The late Miocene Cedar Springs fault system is a high-angle transpressional system in the Silverwood Lake area, western San Bernardino Mountains, southern California. This thesis presents the study of oblique-slip faults with modest amounts of slip, which represent the early stages of fault development by using slip as a proxy for maturity. A structural and geochemical characterization is provided for six fault zones ranging from 39 m of slip to 3.5 km of offset in order to develop a model of fault zone geometry and composition. Basic geometric and kinematic results are provided for an additional 29 small-displacement (cm- to m-scale) faults. The main faults of this study can be divided into the fault core composed of sheared clay gouge and micro breccia, the primary damage zone made up of chemically altered rock with microstructural damage and grain-size reduction, and the secondary damage zone, which is characterized by an increased fracture density relative to the host rock. Although there appears to be a general increase in fault core thickness with increasing slip, the correlation is insignificant when analyzing all faults. Both the primary and secondary damage zones appear to thicken with increased slip on the main fault. Overall, the structure and composition of the faults studied here are similar to those of larger strike-slip and reverse faults. This indicates that the fault core develops early in a fault's history. Subsequent slip appears to be focused along these narrow zones, with some deformation accumulating in the damage zone. Whole-rock geochemical analyses typically show a reduction in the abundance of Na, Al, K, and Ca in the fault core and primary damage zone relative to the host rock. This indicates enhanced fluid-rock interactions in these zones. Calculations of the energy consumed to produce the chemical alteration in the fault core indicate that a considerable amount of the total earthquake energy may be lost to alteration. This thesis concludes that fault processes are similar throughout the different stages of development, and the study of relatively small-displacement faults can therefore be used to understand fault evolution through time and the processes of larger faults in the brittle crust.

Numerous well-preserved, exhumed paleochannels in the Morrison, Cedar Mountain and Dakota Sandstone formations are exposed east of Castle Dale, Utah. These channels consist primarily of point bar complexes and scattered, low sinuosity channels. To determine the vertical and lateral relationships of these channels within the Cedar Mountain and Dakota Sandstone formations, a 1:24,000 scale geologic map covering ~140 km2 was created showing the fluvial sandstones. In the study area the Cedar Mountain Formation consists, from bottom to top, of 2.5-10 m of Buckhorn Conglomerate Member equivalent units, ~80 m of the Ruby Ranch Member, and ~30 m of the Mussentuchit Member. The Dakota Sandstone consists of conglomeratic to sandy, meandering channel fills within the Mussentuchit Member. The Ruby Ranch-Mussentuchit member contact is diagnosed as the top of a laterally extensive, ~10 meter thick, maroon paleosol with calcrete horizons and root traces. When deeply weathered the contact is discernable as a shift from maroon mudstone to a pale green-white, silty mudstone. Like the balance of the Mussentuchit Member overbank deposits, the white-green mudstone is rich in smectitic clays. In the southern one-third of the mapped area, Ruby Ranch Member sandstones are thin, discontinuous channel segments surrounded by floodplain deposits. In the middle to northern area, point bar complexes dominate, some of which are laterally amalgamated. Flow direction data from four meander complexes and a low sinuosity channel indicate an average northeast flow. Dakota Sandstone channels all of which are within the Mussentuchit Member also flowed to the northeast but point bar complexes are both more numerous and more laterally continuous than in the Ruby Ranch Member, indicating deposition in an area with less accommodation space than during Ruby Ranch Member time. The data indicate the Dakota Sandstone consists exclusively of fluvial sandstones encased within the Mussentuchit Member of the Cedar Mountain Formation. Therefore, these units are coeval and simply different facies of the same depositional system. Consequently the Mussentuchit Member is considered a member facies of the Dakota Formation.

Este trabalho tem como objetivo a identificação de feições que permitam (1) a construção do arcabouço crustal profundo e da porção superior do manto em parte da Costa de Angola, (2) a comparação deste arcabouço com o embasamento aflorante e (3) a tentativa de adequar estes resultados aos modelos de ruptura continental já publicados. Para alcançar estes objetivos foi feita a interpretação de cinco linhas sísmicas de reflexão profundas (25 Km de profundidade) na costa de Angola, nas Bacias de Kwanza e Baixo Congo, adquiridas pela ION-GXT. As feições identificadas na sísmica de reflexão auxiliaram na determinação dos limites da crosta continental superior e inferior, no reconhecimento das camadas que compõem a crosta oceânica e na identificação da Descontinuidade de Mohorovicic (que marca o limite entre crosta e manto). A interpretação sísmica associada a dados da literatura (que proporcionaram valores de densidade para os pacotes identificados na interpretação sísmica) permitiram a realização de uma modelagem gravimétrica que foi comparada ao dado gravimétrico adquirido durante a aquisição sísmica. A modelagem gravimétrica serviu para validar a interpretação sísmica, atuando como um controle de qualidade para a interpretação. Caso a anomalia gravimétrica gerada pela modelagem não estivesse de acordo com a anomalia medida, a interpretação sísmica era revista na tentativa de um melhor ajuste entre o resultado modelado e o medido. Este ajuste, no entanto, sempre foi feito honrando os refletores que estavam bem marcados na sísmica. Somado a isto, ainda foi utilizado o dado magnético adquirido no campo, no auxilio da interpretação. O arcabouço crustal obtido com a utilização deste método permitiu a comparação dos resultados da interpretação com os modelos de evolução de margens passivas existentes na literatura, mostrando muitos pontos em comum aos modelos que defendem a possibilidade de ocorrência de manto exumado em margens passivas pobres em magmatismo. A interpretação final destes dados mostrou um domínio proximal marcado por uma crosta continental espessa porém pouco afinada em contato com um domínio distal marcado por uma crosta continental muito afinada (crosta hiper-estirada) e, em direção ao centro do oceano, uma região em que ocorre a exumação do manto. A passagem do domínio proximal para o distal ocorre de forma rápida em uma região denominada Zona de Estrangulamento. À oeste do manto exumado é possível identificar a crosta oceânica. O cruzamento dos resultados obtidos neste trabalho com dados do embasamento aflorante no continente africano sugerem um controle do deste nos valores finais de afinamento da crosta continental sob a bacia e nas regiões de manto exumado. Trabalhos recentes realizados na costa de Angola e do Brasil mostram feições semelhantes às identificadas nesta dissertação. / The main objectives of this study are to identify features on seismic data that allow (1) the building of a deep crustal framework and of the upper portion of the mantle, in part of the Angolan margin; (2) to compare this framework with the adjacent outcropping basement of the African continent and; (3) to try to fit these results to the published continental breakup models. In order to achieve these objectives, five deep reflection seismic lines (25 km of depth) situated in the in Kwanza and Lower Congo Basins on the passive margin of Angola were interpreted. The features identified on seismic were useful to recognize the tripartite division that caracterize the oceanic crust and in defining the Mohorovicic Discontinuity (that represents the limit between crust and mantle). The seismic interpretation associated with the data obtained from the scientific literature (that provided density values for the packages identified on seismic interpretation) allowed the establishment of a gravity modeling that was compared to the gravity data acquired during the seismic acquisition. The gravity model was useful to validate the seismic interpretation, acting as a quality control of the latter. In case of the gravity anomaly generated by the modeling not being in accordance with the measured anomaly, the seismic interpretation was revised in order to obtain a better adjustment between the modeled and the measured result. This adjustment, however, was always done honoring the reflectors that were clearly positioned on seismic. In addition, the magnetic data acquired on the field was used to help on interpretation. The crustal framework obtained by the methodology described above was compared with the passive margin evolution models found on scientific literature, showing some points in common with the models that postulate the occurrence of exhumed mantle in magma-poor passive margins. The final interpretation of these data showed the existence of a proximal domain characterized by a thick continental crust slightly thinned in contact with a distal domain marked by a hyper-extended continental crust. Oceanwards there is a region where the exhumation of the mantle took place. The passage of the proximal to the distal domain is abrupt, here termed as a Necking Zone. Oceanic crust is identified to the west of exhumed mantle. The comparison of the results obtained in this study with data from the outcropping basement on the African continent suggests a basement control on the vales of continental crust thinning attained under the basins and on the regions of exhumed mantle. Recent works done on the Angolan and Brazilian margins show features similar to the ones identified on this dissertation.

Este trabalho tem como objetivo a identificação de feições que permitam (1) a construção do arcabouço crustal profundo e da porção superior do manto em parte da Costa de Angola, (2) a comparação deste arcabouço com o embasamento aflorante e (3) a tentativa de adequar estes resultados aos modelos de ruptura continental já publicados. Para alcançar estes objetivos foi feita a interpretação de cinco linhas sísmicas de reflexão profundas (25 Km de profundidade) na costa de Angola, nas Bacias de Kwanza e Baixo Congo, adquiridas pela ION-GXT. As feições identificadas na sísmica de reflexão auxiliaram na determinação dos limites da crosta continental superior e inferior, no reconhecimento das camadas que compõem a crosta oceânica e na identificação da Descontinuidade de Mohorovicic (que marca o limite entre crosta e manto). A interpretação sísmica associada a dados da literatura (que proporcionaram valores de densidade para os pacotes identificados na interpretação sísmica) permitiram a realização de uma modelagem gravimétrica que foi comparada ao dado gravimétrico adquirido durante a aquisição sísmica. A modelagem gravimétrica serviu para validar a interpretação sísmica, atuando como um controle de qualidade para a interpretação. Caso a anomalia gravimétrica gerada pela modelagem não estivesse de acordo com a anomalia medida, a interpretação sísmica era revista na tentativa de um melhor ajuste entre o resultado modelado e o medido. Este ajuste, no entanto, sempre foi feito honrando os refletores que estavam bem marcados na sísmica. Somado a isto, ainda foi utilizado o dado magnético adquirido no campo, no auxilio da interpretação. O arcabouço crustal obtido com a utilização deste método permitiu a comparação dos resultados da interpretação com os modelos de evolução de margens passivas existentes na literatura, mostrando muitos pontos em comum aos modelos que defendem a possibilidade de ocorrência de manto exumado em margens passivas pobres em magmatismo. A interpretação final destes dados mostrou um domínio proximal marcado por uma crosta continental espessa porém pouco afinada em contato com um domínio distal marcado por uma crosta continental muito afinada (crosta hiper-estirada) e, em direção ao centro do oceano, uma região em que ocorre a exumação do manto. A passagem do domínio proximal para o distal ocorre de forma rápida em uma região denominada Zona de Estrangulamento. À oeste do manto exumado é possível identificar a crosta oceânica. O cruzamento dos resultados obtidos neste trabalho com dados do embasamento aflorante no continente africano sugerem um controle do deste nos valores finais de afinamento da crosta continental sob a bacia e nas regiões de manto exumado. Trabalhos recentes realizados na costa de Angola e do Brasil mostram feições semelhantes às identificadas nesta dissertação. / The main objectives of this study are to identify features on seismic data that allow (1) the building of a deep crustal framework and of the upper portion of the mantle, in part of the Angolan margin; (2) to compare this framework with the adjacent outcropping basement of the African continent and; (3) to try to fit these results to the published continental breakup models. In order to achieve these objectives, five deep reflection seismic lines (25 km of depth) situated in the in Kwanza and Lower Congo Basins on the passive margin of Angola were interpreted. The features identified on seismic were useful to recognize the tripartite division that caracterize the oceanic crust and in defining the Mohorovicic Discontinuity (that represents the limit between crust and mantle). The seismic interpretation associated with the data obtained from the scientific literature (that provided density values for the packages identified on seismic interpretation) allowed the establishment of a gravity modeling that was compared to the gravity data acquired during the seismic acquisition. The gravity model was useful to validate the seismic interpretation, acting as a quality control of the latter. In case of the gravity anomaly generated by the modeling not being in accordance with the measured anomaly, the seismic interpretation was revised in order to obtain a better adjustment between the modeled and the measured result. This adjustment, however, was always done honoring the reflectors that were clearly positioned on seismic. In addition, the magnetic data acquired on the field was used to help on interpretation. The crustal framework obtained by the methodology described above was compared with the passive margin evolution models found on scientific literature, showing some points in common with the models that postulate the occurrence of exhumed mantle in magma-poor passive margins. The final interpretation of these data showed the existence of a proximal domain characterized by a thick continental crust slightly thinned in contact with a distal domain marked by a hyper-extended continental crust. Oceanwards there is a region where the exhumation of the mantle took place. The passage of the proximal to the distal domain is abrupt, here termed as a Necking Zone. Oceanic crust is identified to the west of exhumed mantle. The comparison of the results obtained in this study with data from the outcropping basement on the African continent suggests a basement control on the vales of continental crust thinning attained under the basins and on the regions of exhumed mantle. Recent works done on the Angolan and Brazilian margins show features similar to the ones identified on this dissertation.

Cette thèse a pour but d’étudier l’évolution morpho-structurale et magmatique des marges distales pauvres en magma ainsi que leur réactivation. Cette étude est focalisée sur les marges fossiles distales de la Téthys Alpine. L’étude de la réactivation de ces domaines (l’Err et la Platta, Suisse) montre que les chevauchements alpins réactivent principalement d’anciennes structures de rift. L’Err peut ainsi être restaurée et correspond à un ancien domaine de croute hyper-amincie caractérisé par un système de failles de détachement qui évolue en séquence et conduit à la rupture continentale et à l’exhumation du manteau. La Platta correspond à un domaine de manteau sous continental exhumé associé à une augmentation des additions magmatiques syn-tectoniques dans les parties distales. Ce domaine est interprété comme la relique d’une structure en dôme coiffée par une faille de détachement et recoupée par des failles normales favorisant la mise en place de magma et de fluides. L’approche utilisée a permis de mieux contraindre l’architecture d’une marge distale pauvre en magma et de discuter les processus de formation et de la réactivation des limites de plaque. / The aim of this study is to investigate the morpho-structural and magmatic evolution of magma-poor distal rifted margins, as well as their reactivation. This study is focused on the fossil distal margins of the Alpine Tethys. The study of the reactivation of these domains, (Err and Platta, Switzerland) shows that alpine thrusts principally reworked former rift structures. The Err nappe can be restored as a hyper-extended domain characterized by a system of detachment faults with a complex architecture evolving in-sequence and leads to the continental crust separation and the exhumation of mantle. The Platta nappe corresponds to a subcontinental exhumed mantle domain associated to an increase of syn-tectonic magmatic additions oceanwards. The distal domain is interpreted as the relic of a dome-shaped structure capped by a detachment fault and crosscut by latter normal faults facilitating the emplacement of basalts and fluid circulations. The approach developed in this thesis enabled a better understanding of one distal and ultra-distal magma-poor rifted margin, as well as to discuss processes related to the formation and reactivation of plate boundaries.