intricate natural systems, it is necessary to integrate naturalistic and quantitative methodological apporaches. Numerical process-based modeling (stratigraphic-sedimentary-diagenetic) reduces the uncertainty of prediction of carbonate reservoir properties. The manuscript presents a method of iterative modeling of carbonate systems from stratigraphy to seismic by integrating diagenesis. This approach is based on the coupling of numerical tools and a working approach combining sedimentology, diagenesis, rock physics and seismic simulation. Tests on case studies associated with scientific and industrial issues validated the method.The modeling approach that was developed during the thesis allows to integrate a large number of multi-scale and multidisciplinary data. Models can easily be shared between the disciplines of geosciences. The model continuum along different scales of space (from the basin to the reservoir) and time eases the integration of various data. The obtained synthetic seismic is not a simple geometric convolution, but an integration of sedimentological and diagenetic properties, which allows for an analysis of the stratigraphic significance of the seismic reflectors. This innovative approach integrates naturalistic and quantitative methods, which improve the understanding and prediction of carbonate systems and reservoirs.

Aujourd’hui, la communauté scientifique dispose de jeux de données gravimétriques avec une précision et une résolution spatiale sans précédent qui améliorent nos connaissances du champ gravitationnel terrestre à différentes échelles et longueurs d’ondes, obtenues de mesures du sol à des satellites. Parallèlement à la gravimétrie, l’avancement des observations par satellite fournit à la communauté des modèles d’élévation numérique plus détaillés pour refléter la géométrie de la structure terrestre. Ensemble, ces nouveaux jeux de données offrent une excellente occasion de mieux comprendre les structures et la dynamique de la Terre à l’échelle locale, régionale et mondiale. L'utilisation et l'interprétation de ces données de haute qualité exigent le raffinement des approches standards dans le traitement et l'analyse des données liées à la gravité. Cette thèse consiste en une série d’études visant à améliorer la précision du traitement des données de gravité et gravité de gravité gradients pour les études géodynamiques. Pour ce faire, nous développons un outil, appelé GEEC (Gal Eötvös Earth Calculator), pour calculer précisément les effets gravimétriques dues à tout corps de masse, indépendamment de sa géométrie et de sa distance par rapport aux mesures. Les effets de gravité et des gravité gradients sont calculés analytiquement en utilisant la solution intégrale linéaire d'un polyèdre irrégulier. Les validations aux échelles locale, régionale et mondiale confirment la robustesse des performances du GEEC, où la résolution du modèle, qui dépend à la fois de la taille de la masse corporelle et de sa distance par rapport au point de mesure, contrôle fortement la précision des résultats. Nous présentons une application pour évaluer les paramètres optimaux dans le calcul des gradients de gravité et de gravité dus aux variations de topographie. La topographie joue un rôle majeur dans l'attraction gravitationnelle de la Terre; par conséquent, l'estimation des effets topographiques doit être soigneusement prise en compte dans le traitement des données gravimétriques, en particulier dans les zones de topographie accidentée ou à grande échelle. Pour les études de gravité de haute précision à l'échelle mondiale, le processus de correction de la topographie doit prendre en compte l'effet topographique de la Terre entière. Mais pour les applications locales à régionales basées sur des variations relatives à l'intérieur de la zone, nous montrons que la topographie tronquée à une distance spécifique peut être adéquate, même si ignorer la topographie de cette distance peut générer des erreurs. Pour soutenir ces arguments, nous montrons les relations entre les erreurs relatives à la gravité, la distance de troncature de la topographie et l'étendue de la zone d'étude. Enfin, nous abordons le problème: les mesures GOCE sont-elles pertinentes pour obtenir une image détaillée de la structure d'une plaque de subduction, y compris sa géométrie et ses variations latérales? Les résultats du calcul des avec des modèles de subduction synthétiques calculés à l’altitude moyenne du GOCE (255 km) démontrent que les bords de subduction et les variations latérales du pendage produisent des variations des gradients détectables avec le jeu de données GOCE. Dans l'application à la zone de subduction Izu-Bonin-Mariana (IBM), la topographie et les effets bathymétriques ont été supprimés avec succès. Cependant, dans l'application au cas réel de la zone de subduction Izu-Bonin-Mariana, les caractéristiques géométriques du second ordre du slab sont difficiles à détecter en raison de la présence des effets crustaux restants. Ceci est dû à l'imprécision du modèle crustal global existant qui est utilisée, qui conduit à une élimination impropre de l'effet crustal. / Nowadays, the scientific community has at its disposal gravity and gravity gradient datasets with unprecedented accuracy and spatial resolution that enhances our knowledge of Earth gravitational field at various scales and wavelengths, obtained from ground to satellite measurements. In parallel with gravimetry, the advancement of satellite observations provides the community with more detailed digital elevation models to reflect the Earth’s structure geometry. Together, these novel datasets provide a great opportunity to better understand the Earth’s structures and dynamics at local, regional, and global scales. The use and interpretation of these high-quality data require refinement of standard approaches in gravity-related data processing and analysis. This thesis consists of a series of studies aiming to improve the precision in the chain of gravity and gravity gradient data processing for geodynamic studies. To that aim, we develop a tool, named GEEC (Gal Eötvös Earth Calculator) to compute precisely the gravity and gravity gradients effects of due to any mass body regardless of its geometry and its distance from measurements. The gravity and gravity gradients effects are computed analytically using the line integral solution of an irregular polyhedron. The validations at local, regional, and global scales confirm the robustness of GEEC’s performance, where the resolution of the model, that depends on both size of the body mass and its distance from the measurement point, control strongly the accuracy of the results. We present an application for assessing the optimum parameters in computing gravity and gravity gradients due to topography variations. Topography has a major contribution in Earth gravitational attraction, therefore the estimation of topography effects must be carefully considered in the processing of gravity data, especially in areas of rugged topography or in large-scale studies. For high-accuracy gravity studies at a global scale, the topography correction process must consider the topography effect of the entire Earth. But for local to regional applications based on relative variations within the zone, we show that truncated topography at a specific distance can be adequate, although, ignoring the topography pas this distance could produce errors. To support these arguments, we show the relationships between gravity relative errors, topography truncation distance, and the extent of study zone. Lastly, we approach the issue: Are GOCE measurements relevant to obtain a detailed image of the structure of a subducting plate, including its geometry and lateral variation? The results of gravity gradient forward modelling using synthetic subduction models computed at GOCE’s mean altitude (255 km) demonstrate that both subduction edges and lateral variations of subduction angle produce gravity gradient variations that are detectable with GOCE dataset (∼100 km wavelength and 10 mE amplitude). However, in the application to the real case of Izu-Bonin-Mariana subduction zone, the second-order geometric features of the subducting plate are difficult to be detected due to the presence of the remaining crustal effects. This is caused by the inaccuracy of the existing global crustal model, that leads to inaccurate crustal effect removal.

Abstract The lithospheric conductivity in the westernmost Fennoscandia has been studied using magnetotelluric (MT) data. The western margin of Fennoscandia was significantly affected in Paleozoic by the Caledonian orogeny and later by the rifting of Laurentia and the opening of the Atlantic Ocean c. 80 Ma ago. Magnetotelluric studies have been carried out in two target areas in southern Norway and in western Fennoscandia. The first study resulted in 2-D geoelectric models of two profiles stretching from Oslo to the Norwegian coast. The interpretation suggests that the basement is in general very resistive with a few conductive upper crustal layers, representing the alum shales, and middle crustal conductors possibly imaging the remnants of the closed ocean basins. A more extensive MT study was performed within the project "Magnetotellurics in the Scandes". Measurements were carried in summers of 2011 to 2013, resulting in an array of 279 MT sites. The data allowed us to derive 2-D geoelectric models for the crust and upper mantle as well as 3-D models for the crust. The inversions revealed a resistive upper crust and a conductive lower crust, two upper crustal conductors in the Skellefteå and Kittilä districts, highly conducting alum shales in the Caledonides and a conductive upper crust beneath the Lofoten peninsula. The thickness of the lithosphere is around 200 km in the north and 300 km in the south-west. The Palaeoproterozoic lithosphere is the thickest, not the Archaean, on contrary to a generally accepted hypothesis. A better image of the lithosphere will help to evaluate the proposed mechanisms of the exhumation of the Scandinavian Mountains. The theoretical part of this study is the development of a new multi-resolution approach to 3-D electromagnetic (EM) modelling. Three-dimensional modelling of MT data requires enormous computational resources because of the huge number of data and model parameters. The development of the multi-resolution forward solver is based on the fact that a finer grid resolution is often required near the surface. On the other hand, the EM fields propagate in a diffusive manner and can be sufficiently well described on a grid that becomes coarser with depth. Tests showed that the total run time can be reduced by five times and the memory requirements by three times compared with the standard staggered grid forward solver. / Tiivistelmä Olemme tutkineet litosfäärin sähkönjohtavuutta Fennoskandian länsiosassa magnetotelluurisen (MT) menetelmän avulla. Fennoskandian länsireuna muokkautui merkittävästi paleotsooisena aikana Kaledonidien vuorijonopoimutuksessa sekä myöhemmin mesotsooisena aikana Laurentia-mantereen repeytyessä ja Atlantin valtameren syntyessä noin 80 miljoonaa vuotta sitten. MT-tutkimukset tehtiin Etelä-Norjassa ja Fennoskandian luoteisosassa. Ensimmäisessä tutkimuksessa kallioperän sähkönjohtavuutta kuvattiin kaksiulotteisilla (2-D) johtavuusmalleilla, jotka ulottuvat Oslosta Norjan rannikolle. Mallien tulkinta viittaa siihen, että maan kuori on pääosin hyvin eristävä lukuun ottamatta muutamaa kuoren ylä- ja keskiosassa olevaa johdekerrosta. Yläkuoren johteet edustavat alunaliuskeita ja keskikuoren johteet todennäköisesti suljetuissa merialtaissa syntyneitä hiilipitoisia sedimenttikerrostumia. Laajempi MT-tutkimus tehtiin ”Magnetotellurics in the Scandes” -hankkeessa. Mittauksia tehtiin 279 mittauspisteessä kesinä 2011–2013. Saadun aineiston avulla voitiin laatia 2-D inversiomallit kuoresta ja ylävaipasta sekä 3-D inversiomalli kuoresta. Tulosten mukaan täällä kuoren yläosa on eristävä kun taas kuoren alaosa on sähköä hyvin johtava. Edellisen lisäksi malleissa näkyy yläkuoren johtavat muodostumat Skellefteån ja Kittilän alueilla, korkean johtavuuden alunaliuskeet Kaledonidien alueella sekä johde Lofoottien alla. Litosfäärin paksuus on noin 200 km mittausverkon pohjoisosassa ja noin 300 km lounaassa. Tämän mukaan litosfääri on paksuin varhaisproterotsooisen litosfäärin alueella, ei arkeeisen litosfäärin alueella vastoin yleistä hypoteesia. Tutkimuksen teoreettisessa osassa kehitettiin sähkömagneettiseen mallinnukseen uusi monitasoiseen diskretisointiin perustuva menetelmä. MT-aineiston 3-D käänteisongelman ratkaisu ja siihen liittyvä suora mallintaminen vaativat suuren laskennallisen kapasiteetin, koska havaintojen ja mallin kuvaamiseen tarvittavien parametrien määrä on erittäin suuri. Moniresoluutio-algoritmi perustuu siihen, että mallin hienojakoisempaa diskretisointia tarvitaan yleensä lähellä maan pintaa kun taas syvemmälle edettäessä, sähkömagneettisen aallon diffuusin etenemisen vuoksi, malli voi olla karkeampi. Tietokonesimulaatioiden mukaan suoritusaika on viidennes ja muistitarve kolmannes verrattuna tavanomaiseen suoran laskennan ”staggered grid” -diskretisointiin.

An integrated use of radio magnetotelluric (RMT) and controlled source tensor magnetotelluric (CSTMT) measurements, the so-called CSRMT method, has been employed in environmental and resource exploration studies. A number of case histories, including a groundwater investigation in glacial deposits, a study of fracture zones for geotechnical purposes and a mining exploration study of a copper deposit, are presented in this thesis in order to illustrate the usefulness and capability of the CSRMT method. The resolutions of the estimated models using various types of data are studied. Magnetotelluric transfer functions are used to analyze the dimensionality, the near surface resistivity distortions and the near field effects in the case of CSTMT data analysis. The near field effects in CSTMT data have also been identified by performing 2½D forward modelling. Data analysis, dimensionality tests and forward modelling show that at the lowest frequencies used the CSTMT transfer functions are generally distorted by source effects, except when the source-receiver distances are sufficient large compared with the penetration depth. Regarding CSTMT transfer functions, apparent resistivities are generally less distorted than phases. TM mode transfer functions are more affected by the sources than TE mode, while tipper vectors generally contain source signatures at all frequencies. Based on the analysis of dimensionality and source effects 2D inverse modelling of CSTMT and RMT data, as well as their combination, have been performed under the plane wave assumption. The RMT method proved to be a powerful tool for imaging the upper 50 m near-surface, but their penetration depth reduces as a conductive layer structures cover the targets at depth. The penetration depth can be increased by including the CSTMT data in the modelling if the measurements are in the far field range. The resolution of the deeper parts of the models may be improved by performing a joint inversion of TE and TM modes, if the strike direction is well-defined. Alternatively, inversion of determinant data can be performed, since the determinant data are less affected by 3D structures and source effects. However the resolution of the determinant models is somewhat degraded compared to the models inverted from combined TE and TM modes.

A maneira mais direta de detectar as anomalias da densidade é pelo estudo do potencial gravitacional e de suas derivadas. A disponibilidade global e a boa resolução dos dados do satélite GOCE, aliadas à disponibilidade de dados de gravimetria terrestre, são ideais para a comparação e classificação das bacias de larga escala, como as bacias sedimentares do Solimões e do Amazonas dentro do Craton amazônico. Foram processados um conjunto de dados, produtos GOCE EGG_TRF_2 Level 2, ao longo das trajetórias do satélite para remover o ruído (shift/drift) nos gradientes da gravidade a partir da técnica crossover (XO). Calculamos a redução das massas topográfica a fim de obter os componentes do gradiente da gravidade e anomalia da gravidade usando modelagem direta com prismas esféricos a partir do modelo de elevação digital, ETOPO1. Desta maneira, a comparação dos dados somente do satélite GOCE com as reduções das massas topográficas referentes aos componentes do gradiente da gravidade permitiram estimar quantidades invariantes que trouxeram uma melhoria na interpretação dos dados do tensor de gravidade. Além disso, comparamos dados terrestres do campo de gravidade com dados do campo de gravidade dos modelos geopotenciais EGM2008 e GOCE, uma vez que os dados terrestres podem ser afetados por erros em longos comprimentos de onda devido a erros de nivelamento, diferentes referenciais de altitudes, e aos problemas em interligar diferentes campanhas de medidas da gravidade. Portanto, estimamos uma melhora e uma nova representação dos mapas das anomalias de gravidade e do tensor gradiente da gravidade nas áreas inacessíveis do Craton Amazônico. As observações forneceram novas entradas para determinar campos regionais a partir dados brutos pre-processados (gradiente de gravidade EGG_TRF_2 L2), bem como a partir de um modelo geopotencial mais recente até grau e ordem 250 dos harmonicos esféricos derivados de dados somente do satélite GOCE para a representação do campo de gravidade como geóide, anomalias da gravidade e os componentes tensor da gravidade, os quais foram quantidades importantes para interpretação, modelagem e estudo dessas estruturas. Finalmente, obtivemos um modelo isostático considerando a estrutura de densidade litosférica estudada através de uma modelagem direta 3D da distribuição de densidade por prismas esféricos usando a geometria do embasamento e descontinuidade do Moho. Além do que, constatamos através da modelagem direta das soleiras de diabásios dentro dos sedimentos mostramos que somente as soleiras dentro da Bacia do Amazonas não são as únicas responsáveis pela anomalia de gravidade positiva que coincide aproximadamente com as espessuras máximas dos sedimentos da Bacia. Talvez, isso possa ser também um resultado de movimentos relativos do Escudo das Guianas situado ao norte da Bacia, e o Escudo Brasileiro situado ao sul. Embora isso seja apenas uma evidência adicional preliminar, não podemos confirmá-las a partir das estimativas do campo da gravidade. Portanto, é necessário outros tipos de dados geofísicos, como por exemplo, evidências mais claras advindas do paleomagnetismo. / The most direct way to detect density anomalies is the study of the gravity potential field and its derivatives. The global availability and good resolution of the GOCE mission coupled with the availability of terrestrial gravity data are ideal for the scope of intercomparison and classification of the two large-scale Amazon and Solimoes sedimentary basins into area of the Amazon Craton. The GOCE data set obtained in satellite tracks were processed from EGG_TRF_2 Level 2 Products generated with the correction needed to remove the noise (shift/drift), and so, to recover the individual components of the gravity gradient tensor using the crossover (XO) points technique. We calculated the topographic masses reductions in order to obtain the gravity gradient components and gravity anomaly (vertical component) using forward modelling from tesseroids from Digital Elevation Model, ETOPO1. Thus, the comparison of the only-satellite GOCE data with the reductions of the topographic masses for the gradient components allowed to estimate invariants quantities for bring an improvement in the interpretation of the gravity tensor data. Furthermore, we compared the terrestrial data gravity field with EGM2008 and GOCE-deduced gravity field because the terrestrial fields may be affected by errors at long wavelengths due to errors in leveling, different height references, and problems in connecting different measurement campaigns. However, we have estimated an improvement and new representations of the gravity anomalies maps and gravity gradient tensor components primary in inaccessible areas of the Amazon Craton. GOCE observations provide new inputs to determine the regional fields from the preprocessed raw data (EGG_TRF_2 L2 gravity gradients), as well from the most recent global geopotential model available up to degree and order 250 developed in spherical harmonics derived only-satellite GOCE data for representing of geoid and others gravity field as gravity anomaly and gravity gradient tensor components, which are important quantities for modelling and studying these structures. Finally, we obtained the isostatic model considering the lithospheric density structure studied through a 3D direct modelling of density distribution using the geometry of basement and Moho discontinuity, assumed to be known as initial constraint. In addition, we found through direct modeling sills and sediment has shown that the diabase sills are not the only ones responsible for positive gravity anomaly map that transects the Amazon Basin, roughly coincident with the maximum thickness of sedimentary rocks or the trough of the basin. Maybe, this could be the result of the relative movements of the Guiana Shield, situated at the north of the Amazon basin, and the Brazilian Shield, situated at the south. Although this is only a preliminary additional evidence, we cannot confirm it only from the data of gravity. It is necessary others types of geophysical data, for example, more clear evidences obtained from paleomagnetism.

Cette thèse a été conduite dans le cadre du programme de coopération de recherche Algéro-française SPIRAL (Sismique Profonde et Investigations Régionales du Nord de l’Algérie). Ce projet vise à étudier la structure profonde de la marge algérienne par une approche combinée des techniques sismiques ; grand-angle et multi-canal. Le domaine couvert par la présente étude se concentre dans la région de Jijel dans la marge algérienne orientale. L’objectif principal de notre thèse est d'améliorer en profondeur l'imagerie de la marge algérienne en utilisant une combinaison de données sismiques grand-angle (OBS, sismomètres de fond de l'océan) et multi-canal (MCS). Le but de cette thèse est d'apporter de nouvelles connaissances pour répondre à quelques questions sur la nature de la croûte terrestre, la zone de transition continentale-océanique, la présence du sel messénien, sa distribution et sa relation entre les formations sédimentaires superficielles et les structures crustales. Dans cette étude, notre approche est une inversion jointe des enregistrements grand-angle et des données sismiques multi-canal. Nous avons conduit une série de tomographie des premières arrivées, une inversion jointe des arrivées réfractées et réfléchies ainsi qu’une modélisation gravimétrique. Etant donné que la solution du problème inverse n’est pas unique, deux programmes de tomographie ont été utilisés sur les mêmes données pour la même région d’étude à savoir : FAST (First Arrival Seismic Tomography) et Tomo2D. La tomographie a été suivie par une inversion jointe des arrivées réfractées et réfléchies suivant une approche basée sur la combinaison de la migration en profondeur « Kirchhoff » avant sommation (PSDM) des données de sismique réflexion multi-canal (MCS) et la modélisation directe des enregistrements grand-angle sur le fonds marin (OBS). Afin de vérifier la consistance du modèle de la vitesse avec les données gravimétriques, l’anomalie à l'air libre a été modélisée. Les résultats de l’imagerie conduite dans ce travail montrent la structure de la marge, la croûte continentale, la zone de transition continent-océan et la croûte océanique de la Méditerranée. La structure du modèle confirme les études antérieures basées sur des données bathymétriques, gravimétriques et magnétiques. Cette structure montre essentiellement : - un plateau continental étroit et pente continentale une très raide.- l’Expulsion du sel vers le nord impliquant la formation de diapirs au-dessus du flanc nord du bassin (plaine abyssale).- L’approfondissement et l’épaississement des séquences sédimentaires (bassin sédimentaire) près de la marge algérienne. Le modèle de vitesses obtenu et l’épaisseur des différentes unités structurales formant ce modèle apportent des arguments quantitatifs pour enrichir la connaissance de cette partie de la Méditerranée occidentale. Les couches sédimentaires dans le bassin montrent des vitesses sismiques allant de 1,9 km / s à 3,8 km / s. Les formations messéniennes ont été modélisées en utilisant une vitesse située entre 3,7 km / s à 3,8 km / s. La croûte continentale s’amincit sur une bande étroite de la marge dont la distance est d'environ 15 km. La vitesse de la croûte océanique dans cette région présente deux couches distinctes : l’une caractérisée par des vitesses variant de 4,7 km / s à 6.1 et l’autre de 6.2 à 7.1 km / s. La vitesse du manteau supérieur quant à elle a été modélisée par 7,9 km / s. / This thesis has been conducted within the framework of the Algerian-French research cooperation program SPIRAL (Sismique Profonde et Investigations Régionales du Nord de l’Algérie). This project aims to study the deep structure of the Algerian margin. The area covered by this study focuses in the region of Jijel in eastern Algerian margin.The main objective of our thesis is to improve depth imaging of the Algerian margin using a combined approach of seismic techniques; wide-angle and multi- channel seismic data. The purpose of this thesis is to bring new knowledge to answer some questions about the nature of the crust, the area of continental -oceanic transition, the presence of Messinian salt, its distribution and relationship between surface sedimentary formations and crustal structures.This study presents the results of a deep seismic survey across the north Algerian margin, based on the combination of 2D multi-channel and wide-angle seismic data simultaneously recorded by 41 ocean bottom seismometers deployed along a North-South line extending 180 km off Jijel into the Algerian offshore basin, and 25 land stations deployed along a 100 km-long line, cutting through the Lesser Kabylia and the Tellian thrust-belt.In this study, our approach is a joint inversion of wide-angle seismic recordings (OBS, ocean bottom seismometers) and multi- channel seismic data (MCS). We conducted a series of first arrivals tomography, a joint inversion of reflected and refracted arrivals and gravity modelling. Since the solution of the inverse problem is not unique, two tomography programs were applied using the same data for the same study area; FAST (First Arrival Seismic Tomography) and Tomo2D. Tomography was followed by a joint inversion of reflected and refracted arrivals following an approach based on the combination of Kirchhoff prestack depth migration (PSDM) for MCS data and forward modelling of OBS. To check the consistency of the velocity model with gravity data, the free air anomaly was modeled.The final model obtained using forward modelling of the wide-angle data and pre-stack depth migration of the seismic reflection data provides an unprecedented view of the sedimentary and crustal structure of the margin. The sedimentary layers in the Algerian basin are 3.75 km thick to the north and up to 4.5 to 5 km thick at the foot of the margin. They are characterised by seismic velocities from 1.9 km/s to 3.8 km/s. Messinian salt formations are about 1 km thick in the study area, and are modelled and imaged using a velocity between 3.7 km/s to 3.8 km/s. The crust in the deep sea basin is about 4.5 km thick and of oceanic origin, presenting two distinct layers with a high gradient upper crust (4.7 km/s - 6.1 km) and a low gradient lower crust (6.2 km/s - 7.1 km/s). The upper mantle velocity is constrained to 7.9 km/s. The ocean-continent transition zone is very narrow between 15 km to 20 km wide. The continental crust reaches 25 km thickness as imaged from the most landward station and thins to 5 km over a less than 70 km distance. The continental crust presents steep and asymmetric upper and lower crustal geometry, possibly due to either asymmetric rifting of the margin, an underplated body, or flow of lower crustal material towards the ocean basin. Present-time deformation, as imaged from 3 additional seismic profiles, is characterized by an interplay of gravity-driven mobile-salt creep and active thrusting at the foot of the tectonically inverted Algerian margin.

A maneira mais direta de detectar as anomalias da densidade é pelo estudo do potencial gravitacional e de suas derivadas. A disponibilidade global e a boa resolução dos dados do satélite GOCE, aliadas à disponibilidade de dados de gravimetria terrestre, são ideais para a comparação e classificação das bacias de larga escala, como as bacias sedimentares do Solimões e do Amazonas dentro do Craton amazônico. Foram processados um conjunto de dados, produtos GOCE EGG_TRF_2 Level 2, ao longo das trajetórias do satélite para remover o ruído (shift/drift) nos gradientes da gravidade a partir da técnica crossover (XO). Calculamos a redução das massas topográfica a fim de obter os componentes do gradiente da gravidade e anomalia da gravidade usando modelagem direta com prismas esféricos a partir do modelo de elevação digital, ETOPO1. Desta maneira, a comparação dos dados somente do satélite GOCE com as reduções das massas topográficas referentes aos componentes do gradiente da gravidade permitiram estimar quantidades invariantes que trouxeram uma melhoria na interpretação dos dados do tensor de gravidade. Além disso, comparamos dados terrestres do campo de gravidade com dados do campo de gravidade dos modelos geopotenciais EGM2008 e GOCE, uma vez que os dados terrestres podem ser afetados por erros em longos comprimentos de onda devido a erros de nivelamento, diferentes referenciais de altitudes, e aos problemas em interligar diferentes campanhas de medidas da gravidade. Portanto, estimamos uma melhora e uma nova representação dos mapas das anomalias de gravidade e do tensor gradiente da gravidade nas áreas inacessíveis do Craton Amazônico. As observações forneceram novas entradas para determinar campos regionais a partir dados brutos pre-processados (gradiente de gravidade EGG_TRF_2 L2), bem como a partir de um modelo geopotencial mais recente até grau e ordem 250 dos harmonicos esféricos derivados de dados somente do satélite GOCE para a representação do campo de gravidade como geóide, anomalias da gravidade e os componentes tensor da gravidade, os quais foram quantidades importantes para interpretação, modelagem e estudo dessas estruturas. Finalmente, obtivemos um modelo isostático considerando a estrutura de densidade litosférica estudada através de uma modelagem direta 3D da distribuição de densidade por prismas esféricos usando a geometria do embasamento e descontinuidade do Moho. Além do que, constatamos através da modelagem direta das soleiras de diabásios dentro dos sedimentos mostramos que somente as soleiras dentro da Bacia do Amazonas não são as únicas responsáveis pela anomalia de gravidade positiva que coincide aproximadamente com as espessuras máximas dos sedimentos da Bacia. Talvez, isso possa ser também um resultado de movimentos relativos do Escudo das Guianas situado ao norte da Bacia, e o Escudo Brasileiro situado ao sul. Embora isso seja apenas uma evidência adicional preliminar, não podemos confirmá-las a partir das estimativas do campo da gravidade. Portanto, é necessário outros tipos de dados geofísicos, como por exemplo, evidências mais claras advindas do paleomagnetismo. / The most direct way to detect density anomalies is the study of the gravity potential field and its derivatives. The global availability and good resolution of the GOCE mission coupled with the availability of terrestrial gravity data are ideal for the scope of intercomparison and classification of the two large-scale Amazon and Solimoes sedimentary basins into area of the Amazon Craton. The GOCE data set obtained in satellite tracks were processed from EGG_TRF_2 Level 2 Products generated with the correction needed to remove the noise (shift/drift), and so, to recover the individual components of the gravity gradient tensor using the crossover (XO) points technique. We calculated the topographic masses reductions in order to obtain the gravity gradient components and gravity anomaly (vertical component) using forward modelling from tesseroids from Digital Elevation Model, ETOPO1. Thus, the comparison of the only-satellite GOCE data with the reductions of the topographic masses for the gradient components allowed to estimate invariants quantities for bring an improvement in the interpretation of the gravity tensor data. Furthermore, we compared the terrestrial data gravity field with EGM2008 and GOCE-deduced gravity field because the terrestrial fields may be affected by errors at long wavelengths due to errors in leveling, different height references, and problems in connecting different measurement campaigns. However, we have estimated an improvement and new representations of the gravity anomalies maps and gravity gradient tensor components primary in inaccessible areas of the Amazon Craton. GOCE observations provide new inputs to determine the regional fields from the preprocessed raw data (EGG_TRF_2 L2 gravity gradients), as well from the most recent global geopotential model available up to degree and order 250 developed in spherical harmonics derived only-satellite GOCE data for representing of geoid and others gravity field as gravity anomaly and gravity gradient tensor components, which are important quantities for modelling and studying these structures. Finally, we obtained the isostatic model considering the lithospheric density structure studied through a 3D direct modelling of density distribution using the geometry of basement and Moho discontinuity, assumed to be known as initial constraint. In addition, we found through direct modeling sills and sediment has shown that the diabase sills are not the only ones responsible for positive gravity anomaly map that transects the Amazon Basin, roughly coincident with the maximum thickness of sedimentary rocks or the trough of the basin. Maybe, this could be the result of the relative movements of the Guiana Shield, situated at the north of the Amazon basin, and the Brazilian Shield, situated at the south. Although this is only a preliminary additional evidence, we cannot confirm it only from the data of gravity. It is necessary others types of geophysical data, for example, more clear evidences obtained from paleomagnetism.