Dissertations / Theses on the topic 'Crustal dynamics'

In this thesis, an integrated structural and chemical approach has been used to investigate the spatial and temporal evolution of fluid chemistry, and fluid flow pathways, during crustal shortening. The Taemas Vein Swarm is hosted in a limestone-shale sequence, the Murrumbidgee Group, in the Eastern Belt of the Lachlan Orogen, in New South Wales, Australia. The Taemas Vein Swarm (TVS) is composed of calcite ± quartz veins, hosted in a series of faults and fractures, which extends over an area of approximately 20 km2. The Murrumbidgee Group is composed of several formations, comprising massive grey micritic limestones, redbed sandstones and shales,and thinly interbedded (10–20 cm scale) limestones and shales. ¶ The sedimentary sequence has been folded into a series of upright, open to close folds, and was probably deformed during either mid-late Devonian, or early Carboniferous, crustal shortening. To the east, the Murrumbidgee Group is overthrust by a Silurian volcanic sedimentary sequence along the Deakin-Warroo Fault System. Crosscutting and overprinting relationships demonstrate that vein growth was synchronous with folding, with different vein types related to different fold mechanisms at various stages of fold growth. ¶ Flexural slip folding led to the development of bedding-concordant veins (hereafter called bedding-parallel veins). Flexural flow in semicompetent to incompetent beds caused en echelon extension vein arrays to grow. Decoupling between beds, and dilatancy at fold hinges led to significant vein growth. In addition, fold lock-up led to limb-parallel stretching, and the growth of bedding-orthogonal extension fractures. ¶ Vein growth is inferred to have occurred in a compressional tectonic regime (i.e. sigma3=vertical). Oxygen isotope quartz-calcite thermometry suggests that veins formed at temperatures of 100–200 oC. The depth of vein formation may have been between about 5 and 8 km. Vein textures indicate that growth of veins occurred during multiple cycles of permeability enhancement and destruction. Subhorizontal extension fractures, and faults at unfavourable angles for reactivation, imply that fluid pressures exceeded lithostatic levels during the growth of some veins. Coexisting extension and shear fractures imply that differential stress levels varied over time. ¶ Flexural slip continued throughout folding at Taemas, despite some fold limbs being at angles extremely unfavourable for reactivation ( > 60). As folds approached frictional lock-up, flexural slip continued to occur when supralithostatic fluid pressures were developed. Therefore, large, bedding-discordant faults were not developed to accommodate strain during folding, explaining a deficiency of larger faults in the TVS. ¶ Infiltration of overpressured fluids occurred into the base of the Murrumbidgee Group, and was channelled into a distributed mesh of small faults and fractures. At the point that a connected ‘backbone’ flow network developed in the TVS, highpressure fluids would no longer be available to allow continuing flexural slip on fold limbs approaching lockup. Thereafter, larger faults would develop, which would adjust the fault population in the TVS to a more ‘typical’ displacement-frequency distribution. This had not occurred in the Taemas area by the time crustal shortening ceased. An abundance of small faults, and fracturing driven by invasion of overpressured fluid, implies that the TVS formed via an ‘earthquake swarm’ process. ¶ Modern analytical techniques, utilising laser ablation sampling technology, allow high-spatial resolution chemical data to be collected from syntectonic veins. Insights into the role that fluid-mineral interface processes may have on the chemistry of minerals grown in syntectonic veins were provided by an experimental study. Moderate sized ( < 1−5 mm) synthetic calcite crystals were successfully grown to investigate the uptake of rare earth elements (REE) into calcite. Changes in crystal morphology are linked to variable solution chemistry, which has important implications for the interpretation of hydrothermal vein textures. High-spatial resolution chemical analyses of synthetic calcite crystals demonstrate significant fluctuations in REE concentrations over distances of < 200 μm within calcite crystals. Time-equivalent regions on different crystal faces have significantly different REE concentrations, indicating that fluctuations in calcite trace element composition cannot be interpreted exclusively in terms of changing ‘bulk fluid’ composition. Rare earth element anomalies (Eu/Eu* and Ce/Ce*) are not significantly influenced by compositional zoning, and may be robust indicators of changes in solution bulk chemistry and fluid oxidation state. ¶ Changes in isotopic ratios (13C, 18O and 87Sr/86Sr), and trace element concentrations in veins from the TVS are related to variations in fluid source, flow pathways and chemical conditions (e.g. trace element complexation, precipitation rate, fluid oxidation) during hydrothermal fluid flow. This integrated structural, textural and chemical approach has direct application to the examination of hydrothermal veins in fracture-hosted ore deposits, and may allow the fluid source and/or chemical conditions conducive to the formation of high-grade ore to be discerned. ¶ Vein 18O compositions systematically increase upwards through the Murrumbidgee Group, caused by progressive reaction of an externally derived, low-18O fluid (of probable meteoric origin) with host limestones. Vein 18O and 87Sr/86Sr compositions vary spatially and temporally within the same outcrop, and within individual veins, which is inferred to be caused by the ascent of packages of fluid along constantly changing flow pathways. Fluid-buffered oxygen isotope ratios at the earliest stages of deformation imply that the TVS formed via an ‘invasion percolation’ process. Fluid pathways are inferred to have changed constantly, with fractures ‘toggleswitching’ between high-permeability and low-permeability states, due to repeated fracture opening and sealing events.

Introduction: Through receiver function analysis, this study inquires into some of the most basic properties of the crust below southeastern Sicily (Italy), mostly represented by the Hyblean Plateau. Method: This is accomplished, using P-to-S receiver function (P-RF) technique which involves coordinate rotation and deconvolution, by stacking waveforms from 335 teleseismic events, magnitude 6.0 and larger, to determine the delay in arrival time for several phases of the P-wave coda, relative to the initial P-wave arrival. This information is used to establish a linear relationship between thickness and VP/VS ratio, each of which is stacked using the slant stacking approach for a given station to identify the best-fit thickness and wave speed for the crust below that station. To determine their accuracy these results are compared with previous studies, as well as with synthetically generated receiver functions based on 1D crustal models including dipping layers. Results: The good regional coverage and the fairly dense station spacing (~20 km) leaded to a fairly complete image of the crust-mantle boundary over the entire region that shows strong lateral variations of the crustal thickness with Moho depth varying between 29 and 38 km. In particular, a thinner crust is observed in the central-eastern part of the Hyblean Foreland beneath SSY (Solarino) station and thickening further to the south beneath HMDC (Modica) station (up to 38 km) and to the north beneath HLNI (Lentini) station (up to 35 km). Sharp transitions between thinned and thickened crust are most likely the result of complicated 3D structures attributed to regional geodynamics. Discussion: Since all the 8 considered broadband stations lie in a geodinamically complex area, reliable estimates of the crustal thicknesses below these stations are key requisite for understanding the geologic and tectonic processes that have been dominant in the region, providing valuable information for the numerous earth science disciplines.

Longmen Shan Mountain Belt is a prominent orogeny along the eastern margin of the Tibetan plateau. Its current deformation has significant implications for the Cenozoic tectonics of the Tibetan plateau. The M=8 Wenchuan earthquake substantially ruptured the Longmen Shan mountain in 2008. Numerous tectonics and rheological implications are concluded by this event on crustal dynamics along the eastern margin of the Tibetan plateau. Several high-resolution gravity surveys were conducted before and after the event to investigate the regional isostasy and crustal dynamics. From 2008 to 2011, four gravimetric surveys were carried out along two profiles across southern and northern Longmen Shan from the Sichuan Basin to the Songpan-Graze Terrane. The Bouguer gravity anomalies drop from -162 mGal to -431 mGal in the Aba Basin with a steep gradient of 0.84 mGal/km. There is a significant increase of crustal thickness from 40 km in the Sichuan to more than 60 km in the Tibetan plateau. Negative isostatic anomaly of -30 mGal over 150 km of the Songpan-Graze Terrane infers an over-compensation of excess crustal thickness up to 20 km. Hence, upward isostatic rebound is resulted and coupled with on-going crustal movement. Gravity values change significantly before and after the Wenchuan earthquake, ranging from -1.2 mGal to 0.7 mGal near the epicentral area. Significant thrust slip of 7.5m and normal slip of 4.5 m were simulated along the Beichuan fault and Wenchuan fault by an elastic dislocation theory. The co-existence of thrusting and normal faulting implies both compressional and extensional settings along Longmen Shan. The normal slip corroborates a large-scale crustal extension, lending support to a model with the inflation of lower crustal flow. The two-year post-seismic gravity variations were more than 0.1 mGal near the epicentral area. About 25% of them could be attributed to viscoelastic mantle relaxation. The dynamics topography along the eastern margin of the plateau is proposed to be a consequence of lower crustal flow squeezed by isostatic rebound and topographic load. The strong Yangtze Block is thought to obstruct the crustal flow horizontally and direct it to flow upward beneath Longmen Shan. The steep topography and seismicity along Longmen Shan are then resulted probably from the vertical stress induced in this upward flow.
published_or_final_version
Earth Sciences
Doctoral
Doctor of Philosophy

This thesis investigates electric current signals generated spontaneously in specimens of Carrara marble during deformation under crustal conditions. It extends previous work where similar currents were observed during uniaxial deformation of marble. Since marble is a non-piezoelectric material, one of the main questions is how these currents are related to the mechanical processes of deformation. Another question is whether it is possible to extract from these electric currents information about the deformation dynamics. This is particularly important in light of recent claims that geoelectric anomalies observed in the field are related to crustal deformation and can inform us about changes in the organisation of the fault network in a focal region prior to an earthquake. Using an approach that combines rock deformation experiments and statistical modelling, I examine how these electric currents evolve with deformation at the laboratory scale and make several original discoveries regarding their behaviour. To establish how the current signals varied with experimental condition and deformation mechanism across the brittle-ductile transition, I conducted constant strain rate triaxial compression experiments recording differential electric current flow through the rock samples at various confining pressures, strain rates and pore fluid conditions. I acquired mechanical data, ultrasonic velocities and acoustic emissions simultaneously, along with electric current, to constrain the relationship between electric current and deformation. For the statistical modelling, I used a novel entropy-based model, derived from non-extensive statistical mechanics (Tsallis, 1988), which has the advantage of including a term to account for interactions in the system. Interactions are effectively modelled by the non-extensive q-parameter. Small (nanoAmpere) electric currents are generated and sustained during deformation under all the conditions tested. Spontaneous electric current flow in the dry samples is seen only in the region of permanent deformation and is due to the presence of localised electric dipoles. This current flow is correlated to the damage induced by microcracking, with a contribution from other intermittent ductile mechanisms. Current and charge densities are consistent with proposed models of crack separation charging and migrating charged edge dislocations. The onset of current flow occurs only after a 10% reduction in P-wave velocity, implying that some degree of crack damage and/or crack connectivity is required before current will flow through the samples. Electric current evolution exhibits three separate time-scales of behaviour, the absolute and fluctuating components of which can be related to the evolution of stress, deformation mechanism, damage and localisation of deformation leading up to sample failure. In the brittle regime, electric current exhibits a precursory change as the stress drop accelerates towards failure, which is particularly distinct at dynamic strain rates. Current and charge production depend strongly on the experimental conditions. Power-law relationships are seen with confining pressure and strain rate, with the first corresponding to increased microcrack suppression and the second to time-dependent differences in deformation mechanism across the brittle-ductile transition. In the presence of an ionic pore fluid, electrokinetic effects dominate over solid-state mechanisms but development of the crack network and charge contribution from solid-state deformation processes drive the variation in electrokinetic parameters. Current flow in the dry samples is approximately proportional to stress within 90% of peak stress. In the fluid-saturated samples, proportionality holds from 40% peak stress, with a significant increase in the rate of current production from 90% peak stress, and is associated with fluid flow during dilatancy. This proportionality, together with the power-law relationship between current and strain rate is reminiscent of power-law creep, where deformation rate varies as a power-law function of stress, and suggests that the electric signals could be used as a proxy for stress. High frequency fluctuations in the electric current signal can be described by `fat-tailed' q-Gaussian statistics, consistent with an origin in non-extensive statistical mechanics. These distributions can be explained as arising from superstatistical dynamics (Beck, 2001; Beck and Cohen, 2003), i.e., the superposition of local mechanical relaxations in the presence of a slowly varying driving force. The macroscopic distribution parameters provide an excellent prediction of the experimentally observed mean energy dissipation rate of the system (as modelled by the superstatistical β-parameter), particularly at slow strain rates. Furthermore, characteristic q-values are obtained for different deformation regimes across the brittle-ductile transition, and the evolution of q during deformation reveals a two-stage precursory anomaly prior to sample failure, consistent with the stress intensity evolution as modelled from fracture mechanics. These findings indicate that the dynamics of rock deformation are reflected in the statistical properties of the recorded electric current. My findings support the notion that electric currents in the crust can be generated purely from deformation processes themselves. Scaling up the laboratory results to large stressed rock volumes at shallow crustal pressures and constant crustal strain rates, deformation induced transient telluric current systems may be as large as 1 MA, even accounting for >99% dissipation, which corresponds to a huge accumulated net charge of 10 ZC. This implies that a significant amount of charge from deforming tectonic regions contributes to the Earth's telluric currents and electric field, although due to conduction away from the stressed rock volume, it is unlikely that accumulated charge of this quantity would ever be measured in the field. Electric current evolution and its precursory characteristics can be related to models for electric earthquake precursors and fault-zone damage organisation, developed from field observations, providing experimental support for them. However, given the oscillatory nature of the current evolution observed during cataclastic flow processes in the laboratory, there is a high probability of false alarms. Furthermore, the potential for electric anomalies to be useful as earthquake precursors remains contentious due to the difficulties of separating deformation-induced signals from other telluric noise and the wider issue of establishing a statistically significant link with earthquakes.

Analysis of quartz c-axis fabrics and microstructures from ductily deformed rocks allows for the examination of the kinematics associated with crustal deformation. This thesis expands on the current knowledge of the kinematic evolution of the Himalayas and Scottish Caledonides, by examining samples from the Main Central Thrust (MCT) (Himalayas) and the Sgurr Beag Thrust (SBT) (Scottish Caledonides).  Metamorphic temperatures (Tm) associated above the MCT are inverted; chapter one attempts to test if deformation temperatures (Td) correlate to Tm, indicating that ductile shearing occurred during peak Tm. In the Scottish Caledonides, Td and Tm increase from foreland to hinterland, potentially indicating a right way up thermal structure;  chapter two presents Td and Tm associated with the region around the SBT. Above the MCT, quartz c-axis fabrics yield Td ranging between 500-650 "C, corresponding to the temperatures of dynamic recrystallization for subgrain rotation (SGR) and grain boundary migration (GBM). Up to 1000m above the MCT, Td and Tm are within error of each other, suggesting that shearing occurred during peak Tm; while further away from the MCT  Tm is significantly hotter than Td, suggesting that shearing continued past Tm. Deformation associated with the upper part of the Moine thrust sheet and the SBT yields quartz c-axis fabrics with Td ranging between 395-583 "C, corresponding to the regional dynamic recrystallization. Tm calculations original to this study yield pressure-temperature constraints of 4.8-5.8 kbar and 586-625 "C. Tm is within error of Td, suggesting that deformation and metamorphism were synchronous.
Master of Science

Temporal variation of crustal structure is key to our understanding of Earth processes on human timescales. Often, we expect that the most significant structural variations are caused by strong ground shaking associated with large earthquakes, and recent studies seem to confirm this. Here we test the possibility of using P receiver functions (PRF) to isolate structural variations over time. Synthetic receiver function tests indicate that structural variation could produce PRF changes on the same order of magnitude as random noise or contamination by local earthquakes. Nonetheless, we find significant variability in observed receiver functions over time at several stations located in northeastern Honshu. Immediately following the Tohoku-oki earthquake, we observe high PRF variation clustering spatially, especially in two regions near the beginning and end of the rupture plane. Due to the depth sensitivity of PRF and the timescales over which this variability is observed, we infer this effect is primarily due to fluid migration in volcanic regions and shear stress/strength reorganization. While the noise levels in PRF are high for this type of analysis, by sampling small data sets, the computational cost is lower than other methods, such as ambient noise, thereby making PRF a useful tool for estimating temporal variations in crustal structure.

Biological soil crusts (BSCs) are composed of cyanobacteria, algae, fungi, lichens, liverworts and mosses living in close association with soil particles. The primary objective of this thesis is to examine the dynamics, environmental constraints and habitat preferences of lichen dominated biological soil crusts in the El Cautivo badlands, located in the Tabernas Desert, southeast Spain.

Dry grasslands and heathlands are important habitats for biodiversity conservation and host cryptogam soil crusts (CSC) that greatly contribute to ecosystem functioning. This thesis aims at exploring: the terricolous lichen diversity in dry habitats in a human-impacted lowland (Po Plain, N Italy); the compositional patterns of CSC across dry grasslands and heathlands, also accounting for the dynamic stage of the vegetation (pioneer vs mature); the effects of small-scale disturbances on the three main taxa found in cryptogam-rich dry grasslands (vascular plants, lichens, bryophytes); the potential of CSC in delivering the ecosystem service of storing seeds of vascular plants, in the perspective of habitat restoration. Diversity and dynamics were studied by means of vegetation surveys in circular plots, whose number was area-dependent, located along transects in each habitat patch (= 185 plots in 60 grasslands, 114 plots in 22 heathlands). The % cover of each plant, bryophyte and lichen was recorded, with environmental (soil pH and texture, vegetation structure, altitude, bare soil %), disturbance-related (human trampling, cattle and lagomorphs fecal pellets, wild boar scratches) and climate variables (mean annual temperature and precipitation). The composition in lichens and bryophytes was compared among the 3 habitat types (3 groups) and between their dynamic stages (pioneer vs mature, 6 groups) to understand whether it is habitat- and stage-specific by means of NMDS, PERMANOVA and Indicator Species Analysis. Drivers of cover and species richness of the 3 taxa were analyzed for dry grasslands by means of generalized linear models. The seed storing function was studied taking 5 samples of CSC in 4 acidic grassland patches (= 20 samples), each sample taken at the centre of one plot surveyed in the previous spring. The samples were dryed, crumbled on sterile gardening soil in a controlled situation. All the germinated seedlings were identified and counted. Data were analyzed in comparison to data from the donor plots by means of Kruskal-Wallis test and linear regression, considering all the species and then native and non-native species separately . 33 terricolous lichen species were recorded, of which 13 of conservation concern. In spite of the widespread presence of few common species and the generally low species richness, composition differs significantly between the 3 habitat types and between pioneer vs mature heathlands, less markedly between dynamic stages within each grassland type. Three well-characterized assemblages which include many species of conservation concern were found for both lichens and bryophytes. Cryptogam assemblages are influences also by rainfall, soil features and vegetation structure. Increase of soil pH and disturbance by lagomorph fecal pellets have a negative effect on lichens, as well as their interaction (the negative effect of pellets is more evident at the increase of soil pH). Soil pH, fecal pellets and precipitation have a positive effect on bryophytes. Human trampling and fecal pellets have a negative effect on vascular plants, while increase of soil pH has a positive effect. The interaction of soil pH and pellets has an effect opposite than on lichens (the negative effect of pellets is more evident at the decrease of soil pH). CSC are able to store and release vascular plant seeds which are viable and can germinate when placed in proper conditions. The number of species and individuals of vascular plants germinated from CSC is comparable to what recorded in nature in the donor plots. Native species richness was higher, while native species germinated with less individuals than non-native species. These results are useful in addressing conservation towards the management and protection of all the lowland dry habitats, due to the differentiation among the cryptogam assemblages they host and to the presence of several species of conservation concern.
Dry grasslands and heathlands are important habitats for biodiversity conservation and host cryptogam soil crusts (CSC) that greatly contribute to ecosystem functioning. This thesis aims at exploring: the terricolous lichen diversity in dry habitats in a human-impacted lowland (Po Plain, N Italy); the compositional patterns of CSC across dry grasslands and heathlands, also accounting for the dynamic stage of the vegetation (pioneer vs mature); the effects of small-scale disturbances on the three main taxa found in cryptogam-rich dry grasslands (vascular plants, lichens, bryophytes); the potential of CSC in delivering the ecosystem service of storing seeds of vascular plants, in the perspective of habitat restoration. Diversity and dynamics were studied by means of vegetation surveys in circular plots, whose number was area-dependent, located along transects in each habitat patch (= 185 plots in 60 grasslands, 114 plots in 22 heathlands). The % cover of each plant, bryophyte and lichen was recorded, with environmental (soil pH and texture, vegetation structure, altitude, bare soil %), disturbance-related (human trampling, cattle and lagomorphs fecal pellets, wild boar scratches) and climate variables (mean annual temperature and precipitation). The composition in lichens and bryophytes was compared among the 3 habitat types (3 groups) and between their dynamic stages (pioneer vs mature, 6 groups) to understand whether it is habitat- and stage-specific by means of NMDS, PERMANOVA and Indicator Species Analysis. Drivers of cover and species richness of the 3 taxa were analyzed for dry grasslands by means of generalized linear models. The seed storing function was studied taking 5 samples of CSC in 4 acidic grassland patches (= 20 samples), each sample taken at the centre of one plot surveyed in the previous spring. The samples were dryed, crumbled on sterile gardening soil in a controlled situation. All the germinated seedlings were identified and counted. Data were analyzed in comparison to data from the donor plots by means of Kruskal-Wallis test and linear regression, considering all the species and then native and non-native species separately . 33 terricolous lichen species were recorded, of which 13 of conservation concern. In spite of the widespread presence of few common species and the generally low species richness, composition differs significantly between the 3 habitat types and between pioneer vs mature heathlands, less markedly between dynamic stages within each grassland type. Three well-characterized assemblages which include many species of conservation concern were found for both lichens and bryophytes. Cryptogam assemblages are influences also by rainfall, soil features and vegetation structure. Increase of soil pH and disturbance by lagomorph fecal pellets have a negative effect on lichens, as well as their interaction (the negative effect of pellets is more evident at the increase of soil pH). Soil pH, fecal pellets and precipitation have a positive effect on bryophytes. Human trampling and fecal pellets have a negative effect on vascular plants, while increase of soil pH has a positive effect. The interaction of soil pH and pellets has an effect opposite than on lichens (the negative effect of pellets is more evident at the decrease of soil pH). CSC are able to store and release vascular plant seeds which are viable and can germinate when placed in proper conditions. The number of species and individuals of vascular plants germinated from CSC is comparable to what recorded in nature in the donor plots. Native species richness was higher, while native species germinated with less individuals than non-native species. These results are useful in addressing conservation towards the management and protection of all the lowland dry habitats, due to the differentiation among the cryptogam assemblages they host and to the presence of several species of conservation concern.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 26, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Mian Liu. Vita. Includes bibliographical references.

Dans mon projet, j'ai utilisé les gaz nobles (He, Ne, Ar, Kr et Xe) pour étudier les processus naturels se déroulant dans différents contextes géodynamiques (c.-à-d. subduction, collision continentale, rifting), montrant ainsi comment l'utilisation des gaz rares est fondamentale pour contraindre l'origine des substances volatiles et comment ils permettent une évaluation qualitative et quantitative des processus (interaction eau-gaz-roche) qui se produisent pendant la remontée des fluides de l'intérieur de la Terre vers l'atmosphère. Les résultats de mon projet peuvent être résumés en cinq thèmes principaux : 1) Aperçu de l’histoire du dégazage du manteau terrestre à partir d'analyses de haute précision des gaz rares du gaz magmatique ; 2) Systématique des gaz nobles et des isotopes du carbone sur le volcan Ciomadul, apparemment inactif (Roumanie): Preuve du dégazage volcanique ; 3) Fluides dérivés du manteau dans le bassin sédimentaire de Java oriental, Indonésie ; 4) Dégazage des volatiles du manteau dans un régime tectonique de compression hors du volcanisme: rôle de la délamination continentale ; 5) Dégazage continental de l'hélium dans un contexte tectonique actif (nord de l'Italie) : le rôle de la sismicité
In my project, I used the nobles gases (He, Ne, Ar, Kr and Xe) to investigate natural processes occurring in different geodynamical contexts (i.e., subduction, continental collision, rifting), showing how the use of the noble gases is fundamental to constrain the origin of volatiles, and to investigate the Earth interior. Furthermore, I also used these volatiles to recognize the processes (water-gas-rock interaction) that occur during the fluids up rise from the Earth’s interior to the atmosphere and quantitatively constrain the extents of these processes. The results of my project are summarized in five main topics: 1) Insights into the degassing history of Earth’s mantle from high precision noble gas analysis of magmatic gas 2) Noble Gas and Carbon Isotope Systematics at the Seemingly Inactive Ciomadul Volcano (Romania): Evidence for Volcanic Degassing 3) Mantle‐Derived Fluids in the East Java Sedimentary Basin, Indonesia 4) Outgassing of Mantle Volatiles in Compressional Tectonic Regime Away From Volcanism: The Role of Continental Delamination 5) Continental degassing of helium in an active tectonic setting (northern Italy): the role of seismicity

Les réglementations conduisent à multiplier les évaluations du risque écologique lié au rejet des substances chimiques dans les milieux aquatiques avec pour objectif de protéger les populations naturelles. Cependant, ce niveau de protection visé ne peut être utilisé facilement pour établir un lien direct entre une contamination et ses effets. Pour palier cette difficulté, les approches multi-échelles basées sur l'étude des effets des contaminations sur des marqueurs individuels puis sur l'extrapolation de ces effets au niveau des poipulations à partir de modèles de dynamique de population représentent des démarches prometteuses et commencent à être bien acceptées dans les démarches prédictives.Cependant, leur utilisation pour le diagnostic de la qualité des milieux aquatiques reste pour le moment très rare, d'une part en raison de la forte variabilité des réponses des marqueurs individuels in situ liée à l'influence de divers facteurs environnementaux confondants pour l'évaluation de la toxicité, et d'autre part à cause du manque de pertinence environnementale des modèles actuellement proposés. Centré sur l'utilisation de deux espèces couramment observées dans les cours d'eau européens et présentant des caractéristiques écologiques et phylogéniques contrastées : le crustacé Gammarus fossarum et le mollusque Potamopyrgus antipodarum, ce travail doctoral a permis : 1- de proposer une méthodologie pour prendre en compte l'influence des facteurs de confusion dans le but d'améliorer la lecture des bioessais in situ basés sur la mesure des marqueurs individuels sur des organismes encagés et 2- de développer des modèles de dynamique de population écologiquemnt pertinents
The regulatory framework lead to increase the assessments of the ecological risk linked to the dischaarge of chemical substances in aquatic environment with the aim to protect natural populations. However, this target level of protection cannot be used so easily to etablish a direcet link between a contamination and its effects. In order to overcome this difficulty, the multi-scale approaches based on the study of the effects of the contaminations on individual markers and then on the extrapolation of these effects at the population level with population dynamic models reprensent promising tools and start to bewell accepted in predictive processes. Yet, their use for the diagnosis of water quality remainsrare for the moment, on the one hand, because of the important varaibility of answers of individual makers in situ linked to the influence of diverse confounding environmental factors for the assessments of toxicity and, on the other hand, because pf the lack of environmental relevance of models currently proposed. Focused on the use of 2 species widely observed in European rivers and presenting contrastingecological and phylogenetic characteristics : the Grammar fossarum crutacean and the Potamopyrgus antipodarum mollusc, this doctoral degree first propose a methodology to consider the influenceof confounding factors in order to improve the reading of biological in situ tests based on the measurment of individual markers on caged organisms and second, to develop ecologically relevant population models. Thus, this work allowed to underline the importance of the consideration of confounding factors (i.e. temperature), in different in situ tests based on the measurment of individul markers on caged organisms. Moreover, population models for both species have been defined in order to test the influence of life histories and seasonal variations on demographic sensitivity of populations

À l’heure actuelle, les démarches écotoxicologiques (i.e. bioessais de laboratoire, approches biomarqueurs, tests in situ) évaluent les effets des contaminants majoritairement sur des temps de réponse courts, qui ne correspondent pas à l’échelle temporelle de la dynamique des populations. En plus de la toxicité manifestée au cours de l’exposition chimique, des effets peuvent pourtant s’observer plus tardivement au cours de la vie des organismes, voire de leur descendance. Ces effets différés peuvent avoir une influence importante sur la démographie, la résilience et l’acquisition de tolérance des populations ainsi que leur vulnérabilité face à de nouvelles perturbations environnementales. Leur étude constitue ainsi un véritable enjeu pour améliorer la compréhension des réponses des populations au stress chimique dans les écosystèmes. Dans ce contexte, l’objectif général de cette thèse a été d’explorer les effets intergénérationnels et transgénérationnels de l’exposition aux contaminants et leurs conséquences sur le fonctionnement des populations de l’espèce sentinelle Gammarus fossarum (Crustacé). Le parti-pris expérimental appliqué tout au long de ce travail combinant expérimentation multi-génération et modélisation en dynamique de population, a consisté à mettre en œuvre des expositions limitées à la génération parentale initiale (F0), puis à suivre le développement de trois générations successives en milieu non contaminé. Compte-tenu de l’implication potentiellement importante des mécanismes épigénétiques dans l’apparition d’effets différés, la méthylation globale des cytosines de l’ADN a été explorée pour la toute première fois chez cette espèce. Cette marque épigénétique s’est avérée être sensible au stress thermique, chimique avec le cadmium et à la privation alimentaire dans des conditions contrôlées au laboratoire. Une variabilité importante du niveau de base du biomarqueur entre populations naturelles de Gammarus fossarum a également été observée. Par ailleurs, suite à des expositions parentales de 3 semaines au cadmium et à la 3,4dichloroaniline, nous avons mis en évidence l’existence d’effets en cascade sur les traits d’histoire de vie de G. fossarum jusqu’à la troisième génération de descendants, après plus d’un an d’expérimentation. Nos travaux suggèrent également un rôle prépondérant des compromis entre les traits d’histoire de vie et entre les générations dans l’émergence des effets différés. Ces compromis se traduisent par un maintien de la capacité démographique de la population suite à l’exposition parentale au cadmium et sont ainsi certainement contraints par la stratégie d’histoire de vie de Gammarus fossarum. Au bilan, ces résultats soulignent l’intérêt de mener des études au-delà de la première génération de descendants et de généraliser les études à long terme sur les espèces environnementales non-modèles de laboratoire pour améliorer la compréhension des réponses populationnelles à la contamination et la pertinence écologique de l’évaluation actuelle des risques
Most of the current ecotoxicological approaches (i.e. laboratory bioassays, biomarker, in situ tests) assess the effects of contaminants at the individual level on short response time, that do not match the time scale of population dynamics. In addition to toxicity occurring during the chemical exposure of individuals, effects can arise later along the lifetime of organisms and of their progeny. Such delayed effects can lead to significant impact on population demography, resilience and tolerance, as well as on population vulnerability to new environmental disruptions. Studying these effects is a real challenge to improve the understanding of population response to chemical stress in ecosystems. In this context, the main purpose of this thesis was to explore intergenerational and transgenerational effects of parental contaminant exposure and their consequences on the functioning of the populations in the sentinel species Gammarus fossarum (Crustacea). To do so, challenging oneyear lab experiment together with population dynamics modelling were performed. The experimental statement was to only expose the parental generation (F0) and then to monitor the development of successive generations in an uncontaminated environment. Assuming a prevalent involvement of epigenetic mechanisms in the onset of delayed effects, this work explored for the first time the global genomic cytosine methylation level in Gammarus fossarum. The studied epigenetic mark was shown to be sensitive to heat stress, chemical stress (cadmium) and to food starvation in controlled laboratory conditions. A substantial variability in the basal level between several natural populations of Gammarus fossarum was also recorded. In the light of the multi-generational experiments, cascading effects were observed on G. fossarum life history traits until the third offspring generation after the parental exposure to cadmium or 3,4-dichloroaniline. In addition, a significant role of trade-offs between life-history traits and between generations can be suggested in the emergence of delayed effects. These trade-offs translate into the maintenance of demographic population capacity after the parental cadmium exposure and could be consequently constrained by life history strategy of Gammarus fossarum. Hence, these results highlight the interest of expanding the studied response time beyond the first offspring generation and of studying the long-term effects of chemical stress in non-target environmental species. Such approaches can be suggested to improve the understanding of natural population responses to contamination and to upgrade the ecological relevance of the current risk assessment

Sur la base des faibles variations de contraintes poroélastiques qui sont à l'origine de la séismicité déclenchée localement par la baisse de pression du gisement de Lacq, on tente dans le chapitre 3 d'évaluer les échelles spatiales des connections fluides dans la croûte supérieure à l'aide de la migration des fronts de pression induits. Les séismes associés à la mise en eau d'une retenue artificielle (M 4-5, Monteynard, Vercors, France) permettent par exemple de cartographier des failles sismiques potentielles au sud de l'agglomération grenobloise, les séismes induits jouant alors le rôle de jauges de contrainte. Dans la région de Lacq, à l'aide de modélisations analytiques des transferts de contraintes visco-élastiques et poro-élastiques, on montre qu'on ne peut rejeter a-priori des interactions entre l'extraction du champ de Lacq, les séismes majeurs de la faille Nord-Pyrénéenne distants d'une trentaine de kilomètres, et les séismes locaux à l'aplomb du champ d'hydrocarbure. Le chapitre 4 constitue une synthèse des mécanismes d'instabilités sismiques déclenchées par les exploitations d'hydrocarbures. On isole trois classes de mécanismes de déclenchements des séismes correspondant à des types d'exploitations et à des réponses sismiques (taille-temps-espaces) bien différenciés: augmentation de pression due à l'injection de fluide; baisse de pression due à extraction de fluide, déficit de masse lors d'extraction massive. Les mécanismes de ruptures sont en accord avec les lois de contraintes effectives, et s'expliquent soit par des transferts poroélastiques soit par des compensations isostasiques. Si la sismicité induite par les extractions de fluides reste marginale par rapport au nombre de gisements exploités, la surveillance sismique fine effectuée sur les gisements montre que de nombreux petits séismes (M < 3) sont présents et permettent un suivi in-situ du comportement des réservoirs au cours de l'exploitation. Notre approche de la séismicité à l'aide des séismes induits par des activités humaines montre les limites des lois de la mécanique classique qui, si elles permettent de comprendre et d'évaluer les seuils critiques qui déclenchent les instabilités sismiques, ne peuvent expliquer ni la durée des phénomènes d'instabilités qui sont entretenus durant de nombreuses années ni la taille des instabilités sismiques (Mmax 7). Sur la base des cas mondiaux de séismicité induite on propose la notion de Systèmes Critiques Auto Organisés Induits où l'on peut observer la genèse, la pérennité et la disparition de systèmes critiques dans un contexte, proposé par ailleurs, d'état critique auto-organisé pour l'ensemble de la croûte supérieure.

The Western U.S. has experienced widespread extension during the past 10’s of millions of years, largely within the Basin and Range and Rio Grande Rift provinces. Tomography results from previous studies revealed narrow fast seismic velocity anomalies in the mantle on either side of the Rio Grande Rift as well as at the western edge of the Colorado Plateau. The fast mantle anomalies have been interpreted as down-welling that is part of small scale mantle convection at the edge of extending provinces. It was also found that crust was thicker than average ab¬¬ove the possible mantle down-welling, indicating that mantle dynamics may influence crustal flow. We present results from P/S conversion receiver functions using SIEDCAR (Seismic Investigation of Edge Driven Convection Associated with the Rio Grande Rift) data to determine crustal and lithospheric structure beneath the east flank of the Rio Grande Rift. Crustal and lithosphere thickness are estimated using P-to-S and S-to-P receiver functions respectively. Receiver function migration methods were applied to produce images of the crust and lithosphere. The results show variable crustal thickness through the region with an average thickness of 45 km. The crust achieves its maximum thickness of 60km at 105W longitude, between 33.5N and 32.2N latitude. This observation confirms previous receiver function results from Wilson et al, 2005. Body wave tomography (Rocket, 2011; Schmandt and Humphreys, 2010) using similar data to what we used for the receiver function analysis, shows mantle downwelling closely associated with the thickened crust. We believe that the thickened crust might be due to lower crustal flow associated with mantle downwelling or mantle delamination at the edge of the Rio Grande Rift. In this model the sinking mantle pulls the crust downward causing a pressure gradient within the crust thus causing the flow. Our S-P images show signal from the lithosphere-asthenosphere boundary (LAB) with an average LAB thickness of 100 km but with a sharp transition at about 1050 W from 75 km to over 100 km. The region with abnormally thick crust overlies a region where the lithosphere appears to have a break. We interpret our results as showing that lower lithosphere has and is delaminating near the edge of the Great Plains accompanied by lower crustal flow in some places determined by lower crustal viscosity.
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In this thesis, an integrated structural and chemical approach has been used to investigate the spatial and temporal evolution of fluid chemistry, and fluid flow pathways, during crustal shortening. The Taemas Vein Swarm is hosted in a limestone-shale sequence, the Murrumbidgee Group, in the Eastern Belt of the Lachlan Orogen, in New South Wales, Australia. The Taemas Vein Swarm (TVS) is composed of calcite ± quartz veins, hosted in a series of faults and fractures, which extends over an area of approximately 20 km2. The Murrumbidgee Group is composed of several formations, comprising massive grey micritic limestones, redbed sandstones and shales,and thinly interbedded (10–20 cm scale) limestones and shales. ¶ ...

碩士
國立臺灣師範大學
地球科學系
105
Orogeny refers to the event of making mountain belt. During orogeny, a mountain belt experienced different orogenic stages, including syn-orogeny, post-orogeny, and an-orogeny, with various conditions of temperature, pressure, geochemical signature, stress and fluid pressure. Researchers usually expect to observe different stress regimes corresponding to different orogenic stages. So far, no document had reported the phenomena of stress evolution from reverse faulting via strike-slip faulting to normal faulting stress regimes in stages of syn-orogenic, post-orogenic and an-orogenic, respectively. However, Study of dikes from Kinmen Island can shed light to show the stress evolution of orogeny. The Kinmen Island, located in the southeastern continental margin of Mainland China, cropped out the middle-lower continental crust, which was experienced different deformation and metamorphism during Late Yenshanian Orogeny. Based on previous studies of geochemistry, geochronology, and P-T condition, different types of dikes are identified. They are syn-orogenic dikes of amphibolite (138-132Ma), post-orogenic dikes of pegmatite and aplite (110-100Ma), and an-orogenic dike of gabbro (94-76Ma). The mechanism of dike development is when magma pressure overcomes the minimum stress, magma can create the intrusive dike perpendicular with the minimum stress. By investigating the distribution and attitude of dikes with different lithologies, stress orientation corresponding to the different orogenic stage can be estimated. With the constraint of rock strength, mean stress from geobarometer and vertical stress in each stage, the magnitude of stress field and magma pressure for each stage can be further calculated. This research restructured crustal dynamics evolution during Late Yanshanian Orogeny by measuring the attitude of dike around Kinman and Leiyu island. (1) Compared with orogenic stage and crustal stress regime: syn-orogeny was reverse faulting stress regime, post-orogeny and an-orogeny were normal faulting stress regime. But, the value of post-orogenic stage stress field was strike-slip faulting stress regime. (2) As the syn-orogenic stage, amphibolite and tonalite dike intrusion appeared as low dip angle, which reflected that reverse faulting regime and horizontal maximum stress direction in E-W orientation. This orientation was oblique the orientation of mountain belt, NW-SE. The stress ratio was 0.54±0.18. The fluid ratio was 0.59. The intrusive depth was 24.9km. These result reflected ellipsoid reverse faulting stress regime. The geothermal gradient was 30.1℃/km. Dikes formed in the environment, which fluid pressure were higher than lithostatic pressure. Integrate with outcrop result, the stress regime would change to strike-slip faulting stress regime or normal faulting stress regime. (3)As the post-orogenic stage, this study uses the attitude of pegmatite and aplite dike. Geobarometer uses Al-amp geobarometer inland, SE China. The str ess ratio was 0.69±0.14. The fluid ratio was 1.02. The intrusive depth was 5.5km. These result reflected plate normal faulting stress regime and horizontal maximum stress direction in NW-SE. The geothermal gradient was 93.5℃/km. Dikes formed in the environment, which fluid pressure was higher than lithostatic pressure. (4)Finally, an-orogenic dike intrusion struck NE-SW with steep dip angle direction, which reflected that normal faulting regime and NE-SW horizontal maximum stress direction. The stress ratio was 0.68±0.08. The fluid ratio was 0.72 or 0.17. The intrusive depth was 4.5km. The geothermal gradient was 77.7℃/km. These result reflected plate normal faulting stress regime. Dikes formed in the environment, which fluid pressure were lower than lithostatic pressure. (5)The vertical stress variation, a.k.a. erosion velocity ,in Kinmen area during Late Yanshanian Orogeny, syn-orogenic stage to post-orogenic stage erosion velocity was 0.82-0.49mm/yr, and post-orogenic stage to an-orogenic stage was 0.35-0.04mm/yr.

Ocean-continent convergence and subsequent continental collision are responsible for continental growth, mountain building, and severe tectonic events including volcanic eruptions and earthquake activity. They are also key driving forces behind the extensive thermal and compositional heterogeneities at crustal and mantle depths. Active subduction along the Calabrian Arc in southern Italy and the Hellenic Arc are examples of such collisional tectonics. The first part of this thesis examines the subduction related deformations within the crust beneath the southern Apennines. By modeling regional surface wave recordings of the largest temporary deployment in the southern Apennines, a lower-crustal/upper-mantle low-velocity volume extending down to 50 km beneath the mountain chain is identified. The magnitude (~ 0.4 km/s slower) and anisotropic nature (~ 10%) of the anomaly suggest the presence of hot and partially molten emplacement that may extend into the upper-crust towards Mt. Vulture, a once active volcano. Since the Apulian basement units are deformed during the compressional and consequent extensional events, our observations favor the ``thick-skin'' tectonic growth model for the region. In the deeper mantle, active processes are thermodynamically imprinted on the depth and strength of the phase transitions. This thesis examines more than 15000 SS precursors and provides the present-day reflectivity structure and topography associated with these phase transitions. Through case studies I present ample evidence for both slab penetration into the lower mantle (beneath the Hellenic Arc, Kurile Island and South America) and slab stagnation at the bottom of the Mantle Transition Zone (beneath the Tyrrhenian Sea and eastern China). Key findings include (1) thermal anomalies (~ 200 K) at the base of the MTZ, which represent the deep source for Cenozoic European Rift Zone, Mount Etna and Mount Cameroon volcanism, (2) significant depressions (by 20-40 km) at the bottom of the Mantle Transition Zone beneath subducting slabs, (3) a strong 520-km reflector near subducting slabs, (4) a weak and elevated (15-25 km) 410-km reflector within active deformation zones, (5) strong lower mantle reflectors (~ 900 km) while slabs penetrate into the lower mantle, and (6) consistency between the topography of a 300-km reflector and an exothermic phase transformation.
Geophysics

The accessibility of the Martian atmosphere to spacecraft provides an opportunity to study an ionosphere that differs from our own. Yet, despite the half century of measurements made at Mars, the current state of the neutral atmosphere and its embedded plasma (ionosphere) remains largely uncharacterized. In situ measurements of the neutral and ionized constituents versus height exist only from the two Viking Landers from the 1970s. Subsequent satellite and remote sensing data offer sparse global coverage of the ionosphere. Thermal characteristics of the plasma environment are not well understood. Patchy crustal magnetic fields interact with the Martian plasma in a way that has not been fully studied. Hence, investigating the coupled compositional, thermal and crustal-field-affected properties of the ionosphere can provide insight into comparative systems at Earth and other planets, as well as to atypical processes such as the solar wind interaction with topside ionospheric plasma and associated pathways to escape. Ionospheric models are fundamental tools that advance our understanding of complex plasma systems. A pre-existing one-dimensional model of the Martian ionosphere has been upgraded to include more comprehensive chemistry and transport physics. This new BU Mars Ionosphere Model has been used to study the composition, thermal structure and dynamics of the Martian ionosphere. Specifically: the sensitivity of the abundance of ions to neutral atmospheric composition has been quantified, diurnal patterns of ion and electron temperatures have been derived self-consistently using supra-thermal electron heating rates, and the behavior of ionospheric plasma in crustal field regions was simulated by constructing a two-dimensional ionospheric model. Results from these studies were compared with measurements and show that (1) ion composition at Mars is highly sensitive to the abundance of neutral molecular and atomic hydrogen, (2) lighter ions heat up more efficiently than heavier ones and provide additional heating sources for cooler plasma, and (3) crustal field morphology affects plasma dynamics and structure at Mars in a way that is consistent with observations. Finally, model predictions of ion composition and plasma temperatures are provided for observations to be made by several instruments on board the upcoming 2013 MAVEN orbiter.

abstract: Seismic observations have revealed two large low shear velocity provinces (LLSVPs) in the lowermost mantle beneath Pacific and Africa. One hypothesis for the origin of LLSVPs is that they are caused by accumulation of subducted oceanic crust on the core-mantle boundary (CMB). Here, I perform high resolution geodynamical calculations to test this hypothesis. The result shows that it is difficult for a thin (~ 6 km) subducted oceanic crust to accumulate on the CMB, and the major part of it is viscously stirred into the surrounding mantle. Another hypothesis for the origin of LLSVPs is that they are caused by thermochemical piles of more-primitive material which is remnant of Earth's early differentiation. In such case, a significant part of the subducted oceanic crust would enter the more-primitive reservoir, while other parts are either directly entrained into mantle plumes forming on top of the more-primitive reservoir or stirred into the background mantle. As a result, mantle plumes entrain a variable combination of compositional components including more-primitive material, old oceanic crust which first enters the more-primitive reservoir and is later entrained into mantle plumes with the more-primitive material, young oceanic crust which is directly entrained into mantle plumes without contacting the more-primitive reservoir, and depleted background mantle material. The result reconciles geochemical observation of multiple compositional components and varying ages of oceanic crust in the source of ocean-island basalts. Seismic studies have detected ultra-low velocity zones (ULVZs) in some localized regions on the CMB. Here, I present 3D thermochemical calculations to show that the distribution of ULVZs provides important information about their origin. ULVZs with a distinct composition tend to be located at the edges of LLSVPs, while ULVZs solely caused by partial melting tend to be located inboard from the edges of LLSVPs. This indicates that ULVZs at the edges of LLSVPs are best explained by distinct compositional heterogeneity, while ULVZs located insider of LLSVPs are better explained by partial melting. The results provide additional constraints for the origin of ULVZs.
Dissertation/Thesis
Doctoral Dissertation Geological Sciences 2015