Dissertations / Theses on the topic 'Volcano-tectonic'

Accelerating rates of volcano-tectonic (VT) earthquakes are a common precursor to volcanic eruptions and reflect fracture growth within the edifice. Theoretical models interpret the patterns in terms of failure of the volcanic edifice under the magmatic load and promise improved eruption forecasting. However, many eruptions at frequently active basaltic volcanoes are reported to begin with little change in the rate of VT earthquakes, apparently in conflict with edifice failure models. This thesis investigates the spatial and temporal patterns of VT earthquakes associated with eruptive and intrusive dyke injection at three of the best studied basaltic volcanoes, Kilauea and Mauna Loa (Hawaii) and Mt Etna (Sicily), in order to constrain the processes controlling the approach to eruption and test the applicability of edifice failure models. Approximately one third of dyke injection events are preceded by more than 4 weeks of exponentially accelerating rates of earthquakes. The trends are consistent with a model where deformation is controlled by the growth of independent fractures driven by increased magma pressure. Relations between acceleration parameters, such as the total number of earthquakes and characteristic timescale, provide information as to the likely timing of dyke injection. No evidence is found for short-term power-law accelerations in the rates of earthquakes thought to correspond to the linkage of fractures and observed at subduction zone volcanoes. The seismicity associated with the remaining events has characteristics indicating that flank instability is involved in triggering injection, either through the progressive reduction in the horizontal compressive stress by flank slip or through an episode of accelerated flank slip (a so-called slow earthquake). These observations suggest that: 1) an edifice failure model provides a good basis for understanding the approach to basaltic eruptions, but 2) at unstable volcanoes, modifications of the model are required to account for the influence of flank slip.

The rift volcano Nyamuragira in D.R. Congo regularly produces large- volume lava flows resulting from flank fissure eruptions. The eruptions are usually fed by near-vertical dykes whose orientation and location are controlled by local and regional stress. Fissuring occasionally occurs within the summit caldera, but dyke emplacement and fissuring is usually confined to the flanks along preferential zones of weakness which radiate away from the 2 x 2.2 km caldera. Space-borne Synthetic Aperture Radar Interferometry (InSAR) was used to measure eo-eruptive and inter-eruptive surface deformation at the volcano between 1996 and 2010 (8 eruptions). The largest line-of-sight (LOS) displacement due to dyke emplacement (42 cm) was recorded during the 2002 eruption. Previously unreported displacements have been measured for the 1998, 2001 and 2004 eruptions. Numerical modelling of the 2006 and 2010 eruptive events was tried. The . orientation and size of the dykes is, however, poorly constrained, and the nature of subsurface connectivity with the caldera is not known. Both dykes were emplaced on the southern flank and are aligned with a NNW-trending fracture zone running between Nyamuragira and nearby Nyiragongo. Two methods using regression analyses on time-series data were devised to model and remove lava flow subsidence signals from interferograms. Subsidence signals> 3cm/year have been measured and are a function of time and lava thickness. Linear rate subsidence models were found to be appropriate for most lava flows. Detailed mapping of the recent lava flows of Nyamuragira has also better constrained their location and spatial extent. By stacking interferograms we obtained mean deformation maps of the volcano revealing inter-eruptive deformation: 1. Uplift within the Eastern Pit Crater and inflation of the summit prior to the 2010 eruption; 2. Post- eruptive deflation centred on the 2010 eruption site; 3. Long-period subsidence beneath the Western Crater and rifring of the caldera and 1 immediate flanks; 4. Long-period subsidence centred on the 2006 eruptive vent thought to be associated with visco-elastic relaxation of a cooling magma body; 5. Similar subsidence fields centred on the 1998 and 2002 eruptive vents; 6. Anomalous subsidence associated with the 1991-93 lava flow; 7. The existence of an apparently stable, fault-bounded, and dyke- resistant block of Precambrian crust beneath the NW flank of the volcano, probably related to the Western Border Fault.

A multi-prong approach was taken in this dissertation to understand volcanic processes from both a long-term and more immediate hazard perspective. In the long-term, magma sources within the crust may produce measurable surficial response and long-wavelength gravity anomalies that provide information about the extent and depth of this magma. Long-term volcanic hazard forecasting is also improved by developing as complete a record as possible of past events. In the short-term, a long-standing question has been on the casting of precursory volcanic activity in terms of future volcanic hazards. Three studies are presented in this dissertation to address these issues. Inversion of high-resolution ground magnetic data in Amargosa Valley, NV indicates that anomaly B could be generated by a buried shield volcano. This new information changes the event count in this region which in turn affects the overall volcanic hazard estimation. Through the use of Finite Element Models (FEM) an in-depth characterization of the surficial response to magma underplating is provided for the Tohoku Volcanic Arc, Japan. These models indicate that surficial uplift was dominantly driven by mid-crustal intrusions and the magnitude and wavelength of this uplift was mainly controlled by the elastic layer thickness. In Dominica, seismic data were used as weights in spatial intensity maps to generate dynamic volcanic hazard maps influenced by changes in seismicity. These maps show an increasing trend in the north that may be indicative of an increase in earthquake and volcanic hazards.

Continental rifting, like other plate tectonic processes, plays a large role in shaping the Earth's crust. Active rift zones evolve from repeated tectonic and magmatic events including volcanic activity. Through investigations of currently and previously active rifts, scientists have discovered considerable interactions between these tectonic and magmatic processes during a rift's evolution; however questions remain about these interactions especially in youthful stages of rifts. We investigate an early phase magma-rich section of the East African Rift System (EARS), named the Eastern Branch to assess volcano-tectonic interactions. The Eastern Branch of the EARS consists of volcanically rich rifts that are actively spreading the Nubian Plate, Somalian plates, and Victoria block at different evolutionary stages making it an ideal study area for volcano-tectonic interactions. Our initial investigation of active volcano-tectonic interactions centered on a rifting event that occurred between 2007-2008 in the Natron Rift, a rift segment in the southern Eastern Branch located in Northern Tanzania. This rifting event contained multiple occurrences of tectonic, magmatic, and volcanic activity in close proximity. We examine the stress transferred from these events to the Natron Fault, which is the major border fault in the area, with analytical modeling using the USGS program Coulomb 3.4. We processed Global Positioning System (GPS) data that recorded slip on the major border fault in the region in early January 2008 and test which events could generate large enough stress changes to trigger the observed slip using a previously defined threshold of 0.1 MPa. These initial models were created using simplified model parameters, such as an elastic homogeneous half-space, and find that 1) magmatically induced stress perturbations have the potential to trigger fault slip on rift border faults, 2) magmatic events have the potential to trigger strike‐slip motions on a rift border fault, and 3) the proximity of magmatic activity may affect occurrences of slip on adjacent border faults. We then further investigate volcano-tectonic interactions in the Natron Rift by testing using numerical modeling with the CIG finite element code PyLith. We systematically test how adding topography, heterogeneous materials, and various reservoir volumes to a deflating 3 km deep magma reservoir system at the active volcano Ol Doinyo Lengai can affect stress transfer to the adjacent Natron Fault. We compare eight models with variations in topography, material properties, and reservoir volumes to calculate the percent differences between the models; to test their effects on the stress change results. We find that topography plays the largest role with the effect increasing with reservoir size. Finally, we seek to improve the capability of investigating volcano-tectonic interactions in the Natron Rift at faster time- scales by improving Global Navigation Satellite System (GNSS) positioning data (latitude, longitude, and height) collection and distribution capabilities. In the final part of this work, we describe a new Python-based data broker application, GNSS2CHORDS, that can stream real-time centimeter precision displacement data distributed by UNAVCO real-time GNSS data services to an online EarthCube cybertool called CHORDS. GNSS2CHORDS is applied to the TZVOLCANO GNSS network that monitors Ol Doinyo Lengai in the Natron Rift and its interactions with the adjacent rift border fault, the Natron Fault. This new tool provides a mechanism for assessing volcano-tectonic interactions in real-time. In summary, this work provides a new avenue for understanding volcano-tectonic interactions at unprecedented, 1-second time-scales, demonstrates slip can be triggered by small stress changes from magmatic events during early phase rifting, and provides insights into the key role of volcanic topography during volcano-tectonic interactions.
Doctor of Philosophy
Investigating interactions between active volcanoes and tectonics (fault zones) is important for understanding how continental rifts grow and evolve over time. Modern researchers use geodetic data, geologic models, and computer simulations of rift processes; like volcanic eruptions and fault movement; to understand how stress in transferred and material deforms due to rift activity. We are especially interested in understanding the stress interactions when volcanic eruptions and earthquakes happen together over a short time period. Our projects apply these tools to examine a segment of the largest active continental rift zone, the Natron Rift in the East African Rift System (EARS), to understand more about the details of these volcano-tectonic interactions when continents break apart (rifting). We first present results that stress transferred to the Natron Fault associated with magmatic activity from the volcano Ol Doinyo Lengai may trigger a major fault to move. Next, we continue our investigations into volcano-tectonic interactions by seeing how volcanic properties could affect stress transferred in the Natron Rift region. We choose to initially test stress variations associated with different 1) topography surfaces, 2) material properties, and 3) reservoir volumes associated with the volcano Ol Doinyo Lengai using a more advanced computer modeling approach. This deeper investigation provides information about the individual roles these parameters play in a younger rift region. We present results that topography has the most influence on the stress transferred to the Natron Fault in our models, and that the other parameters did not play a large role in influencing the stress transferred. Finally we work to increase the ability for researchers to perform geodetic studies in the Natron Rift by providing a new method to share surface displacement data at an unprecedented 1 position a second rate (near real-time). This new method is a data broker application called GNSS2CHORDS that can stream cm precision displacement data to an online cybertool called CHORDS. With our models and data provided through open source methods this work contributes significantly to our understanding of volcano-tectonic interactions.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 106-119).
Portland, Oregon, lies within an active tectonic margin, which puts the city at risk to hazards from earthquakes and volcanic eruptions. The young Juan de Fuca microplate is subducting under North America, introducing not only arc magmatism into the overlying plate, but also interplate and intraplate seismicity related to the subduction zone. Large crustal earthquakes are also probable in Portland because of the oblique strike-slip Portland Hills Fault zone. These hazards create risk to Portland residents and infrastructure because of pre-existing vulnerabilities. Much of Portland's downtown area, including the government and business districts, is at risk of ground shaking infrastructure damage, liquefaction and landslides due to earthquakes. Additionally, the city is within 110 km of three active Cascadia stratovolcanoes, two of which pose hazards from tephra and lahars. Though the city is under the umbrella of four emergency response plans-city, county, state and federal-there are critical gaps in mitigation strategies, emergency exercises and community education and outreach. Portland cannot prevent earthquakes or volcanic eruptions, but the city can reduce its vulnerability to these hazards.
by Alexandra M. Jordan.
S.B.

The Central Indian Ridge (CIR) between 18° and 21°S shows significant morphological variation at a relatively constant spreading rate (between 47 and 51mmyr-1). High resolution TOBI sidescan sonar data (cruise CD127) and multibeam bathymetry data (Magofond 2 cruise), complemented by regional geophysical and geochemical datasets, provide an important opportunity to examine the processes controlling morphological and volcano-tectonic variations along the CIR. The CIR is situated on an elevated plateau formed from a temporally persistent and robust melt supply to the ridge axis. Analysis of the data shows that the fracture zones have a significant structural control on along-axis morphology and melt supply, partitioning the ridge into three morphologically defined regions. The central region (Region B) bounded by two of the fracture zones, contains segments which show rifted axial morphologies characteristic of slow-spreading ridges. Regions A and C show patterns of variable volcanic robustness along-axis associated with the supply and availability of melt to the ridge. Tectonic analysis correlates with inter- and intra-segment trends in morphology and volcanic structure, further highlighting regions of robust or deficient melt supply. Strong relationships are also revealed between the tectonic parameters of fault length, spacing and density along-axis. Finite difference analysis is used to model the Non-Transform Discontinuities along the CIR and Mid-Atlantic Ridge to understand patterns of strain within their interiors. The results indicate the presence of a damage zone ahead of a propagating segment tip, providing increased crustal permeability and a greater potential for hosting hydrothermal circulation. Analysis of geochemical data along the CIR identifies five hydrothermal plume signatures, three of which are coincident with the locations of NTDs in the study area, correlating with the findings of the numerical analysis. A detailed model of the CIR demonstrates that thermal variation influenced by ridge structure can produce significant variations in morphology and volcano-tectonic distribution at a constant spreading rate.

Volcanic activity, and the resultant deposits and structures at the Earth's surface, are the outcome of the inner workings of underground magmatic plumbing systems. These systems, essentially, consist of magma reservoirs which supply magma to the surface through volcanic conduits feeding volcanic eruptions. The mechanics and structure of plumbing systems remain largely unknown due to the obvious challenges involved in inferring volcanic processes occurring underground from observations at the surface. Nevertheless, volcanologists are beginning to gain a deeper understanding of the workings and architecture of magmatic plumbing systems from geophysical observations on active volcanoes, as well as from geological studies of the erosional remnants of ancient volcanic systems. In this work, I explore the relationship between the structure and mechanics of shallow plumbing systems and the volcanic eruptions these systems produce. I attempt to contribute to the understanding of this complex relationship by linking geological and geophysical observations of an eroded basaltic subvolcanic system, and the eruptive and tectonic activity of an active volcano, with mathematical models of magma ascent and stress transfer. The remarkable exposures of the Carmel outcrop intrusions, near the San Rafael swell, southeast Utah, U. S. A., allow detailed geological and geophysical observations of the roots of volcanic conduits that emerge from a subhorizontal magma feeder reservoir. These observations reveal a new mechanism for magma ascent and eruption triggering through gravitational instabilities created from an underlying feeding sill, and shed light on the mechanics of sill emplacement. Geophysical and geological observations of the 1999 and xii 1992 eruptions of the Cerro Negro volcano, Nicaragua, are used to explore the coupling between changes in the stress field and the triggering of volcanic eruptions, and magma ascent through the shallow crust. Modeling results of stress transfer and conduit flow highlight the importance of the surrounding stress field and geometry of the volcanic conduits that comprise shallow plumbing systems.

Forecasting eruptions using volcano seismology is a subject that affects the lives and property of millions of people around the world. However, there is still much to learn about the inner workings of volcanoes and how this relates to the chance of eruption. This dissertation attempts to increase the breadth of knowledge aimed at helping to understand when a volcano is likely to erupt and how large that eruption might be. Chapters 2 and 3 focus on a technique that uses changes in the local stress field beneath a volcano to determine the source of these changes and help forecast eruptions, while Chapter 4 focuses on a technique that shows great potential to be used to image magma chambers beneath volcanoes by using receiver functions. In Chapters 2 and 3 the source mechanisms of shallow volcano-tectonic earthquakes recorded at Mount St. Helens are investigated by calculating hypocenter locations and fault plane solutions (FPS) for shallow earthquakes recorded during two eruptive periods (1981-1986 and 2004-2008) and two non-eruptive periods (1987-2004 and 2008-2011). FPS show a mixture of normal, reverse, and strike-slip faulting during all periods, with a sharp increase in strike-slip faulting observed in 1987-1997 and an increase in normal faulting between 1998 and 2004 and again on September 25-29, 2004. FPS P-axis orientations (a proxy for ó1) show a ~90° rotation with respect to regional ó1 (N23°E) during 1981-1986 and 2004-2008, bimodal orientations (~N-S and ~E-W) during 1987-2004, and bimodal orientations at ~N-E and ~S-W from 2008-2011. These orientations are believed to be due to pressurization accompanying the shallow intrusion and subsequent eruption of magma as domes during 1981-1986 and 2004-2008, and the buildup of pore pressure beneath a shallow seismogenic volume during 1987-2004 and 2008-2011. Chapter 4 presents a study using receiver functions, which show the relative response of the Earth beneath a seismometer. Receiver functions are produced by deconvolving the vertical component of a seismogram from the horizontal components. The structure of the ground beneath the seismometer can then be inferred from the arrivals of P-to-S converted phases. Receiver functions were computed for the Katmai Volcanic Group, Alaska, at two seismic stations (KABU and KAKN) between January 2005 and July 2011. Receiver functions from station KABU clearly showed the arrival of the direct P-wave and the arrival from the Moho; however, receiver functions from station KAKN did not show the arrival from the Moho. In addition, changes in the amplitude and polarity of arrivals on receiver functions suggested that the structure beneath both KABU and KAKN was complex. Station KABU is likely underlain by dipping layers and/or anisotropy, while station KAKN may lie over a basin structure, an attenuating body, or some other highly complex structure. However, it is impossible to say for certain what the structure is under either station as the azimuthal coverage is poor and thus the structure is unable to be modeled. This dissertation also includes a section (Chapter 6) on the assessment of spreadsheet-based modules used in two Introductory Physical Geology courses at the University of South Florida (USF). When faculty at USF began using spreadsheet-based modules to help teach students math and geology concepts the students complained that they spent more time learning how to use Excel than they did learning the concepts presented in the modules. To determine whether the sharp learning curve for Excel was hindering learning we divided the students in two Introductory Physical Geology courses into two groups: one group was given a set of modules which instructed them to use Excel for all calculations; the other group was simply told to complete the calculations but was not instructed what method to use. The results of the study show that whether or not the students used Excel had very little to do with the level of learning they achieved. Despite complaints that Excel was hindering their learning, students in the study attained high gains for both the math and geology concepts presented in the modules whether they used Excel or not.

Dans cette thèse, 47 nouveaux âges ont été obtenus par la technique Cassignol-Gillot. La très bonne reproductibilité des âges obtenus, ajoutée à une stricte cohérence observée entre les édifices volcaniques, supporte l'utilisation de la méthode K-Ar dans la datation des laves des Carpates orientales (Călimani-Gurghiu-Harghita ; CGH) et des dépôts d'ignimbrite du Miocène des Carpates occidentales (les monts de Mátra et Bükk). Dans la partie orientale de la chaîne, les données géochronologiques ont été combinées avec des analyses géomorphologiques pour contraindre l'histoire volcanique et calculer leur taux de construction et d'érosion. Parallèlement, dans la partie occidentale de la chaîne, les données géochronologiques obtenues ont été combinées aux données paléomagnétiques disponibles pour affiner leur stratigraphie. La chaîne des Carpates orientales a connu une migration de son activité éruptive le long de l’arc du Miocène au Quaternaire. Ici, une méthodologie novatrice et complexe apporte de nouvelles contraintes géochronologiques et géomorphologiques sur l'évolution des 20 volcans de la chaîne. Les nouveaux âges ont permis de contraindre leur durée d’activité Par exemple Seaca-Tătarca (6,79-6,47 Ma), Vârghiş (5,47-4,61 Ma) ou de dater l’activité volcanique la plus récente de Călimani. Pour le complexe volcanique de Ciomadul, composé d'une douzaine de dômes de lave, l’activité volcanique a été contrainte entre 704±18 et 28±1ka (<1 Ma) interrompue de périodes de repos. En parallèle, des reconstructions numériques de paléo-topographies volcaniques ont été réalisées dans le but de quantifier leur forme à la fin de leur construction. Les résultats déduits de nos reconstructions ont donné un volume total de matériel émis de 2300km3 sur toute la chaîne avec, à l’échelle de chaque volcan, une large gamme de variation de leur taille (3±3 à 592±115 km³). Ces volumes montrent une nette diminution du nord au sud de la chaîne avec des valeurs de 910, 880, 279 et 165 km³ pour des secteurs géographiques de Călimani, Gurghiu, North Harghita et South Harghita respectivement. Combinés aux âges, ces volumes ont permis de calculer un taux de construction moyen de 200km³/Ma pour toute la chaîne, représenté par deux groupes distincts ; un groupe caractérisé par des taux de construction de 137 km³/Ma caractéristiques des vieux volcans (11-3,6 Ma) suivi d'un groupe avec des taux de construction de 28km³/Ma pour les volcans Plio-Quaternaires. La comparaison des volcans reconstruits et ceux actuels a permis de calculer un volume érodé total de 524±125km³, correspondant à une dénudation moyenne de 22% et à un taux d'érosion moyen de 20m/Ma pour la chaîne de CGH. Suite aux fluctuations climatiques enregistrées le long de cette chaîne, les taux d'érosion caractéristiques de ces grandes périodes climatiques ont été calculés dans le but de montrer le rôle qu’a joué le climat sur les taux d’érosion. Le taux d'érosion le plus élevé de 38m/Ma a été obtenu pour la période régie par un climat continental subtropical modéré transitionnel (9,5-8,2 Ma). Pour la période climatique continentale modérée (8,2-6,8 Ma), caractérisée par des conditions climatiques beaucoup moins humides, un taux d'érosion de 14 m/Ma est proposé. Pour la période correspondant à un climat continental avec identification de périodes semi-arides (6,8-5,8 Ma), un taux d'érosion de 7 m/Ma a été calculé. Pour les volcans Plio-Quaternaires ayant connus des cycles interglaciaires/glaciaires, un taux d'érosion de 28m/Ma a été obtenu. Une telle approche morphométrique et géochronologique quantitative démontre son efficacité à étudier le dynamisme volcanique, y compris les processus de construction et d'érosion au fil du temps. Dans la partie occidentale des Carpates, les âges obtenus sur les coulées de lave de Börzsöny contraignent sa période d'activité entre 14,3-15,1 Ma. Pour les dépôts ignimbritiques de Bükk, les résultats K-Ar évoluent entre 12,7-16,5 Ma
In this PhD thesis, 47 new ages have been obtained by the Cassignol-Gillot technique. The very good reproducibility of the ages obtained in this study, added to a strict consistency observed between the volcanic edifices, support the use of the K-Ar method in the dating of the East Carpathian lavas (Călimani-Gurghiu-Harghita) and ignimbrite deposits of the North Hungarian (Mátra and Bükk Mts. [western Carpathians]). In the Eastern part, this new geochronological dataset has been combined with geomorphological analyses to constrain the volcanic history as well as to compute construction and erosion rates of those volcanoes. In parallel, in the western part geochronological dataset has been combined with available paleomagnetic data to refine their stratigraphy. The East Carpathian volcanic range experienced an along-arc, Late Miocene to Quaternary migration of eruptive activity. Here, a novel and complex methodology are presented that yields new geochronological and geomorphological constraints on the evolution of the 20 volcanic edifices. New unspiked K-Ar ages either constrain their lifespan (6.79- 6.47 Ma for Seaca-Tătarca; 5.47- 4.61 Ma for Vârghiş) or date the youngest volcanic activity (central Călimani). For Ciomadul volcanic complex composed by a dozen of lava domes, which hosts the recent volcanic activity since the last 1 Ma, its activity has been constrained between 704± 18 ka and 28 ± 1 ka with several quiescence periods. In parallel, numerical reconstructions of volcanic paleo-topographies were performed to quantify their shape at the end of their construction stage. The inferred initial volcano size shows a wide range (3±3 to 592±115 km³), making up the four main successive volcanic segments (910, 880, 279 and 165 km³ for Călimani, Gurghiu,North Harghita and South Harghita segment, respectively) totalizing 2300 km³. Volume and age constraints allowed computing an average growth rate of 200 km³/Ma for the whole range, characterized by an initial moderate growth rate (137 km³/Ma) of the older volcanoes (11-3.6 Ma) followed by a lower growth rate (28 km³/Ma) obtained for the Plio-Quaternary volcanoes. Comparing reconstructed and current topographies yielded a total eroded volume of 524±125 km³, defining averaged denudation of 22% and a 20 m/Ma erosion rate. Erosion rates for major climatic periods were computed, which highlight the contrasting climatic contexts since 11 Ma. The highest erosion rate (38 m/Ma) occurred during a transitional moderate subtropical continental climate period (9.5-8.2 Ma). An intermediate erosion rate (14m/Ma) characterized a moderate continental climate period (8.2-6.8 Ma) when conditions became less humid. The lowest erosion rate (7 m/Ma) reflects the prevailing continental but occasionally semi-arid climate (6.8-5.8 Ma). The highest erosion rate (28m/Ma) was obtained for Plio-Quaternary times during the interglacial/glacial cycles. Such a quantitative morphometric and geochronological approach demonstrates its efficiency to study volcanic dynamism, including both constructional and erosional processes, through time. In the western part of the Carpathian range, the new ages obtained on the lava flows of Börzsöny made it possible to constraint its period of activity between 14.27 - 15.11 Ma. For the Miocene ignimbrite of Bükk foreland, the new K-Ar results range between 12.7 - 16.5 Ma

L'activité volcanique Cénozoïque de la plaque arabique offre l’exemple d’un volcanisme intra-plaque développé dans un contexte géodynamique complexe. Après la construction des trapps basaltiques du plateau yémeno-ethiopien, vers 31 Ma, à partir de l’Oligocène terminal, une importante activité volcanique se développe, liée à la déchirure du bouclier arabo-nubien (l’ouverture de la Mer Rouge) et la convergence des plaques Arabique et Eurasienne (zone de suture du Bitlis-Zagros). Au nord de la plate-forme arabique, le volcanisme syrien s’implante dans un contexte général de compression, autour de la ceinture de plissement des Palmyrides et des zones de déformation adjacentes (graben de l'Euphrate et système de faille de la Mer Morte). Cette thèse porte sur l'évolution volcano-tectonique de la partie nord de la plaque Arabique, en particulier celle de la Syrie, combinant des études géochronologiques, géochimiques et morpho-structurales et modélisation géophysique. Notre analyse morpho-structurale de la province volcaniques de Harrat Ash Shaam (HASV), au sud des Palmyrides, a permis de caractériser numériquement plus de 800 cônes volcaniques monogéniques répartis entre le Sud Syrien, la Jordanie et le Nord de l’Arabie Saoudite. Cette étude de la distribution des cônes volcaniques, jointe aux données existantes sur l’épaisseur de la couverture sédimentaire traversée démontre que la corrélation négative constante entre l’intensité des éruptions volcaniques et la profondeur au socle est, de fait, influencée par le contexte tectonique. L’analyse normative de la distribution des cônes volcaniques, comparée à l'épaisseur des sédiments, est essentielle pour caractériser la tectonique d'extension dans des différentes zones. La télédétection, les observations sur le terrain, et notre base de données de plus de 40 nouvelles datations potassium-argon, entre 50 ka et 18 Ma, nous permettent de préciser l’évolution volcano-tectonique de la Syrie. Cette approche pluri-disciplinaire, appliquée au plateau du Al-Lajat, le champ volcanique le plus récent de HASV, nous a permis, d’abord, de proposer un modèle chronologique pour le processus d'altération en relation aux changements paléoclimatiques du Quaternaire. Elle a surtout permis de reconstituer l'évolution volcano-tectoniques du Nord de la plaque arabique, au cours du Cénozoïque et de situer différents styles d’extension responsables de l’activité volcanique. Le volcanisme commence à la fin de l’Oligocène et au Miocène inférieur, entre ~ 26 Ma et ~ 16 Ma, au sud des Palmyrides, dans la province de HASV, dans un contexte tectonique extensif. Du Miocène au Quaternaire, entre ~ 19 Ma et ~ 0,08 Ma, des champs volcaniques se développe au nord des Palmyrides, conséquence d’extensions tectoniques de second ordre. A partir du milieu du Miocène, la compression augmente et le développement magmatique se poursuit potentiellement dans une ambiance tectonique de rotation antihoraire. Au sud des Palmyrides cela correspond à l’activité volcanique constante au cours des 13 derniers millions d’années. Au nord, cette phase d’activité liée à la tectonique de rotation est concentrée dans l’espace et le temps ; elle correspond au Plateau d’Homs, dans le NW Palmyre, entre 6,3 et 4,3 Ma.Nous proposons un nouveau modèle d'évolution volcano-tectoniques pour la province volcanique de HASV. Il souligne le rôle essentiel joué par l'hétérogénéité de la lithosphère (sous les chaînes du Liban – anti-Liban et la zone de plissement des Palmyrides) dans la formation du volcanisme à partir du milieu du Miocène. Nos modèles géophysiques permettent d’estimer à ~150 km la profondeur moyenne de la limite lithosphère-asthénosphère. A l’analyse des données géochimiques des laves, la zone à l’ouest de HASV où cette limite apparaît moins profonde, à ~ 110 km, s’expliquerait par une anomalie thermique plutôt que par une remontée asthénosphérique. Géochimiquement, les laves Cénozoïques syriennes sont alcalines et sub-alcalines et présentent les caractères de magma émis dans un contexte continental intra-plaque. Ce sont des basanites et des téphrites, des basaltes, des andésites et des trachy-andésites basaltiques et des trachybasaltes. 30 échantillons des différentes provinces volcaniques syriennes montrent une variation significative des signatures des éléments traces incompatibles. Le processus de genèse de ces magmas montre une influence négligeable de la contamination crustale, et un effet de la cristallisation fractionnée limité à l'olivine et au clinopyroxène. Nos résultats montrent que les laves syriennes ont été produites par des taux variables de fusion partielle à partir de niveaux différents dans le manteau lithosphériques présentant localement des hétérogénéités. Le rapport LREE / MREE nous permet de montrer non seulement comment le degré de fusion partielle varie spatialement et temporellement au cours des derniers 18 Ma, mais encore d’illustrer comment varie le degré et le style de la tectonique au cours de cette période. L’une des conséquences de ce contexte tectonique pourrait être la migration d’hydrocarbures vers l’ouest du fait de l’extension crustale au Plio-Quaternaire dans la zone du graben de l’Euphrate à l’Est ; cette migration pourrait être guidée vers une zone de la croûte préalablement fracturée située au NW de la Syrie.En conclusion, le volcanisme cénozoïque de la Syrie résulte d’une tectonique extensive, influencée périodiquement par la convergence arabo-eurasienne, au nord et à l’est, convergence qui provoque des styles tectoniques de rotation ; cette tectonique contrôle la fusion partielle à différents niveaux dans le manteau. Le volcanisme du Nord de la plaque arabique se développe dans le cadre de l’ouverture de la Mer Rouge et débute en même temps que l’activité au sud de la mer Rouge. Il se poursuit jusqu’à la période historique, progressivement amorti vers le nord, l’extension étant contrariée par le cadre compressif à la marge Arabie-Eurasie
The Cainozoic volcanic activity in the Arabian plate offers an excellent opportunity to study the intra-plate volcanism related to a complex tectonic setting. After the emplacement of the Yemeni-Ethiopian continental flood basalt plateau, ~ 31 Ma, since the Late Oligocene, widespread volcanic activity has erupted, accompanying the separation of the Arabian-Nubian Shield (development of Red Sea rifting) and the convergence between the Arabian and Eurasian plates (building of the Bitlis-Zagros thrust belts). In the northern part of the Arabian platform, the Syrian volcanism has taken place in a general compressional context, surrounding the Palmyride fold belt and adjacent to other deformation zones (e.g. the Euphrates graben and Dead Sea fault system). This thesis focuses on the volcano-tectonic evolution of the northern part of the Arabia plate, particularly in Syria, and essentially combines geochronological, geochemical, and morpho-structural studies, in addition to supplementary geophysical models. Our morpho-structural analyses of the Harrat Ash Shaam volcanic province (HASV) to the south of Palmyride, digitally characterise more than 800 monogenic volcanic cones placed in Syria, Jordan, and Saudi Arabia. These new data, together with the availability of sediment thickness data, give rise to a new volcano-tectonic approach. This study shows that the consistent negative correlation between the intensity of volcanism and basement depth is influenced by the tectonic setting. The normative analysis of the distribution of volcanic cones in relation to sediment thicknesses is critical when comparing the extension of tectonics in different zones. Remote sensing imagery, field work and our > 40 new K-Ar ages dataset ranging from ~0.05 million years (Ma) to ~18 Ma allow us to precise the Syria volcano-tectonic evolution through time. Regarding the youngest lava flows of HASV, the integration of the results makes it possible to suggest a chronological model for the alteration processes in relation to Quaternary palaeoclimatic changes. We reconstruct the volcano-tectonic evolution in Syria during the Cainozoic, and suggest different extension styles to explain the volcanism. It started during the Late Oligocene and the Early Miocene, between ~26 Ma and ~16 Ma to the South of Palmyride at HASV in an extensional tectonic context. From the Miocene to the Quaternary, between ~19 Ma and ~0.08 Ma, the volcanism developed to the North under second order extension tectonic conditions. Since the Mid-Miocene, the compression has increased and the magma erupted in relation with a possible counter-clockwise rotation tectonic relative motion. South of Palmyride it corresponds to the widespread eruptive phase during the last 13 Ma. To the North, this phase, linked to rotational tectonics appears concentrated in superficies and time; it corresponds to the Homs plateau, NW Palmyride, between 6.3 and 4.3 Ma. We suggest a new volcano-tectonic evolution model for the HASV. It highlights the essential role of lithosphere heterogeneity beneath Lebanon, in particular the anti Lebanon Mountains and Palmyride thrust belts, in triggering the Mid-Miocene volcanism. Our geophysical models estimate mean lithosphere – asthenosphere boundaries at about 150 km depth. According to geochemical data, the zone of shallowest depth ~110 km, W of HASV, could be the result of a thermal anomaly, instead of an asthenospheric upwelling. Geochemically, the Cainozoic Syrian lavas are alkaline and subalkaline rocks, typical of magma emitted in continental intraplate contexts. They are basanites and tephrites, basalts, basaltic andesites, basaltic trachyandesites, and trachybasalts. Thirty samples from different Syrian volcanic provinces show significant variation in terms of incompatible trace element signatures. Crustal contamination plays a negligible role in the process of magma genesis, as does crystal fractionation, essentially restricted to olivine and clinopyroxene. Our results show that the Syrian lava has been generated by variable rates of partial melting from different levels of a locally heterogeneous lithospheric mantle. The LREE/MREE ratio not only illustrates how the degree of partial melting was changed spatially and temporally during the last ~18 Ma, but it also illustrates how the degree and style of extension tectonics changed through time

In eastern Australia, the New England Fold Belt (NEFB) comprises an ancient convergent margin that was active from the Paleozoic until the late Mesozoic. Considerable effort has been expended in understanding the development of this margin over the past twenty years. However, proposed tectonic models for the orogen have either been too broad, ignoring contradictory local evidence, or too locally specific without paying attention to the 'big picture'. The research presented in this work addresses the issue of appropriate scale and depth of geological detail by studying the NEFB at the terrane-scale. Using one succession, the Silverwood Group of southeast Queensland, this work demonstrates that detailed sedimentological studies and basin analysis at the terrane-scale can help to refine hypotheses regarding the tectonic evolution of the NEFB. The Silverwood Group (Keinjan terrane), located approximately 140 km southwest of Brisbane, Australia, is a succession of arc-related basins that developed within an ancient intraoceanic island-arc during the mid-Cambrian to Late Devonian. From the base of the succession, the group consists of five formations totalling -9700 m. These include the Risdon Stud Formation (2500 m), Connolly Volcanics (2400 m), Bald Hill Formation (2450 m), Ormoral Volcanics (600 m) and the Bromley Hills Formation (1700 m). The Long Mountain Breccia Member (300m) is a separate unit which forms the lower part of the Bromley Hills Formation. The entire succession has been thrust west over the Late Devonian to Early Carboniferous Texas beds. Elsewhere, the Silverwood Group is unconformably overlain by and faulted against Early to Late Permian units including the Rokeby beds, Wallaby beds, Tunnel beds, Fitz Creek beds, Eight Mile Creek beds, Rhyolite Range beds and Condamine beds. Of these Permian units, all but the Condamine beds form part of the Wildash Succession. To the west, southwest and south, the Silverwood Group is intruded by the Late Triassic Herries and Stanthorpe Adamellites. All of these sequences and the two plutonic intrusives are unconformably overlain by the Jurassic sediments of the Marburg Sandstone. The Silverwood Group and Texas beds consist of various lithologies including grey, purple- grey, green and green-grey volcaniclastic conglomerates, sandstones, siltstones or mudstones, massive and laminated chert, polymict or monomict breccias, muddy breccias, muddy sandstones, and volcanic rocks. Volcanic rocks include various tholeiitic metabasites, dolerite, meta-andesites and infrequent metadacite. In the Silverwood Group, these volcanic rocks are often accompanied by mafic pyroclastic rocks (e.g. peperite and hyaloclastite). Facies analyses of these lithologies has led to the recognition of 19 deep-marine turbiditic and volcanic/volcaniclastic facies that were deposited by three main processes: i) gravity-flow processes (e.g. low- and high-density volcaniclastic turbidites and mass-flows), ii) chemical/biological processes (siliceous oozes- chert) and iii) direct initiation by volcanic processes (e.g. flows, hypabyssal intrusions and associated pyroclastic facies). For the Silverwood Group, the defined facies occur in distinct vertical associations that form recognisable 3rd and 4th-order architectural elements such as channel, levee, suprafan lobe, outer-fan, basin plain, mass transport complex, volcanic flows, syn-sedimentary sills and syn-sedimentary emergent cryptodomes. These architectural elements are represented in a series of deep-marine depositional environments including slope, shelf-edge failure, submarine-fan and subaqueous basaltic volcanoes. The Risdon Stud Formation and parts of the Connolly Volcanics were deposited along a 'normal' clastic or mud, mud/sand-rich and/or sand/mud-rich slope. Both upper and lower slope environments are represented and in both formations, the slope is speculated to have faced eastwards and prograded away from an active arc located west. Sediments from both successions accumulated at palaeodepths of 1200 to 2000 m. Although sediments from the upper part of the Bald Hill Formation were also deposited on a slope, these sequences have subsequently collapsed into the depocentre to form extensive slump deposits accompanied by olistoliths of older arc crust. The lower part of the Bald Hill Formation formed by similar processes, although the failure was far more extensive (>20 km along strike). This latter part of the formation is interpreted to be a major shelf-edge failure succession. Upper parts of the Bald Hill Formation also accumulated at palaeodepths of 1200 to 2000 m, but the deposition of these sediments occurred farthest from the shelf and at the greatest depth compared to the Risdon Stud Formation and Connolly Volcanics. Lower parts of the Bald Hill Formation were deposited at palaeodepths of approximately 1700 m. Subaqueous basaltic volcanoes are prominent in the Connolly Volcanics, Bald Hill Formation and Ormoral Volcanics. In the Bald Hill Formation, igneous rocks were emplaced into the shelf-edge failure succession as a series of syn-sedimentary sills and cryptodomes. These high-level hypabyssal rocks occasionally became emergent above the sediment-water interface, whereupon they were partially resedimented. In some parts of the Bald Hill Formation, the hypabyssal intrusions were blanketed by basin plain deposits that are contemporaneous with the slumps and olistoliths in the upper part of the formation. The intrusive rocks were emplaced at 1700 m palaeodepth. Unlike the Bald Hill Formation, the Ormoral Volcanics and lower parts of the Connolly Volcanics form thick accumulations of extrusive volcanic and pyroclastic rocks that built a significant volcanic pile. Volcanic and pyroclastic facies within these successions were deposited proximal to their source (0-10 km of vent). Extrusive rocks within the Ormoral Volcanics are thought to be derived from intrabasinal fissure-vents located at palaeodepths of 1700 to 3100 m. Igneous rocks from the Connolly Volcanics, Bald Hill Formation and Ormoral Volcanics have the petrological and geochemical characteristics of back-arc basin basalts (BAB) that were sourced from undepleted to slightly enriched Fertile MORB Mantle-wedge (FMM). The FMM material was variably enriched in trace elements by fluids derived from the subducting slab prior to emplacement of the igneous rocks. Immediately following emplacement, these rocks were hydrothermally metamorphosed under conditions of low-pressure and transitional low to high-temperature (200-300 °C). By contrast, igneous rocks within the Texas beds lack enrichment in subduction components and are characteristic of N-MORB. The Bromley Hills Formation is a sand-rich point-source submarine fan deposited at palaeodepths of 500 to 2000 m. The fan was initiated by a mass transport complex resulting from subaerial collapse of a basaltic-andesitic stratovolcano. The submarine fan is characterised by two repetitive stages of retrogressive sedimentation during which channel-levee elements (inner-fan channels) are overlain by suprafan lobe elements (mid-fan) and then by outer-fan deposits as sea-level rises within the depocentre. Both inner-fan channels and suprafan lobes show centralised stacking patterns with limited lateral migration that indicate the depocentre was laterally restricted during sedimentation (e.g. submarine ridges). The Bromley Hills Formation exhibits all the characteristics typical of an active margin fan that formed by a combination of tectonic stage initiation followed by eustatically controlled regressive deposition. Volcaniclastic sediments of the Silverwood Group range in composition from lithic to lithic- feldspathic wackes and arenites, although they are mainly lithic or feldspathic-lithic wackes and arenites. Many samples are tuffaceous (25-75% pyroclasts), particularly those from the Connolly Volcanics, Ormoral Volcanics and Bromley Hills Formation. Samples in the Bald Hills Formation and Texas beds can be classified as quartz-rich. The majority of the Silverwood Group was sourced from an undissected intraoceanic island-arc, although sediments within the Bald Hill Formation exhibit a provenance that is characteristic of uplift within the arc (recorded as a 'strike-slip continental arc' model). Epiclastic sediments from the Texas beds were sourced from a transitional to dissected continental arc. Formations of the Silverwood Group were mostly deposited in a series of intra-arc basins within an ancient intra-oceanic island arc, although the lowermost formation developed in a marginal basin (Risdon Stud Formation). All of the basins were located east of the active arc (behind the arc), keeping in mind the present location of the Group relative to the Texas-Coffs Harbour megafold. The entire succession formed during four-phases of arc-related basin development that coincide with major changes in the strain regime of the arc. From the base of the succession, these changes are: I) mid Cambrian to late Silurian marginal basin sedimentation- relative compression within the arc (Risdon Stud Formation), II) late Silurian to Early Devonian intra-arc rifting- relative extension within the arc (Connolly Volcanics), Ill) Early to early Middle Devonian basin collapse followed by intra-arc rifting- relative extension to compression (Bald Hill Formation and Ormoral Volcanics) and IV) early Middle to Late Devonian intra-arc submarine fan sedimentation- relative compression (Bromley Hills Formation). Comparing the Silverwood Group against equivalent terranes of Cambrian to Devonian age within the New England Fold Belt (NEFB) suggests that the Gamilaroi terrane, Calliope Volcanic Assemblage, Willowie Creek beds and Silverwood Group all formed as one intraoceanic island-arc during the Early to Late Devonian. Prior to this, significant differences in the sedimentological evolution of these terranes suggests that they occupied different positions relative to each other within the one arc. It is proposed that the NEFB formed as a result of dual west-directed subduction zones during the Cambrian to Middle Devonian period. During this time, a single intraoceanic island-arc located seaward of the Australian craton developed above a west-directed subduction zone. This arc was separated from the craton by a marginal sea. A second west-directed subduction zone was located beneath a continental arc developed on the Australian craton. Cambrian to Early Devonian terranes within and along the Peel Fault are proposed to form a part of the ancient subduction zone present beneath the intraoceanic island-arc (Weraerai and Djungati terranes). Collision of the intraoceanic island-arc occurred during the Late Devonian, at which point west-directed subduction occurred beneath the Australian craton and the accreted intraoceanic island-arc. Following collision, a new continental volcanic arc was established that was active during the Late Devonian to Early Carboniferous.

The Mono Basin of eastern California provides an ideal laboratory in which to study the interaction of volcanic and tectonic processes. The late Quaternary geological record of volcanic activity and range-front faulting is relatively complete in the basin. Range-front faults of the Sierra Nevada offset dateable late Pleistocene glacial moraines, thus affording the opportunity to estimate range-front slip rates. The first two chapters concern dating of moraines that are offset by range-front faults.

In Chapter One, I discuss the ages of the glacial moraines of the Mono Basin and their correlation between canyons. I dated the moraines by studying their morphology and the relative weathering of granitic boulders atop their crests, and by use of the clast-sound velocity (CSV) dating technique. The CSV technique consists of measuring the p-wave speed (Vₚ) in morainal boulders. Vₚ decreases with age as boulders weather. Clast-sound velocities enabled statistical division of moraines in each canyon into differently weathered deposits. Relative weathering features of boulder surfaces further helped discern age differences between moraines in a single canyon. Finally, CSV, relative weathering and moraine morphology, considered together, allowed correlation of moraines to an established glacial sequence, and therefore, correlation between canyons. Regression of mean Vₚ against best estimates of glaciation ages within the glacial sequence provided a further check on the validity of the correlations.

Moraines in all major canyons from Lee Vining south were correlative with the standard late Pleistocene sequence of Tioga, Tenaya, Tahoe and Mono Basin deposits. At Lundy Canyon, however, Tahoe and Tenaya moraines are poorly, if at all, preserved. The prominent moraines extending into the basin are probably of Tioga age. Poor preservation of Tenaya and Tahoe deposits may be due to the narrow, steep-sided morphology of Lundy Canyon, and rapid down-dropping on the range-front fault.

In Chapter Two, I discuss the application of a new quantitative dating technique to the moraines of Lee Vining Canyon. At Lee Vining Canyon, I measured cross-sectional profiles of lateral moraines of different ages to determine whether the degree to which they have been degraded could be used as a relative-dating method. Correlation of the degree of moraine degradation against an independent measure of age suggested that relative ages of late Pleistocene lateral moraines can be inferred from moraine profiles.

Analysis of the degradation of moraine profiles with a diffusion model resulted in equations that relate profile width and maximum slope angle to age. In accordance with the diffusion model, the functional relationship between profile width and estimated age was found to be nearly linear for the moraines of Lee Vining Canyon. Fits of model to data were good, despite evidence of transport of material by non-linear diffusive processes along some of the profiles.

Maximum slope angle is inversely proportional to age according to the diffusion model. Regression of mean maximum slope angle against inverse age for the group of moraines from Lee Vining Canyon suggested that the relationship between the two variables is expressed by the diffusion model.

Deviations of model profile shapes from true shapes suggested that in addition to moraine age, initial profile shape and non-diffusive degradation processes are important in controlling the relationship between slope parameters and age over spans of 10⁴ years.

In Chapter Three, I use moraine ages determined in Chapter One to estimate slip rates of range-front faults. For Chapter Three, I measured fault-scarp profiles on the dated lateral moraines of the Mono Basin to determine fault slip rates. I compared these data with what can be deduced about the extension rate due to dike intrusion underneath the Mono Craters. I then considered extension rates in the context of regional strain patterns to infer the mode of deformation and strain relief in the Mono Basin during late Quaternary time.

The extension-rate data indicate that dikes are being intruded underneath the Mono Craters in response to crustal stretching, and because of this, are now accommodating elastic strain that was once accommodated by range-front normal faulting. The section of the range front near the craters accommodated as much as 1 mm/yr of extension until 40,000 to 70,000 years ago. For the past 40,000 to 70,000 years, this section of range front has become inactive, even though extension along the range front to north and south has continued at up to 0.9 mm/yr. Dikes have been intruding underneath the Mono Craters for the past 40,000 years. Depending upon the assumptions used to calculate dike intrusion rates, the dikes accommodate 1 mm/yr of tectonic extension that was previously accommodated by range-front faulting.

Consideration of the extension rates in the context of regional tectonic strain patterns suggests that the Mono Craters are forming along one of the extensional boundary structures of a pull-apart basin, the other extensional boundary of which is the deactivated range-front segment.

If the Mono Craters represent an early stage of caldera formation, then their formation within a pull-apart zone may indicate that this is an ideal tectonic environment in which to form certain types of calderas.

A 5km swath-width SeaMARC I sidescan sonar survey, conducted over the zone of overlap between the southern rift zone of Axial Volcano and the northern tip of the Vance spreading segment on the Juan de Fuca Ridge (between 45°24'N and 45°50'N latitude), was analyzed to locate the present position of the Juan de Fuca spreading axis, and to determine the tectonic and volcanic structure of the seafloor. Sidescan data were processed in concert with the ship's Loran-C navigation to construct navigated, orthorectified mosaics of the sidescan imagery. In order to navigate the sidescan swaths, a simple numerical model was developed to describe the tracking behavior of the towed sidescan vehicle. Successive positions and orientations of the sidescan towfish were estimated, and were used to assign latitude/longitude values to individual sidescan pixels. Navigated sidescan pixels were mapped by computer onto an absolute (latitude/longitude) reference grid, and the resulting sidescan mosaic was compared directly to existing high-resolution SeaBeam bathymetry in order to discriminate the effects of large- and small-scale roughness on the observed backscatter distribution. The Juan de Fuca spreading axis between 45°25'N and 45°39'N is located within the axial valley of the Vance segment. Relative age relationships, based on crosscutting and superposition principles, indicate that the most recent volcanism within the axial valley has occurred along the valley's central ridge, and that the most recent resolvable extension within the axial valley has been concentrated between the central ridge and west valley wall. The Vance segment terminates at 45°39'N, and is not associated with a transform fault. The south rift zone of Axial volcano is a constructional volcanic feature that is not faulted, and a discrete axis of spreading over the south flank of Axial volcano is not resolvable in the sidescan imagery; however, the spreading locus north of 45°39'N is constrained to a zone between 130°06'W and 129°54'W. The lack of a well-defined spreading axis north of 45°39'N indicates that the physical manifestation of the divergent plate boundary has been modified or masked by hotspot volcanic processes associated with Axial volcano such that a definitive locus of spreading is not expressed in the surface morphology.
Graduation date: 1989

Four multicyclic complex calderas and smaller ignimbrite shields located within the Altiplano Puna Volcanic Complex of the Central Andes (APVC) erupted 13000 km�� of magma within the last 11 Ma. One of the largest and most complex of these is the Cerro Guacha Caldera. Ar-Ar age determinations and paleomagnetic directions suggest that the Cerro Guacha Caldera was formed by two major eruptions, caldera collapse, resurgence cycles and several smaller eruptions. Two major ignimbrites (> 600 km��) are found with ������Ar-�����Ar from biotites and sanidines of 5.65 �� 0.01Ma for the 1300 km�� (magma volume) Guacha ignimbrite and 3.49 �� 0.01Ma for the 800 km�� Tara Ignimbrite. The last major eruption occurred on the western flank producing the 1.72 �� 0.02 Ma Puripica Chico Ignimbrite with a volume of approximately 10 km��. Characteristic remanent magnetization data (ChRM) for these ignimbrites show that the Guacha has reverse polarity, while the Tara is normally polarized and the magnetic fingerprints have allowed their current full extents to be identified. A conspicuous lineament of volcanic structures in the eastern part of the caldera, bordering a caldera moat, filled out welded ignimbrites and sedimentary lacustrine sequences suggest an earlier 60x40 km outer collapse associated with the Guacha explosive episode. A central graben formed on the Guacha welded ignimbrite is related to a first episode of resurgence. Evidence of a second 30 x15 km inner collapse includes offset of welded Guacha ignimbrites and alignment of lava domes associated with the Tara ignimbrite. A second resurgence episode is suggested by the presence of an uplifted central block consisting primarily of welded Tara ignimbrite. As a whole the three ignimbrites (Guacha, Tara and Puripica Chico) share the same petrological and geochemical characteristics: high-K series, compositional ranges from dacite to rhyolite, with andesitic members present as lavas (for the Guacha and Puripica Chico Ignimbrites) and as pumices (for the Tara Ignimbrite). Highest silica content is found in the Chajnantor dome. Rayleigh modeling for Ba, Rb and Sr suggests at least 60% of crystal fractionation to account for the compositional variation between the Guacha andesite and the Chajnantor dome. Dy/Hb ratio increases with time from the Guacha andesite to the Negreal andesite suggesting stabilization of garnet owing to crustal thickening. Fe-Ti exchange geothermometry for the Tara Ignimbrite yielded log fO��� values ranging from -13.06 to -13.38 and temperatures of 714�� to 801��C. Amphibole geobarometry yielded pressures ranging from 150 to 180 MPa equivalent to 5.3 and 6.4 km depth respectively for the Tara Ignimbrite; the pressures range between 133 to 242 MPa, equivalent to 5.0 to 9.2 km depth for the Guacha Ignimbrite. The zircon saturation method yielded saturation temperatures of 716�� and 705��C for the Guacha and Chajnantor dome respectively and 784��C for the Tara Ignimbrite. The zircon crystallization range for the magmas of the Cerro Guacha Caldera is 1.25 Ma for the Guacha Ignimbrite; 1.09 Ma for the Puripica Chico Ignimbrite and 0.95 Ma for the Tara Ignimbrite. Recycling of antecrystic zircons within the caldera magmas is continuos through time.
Graduation date: 2012

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2015.
The Palaeoproterozoic Baoulé-Mossi domain of the West African Craton in northeastern Burkina Faso hosts numerous gold deposits such as Essakane and Tarpako. Integrated strato-tectonic, geophysical, geochemical, geochronological, regional stratigraphic framework and metallogenic studies of the Oudalan-Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane have provided new insight into the geotectonic evolution of the northeastern part of Burkina Faso. This work outlines the structural context and architecture necessary for forming these deposits. In this work, a new strato-tectonic model is proposed for the area by integrating field data and geophysical, geochemical, and geochronological data. The integrated data highlights and characterizes the setting of the Essakane gold mine and gold camp relative to the location of other regional gold deposits, metamorphosed Birimian Supergroup, intrusive rocks and shear zones. Structural, geochemical and geochronological analyses have helped to clarify the geological evolution of the Oudalan-Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane during the Tangaean (D1) and Eburnean (D2) orogenies through to the Wabo Tampelse Event (D3). Further to these, zircon U-Pb geochronology data have demonstrated that the Oudalan-Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane represent some of the oldest outcropping geology in the Palaeoproterozoic Baoulé-Mossi domain recognised to date. The geochronology and geology suggest that the basement or a pre- Birimian crust to the Birimian Supergroup may be found in the northeast of Burkina Faso. The Eburnean Orogeny in northeastern Burkina Faso is preceded by two phases of deformation (D1-x and D1), and two phases of magmatism. The first, D1-x, is associated with the emplacement of the Dori Batholith at the onset of D1 (2164 – 2141 Ma). D1 ductile-brittle deformation formed F1 folds and discrete high-strain mylonite zones that deformed the Oudalan- Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane during a southwestdirected palaeo-principal compressive stress. The pre-Birimian to Birimian supracrustal rocks and intrusions were regionally metamorphosed during D1 to greenschist to amphibolite facies with development of mineral assemblage of quartz-chlorite-muscovite ± chloritoid to biotite-potash feldspar ± hornblende. D1 is also associated with volcanic arc type calc-alkaline magmatism, producing TTGs enriched in heavy rare earth elements. The Eburnean Orogeny (2130 – 1980 Ma) is characterised by northwest-southeast shortening; it was followed by north-northwest - south-southeast shortening with development of northeast trending sinistral strike-slip faults and shears. D2 brittle-(ductile) deformation is manifested by refolding of F1 by northeast-trending F2, and development of a pervasive northeast-trending S2 to S2-C foliation. Metamorphic grade attained greenschist facies during D2, with development of mineral assemblage of quartz-chlorite-muscovite ± actinolite. The Wabo Tampelse (D3) deformation event is brittle in character and does not significantly affect the regional geological architecture in the study area.

Realistic probabilistic hazard forecasts for re-awakening volcanoes rely on making an accurate estimation of their past eruption frequency and magnitude for a period long enough to view systematic changes or evolution. Adding an in-depth knowledge of the local underlying magmatic or tectonic driving processes allows development of even more robust eruption forecasting models. Holocene tephra records preserved within lacustrine sediments and soils on and surrounding the andesitic stratovolcano of Mt. Taranaki (Egmont Volcano), New Zealand, were used to 1) compile an eruption catalogue that minimises bias to carry out frequency analysis, and 2) identify magmatic processes responsible for variations in activity of this intermittently awakening volcano. A new, highly detailed eruption history for Mt. Taranaki was compiled from sediment sequences containing Holocene tephra layers preserved beneath Lakes Umutekai and Rotokare, NE and SE of the volcano’s summit, respectively, with age control provided by radiocarbon dating. To combine the two partly concurrent tephra records both geochemistry (on titanomagnetite) and statistical measures of event concurrence were applied. Similarly, correlation was made to proximal pyroclastic sequences in all sectors around the 2518 m-high edifice. This record was used to examine geochemical variations (through titanomagnetite and bulk chemistry) at Mt. Taranaki in unprecedented sampling detail. To develop an unbiased sampling of eruption event frequency, a technique was developed to distinguish explosive, pumice-forming eruptions from dome-forming events recorded in medial ash as fine-grade ash layers. Recognising that exsolution lamellae in titanomagnetite result from oxidation processes within lava domes or plugs, their presence within ash deposits was used to distinguish falls elutriated from blockand- ash flows. These deposits are focused in particular catchments and are hence difficult to sample comprehensively. Excluding these events from temporal eruption records, the remaining, widespread pumice layers of sub-plinian eruptions at a single site of Lake Umutekai presented the lowest-bias sampling of the overall event frequency. The annual eruption frequency of Mt. Taranaki was found to be strongly cyclic with a 1500-2000 year periodicity. Titanomagnetite, glass and whole-rock chemistry of eruptives from Mt. Taranaki’s Holocene history all display distinctive compositional cycles that correspond precisely with the event frequency curve for this volcano. Furthermore, the largest known eruptions from the volcano involve the most strongly evolved magmas of their cycle and occur during the eruptive-frequency minimum, preceding the longest repose intervals known. Petrological evidence reveals a two-stage system of magma differentiation and assembly operating at Mt. Taranaki. Each of the identified 1500-2000 year cycles represent isolated magma batches that evolved at depth at the base of the crust before periodically feeding a mid-upper crustal magma storage system.

Tese de Doutoramento em Geologia, especialidade de Geodesia.
O enquadramento geodinâmico do arquipélago dos Açores, aliado às suas características geológicas, geoquímicas, geofísicas e as frequentes manifestações das actividades sísmica e vulcânica, têm motivado o avanço de estudos multidisciplinares, em particular, aplicados a sistemas vulcânicos e tectónicos como complemento à mitigação de riscos geológicos. Neste contexto, desde 1999 que o Centro de Vulcanologia e Avaliação de Riscos Geológicos (CVARG) da Universidade dos Açores (UAc) tem vindo a desenvolver estudos no domínio da deformação crustal de forma a contribuir para o enriquecimento do conhecimento científico sobre a evolução do estado da deformação dos sistemas vulcano-tectónico activos da região dos Açores. Consequentemente, o presente trabalho tem como objectivo a compreensão dos processos de deformação crustal dos sistemas vulcano-tectónicos das ilhas Terceira, S. Jorge e Graciosa, tendo-se para o efeito procedido à implementação de um sistema de processamento / tratamento automático de dados GPS. [...].
ABSTRACT: The geodynamic setting of the Azores archipelago, allied to the geological, geochemical, geophysical and to the frequent manifestations of seismic and volcanic activities have motivated a number of multidisciplinary studies applied to the volcanic and tectonic systems as a complement for the mitigation of geological risks In this context, since 1999 the Centre for Volcanology and Geological Risks Assessment (CVARG) of the University of the Azores (UAc) has been developing studies in the field of crustal deformation contributing for the growth of the scientific knowledge regarding the deformation evolution of the active volcano-tectonic from the Azores. Consequently, the present work aims to the understanding of the processes of crustal deformation of the volcano-tectonic systems of Terceira, S. Jorge and Graciosa islands. For this an automatic processing / treatment GPS data system was implemented. [...].

Studying recent volcanic and tectonic events in the Red Sea region is important for improving our knowledge of the Red Sea plate boundary and for regional geohazard assessments. However, limited information has been available about the past activity due to insufficient in-situ data and remoteness of some of the activity. In this dissertation, I have used satellite remote sensing to derive new information about several recent volcanic and tectonic events in the Red Sea region. I first report on three volcanic eruptions in the southern Red Sea, the 2007-8 Jebel at Tair eruption and the 2011-12 & 2013 Zubair eruptions, which resulted in formation of two new islands. Series of high- resolution optical images were used to map the extent of lava flows and to observe and analyze the growth and destructive processes of the new islands. I used Interferometric Synthetic Aperture Radar (InSAR) data to study the evolution of lava flows, to estimate their volumes, as well as to generate ground displacements maps, which were used to model the dikes that fed the eruptions. I then report on my work of the 2009 Harrat Lunayyir dike intrusion and the 2004 Tabuk earthquake sequence in western Saudi Arabia. I used InSAR observations and stress calculations to study the intruding dike at Harrat Lunayyir, while I combined InSAR data and Bayesian estimation to study the Tabuk earthquake activity. The key findings of the thesis are: 1) The recent volcanic eruptions in the southern Red Sea indicate that the area is magmatically more active than previously acknowledged and that a rifting episode has been taken place in the southern Red Sea; 2) Stress interactions between an ascending dike intrusion and normal faulting on graben-bounding faults above the dike can inhibit vertical propagation of magma towards the surface; 3) InSAR observations can improve locations of shallow earthquakes and fault model uncertainties are useful to associate earthquake activity with mapped faults; 4). The successful application of satellite remote sensing technologies in studying the recent volcanic and tectonic processes in the Red Sea region implies that remote sensing data are an important resource for the local authorities to monitor geohazards.