Common brown colour in natural diamond forms by plastic deformation during storage in the subcontinental lithospheric mantle (SCLM). Dislocation movement generates vacancies, which aggregate into clusters of perhaps 30–60 vacancies. Positron annihilation lifetime spectroscopy (PALS) and electron energy loss spectroscopy (EELS) support such vacancy clusters as the cause of brown colour. Brief treatment in a high-pressure–high-temperature (HPHT) vessel at 1800–2700 °C can destroy the brown colour. There has been speculation that similar colour removal should occur continuously at depth in the SCLM. Diamonds are stored at 900–1400 °C in the SCLM, according to inclusion thermometry. The effect of temperature on the time required to destroy brown colour has been calculated from published data. The activation energy for the breakup of vacancy clusters is a critical component. The time required to destroy brown colour in the SCLM is significant at the scale of geological time. Brown diamonds should easily maintain their colour for millions of years during cooler mantle storage at or below about 1000 °C. Warmer temperatures toward the base of the lithosphere may be able to reduce or eliminate brown colour within thousands of years. The survival of brown colour in the lithospheric mantle does not require the colour to be formed late in the storage history nor does it require metastable storage in the graphite stability field. Crystal strain is preserved upon loss of brown colour during HPHT treatment. Inhomogeneous crystal strain was measured in 18 natural diamonds using micro-X-ray diffraction (μXRD) χ-dimension peak widths. There is a correlation between strain and depth of brown colour. None of the colourless diamonds examined have high strain, as should be expected for a diamond that has gained and lost brown colour. This suggests that removal of brown colour is not a common natural occurrence. Infrared spectroscopy was used to determine nitrogen concentration and aggregation state in 60 natural diamonds. A loose association was found between brown colour and lower total nitrogen content. Within single diamonds, regions with less nitrogen tend to exhibit more anomalous birefringence due to strain. Colour zoned diamonds tend to have less nitrogen in the darker brown regions. This supports the hypothesis that diamonds with less nitrogen are more susceptible to plastic deformation and the development of brown colour. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2009-09-17 17:10:11.078

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Convection in the Earth's mantle is a complicated phenomenon that causes various tectonic activities and affects mantle evolution on geologic time scales (billions of years). It is a subject as yet not fully understood. The early success of the high Rayleigh number constant viscosity theory was later tempered by the absence of plate motion when the viscosity is more realistically strongly temperature dependent. A similar problem arises if the equally strong pressure dependence of viscosity is considered, since the classical isothermal core convection theory would then imply a strongly variable mantle viscosity, which is inconsistent with results from postglacial rebound studies. We consider a mathematical model for Rayleigh-Bénard convection in a basally heated layer of a fluid whose viscosity depends strongly on both temperature and pressure, defined in an Arrhenius form. The model is solved numerically for extremely large viscosity variations across a unit aspect ratio cell, and steady solutions are obtained. To improve the efficiency of numerical computation, we introduce a modified viscosity law with a low temperature cut-off. We demonstrate that this simplification results in markedly improved numerical convergence without compromising accuracy. Continued numerical experiments suggest that narrow cells are preferred at extreme viscosity contrasts. We are then able to determine the asymptotic structure of the solution, and it agrees well with the numerical results. Beneath a stagnant lid, there is a vigorous convection in the upper part of the cell, and a more sluggish, higher viscosity flow in the lower part of the cell. We then offer some comments on the meaning and interpretation of these results for planetary mantle convection.

xv, 108 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. / Studies on seismic attenuation are an important complement to those on seismic velocity, especially when interpreting results in terms of temperature. But estimation of attenuation (t*) is more computationally involved and prone to contamination by noise, especially signal-generated noise. We have examined the effects of various forms of synthetic noise on t* estimation using time and frequency domain methods with varying window lengths and data frames of reference. We find that for S-waves, error due to noise can be reduced by rotating the data into the estimated polarization direction of the signal, but unless the exact nature of the noise is known, no method or window size is clearly preferable. We recommend the use of multiple estimation methods including a careful assessment of the uncertainty associated with each estimate, which is used as a weight during inversion for 1/Q. Our synthetic tests demonstrate that the misfit between actual and estimate-predicted traces or spectra correlates with t* error, and a similar relationship is suggested for real data. Applying this approach to data from the Yellowstone Intermountain Seismic Array, we employ two important constraints during inversion. First, we scale the misfit values so that the resulting weights are comparable in magnitude to the squares of the eventual data residuals. Second, we smooth the model so that the maximum attenuation (1/Q) does not exceed a value which would totally explain the observed velocity anomaly. The tomographic models from all the estimation methods are similar, but in the vicinity of the Yellowstone mantle plume, S-wave models show greater attenuation than do P-wave models. We attribute this difference to greater focusing by the plume of S-waves. All models show relatively high attenuation for the plume at depth, but above 250 km attenuation in the plume drops rapidly to values less than those of the surrounding mantle. We attribute this drop to the onset of partial melting, which dehydrates the olivine crystals, suppressing dislocation mobility and thereby attenuation. These attenuation models suggest excess plume temperatures at depth which are too low to support a plume origin in the lower mantle. This dissertation includes unpublished co-authored material. / Committee in charge: Eugene Humphreys, Chairperson, Geological Sciences; Emilie Hooft Toomey, Member, Geological Sciences; Douglas Toomey, Member, Geological Sciences; James Isenberg, Outside Member, Mathematics

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.

Orientador: Francisco Sergio Bernardes Ladeira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociencias / Made available in DSpace on 2018-08-11T22:47:00Z (GMT). No. of bitstreams: 1 Sabio_GessikaPollonPuerta_M.pdf: 4540302 bytes, checksum: 79891642e3dc458939eec117d59ee7b1 (MD5) Previous issue date: 2008 / Resumo: A realização de pesquisas voltadas à obtenção de dados qualitativos e quantitativos do manto intempérico de encostas de ambientes tropicais úmidos, é extremamente escassa. O conhecimento de dados de profundidade e de volume do manto intempérico, principalmente, nas áreas de risco de escorregamentos de massa, podem ser muito úteis para o estabelecimento de ações preventivas e de monitoramento de caráter estrutural. A presente pesquisa objetivou realizar o cálculo do volume do manto intempérico, nas encostas da bacia do rio Tavares, no município de Ubatuba - SP. Para tal foram utilizados procedimentos de campo, basicamente através da realização de tradagens, unidos às rotinas e análises geoestatísticas de um Sistema de Informação Geográfica, com o fim de obter como resultado um Modelo Digital de Elevação que representasse a profundidade do manto intempérico da área de estudo e, conseqüentemente, revelasse o volume de material compreendido entre a superfície e o contato manto/rocha. Após a realização de todas as etapas necessárias para a elaboração do Modelo Digital de Elevação, foram elaboradas diversas hipóteses que tentassem explicar o fato de que, após a validação, o modelo foi considerado inviável para aplicação. / Abstract: The completion, implementation or realization of researches aimed to the qualitative and quantitative data of the weathering mantle of slopes of humid tropical environments is extremely scarce. Knowledge of thickness and volume data of the weathering mantle, mainly in the landslides risk areas, may be very useful for the establishment of preventive measures and monitoring of structural character. This research aimed to perform the calculation of the weathering mantle volume of the slopes of Tavares river basin, in Ubatuba - SP. For this, were used such field procedures and geostatistical analyses of a Geographic Information System in order to obtain as a result a Digital Elevation Model that represents the thickness of the weathering mantle of the study area and thus reveal the volume of material between the surface of soil and the mantle/rock contact. After of the completion of all this steps, were compiled some hypotheses that attempt to explain why, after the validation, the model was considered impracticable to apply. / Mestrado / Análise Ambiental e Dinâmica Territorial / Mestre em Geografia

Mantle cell lymphoma (MCL) is a rare B cell neoplasm that accounts for approximately 4-8% of non-Hodgkin’s lymphomas (NHLs). The median age at diagnosis is 65 years with a male to female predominance of 3:1. It has also been demonstrated that female MCL patients have a greater response to therapy, especially immunomodulatory therapy compared to male MCL patients. The concept of cancer immunosurveillance is well described and it is perceived that females mount a greater immune response compared to males. In addition, although lymphomas are generally not perceived to be hormone controlled, epidemiological studies have demonstrated lower prevalence of lymphoma in females taking exogenous oestrogen. This aim of this thesis was to explore the gender difference observed in MCL. The study investigated the difference in the quantity of immune cells in the peripheral blood and lymph node biopsies of untreated male and female MCL patients. There was a significantly greater number of T cells in the peripheral blood of male MCL patients compared to the female MCL patients. Conversely, greater numbers of immune cells were observed in the lymph node biopsies of female MCL patients compared to male MCL patients. In addition, four NK cell activating receptors; NKp46, NKp44, NKp30 and NKG2D were examined to determine if their expression was different between the genders. The cell mediated cytotoxic function of the immune cells (PBMCs) from male and female MCL patients and healthy controls was also examined. Interestingly the healthy controls exhibited greater cytotoxicity compared to the MCL patients. PBMCs were incubated with oestrone (female hormone in postmenopausal women), lenalidomide and IL-2 to further investigate the effects of these on the immune cells from male and female MCL patients. Incubation with IL-2 resulted in a significant increase in the cytotoxicity activity of male MCL patients but not female MCL patients in this cohort. The lymph node biopsies from MCL patients were examined for the presence of oestrogen receptors. Oestrogen receptor β was predominantly expressed on MCL cells in all the biopsies examined. This is an area that warrants further studies. This thesis provides some insight into the mechanisms that may influence the gender difference observed in MCL, however further studies are needed.

A tear in the subducting Nazca slab is located between the end of the Pampean flat slab and normally subducting oceanic lithosphere. Tomographic studies suggest mantle material flows through this opening. The best way to probe this hypothesis is through observations of seismic anisotropy, such as shear wave splitting. We examine patterns of shear wave splitting using data from two seismic deployments in Argentina that lay updip of the slab tear. We observe a simple pattern of plate-motion-parallel fast splitting directions, indicative of plate-motion-parallel mantle flow, beneath the majority of the stations. Our observed splitting contrasts previous observations to the north and south of the flat slab region. Since plate-motion-parallel splitting occurs only coincidentally with the slab tear, we propose mantle material flows through the opening resulting in Nazca plate-motion-parallel flow in both the subslab mantle and mantle wedge.

abstract: The transport of hydrogen to the Earth’s deep interior remains uncertain. The upper mantle minerals have very low hydrogen solubilities (hundreds of ppm). The hydrogen storage capability in the transition zone minerals (2 wt%) is high compared to those of the upper mantle. The hydrogen storage in the lower mantle is not well known. The main minerals in the lower mantle bridgmanite and ferropericlase have very low hydrogen storage capacities (less than 20 ppm). In order to further understand the hydrogen storage in the lower mantle, a series of experiments had been conducted to simulate the environment similar to the Earth’s mantle. The experiments with hydrous Mg2SiO4 ringwoodite (Rw) show that it converts to crystalline dense hydrous silica, stishovite (Stv) or CaCl2-type SiO2(mStv), containing ∼1 wt% H2O together with bridgmanite (Brd) and MgO at the pressure-temperature conditions expected for lower mantle depths between approximately 660 to 1600 km. Brd would break down partially to dense hydrous silica (6–25 mol%) and(Mg,Fe)O in mid-mantle regions with 0.05–0.27 wt% H2O. The hydrous stishovite has a CaCl2 structure, which is common among hydrous minerals in the lower mantle. Based on this observation, I hypothesize the existence of hydrous phases in the lower mantle. The experiments found a new hexagonal iron hydroxide (η-Fe12O18+x/2Hx) between the stability fields of the epsilon and pyrite-type FeOOH at 60–80 GPa and high temperature. The new phase contains less H2O, limiting the H2O transport from the shallow to the deep mantle in the Fe–O–H system. Possible hydrogen storage in Ca-perovskite was studied. CaPv could contain 0.5–1 wt% water and the water in CaPv could distort the crystal structure of CaPv from cubic to tetragonal structure. In conclusion, hydrogen can be stored in hydrous stishovite in the shallower depth of the lower mantle. At greater depth, the new η phase and pyrite-type phase would take over the hydrogen storage. The role of CaPv in deep water storage needs to be considered in future studies. / Dissertation/Thesis / Doctoral Dissertation Natural Science 2019