Le Yasur est un petit stratovolcan situé au coeur d'une grande caldeira, dans la partie sud-est de l'Ile de Tanna (Sud Vanuatu). Le cratère sommital est occupé par trois évents : les évents A et B dans le sous-cratère sud et l'évent C dans le sous-cratère nord. L'activité du Yasur est caractérisée par des explosions de bulles de gaz et l'émission de petits panaches de cendres. Afin de mieux comprendre les processus volcaniques qui se produisent au sein de l'édifice, un large réseau de capteurs, comprenant 12 antennes sismiques et 10 stations large-bande, a été déployé autour du Yasur en 2008, enregistrant le signal sismique en continu. Le modèle de vitesse de la structure superficielle du volcan ainsi que de la caldeira de Siwi a été estimé jusqu'à 200 m de profondeur en utilisant les méthodes SPAC et f-k - deux techniques d'analyse du bruit ambiant inclues dans le logiciel Geospy - sur les signaux enregistrés par sept antennes. Quatre zones principales ont été distinguées et interprétées en terme de couches géologiques et de répartition des fluides (aquifère, système hydrothermal) dans la structure volcanique. Le modèle de vitesse a ensuite été intégré dans un algorithme de tracé de rai et combiné à une méthode de triangulation sismique pour localiser la source des explosions et des événements longue période. Les localisations ont permis de suivre l'évolution de l'activité en 2008 dans les différents évents, et de proposer deux modèles de dynamique éruptive pour expliquer la périodicité des explosions stromboliennes et l'intense activité observée au Yasur. Les localisations ont également permis l'estimation de la vitesse d'ascension des poches de gaz ainsi qu'une estimation de la géométrie du conduit volcanique. / Yasur is a small stratovolcano located inside a large caldeira, in the south-eastern part of Tanna Island (South Vanuatu). The summit crater is occupied by three vents: the vents A and B in the southern subcrater and the vent C in the northern subcrater. Yasur's activity is characterized by explosions of gas bubbles and the emission of small ash plumes. In order to better understand the volcanic processes that occured inside the edifice, a large seismic network, consisting of 12 antennas and 10 broadband stations, was deployed around Yasur volcano in 2008, recording continuously the seismic signal. The superficial velocity structure of Yasur volcano and of the Siwi caldeira was estimated up to 200 meters using the Spatial Autocorrelation and the frequency-wavenumber techniques - two ambient noise methods included in the software Geopsy - on seismic signals recorded by seven antennas. Four main areas were distinguished and interpreted in terms of geological layers and fluid distribution (aquifer, hydrothermal system) inside the volcanic structure. The velocity structure was inserted in a ray tracing algorithm and combined to a seismic triangulation method to locate sources of explosion quakes and LP events. Locations allow to follow the evolution of the 2008 Yasur's activity in the different vents and to propose two eruptive dynamics models to explain the periodicity of the strombolian explosions and the intense activity observed at Yasur volcano. Locations also allow the estimation of the slug rise velocity and an estimate of the volcanic pipe geometry.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22259号 / 理博第4573号 / 新制||理||1657(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 James Mori, 教授 久家 慶子, 教授 岩田 知孝 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The Lower Cretaceous Cedar Mountain Formation preserves several vertebrate faunas and has the potential of providing critical timing information pertaining to Early Cretaceous dinosaurs and the Sierran magmatic arc. Historically, the Morrison/Cedar Mountain contact and the duration of the unconformity between them have been difficult or impossible to determine because 1) the formations were deposited in similar environments, 2) the basal Cedar Mountain Formation is composed of reworked Morrison Formation, and 3) there are no radiometric ages for the lower Cedar Mountain Formation. A stratigraphic study through central Utah reveals a diagnostic suite of pedogenic and sedimentologic characters across the previously enigmatic boundary. The uppermost Morrison Formation is characterized by redoximorphic paleosol features, including iron concentrations, manganese-coated grains, and intense red-purple-green mottling. Upsection increases in chert-pebble lags and channelized conglomerates within the paleosol section indicate a period of reduced accommodation space in the Tithonian. The paleosols are usually capped by a groundwater or pedogenic carbonate. This unit is consistently present from Green River, Utah to the Utah-Colorado border. The lower Cedar Mountain Formation above this package is a poorly sorted mixture of fine-grained material and sand-gravel sized chert grains. Within a sequence stratigraphic framework, these characters record a terrestrial sequence boundary in the uppermost Morrison Formation and degradational-aggradational systems tracts in the Cedar Mountain Formation. To resolve the lack of age control for the basal Cedar Mountain Formation, a geochronologic zircon study was conducted near the Dalton Wells dinosaur quarry, Moab, Utah. The Dalton Wells quarry, along with numerous other fossil assemblages occurs in the basal Yellowcat Member. Zircons from the Dalton Wells quarry and a correlative eggshell site place the age of this horizon near the Barremian/Aptian boundary at ~124 Ma. Thus, the Yellowcat fauna is time equivalent with the feathered dinosaurs of the Yixian Formation, of Liaoning, China. This age constrains the Morrison/Cedar Mountain unconformity to a period of magmatic quiescence in western North America from 148 Ma-124 Ma. The basal Cedar Mountain age coincides with renewed magmatic activity at ~125 Ma. The Cedar Mountain Formation covers a period of 27 Myr and likely contains numerous small unconformities.

No description available.

En el Perú existen zonas afectadas por la geología volcánica ya que disponen de insumos naturales llamados cenizas volcánicas. Este es un material formado por pequeños fragmentos de lavas silíceas de granos finos de colores blanquecinos, blandos y deleznables. Suelen presentar diversos grados de cementación, de tipo fisil, lo que los identifica en la categoría de suelos colapsables. Es por ello, que para la construcción del pavimento se requiere realizar la estabilización o mejoramiento de la subrasante para el siguiente proyecto que se desarrolla entre Arequipa y Moquegua. La presente investigación tiene como objetivo evaluar el uso de agregados marginales con cenizas volcánicas para el diseño de losa de concreto hidráulico referida, la misma que como estructura será evaluada con los resultados del módulo de flexión y esfuerzo crítico. Los resultados demostraron que, en la caracterización de agregados finos al contener cenizas volcánicas, no cumplan con todos los requerimientos propuestos en la norma peruana (EG-2013) del manual de carreteras. Sin embargo, el American Concrete Institute (ACI) incorpora excepciones para condiciones particulares de los áridos, posibilitando su uso a partir del cumplimiento de la resistencia y durabilidad requerida. Se propuso realizar el diseño de una mezcla de concreto para una resistencia teórica de f´c= 280 kg/cm2. Sin embargo, al ensayar las probetas a los 28 días de curado se obtuvo una resistencia de f´c= 380 kg/cm2 esto se debe a la estrecha relación positiva que presenta la ceniza volcánica con el cemento puzolánico empleado para la mezcla. / In Peru there are areas affected by volcanic geology and that have natural inputs called volcanic ash. This is a material formed by small fragments of siliceous lavas of fine grains of whitish, soft and delectable colors. They usually present varying degrees of cementation, of the fisile type, which identifies them in the category of collapsible soils. That is why, for the construction of the pavement it is necessary to perform the stabilization or improvement of the subgrade for the next project that is developed between Arequipa and Moquegua. The purpose of this research is to evaluate the use of marginal aggregates with volcanic ash for the design of the loss of referred hydraulic concrete, which will be determined as a structure with the results of the flexural and critical stress module. The results showed that, in the characterization of fine aggregates containing volcanic ash, they do not require all the requirements proposed in the Peruvian standard (EG-2013) of the road manual. However, the American Concrete Institute (ACI) incorporates the specific conditions of the aggregates, which allows its use based on compliance with the required strength and durability. It was proposed to design a concrete mix for a theoretical strength of f´c = 280 kg / cm2. However, when testing the probes after 28 days of curing, a resistance of f'c = 380 kg / cm2 was obtained, due to the close positive relationship between volcanic ash and the pozzolanic cement used for the mixture. / Tesis

The Snake River Plain (SRP) is one of the best-preserved examples of continental hotspot volcanis, with a continuous record of volcanism that extends over 16 Ma to the present. Yellowstone-Snake River Plain records the migration of plume-tail volcanism from inception at the Bruneau-Jarbridge caldera complex at 12.6 Ma to its present locus, under the Yellowstone Plateau. Records kept by the Snake River Plain volcanic actions include rhyolite lavas and ignimbritesm minor coeval basalts, and an overlying veneer of younger basalts. The central SRP has received comparatively little attention in the past. The Kimama core hole was drilled as part of Project Hotspot, the Snake River Scientific Drilling Project, which seeks to understand the long-term volcanic and sediment logical history of the SRP volcanic province. The Kimama core hole is the only part of the SRP that has not been scientifically drilled and cored to a significant depth in the past. Investigations of subsurface stratigraphy in continental volcanic provinces such as the SRP-YP are limited by the by the relatively low depth and spatial distribution of cored wells. The study of the Kimama core provides us with a continuous record of basalt and minor sediment deposition. The long-term volcanic history of the SRP, documented by moving magma and its composition, demonstrates that magmatism is mantle plume-derived. Our investigation of the Kimama core, combined with new mantle tomography, provides evidence that refutes non-plume models for the origin of the Snake River Plain volcanic province.

Rhyolite lava flows are found at two dome complexes at Graveyard Butte and Gordon Butte, Mount Hood Quadrangle, Oregon. At Graveyard Butte, the White River has cut a winding canyon 150 m deep, exposing at its base, a 40-meter-thick outcrop of flow-banded rhyolite (73 wt.% SiO2, 3.67±0.01 Ma) that laterally extends along the canyon wall for about 1 km. Stratigraphically above the flow-banded rhyolite is locally-erupted iron-rich andesites (lava flows, agglutinate and other pyroclastic rocks as well as clastic debris), a rhyolitic ash-flow tuff (74 wt.% SiO2), and the 2.77±0.36 Ma tholeiitic basalt lava flows of Juniper Flat (Sherrod and Scott, 1995). Roughly 2 km downstream, a phenocryst-poor, maroon-colored rhyolite (3.65±0.01 Ma) is visible again, forming steep canyon walls for about 1.6 km. A compositionally similar silicic unit is found 18 km to the northwest of Graveyard Butte at Gordon Butte. Exposed units along Gordon Butte's Badger Creek (3.64±0.03 Ma) and the southeastern upper slopes of Gordon Butte include rhyolite flows (69.6-72.1 wt.% SiO 2). The rhyolite lava flows at Graveyard Butte and Gordon Butte's Badger Creek are nearly chemically indistinguishable and both contrast with the younger rhyolitic ash-flow tuff at Graveyard Butte and lava flows on Gordon Butte's Upper Slopes. The rhyolites of Graveyard Butte and Badger Creek are richer in Nb and Zr (30-40 ppm and 487-530 ppm, respectively) than the younger rhyolitic tuff and Upper Slopes flows (13-19 ppm and 235-364 ppm, respectively) and share characteristics with A-type granitoids. The rhyolite lavas are porphyritic (~7%) with the porphyroclasts comprising primarily individual feldspars (250-500 µm in length) with ragged margins, oscillatory zoning and less commonly, spongy cores. Other phenocrystic phases include fayalitic olivine, Fe-rich clinopyroxene, and Fe-Ti oxides. A-type-like incompatible trace-element-enriched compositions as well as mineralogical indicators suggest rhyolite lava flows at Graveyard Butte and Gordon Butte's Badger Creek are likely generated in an extensional tectonic setting. A possible geotectonic framework for generation of these rhyolite lavas is the northward propagating intra-arc rift of the Oregon Cascades.

No description available.

Baggalútar are well-rounded spheroids that typically measures 16-18 mm in size and have a brownreddish appearance. They can be found in the Hvalfjörður bay in SW Iceland. There are manydescriptions in literature and on the internet that Baggalútar are volcanic spherulites formed by quartzor cristobalite spheres growing out of a common centre and there is also a broadly accepted consensusof this theory. However, despite this consensus that Baggalútar are volcanic spherulites there exist nodetailed investigation of their origin. The aim of the thesis is to investigate what Baggalútar is exactlyand how they form. This is achieved by using a combination of petrographic observations with apolarization microscope, mineral chemistry from electron microprobe analysis and measurements oftheir magnetic properties. The results are compared with different geological and anthropological spheroids, spherulites,nodules and concretions. The petrographic observations show that they predominantly consist of finegrained basaltic tephra (groundmass) together with zeolites infilling voids. Analyses of mineralchemistry indicate that the groundmass consists of augitic pyroxene, plagioclase, and two differentoxides where one classifies as titanomagnetite. The magnetic measurements support this by showing aCurie temperature at approximately 460-470 °C which is likely to be titano-magnetite. Although thedifferent geological and anthropological processes that typically results spheroidal shapes have somesimilarities that could explain the formation of baggalútar, most of these can be excluded for differentreasons. The internal textures of baggalútar strongly indicate that the shape is controlled by externalfactors, like weathering or erosion from beach outcrops. This could explain the spherical shape of asingle baggalút, but it fails to explain the spheroidal shapes of individual baggalútar joined together inclusters. / Baggalútar är väl rundade sfäroider som vanligtvis mäter 16–18 mm i storlek och har ett brunt rödaktigtutseende. De hittas i Hvalfjörðurbukten i SW Island. Det finns många beskrivningar i litteraturen ochpå internet som säger att Baggalútar är vulkaniska sfäruliter som bildas av kvarts- eller kristobalitsfärersom växer fram ur ett gemensamt centrum och det finns också en allmänt accepterad konsensus omdenna teori. Men trots denna konsensus om att Baggalútar är vulkaniska sfäruliter finns det ingendetaljerad undersökning av deras ursprung. Syftet med avhandlingen är att undersöka exakt vadBaggalútar är och hur de bildas. Detta uppnås genom att använda en kombination av petrografiskaobservationer med ett polarisationsmikroskop, mineralkemi från elektronmikrosondanalys ochmätningar av deras magnetiska egenskaper. Resultaten jämförs med olika geologiska och antropologiska sfäroider, sfäruliter, noduler ochkonkretioner. De petrografiska observationerna visar att de till övervägande del består av finkornigbasaltisk tefra (grundmassa) tillsammans med zeoliter som fyller ut tomrum. Analyser av mineralkemivisar att grundmassan består av augitisk pyroxen, plagioklas och två olika oxider där den enaklassificeras som titanomagnetit. De magnetiska mätningarna stödjer detta genom att visa en Curietemperatur på cirka 460–470 °C som sannolikt är titanomagnetit. Även om de olika geologiska ochantropologiska processerna som vanligtvis resulterar i sfäroida former har vissa likheter som kanförklara bildandet av baggalútar, kan de flesta av dessa uteslutas av olika anledningar. Baggalútars inretexturer indikerar starkt att formen styrs av yttre faktorer, som väderpåverkan eller erosion frånstrandhällar. Detta kan förklara den sfäriska formen av en enda baggalút, men det misslyckas med attförklara de sfäriska formerna av individuella baggalútar i sammanfogade kluster.

No description available.