No description available.

The surface expression of upper crustal deformation varies widely based on geologic settings. Normal faults within an intra-arc basin, strike-slip faulting within a wide shear zone, and creeping fault behavior all manifest differently and require a variety of techniques for analysis. In this dissertation I studied three different actively deforming regions across a variety of geologic settings. First, I explored the drivers of extension within the La Pine graben in the Oregon Cascades. I mapped >20 new Quaternary faults and conducted paleoseismic trenching, where I found evidence for a mid-late Holocene earthquake on the Twin Lakes maar fault. I suggest that tectonics and not volcanism is responsible for the most recent deformation in the region based on fault geometries and earthquake timings, although more research is needed to tease out finer temporal and genetic relationships between tectonics and volcanism regionally. Second, I investigated the rupture pattern and earthquake history of the Calico fault system in the Eastern California Shear Zone. We mapped ~18 km of continuous rupture, with a mean offset of 2.3 m based on 39 field measurements. We also found evidence for two earthquakes, 0.5 - 1.7 ka and 5.5 - 6.6 ka through paleoseismic trenching. We develop a number of different multifault rupture scenarios using our rupture mapping and rupture scaling relationships to conduct Coulomb stress change modeling for the most recent earthquake on the Calico fault system. We find that the most recent event places regions adjacent to the fault in a stress shadow and may have both delayed the historic Landers and Hector Mine ruptures and prevented triggering of the Calico fault system during those events. Last, I studied the spatial distribution of the southern transition zone of the creeping section of the San Andreas fault at Parkfield, CA to determine if it shifted in response to the M6 2004 Parkfield earthquake. I used an Iterative Closest Point algorithm to find the displacement between two lidar datasets acquired 13 years apart. I compared creep rates measured before the 2004 earthquake to creep rates calculated from my lidar displacement results and found that there is not a discernible change in the overall pattern or distribution of creep as a response to the 2004 earthquake. Peaks within the lidar displacement results indicate complexity in the geometry of fault locking. / Doctor of Philosophy / Fault behavior varies widely across different regions, depending on the type of fault and local geology. In this dissertation I examine three regions with different mechanisms controlling deformation within them. First, I study the relationship between volcanic and tectonic induced faulting in the La Pine graben in the Oregon Cascades. While volcanoes and tectonics can both produce faults within a region, the surface expression of those faults changes depending on the underlying driver. I map > 20 new faults in the La Pine graben. I also conduct paleoseismic trenching on one of the newly identified faults, the Twin Lakes maar fault, and find that its most recent rupture occurred < 7.6 ka. I conclude that tectonism is the dominant driver of faulting within the La Pine graben based on the fault geometries and timing between identified regional earthquakes and volcanism. Second, I explore recent rupture on the Calico fault system in the Eastern California Shear Zone, which is a wide region across eastern California where deformation is distributed among many faults. Faulting in this region is complex, with some earthquakes occurring on multiple connected faults. I conducted a paleoseismic survey to determine the timing of the most recent earthquake(s) on the Calico fault system. This trenching effort found evidence for 1-2 earthquakes, the most recent occurring 0.5 – 1.7 ka. I use the rupture mapping and earthquake timing to develop a number of various rupture scenarios. I use these scenarios as inputs for computer modeling to explore the regional stress changes from these events and find that they reduce the overall stress in the area, elongating the amount of time between regional earthquakes. Last, I examine how creeping fault behavior on the San Andreas fault near Parkfield, CA changes as a response to an earthquake. Creeping behavior is where the two sides of a fault are continuously moving past one another. I examine the spatial distribution of where the San Andreas fault transitions from creeping to locked behavior by differencing two high-resolution lidar topographic datasets taken after the M6 2004 Parkfield earthquake. I compare my displacement results to pre-2004 datasets and conclude that the transition zone did not appreciably change as a result of the earthquake.

Malea Planum is a volcanic plain on the southern rim of Hellas Planitia, the largest impact basin on Mars. Four large circular structures on Malea Planum have traditionally been identified as paterae, or low relief, central vent volcanoes (Plescia and Saunders, 1979). A geologic map was constructed and new crater counts made to explore the ages and origins of the paterae. Amphitrites and Peneus Paterae have radial patterns of wrinkle ridges on their flanks and distinct summit calderas (95 km and 130 km across) with arcuate bounding scarps. In contrast, Malea and Pityusa Paterae are broad depressions with diameters greater than 400 km. In some ways Pityusa and Malea Paterae resemble old, filled impact craters (Plescia, 2003) but they also have characteristics of volcanic subsidence features (Roche et al., 2000). A very strong positive gravity anomaly is centered over Amphitrites and smaller positive anomalies are associated with Peneus and Malea Paterae. A slight annular positive anomaly is associated with Pityusa. The geology of the Malea Planum Region has been influenced by impact cratering, volcanic, tectonic, fluvial, and most recently, eolian processes. The Noachian was dominated by impact cratering, the formation of Hellas Basin, and the eruption of flood lavas. Malea Planum formed during the mid- to late-Noachian, likely the result of sills liquefying the volatile-rich crust. Malea and Pityusa Paterae formed during the late Noachian. The Hesperian was marked by the formation of Peneus and Amphitrites and complex valley networks. During the mid-Hesperian, southern Malea Planum may have been covered by a very thick polar mantle deposit that melted and sublimated during the late Hesperian. Smaller episodes of polar mantle deposition continued through the Amazonian to the present. The Amazonian is also characterized by eolian activity creating dune fields, etched surfaces, and dust devil tracks. Based on the topographic and geophysical evidence, Amphitrites and Peneus are typical highland paterae. We conclude that a mid-crustal sill complex similar to that thought to exist beneath the eastern Snake River Plain in Idaho may be the best explanation for the formation of Malea and Pityusa Paterae. A lack of associated flow features on the surface suggests that the loads are the result of an accumulation of dense intrusions. A surficial load (e.g., lava flows) is insufficient to cause the amount of subsidence observed. A mid-crustal mafic or ultra-mafic sill or a dense network of sills and dikes may have contributed to the subsidence.

No description available.

De l’observation microscopique d’une lame mince à l’observation mégascopique d’une province volcano-plutonique par télédétection (SRTM, Landsat), ce travail s’intéresse aux méthodes de comptage, aux traitements statistique et fractale des tailles, formes, orientations et distributions spatiales ainsi qu’à l’interprétation pétrogénétique et/ou géodynamique de différents marqueurs géologiques (cristaux, linéaments, cônes volcaniques…) associés au volcano-plutonisme phanérozoïque d’Afrique équatoriale (Ligne du Cameroun et régions voisines).<p><p>L’analyse à l’échelle microscopique de la distribution de taille de grains et des textures de roches volcaniques et mantelliques (laves et enclaves provenant de l’île de Bioko, golfe de Guinée) a permis de mettre en évidence l’importance d’une quantification objective des paramètres de taille et des relations entre les phases minérales. Après avoir appliqué et discuté les résultats obtenus par les méthodes dites de « distribution de tailles de grains » ou CSD (Crystal Size Distribution), les relations spatiales entre les cristaux et donc les textures ont été étudiées par analyse fractale classique puis grâce à l’entropie de Shannon, dont il s’agit de la première application 2D. La généralisation de ces méthodes de comptage à des objets géologiques de plus grande taille (linéaments, cônes volcaniques…) par le biais des images satellites (Landsat) et modèles numériques de terrain (MNT) issus des données SRTM, a permis d’aborder de manière objective, sur un nombre suffisant de mesures, la morphostructure de la région étudiée. L’ensemble des données morpho-structurales, soit 15.171 linéaments, 8.092 cônes volcaniques ou complexes annulaires, d’une vaste zone de plus de 2.700.000 km2 autour du golfe de Guinée, ont permis d’élaborer plusieurs modèles structuraux locaux qui, synthétisés dans une vue spatio-temporelle complète depuis le Carbonifère jusqu’à l’actuel, ont permis de redéfinir l’évolution géodynamique de la région.<p><p>Cette zone mobile complexe, pincée entre le craton congolais et le craton ouest-africain, est caractérisée par un soubassement précambrien, réactivé lors de la mise en place des grands bassins sédimentaires et ensembles magmatiques phanérozoiques. Contrairement à un modèle unique, souvent invoqué, l’évolution géologique régionale se présente comme une suite de régimes transcurrents dextres se déplaçant spatialement autour des directions N80 au Jurassique, N120 au Crétacé et N30 du Paléogène à l’actuel. L’intégration des nombreuses données géochimiques et isotopiques de la littérature aux modèles géodynamiques de ce travail oblige à globaliser le magmatisme cénozoïque à l’échelle de l’Afrique équatoriale dans son ensemble qui se présente alors comme un « ensemble » magmatique cohérent.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Graduation date: 2005

No description available.

Zugleich: Diss. Freiburg (Breisgau), 2007. / Literaturverz.

Zugleich: Diss. Freiburg (Breisgau), 2007. / Literaturverz.

Les effondrements massifs de flancs sont des évènements destructeurs qui affectent tous les édifices volcaniques. Ces effondrements peuvent impliquer quelques dizaines, voire centaines de km3 de roche. Les volcans boucliers océaniques, bien que possédant de faibles pentes, sont également affectés par ces épisodes destructeurs, entraînant la formation de tsunamis. Dans le contexte de bouclier océanique, ces déstabilisations n’ont jamais été observées. Actuellement, seules des reliques sont présentes sur les îles volcaniques, avec la présence de cicatrices d’effondrements, de dépôts détritiques en mer ou de dépôts de tsunami sur les îles voisines. Les relations entre le magmatisme des volcans boucliers et les effondrements de flanc sont peu contraintes. Afin de mieux comprendre ces relations, deux effondrements de flanc de volcans boucliers océaniques ont été étudiés : l’effondrement de Monte Amarelo sur l’île de Fogo, dans l’archipel du Cap Vert, et l’effondrement de Güímar, situé sur la rift-zone Nord-Est de Tenerife, dans l’archipel des Canaries. Les deux archipels résultent de l’activité d’un panache mantellique sous la plaque africaine.Les produits volcaniques pré et post-effondrement de ces deux secteurs ont été étudiés d’un point de vue géochimique (majeurs, traces, isotopes Sr-Nd-Pb), pétrologique et géochronologique (K-Ar, Ar-Ar), de manière à identifier à la fois les sources et les processus magmatiques mis en jeu lors de leur formation. L’évolution temporelle des sources, ainsi que des processus magmatiques, a été reconstruite afin d’identifier d’éventuels liens avec l’effondrement de flanc étudié.Les résultats montrent que l’évolution du magmatisme de l’île de Fogo amène à la formation de zones superficielles de stockage, de complexes intrusifs et d’éruptions explosives conduisant à de nouvelles instabilités de l’édifice. Suite à l’effondrement, ces zones de stockage sont déstabilisées en quelques milliers d’années. Les processus magmatiques lithosphériques (assimilation, fusion partielle) sont également perturbés mais sur une période plus longue (plusieurs dizaines de milliers d’années). L’effondrement de Güímar ne montre aucun lien avec le magmatisme de l’île de Tenerife.La différence principale entre ces deux contextes est la localisation de la zone effondrée par rapport au système magmatique. En effet, l’effondrement de Güímar est situé en périphérie du système magmatique et ne montre aucun lien avec ce dernier ; à l’inverse l’effondrement du Monte Amarelo, situé à l’aplomb du système magmatique, se répercute rapidement sur ce système à faible profondeur, mais également à des profondeurs lithosphériques avec un délai plus long. / Massive flank collapses are destructive events that affect all volcanic edifices. They can take off huge volumes of rock, from tens to hundreds km3. Oceanic shield volcanoes are also affected by such events even if they have shallow slopes, thus, tsunamis could also be generated in this context. However, a shield volcano flank collapse has never been observed. Nowadays, only relics are visible, such as collapse scars, detritic deposit offshore or tsunami deposits on nearby islands. The relationships between collapse and magmatic history of oceanic shield volcanoes are poorly constrained. Two flank collapses are studied in this thesis, with the aim to better understand these relationships: the Monte Amarelo collapse, on Fogo Island (Cape Verde), and the Güímar collapse, located on North-East rift-zone of Tenerife (Canary Islands). Those archipelagos are the result of hot spot activity below the African plate. Geochemical (major and trace elements, and Sr-Nd-Pb isotopes), petrological and geochronological (K-Ar and Ar-Ar) analyses were carried out on volcanic samples as to identify the source and magmatic processes at stake during magma genesis. The temporal evolution of source and magmatic processes is reconstructed in order to track possible links with the flank collapse. The magmatic system of Fogo Island evolves through time, favouring the formation of superficial storage zones, intrusive complex and explosive eruptions prior to the collapse, which participate to the instability of the edifice. Following the Monte Amarelo collapse, shallow storage zones are destabilized within a few thousand years. Lithospheric magmatic processes (assimilation, partial melting) are also affected but on a longer timescale (tens of thousands years). The Güímar collapse shows no links with the magmatic evolution of Tenerife Island. The main difference between the two collapses is the location of the collapse area with respect to the plumbing system. Güímar collapse is located at the periphery of the plumbing system and show no link with the magmatic history. Contrariwise, the Monte Amarelo collapse is located directly above the plumbing system and influence rapidly the superficial plumbing system, and the deep plumbing system in the long term.