Master of Science / Department of Geology / Matthew E. Brueseke / The Southern Oklahoma rift zone (SOA), which stretches from southern Oklahoma through the Texas panhandle and into Colorado and New Mexico, contains extensive bimodal mafic-silicic magmatism related to the opening of the Iapetus Ocean during the late Precambrian and early Cambrian. Within the SOA, the subsurface in and adjacent to the Arbuckle Mountains in southern Oklahoma contains thick packages of mafic to intermediate lava flows interlayered with thick, extensive rhyolite lava flows and lesser silicic intrusive bodies, which were first described during a 1982 drill test (Hamilton Brothers Turner Falls well) in the region. Well cuttings of these units were collected from that well and three others (Pan-Am Williams D-2, Pan-Am Jarman, Pan-Am Newberry). This study is focused on these mafic-intermediate lava flows, which represent an important stage in the evolution of the SOA and provide insights into the formation and tectonomagmatic evolution of the rift zone. The estimated 210,000 km[superscript]3 of mafic rocks in the SOA were extruded as a result of the break-up of Pannotia and the formation of the failed arm of a three-armed radial rift system. Samples analyzed from the wells plot as basalts to andesites on the TAS diagram of Le Bas et al (1986) and as subalkaline-alkaline basalts to andesite-trachyandesites on the Zr/TiO[subscript]2 vs. Nb/Y diagram of Winchester and Floyd (1977). They are dominantly tholeiitic on multiple discrimination diagrams including those of Miyashiro (1974) and Irvine and Baragar (1971). The lava flows contain traits common with EMI OIB coupled with upper crustal contamination, such as Zr/Nb values ranging from 8 to 10, Ba/Nb values ranging from 10 to 20, and K/Nb values ranging from 300 to 600. Chemostratigraphic comparisons between each well reveal up to five lava flow packages within the larger mafic-intermediate sequence, at least in the vicinity of the sampled wells. When compared with intrusive mafic rocks outcropped in the Wichita Mountains, the SOA lava flows display geochemical traits most similar to those of the Roosevelt Gabbros, suggesting a possible co-genetic relationship. Overall, the whole rock chemical characteristics coupled with comparisons with other large igneous provinces (Columbia River and Oregon Plateaus, East African Rift System) indicate that the SOA lava flows are the result of flood basalt volcanism.

<p> The Grenville Province represents the remains of a collisional orogeny ca. 1.2 - 1.0 Ga and contains the Central Metasedimentary Belt (CMB). Generally thought to represent one or more accreted island arcs, the CMB is located between belts of highgrade gneisses and contains a number of identified structural terranes. Neodymium (Nd) model ages of the high-grade gneisses on either side of the CMB yield similar values (~1.5 Ga) while the average model age within the CMB is usually more juvenile (<1.3 Ga). This distinction, along with observations about the geometrical shape of the juvenile zone, has led to the creation of an alternative model for the development of the CMB in the Grenville Province as developed by Dickin and McNutt, (2007). The new model equates the CMB with an ensimatic rift zone with an en echelon morphology consisting of a series of segments with NNE trends, separated by one or more horsts of older crustal rock. The development of the CMB under these conditions implies that restricted access to seawater may have facilitated limestone deposition prior to major biogenic influences, and thus the morphology of the rift is defined in part by the extent of the Grenville marble outcrops. </p> <p> The present study tests this model through the use of 80 new Nd isotope analyses to map the NW boundary of the CMB, known as the Central Metasedimentary Belt Boundary Zone (CMBBZ), west of Bancroft, Ontario. Within this part of the CMBBZ, the age boundary between pre-Grenvillian and juvenile gneisses is relatively sharp (1 - 4 km wide) and this age boundary makes a near 90-degree tum from a NNE trend near Minden to an E-W trend near Haliburton. Two blocks of older material are located within the juvenile terranes of the CMB, which are interpreted as being blocks of older crust rifted from the walls of the older Muskoka domain to the north of the study region. These structures are analogous to similar horsts of older crustal material found in the Afar region of East Africa. Therefore, we suggest that the locus of the CMBBZ was constrained by older structures, representing a transition from the side of a rift zone segment south of Minden, to the truncated end of this rift segment between Haliburton and Bancroft. Hence, the detailed structure of the CMBBZ in this region provides further evidence in support of the rift zone model. </p> / Thesis / Master of Science (MSc)

La croissance des volcans océaniques est fréquemment ponctuée par des effondrements latéraux géants qui peuvent générer des avalanches de débris volumineuses et engendrer des tsunamis dévastateurs. Néanmoins, les causes, les mécanismes et les conséquences de telles déstabilisations, critiques pour la caractérisation des aléas, demeurent largement incompris.L'île de Tenerife (Canaries, Espagne) constitue une cible privilégiée pour étudier ces phénomènes. Son évolution récente inclue le développement d'un volcan central différencié et d'une ride volcanique proéminente le long d'une rift-zone principale NE-SW (NERZ). Durant le dernier Myr, ces systèmes ont été tronqués par trois effondrements de flanc géants, dont la semelle est partiellement accessible à la faveur de galeries souterraines à usage hydrogéologique.Cette thèse développe une analyse systématique des relations entre construction volcanique et instabilités récurrentes le long de l’axe de la NERZ. L'approche inclut des investigations de terrain en surface et dans les galeries, afin de reconnaître et d’échantillonner les séquences volcaniques affectées par chaque effondrement et remplissant leurs structures; la datation K/Ar Cassignol-Gillot sur phases séparées pour en contraindre l’âge précisément ; des reconstructions morphologiques 3D afin d'estimer le volume des édifices et des structures gravitaires; des analyses chimiques sur roches totales, visant à caractériser l’évolution de la composition des laves avant et après chaque déstabilisation.Les nouveaux résultats montrent le fonctionnement intermittent des différents tronçons la NERZ, avec un schéma récurrent comprenant :1) la croissance rapide d'un édifice imposant, dont la charge induit la création de niveaux de stockage superficiels et l’éruption de termes différenciés visqueux, favorisant l'inflation locale de la structure et sa déstabilisation2) la rupture proprement dite, datée à environ 840 ka, 525 ka et 175 ka (glissements de Güimar, La Orotava et Icod, respectivement)3) une réponse éruptive immédiate, impliquant la vidange rapide (<50kyr) du système d’alimentation, et le comblement des loupes de glissement sous des dizaines de km3 de lave.4) Un déplacement consécutif de la construction volcanique vers les secteurs moins matures de la NERZ (moindre épaisseur de l'édifice/moindre pression lithostatique)Nous montrons que les phénomènes de charge/décharge ont une influence primordiale sur le développement des instabilités gravitaires et l'évolution des systèmes d'alimentation des îles océaniques. / The growth of oceanic volcanoes is frequently punctuated by large flank collapses, which can generate voluminous debris avalanches and destructive tsunamis. The causes, the mechanisms and the consequences of such instabilities, crucial for risk assessment, remain poorly understood.Tenerife (Canary Islands, Spain) is a target of particular interest to study such phenomena. Its recent evolution includes the development of a large silicic central volcano and a prominent volcanic ridge along a main NE-SW trending rift zone (NERZ). During the last Myr, these volcanic systems have been truncated by three large flank collapses, the base of which is partly accessible through underground water mining galleries.This thesis develops a systematic analysis of the relationships between volcanic construction and recurrent flank instabilities along the NERZ. Our approach includes field investigations at the surface and in the galleries to identify and sample the volcanic units affected by each landslide and the successions filling their scar; unspiked K/Ar dating (Cassignol-Gillot technique) on fresh separated groundmass to constrain precisely the timing of the landslides; 3-D morphological reconstructions to estimate the volume of the edifices and landslides structures; and whole-rock geochemical analyses to characterize the compositional evolution of the magma prior to and after each collapse event.Our new results show the intermittent functioning of the various sections of the NERZ with a recurrent pattern comprising:(1) The rapid construction of a large volcanic edifice. The resulting load favors the creation of superficial storage levels, the associated evolution of the magma and the eruption of viscous differentiated terms, favoring local inflation of the structure and its destabilization(2) The collapse of a flank of the NERZ, dated at ca. 840 ka, 525 ka, and 175 ka (Güimar, La Orotava and Icod, events respectively)(3) An immediate eruptive response, implying the rapid emptying (<50kyr) of the feeding system and the filling of the landslide scars under tens of km3 of lava.(4) The subsequent displacement of volcanic activity towards the less mature sectors (lower thickness/lower lithostatic pressure).We show here that loading/unloading processes have a strong influence on the development of gravitational instabilities and the evolution of the magma feeding systems on such large intraplate volcanic islands.

No description available.

Three-fifths of the Earth’s crust has been built at oceanic spreading centres in the last 160 million years. To explore crustal extension processes and the architecture of these constructive plate boundaries I have studied the oceanic rift in Iceland. Here the Mid Atlantic Ridge is anomalously elevated above sea level and thus easier to instrument. I have deployed and operated a dense network of seismometers in the remote volcanic highlands in central Iceland, and used the passive seismic data collected from this network to explore crustal structure and volcanic processes in the extensional rift zones. My analysis of persistent seismicity located in an intervening region between individual spreading segments, uniquely records the segmentation of plate spreading on the scale of individual volcanic systems. Precise location and characterisation of micro-earthquakes identifies a series of faults subparallel to the rift fabric, and source mechanisms define left-lateral strike-slip motion on these faults. This extremely high quality microseismic data reveals transform motion being accommodated by bookshelf faulting in a concentrated region between two such volcanic systems, providing evidence for the localisation of spreading in the discrete volcanic systems. While transform motion between spreading centres appears to be accommodated on a continuous basis, the extension of the brittle upper crust within the spreading centres occurs episodically during rifting events. Our local seismic network fortuitously recorded such a rifting episode in August 2014, during which the opening of a 5 metre wide dyke triggered a huge increase in seismicity across large areas of the rift zone. Stress-seismicity-rate modelling of this triggered seismicity, along with geodetic constraints on the deformation, provided a remarkable opportunity with which it was possible to prove the existence of stress-shadowing, a challenge which has eluded earthquake seismologists for decades. Using the excellent coverage of our extended seismic network I have also generated a new high resolution image of the regional crustal seismic structure using surface waves extracted from ambient seismic noise. The structure reveals low seismic velocities which are closely correlated with the volcanic rift zones, and faster wavespeeds in the older and non-volcanically active Tertiary crust. The strongest anomalies are seen in the north-west of the Vatnajökull icecap, at the location of thickest crust and inferred centre of the underlying mantle plume. Inversion for shear wave velocity structure shows high velocity-gradients in the top 10 km, defining a thickened extrusive upper crust in Iceland compared to standard oceanic crust, where it is normally 2–3 km thick. Below this, the shear wave velocity structure reveals a distinct low-velocity zone in the mid crust between 14–20 km depth, which is widespread across Iceland and shallows into the active volcanic rifts. This extensive feature suggests high mid-crustal temperatures and a high temperature-gradient between the extrusives of the upper crust and the intrusive mid-to-lower crust in Iceland.

Die einer unterschiedlichen Genese zuordenbaren tektonischen Strukturen, welche sich im Raum des Thüringer Waldes bündeln, formten in einem gerichteten Entwicklungsablauf das komplizierteste und vielseitigste hochoberkarbonisch-unterpermische Strukturgebäude Mitteleuropas. In dieser Arbeit wird der Versuch einer Synthese der strukturellen und der daran geknüpften vulkanogen-sedimentären Entwicklung innerhalb der permokarbonischen Thüringer Wald-Senke und ihres unmittelbaren mitteleuropäischen Umfeldes unternommen. Sie stützt sich dabei maßgeblich auf die Ergebnisse langfristig durchgeführter Kartierungsarbeiten, die in diskontinuierlichen Bearbeitungsphasen seit 1957 bis in die 90er Jahre des vergangenen Jahrhunderts erfolgten. Einbezogen werden die Ergebnisse von insgesamt 54 Forschungs- und Erkundungsbohrungen, die zu einem Großteil im Kontext dieser Arbeiten geteuft worden sind. 36 Bohrprofile werden hier erstmals vollständig beschrieben und publiziert. Neben einer nochmaligen Überprüfung der gesamten lithostratigraphischen Abfolge in der permokarbonischen Thüringer Wald-Senke besteht die Zielstellung der Arbeit in deren Einbindung in die regionale mitteleuropäische strukturelle Entwicklung während dieser Zeitspanne, beginnend bei den potenziellen variszisch-kollisional angelegten Wurzeln der permokarbonischen Strukturen, über ihre weitere tektono-magmatische Ausgestaltung bis hin zur Ausprägung der postvariszischen Großschollenfelderung Mitteleuropas am Ende des Permokarbons.

Die einer unterschiedlichen Genese zuordenbaren tektonischen Strukturen, welche sich im Raum des Thüringer Waldes bündeln, formten in einem gerichteten Entwicklungsablauf das komplizierteste und vielseitigste hochoberkarbonisch-unterpermische Strukturgebäude Mitteleuropas. In dieser Arbeit wird der Versuch einer Synthese der strukturellen und der daran geknüpften vulkanogen-sedimentären Entwicklung innerhalb der permokarbonischen Thüringer Wald-Senke und ihres unmittelbaren mitteleuropäischen Umfeldes unternommen. Sie stützt sich dabei maßgeblich auf die Ergebnisse langfristig durchgeführter Kartierungsarbeiten, die in diskontinuierlichen Bearbeitungsphasen seit 1957 bis in die 90er Jahre des vergangenen Jahrhunderts erfolgten. Einbezogen werden die Ergebnisse von insgesamt 54 Forschungs- und Erkundungsbohrungen, die zu einem Großteil im Kontext dieser Arbeiten geteuft worden sind. 36 Bohrprofile werden hier erstmals vollständig beschrieben und publiziert. Neben einer nochmaligen Überprüfung der gesamten lithostratigraphischen Abfolge in der permokarbonischen Thüringer Wald-Senke besteht die Zielstellung der Arbeit in deren Einbindung in die regionale mitteleuropäische strukturelle Entwicklung während dieser Zeitspanne, beginnend bei den potenziellen variszisch-kollisional angelegten Wurzeln der permokarbonischen Strukturen, über ihre weitere tektono-magmatische Ausgestaltung bis hin zur Ausprägung der postvariszischen Großschollenfelderung Mitteleuropas am Ende des Permokarbons.