Global ETD Search
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 73 for “"Asthenosphere"”.
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Seismic Imaging of the Global Asthenosphere using SS Precursors
The asthenosphere, a weak layer beneath the rigid lithosphere, plays a fundamental role in the operation of plate tectonics and mantle convection. While this layer is often characterized by low seismic velocity and high seismic attenuation, the global structure of the asthenosphere remains poorly …
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Seismic imaging of the lithosphere-asthenosphere boundary with a dense broadband array in central California
… extent of interruption of the lithosphere-asthenosphere boundary (LAB). The study area spans the location of two plausible origins for the anomaly, the Monterey microplate (Wang et al., 2013) and Sierra Nevada batholith (Ducea & Saleeby, 1998). Results include 918 binned receiver functions …
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Mantle flow and lithosphere-asthenosphere coupling beneath the southwestern edge of the North American craton: constraints from shear-wave splitting measurements
… anisotropy mostly originate from the upper asthenosphere, through simple shear between the partially coupled lithosphere and asthenosphere"--Abstract, page iv.</p>
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Geophysical and petrological constraints on ocean plate dynamics
… forms at mid-ocean ridges as the underlying asthenosphere rises, melts, and flows away from the ridge axis. In Chapters 2 and 3, I present the results from partial melting experiments of mantle peridotite that were conducted in order to examine the mantle melting point, or solidus, beneath a …
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Geophysical and petrological constraints on ocean plate dynamics
… forms at mid-ocean ridges as the underlying asthenosphere rises, melts, and flows away from the ridge axis. In Chapters 2 and 3, I present the results from partial melting experiments of mantle peridotite that were conducted in order to examine the mantle melting point, or solidus, beneath a …
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LATERALLY HETEROGENEOUS SEISMIC ANISOTROPY INVESTIGATED BY SHEAR WAVE SPLITTING ANALYSES
… observed anisotropy mainly comes from the upper asthenosphere at ~ 250 km and can be explained by a simple geodynamic model invoking absolute plate motion related to simple shear in the lithosphere-asthenosphere transitional layer and mantle flow deflected by the thick lithospheric root of the …
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A model of the crust and upper mantle structure of the Hellenic and Cyprus subduction zones constrained by gravity and seismic data
… the Hellenic and Cyprus trenches. The hot asthenosphere might have induced thermal erosion on the crust beneath southwestern Anatolia. To determine the effects of the hot asthenospheric material on crustal structure, 2.5-D and 3-D gravity models of the Aegean-Anatolian region (24°-33° E and …
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Melt generation in the Earth's mantle at Convergent Plate Margins
… formed by mantle upwelling near the lithosphere-asthenosphere boundary caused by plate subduction, not by a mantle plume (Chapter 4). A geodynamic and petrologic study (Chapter 5) of asthenospheric flow at the margins of thick continental lithosphere reveals small degree melts of the mantle may …
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Receiver function study in northeast Tibet and adjacent boundaries
… Moho geometry and constraints on the lithosphere-asthenosphere boundaries (LAB). The average crustal thickness is about 50km for the northeastern corner of the Tibetan plateau. The deepest Moho is found along the Kunlun Fault zone in the northern Tibetan plateau. We also observed the presence of a …
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Tectonic implications of mantle source changes recorded by Eocene-Oligocene basalts from the Dillon volcanic field southwest Montana (USA)
… ⁸⁷Sr/⁸⁶Sr (0.7043-0.7049) which might suggest an asthenosphere source, however, these rocks have lower, and thus more enriched, ¹⁴³Nd/¹⁴⁴Ndi (0.51203-0.51232), unlike any other documented regional Cenozoic volcanics and we suggest this likely reflects lower crustal interaction. We propose that the …
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Gravity constraints on extension and magmatism in the northernmost Rio Grande rift, northern Colorado
… gravity model to constrain lithosphere and upper asthenosphere density structure. The results are illustrated along three E-W oriented cross sections cutting Middle Park, the Rabbit Ears Range and North Park. The observed gravity field along these profiles correlate with the topography, showing …
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SEISMIC VELOCITY, RADIAL ANISOTROPY IN THE CRUST AND UPPER MANTLE OF NORTHEASTERN TIBETAN PLATEAU FROM SURFACE WAVE TOMOGRAPHY
… and partial melting resulted from localized asthenosphere upwelling after the delamination of a thick lithosphere root beneath the bend. In the second part of the dissertation, a 3-D SH velocity (VSH) model was obtained from the Love wave phase velocities at 13 periods from 20 to 91 s, and …
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Enhanced imaging of deep lithospheric and shallow near surface structures through innovations in seismic interferometry and array processing.
… negative velocity gradient at the Lithosphere-Asthenosphere Boundary (LAB) at approximately 90 km depth. The detection of this event in a relatively high-frequency band, combined with its positive polarity in autocorrelograms, indicates a steep velocity gradient at the LAB consistent with …
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Low viscosity channels and the stability of long wavelength convection
… a low viscosity channel, akin to the Earth's asthenosphere, are characterized by long wavelength flow structure. Boundary layer theory predicts that as the viscosity of the channel decreases, the wavelength that maximizes heat transfer increases. As a pattern selection criterion, this analysis …
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A Geodynamic Investigation of Magma-Poor Rifting Processes and Melt Generation: A Case Study of the Malawi Rift and Rungwe Volcanic Province, East Africa
… is focused on investigating the lithosphere-asthenosphere interactions beneath the Malawi Rift, a segment of the magma-poor Western Branch of the East African Rift (EAR). Chapter 2 and 3 are focused on investigating the sources of melt beneath the Rungwe Volcanic Province (RVP), an anomalous …
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Tidal gravity anomalies in southeastern North America
… distribution of values from regions where the asthenosphere is at intermediate depth, the stress conditions are not excessive, and geothermal heat flow is approximately 60 mW/m².
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INFERRED RHEOLOGY AND UPPER MANTLE CONDITIONS OF WESTERN NEVADA AND SOUTHERN CALIFORNIA-NORTHWEST MEXICO
… the mechanical nature of the lithosphere and asthenosphere using 3D finite element models. When we combine our inferred viscosity structure with calculations of conductive geothermal gradients and models of mantle melting, we can infer environmental conditions of the upper mantle like water …
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The primary structures and fabrics of the upper mantle and lower oceanic crust from ophiolite complexes
… fossilised into the lithospheric mantle at the asthenosphere-lithosphere boundary. This fossilisation occurs during the offaxis, dominantly horizontal, flow of the asthenosphere. A study of the orientations of the D1 and D2 shearing structures from the different areas shows that they have …
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Seismic and numerical constraints on the formation and evolution of oceanic lithosphere
… that make the lithosphere strong relative to the asthenosphere, and we lack a reference model for ordinary lithospheric structure that can serve as a baseline for comparing geophysical observations across locations. Chapters 2 and 3 of this thesis investigate the seismic structure of a portion of …
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Characterization of secondary mantle convection from geophysical data and models
… SAVANI and S40RTS to infer the lithosphere/asthenosphere boundary, and the destabilization of the lithosphere, induced by secondary mantle convection. Former studies, based on numerical and experimental models report that secondary convection would occur as sub-lithospheric longitudinal …
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