Dissertations / Theses on the topic 'Mantel plumes'
To see the other types of publications on this topic, follow the link: Mantel plumes.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Mantel plumes.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Treml, Markus. "The Seismic Signature of Mantle Plumes." Diss., lmu, 2006. http://nbn-resolving.de/urn:nbn:de:bvb:19-62692.
Full text
2
Styles, Elinor Elizabeth. "Seismic expressions of thermochemical mantle plumes." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/9002.
Full textAbstract:
Over the last decade of geophysical research the concepts of hotspots and plumes have taken a central role in discussions of the interior structure of the Earth and global geodynamic plate and convection models. In this study, I focus on the ability of thermal and/or thermochemical plumes to reproduce global and regional seismic observations at hotspot locations on Earth. In order to make meaningful interpretations of seismic images from global tomographic images I begin with an investigation into the physical meaning of seismic reference models and a full exploration of the temperature and compositional sensitivities of mantle seismic velocities, utilising a fully consistent forward modelling approach with up-to-date mineral physics parameters and associated uncertainties. I determine that, despite three-dimensional complexity of the mantle, averaged seismic structure reflects the average radial physical structure of the mantle except near phase boundaries and within thermal boundary layers. In the second half of the study I produce synthetic plume signatures by converting the thermo-chemical strutures of a range of plausible dynamic whole mantle plumes into seismic velocities-including the effect of seismic resolution in global tomographic models by convolution of the seismic structures with a resolution filter for the global model S40RTS. Quantitative comparison of synthetic signatures with global seismic observations beneath a number of hotspots indicates that more than half of all studied locations are underlain by low-velocity anomalies with widths and magnitudes compatible with thermal plumes. Other locations, e.g. Iceland, require plumes with time-dependent morphologies, modified by chemistry or phase buoyancy forces. I next forward model the predicted transition zone seismic structure for a number for thermal and thermochemical whole mantle plume scenarios, before commenting on suitability of using transition zone thickness beneath hotspots as a proxy for temperature. Lastly, I finish with a discussion of how such an analysis might be extended to other terrestrial planets, such as Mars.
3
Mailer, Tina. "Neon, Helium and Argon isotope systematics of the Hawaiian hotspot." Phd thesis, Universität Potsdam, 2009. http://opus.kobv.de/ubp/volltexte/2009/3963/.
Full textAbstract:
This study presents noble gas compositions (He, Ne, Ar, Kr, and Xe) of lavas from several Hawaiian volcanoes. Lavas from the Hawaii Scientific Drilling Project (HSDP) core, surface samples from Mauna Kea, Mauna Loa, Kilauea, Hualalai, Kohala and Haleakala as well as lavas from a deep well on the summit of Kilauea were investigated.
Noble gases, especially helium, are used as tracers for mantle reservoirs, based on the assumption that high 3He/4He ratios (>8 RA) represent material from the deep and supposedly less degassed mantle, whereas lower ratios (~ 8 RA) are thought to represent the upper mantle.
Shield stage Mauna Kea, Kohala and Kilauea lavas yielded MORB-like to moderately high 3He/4He ratios, while 3He/4He ratios in post-shield stage Haleakala lavas are MORB-like.
Few samples show 20Ne/22Ne and 21Ne/22Ne ratios different from the atmospheric values, however, Mauna Kea and Kilauea lavas with excess in mantle Ne agree well with the Loihi-Kilauea line in a neon three-isotope plot, whereas one Kohala sample plots on the MORB correlation line.
The values in the 4He/40Ar* (40Ar* denotes radiogenic Ar) versus 4He diagram imply open system fractionation of He from Ar, with a deficiency in 4He. Calculated 4He/40Ar*, 3He/22Nes (22NeS denotes solar Ne) and 4He/21Ne ratios for the sample suite are lower than the respective production and primordial ratios, supporting the observation of a fractionation of He from the heavier noble gases, with a depletion of He with respect to Ne and Ar. The depletion of He is interpreted to be partly due to solubility controlled gas loss during magma ascent. However, the preferential He loss suggests that He is more incompatible than Ne and Ar during magmatic processes. In a binary mixing model, the isotopic He and Ne pattern are best explained by a mixture of a MORB-like end-member with a plume like or primordial end-member with a fractionation in 3He/22Ne, represented by a curve parameter r of 15 (r=(³He/²²Ne)MORB/(³He/²²Ne)PLUME or PRIMORDIAL).
Whether the high 3He/4He ratios in Hawaiian lavas are indicative of a primitive component within the Hawaiian plume or are rather a product of the crystal-melt- partitioning behavior during partial melting remains to be resolved.Ozeaninselbasalte (OIBs), die durch Intraplatten-Vulkane gebildet werden wie z.B. Hawaii, sind geochemisch oft durch variable Isotopensignaturen charakterisiert, die verschiedene Mantelquellen widerspiegeln. Diese Variationen können über kurze Distanzen auf lokalem Maßstab auftreten. Im Rahmen dieser Arbeit wurden Edelgasisotopenzusammensetzungen (He, Ne, Ar, Kr, Xe) verschiedener hawaiianischer Vulkane ermittelt. Bohrkernproben vom Hawaii Scientific Drilling Project (HSDP), Oberflächenproben von den Vulkanen Mauna Kea, Mauna Loa, Kilauea, Hualalai, Kohala und Haleakala, sowie Proben aus einer Bohrung am Gipfel des Kilauea wurden untersucht. Edelgase, insbesondere Helium, dienen als geochemische Tracer. Dies ist auf der Annahme begründet, dass hohe 3He/4He Verhältnisse (> 8 RA) (RA ist das atmosphärische 3He/4He Verhältnis) Material aus dem tiefen Erdmantel repräsentieren, während niedrigere 3He/4He Verhältnisse (~ 8 RA) dem oberen Erdmantel entsprechen. Mauna Kea, Kohala und Kilauea Laven erreichten 3He/4He Verhältnisse zwischen 8 und 18 RA, während Haleakala Laven 3He/4He Verhältnisse von ~ 8 RA nicht überschreiten. Nur wenige Proben zeigten 20Ne/22Ne und 21Ne/22Ne Verhältnisse unterschiedlich vom Luftwert, was auf eine Herkunft aus dem tiefen Erdmantel schließen lässt. Edelgasisotopenwerte weisen auf eine Fraktionierung von He und Ar hin, mit einem Defizit an He. Berechnete 4He/40Ar*, 3He/22Nes (22NeS ist solares Ne) and 4He/21Ne Verhältnisse für die Proben sind niedriger als die entsprechenden Produktions- und primordialen Verhältnisse. Dies unterstützt die Beobachtung einer Fraktionierung von He gegenüber den schwereren Edelgasen, mit einer Verarmung von He gegenüber Ne und Ar. Ein beitragender Faktor bei der He Verarmung ist der löslichkeitskontrollierte Gasverlust während des Magmenaufstiegs. Der bevorzugte Verlust von He lässt jedoch auch darauf schließen, dass He sich bei magmatischen Prozessen inkompatibler verhält als Ne und Ar. Inwiefern die hohen 3He/4He Verhältnisse in hawaiianischen Laven ihren Ursprung in primitiven Komponenten innerhalb des hawaiianischen Plumes haben oder vielmehr in dem Verteilungsverhalten zwischen Mineralphase und Schmelze begründet sind, bleibt zu klären.
4
Xue, Jing. "Wavefront Healing and Tomographic Resolution of Mantle Plumes." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/50423.
Full textAbstract:
To investigate seismic resolution of deep mantle plumes as well as the robustness of the anti-correlation between bulk sound speed and S wave speed imaged in the lowermost mantle, we use a Spectral Element Method (SEM) to simulate global seismic wave propagation in 3-D wavespeed models and measure frequency-dependent P-, S-, Pdiff- and Sdiff-wave traveltime anomalies caused by plume structures in the lowermost mantle. We compare SEM time delay measurements with calculations based on ray theory and show that an anti-correlation between bulk sound speed and S-wave speed could be produced as an artifact. This is caused by different wavefront healing effects between P waves and S waves in thermal plume models. The bulk sound speed structure remains poorly resolved when P-wave and S-wave measurements are at different periods with similar wavelength. The differences in wave diffraction between the two types of waves depend on epicentral distance and wave frequency. The artifact in anti-correlation is also confirmed in tomographic inversions based on ray theory using Pdiff and Sdiff time delay measurements made on the SEM synthetics. This indicates a chemical origin of "superplumes" in the lowermost mantle may not be necessary to explain observed seismic traveltimes. The same set of Pdiff and Sdiff measurements are inverted using finite-frequency tomography based on Born sensitivity kernels. We show that wavefront healing effects can be accounted for in finite-frequency tomography to recover the true velocity model.Master of Science
5
Bredow, Eva [Verfasser], and Bernhard [Akademischer Betreuer] Steinberger. "Geodynamic models of plume-ridge interaction : case studies of the Réunion, Iceland and Kerguelen mantle plumes / Eva Bredow ; Betreuer: Bernhard Steinberger." Potsdam : Universität Potsdam, 2017. http://d-nb.info/1219514403/34.
Full text
6
Halkett, Angus Rex William. "Mantle plumes and the sedimentary record : onshore-offshore India." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268908.
Full text
7
Hassan, Raquibul. "Dynamics of Mantle Plumes and Their Influence on Paleotopography." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15171.
Full textAbstract:
The present-day structure of the Earth’s mantle, as revealed by an array of geophysical and geochemical observations, features plumes that rise from the deep lower mantle to the base of the lithosphere. Arrival of plume heads beneath the lithosphere is associated with the formation of large igneous provinces on the Earth’s surface. Following the eruption of a plume head, long-lived plume tails are responsible for continued magmatism associated with volcanic hotspot tracks, while dynamic topography associated with their interactions with continental lithosphere bears important implications for the evolution of paleotopography. This thesis investigates the spatial distribution of mantle plumes that erupted over the last 200 Myrs, their subsequent lateral migration and their influence on paleotopography. We investigate the influences of lower mantle chemical heterogeneities on the nucleation and eruption of plumes in paleogeographically constrained global models of mantle convection spanning the last 200 Myrs. We show that plume eruption locations in models with a chemically anomalous lower mantle are highly correlated with reconstructed eruption locations of large igneous provinces that erupted over the last 200 Myrs — those in purely thermal models show a weaker correlation. Plumes in thermochemical models are anchored to peaks of ridges extant within large-scale thermochemical structures that can morph and migrate laterally in response to subduction-induced flow. Subsequently, we derive spatiotemporal analytics of flow in the deepest lower mantle and show that edges of these thermochemical structures can undergo rapid asymmetric deformation in regions of strong coherent subduction-induced flow. Consequently, rapid motion of plume sources anchored to these regions causes the plumes to become strongly tilted. We show that the sharp bend in the Hawaiian-Emperor hotspot track is a consequence of the interplay of plume tilt and lateral advection of plume source. Asymmetric deformation of the thermochemical structure under the Pacific over the last 140 Myrs may explain the morphological diversity of surface hotspot tracks associated with deep mantle plumes in the Pacific. Moreover, we show that analogous flow dynamics caused the Afar plume and the thermochemical structure under Africa to migrate southward over the lifetime of the plume. Our analysis suggests that the space-time distribution of plume-related magmatism in east Africa and the associated trends in geochemical data are better explained by a moving Afar plume. We develop a new scalable code to investigate the influence of transient plume-related dynamic topography on the evolution of paleodrainage systems. Based on simple qualitative models of geomorphology, we suggest that a dynamic topography swell associated with the southward propagating Afar plume may have induced a reorganization of regional paleodrainage systems in east Africa.
8
Adena, Katherine Jane Daly. "Geochemical probing of mantle plume dynamics." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.707705.
Full text
9
Ito, Garrett Tetsuo. "Mantle plume-midocean ridge interaction : geophysical observations and mantle dynamics." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/59638.
Full text
10
Mota, Carlos Eduardo Miranda. "Petrogênese e geocronologia das intrusões alcalinas de Morro Redondo, Mendanha e Morro de São João: caracterização do magmatismo alcalino no Estado do Rio de Janeiro e implicações geodinâmicas." Universidade do Estado do Rio de Janeiro, 2012. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=5883.
Full textAbstract:
Os modelos para a formação de plútons alcalinos da Província Alcalina do Sudeste Brasileiro ou Alinhamento Poços de Caldas-Cabo Frio associam a gênese destas rochas a grandes reativações ou a passagem de uma pluma mantélica, registrada pelo traço de um hot spot. O objetivo desta tese é, apresentar novos dados e interpretações para contribuir com a melhor elucidação e discussão destes modelos. Os estudos incluem mapeamento, petrografia, litogeoquímica, geoquímica isotópica de Sr, Nd e Pb e datação 40Ar/39Ar. As intrusões selecionadas correspondem ao Morro Redondo, Mendanha e Morro de São João, no Rio de Janeiro, localizados em posições distintas no alinhamento Poços de Caldas-Cabo Frio. A intrusão alcalina do Morro Redondo é composta majoritariamente de nefelina sienitos e sienitos com nefelina, com rara ocorrência de rochas máficas e é caracterizada por uma suíte alcalina sódica insaturada em sílica, de caráter metaluminosa a peralcalina. Esta intrusão foi datada em aproximadamente 74 Ma (idade-platô 40Ar/39Ar). A intrusão alcalina do Mendanha é composta por diversos tipos de rochas sieníticas, além de brechas e estruturas subvulcânicas, como rochas piroclásticas e diques e caracteriza-se por ser uma suíte alcalina sódica saturada em sílica, de caráter metaluminosa, diferente do que ocorre no Marapicu, este subsaturado em sílica. Esta intrusão apresentou duas idades-platô 40Ar/39Ar distintas de magmatismo: 64 Ma para as rochas do Mendanha e 54 Ma em dique de lamprófiro, registrando magmatismo policíclico. O Morro do Marapicu foi datado em aproximadamente 80 Ma. Já a intrusão alcalina do Morro de São João possui uma ampla variedade de litotipos saturados a subsaturados em sílica, tais como sienitos, álcali-sienitos e monzossienitos (alguns portadores de pseudoleucita), com variedades melanocráticas, tais como malignitos e fergustios. Estas rochas definem suas distintas suítes alcalinas subsaturadas em sílica: Uma de composição sódica e outra potássica. Há também uma suíte alcalina saturada em sílica, definida por gabros alcalinos e shonkinitos. A petrogênese destas intrusões corresponde ao modelo de cristalização fracionada, com assimilação de rochas encaixantes (AFC) como indicado pela alta variabilidade de razões isotópicas de estrôncio. No Morro de São João é sugerido o modelo de mistura magmática. Estas intrusões foram geradas a partir de magmas mantélicos enriquecidos, possivelmente associados à antiga zona de subducção relacionada ao orógeno Ribeira. Em razão das novas idades obtidas, o modelo de hot spot proposto fica prejudicado, visto que o Marapicu é de idade mais antiga das intrusões analisadas, o que era esperado para o Morro Redondo. Alguns modelos projetam plumas mantélicas com aproximadamente 1000 km de diâmetro, o que poderia explicar o Mendanha ser contemporâneo ao Morro de São João. As assinaturas isotópicas obtidas para as intrusões não se associam à assinatura isotópica de Trindade e, caso o modelo de plumas mantélicas seja o correto, a pluma que teria maior semelhança de assinatura isotópica é a pluma de Tristão da Cunha.The models for formation of alkaline plutons of the Southeastern Brazil Alkaline Province or Poços de Caldas-Cabo Frio Magmatic Lineament, which genetic modeling associates crust reactivations or mantle plumes, with definition of a hot spot track. The objective of this work is to report new data and interpretations to contribute to a better understanding and discussion about the model of alkaline rock generation. The studies involved geological mapping, petrography, litogeochemistry, Sr-Nd-Pb isotopes and 40Ar/39Ar geochronology. The selected alkaline complexes are the Morro Redondo, Mendanha and Morro de São João, located at Rio de Janeiro State. These intrusions are well-distributed along the Poços de Caldas-Cabo Frio Magmatic Lineament. The Morro Redondo alkaline intrusion is composed mainly by nepheline syenites and nepheline-bearing syenites and mafic rocks are rare. It was defined as a sodic silica-undersaturated alkaline suite, with metaluminous to peralkaline characteristics. The intrusion was dated at 74 Ma (40Ar/39Ar plateau age). The Mendanha alkaline intrusion is compose by various types of syenitic rocks, breccias and subvulcanic structures, as pyroclastic rocks and dikes. It was defined by a sodic silica-saturated alkaline suite with metaluminous characterisics. The intrusion presented two distinct 40Ar/39Ar ages for the magmatism: 64 Ma for Mendanha rocks and 54 Ma to lamprophyre dike, which illustrates a polycyclic magmatism. The Morro do Marapicu 40Ar/39Ar age yielded 80 Ma. The Morro de São João alkaline intrusion has a large variety of silica-undersaturated to silica-saturated rocks, as syenites, alkali-syenites and monzosyenites (some pseudoleucite-bearing), with melanocratic varieties, as malignites and ferguites. These rocks defined distinct alkaline silica-undersaturated suggenting sodic and potassic types. There was found an alkaline silica-saturated suite, defined by alkaline gabbros and shonkinites. The petrogenesis of these intrusions corresponds to the fractional crystallization, with assimilation of host rocks, and the crustal contamination is indicated by high variability of Sr isotope ratios. For Morro de São João origin is suggested a K-Na bimodal magma. These intrusions were generated from enriched mantle-derived magmas, possible associated to ancient subduction zone of Ribeira orogen. In terms of the new 40Ar/39Ar data, the hot spot model is not plausible, because the Morro do Marapicu is older than the other studied intrusions. Some models projected mantle plumes with 1000 Km size, what may explain the reason for Mendanha and Morro de São João have the nearly the same age. The obtained isotopic signatures for these intrusions were not associated to Trindade signature and, if the mantle plumes model is correct, the plume that has the most similar signature is Tristão da Cunha.
11
Staples, Robert Kay. "Crustal structure above the Iceland mantle plume." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627379.
Full text
12
Watson, Sarah Penelope. "Hotspots and volcanism." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386840.
Full text
13
Liu, Mian. "Evolution of mid-plate hotspot swells, mantle plumes, and Hawaiian basalts." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184924.
Full textAbstract:
Studies of the evolution of hotspot swells, mantle plumes, and Hawaiian basalts are presented in three parts in this dissertation. In part 1, the evolution of mid-plate hotspot swells are simulated numerically as an oceanic plate rides over a hot, upwelling mantle plume. The transient heat transfer equations, with time- and space-dependent boundary conditions, are solved in cylindrical coordinates. Geophysical data are used to constrain the models. Formation of the Hawaiian swell requires a mechanism of convective thinning of the lithosphere. The models constrain the Hawaiian heat source to have a maximum anomalous temperature of 250-300°C, and a perturbing heat flux 5-6 times the background value. On the other hand, the Bermuda swell is likely produced by heat conduction due to weakness of the heat source. In part 2, an analytic model of axisymmetric mantle plumes is presented. Plume parameters beneath the lithosphere, which are constrained from the swell models, are used to infer the plume source regions. The Hawaiian plume likely originates near the core-mantle boundary, but other hotspots may have shallower sources. Chemical plumes are much narrower than thermal plumes because of low chemical diffusivity in the mantle. For mantle plumes driven by combined thermal-chemical diffusion, the chemical signature of the source regions may only be observed near plume centers. Finally, melt generation and extraction along the Hawaiian volcanic chain are discussed in part 3. As a part of the plate moves over the heat source, melting largely takes place in the region where the lithospheric material is engulfed and swept away by the flow of the heat source. At least three mantle components must be involved in the melt generation: the plume material, the asthenosphere, and the engulfed lithospheric material. Significant amount of melts may also come from direct melting of the upwelling plume at depths below the initial plate-plume boundary. Melt extracts continuously from an active partial melting zone of 10-20 km thick, which moves outward as heating and compaction proceed. The models explain quantitatively the general characteristics of Hawaiian volcanism as the result of plume-plate interaction.
14
Smallwood, John Richard. "Oceanic crust formed near the Iceland mantle plume." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627183.
Full text
15
Franken, Thijs. "Analysing partial melting in the Réunion mantle plume." Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7129.
Full textAbstract:
La fusion partielle dans la partie supérieure du manteau est fréquente dans les zones de remontée d’eau du manteau, comme les rifts, les dorsales médio-océaniques et les points chauds. Des zones de faible vitesse d’ondes de cisaillement dans le manteau peu profond (∼ 80 km) sont souvent associées à ces endroits, révélant des anomalies de vitesse de 4 à 5 % généralement attribuées à la présence de matériau fondu. Cependant, les études sur la quantité de matière fondue responsable de la réduction de la vitesse conduisent, suivant leur nature, à des conclusions différentes: les résultats expérimentaux de la pétrologie, des observations géochimiques et des modèles géodynamiques suggèrent une rétention de la matière fondue inférieure à 1 %, alors que les interprétations sismiques exigent une rétention supérieure à 1%. Dans cette thèse, j’essaie de résoudre le désaccord sur la rétention de la masse fondue dans l’asthénosphère en croisant des modèles de production de matériau en fusion et de propagation des ondes sismiques pour relier directement les conditions géodynamiques de la fusion partielle aux observations sismiques du panache mantellique de la Réunion. J’ai mis au point un modèle 1D de production de fusion qui évalue la rétention de la matière fondue selon le coefficient de perméabilité, la températures initiale du manteau et la vitesses de remontée d’eau selon un problème de Stokes modifié supposant un écoulement poreux. 210 scénarios de modèles de fusion sont convertis en vitesses d’ondes P et S sismiques anharmoniques à l’aide d’une base de données de paramètres minéraux, qui sont ensuite incorporés dans le modèle de référence de la terre ak135 pour générer des sismogrammes synthétiques des scénarios de fusion pour 21 tremblements de Terre. J’analyse l’effet du matériau fondu sur les composantes radiale, transversale et verticale de l’onde pour les arrivées de phase P, S, Pdiff et SKS. Grâce à une procédure automatisée de corrélation croisée, je calcule les différences relatives de temps de parcours entre les sismogrammes observés et les 210 traces synthétiques, pour chacun des 21 événements, 4 arrivées de phase, 3 composantes d’onde et 4 fréquences différentes de filtrage. J’analyse 70 896 points de données de temps de parcours relatifs pour trouver une solution optimale rendant compte des temps de parcours relatifs entre les traces du modèle et les observations sismiques, afin de découvrir quel scénario de fusion décrit le manteau supérieur sous la Réunion. La solution au scénario du modèle le mieux adapté n’est pas unique, puisque plusieurs combinaisons du coefficient de perméabilité, de température et de vitesse de remontée peuvent donner la même solution. En analysant séparément la distribution des paramètres du modèle sur la solution de temps de parcours relatif minimisé des 70 896 points de données pour les différentes arrivées de phase et composantes des ondes, on peut identifier deux régimes probables des conditions du manteau supérieur pouvant rendre compte des observations sismiques. Les conditions de manteau sous la Réunion se situent soit dans la plage de température de 1300 à 1350°C avec des fractions en fusion de ∼ 1 %, soit dans la plage de température de 1400 à 1450 °C avec des fractions en fusion inférieures à 0,3 %. Les contraintes des études sur la température du manteau supérieur, la perméabilité et les vitesses de transport du matériau fondu correspondent à ce dernier cas, ce qui souligne qu’une faible rétention de matériau fondu dans le manteau peu profond sous la Réunion satisfait simultanément les observations sismiques et les conditions géodynamiques prévuesPartial melting in the upper mantle is prevalent in areas of mantle upwelling such as rifts, mid-ocean ridges and hotspots. The presence of low shear-wave velocity zones in the shallow mantle (∼ 80km) are often associated with these locations, revealing velocity anomalies of −4 to −5% which are generally attributed to the presence of melt. However, studies on the quantity of melt responsible for the velocity reduction are divided, where experimental results from petrology, geochemical observations and geodynamical models suggest melt retention of < 1%, whereas seismic interpretations call for 1 > %. In this thesis I attempt to resolve the disagreement on melt retention in the asthenosphere by combining forward modelling of melt production and seismic wave propagation to relate geodynamic condition of partial melting directly to seismic observations of the Réunion mantle plume. I developed a 1D model of melt production that approximates melt retention for a range of permeability coefficients, initial mantle temperatures and upwelling velocities through a set of modified Stokes equations assuming porous flow. 210 melting model scenarios are converted to anharmonic seismic P- and S-wave velocities using a mineral parameter database, which are embedded into the ak135 earth reference model to generate synthetic seismograms of the melting scenarios for 21 source events using the Direct Solution Method for a laterally homogeneous and spherically symmetrical Earth. I explore the effect of melt presence on the radial, transverse and vertical wave component for the P, S, Pdiff and SKS phase arrivals, band-pass filtered to upper corner frequencies of 0.05, 0.1, 0.15 and 0.2 Hz. Through an automated cross-correlation procedure I compute relative traveltime differences between the observed seismograms and the 210 synthetic model traces for each iteration of the 21 source events, 4 phase arrivals, 3 wave components, and 4 band-pass filter frequencies. I analyse 70,896 relative traveltime datapoints to reach a solution for the minimised relative traveltimes between the model traces and the seismic observations, in order to discover which melting model scenario describes the upper mantle beneath Réunion. The solution to the best-fit model scenario is non-unique, since several combinations of the permeability coefficient, temperature and upwelling velocity give the same solution. By seperately analysing the parameter distribution of the free model parameters over the minimised relative traveltime solution of the 70,896 datapoints for the different phase arrivals and wave components, two likely regimes of upper mantle conditions can be constrained that can resolve the seismic observations. These regimes indicate that mantle conditions beneath Réunion are either in the 1300−1350 °C temperature range with melt fractions of ∼ 1%, or in the 1400−1450 °C temperature range with melt fractions of < 0.3%. Constraints from studies on upper mantle temperature, permeability and melt transportation velocities correspond to the latter case, showing that low retention of melt in the shallow mantle beneath Réunion simultaneously satisfy seismic observations and the expected geodynamic conditions
16
Xu, Guangping. "Origin of geochemical heterogeneity in the mantle : constraints from volcanism associated with Hawaiian and Kerguelen mantle plumes." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42275.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007.Includes bibliographical references.
Lavas derived from long-lived mantle plumes provide important information of mantle compositions and the processes that created the geochemical heterogeneity within the mantle. Kerguelen and Hawaii are two long-lived mantle plumes and lavas associated with them have very different geochemical characteristics. In this thesis I studied the geochemical compositions of the lavas associated with Kerguelen plume (Mt. Capitole in Kerguelen Archipelago) and Hawaiian plume (Mauna Kea, East Molokai and West Molokai volcanoes) to understand what processes contributed to the geochemical variations observed in Kerguelen and Hawaiian lavas and the geochemical structure of the mantle beneath them. Mt. Capitole is in the central part of the Kerguelen Archipelago and is attributed to Cenozoic volcanism arising from the Kerguelen hotspot. Based on the study of Mt. Capitole and previous isotopic data for the Kerguelen Plateau, Kerguelen Archipelago and Heard Island, I propose that two stages of mixing can explain the significant Sr, Nd, Hf and Pb isotopic heterogeneity. The first mixing process, best shown by the submarine lavas from Northern Kerguelen Plateau, is between a depleted component (i.e., relatively low 87Sr/86Sr with high 143Nd/144Nd and 176Hf/177Hf), probably related to Southeast Indian Ocean mid-ocean ridge basalt, but possibly intrinsic to the Kerguelen plume, and an enriched Kerguelen plume component. From -34 Ma to <1 Ma, on average the proportion of the depleted component decreased. Subsequently, a second mixing process involved addition of a component with relatively high 87Sr/86Sr (>0.7060) and low 143Nd/144Nd (<0.5125) and 176Hf/177Hf (<0.2827) and non-radiogenic Pb isotope ratios (<17.9 for 206Pb/204Pb).
(cont.) I infer that this component was lower continental crust. At Hawaii there are systematic geochemical differences between the < 3 My Hawaiian shields forming the subparallel spatial trends, known as Loa and Kea. East Molokai (> 1.5 Ma), the oldest volcano on the Kea-trend, maintains the Kea-like geochemical characteristics. As East Molokai and other Kea-trend volcanoes (Mauna Kea, Kohala, Haleakala and West Maui) migrate away from the hotspot and evolve from the shield to postshield stage, isotopic ratios of 87Sr/86Sr decrease and 143Nd/144Nd and 176Hf/177Hf increase in postshield lavas; however, all Kea postshield lavas have similar ratios of Sr, Nd, Hf and Pb showing that the periphery of the hotspot sampled by Kea-trend postshield lavas had long-term geochemical homogeneity (>1.5 My). The temporal changes in Sr, Nd and Hf isotope ratios are attributed to incorporation of a depleted component that dominantly sampled by rejuvenated stage lavas. This depleted component has Kea-trend Pb isotopic characteristics, relatively low 208Pb/204pb at a given 206Pb/204Pb, and it is probably not related to oceanic lithosphere or the source of mid-ocean ridge basalt. The Loa-Kea spatial geochemical differences end at West Molokai shield (- 1.9 Ma) which is the oldest Loa-trend volcano on the double parallel chains. West Molokai shield includes lavas with Loa- and Kea-like geochemical characteristics; a mixed Loa- Kea source is required. In contrast, West Molokai postshield lavas are exclusively Kea-like. This change in source geochemistry can be explained by the observed change in strike of the Pacific plate near Molokai Island so that as West Molokai volcano moved away from a mixed Loa-Kea source it sampled only the Kea side of a bilaterally zoned plume (Abouchami et al., Nature, v434, 2005).
by Guangping Xu.
Ph.D.
17
Hards, Victoria L. "The evolution of the Snaefell Volcanic Centre, eastern Iceland." Thesis, Durham University, 1995. http://etheses.dur.ac.uk/1452/.
Full text
18
Agrusta, Roberto. "How do mantle plumes help to thin and break up the lithosphere?" Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20135/document.
Full textAbstract:
On propose traditionnellement que les panaches mantelliques jouent un rôle important dans l'amincissement de la lithosphère. Des données sismologiques sous Hawaïi et Cape Verde suggèrent une limite lithosphère-asthénosphère (LAB) jusqu'à 50 km plus superficielle qu'autour. Des modèles numériques ont montré, en effet, qu'une convection à petite échelle (SSC, pour small-scale convection) dans la couche à faible viscosité formée à la base de la lithosphère par l'accumulation de la matière des panaches peut être un mécanisme efficace d'érosion du manteau lithosphérique. Cependant, ces modèles montrent que, si la plaque se déplace, l'érosion thermo-mécanique de la lithosphère ne dépasse pas 30 km. Afin de mieux étudier les interactions panache/lithosphère, et d'ainsi caractériser les paramètres contrôlant cette érosion, nous avons effectué des simulations numériques en 2D qui utilisent un modèle pétro-thermomécanique basé sur des approches en différences finies associées à des marqueurs actifs. Nous avons focalisé sur : (1) la dynamique de la SSC dans la couche à faible viscosité formée par étalement du panache à la base de la lithosphère et (2) l'effet de la fusion partielle sur cette dynamique. La plaque lithosphérique et le manteau sous-jacent sont caractérisés par une composition péridotitique homogène à viscosité newtonienne dépendante de la température et de la pression. Une vitesse constante, comprise entre 5 et 12,5 cm/an, est imposée au sommet de la plaque. Les panaches sont créés en imposant une anomalie thermique de 150 à 350 K en base du modèle (700 km de profondeur). La fusion partielle est calculée à partir d'un paramétrization des solidus et liquidus pour la fusion anhydre des péridotites. Nous modélisons la déplétion de la péridotite et son effet sur la fusion partielle en supposant que le degré de fusion ne peut qu'augmenter au cours du temps. Le liquide est accumulé jusqu'à un seuil et la masse fondue en excès est extraite instantanément. La rhéologie de la péridotite partiellement fondue est déterminée utilisant une constitutive relation basée sur un modèle de contiguïté, qui permet de prendre en compte les effets de la distribution de matière liquide à l'échelle de grain. La densité varie en fonction du degré de fusion partielle et de la déplétion du résidu solide. Nous analysons la cinématique du panache lors de son interaction avec une plaque mobile, la dynamique de la convection à petite-échelle (SSC) et le rajeunissement thermique de la lithosphère qui en résulte. Le temps de démarrage et la vigueur de la SSC et, par conséquent, le nouvel état d'équilibre thermique de la lithosphère à l'aplomb du panache dépendent du nombre de Rayleigh (Ra) dans la couche instable à la base de la lithosphère, qui est contrôlé par l'anomalie de température et la rhéologie dans cette couche. Pour des panaches chauds et vigoureux, le démarrage de la SSC ne dépend pas de la vitesse de la plaque. Pour des panaches plus faibles, le temps de démarrage diminue avec l'augmentation de la vitesse de la plaque. Ce comportement est expliqué par une différence dans la structure thermique de la lithosphère, due à des échanges diffusifs à la base lithosphère plus efficaces pour des panaches lents. La diminution de la viscosité associée à la présence de magma et la diminution de la densité du résidu solide accélèrent le démarrage et accroissent la vigueur de la SSC, entraînant une érosion plus efficace et plus proche du point d'impact de panache sous la lithosphèreMantle plumes are traditionally proposed to play an important role in thinning the lithosphere. Seismic images beneath Hawaii and Cape Verde, for instance, show a lithosphere-asthenosphere boundary (LAB) up to 50 km shallower than the surroundings. However, previous numerical modeling of plume-lithosphere interaction implies that unless the plate is stationary the thermo-mechanical erosion of the lithosphere does not exceed 30 km. We used 2D petrological-thermo-mechanical numerical models based on a finite-difference method on a staggered grid and marker in cell method to further study the plume-lithosphere interaction. We focused on: (1) analyzing the dynamics of the small-scale convection (SSC) in the plume wake as a function of the plume vigor and plate velocity and (2) quantifying the effect of partial melting on this SSC. A homogeneous peridotite composition with a Newtonian temperature- and pressure-dependent viscosity is used to simulate both the plate and the convective mantle. A constant velocity, ranging from 5 to 12.5 cm/yr, is imposed at the top of the plate. Plumes are created by imposing a thermal anomaly of 150 to 350 K on a 50 km wide domain at the base of the model (700 km depth); the plate right above the thermal anomaly is 40 Myr old. Partial melting is modeled using the batch-melting solidus and liquidus in anhydrous conditions. We model the progressive depletion of peridotite and its effect on partial melting by assuming that the melting degree only strictly increases through time. Melt is accumulated until a porosity threshold is reached and the excess melt is instantaneously extracted. The rheology of the partially molten peridotite is determined using a viscous constitutive relationship based on a contiguity model, which enables to take into account the effects of grain-scale melt distribution. The density varies as a function of the melt fraction and of the depletion of the residue. We analyze the kinematics of the plume as it impacts a moving plate, the dynamics of time-dependent small-scale convection (SSC) instabilities developing in the low-viscosity layer formed by spreading of hot plume material at the lithosphere base, and the resulting thermal rejuvenation of the lithosphere. The onset time and the vigor of SSC and, hence, the new equilibrium thermal state of the lithosphere atop the plume wake depends on the Rayleigh number (Ra) in the unstable layer at the base of the lithosphere, which is controlled by the temperature anomaly and rheology in the plume-fed layer. For vigorous, hot plumes, SSC onset times do not depend on plate velocity. For more sluggish plumes, SSC onset times decrease with increasing plate velocity. This behavior is explained by differences in the thermal structure of the lithosphere, due to variations in the spreading behavior of the plume material at the lithosphere base. Reduction of the viscosity in partial molten domains and decrease in density of the depleted residuum accelerate and enhance the vigor of small-scale convection in the plume-fed low-viscosity layer at the lithosphere base. It also reduces SSC onset times, leading to more effective erosion closer to the plume-lithosphere impact
19
Kahn, Aaron M. "Geophysical attributes of earth's hotspots and their potential associations with mantle plumes /." Columbus, Ohio : Ohio State University, 2004. http://hdl.handle.net/1811/6087.
Full text
20
Poore, Heather Rachel. "Neogene epeirogeny and the Iceland Plume." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612116.
Full text
21
Pears, M. I. B. "Stall and collapse in mantle plumes : an experimental and numerical fluid dynamics perspective." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1465981/.
Full textAbstract:
Collapsing thermal plumes were investigated through experimental and numerical simulations. Collapsing plumes are an uncommon fluid dynamical phenomenon, usually observed when the heat source is removed. A series of fluid dynamical experiments were conducted on thermal plumes at a variety of temperature and viscosity contrasts, in a cubic plexiglas tank of inner side dimension 26.5cm and no-slip sides. The fluid was heated by a small 2cm diameter heater. Experimental fluids included Lyle’s Golden syrup and ADM’s Liquidose 436 syrup, which have strongly temperature-dependent viscosities and high Prandtl numbers (10³-10⁵ at experimental conditions). Visualisation techniques included white light shadowgraphs and Stereoscopic Particle Image Velocimetry (SPIV) of the tank's central plane. Temperature contrasts ranged from 3-60°C, and two differing forms of collapse were identified. At very low temperature differences stalled collapse was observed, where the plumes stall in the lower third of the tank before collapsing. At temperature differences between 7-23°C normal plume evolution occurred, until lenticular collapse developed between midway and two-thirds of the distance from the base of the tank. The lens shape originated in the top of the head and was present throughout collapse. At temperatures above ΔT=23°C, the plumes followed the expected growth and shape and the head flattened out at the top of the tank. Thermal collapse remains difficult to explain given experimental conditions (continuous heating). Instead, it is possible that small density differences arising from crystallisation at ambient temperatures changes plume buoyancy and therefore induces lenticular collapse. The evolution of the refractive index of the syrup through time to ascertain this possibility was measured. Additionally, SPIV revealed the presence of a large, downwelling, low velocity mass in the tank that inhibited the growth of low temperature difference stalled collapse plumes. In the mantle it is likely that the stalled collapse plumes would be unable to be detected by tomography because they would be unable to traverse far from the thermal boundary layer and would collapse back to the base. This would mean that they would have little impact on redistributing material in the mantle. The plumes in this stalled collapse regime had rise times comparable to diffusion times, which is an additional reason for the collapse. The lenticular collapse in the mantle could cause depletion of a deep-source and redistribute the material in the region where the plume began to collapse with some material flowing back to the base of the mantle. Numerical simulations using Fluidity (Fluidity, is an adaptive mesh finite element package) were undertaken to explore the parameter range where the two collapse phenomena were observed experimentally. These simulated plumes did not show signs of collapse in the purely thermal simulation but at temperature differences up to 14°C the plumes stalled and were unable to ascend to the top of the tank. The aspect ratio of the tank was changed to explore the effect this had on plume stalling. At increased tank height the plume ascended further in the tank whilst the conduit radius remained constant. However, the very low temperature difference plumes remained unable to reach the upper surface of the tank. In contrast, when the tank width was increased the plumes ascended a little further in the tank but stalled at an earlier time and the plume conduit width generally increased. This implied that the tank width was inhibiting the growth of the plume marginally. Therefore, changing the aspect ratio of the tank does not inhibit the stalling of the simulated plumes and is unlikely to be influencing the experimental plumes growth, stalling and collapse.
22
Tan, Eh Ahrens T. J. "I. Multi-scale dynamics of mantle plumes : and II. Compressible thermo-chemical convection and the stability of mantle superplumes /." Diss., Pasadena, Calif. : Caltech, 2006. http://resolver.caltech.edu/CaltechETD:etd-05142006-210236.
Full text
23
Smit, Yvonne. "The Snaefellsnes transect : a geochemical cross-section through the Iceland Plume." Thesis, Open University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247048.
Full text
24
Mazza, Sarah Elizabeth. "Understanding Non-Plume Related Intraplate Volcanism." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/83554.
Full textAbstract:
Intraplate volcanism is a worldwide phenomenon producing volcanoes away from active plate boundaries, a process that cannot yet be sufficiently explained by plate tectonic processes, and thus is still a missing piece in the understanding of the dynamics and evolution of our planet. Models for the formation of intraplate volcanism are dominated by mantle plumes, but alternative explanations, such as adiabatic decompression triggered by lithospheric delamination, and edge driven convection (EDC), could be responsible for magmatism. This dissertation explores intraplate volcanic locations that do not fit the mantle plume model, and presents geochemical evidence for lithospheric delamination and edge driven convection for the cause of volcanism.
I studied an Eocene volcanic swarm exposed in the Appalachian Valley and Ridge Province of Virginia and West Virginia, which are the youngest known igneous rocks along the Eastern North American Margin (ENAM). These magmas provide the only window into the most recent deep processes contributing to the post-rift evolution of this margin. This study presents the first high precision 40Ar/39Ar ages along with new geochemical data, and radiogenic isotopes that constrain the melting conditions and the timing of emplacement. Modeling of the melting conditions suggests that melting occurred under conditions slightly higher than average mantle beneath mid-ocean ridges. Asthenosphere upwelling related to localized lithospheric delamination is a possible process that can explain the intraplate signature of these magmas that lack evidence of a thermal anomaly.
The Virginia-West Virginia region of the ENAM also preserves a second post-rift magmatic event in the Late Jurassic. By studying both the Late Jurassic and Eocene magmatic events we can better understand the post-rift evolution of passive margins. This study presents a comprehensive set of geochemical data that includes new 40Ar/39Ar ages, major and trace-element compositions, and analysis of radiogenic isotopes to further constrain their magmatic history. Modeling suggests that the felsic volcanics from both the Late Jurassic and Eocene events are consistent with fractional crystallization. Lithospheric delamination is the best hypothesis for magmatism in Virginia/West Virginia, due to tectonic instabilities that are remnant from the long-term evolution of this margin, resulting in a 'passive-aggressive' margin that records multiple magmatic events long after rifting ended.
Finally, Bermuda is an intraplate volcano that has been historically classified as mantle plume related but evidence to support the plume model is lacking. Instead, geophysics have argued that EDC is the best model to explain Bermuda volcanism. This study presents the first geochemical analysis of Bermuda volcanism, and found that Bermuda was built by two different magmatic processes: melting of carbonated peridotite to produce silica under-saturated, trace element enriched volcanics and melting of an enriched upper mantle component that produced silica saturated volcanics. We attribute the cyclicity of silica under-saturated and silica saturated volcanics to EDC melting.Ph. D.
25
Wölbern, Ingo. "Spuren des Plumes und Strukturen des oberen Mantels unter Hawaii abgeleitet aus konvertierten Wellen /." [S.l.] : [s.n.], 2003. http://www.gfz-potsdam.de/bib/pub/str0405/0405.htm.
Full text
26
Wölbern, Ingo. "Spuren des Plumes und Strukturen des oberen Mantels unter Hawaii abgeleitet aus konvertierten Wellen." [S.l. : s.n.], 2004. http://www.diss.fu-berlin.de/2004/172/index.html.
Full text
27
Gee, Margaret Anne Mary. "Volcanology and geochemistry of Reykjanes Peninsula : plume-mid-ocean ridge interaction." Thesis, Royal Holloway, University of London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313752.
Full text
28
Georgen, Jennifer E. "Interactions between mantle plumes and mid-ocean ridges : constraints from geophysics, geochemistry, and geodynamical modeling." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/29052.
Full textAbstract:
Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2001."September 2001." Vita. Page 223 blank.
Includes bibliographical references.
This thesis studies interactions between mid-ocean ridges and mantle plumes using geophysics, geochemistry, and geodynamical modeling. Chapter 1 investigates the effects of the Marion and Bouvet hotspots on the ultra-slow spreading, highly-segmented Southwest Indian Ridge (SWIR). Gravity data indicate that both Marion and Bouvet impart high-amplitude mantle Bouguer anomaly lows to the ridge axis, and suggest that long-offset transforms may diminish along-axis plume flow. Building upon this observation, Chapter 2 presents a series of 3D numerical models designed to quantify the sensitivity of along-axis plume-driven mantle flow to transform offset length, spreading rate, and mantle viscosity structure. The calculations illustrate that long-offset transforms in ultra-slow spreading environments may significantly curtail plume dispersion. Chapter 3 investigates helium isotope systematics along the western SWIR as well as near a global array of hotspots. The first part of this study reports uniformly low 3He/4He ratios of 6.3-7.3 R/Ra along the SWIR from 9⁰-24⁰E, compared to values of 8 +/- 1 Ra for normal mid-ocean ridge basalt. The favored explanation for these low values is addition of (U+Th) into the mantle source by crustal and/or lithospheric recycling. Although high He/4He values have been observed along the SWIR near Bouvet Island to the west, there is no evidence for elevated 3He/4He ratios along this section of the SWIR. The second part of Chapter 3 investigates the relationship between 3He/4He ratios and geophysical indicators of plume robustness for nine hotspots.
(cont.) A close correlation between a plume's flux and maximum 3He/4He ratio suggests a link between plume upwelling strength and origination in the deep, relatively undegassed mantle. Chapter 4 studies 3D mantle flow and temperature patterns beneath oceanic ridge-ridge-ridge triple junctions (TJs). In non-hotspot-affected TJs with geometry similar to the Rodrigues TJ, temperature and upwelling velocity along the slowest-spreading of the three ridges are predicted to increase within a few hundred kilometers of the TJ, to approach those of the fastest-spreading ridge. Along the slowest-spreading branch in hotspot-affected TJs such as the Azores, a strong component of along-axis flow directed away from the TJ is predicted to advect a hotspot thermal anomaly away from its deep-seated source.
by Jennifer E. Georgen.
Ph.D.
29
Pritchard, Matthew James. "A seismological study of the mantle beneath Iceland." Thesis, Durham University, 2000. http://etheses.dur.ac.uk/4609/.
Full textAbstract:
Iceland has long been thought to be underlain by a thermal upwelling, or plume, rising from deep within the mantle. This study tests this hypothesis, by a) seeking evidence for a plume in the lower mantle in azimuth anomalies at the NORSAR array and b) mapping the three-dimensional structure of the mantle beneath Iceland using teleseismic tomography and data from an Iceland-wide broadband seismometer network. A temporary network of 30 digital broadband, three-component seismographs was deployed 1996-1998 to complement the existing, permanent seismic network on Iceland. This created a dense, well-distributed network. 3159 P-wave and 1338 S-wave arrival times were measured and inverted for velocity structure using the ACH method of teleseismic tomography. The preferred models are well-resolved down to -400 km, and reveal a low-velocity body with anomaly up to -2.9% in V(_p)) and -4.9% in V(_s) beneath central Iceland. This persists throughout the entire model depth range. The amplitudes of the anomalies imply an excess temperature of 200-300 K relative to the surrounding mantle. The morphology of the anomaly changes from cylindrical to tabular at 250-300 km depth, a feature that resolution tests suggest is real. This is consistent with the predictions of some convection models and suggests that the plume is restricted to the upper mantle. Anomalies in v(_p) and v(_s) provide evidence for lateral flow of material beneath the Reykjanes Ridge to the southeast in the depth range 50-200 km. Similar anomalies are present beneath the Kolbeinsey Ridge to the north only beneath 160 km. This shows that flow outwards beneath the Kolbeinsey Ridge is blocked by the Tjörnes Fracture Zone above 160 km. Azimuthal anomalies detected on the NORSAR array for rays travelling beneath Iceland at 1,500 km depth are consistent with a plume beneath Iceland at this lower-mantle depth with a Gaussian radius of 125 km and a strength of 1.5%. The observations do not serve as proof for such an anomaly because the solution is not unique. V(_p)/V(_s) ratios are 1% high throughout most of the plume, and up to 3.2% high at depths of 100-300 km beneath central and east-central Iceland. This suggests that up to a few percent of melt pervades the entire plume.
30
MacLeod, Sarah J. "Characteristics of extinct spreading centers and the relationship between spreading ridges, hotspots and deep mantle structure." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/17988.
Full textAbstract:
Oceanic spreading ridges and mantle plumes represent the vehicles through which heat is lost from the deep Earth and govern the distribution of most basic volcanism at Earth’s surface. Despite numerous hotspots located in close proximity to spreading ridges, generally, hotspots are seen to be independent of them. This study catalogues extinct spreading ridges and their physical and spreading characteristics to understand ridge evolution. Variability of ridges related to tectonic subtype is described and compared with active ridges. Uncertain extinct spreading ridges are compared with ‘characteristic’ extinct ridges and a number of possible new ridges are identified. The spatial correlation of hotspots with active plate boundaries through time is assessed, including reorganizations of spreading ridges at times of major ridge jumps. This evaluation determines that over the last 100 m.y. spreading ridges have been closer to hotspots than expected by random distribution, as they are at present-day. After ridge jumps, spreading ridges are more often located closer to a hotspot, particularly when microcontinents are formed. In contrast, subduction zones are generally further from hotspots than expected by a random distribution over the last 100 m.y., particularly those likely to have a deep mantle origin. To explore relationships of plumes and deep mantle structure with surface tectonics spherical geodynamic models are evaluated, using different tectonic reconstructions for boundary conditions. First order behavior and motion of modelled hotspots are compared with observations of present-day hotspots and their trails. Evolution of large-scale modelled anomalous dense structures in the deep mantle are quantified. The direction and rate of boundary retreat or advance for the African, Pacific and ‘Perm’ anomalies are described and overlap with large low-shear wave seismic provinces evaluated. Insight is gained on behavior of plumes and deformation of deep mantle structures.
31
Delavault, Helene. "L'alignement volcanique de Pitcairn-Gambier : étude pétrologique et géochimique de la partie sud-est du panache polynésien." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU020/document.
Full textAbstract:
Le volcanisme de point chaud est l'une des activités les plus intrigantes de la Terre. L'origine de ce type de volcanisme est encore débattue mais il est largement admis que les panaches sont formés de matériel chaud qui peut potentiellement entrainer avec lui des matériaux recyclés. La plupart des études se concentrent sur les panaches puissants montrant une forte production magmatique comme Hawaï ou la Réunion, mais les panaches montrant une plus faible production magmatique comme la Polynésie (Pacifique sud), peuvent apporter des informations complémentaires.Ce travail consiste en une étude pétrologique et géochimique de la chaine de Pitcairn-Gambier, située au sud-est du panache Polynésien. Ce travail s'organise autour de mesures en éléments majeurs et en trace, de compositions isotopiques en Pb, Sr, Nd et Hf sur une centaine d'échantillons, et autour d'analyses ponctuelles sur olivines et sulfures contenus dans certains échantillons.Les compositions isotopiques et élémentaires montrent une évolution systématique avec le temps (de Mururoa, île la plus vieille, aux monts sous-marins de Pitcairn les plus jeunes), depuis des compositions isotopiques « HIMU jeunes » avec une forte anomalie positive en Nb (1.8) jusqu'à des compositions isotopique EMI typiques avec une faible anomalie négative en Nb (0.8). Les différents modèles développés dans cette thèse ont permis de dater, contraindre la lithologie et la proportion des composants recyclés dans la source de ces îles. Les îles de Mururoa, Fangataufa et Gambier possèdent dans leur source de la croûte basaltique recyclée de 1.5 Ga ainsi que des sédiments âgés de 1-1.5 Ga (<0.36%). L'étude ciblée de l'île de Gambier met en évidence une source plutôt froide (~1450°C) comparée aux autres panaches comme Hawaï (1550°C). La source de l'île de Pitcairn et de ses monts sous-marins se révèle extrêmement différente car elle contient non seulement de la croûte basaltique recyclée (1.5 Ga) mais également jusqu'à ~18% de cherts archéens (~2.5 Ga). La présence inattendue de cherts archéens dans la source des îles de Pitcairn qui ont les valeurs EM1 les plus prononcées des OIB, remet en cause les autres théories développées pour tenter de contraindre ce composant.Les anomalies positives en Nb indiquent la présence dans la source de croûte basaltique recyclée. La diminution de cette anomalie au cours du temps le long de la chaîne est expliquée par l'augmentation progressive du taux de sédiments dans la source du panache, les sédiments possédant une anomalie négative en Nb.Les hétérogénéités isotopiques et élémentaires mises en évidence dans cette étude sont expliquées par fusion, sous chaque île, de matériel de composition et d'âge différents. Un modèle possible pour expliquer la structure de l'ensemble du panache polynésien, consiste en de «petits panaches» générés à partir d'un super-panache. Ces petits panaches produisent alors de petits alignements, et échantillonnent de manière imprévisible les différents matériels présents dans le super-panache. L'ensemble des données et modèles proposés dans cette thèse offre un nouvel angle pour apprécier la variabilité géochimique du panache Polynésien et à plus grande échelle de nouvelles perspectives pour comprendre les processus de recyclage au sein du manteau terrestrePlume volcanism is one of the most puzzling features of present-day activities of the Earth. The origin of this type of volcanism remains a matter of debate, but it is generally agreed that its source is hot material containing some potentially recycled material. Most studies have focused on ‘strong' plumes with high magmatic production, e.g. Hawaii or Réunion, but weaker plumes such as Polynesia (South Pacific) may provide useful complementary information.This work presents a petrological and geochemical study of the Pitcairn-Gambier chain, situated at the South East of the Polynesian plume. I report major and trace element concentrations and Pb, Sr, Nd and Hf isotopic measurements of ~100 samples as well as probe analyses on olivine and sulphides in a few selected samples.Both isotopes and trace elements show a strong correlation with the age of the volcanoes (from the oldest island of Mururoa to the younger Pitcairn Seamounts), from « Young HIMU » isotopic compositions associated with high positive Nb anomalies (1.8), to typical EMI compositions with a slight negative anomaly (0.8). Geochemical modeling enables to constrain the age, the nature and the proportion of the recycled components in the source. Mururoa, Fangataufa and Gambier show in their source, the presence of 1.5 Gy recycled oceanic crust, along with 1-1.5 Gy sediments (<0.36%). The source of Gambier Island basalts is ‘cold' (~1450°C) compared to that of other plumes like Hawaii (1550°C). In contrast, the Pitcairn Island and Seamounts source is different as it contains 1.5 Gy recycled basaltic oceanic crust, as well as up to ~18% Archean (~2.5 Ga) cherts. The unexpected discovery of Archean cherts in the source of Pitcairn islands (which have the most extreme EMI compositions) is at odd with previous models on the origin of the EMI component.Positive Nb anomalies indicate the presence of recycled oceanic crust in the source, and this anomaly decreases with time along the chain. This feature can be explained by the increasing contribution of the sediment input in the source of the plume, since sediments display a negative Nb anomaly.The isotopic heterogeneities evidenced in this study are best explained by melting, beneath the islands, of different materials with various ages and compositions. The general structure of the Polynesian plume can be explained by the presence of small plumes generated from a superplume. These small plumes create small alignments, and they randomly sample various materials present in the plume. Overall the data and models in this study give new insights into the geochemical variations observed across the Polynesian plume, and at a larger scale they provide new perspectives to better understand crustal recycling processes and the evolution of the mantle through time
32
Williams, Alice Josiane. "The nature of the chemically enriched components of the Iceland mantle plume." Thesis, University of Edinburgh, 2005. http://hdl.handle.net/1842/14667.
Full textAbstract:
The main intentions of this research are to identify and characterise enriched components in the sub-Icelandic mantle and to determine their origins and relationships with other mantle components. Helium, strontium, neodymium and lead isotope data, in conjunction with major and trace element data, allow the characterisation of enriched mantle sources in the flank-zones. Postglacial olivine- and pyroxene-bearing basalt samples have been collected from each of three flank-zones. Pyroxene 3He/4He may have been affected by pre- or post-eruptive addition of radiogenic 4He, but olivine 3He/4He represent the time-integrated 3He/(U+Th) of the mantle source. Published oxygen isotope data indicate that the flank-zone basalts have not been affected by crustal contamination. Coherent trends in He-Sr-Nd-Pb isotope co-variation diagrams allow the identification of three distinct enriched components in the North Atlantic mantle. Each enriched component is characterised by lower 3He/4He (< 6 Ra) and 143Nd/ 144Nd and more radiogenic Pb and Sr isotope ratios than the depleted mantle components sampled in the rift-zones and along the MAR. One enriched component, EIl, is most prevalent in the mantle beneath the SFZ. It is distinguished from the other enriched components by its extreme Pb isotope composition (206Pb/204Pb > 19.4). It is probably derived from recycled oceanic crust (a young-HIMU-like component). The second enriched component, EI2, is only sampled at Öræfajökull (EFZ), and is distinguished by its extreme 87Sr/86Sr (> 0.7037) and positive D7/4. Its isotopic composition most likely has its origins in recycled pelagic or terrigenous sediments. The third enriched component, E13, dominates the Jan Mayen (North Atlantic) and Snæfell (EFZ) mantle sources. It has similar Sr, Nd and He isotopic compositions to EIl, but is characterised by less-radiogenic Pb isotope ratios ( 206Pb/204Pb ~ 18.6). It is also most likely derived from young recycled oceanic crust. Enriched mantle beneath Snæfellsnes appears to be derived from mixing of EIl and EI3. Two depleted components (DI1 and DI2) are required to explain negative trends in He-Sr, He-Nd or He-Pb co-variation diagrams. They have similar Sr, N d and Pb isotopic compositions to each other, but can be distinguished on the basis of 3He/4He. DI1 is characterised by 3He/4He ~45 Ra and represents the depleted Iceland plume component. DI2 is characterised by lower 3He/4He (7-9 Ra) and represents the depleted component in the N-MORB mantle. Only a very small contribution of DI1 can change the 3He/4He of a source without affecting its Sr; Nd or Pb isotopic composition. A mixing model is presented which enables plume-derived enriched components to be distinguished from those present in the shallow asthenospheric mantle. Only EIl appears to be intrinsic to the plume, whereas EI2 and EI3 are upper-mantle heterogeneities.
33
Harrison, Lauren Nicole. "Isotopic and chemical heterogeneity of the Hawaiian mantle plume : evaluating mantle geodynamics and characterization of the Loa geochemical trend." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/63408.
Full textAbstract:
The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
34
Starkey, Natalie. "Evolution of the Earth's mantle-crust-atmosphere system from the trace element and isotope geochemistry of the plume-mantle reservoir." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/5934.
Full textAbstract:
The 62 million year old lava flows of Baffin Island and West Greenland represent the earliest phase of magmatism in the North Atlantic Igneous Province (NAIP). These picritic lavas are characterised by high magnesium contents owing to their high proportion of olivine crystals. The parental magmas for the picrites are likely to have accumulated olivine crystals on their transit through the lithosphere and crust. Debate over the origin of accumulated crystals in the lavas results in uncertainty in the temperature and composition of the parental magmas for the early NAIP. The magnesium-rich olivine crystals (up to Fo93) in the picrites of this study are shown not to have a xenocrystic origin. The samples, therefore, support the inference of high potential temperatures for the Baffin Island-West Greenland magmas, ~200oC above ambient mantle. The picrites of Baffin Island and West Greenland display the highest terrestrial magmatic 3He/4He (up to 50 Ra, where Ra is the atmospheric value 1.39 x 10-6), values that are considerably higher than the highest 3He/4He in contemporary ocean island basalts, which reach a maximum of ~30 Ra. High 3He/4He in Baffin Island and West Greenland are associated with a wide range of incompatible trace element and lithophile radiogenic isotopic compositions, not dissimilar to the range of compositions displayed by lavas at mid-ocean ridges, and overlapping the range displayed by most northern hemisphere ocean island basalts. Crustal contamination modelling in which high-grade Proterozoic crustal basement rocks are mixed with depleted parents cannot account for the compositional trends displayed by the picrites. Major and trace element compositions were determined on melt inclusions in high- 3He/4He picrites that span a wide range of whole-rock incompatible trace element and radiogenic isotopic compositions. The melt inclusions support the findings from the whole-rock study since melt inclusion compositions reflect the composition of their associated whole-rock, with no anomalous compositions present. In addition, there is no evidence for a contribution of a proportion of depleted melts to the source of the relatively enriched whole-rock samples. Therefore, since all melt inclusions were contained within high-3He/4He samples, it is shown that high 3He/4He is a feature of both depleted and relatively enriched melt compositions. The wide range in whole-rock compositions of the Baffin Island and West Greenland picrites represents that of the sub-lithospheric mantle source region and is inconsistent with derivation of the picrites from residues of ancient mantle depletion. The apparent decoupling of helium from trace elements and radiogenic isotopes is hard to reconcile with simple mixing of a high-helium concentration, high-3He/4He reservoir with various depleted and enriched helium-poor mantle reservoirs. It is possible that primordial helium has diffused into a reservoir with a composition similar to that of the convecting upper mantle. However, this must have occurred after the development of existing mantle heterogeneity. The high-3He/4He picrites require the existence of a deep, primordial helium-rich reservoir. Whether this reservoir is present in the upper or deep mantle, or even the core, remains uncertain.
35
Trela, Jarek. "The Evolution of the Galapagos Mantle Plume: From Large Igneous Province to Ocean Island Basalt." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/77438.
Full textAbstract:
Mantle plumes are anomalously hot, narrow upwellings of mantle material that originate at the core-mantle boundary. As plumes rise they may form volumetrically large "heads" (~1000 km in diameter) with narrower (~100 km) "tails." Plume head melting is thought to form Large Igneous Provinces (LIPs), vast outpourings of basaltic lava (~106 km3), while plume tail melting forms linear chains of ocean island basalts (OIBs) similar the Emperor-Hawaii Seamount chain. Mantle plume derived melts indicate that these structures sample deep Earth geochemical and lithological heterogeneities. Studying plume-derived lavas can clarify important planetary-scale questions relating to the accretion of the Earth, primordial geochemical reservoirs, the fate of subducted materials, planetary differentiation, and convective mixing.Ph. D.
36
Robinson, Danielle D. Sandvol Eric Alan. "Seismic anisotropy beneath the southern Puna Plateau." Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/5362.
Full textAbstract:
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. Title from PDF of title page (University of Missouri--Columbia, viewed on December 30, 2009). Thesis advisor: Dr. Eric Sandvol. Includes bibliographical references.
37
Korenaga, Jun 1970. "Magmatism and dynamics of continental breakup in the presence of a mantle plume." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/55334.
Full textAbstract:
Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2000.Includes bibliographical references (p. 255-270).
This thesis studies the dynamics of mantle melting during continental breakups by geophysical, geochemical, and numerical analyses. The first part focuses on the mantle melting and crustal accretion processes during the formation of the Southeast Greenland margin, on the basis of deep-crustal seismic data. A new seismic tomographic method is developed to jointly invert refraction and reflection travel times for a compressional velocity structure, and a long-wavelength structure with strong lateral heterogeneity is successfully recovered, including 30- to 15-km-thick igneous crust within a 150-km-wide continent-ocean transition zone. A nonlinear Monte Carlo analysis is also conducted to establish the absolute uncertainty of model parameters. The derived crustal structure is first used to resolve the origin of a margin gravity high, with new inversion schemes using both seismic and gravity constraints. Density anomalies producing the gravity high seem to be confined within the upper crust, not in the lower crust as suggested for other volcanic margins. A new robust framework is then developed for the petrological interpretation of the velocity structure of igneous crust, and the thick igneous crust formed at the continentocean transition zone is suggested to have resulted from vigorous active upwelling of mantle with only somewhat elevated potential temperature. In the second part, the nature of mantle melting during the formation of the North Atlantic igneous province is studied on the basis of the major element chemistry of erupted lavas. A new fractionation correction scheme based on the Ni concentrations of mantle olivine is used to estimate primary melt compositions, which suggest that this province is characterized by a large degree of major element source heterogeneity. In the third part, the nature of preexisting sublithospheric convection is investigated by a series of finite element analyses, because the strength of such convection is important to define the "normal" state of mantle, the understanding of which is essential to identify any anomalous behavior of mantle such as a mantle plume. The results suggest that small-scale convection is likely in normal asthenosphere, and that the upwelling velocity in such convection is on the order of 1- 10 cm/yr.
by Jun Korenaga.
Ph.D.
38
Pilidou, Sylvana Demetriou. "Upper mantle shear-wave velocity and anisotropy structure beneath the North-Atlantic : a seismic image of the Iceland mantle plume." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615904.
Full text
39
Kundargi, Rohan. "Melting and dehydration within mantle plumes and the formation of sub-parallel volcanic trends at intra-plate hotspots." Thesis, Boston University, 2013. https://hdl.handle.net/2144/12802.
Full textAbstract:
Thesis (M.A.)--Boston University
PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.One of the defining characteristics of plume-fed hotspots is the formation of a linear chain of age-progressive volcanoes [Wilson, 1963; Morgan, 1972; Courtillot et al, 2003]. The most prominent example of this is the Hawaii-Emperor Seamount Chain, a 6000-km long age-progressive chain of volcanoes that stretch from the present-day island of Hawaii to the Aleutian Trench [van Ark and Lin, 2004; Sharp and Clague, 2006] However, recent volcanism at Hawaii does not form a simple linear trend, but rather is organized into two physically distinct sub-parallel chains, known as the Loa and Kea trends [Jackson, 1972]. Furthermore, recent studies have revealed that volcanism at several other hotspots, including the Samoa [Workman et al., 2004], Marquesas [Chauvel et al., 2009; Huang et al., 2011], and Society [Payne et al., submitted] hotspots are similarly organized into sub-parallel trends. Hieronymus and Bercovici [1999] developed a model in which lithospheric flexure in response to loading and combined with a change in plate motion, could generate sub-parallel trends of discrete volcanoes at plume-fed hotspots. Here, we develop an alternative mechanism for the formation of dual-chain volcanism at hotspots in which melting and dehydration of upwelling material within the plume conduit creates a buoyant, highly viscous plug of residuum that extends downwards from the base of the lithosphere above the plume conduit, causing the flow to bifurcate [Hall and Kincaid, 2003]. We report on a series of 3-D numerical experiments using CitcomCU in which an upwelling plume impinges on the base of an overriding oceanic plate. These experiments employ a diffusion creep rheology that includes the effect of water content on viscosity. Melting and dehydration are modeled using a Lagrangian particle method. This study analyzes the effect of dehydration on a plume-lithosphere setting, displaying results for both end members. Our results demonstrate the formation of the proposed viscous plug is plausible within a range of parameter space relevant to the Earth. The presence of this plug inhibits upwelling directly above the plume conduit, diverting plume flow to the edges of the plug and effectively bifurcating magma production in the mantle in the process.
40
Peto, Maria Kocsisne. "Application of noble gas isotopic systems to identify mantle heterogeneities." Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:13070050.
Full textAbstract:
This study addresses the origin of the combined He-Ne-Ar-Xe noble gas isotopic variation in mantle derived oceanic basalts. High precision heavy noble gas compositions of basalts from the Rochambeau Rift along the Northwestern Lau Basin, the Gakkel Ridge, the Southeast Indian Ridge and the South Atlantic Ridge presented here confirms fundamental differences between the volatile constituents of the depleted mid-ocean ridge basalt (MORB) source and plume sources. We find that the depleted MORB mantle is characterized by systematically lower proportions of Pu-fission derived Xe than the Iceland plume and the Samoan-like plume sampled at the Rochambeau Rift. These two plume sources are associated with low radiogenic \(^{129}Xe/^{130}Xe\) ratios that are not attributable to recycled atmosphere and must sample ancient (4.45 Ga) volatile rich mantle reservoir that experienced a lower degree of mantle processing than the depleted MORB source. I report \(^{128}Xe/^{130}Xe\) ratios in excess with respect to the atmosphere in deeply erupting Gakkel lavas, similar to mantle derived volatiles in natural gas samples. Deconvolution of fission derived xenon isotopes indicate that natural gas samples and the Gakkel MORBs are derived from the same volatile depleted mantle reservoir. The radiogenic He isotopic composition, the low estimated ratio of Pu to U derived xenon isotopes, and the low \(^{129}Xe/^{130}Xe_E\) ratio found in the source of the West Volcanic Zone (WVZ) along the Gakkel Ridge indicates the presence of increased amounts of recycled atmospheric volatiles. I suggest that the low \(^{129}Xe/^{130}Xe\) ratio beneath the WVZ cannot be explained by sampling an ancient (>4.45 Ga) lithospheric mantle component that evolved in isolation from convection throughout Earth's history. Instead, the Xe isotopic composition may be consistent with the presence of subduction derived metasomatizing fluids with atmospheric heavy noble gases trapped in the sub-continental lithospheric mantle sampled along the ridge. Available Ne isotope MORB data and new high precision Ne data presented in this study (including basalts from the East Pacific Rise, the Galapagos Spreading Center, and the Juan de Fuca Ridge) allows me to construct a combined He-Ne isotope distribution and infer first order source mixing systematics in the upper mantle.Earth and Planetary Sciences
41
Arnould, Maëlis. "Some surface expressions of mantle convective instabilities." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/19901.
Full textAbstract:
The multiple interactions between Earth’s mantle and lithosphere, which is the upper boundary layer of mantle convection, generate lateral (plate tectonics) and vertical (dynamic topography) motions of Earth's surface. Understanding the influence of the dynamics of mantle convective instabilities on the surface is fundamental to improve our interpretations of a large range of surface observations, such as the formation of sedimentary basins, continental motions, the location of hotspots, the presence of gravity anomalies or sea-level variations. This thesis aims at using numerical models of whole-mantle convection self-generating plate-like tectonics to study the impacts of the development and the dynamics of mantle convective instabilities (such as slabs or mantle plumes) on the continuous reshaping of the surface. First, I focus on the effect of the coupling between mantle convective motions and plate tectonics on the development of dynamic topography at different spatio-temporal scales. The results suggest that Earth's surface can deform over large spatio-temporal scales (> 104 km and several hundreds of millions of years) induced by whole-mantle convection to small-scales (< 500 km and five million years) arising from small-scale upper-mantle convection. I show that subduction initiation and slab break-off events control the existence of intermediate scales of dynamic topography (between 500 and 104 km). A second aim of this thesis is to understand the dynamics of mantle plumes and their interactions with surface. I first characterize in detail the behavior of mantle plumes arising in models of whole-mantle convection self-generating plate-like tectonics, in light of surface observations. Then, I quantify the lateral motions of mantle plumes and unravel the sources of their drift. Finally, I use observations of the mantle thermal signature of plume/ridge interactions to reconstruct the relative motions between the Azores mantle plume and the Mid-Atlantic Ridge.
42
Spice, Holly Elizabeth. "Viscosity of fayalite melt at high pressure and the evolution of the Iceland mantle plume." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/20971.
Full textAbstract:
Part 1 The viscosity of silicate melts is a fundamental physical property that determines the mobility and transport behaviour of magma on the surface and in planetary interiors. The viscosity of liquid fayalite (Fe2SiO4), the Fe-rich end-member of the abundant upper mantle mineral olivine, was determined up to 9.2 GPa and 1850 °C using in situ falling sphere viscometry and X-ray radiography imaging. The viscosity of liquid fayalite was found to decrease with pressure both along the melting curve and an isotherm, with temperature having very little influence on viscosity at high pressure. This work is the first to determine the viscosity of a highly depolymerized silicate melt at high pressure as only recent advances in experimental techniques have allowed the difficulties associated with studying depolymerized liquids at high pressure to be overcome. The results are in contrast with previous studies on moderately depolymerized silicate melts such as diopside and peridotite which found viscosity to initially increase with pressure. In accordance with recent in situ structural measurements on liquid fayalite, the viscosity decrease is likely a result of the increase in Fe-O coordination with pressure. The results show that the behaviour of silicate melts at depth is strongly dependent on the melt structure and composition. Part 2 The magnitude of the thermal anomaly at hotspot locations has a fundamental influence on the dynamics of mantle melting and therefore has an important role in shaping the surface of our planet. The North Atlantic Igneous Province (NAIP) is the surface expression of a major mantle plume and is unique in the fact that it has a complete magmatic history. The highest 3He/4He volcanic rocks on Earth are found in the early NAIP picrites of West Greenland and Bafin Island and high 3He/4He rocks are still erupted on Iceland today. However, the relationship between 3He/4He and mantle plumes has remained enigmatic. The main aim of this work is to use the ideal opportunity provided by the NAIP to investigate the relationship between temperature, mantle melting dynamics and helium isotopes within a mantle plume. The magmatic temperatures of a suite of picrites and primitive basalts spanning the spatial and temporal range of the NAIP was determined using traditional olivine-melt thermometry, a forward mantle melting model and the newly developed Al-in-olivine thermometer. This study is the first to provide a detailed petrologic approach to investigating the mantle temperature of the NAIP throughout its magmatic history and is the first to compare all three techniques in detail. The Al-in-olivine thermometer was found to be the most robust proxy for mantle temperature. The early stage of volcanic activity in the NAIP is associated with the arrival of the ancestral Iceland plume head and resulted in a uniform temperature anomaly with Al-in-olivine temperatures 250-300° above that of ambient MORB across an area 2000 km in diameter. In addition, the temperature of the plume is shown to have been subject to large temperature fluctuations on a timescale of 107 years and is currently increasing, which has had profound effects on the melting dynamics and bathymetry of the North Atlantic region. Using existing and new 3He/4He measurements, no clear relationship between 3He/4He and temperature is observable. However, it is noted that the maximum 3He/4He of primitive basalts from the NAIP has decreased through time. These relationships are explicable if the high 3He/4He reservoir is located in either the core or the core-mantle boundary (CMB), from which helium diffuses into the lower mantle. The high 3He=4He signature is incorporated into a plume when it breaks away from the base of the mantle and over the lifetime of the plume, the 3He/4He source is gradually depleted. The temperature of the plume can vary independently in responses to heat flow at the CMB, which is in turn related to changes in mantle convection. Global plate tectonics and mantle processes are therefore intricately linked with melting dynamics at hotspot locations.
43
Genske, Felix [Verfasser], and Karsten [Akademischer Betreuer] Haase. "Assessing the heterogeneous source of the Azores mantle plume / Felix Genske. Betreuer: Karsten Haase." Erlangen : Universitätsbibliothek der Universität Erlangen-Nürnberg, 2013. http://d-nb.info/1033029955/34.
Full text
44
Schoonman, Charlotte Maria. "Vertical motions at the fringes of the Icelandic plume." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/267950.
Full textAbstract:
The Icelandic mantle plume has had a profound influence on the development of the North Atlantic region over its 64 Myr existence. Long-wavelength free-air gravity anomalies and full waveform tomographic studies suggest that the planform of the plume is highly irregular, with up to five fingers of hot asthenosphere radiating away from Iceland beneath the lithospheric plates. Two of these fingers extend beneath the British Isles and southern Scandinavia, where departures from crustal isostatic equilibrium and anomalous uplift have been identified. In this study, the spatial extent of present-day dynamic support associated with the Icelandic plume is investigated using receiver function analysis. Teleseismic events recorded at nine temporary and 59 permanent broadband, three-component seismometer stations are used to calculate 3864 P-to-S crustal receiver functions. The amplitude and arrival time of particular converted phases are assessed, and H-k stacking is applied to estimate bulk crustal properties. Sub-selections of receiver functions are jointly inverted with Rayleigh wave dispersion data to obtain crustal VS profiles at each station. Both inverse- and guided forward modelling techniques are employed, as well as a Bayesian, trans-dimensional algorithm. Moho depths thus obtained are combined with seismic wide-angle and deep reflection data to produce a comprehensive crustal thickness map of northwestern Europe. Moho depth is found to decrease from southeast (37 km) to northwest (26 km) in the British Isles and from northeast (46 km) to southwest (29 km) in Scandinavia, and does not positively correlate with surface elevation. Using an empirical relationship, crustal shear wave velocity profiles are converted to density profiles. Isostatic balances are then used to estimate residual topography at each station, taking into account these novel constraints on crustal density. Areas of significant residual topography are found in the northwestern British Isles (1400 m), southwestern Scandinavia (464 m) and Denmark (620 m), with convective support from the Icelandic plume as its most likely source. Finally, the irregular planform of the Icelandic plume is proposed to be a manifestation of radial viscous fingering due to a Saffman-Taylor instability. This fluid dynamical phenomenon occurs when less viscous fluid is injected into a layer of more viscous fluid. By comparing the thermal and convective characteristics of the plume with experimental and theoretical results, it is shown that viscous fingering could well explain the present-day distribution of plume material.
45
Parnell-Turner, Ross Ernest. "Observations of transient mantle convection in the North Atlantic Ocean." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648620.
Full text
46
Saal, Alberto Edgardo. "Evaluating mantle and crustal processes using isotope geochemistry." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/69186.
Full textAbstract:
Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2000."September 1999."
Includes bibliographical references.
Geochemical studies are fundamental for understanding how the dynamic Earth works and evolves. These studies place constraints on the composition, formation, age, distribution, evolution and scales of geochemically distinct reservoirs such as the Earth's crust, mantle and core. In this dissertation the strategy has been to work on a broad range of topics to evaluate crustal and mantle processes. This study presents Re-Os systematics to constrain the composition, formation and age of the lower continental crust and the mantle lithosphere, examines melt inclusion from oceanic island basalts to evaluate the scale of the mantle heterogeneities, and uses U-series isotope to constrain geodynamic parameters, such as the upwelling velocities and porosities of mantle plumes. The lower continental crust plays a pivotal role in understanding the composition and evolution of the continental crust and the petrogenesis of continental basalts.
by Alberto Edgardo Saal.
Ph.D.
47
Villagomez, Diaz Darwin R. 1973. "Crustal and upper mantle structure beneath the Galapagos arechipelago from seismic tomography." Thesis, University of Oregon, 2010. http://hdl.handle.net/1794/11071.
Full textAbstract:
xv, 151 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.To explain the origin of several distinct aspects of the Galápagos volcanic hotspot, such as the broad geographical extent of recent volcanism and the unusual pattern of geochemical anomalies, we conducted seismic tomography studies of the upper mantle and crust beneath the Galápagos Archipelago. The studies combine measurements of group and phase velocities of surface waves and delay times of body waves. We find that upper mantle seismic velocities are lower than those beneath other regions of comparable age in the Pacific and consistent with an excess temperature of 30 to 150°C and ∼0.5% melt. We attribute the excess temperature and presence of melt to an upwelling thermal mantle plume. Crustal seismic velocity is up to 25% lower than that of very young crust at the East Pacific Rise (EPR) and is comparable to that of Hawaii, which we attribute to heating by increased intrusive activity above the Galápagos plume and the construction of a highly porous volcanic platform. In addition, we find that the Galápagos hotspot is underlain by a high-velocity region whose thickness varies from 40 to 100 km. The tomographic images reveal that the upwelling mantle plume tilts northward (towards the nearby Galápagos Spreading Center) as it rises and then spreads laterally when it reaches the bottom the lid. The lid, which we attribute to residuum from melting, is thickest where it is farthest from the spreading center, suggesting that ridge processes may affect the generation and amount of thinning of the residuum layer. In addition, the thickness of the lid correlates well with the geographical pattern of geochemical anomalies of erupted lavas, suggesting that the lid may control the final depth of decompression melting. We conclude that many of the distinct characteristics of the Galápagos can be attributed to the interaction of the upwelling plume with the lid and the nearby ridge. We further suggest that the ridge affects the geometry of plume upwelling in the upper mantle and also the pattern of lateral spreading of the plume due to its effect on the thickness of the residuum layer. This dissertation includes previously published co-authored material.
Committee in charge: Dr. Douglas R. Toomey, Chairperson; Dr. Eugene Humphreys, Member; Dr. Emilie Hooft Toomey, Member; Dr. Paul Wallace, Member; Dr. John Conery, Outside Member
48
Wölbern, Ingo [Verfasser]. "Spuren des Plumes und Strukturen des oberen Mantels unter Hawaii abgeleitet aus konvertierten Wellen / Geoforschungszentrum Potsdam. Von Ingo Wölbern." Potsdam : Geoforschungszentrum, 2004. http://d-nb.info/97182438X/34.
Full text
49
Dannberg, Juliane [Verfasser], Stephan Vladimir Akademischer Betreuer] Sobolev, Michael [Akademischer Betreuer] [Weber, and Volker [Akademischer Betreuer] John. "Dynamics of mantle plumes : linking scales and coupling physics / Juliane Dannberg ; Stephan Vladimir Sobolev, Michael H. Weber, Volker John." Potsdam : Universität Potsdam, 2016. http://d-nb.info/1218400463/34.
Full text
50
Dannberg, Juliane [Verfasser], Stephan Vladimir [Akademischer Betreuer] Sobolev, Michael H. [Akademischer Betreuer] Weber, and Volker [Akademischer Betreuer] John. "Dynamics of mantle plumes : linking scales and coupling physics / Juliane Dannberg ; Stephan Vladimir Sobolev, Michael H. Weber, Volker John." Potsdam : Universität Potsdam, 2016. http://d-nb.info/1218400463/34.
Full text