Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Bibliography: leaf 40. / by James Louis Franklin. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996. / Includes bibliographical references (p. 270-284). / by Matthias Georg Imhof. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 21-26). / The Avalon terrane in Newfoundland includes the Ediacaran Gaskiers Formation, which has been associated with a Snowball glaciation event. The complicated regional stratigraphy and lack of precise geochronological constraints has made it difficult to determine the spatial and temporal extent of the Gaskiers glaciation. Recent recognition of a diamictite facies on the nearby Bonavista Peninsula correlative with the Gaskiers diamictite has allowed for new, high-precision geochronological constraints on the Gaskiers glaciation and constrains the duration of the event to less than 390 ±320 kyr. The Snowball Earth hypothesis requires that glaciation continued for several millions of years so that CO2 could build up to high enough levels in the atmosphere for catastrophic deglaciation; the short duration of the Gaskiers event makes it unlikely to have been a Snowball event. Further geochronological studies are needed to determine whether the Gaskiers glaciation was a discrete event or if it was a glacial maximum in a longer Ediacaran ice age. / by Judy Pu. / S.B.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1991. / Includes bibliographical references (leaves 173-182). / by Jeffrey A. Meredith. / Sc.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998. / Includes bibliographical references (p. 27-28). / Recent seismological measurements of the Pacific oceanic structure have detected a positive correspondence between surface topography, seismic wave speed, and the geoid (gravitational potential). High seismic wave speed indicates cold material sinking, which pulls the surface downward. Thus, topographic lows are expected to correlate with seismic wave speed highs, contrary to the new seismic measurements. We propose models which include two segregated materials, representing the fertile upper mantle and the residue from crustal melting, in order to decouple the surface topography from subsurface convection and create a positive correlation between topography and wave speed. We add a low viscosity zone beneath the residue to enhance the density contribution to the geoid anomaly and ensure that its sign is in phase with that of the surface topography and wave speed. Our models produce surface topography and geoid anomalies comparable to the recent seismological measurements. These models offer constraints on the strength of the low viscosity zone as well as the density difference between the residue and the upper mantle. / by Mary Alexandra Agner. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / Includes bibliographical references (leaves 128-130). / As part of an ongoing effort to renovate the George R. Wallace Astrophysical Observatory, a new control system and imaging instrument were implemented for the 24-inch telescope. A redesigned telescope drive mechanism and an adaptation of the Lowell Observatory MOVE control system were installed to automate telescope operations. The telescope optics were configured to an f/15 Cassegrain with a resolution of 1 arcsecond, and a large-format commercial CCD detector was installed. The optical configuration gave a pixel scale of 0.55 arcseconds/pixel, covering a field of 0.220 across the diagonal of the detector. As a demonstration of the upgraded system, photometric and astrometric measurements were made to an accuracy of 0.1 magnitudes and better than 1 arcsecond, respectively, under poor atmospheric conditions. / by Janet P. Wu. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010. / "September 2010." Cataloged from PDF version of thesis. / Includes bibliographical references. / Field studies, major and trace element geochemistry, isotopes, petrography, phase equilibrium experiments and thermodynamics are used investigate and understand primitive melts from the Earth and the Moon. Chapter 1 investigates spinifex orthopyroxene compositions from the komatiites of Commondale, South Africa, and uses phase equilibrium experiments to illustrate that the Commondale Komatiites were hydrous magmas when they were emplaced. Hydrous komatiites provide evidence for the existence of subduction zone volcanism during the Archean, and decreases the temperature required to explain komatiites volcanism, which is the major physical evidence used to determine the mantle potential temperature of the Archean. Chapter 2 uses phase equilibrium experiments investigate the origin of the Apollo 15 green glasses from the Moon. Garnet-lherzolite saturated experiments are used to calibrate a melting algorithm used to estimate the chemical compositions of melts of a primordial lunar mantle. Mixing models are used to reproduce the Apollo 15 green glass compositions. These models are consistent with primordial melts assimilating late stage lunar magma ocean cumulates to produce the green glasses. This provides evidence for the magma overturn hypothesis, as well as evidence that the lunar magma ocean may not have been whole moon. Chapter 3 uses phenocryst petrology, Os-isotopes, major and trace element geochemistry and petrography to argue for the formation of primitive magnesian andesites of Mt. Shasta and Mt. Lassen as primary mantle melts. Recent proposals that primitive magnesian andesites form by mixing dacites with subvolcanic peridotite are disproven. Samples of these lavas from newly discovered localities provide clear evidence for a mantle origin for these melts. Understanding the primitive melts present in the Cascade volcanoes will yield greater insight into the mantle processes involved in the plumbing of the sub-arc mantle. Chapter 4 develops a ternary regular solution model for Au-Pd-Fe alloys and uses this with Fe-exchange experiments to model the dependence of alloy composition on the oxygen fugacity. Au-Pd alloy capsules are essential to hydrous phase equilibrium studies at high-pressure and high-temperature, and the use of this model allows for the quantification of the oxygen fugacity of these experiments without compromising sample volume. / by Jay Arthur Barr. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 2001. / Includes bibliographical references (p. 203-208). / Linear quasi-geostrophic theory predicts an exponential amplitude increase with height for Rossby waves propagating vertically through a stratified atmosphere, as a result of wave activity density conservation. At the same time layer-wise conservation of potential enstrophy constrains wave amplitudes, given the limited amount of potential enstrophy available in the initial mean flow. A break down of linear theory is thus expected above a certain critical wave amplitude, raising the question of how the non-linear flow reacts to limit the vertical penetration of waves. Keeping in mind the potential importance for the dynamics of the winter stratosphere, where strong wave penetration and amplitude growth are often observed, the issue of wave saturation in a non-linear flow is examined in a generally abstract context, through a variety of simple model studies. We thus consider the cases of a topographically forced barotropic beta plane channel model, of vertical propagation through a three-dimensional beta plane channel model, and of a polar coordinate model with realistic basic state and geometry. In the barotropic model transient wave growth is forced through the use of bottom topography and the deviations of the non-linear flow evolution from the predictions of both a linear and a quasi-linear analytical solution are examined for strong topographic anomalies. The growth of the forced wave is found to decelerate the zonal mean flow which in turn reduces the topographic forcing. Wave-mean flow interactions are thus found to be sufficient in leading to saturation of the eddy amplitudes. Interestingly it is the formation of zonal mean easterlies, rather than the depletion of mean available potential enstrophy, that is found to be the crucial factor in the saturation dynamics. Similar results are obtained for the case of vertical propagation through a three dimensional beta plane channel. The vertical penetration of the forced wave is shown to cause a reduction of the zonal mean winds and mean potential vorticity gradients in the center of the channel, eventually leading to the formation of either a critical line or a refractive index turning surface. In both cases the penetration of the wave to high altitudes is prohibited, thus constraining wave amplitudes. While signs of non-linear behaviour are clear in synoptic maps of potential vorticity, wave-wave interactions are found to play a secondary role in the saturation process. The results of the three-dimensional beta plane channel model are then extended to a more realistic set-up, using a polar coordinate model with a basic state based on the observed winter stratosphere climatology. The basic conclusions of the idealized study are shown to remain unchanged. / by Constantine Giannitsis. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2009. / Cataloged from PDF version of thesis. Original thesis missing page 1, the Abstract page. / Includes bibliographical references (page 32). / Introduction - The Beni Bousera ultramafic massif is an orogenic lherzolite in northern Morocco, and is part of a large series of ultramafic massifs (Chalouan and Michard, 2004). Like all orogenic lherzolite the method of emplacement into the upper crust is not well understood (Reuber et al., 1982). In this thesis, the Filali gneiss, Kinzingite gneisss, and leucocratic dikes were studied in order to find out their contact relationship with the ultramafic body. A detailed cross section was completed starting in the south, 2 kilometers from the contact, up to the contact. The detailed structures of the exposed gneiss along a transect towards the contact between the host gneiss and ultramafic was studied. Additionally, pressure and temperature estimates on three samples along the transect has been conducted. / by Alison Piasecki. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, September 2007. / "August 2007." / Includes bibliographical references. / The link between environmental and evolutionary change is investigated in the Ediacaran Period (- 635 - 541 million years ago (Ma), an interval where we see the emergence of macroscopic animals along with large perturbations to the carbon and sulfur cycles. Paleoenvironmental reconstruction used the carbon and sulfur isotopic composition of sedimentary minerals and organic matter, supplemented by geochemical and molecular biomarker proxies, of strata from the Huqf Supergroup, Sultanate of Oman. Within Ediacaran strata, three successive stages of geochemical oxidation are observed and correlated to episodes of biological evolution. The second stage corresponds to the large Shuram 613Ccarb excursion and is identified with the oxidation of an organic carbon reservoir. An extreme enrichment in sulfur isotopes occurs in the overlying strata spanning the Ediacaran-Cambrian (E-C) boundary. This interval is characterized using paired sulfate and pyrite sulfur isotopes to quantify pyrite burial and the isotopic composition of sulfur entering the ocean, which leads to a reinterpretation of existing Phanerozoic data. These strata contain sulfates in two forms (carbonate-associated sulfate: CAS, and anhydrite), providing an opportunity to investigate isotopic offsets reported between these seawater sulfate proxies. The results indicate that changing basin restriction can significantly alter the isotopic composition of gypsum/anhydrite and suggest that CAS is the most reliable proxy for the reconstruction of the marine sulfur cycle. A combination of geochemical and biomarker proxies were used to investigate the biological and environmental changes across the Ediacaran- Cambrian boundary. / (cont.) In the Huqf strata, a crash in the photic zone primary production is observed immediately before the geochemical evidence for anoxia that is typically associated with the extinction of the Ediacaran organisms at the E-C boundary. All of these studies rely on interpretations made from geochemical data, which depend on how representative of depositional conditions (local, regional, or global) a given dataset is. Carbon and sulfur isotopes are characterized from replicate sections of the Huqf Supergroup strata to assess the basin-scale (-1,000km) reproducibility of these signals. The trends in the sulfur isotopic record were reproducible across the basin and serve to correlate sections lacking distinctive carbon isotopes or lithologies. / by David Andrew Fike. / Ph.D.