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Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 55 for “"Lower mantle"”.
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Geomagnetic Impulses and the Electrical Conductivity of the Lower Mantle
… primarily because of their implications for lower mantle conductivity. A major point of discussion has been whether they were of internal or external origin, and to what extent external fields determine their apparent time-scale. A large quantity of monthly means of the geomagnetic field is …
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The effect of trivalent cations on the major lower mantle silicates
… at pressures corresponding to the upper lower mantle. Ferric iron in perovskite undergoes a spin-pairing transition from the high spin state to low spin in the octahedral site. Ferric iron in the dodecahedral site remains high spin. In the absence of aluminum, the spin transition is …
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Developing Levitation Laser-Fused Glasses as Proxies for Lower Mantle Experiments: a Methodological Approach
Observations of heterogeneities in Earth’s mantle motivate studies of mantle phase assemblages with variable composition. As samples cannot be directly collected from these regions, synthetic glasses can act as analogues for mantle melt and starting materials for high-pressure synthesis of stable …
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Single-crystal elasticity of Al-rich phases in the Earth’s transition zone and lower mantle
… must produce chemical heterogeneities in the mantle, which may explain some instances of lateral heterogeneity in seismic wave velocities. Seismic observations of the Earth’s interior provide the only method to investigate the mantle at the depth and scale required to understand its chemistry …
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The Effect of Minor Elements on the Physical and Chemical Properties of Lower Mantle Minerals at High-Pressure
… and crystal chemistry of minerals in Earth's lower mantle are of general importance for the interpretation of seismic wave observations, geochemical modeling, and geodynamic simulations. Aluminum-bearing (Mg,Fe)SiO3 perovskite and (Mg,Fe)O ferropericlase are proposed to be the most abundant …
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Investigation of the properties of iron-bearing alloys and silicates and their implications for the Earth’s lower mantle and core
… perovskite comprises about 80% of the Earth’s lower mantle by volume, leaving ~ 15% to (Mg,Fe)O ferropericlase and ~ 5% to CaSiO3 perovskite. Therefore characteristics of the lower mantle would be determined mostly by the properties of the silicate perovskite and ferropericlase. While high-spin …
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Iron spin crossovers at high pressures and temperatures and their effects on materials relevant tot he Earth’s lower mantle and core
… in pyrolitic model system of the Earth’s lower mantle. The goal is first to understand the nature of the Fe spin crossover in respect to its oxidation state and second to estimate the consequences of their occurrence to processes and the structure in the Earth. Central tools in these …
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Iron oxidation in (Mg,Fe)0: Calibration of the Flank method on synthetic samples and applications on natural inclusions from lower mantle diamonds
… mineral found in diamonds originating in the lower mantle (more than 50% of occurrences). It is well known that the Fe3+ concentration in (Mg,Fe)O is sensitive to oxygen fugacity, even at high pressures. Therefore, the determination of Fe3+/Fetot in such inclusions provides a direct method for …
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Receiver function investigations of mantle transition zone and crustal structure in East Africa and Northeast Asia
… the structure and evolution of the crust, upper mantle, and the mantle transition zone (MTZ) are still controversial. The MTZ discontinuities beneath the study area are imaged by stacking an unprecedented volume of receiver functions (RFs). The normal MTZ thickness beneath the Western Branch of …
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Energy-domain synchrotron radiation Mössbauer source for physics under extreme conditions
… Earth. In the materials that make up the Earth’s lower mantle iron may exist in different valence, spin states and crystallographic environments. Most of the existing experimental techniques either do not allow to separately follow evolution of different iron sites or are not suitable for …
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Seismic Studies of Subducted Lithosphere Beneath Fiji: Evidence for a Petrologic Anomaly
… of prominent anomalies of high VP and VS in the lower mantle implies that a large amount of recently subducted material remains above the lower mantle. This inference is also evident from a subhorizontal swath of outboard earthquakes in the transition zone that is up to one thousand kilometers …
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Iron in oxides, silicates and alloys under extreme pressure-temperature conditions
… (Pv) comprises around 80 vol% of the Earth's lower-mantle, making it by volume the most abundant mineral in our planet, and and there is no doubt that Pv in the mantle contains Fe and Al. However, the exact concentrations are unknown, as well as the effect of pressure on physical properties of …
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Seismic imaging of the mantle transition zone
… high-resolution seismo-stratigraphy of the upper mantle transition zone. The generalized Radon transform (GRT) is based on the single scattering approximation and maps singularities (reflections) in broad-band data into singularities (reflectors/scatters) in the medium. It is able to detect and …
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Elasticity across the post-stishovite transition in subducted basalt
… (Vₛ) anomalies near subducting slabs in the lower mantle, indicating chemical anomalies at depth. Subducting slabs transport surface hydrated mid-ocean ridge basalt (MORB) into deep Earth, which is chemically and physically distinct from the surrounding mantle. Physical properties of MORB …
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Experimental Constraints on Silicate Perovskite Forming Reactions and Elastic Properties: Geophysical Implications for Chemical Heterogeneity in the Deep Mantle
… order to understand how the composition of the mantle may influence mineral stability and elastic properties and how these may influence seismic properties of the deep mantle. The phase relations of calcium perovskite have been studied in high pressure and temperature experiments to examine the …
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High-pressure and high-temperature structural and electronic properties of (Mg,Fe)O and FeO
… Earth as the second most abundant mineral in the lower mantle after (Mg,Fe)SiO3 perovskite. A combined experimental and theoretical study was carried out in order to determine structural and electronic properties of ferropericlase over a broad pressure and temperature range. The phase diagram of …
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The carbon speciation in the Earth’s interior as function of pressure, temperature and oxygen fugacity
… the speciation of volatile elements both in the mantle and in mantle derived magmas. Carbon is one of the principal elements to be affected in this way because under reducing conditions it forms graphite or diamond, and under oxidizing conditions carbonate (or CO2-bearing) minerals and melts. The …
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Dynamics of the North American Plate: Numerical Development, Mantle Flow Modeling, and Receiver Function Analysis
… of the whole plate. Recently, a new generation mantle convection code, ASPECT (Advanced Solver for Problems in Earth ConvecTion) equipped with fully adaptive mesh refinement (AMR) technology opens up the potential to build a multi-scale global mantle flow model with a local high-resolution focus …
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Does the theory of parameterized conveciton apply to layered mantle convection?
… numerous models for convection of the Earth's mantle, the end cases of which are whole-mantle convection and layered convection. Heat flow is an important consideration in the evalution of these models. Simple thermal evolution models based on boundary layer theory have in the past been used to …
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