Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 59-66). Also available on the World Wide Web.

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1983. / Bibliography: leaves 441-472. / Microfiche. / xvii, 472 leaves, bound ill., maps 29 cm

Thesis (Ph. D.)--University of Washington, 1988. / Vita. Bibliography: leaves [264]-290.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2003. / Includes bibliographical references (leaves 65-68).

No description available.

Seamounts, or submarine volcanos, have two distinct phases: the formation phase when the seamount is magmatically active and the passive phase when the seamount is transporting on the seafloor until subduction. Being able to understand various aspects of seamounts both in the formation and passive phase can enhance our understanding of volcanic processes and how seamounts can influence other processes such as crustal deformation, plate subduction, and earthquake generation. The purpose of this thesis is to examine seamounts on the Juan de Fuca plate both in the formation and passive phases. The first three chapters of this thesis focuses on understanding the subsurface properties and volcanic processes of Axial Seamount, an active seamount located on the Juan de Fuca Ridge. The fourth and final chapter focuses on understanding how seamounts influence subduction and the seismogenic properties of the Cascadia Subduction Zone. In chapter 1, I analyze multichannel seismic data to characterize the internal crustal structure of the rift zones of Axial Seamount. The new reflectivity images reveal small and discontinuous crustal magma bodies beneath and in the vicinity of the rift zone lava flows from the three most recent eruptions. We also image wide magma bodies within the overlap regions between the rift zones and neighboring segments of Juan de Fuca Ridge. Collectively the new observations indicate that multiple small crustal magma bodies underlie Axial and likely contribute to rift zone magmatism with implications for interpretations of seismicity patterns and lava flow compositions. In chapters 2 and 3, I process over 7 years of continuous seismic noise at Axial Seamount and use cross-correlation functions to calculate the relative seismic velocity (dv/v) changes beneath the caldera. I find a long-term trend of decreasing velocity during rapid inflation, followed by slight increase in velocities as background seismicity increases and inflation rate decreases. I also observe small short-term increases in dv/v which coincide with short-term deflation events. The observations of changes in dv/v and their correlation with other geophysical data provide insights into how the top ~1 km of the crust at Axial Seamount changes in response to subsurface magma movement and capture the transition from a period of rapid reinflation to a period where the caldera wall faults become critically stressed and must rupture to accommodate further inflation. From the relative seismic velocity variations, I also observe a strong annual pattern constrained within the 0.1-0.2Hz filter band. This annual pattern correlates well with timing and location of storm activity within the Pacific Ocean. Through the comparison of annual variation with ocean data, we determine that the annual pattern observed is likely an apparent velocity change due to changes in the seismic noise source. Lastly, in chapter 4, I utilize multichannel seismic data and high-resolution P-wave velocity (Vp) models of the CASIE21 expedition to calculate residual Vp models to examine properties of the sediments relative to seamounts on the incoming plate. At one of the larger seamounts located within 25km of the deformation front, I show evidence consistent with predicted stress effects of buried topography where there is an increase in normal stresses landward and a stress shadow seaward of the seamount, which can alter and impact rupture patterns along the margin. I also show evidence for signatures of enhanced hydrothermal circulation at seamounts near the deformation front which show that seamounts can be potential carriers of additional fluid into the margin when subducted. In additional to looking at the sediments relative to the seamounts, I also evaluate properties of a high Vp basal layer that is prevalent on all of the lines which can provide insights into the earthquake rupture and tsunami potential for the area.

L’interprétation structurale de sections de Sismique Réflexion Multitrace-2D acquises pendant la campagne SISTEUR sur la marge de l’Équateur Central et migrées en profondeur avant sommation (PSDM) a été combinée avec la bathymétrie multifaisceaux, des modèles tomographiques de sismique grand-angle OBS, un modèle d’inversion GPS, et 13 années de sismicité relocalisée, afin de déchiffrer les causes de la variabilité de la sismicité et du Couplage Inter Sismique (CIS) le long de la subduction. La partie marine de cette marge est étroite et érosive. Elle chevauche vers l’Ouest, à 4.7 cm/an, la Ride de Carnégie. Le segment nord de la zone d’étude est bloqué, et aucun chenal de subduction n’est identifié. Ce segment révèle la présence d’un important (50 X 40+ km) massif océanique (MO) subduit, haut de ~2.5 km, et dont le flanc arrière plonge vers le continent de 2-4°, et coïncide avec la zone de CIS bloquée, et avec le socle océanique résistant (Vp= 5 km/s) de la marge. Le flanc avant du MO déduit de notre étude coïncide avec une zone de CIS partiel et des essaims de séismes chevauchant déformant le socle de la marge. A l’inverse, le segment sud est découplé, et affiche une pente sous-marine très perturbée avec des escarpements abrupts. Le contact interplaque plonge de 6-7° sous le continent et porte des monts sous-marins isolés séparés par un chenal de subduction de ~1km d’épaisseur qui agit comme lubrifiant. Un scénario en 3 étapes est proposé pour la subduction d’un MO de forme émoussée sous la marge résistante de l’Ile La Plata. Un modèle cinématique est proposé pour rendre compte de la surrection de l’île de La Plata en réponse au MO au cours des derniers 1.3-1.4 Ma. / The structural interpretation of 2D-Pre-stack Depth Migrated Multichannel Seismic Reflection sections collected during the SISTEUR cruise across the Ecuadorian margin was combined with multibeam bathymetry, OBS wide-angle tomographic models, a GPS inversion model, and 13 years of relocated seismicity to decipher the causes of the along-trench variability of the seismicity and Inter-Seismic Coupling (ISC). The margin submarine part is narrow and dominated by subduction erosion. It is underthrust eastward at 4.7 cm/yr by Carnegie Ridge, and figures a decoupled subduction centered over La Plata Island region. Our study shows that the Central Ecuador margin divides in two contrasting segments with dissimilar long-lived physical properties that may account for their specific ISC and seismicity patterns. The locked northern segment shows a smooth outer-wedge slope scalloped by a gentle re-entrant. No subduction channel is detected across this segment that reveals a broad 50 X 40+ km, ~2.5-km-high subducted Oceanic Massif (OM), which dips landward 2-4°, which coincides with the strong (Vp= 5 km/s) oceanic margin basement. In contrast, the decoupled southern segment shows a highly disrupted outer-wedge seafloor. The plate interface dips landward ~6-7°, and is spotted by isolated seamounts separated by a ~1 km-thick subduction channel that may act as a lubricant favoring inter-plate decoupling. A 3-step scenario is put forward for the subduction of a low-drag shaped OM beneath the resistant margin wedge of La Plata Island. Moreover, a kinematic model accounting for the uplift history of La Plata Island is proposed as a result of the OM subduction over the last 1.3-1.4 Myr.

Thesis (M. Sc.)--Carleton University, 2008. / Includes bibliographical references (p. 157-168). Also available in electronic format on the Internet.

Seamounts play an important role in facilitating the exchange of elements between the oceanic lithosphere and the overlying seawater. This water-rock interaction is caused by circulating seawater and controls the chemical exchange in submarine and sub-seafloor rocks. The exchange mechanism plays a major role in determining the final composition of these submarine rocks. This investigation is designed to evaluate the (i) degree of alteration and element mobility, (ii) to identify relations between alteration types and (iii) to characterise the chemical processes that takes place during seafloor and sub-seafloor alteration in the Central Atlantic region. The investigated submarine rocks are typically altered. They are composed mostly of calcite and clay minerals in addition to original magmatic feldspar, olivine, pyroxene, quartz, biotite, and amphibole.  Elemental analyses show that submarine rocks with high water-rock ratio have experienced near complete loss of Silica and alkali elements to seawater but are enriched in calcium and phosphorous. In addition, there is a strong enrichment of trace elements such as Sr, Ti, Rb and trivalent REEs in altered submarine samples that are likely residual in character. Oxygen and hydrogen isotopic values indicate a low temperature alteration process at less than 50℃.  Nannofossils were present in one sample and investigation suggests that the seamount south of El Hierro evolved from a young Canary activity rather than the early Cretaceous magmatic events as has been argued previously. / Djuphavsberg spelar en viktig roll för att underlätta utbytet av element mellan den oceaniska litosfären och det överliggande havsvattnet. Interaktionen mellan vattnet och bergarterna orsakas av cirkulerande havsvatten och kontrollerar det kemiska utbytet i undervattensbergarterna och som även spelar en viktig roll för att bestämma de slutliga produkterna i dessa bergarter. Undersökningen syftar till att (i) utvärdera graden av kemisk omvandling och rörlighet av elementen, (ii) identifiera samband mellan olika omvandlingstyper och (iii) att karakterisera de kemiska processer som äger rum vid kemisk omvandling av bergarter vid och under havsbottnen i Centralatlanten. De undersökta undervattensbergarterna är generellt kemiskt omvandlade och består av kalcit och lermineral utöver ursprungligt magmatiskt fältspat, olivin, pyroxen, kvarts, biotit och amfibol. Elementanalyser visar att de undervattensbergarter med en hög vatten-berg kvot har förlorat i stort sett all Si och nästan alla alkaliska element till havsvattnet medan en anrikning har skett av kalcium och fosfor. Dessutom har det i de omvandlade undervattensproverna skett en tydlig anrikning av spårämnena Sr, Ti, Rb och av trivalenta sällsynta jordartsmetaller. Syre- och väteisotopvärden indikerar en omvandlingsprocess vid låga temperaturer mindre än 50 °C. I ett prov fanns nannofossiler och en undersökning av dessa tyder på att djuphavsberget söder om El Hierro bildades under en yngre vulkanisk aktivitet än den magmatiska aktivitet som tidigare föreslagits som ägde rum under perioden Krita.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho de mestrado estudou a ilha de Martin Vaz e cinco montes submarinos da Cadeia Vitória-Trindade Columbia, Dogaressa, Davis, Jaseur e Montague. Martin Vaz é um conjunto de ilhas formado pela ilha principal - Martin Vaz, duas ilhotas íngremes e inacessíveis - a Ilha do Norte e a Ilha do Sul além de vários rochedos menores, como o Rochedo Agulha, espalhados a 48 km a leste de Trindade, perfazendo uma área total de 0,3 km. Martin Vaz, assim como os montes submarinos, pertencem a chamada Cadeia Vitória-Trindade, estão inseridos em um contexto tectônico regional cujo trend W-E sugere representar o track da pluma mantélica de Trindade quando da passagem da Placa Sul Americana sobre ela desde o Terciário (CROUGH et al., 1980; OCONNOR & DUNCAN, 1990, GIBSON et at., 1997). A petrografia das amostras de Martin Vaz indica haver basanitos parcialmente alteradas, melanocráticas, textura afanítica, porosas, apresentando vesículas em torno de 1,0-5,0 milímetros. Apresenta fenocristais de piroxênio além de alguns fenocristais de olivina verde-oliva translúcido variando de 1,0-3,0 milímetros. A ilha principal apresenta também diques e necks fonolíticos apresentando matriz microlítica alterada, orientada, de cor verde apresentando minerais ripiformes de cor branca (feldspato alcalino) e outros de cor violácea (titanoaugita) além de pequenos opacos. Pequenos fenocristais de aegerina-augita fortemente pleocroica, alguns apresentando geminação simples, por vezes zonado, apresenta extinção variando de c &#8743; &#945; ou X = 23 a 33 (medida de 10 grãos). Biotita laranja amarronzada com textura poiquilítica (1,0 mm), minúsculos cristais euédricos de titanita (raros), além de cristais pseudohexagonais isotrópicos alterados de analcita e carbonatos. As amostras utilizadas neste trabalho de mestrado possuem valor mínimo de 33.91 % SiO2 (TRIM-01D) e máximo de 52,2 (MVA-01) variando de ultrabásicas a básicas. Através da análise dos óxidos SiO2 e MgO é possível distinguir dois grupos de rochas para Martin Vaz: um ultramáfico magnesiano (<42% SiO2 e >7% MgO) e um básico (>45% SiO2) e, para os montes submarinos, dois grupos: um ultramáfico magnesiano (>9% MgO <42% SiO2) e um básico (>45% SiO2 e com valores de MgO em torno de 4%). As análises de Ar-Ar para as quatro amostras de Martin Vaz apresentam idades para o derrame de basanito variando de 320366 Ka (MVA-10) à 623127 Ka (MVA-04). A única amostra datada representando do dique de fonólito é a MVA-05B e obteve idade de 64984 Ka, indicando ser contemporânea ao derrame basanítico. / This master's thesis studied the island of Martin Vaz and five seamounts of the Vitoria-Trindade Ridge - Columbia, Dogaressa, Davis, Jaseur and Montague. Martin Vaz is a group of islands formed by the main island - Martin Vaz, two steep and inaccessible islands - the North Island and South Island and several smaller rocks, as the Agulha Rock, around 48 km east of Trindade,making a total area of 0.3 km. Martin Vaz and seamounts belong to the Vitoria-Trindade Ridge,and are embedded in a context where the W-E regional tectonic trend suggests to represent the track of the Trindade mantle plume when the South American Plate passed on it since the Tertiary (Crough et al. 1980; O'Connor & DUNCAN, 1990, Gibson et at. 1997). The petrography of the samples indicates that the basanites in Martin Vaz are partially altered, melanocratic,aphanitic texture, porous, presenting vesicles around 1.0 to 5.0 millimeters. Displays phenocrysts of pyroxene and some translucent olivine ranging from 1.0 to 3.0 millimeters. These basanitics samples are also described in the seamounts studied in this work and they are Columbia, Dogaressa, Davis, Jaseur and Montague seamounts. The main island has also phonolitic dikes and necks with altered oriented matrix featuring white sheet-like mineral (alkali feldspar) and purple (titanoaugite) beyond small opaques. Small aegerine-augite phenocrysts strongly pleocroic, which some have simple twinning and sometimes zoned. They presents extinction varying from X c &#8743; &#945; = 23 or 33. Kaersutite with poiquilitic texture (1.0 mm), tiny crystals of euhedral titanite (rare), and isotropic crystals pseudohexagonais altered nosean and carbonates are also observed The samples used in this study have minimum value of 33.91 wt% SiO2 (TRIM-01D) and a maximum of 52.2wt% (AMM-01) ranging from basic to ultrabasic. Through analysis of the oxides SiO2 and MgO is possible to distinguish two groups of rocks to Martin Vaz: an ultramafic magnesium (<42% SiO2 and> 7% MgO) and one basic (> 45% SiO2) and for seamounts, two groups: an ultramafic magnesium (> 9% MgO <42% SiO2) and one basic (> 45% SiO2 and MgO values around 4%). Ar-Ar Analyses for four samples of Martin Vaz present ages to basanites varying from 320 366 Ka (MVA-10) to 623 127 Ka (MVA-04). A single sample representing the phonolite dike dated is the MVA-05B and obtained age of 649 84 ka,indicating to be contemporary with basanite extrusion.