Isotope dilution thorium and uranium analyses of the Harleton chondrite show a\r\nlarger scatter than previously observed in equilibrated ordinary chondrites (EOC). The\r\nlinear correlation of Th/U with 1/U in Harleton (and all EOC data) is produced by\r\nvariation in the chlorapatite to merrillite mixing ratio. Apatite variations control the U\r\nconcentrations. Phosphorus variations are compensated by inverse variations in U to\r\npreserve the Th/U vs. 1/U correlation. Because the Th/U variations reflect phosphate\r\nampling, a weighted Th/U average should converge to an improved solar system Th/U.\r\nWe obtain Th/U=3.53 (1-mean=0.10), significantly lower and more precise than previous\r\nestimates.
\r\n\r\nTo test whether apatite also produces Th/U variation in CI and CM chondrites, we\r\nperformed P analyses on the solutions from leaching experiments of Orgueil and\r\nMurchison meteorites.
\r\n\r\nA linear Th/U vs. 1/U correlation in CI can be explained by redistribution of\r\nhexavalent U by aqueous fluids into carbonates and sulfates.
\r\n\r\nUnlike CI and EOC, whole rock Th/U variations in CMs are mostly due to Th\r\nvariations. A Th/U vs. 1/U linear correlation suggested by previous data for CMs is not\r\nreal. We distinguish 4 components responsible for the whole rock Th/U variations: (1) P\r\nand actinide-depleted matrix containing small amounts of U-rich carbonate/sulfate phases\r\n(similar to CIs); (2) CAIs and (3) chondrules are major reservoirs for actinides, (4) an\r\neasily leachable phase of high Th/U. likely carbonate produced by CAI alteration.\r\nPhosphates play a minor role as actinide and P carrier phases in CM chondrites.
\r\n\r\nUsing our Th/U and minimum galactic ages from halo globular clusters, we\r\ncalculate relative supernovae production rates for 232Th/238U and 235U/238U for different\r\nmodels of r-process nucleosynthesis. For uniform galactic production, the beginning of the\r\nr-process nucleosynthesis must be less than 13 Gyr. Exponentially decreasing production is also\r\nconsistent with a 13 Gyr age, but very slow decay times are required (less than 35 Gyr),\r\napproaching the uniform production. The 15 Gyr Galaxy requires either a fast initial\r\nproduction growth (infall time constant less than 0.5 Gyr) followed by very low decrease (decay\r\ntime constant greater than 100 Gyr), or the fastest possible decrease (\u22488 Gyr) preceded by slow in fall\r\n(\u22487.5 Gyr).
\r\n", "doi": "10.7907/hfsz-ym11", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:14479", "collection": "thesis", "collection_id": "14479", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01202022-231109666", "type": "thesis", "title": "I. Rhenium and Iridium in Natural Waters. II. Methyl Bromide: Ocean Sources, Ocean Sinks, and Climate Sensitivity. III. CO\u2082 Stability and Heterogeneous Chemistry in the Atmosphere of Mars", "author": [ { "family_name": "Anbar", "given_name": "Ariel David", "orcid": "0000-0002-6015-7750", "clpid": "Anbar-Ariel-David" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" } ], "thesis_committee": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Farley", "given_name": "Kenneth A.", "orcid": "0000-0002-7846-7546", "clpid": "Farley-K-A" }, { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Part I: Rhenium and iridium were measured in natural waters by isotope dilution and negative thermal ionization mass spectrometry, following clean chemical separation from 200 mL (Re) and 4 L (Ir) samples. In the Pacific\r\nOcean, Re is well-mixed in the water column, confirming predictions of conservative behavior. The Re concentration is 7.42 \u00b1 0.04 ng kg\u207b\u00b9. The concentration of Ir in the oceans is fairly uniform with depth and location, ranging from 2.9 to 5.7 x 10\u2078 atoms kg\u207b\u00b9. Pristine river water contains \u2248 20 x 10\u2078 atoms kg\u207b\u00b9 while polluted rivers have 50 - 100 x 10\u2078 atoms kg\u207b\u00b9. Concentrations in the Baltic Sea are much lower than expected from conservative estuarine mixing, indicating rapid removal of \u224875% of riverine Ir. Under oxidizing conditions, Ir is scavenged by Fe-Mn oxyhydroxides. Ir is enriched in anoxic waters relative to overlying oxic waters, indicating that anoxic sediments are not a major Ir sink. The residence time of dissolved Ir in the oceans is 10\u00b3 - 10\u2074 years, based on these and other observations. The amount of Ir in Ktr boundary sediments is \u224810\u00b3 times the total quantity in the oceans.
\r\n\r\nPart II: The biogeochemistry of methyl bromide (CH\u2083Br) in the oceans was studied using a steady-state mass-balance model. CH\u2083Br concentrations are sensitive to temperature and the rate of CH\u2083Br production. Model production rates correlate strongly with chlorophyll concentrations, indicating CH\u2083Br biogenesis. This correlation explains discrepancies between two observational studies, and supports suggestions that the ocean is a net sink for atmospheric CH\u2083Br. The Southern Ocean may be a CH\u2083Br source.
\r\n\r\nPart III: High resolution, temperature-dependent CO\u2082 cross sections were incorporated into a 1-D photochemical model of the Martian atmosphere. The calculated CO\u2082 photodissociation rate decreased by as much as 33% at some\r\naltitudes, and the photodissociation rates of H\u2082O and O\u2082 increased by as much as 950% and 80%, respectively. These results minimize or even reverse the sense of the CO\u2082 chemical stability problem due to increased production of HO\u2093 species which catalyze CO oxidation. The effect of heterogeneous chemistry on the abundance and distribution of HO\u2093 was assessed using observations of dust and ice aerosols and laboratory adsorption data.\r\nAdsorption of HO\u2082 can deplete OH in the lower atmosphere enough to significantly reduce the CO/CO\u2082 ratio.
", "doi": "10.7907/rrjq-k179", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:8653", "collection": "thesis", "collection_id": "8653", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09042014-150651827", "primary_object_url": { "basename": "Blum_jd_1990.pdf", "content": "final", "filesize": 39778705, "license": "other", "mime_type": "application/pdf", "url": "/8653/1/Blum_jd_1990.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Geochemistry and Resonance Ionization of Platinum-Group Elements", "author": [ { "family_name": "Blum", "given_name": "Joel David", "clpid": "Blum-Joel-David" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "thesis_committee": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Experimental studies were conducted with the goals of 1) determining the origin of Pt-group element (PGE) alloys and associated mineral assemblages in refractory inclusions from meteorites and 2) developing a new ultrasensitive method for the in situ chemical and isotopic analysis of PGE. A general review of the geochemistry and cosmochemistry of the PGE is given, and specific research contributions are presented within the context of this broad framework.
\r\n\r\nAn important step toward understanding the cosmochemistry of the PGE is the determination of the origin of POE-rich metallic phases (most commonly \u03b5Ru-Fe) that are found in Ca, AJ-rich refractory inclusions (CAI) in C3V meteorites. These metals occur along with \u03b3Ni-Fe metals, Ni-Fe sulfides and Fe oxides in multiphase opaque assemblages. Laboratory experiments were used to show that the mineral assemblages and textures observed in opaque assemblages could be produced by sulfidation and oxidation of once homogeneous Ni-Fe-PGE metals. Phase equilibria, partitioning and diffusion kinetics were studied in the Ni-Fe-Ru system in order to quantify the conditions of opaque assemblage formation. Phase boundaries and tie lines in the Ni-Fe-Ru system were determined at 1273, 1073 and 873K using an experimental technique that allowed the investigation of a large portion of the Ni-Fe-Ru system with a single experiment at each temperature by establishing a concentration gradient within which local equilibrium between coexisting phases was maintained. A wide miscibility gap was found to be present at each temperature, separating a hexagonal close-packed \u03b5Ru-Fe phase from a face-centered cubic \u03b3Ni-Fe phase. Phase equilibria determined here for the Ni-Fe-Ru system, and phase equilibria from the literature for the Ni-Fe-S and Ni-Fe-O systems, were compared with analyses of minerals from opaque assemblages to estimate the temperature and chemical conditions of opaque assemblage formation. It was determined that opaque assemblages equilibrated at a temperature of ~770K, a sulfur fugacity 10 times higher than an equilibrium solar gas, and an oxygen fugacity 10\u2076 times higher than an equilibrium solar gas.
\r\n\r\nDiffusion rates between -\u03b3Ni-Fe and \u03b5Ru-Fe metal play a critical role in determining the time (with respect to CAI petrogenesis) and duration of the opaque assemblage equilibration process. The diffusion coefficient for Ru in Ni (DRuNi) was determined as an analog for the Ni-Fe-Ru system by the thin-film diffusion method in the temperature range of 1073 to 1673K and is given by the expression:
\r\n\r\nDRuNi (cm\u00b2 sec\u207b\u00b9) = 5.0(\u00b10.7) x 10\u207b\u00b3 exp(-2.3(\u00b10.1) x 10\u00b9\u00b2 erg mole\u207b\u00b9/RT) where R is the gas constant and T is the temperature in K. Based on the rates of dissolution and exsolution of metallic phases in the Ni-Fe-Ru system it is suggested that opaque assemblages equilibrated after the melting and crystallization of host CAI during a metamorphic event of \u2265 10\u00b3 years duration. It is inferred that opaque assemblages originated as immiscible metallic liquid droplets in the CAI silicate liquid. The bulk compositions of PGE in these precursor alloys reflects an early stage of condensation from the solar nebula and the partitioning of V between the precursor alloys and CAI silicate liquid reflects the reducing nebular conditions under which CAI were melted. The individual mineral phases now observed in opaque assemblages do not preserve an independent history prior to CAI melting and crystallization, but instead provide important information on the post-accretionary history of C3V meteorites and allow the quantification of the temperature, sulfur fugacity and oxygen fugacity of cooling planetary environments. This contrasts with previous models that called upon the formation of opaque assemblages by aggregation of phases that formed independently under highly variable conditions in the solar nebula prior to the crystallization of CAI.
\r\n\r\nAnalytical studies were carried out on PGE-rich phases from meteorites and the products of synthetic experiments using traditional electron microprobe x-ray analytical techniques. The concentrations of PGE in common minerals from meteorites and terrestrial rocks are far below the ~100 ppm detection limit of the electron microprobe. This has limited the scope of analytical studies to the very few cases where PGE are unusually enriched. To study the distribution of PGE in common minerals will require an in situ analytical technique with much lower detection limits than any methods currently in use. To overcome this limitation, resonance ionization of sputtered atoms was investigated for use as an ultrasensitive in situ analytical technique for the analysis of PGE. The mass spectrometric analysis of Os and Re was investigated using a pulsed primary Ar\u207a ion beam to provide sputtered atoms for resonance ionization mass spectrometry. An ionization scheme for Os that utilizes three resonant energy levels (including an autoionizing energy level) was investigated and found to have superior sensitivity and selectivity compared to nonresonant and one and two energy level resonant ionization schemes. An elemental selectivity for Os over Re of \u2265 10\u00b3 was demonstrated. It was found that detuning the ionizing laser from the autoionizing energy level to an arbitrary region in the ionization continuum resulted in a five-fold decrease in signal intensity and a ten-fold decrease in elemental selectivity. Osmium concentrations in synthetic metals and iron meteorites were measured to demonstrate the analytical capabilities of the technique. A linear correlation between Os\u207a signal intensity and the known Os concentration was observed over a range of nearly 10\u2074 in Os concentration with an accuracy of ~ \u00b110%, a millimum detection limit of 7 parts per billion atomic, and a useful yield of 1%. Resonance ionization of sputtered atoms samples the dominant neutral-fraction of sputtered atoms and utilizes multiphoton resonance ionization to achieve high sensitivity and to eliminate atomic and molecular interferences. Matrix effects should be small compared to secondary ion mass spectrometry because ionization occurs in the gas phase and is largely independent of the physical properties of the matrix material. Resonance ionization of sputtered atoms can be applied to in situ chemical analysis of most high ionization potential elements (including all of the PGE) in a wide range of natural and synthetic materials. The high useful yield and elemental selectivity of this method should eventually allow the in situ measurement of Os isotope ratios in some natural samples and in sample extracts enriched in PGE by fire assay fusion.
\r\n\r\nPhase equilibria and diffusion experiments have provided the basis for a reinterpretation of the origin of opaque assemblages in CAI and have yielded quantitative information on conditions in the primitive solar nebula and cooling planetary environments. Development of the method of resonance ionization of sputtered atoms for the analysis of Os has shown that this technique has wide applications in geochemistry and will for the first time allow in situ studies of the distribution of PGE at the low concentration levels at which they occur in common minerals.
", "doi": "10.7907/KXRF-AQ49", "publication_date": "1990", "thesis_type": "phd", "thesis_year": "1990" }, { "id": "thesis:5746", "collection": "thesis", "collection_id": "5746", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04282010-113920823", "type": "thesis", "title": "Isotopic Heterogeneity in Calcium-Aluminum-Rich Meteoritic Inclusions", "author": [ { "family_name": "Brigham", "given_name": "Cheryl A.", "clpid": "Brigham-Cheryl-A" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" } ], "thesis_committee": [ { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Calcium-Aluminum-rich inclusions (CAI), found in meteorites, are among the oldest known solids identified in the solar system. Analyses of CAI have provided constraints on physical and chemical conditions that existed just prior to, and during planetary formation. A few rare inclusions, called FUN (for Fractionation and Unknown Nuclear effects), exhibit large isotopic anomalies and have provided insight into nucleosynthetic and nebular processes.
\r\n\r\nIn this thesis, data obtained on the petrography, chemistry and isotopic compositions of CAI, identified in the carbonaceous chondrite Allende, are used as tracers to address several specific questions: 1) What are the relationships between fine and coarse-grained CAI? 2) What are the differences, in composition and origin, between FUN inclusions and isotopically normal CAI? 3) What was the role of volatility-controlled processes, such as distillation and condensation, in the evolution of CAI? 4) What was the role of chemical alteration and isotopic reequilibration in the evolution of CAI?
\r\n\r\nIsotopic data were obtained by thermal ionization and ion microprobe mass spectrometry for individual grains within both fine and coarse-grained CAI, and correlated with petrographic and chemical observations. Evidence is presented for the enrichment of fine-grained inclusions in the lighter isotopes of Mg, in contrast to coarse-grained CAI, which are enriched in the heavier isotopes. Isotopic heterogeneity was observed within both fine and coarse-grained inclusions. Heterogeneity is discussed in the context of primary and secondary phases, mineral alteration processes, and isotopic reequilibration.
\r\n\r\nA new class of coarse-grained inclusion, characterized by a distinct purple color and high spinel contents (\u226550%), were identified and found to exhibit a high frequency (20%) of FUN isotopic anomalies. Four new FUN inclusions were identified and studied in detail. The correlated isotopic fractionation for Mg, Si, and Cr in these inclusions, suggests the importance of volatility-controlled formation processes. A model is presented for the evolution of FUN inclusions, involving distillation of ordinary chondritic material, with a mass loss of around 70%, followed by exchange with isotopically normal reservoirs. The high spinel contents and large isotopic fractionation of these inclusions, may indicate that they formed at higher temperatures than isotopically normal CAI.
", "doi": "10.7907/TYS3-HQ41", "publication_date": "1990", "thesis_type": "phd", "thesis_year": "1990" }, { "id": "thesis:7945", "collection": "thesis", "collection_id": "7945", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08262013-145328209", "type": "thesis", "title": "The \u00b2\u2076Al(p,\u03b3)\u00b2\u2077Si Reaction: Stellar Origins of Galactic \u00b2\u2076Al", "author": [ { "family_name": "Vogelaar", "given_name": "Robert Bruce", "clpid": "Vogelaar-Robert-Bruce" } ], "thesis_advisor": [ { "family_name": "Kavanagh", "given_name": "Ralph William", "clpid": "Kavanagh-R-W" } ], "thesis_committee": [ { "family_name": "Kavanagh", "given_name": "Ralph William", "clpid": "Kavanagh-R-W" }, { "family_name": "Barish", "given_name": "Barry C.", "clpid": "Barish-B-C" }, { "family_name": "Boehm", "given_name": "Felix H.", "clpid": "Boehm-F-H" }, { "family_name": "Papanastassiou", "given_name": "Dimitri A.", "clpid": "Papanastassiou-Dimitri-A" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "To explain the \u00b2\u2076Mg isotopic anomaly seen in meteorites (\u00b2\u2076Al daughter) as well as the observation of 1809-keV \u03b3 rays in the interstellar medium (live decay of \u00b2\u2076Al) one must know, among other things, the destruction rate of \u00b2\u2076Al. Properties of states in \u00b2\u2077Si just above the \u00b2\u2076Al + p mass were investigated to determine the destruction rate of \u00b2\u2076Al via the \u00b2\u2076Al(p,\u03b3)\u00b2\u2077Si reaction at astrophysical temperatures.
\r\n\r\nTwenty micrograms of \u00b2\u2076Al were used to produce two types of Al\u2082O\u2083 targets by evaporation of the oxide. One was onto a thick platinum backing suitable for (p,\u03b3) work, and the other onto a thin carbon foil for the (\u00b3He,d) reaction.
\r\n\r\nThe \u00b2\u2076Al(p,\u03b3)\u00b2\u2077Si excitation function, obtained using a germanium detector and voltage-ramped target, confirmed known resonances and revealed new ones at 770, 847, 876, 917, and 928 keV. Possible resonances below the lowest observed one at E\u209a = 286 keV were investigated using the \u00b2\u2076Al(\u00b3He,d)\u00b2\u2077Si proton-transfer reaction. States in \u00b2\u2077Si corresponding to 196- and 286-keV proton resonances were observed. A possible resonance at 130 keV (postulated in prior work) was shown to have a strength of \u03c9\u03b3 less than 0.02 \u00b5eV.
\r\n\r\nBy arranging four large NaI detector as a 47\u03c0 calorimeter, the 196-keV proton resonance, and one at 247 keV, were observed directly, having \u03c9\u03b3 = 55 \u00b1 9 and 10 \u00b1 5 \u00b5eV, respectively.
\r\n\r\nLarge uncertainties in the reaction rate have been reduced. At novae temperatures, the rate is about 100 times faster than that used in recent model calculations, casting some doubt on novae production of galactic \u00b2\u2076Al.
", "doi": "10.7907/vbh6-nk69", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:8006", "collection": "thesis", "collection_id": "8006", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10232013-113130725", "type": "thesis", "title": "Chemical and Mineralogical Characterization of Micro-Inclusions in Diamonds", "author": [ { "family_name": "Navon", "given_name": "Oded", "clpid": "Navon-Oded" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" } ], "thesis_committee": [ { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Armstrong", "given_name": "John T.", "clpid": "Armstrong-John-T" }, { "family_name": "Hutcheon", "given_name": "Ian D.", "clpid": "Hutcheon-Ian-D" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Wyllie", "given_name": "Peter J.", "clpid": "Wyllie-P-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Secondary-ion mass spectrometry (SIMS), electron probe analysis (EPMA), analytical scanning electron microscopy (SEM) and infrared (IR) spectroscopy were used to determine the chemical composition and the mineralogy of sub-micrometer inclusions in cubic diamonds and in overgrowths (coats) on octahedral diamonds from Zaire, Botswana, and some unknown localities.
\r\n\r\nThe inclusions are sub-micrometer in size. The typical diameter encountered during transmission electron microscope (TEM) examination was 0.1-0.5 \u00b5m. The micro-inclusions are sub-rounded and their shape is crystallographically controlled by the diamond. Normally they are not associated with cracks or dislocations and appear to be well isolated within the diamond matrix. The number density of inclusions is highly variable on any scale and may reach 10\u00b9\u00b9 inclusions/cm\u00b3 in the most densely populated zones. The total concentration of metal oxides in the diamonds varies between 20 and 1270 ppm (by weight).
\r\n\r\nSIMS analysis yields the average composition of about 100 inclusions contained in the sputtered volume. Comparison of analyses of different volumes of an individual diamond show roughly uniform composition (typically \u00b110% relative). The variation among the average compositions of different diamonds is somewhat greater (typically \u00b130%). Nevertheless, all diamonds exhibit similar characteristics, being rich in water, carbonate, SiO\u2082, and K\u2082O, and depleted in MgO. The composition of micro-inclusions in most diamonds vary within the following ranges: SiO\u2082, 30-53%; K\u2082O, 12-30%; CaO, 8-19%; FeO, 6-11%; Al\u2082O\u2083, 3-6%; MgO, 2-6%; TiO\u2082, 2-4%; Na\u2082O, 1-5%; P\u2082O\u2085, 1-4%; and Cl, 1-3%. In addition, BaO, 1-4%; SrO, 0.7-1.5%; La\u2082O\u2083, 0.1-0.3%; Ce\u2082O\u2083, 0.3-0.5%; smaller amounts of other rare-earth elements (REE), as well as Mn, Th, and U were also detected by instrumental neutron activation analysis (INAA). Mg/(Fe+Mg), 0.40-0.62 is low compared with other mantle derived phases; K/AI ratios of 2-7 are very high, and the chondrite-normalized Ce/Eu ratios of 10-21 are also high, indicating extremely fractionated REE patterns.
\r\n\r\nSEM analyses indicate that individual inclusions within a single diamond are roughly of similar composition. The average composition of individual inclusions as measured with the SEM is similar to that measured by SIMS. Compositional variations revealed by the SEM are larger than those detected by SIMS and indicate a small variability in the composition of individual inclusions. No compositions of individual inclusions were determined that might correspond to mono-mineralic inclusions.
\r\n\r\nIR spectra of inclusion- bearing zones exhibit characteristic absorption due to: (1) pure diamonds, (2) nitrogen and hydrogen in the diamond matrix; and (3) mineral phases in the micro-inclusions. Nitrogen concentrations of 500-1100 ppm, typical of the micro-inclusion-bearing zones, are higher than the average nitrogen content of diamonds. Only type IaA centers were detected by IR. A yellow coloration may indicate small concentration of type IB centers.
\r\n\r\nThe absorption due to the micro-inclusions in all diamonds produces similar spectra and indicates the presence of hydrated sheet silicates (most likely, Fe-rich clay minerals), carbonates (most likely calcite), and apatite. Small quantities of molecular CO\u2082 are also present in most diamonds. Water is probably associated with the silicates but the possibility of its presence as a fluid phase cannot be excluded. Characteristic lines of olivine, pyroxene and garnet were not detected and these phases cannot be significant components of the inclusions. Preliminary quantification of the IR data suggests that water and carbonate account for, on average, 20-40 wt% of the micro-inclusions.
\r\n\r\nThe composition and mineralogy of the micro-inclusions are completely different from those of the more common, larger inclusions of the peridotitic or eclogitic assemblages. Their bulk composition resembles that of potassic magmas, such as kimberlites and lamproites, but is enriched in H\u2082O, CO\u207c\u2083, K\u2082O, and incompatible elements, and depleted in MgO.
\r\n\r\nIt is suggested that the composition of the micro-inclusions represents a volatile-rich fluid or a melt trapped by the diamond during its growth. The high content of K, Na, P, and incompatible elements suggests that the trapped material found in the micro-inclusions may represent an effective metasomatizing agent. It may also be possible that fluids of similar composition are responsible for the extreme enrichment of incompatible elements documented in garnet and pyroxene inclusions in diamonds.
\r\n\r\nThe origin of the fluid trapped in the micro-inclusions is still uncertain. It may have been formed by incipient melting of a highly metasomatized mantle rocks. More likely, it is the result of fractional crystallization of a potassic parental magma at depth. In either case, the micro-inclusions document the presence of highly potassic fluids or melts at depths corresponding to the diamond stability field in the upper mantle. The phases presently identified in the inclusions are believed to be the result of closed system reactions at lower pressures.
", "doi": "10.7907/A88J-S465", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:4031", "collection": "thesis", "collection_id": "4031", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10112005-103528", "type": "thesis", "title": "High Precision Thorium-230 Ages of Corals and the Timing of Sea Level Fluctuations in the Late Quaternary", "author": [ { "family_name": "Edwards", "given_name": "Richard Lawrence", "clpid": "Edwards-Richard-Lawrence" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" } ], "thesis_committee": [ { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Sieh", "given_name": "Kerry E.", "clpid": "Sieh-K-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Mass spectrometric techniques for the measurement of \u00b2\u00b3\u2070Th and \u00b2\u00b3\u2074U have been developed. These techniques have made it possible to reduce the analytical errors in \u00b2\u00b3\u2070Th dating of corals using very small samples. Samples of 8 x 10\u2077 atoms of \u00b2\u00b3\u2070Th can be measured to an accuracy of \u00b1130% (2 sigma), 6 x 10\u2078 atoms of \u00b2\u00b3\u2070Th can be measured to an accuracy of \u00b129%, and 3 x 10\u00b9\u2070 atoms of \u00b2\u00b3\u2070Th can be measured to an accuracy of \u00b12%. The time range over which useful data on corals can now be obtained ranges from 15 to 500,000 years. The error in age (based on analytical error) for a sample that is 18 years old \u00b13 years (2 sigma). The error is \u00b15 years at 180 years, \u00b144 years at 8294 years, and \u00b11 ky at 123.1 ky. For young corals, this approach may be preferable to \u00b9\u2074C dating.
\r\n\r\nFluctuations in climate result in changes in sea level because the ice stored in continental glaciers is ultimately derived from the ocean. Certain species of coral grow close to the sea surface. Fossils of these species therefore record the former height of the sea surface. The precision with which the age of a coral can now be determined makes it possible to determine, with some precision, the timing of sea level fluctuations in the late Quaternary. This record will allow a critical test of the Milankovitch hypothesis, which predicts the timing of Pleistocene climate fluctuations from changes in the distribution of solar insolation that result from changes in the earth's orbital geometry. Analyses of a number of corals that grew during the last interglacial period yield ages of 122 to 130 ky. The ages coincide with or slightly postdate the summer solar insolation high at 65\u00b0N latitude, which occurred 128 ky ago. This supports the idea that changes in Pleistocene climate can be the result of orbital forcing.
\r\n\r\nApparent fluctuations in sea level recorded on tectonically active shorelines are the result of both sea level change and vertical tectonic movement. If the record of sea level change is known (e.g., from the coral record in a stable area), this record can be subtracted from the record of apparent sea level change, in the tectonically active area, to yield a record of vertical tectonic movement. The precision with which coral ages can now be determined may allow us to resolve the ages of individual coseisimic uplift events and thereby date prehistoric earthquakes.
\r\n\r\nThis possibility has been examined at two localities, northwest Santo Island and north Malekula Island, Vanuatu. Previous work (Taylor et al., 1980, 1985a, 1987) showed (using the counting of annual growth bands to determine ages) that the tops of partially emerged coral heads at each locality died at the same time as the last major earthquake at each locality (MS = 7.5, 1973, on northwest Santo; and MS = 7.5, 1965, on north Malekula). It was concluded that the tops of these coral heads were killed by coseismic uplift. At each locality, there were also completely emerged coral heads, which were inferred to have been killed by earlier coseismic uplift events. These could not be dated by growth band counting because the coral heads were completely dead.
\r\n\r\nThe accuracy of \u00b2\u00b3\u2070Th ages of very young corals was tested by dating portions of three corals whose ages were known from the counting of growth bands. Within analytical error, the \u00b2\u00b3\u2070Th ages were the same as the growth band ages for all three samples (dates of growth by counting growth bands - A.D. 1971 to 1973, A.D. 1935 to 1939, and A.D. 1804 to 1810; dates of growth from \u00b2\u00b3\u2070Th measurements - A.D. 1969 \u00b1 3, A.D. 1932 \u00b1 5, and A.D. 1806 5 [2 sigma \u00b11) demonstrating that the \u00b2\u00b3\u2070Th ages were accurate.
\r\n\r\nThe \u00b2\u00b3\u2070Th growth dates of the surfaces of adjacent emerged coral heads, collected from the same elevation (1.2 m) on northwest Santo Island, were, within analytical error, identical (A.D. 1866 \u00b1 4 and A.D. 1864 \u00b1 4). This indicates that the corals died at the same time and is consistent with the idea that they were killed by coseismic uplift. Similar adjacent coral heads on north Malekula Island yielded \u00b2\u00b3\u2070Th growth dates of A.D. 1729 \u00b1 3 and A.D. 1718 \u00b1 5. The ages are similar but analytically distinguishable. The difference may be due to erosion of the outer, younger, portion of the latter coral head. Using the date of the large historical earthquake at each locality and the \u00b2\u00b3\u2070Th growth date of the emerged corals at each locality, recurrence intervals of 108 years for northwest Santo and 236 years for north Malekula are calculated.
\r\n\r\nThis experiment has shown that it is possible to date corals that grew in the past several centuries to accuracies of \u00b13 to \u00b15 years (2 sigma). The main problems with applying this approach to determine seismic histories will be associated with the preservation of fossil corals that have been killed by coseimic uplift and the ability to identify such features in the field.
", "doi": "10.7907/S2FW-0463", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:11448", "collection": "thesis", "collection_id": "11448", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04052019-172938000", "type": "thesis", "title": "Magmons: Solitary Waves Arising in the Buoyant Ascent of Magma by Porous Flow through a Viscously Deformable Matrix", "author": [ { "family_name": "Scott", "given_name": "David Russell", "clpid": "Scott-David-Russell" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The dynamics of partially molten regions of the Earth's mantle are studied using a combination of theoretical, experimental, and numerical techniques. The physical model is based on experimental observations of partially molten ultramafic rocks and incorporates two elements: buoyancy-driven porous flow of magma through a viscously deformable matrix, and buoyancy-driven circulation of the whole rock.
\r\n\r\nThe first element of this model is analogous to buoyancy-driven pipe flow of a liquid through a denser and more viscous wall fluid. Laboratory experiments on this system illustrate the phenomenon of solitary waves. These are waves of larger pipe radius that ascend a uniform pipe of smaller radius. The waves are very nearly conserved in collisions. These, and the corresponding waves of higher porosity that arise in one-dimensional porous flow, are characterized further by analysis and numerical experiments.
\r\n\r\nThe full system, incorporating circulation in a multidimensional porous medium, also displays solitary waves governed by the same basic processes as the one-dimensional waves. Analysis and numerical experiments show that the multidimensional waves have a circular or spherical form.
\r\n\r\nA possible natural manifestation of this fluid dynamical phenomenon is in igneous processes. Magmons, as the waves are called in that setting, probably have wavelengths of kilometers and velocities of centimeters per year. Magma ascent in magmons may account for episodicity in igneous emplacement. Also, a magmon can collect and mobilize a small degree of partial melt without disturbing its geochemical signature. In a partially molten region the characteristic wavelength of magmons will always be superimposed on that of large scale variations in porosity.
", "doi": "10.7907/mvdj-ty73", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:3133", "collection": "thesis", "collection_id": "3133", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08152006-132531", "primary_object_url": { "basename": "Piepgras_dj_1984.pdf", "content": "final", "filesize": 13047842, "license": "other", "mime_type": "application/pdf", "url": "/3133/1/Piepgras_dj_1984.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Isotopic Composition of Neodymium in the Marine Environment: Investigations of the Sources and Transport of Rare Earth Elements in the Oceans", "author": [ { "family_name": "Piepgras", "given_name": "Donald John", "clpid": "Piepgras-Donald-John" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" }, { "family_name": "Patterson", "given_name": "Clair C.", "clpid": "Patterson-C-C" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "In this study, the isotopic composition of neodymium in the marine environment has been determined from analysis of marine ferromanganese precipitates and seawater. An initial survey of the isotopic composition of Nd in the marine environment was made utilizing the analyses of authigenic ferromanganese sediments. These included ferromanganese nodules, metalliferous sediments, and hydrothermal ferromanganese crust deposits. Large variations in \u03b5Nd(0) values are observed which exhibit a clear separation of the ocean basin. Nd isotopic variations within an ocean basin fall within a relatively small, well defined range which is characteristic of the ocean basin sampled. Based on these results, the following average 143Nd/144Nd ratios for the ocean basins have been determined: Atlantic Ocean, \u03b5Nd(0) \u2248 -12; Indian Ocean, \u03b5Nd(0) \u2248 -8; Pacific Ocean, \u03b5Nd(0) \u2248 -3. These values are considerably lower than \u03b5Nd(0) values associated sources having oceanic mantle affinities, indicating that the REE in the oceans are dominated by continental sources. Therefore, the variations must reflect primarily the age and 147Sm/144Nd ratio of the continental masses being sampled.
\r\n\r\nDirect measurements of the isotopic composition of Nd in seawater samples from the Atlantic and Pacific are in excellent agreement with the values determined from the ferromanganese sediments indicating that these sediments accurately reflect the isotopic composition of Nd dissolved in seawater. The results clearly demonstrate the existence of distinctive Nd isotopic differences in waters of the major ocean basins. These values correspond to a difference in the absolute abundance of 143Nd between the Atlantic and the Pacific Oceans of ~ 10(6) atoms 143Nd per gram of seawater. In addition to the isotopic differences observed between the ocean basins, smaller but distinctive variations are observed in the water column of both the Pacific and the Atlantic, indicating different sources of REE at different levels in the water column. This suggests that it may be possible to distinguish the sources of water masses within an ocean basin on the basis of Nd isotopic composition.
\r\n\r\nThe isotopic composition of Nd was determined in seawater samples from the Drake Passage in order to monitor the exchange of REE between the Pacific and Atlantic Oceans. The Antarctic Circumpolar Current, which flows eastward through this passage, represents the primary conduit through which the major ocean basins communicate with each other. The isotopic composition of Nd is found to be uniform with depth at all stations and corresponds to \u03b5Nd(0) \u2243 -9.0. This value is intermediate between the values for the Atlantic and the Pacific and indicates that the Antarctic Circumpolar Current consists of about 70 percent Atlantic water. By using a box model to describe the exchange of water between the Southern Ocean and the ocean basins to the north together with the isotopic results, an upper limit of approximately 33 million cubic meters per second is calculated for the rate of exchange between the Pacific and the Southern Ocean.
\r\n\r\nThe concentration of Nd exhibits a regular increase with depth at all locations studied. In contrast, Nd isotopic compositions can exhibit substantial variations in the water column which vary depending on the location. Where isotopic differences in the water column occur, substantial lateral transport of REE from different sources and at different levels in the water column is required to maintain these differences. It is shown that the concentration gradients are established without significantly affecting the isotopic distribution, and that the enrichment of Nd in the deep water cannot be a result of resolution of REE scavenged from surface waters.
\r\n\r\nThe isotopic distributions are compared to water mass analyses based on temperature and salinity characteristics in the water column at the various sampling locations. It is shown that differences in isotopic compositions in the water column are well correlated with changes in the temperature and salinity characteristics. Thus, the isotopic distributions are fully consistent with the circulation of major water masses. This indicates that while Nd is nonconservative in concentration, the isotopic composition is conserved and can be used as a tracer for studying the origin and circulation of water masses.
\r\n\r\nThe results of these studies have provided some important contributions to the understanding of trace element transport in the oceans. First, the Nd isotopic differences in the water column clearly indicate that transport of Nd from the surface to the deep ocean cannot account for the observed increase in concentration of Nd with depth. These isotopic differences must be maintained by lateral transport of the REE and indicates that the concentration gradients of the REE and possibly other trace elements must also be related in part to lateral transport processes. Second, the close correlation observed between changes in Nd isotopic compositions and temperature-salinity relationships in the water column indicates that the lateral transport of REE in the oceans is directly related to the origin and flow of water masses. Thus, the isotopic composition of Nd in seawater is shown to be a useful tracer for studying the sources of injection and transport of trace elements in the oceans.
\r\n\r\nIn addition to the seawater studies, the concentrations and isotopic compositions of Nd and Sr were determined in hydrothermal solutions emanating from hot springs on the crest of the East Pacific Rise at 21\u00b0N and at Guaymas Basin, Gulf of California. This study represents the first effort to measure the Nd isotopic compositions in hydrothermal solutions. Endmember samples (T = 350\u00b0C) from 21\u00b0N exhibit a small range in \u03b5Sr values from -13.4 to -15.7. Correcting to CMg = 0, the pure hydrothermal solutions are estimated to have \u03b5Sr \u2243 -18. These results indicate that the fluids have undergone extensive but not complete exchange with Sr in the depleted oceanic crust (\u03b5Sr \u2243 -30). CSr ranges from 5.8 to 8.7 ppm and is similar to seawater (7.6 ppm) indicating that there must be buffering. Hydrothermal solutions from Guaymas Basin (T = 315\u00b0C) rise through several hundred meters of sediment before reaching the sea floor. One sample from here has \u03b5Sr = +5.8, indicating that the solutions have reacted first with oceanic crust and then sediments. The high Sr concentration in this sample (19.3 ppm) is consistent with late stage interaction between the ascending fluid and carbonate rich sediments.
\r\n\r\nNd shows a wide range in concentration and isotopic compositions in solutions from 21\u00b0N. CNd ranges from 20 to 659 pg/g, indicating substantial enrichments of Nd over typical seawater concentrations of ~3 to 4pg/g. \u03b5Nd ranges from -10.8 to +7.9. The data clearly show substantial contributions of Nd from depleted oceanic crust to many of the samples analyzed. In spite of enrichments in Nd of up to about 100 times seawater, none of the samples have \u03b5Nd values equal to MORB (\u03b5Nd \u2243 +10). One sample from Guaymas Basin has \u03b5Nd = -11.4 consistent with leaching of Nd from sediments derived from old, continental sources. There is some inconsistency in the Nd isotopic data indicating that there is a possibility of contamination during sampling and/or handling of the solutions.
", "doi": "10.7907/GATW-C580", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:3133", "collection": "thesis", "collection_id": "3133", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08152006-132531", "primary_object_url": { "basename": "Piepgras_dj_1984.pdf", "content": "final", "filesize": 13047842, "license": "other", "mime_type": "application/pdf", "url": "/3133/1/Piepgras_dj_1984.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Isotopic Composition of Neodymium in the Marine Environment: Investigations of the Sources and Transport of Rare Earth Elements in the Oceans", "author": [ { "family_name": "Piepgras", "given_name": "Donald John", "clpid": "Piepgras-Donald-John" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" }, { "family_name": "Patterson", "given_name": "Clair C.", "clpid": "Patterson-C-C" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "In this study, the isotopic composition of neodymium in the marine environment has been determined from analysis of marine ferromanganese precipitates and seawater. An initial survey of the isotopic composition of Nd in the marine environment was made utilizing the analyses of authigenic ferromanganese sediments. These included ferromanganese nodules, metalliferous sediments, and hydrothermal ferromanganese crust deposits. Large variations in \u03b5Nd(0) values are observed which exhibit a clear separation of the ocean basin. Nd isotopic variations within an ocean basin fall within a relatively small, well defined range which is characteristic of the ocean basin sampled. Based on these results, the following average 143Nd/144Nd ratios for the ocean basins have been determined: Atlantic Ocean, \u03b5Nd(0) \u2248 -12; Indian Ocean, \u03b5Nd(0) \u2248 -8; Pacific Ocean, \u03b5Nd(0) \u2248 -3. These values are considerably lower than \u03b5Nd(0) values associated sources having oceanic mantle affinities, indicating that the REE in the oceans are dominated by continental sources. Therefore, the variations must reflect primarily the age and 147Sm/144Nd ratio of the continental masses being sampled.
\r\n\r\nDirect measurements of the isotopic composition of Nd in seawater samples from the Atlantic and Pacific are in excellent agreement with the values determined from the ferromanganese sediments indicating that these sediments accurately reflect the isotopic composition of Nd dissolved in seawater. The results clearly demonstrate the existence of distinctive Nd isotopic differences in waters of the major ocean basins. These values correspond to a difference in the absolute abundance of 143Nd between the Atlantic and the Pacific Oceans of ~ 10(6) atoms 143Nd per gram of seawater. In addition to the isotopic differences observed between the ocean basins, smaller but distinctive variations are observed in the water column of both the Pacific and the Atlantic, indicating different sources of REE at different levels in the water column. This suggests that it may be possible to distinguish the sources of water masses within an ocean basin on the basis of Nd isotopic composition.
\r\n\r\nThe isotopic composition of Nd was determined in seawater samples from the Drake Passage in order to monitor the exchange of REE between the Pacific and Atlantic Oceans. The Antarctic Circumpolar Current, which flows eastward through this passage, represents the primary conduit through which the major ocean basins communicate with each other. The isotopic composition of Nd is found to be uniform with depth at all stations and corresponds to \u03b5Nd(0) \u2243 -9.0. This value is intermediate between the values for the Atlantic and the Pacific and indicates that the Antarctic Circumpolar Current consists of about 70 percent Atlantic water. By using a box model to describe the exchange of water between the Southern Ocean and the ocean basins to the north together with the isotopic results, an upper limit of approximately 33 million cubic meters per second is calculated for the rate of exchange between the Pacific and the Southern Ocean.
\r\n\r\nThe concentration of Nd exhibits a regular increase with depth at all locations studied. In contrast, Nd isotopic compositions can exhibit substantial variations in the water column which vary depending on the location. Where isotopic differences in the water column occur, substantial lateral transport of REE from different sources and at different levels in the water column is required to maintain these differences. It is shown that the concentration gradients are established without significantly affecting the isotopic distribution, and that the enrichment of Nd in the deep water cannot be a result of resolution of REE scavenged from surface waters.
\r\n\r\nThe isotopic distributions are compared to water mass analyses based on temperature and salinity characteristics in the water column at the various sampling locations. It is shown that differences in isotopic compositions in the water column are well correlated with changes in the temperature and salinity characteristics. Thus, the isotopic distributions are fully consistent with the circulation of major water masses. This indicates that while Nd is nonconservative in concentration, the isotopic composition is conserved and can be used as a tracer for studying the origin and circulation of water masses.
\r\n\r\nThe results of these studies have provided some important contributions to the understanding of trace element transport in the oceans. First, the Nd isotopic differences in the water column clearly indicate that transport of Nd from the surface to the deep ocean cannot account for the observed increase in concentration of Nd with depth. These isotopic differences must be maintained by lateral transport of the REE and indicates that the concentration gradients of the REE and possibly other trace elements must also be related in part to lateral transport processes. Second, the close correlation observed between changes in Nd isotopic compositions and temperature-salinity relationships in the water column indicates that the lateral transport of REE in the oceans is directly related to the origin and flow of water masses. Thus, the isotopic composition of Nd in seawater is shown to be a useful tracer for studying the sources of injection and transport of trace elements in the oceans.
\r\n\r\nIn addition to the seawater studies, the concentrations and isotopic compositions of Nd and Sr were determined in hydrothermal solutions emanating from hot springs on the crest of the East Pacific Rise at 21\u00b0N and at Guaymas Basin, Gulf of California. This study represents the first effort to measure the Nd isotopic compositions in hydrothermal solutions. Endmember samples (T = 350\u00b0C) from 21\u00b0N exhibit a small range in \u03b5Sr values from -13.4 to -15.7. Correcting to CMg = 0, the pure hydrothermal solutions are estimated to have \u03b5Sr \u2243 -18. These results indicate that the fluids have undergone extensive but not complete exchange with Sr in the depleted oceanic crust (\u03b5Sr \u2243 -30). CSr ranges from 5.8 to 8.7 ppm and is similar to seawater (7.6 ppm) indicating that there must be buffering. Hydrothermal solutions from Guaymas Basin (T = 315\u00b0C) rise through several hundred meters of sediment before reaching the sea floor. One sample from here has \u03b5Sr = +5.8, indicating that the solutions have reacted first with oceanic crust and then sediments. The high Sr concentration in this sample (19.3 ppm) is consistent with late stage interaction between the ascending fluid and carbonate rich sediments.
\r\n\r\nNd shows a wide range in concentration and isotopic compositions in solutions from 21\u00b0N. CNd ranges from 20 to 659 pg/g, indicating substantial enrichments of Nd over typical seawater concentrations of ~3 to 4pg/g. \u03b5Nd ranges from -10.8 to +7.9. The data clearly show substantial contributions of Nd from depleted oceanic crust to many of the samples analyzed. In spite of enrichments in Nd of up to about 100 times seawater, none of the samples have \u03b5Nd values equal to MORB (\u03b5Nd \u2243 +10). One sample from Guaymas Basin has \u03b5Nd = -11.4 consistent with leaching of Nd from sediments derived from old, continental sources. There is some inconsistency in the Nd isotopic data indicating that there is a possibility of contamination during sampling and/or handling of the solutions.
", "doi": "10.7907/GATW-C580", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:11316", "collection": "thesis", "collection_id": "11316", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12142018-091056975", "primary_object_url": { "basename": "Shaw_HF_III_1984.pdf", "content": "final", "filesize": 99999823, "license": "other", "mime_type": "application/pdf", "url": "/11316/1/Shaw_HF_III_1984.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Sm-Nd and Rb-Sr Isotopic Systematics of Tektites and Other Impactites, Appalachian Mafic Rocks, and Marine Carbonates and Phosphates", "author": [ { "family_name": "Shaw", "given_name": "Henry Francis, III", "orcid": "0000-0003-0681-5430", "clpid": "Shaw-Henry-Francis-III" } ], "thesis_advisor": [ { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis is made up of three separate studies, each using the Sm-Nd and Rb-Sr isotopic systems to solve a problem of geologic interest.
\r\n\r\nIn the first study it is shown that Sm-Nd and Rb-Sr analyses of tektites and other impactites can be used to place constraints on the age and provenance of the target materials which were impact melted to form these objects. Tektites have large negative values of \u03b5Nd(0) which are uniform within each tektite group, while the \u03b5Sr(0) values are large positive and show considerable variation within each group. The chemical, trace element, and isotopic compositions of tektites are consistent with their production by melting of sediments derived from old continental crust. Each tektite group is characterized by a uniform Nd model age, TNdCHUR, interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites: (1) ~1.15AE for Australasian tektites; (2) ~1.9AE for Ivory Coast tektites; (3) ~0.9AE for moldavites; (4) ~0.65AE for North American tektites; and (5) ~0.9AE for high-Si irghizites. Sr model ages, TSrUR, are variable within each group, reflecting Rb-Sr fractionation during weathering and sedimentation. In the favorable limit of very high Rb/Sr ratios TSrUR approaches the time of sedimentation of the parent material which melted to form the tektites. Australasian tektites are derived from ~0.25AE sediments, moldavites from ~0.0AE sediments, and Ivory Coast tektites from ~0.95AE sediments. The parent sediments of the other tektite groups have poorly constrained ages. The isotopic data on the moldavites and Ivory Coast tektites are consistent with their derivation from the Ries and Bosumtwi Craters, respectively. Irghizites are isotopically distinct from the Australasian tektites and are probably not related. Sanidine spherules from an iridium-rich Cretaceous-Tertiary boundary clay were heavily overprinted with seawater-derived Sr and Nd during diagenesis. The inferred initial isotopic composition of the sanidine itself is \u03b5Nd(T) = +2 and \u03b5Sr(T) = +5. These results show that the spherules were not derived from old continental crust or meteoritic potassium feldspar. These objects may represent an impact melt of a mixture of basaltic oceanic crust and overlying sediments and are consistent with an oceanic impact at the Cretaceous-Tertiary boundary. The isotopic data are also consistent with an origin by authigenic growth of the spherules from young detrital material.
\r\n\r\nThe second study in this thesis uses the Sm-Nd and Rb-Sr isotopic systematics of mafic rocks from the Appalachians to place constraints on their origin. Isotopic analyses of modern oceanic basalts and ophiolites have shown that both modern and ancient oceanic crust have a characteristic Nd and Sr isotopic signature indicative of derivation from a depleted mantle reservoir. It also appears that the Nd isotopic system is not appreciably disturbed by metamorphism. These isotopic characteristics have been extended to the Pt. Sal, Kings-Kaweah, and Josephine Ophiolites of California. These characteristics are used in an attempt to identify pieces of proto-Atlantic oceanic crust among the mafic and ultramafic rocks of the Appalachians. Sm-Nd mineral isochrons for the Baltimore Mafic Complex, Md (BMC) yield an age of 490\u00b120 My which is interpreted as the igneous crystallization age. BMC whole rock samples do not define isochrones and have initial isotopic compositions of -6.4 < \u03b5Nd(T) < -2.2, +51 < \u03b5Sr(T) < +115. \u03b5Nd(T) and \u03b5Sr(T) are anti-correlated. This is not the signature of depleted mantle and oceanic crust, but is similar to old continental crust. It is proposed that the BMC is a mafic continental intrusion, possibly subduction related, which was contaminated with old continental crust during emplacement. Whole rock samples from the Thetford Mines Complex, Qe (TMC) do not define isochrons and have -1.5 < \u03b5Nd(T) < +4.2, +2.6 < \u03b5Sr(T) < +114. These data do not in any way reflect the signature of normal oceanic crust. These results are in contrast with geologic relationships which show the TMC to have the characteristics of an ophiolite complex. The TMC is chemically and isotopically similar to a class of other ophiolites which have affinities to modern boninites. The TMC may therefore represent an ophiolite formed under an arc complex. The Chunky Gal Amphibolite, N.C., Lake Chatuge complex, N.C., and Hazen's Notch Amphibolite, Vt., were found to have a depleted mantle signature with +5 < \u03b5Nd(T) < +8 and may be fragments of oceanic crust. The Webster-Addie body, N.C., has \u03b5Nd(T) ~-1, \u03b5Sr(T) ~+30 and is not isotopically similar to oceanic crust or the other North Carolina mafic bodies analyzed. From these isotopic results it is clear that Appalachian mafic rocks have diverse origins, some are continental intrusives (BMC), others are probably fragments of oceanic crust (Vermont and N. Carolina amphibolites). Future models for the development of the Appalachians must allow for these various origins. The possibility that some ophiolites are not normal oceanic crust but have an origin in a partially continental setting or as anomalous oceanic crust will require further attention.
\r\n\r\nThe final study is an exploration of the possibility of establishing the Nd isotopic variations in seawater over geologic time by analysing a marine sedimentary phase which records and preserves the \u03b5Nd(T) value of the seawater in which it formed. Apatite and CaCO3 (calcite and aragonite) are examined as possible such phases. Modern biogenic and inorganic calcite and aragonite were found to have low REE concentrations: Nd = 0.2 to 65 ppb. The \u03b5Nd(0) values of Atlantic (-8.3 to -9.6) and Pacific (-0.1 to -1.3) carbonates are distinctly different and reflect the isotopic composition of Nd in the seawater in which they formed. The high concentrations of REE measured in limestones and carbonate fossils cannot be primary but must be due to the presence of other phases in the carbonate of the introduction of REE during diagenesis. Modern biogenic apatite also has a low REE content (<150 ppb Nd), but appears to quickly scavenge REE from seawater. Levels up to 1000 ppm Nd can be reached by this process. Inorganically precipitated apatite from phosphorites also has high concentrations of seawater-derived REE. A seawater-like REE pattern with a characteristic negative Ce-anomaly is often preserved by sedimentary apatite and apatite samples of the same age from different localities bordering a common sea record a common value of \u03b5Nd(T). These characteristics suggest that apatite can be used to trace the evolution of \u03b5Nd(T) in ancient seawater. The values of \u03b5Nd(T) in seawater as inferred from analyses of conodonts and phosphorite apatite range between -1.7 and -8.9 over the last 700My. These values lie in the range of modern seawater values and show no evidence for drastic changes in the sources for Nd in seawater during this time. High values of seawater \u03b5Nd(T) in the Triassic and latest Precambrian may correlate with the breakup of large continental landmasses. The initial \u03b5Nd(T) = -15.0 of the 2AE old Rum Jungle phosphorite requires the presence of -1.5AE old continental crust at 2AE ago. This demonstrates how the \u03b5Nd value of ancient seawater can be used to constrain the age of the exposed crust as a function of time.
", "doi": "10.7907/x0zc-7w22", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:11316", "collection": "thesis", "collection_id": "11316", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12142018-091056975", "primary_object_url": { "basename": "Shaw_HF_III_1984.pdf", "content": "final", "filesize": 99999823, "license": "other", "mime_type": "application/pdf", "url": "/11316/1/Shaw_HF_III_1984.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Sm-Nd and Rb-Sr Isotopic Systematics of Tektites and Other Impactites, Appalachian Mafic Rocks, and Marine Carbonates and Phosphates", "author": [ { "family_name": "Shaw", "given_name": "Henry Francis, III", "orcid": "0000-0003-0681-5430", "clpid": "Shaw-Henry-Francis-III" } ], "thesis_advisor": [ { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis is made up of three separate studies, each using the Sm-Nd and Rb-Sr isotopic systems to solve a problem of geologic interest.
\r\n\r\nIn the first study it is shown that Sm-Nd and Rb-Sr analyses of tektites and other impactites can be used to place constraints on the age and provenance of the target materials which were impact melted to form these objects. Tektites have large negative values of \u03b5Nd(0) which are uniform within each tektite group, while the \u03b5Sr(0) values are large positive and show considerable variation within each group. The chemical, trace element, and isotopic compositions of tektites are consistent with their production by melting of sediments derived from old continental crust. Each tektite group is characterized by a uniform Nd model age, TNdCHUR, interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites: (1) ~1.15AE for Australasian tektites; (2) ~1.9AE for Ivory Coast tektites; (3) ~0.9AE for moldavites; (4) ~0.65AE for North American tektites; and (5) ~0.9AE for high-Si irghizites. Sr model ages, TSrUR, are variable within each group, reflecting Rb-Sr fractionation during weathering and sedimentation. In the favorable limit of very high Rb/Sr ratios TSrUR approaches the time of sedimentation of the parent material which melted to form the tektites. Australasian tektites are derived from ~0.25AE sediments, moldavites from ~0.0AE sediments, and Ivory Coast tektites from ~0.95AE sediments. The parent sediments of the other tektite groups have poorly constrained ages. The isotopic data on the moldavites and Ivory Coast tektites are consistent with their derivation from the Ries and Bosumtwi Craters, respectively. Irghizites are isotopically distinct from the Australasian tektites and are probably not related. Sanidine spherules from an iridium-rich Cretaceous-Tertiary boundary clay were heavily overprinted with seawater-derived Sr and Nd during diagenesis. The inferred initial isotopic composition of the sanidine itself is \u03b5Nd(T) = +2 and \u03b5Sr(T) = +5. These results show that the spherules were not derived from old continental crust or meteoritic potassium feldspar. These objects may represent an impact melt of a mixture of basaltic oceanic crust and overlying sediments and are consistent with an oceanic impact at the Cretaceous-Tertiary boundary. The isotopic data are also consistent with an origin by authigenic growth of the spherules from young detrital material.
\r\n\r\nThe second study in this thesis uses the Sm-Nd and Rb-Sr isotopic systematics of mafic rocks from the Appalachians to place constraints on their origin. Isotopic analyses of modern oceanic basalts and ophiolites have shown that both modern and ancient oceanic crust have a characteristic Nd and Sr isotopic signature indicative of derivation from a depleted mantle reservoir. It also appears that the Nd isotopic system is not appreciably disturbed by metamorphism. These isotopic characteristics have been extended to the Pt. Sal, Kings-Kaweah, and Josephine Ophiolites of California. These characteristics are used in an attempt to identify pieces of proto-Atlantic oceanic crust among the mafic and ultramafic rocks of the Appalachians. Sm-Nd mineral isochrons for the Baltimore Mafic Complex, Md (BMC) yield an age of 490\u00b120 My which is interpreted as the igneous crystallization age. BMC whole rock samples do not define isochrones and have initial isotopic compositions of -6.4 < \u03b5Nd(T) < -2.2, +51 < \u03b5Sr(T) < +115. \u03b5Nd(T) and \u03b5Sr(T) are anti-correlated. This is not the signature of depleted mantle and oceanic crust, but is similar to old continental crust. It is proposed that the BMC is a mafic continental intrusion, possibly subduction related, which was contaminated with old continental crust during emplacement. Whole rock samples from the Thetford Mines Complex, Qe (TMC) do not define isochrons and have -1.5 < \u03b5Nd(T) < +4.2, +2.6 < \u03b5Sr(T) < +114. These data do not in any way reflect the signature of normal oceanic crust. These results are in contrast with geologic relationships which show the TMC to have the characteristics of an ophiolite complex. The TMC is chemically and isotopically similar to a class of other ophiolites which have affinities to modern boninites. The TMC may therefore represent an ophiolite formed under an arc complex. The Chunky Gal Amphibolite, N.C., Lake Chatuge complex, N.C., and Hazen's Notch Amphibolite, Vt., were found to have a depleted mantle signature with +5 < \u03b5Nd(T) < +8 and may be fragments of oceanic crust. The Webster-Addie body, N.C., has \u03b5Nd(T) ~-1, \u03b5Sr(T) ~+30 and is not isotopically similar to oceanic crust or the other North Carolina mafic bodies analyzed. From these isotopic results it is clear that Appalachian mafic rocks have diverse origins, some are continental intrusives (BMC), others are probably fragments of oceanic crust (Vermont and N. Carolina amphibolites). Future models for the development of the Appalachians must allow for these various origins. The possibility that some ophiolites are not normal oceanic crust but have an origin in a partially continental setting or as anomalous oceanic crust will require further attention.
\r\n\r\nThe final study is an exploration of the possibility of establishing the Nd isotopic variations in seawater over geologic time by analysing a marine sedimentary phase which records and preserves the \u03b5Nd(T) value of the seawater in which it formed. Apatite and CaCO3 (calcite and aragonite) are examined as possible such phases. Modern biogenic and inorganic calcite and aragonite were found to have low REE concentrations: Nd = 0.2 to 65 ppb. The \u03b5Nd(0) values of Atlantic (-8.3 to -9.6) and Pacific (-0.1 to -1.3) carbonates are distinctly different and reflect the isotopic composition of Nd in the seawater in which they formed. The high concentrations of REE measured in limestones and carbonate fossils cannot be primary but must be due to the presence of other phases in the carbonate of the introduction of REE during diagenesis. Modern biogenic apatite also has a low REE content (<150 ppb Nd), but appears to quickly scavenge REE from seawater. Levels up to 1000 ppm Nd can be reached by this process. Inorganically precipitated apatite from phosphorites also has high concentrations of seawater-derived REE. A seawater-like REE pattern with a characteristic negative Ce-anomaly is often preserved by sedimentary apatite and apatite samples of the same age from different localities bordering a common sea record a common value of \u03b5Nd(T). These characteristics suggest that apatite can be used to trace the evolution of \u03b5Nd(T) in ancient seawater. The values of \u03b5Nd(T) in seawater as inferred from analyses of conodonts and phosphorite apatite range between -1.7 and -8.9 over the last 700My. These values lie in the range of modern seawater values and show no evidence for drastic changes in the sources for Nd in seawater during this time. High values of seawater \u03b5Nd(T) in the Triassic and latest Precambrian may correlate with the breakup of large continental landmasses. The initial \u03b5Nd(T) = -15.0 of the 2AE old Rum Jungle phosphorite requires the presence of -1.5AE old continental crust at 2AE ago. This demonstrates how the \u03b5Nd value of ancient seawater can be used to constrain the age of the exposed crust as a function of time.
", "doi": "10.7907/x0zc-7w22", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:3334", "collection": "thesis", "collection_id": "3334", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09052006-083506", "primary_object_url": { "basename": "Prendergast_md_1983.pdf", "content": "final", "filesize": 3852626, "license": "other", "mime_type": "application/pdf", "url": "/3334/1/Prendergast_md_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Linear Programming Methods for the Numerical Solution of Parabolic Equations Backwards in Time", "author": [ { "family_name": "Prendergast", "given_name": "Michael David", "orcid": "0000-0003-1532-9127", "clpid": "Prendergast-Michael-David" } ], "thesis_advisor": [ { "family_name": "Franklin", "given_name": "Joel N.", "clpid": "Franklin-J-N" } ], "thesis_committee": [ { "family_name": "Keller", "given_name": "Herbert Bishop", "clpid": "Keller-H-B" }, { "family_name": "Fornberg", "given_name": "Bengt", "clpid": "Fornberg-Bengt" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Franklin", "given_name": "Joel N.", "clpid": "Franklin-J-N" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "This thesis investigates linear programming methods for the numerical solution of parabolic equations backwards in time. These problems are ill-posed. Hence an approximate numerical solution for such problems can only be obtained if additional constraints (called a regularization) are imposed on the solution in order to guarantee its stability under small perturbations. Previous authors have implemented regularizations on the backward heat equation which used (linear or nonlinear) least squares, or linear programming. These regularizations use the exact form of the kernel for the heat equation, however, and so are not generalizable to problems with an unknown kernel or unknown eigenfunction expansion. Furthermore, the least squares methods can not easily handle the nonnegativity constraint that a positive temperature, for example, must have.
\r\n\r\nIn the first part of this thesis, linear regularizations which can be used to solve any linear parabolic equation on a finite domain backwards in time are introduced. It is then shown how a numerical approximation to the solution of the regularized problem can be obtained by using linear programming and any stable and consistent difference method (such as Crank-Nicholson). The convergence of these algorithms is shown to be a direct consequence of the Lax equivalence theorem. The stability, accuracy, and results of actual numerical experiments using this linear programming method are analyzed.
\r\n\r\nThe second part of this thesis shows how these regularizations can be used on weakly nonlinear equations. This is done by introducing a successive approximation method, and solving a linear program at each step in the iteration. The stability, accuracy, and results of numerical experiments for this algorithm are also examined.
\r\n", "doi": "10.7907/rwq0-z817", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:3334", "collection": "thesis", "collection_id": "3334", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09052006-083506", "primary_object_url": { "basename": "Prendergast_md_1983.pdf", "content": "final", "filesize": 3852626, "license": "other", "mime_type": "application/pdf", "url": "/3334/1/Prendergast_md_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Linear Programming Methods for the Numerical Solution of Parabolic Equations Backwards in Time", "author": [ { "family_name": "Prendergast", "given_name": "Michael David", "orcid": "0000-0003-1532-9127", "clpid": "Prendergast-Michael-David" } ], "thesis_advisor": [ { "family_name": "Franklin", "given_name": "Joel N.", "clpid": "Franklin-J-N" } ], "thesis_committee": [ { "family_name": "Keller", "given_name": "Herbert Bishop", "clpid": "Keller-H-B" }, { "family_name": "Fornberg", "given_name": "Bengt", "clpid": "Fornberg-Bengt" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Franklin", "given_name": "Joel N.", "clpid": "Franklin-J-N" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "This thesis investigates linear programming methods for the numerical solution of parabolic equations backwards in time. These problems are ill-posed. Hence an approximate numerical solution for such problems can only be obtained if additional constraints (called a regularization) are imposed on the solution in order to guarantee its stability under small perturbations. Previous authors have implemented regularizations on the backward heat equation which used (linear or nonlinear) least squares, or linear programming. These regularizations use the exact form of the kernel for the heat equation, however, and so are not generalizable to problems with an unknown kernel or unknown eigenfunction expansion. Furthermore, the least squares methods can not easily handle the nonnegativity constraint that a positive temperature, for example, must have.
\r\n\r\nIn the first part of this thesis, linear regularizations which can be used to solve any linear parabolic equation on a finite domain backwards in time are introduced. It is then shown how a numerical approximation to the solution of the regularized problem can be obtained by using linear programming and any stable and consistent difference method (such as Crank-Nicholson). The convergence of these algorithms is shown to be a direct consequence of the Lax equivalence theorem. The stability, accuracy, and results of actual numerical experiments using this linear programming method are analyzed.
\r\n\r\nThe second part of this thesis shows how these regularizations can be used on weakly nonlinear equations. This is done by introducing a successive approximation method, and solving a linear program at each step in the iteration. The stability, accuracy, and results of numerical experiments for this algorithm are also examined.
\r\n", "doi": "10.7907/rwq0-z817", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:1324", "collection": "thesis", "collection_id": "1324", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04102003-122837", "primary_object_url": { "basename": "gillespie_ar_1982.pdf", "content": "final", "filesize": 50336898, "license": "other", "mime_type": "application/pdf", "url": "/1324/14/gillespie_ar_1982.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Quaternary Glaciation and Tectonism in the Southeastern Sierra Nevada, Inyo County, California", "author": [ { "family_name": "Gillespie", "given_name": "Alan Reed", "clpid": "Gillespie-Alan-Reed" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" }, { "family_name": "Sharp", "given_name": "Robert P.", "clpid": "Sharp-R-P" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Clark", "given_name": "M. M.", "clpid": "Clark-M-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The southeastern Sierra Nevada consists of three geographic regions. From west to east, they are: an upland region across the crest, a steep east-facing escarpment along which Owens Valley has partly subsided, and foothill blocks intermediate to the Sierra Nevada and Owens Valley. Farther east, Owens Valley is a deep graben separating the Sierra Nevada and the Inyo Range.
\r\n\r\nThe main goals of this thesis were the detailed mapping of Quaternary glacial and other deposits in these regions, dating of critical events, and geomorphic analysis of the range front. The focus was on Pleistocene moraines near the range front. The motivation of this research was to improve our understanding of the chronology of Pleistocene events, to characterize details of the tectonic history of the Sierra, to infer faulting, erosion, and deposition rates, and to provide a basis for the comparison of the Quaternary geology in the southeastern Sierra and in more intensively studied regions in the central and northern Sierra and elsewhere.
\r\n\r\nThe study area extended from the alluvial fans of Owens Valley west to the Sierra crest from latitude 36\u00b045' N to 37\u00b000' N. It included the southern part of the Big Pine volcanic field, an eruptive center for basaltic lavas for most of the Pleistocene Epoch. Elevations within the study area ranged from about 1000 m (Owens Valley) to about 4000 m (peaks along the crest).
\r\n\r\nThroughout the study area the principal rocks are granodiorite and quartz monzonite of Cretaceous age. Plutons are rather small, and individual drainages generally include more than one. In the southern part of the study area, Jurassic-Triassic metavolcanic rocks are found as roof pendants. These rocks, originally ranging in composition from basalt to rhyolite, are most common near the Sierra crest. In the northern canyons of the study area, Paleozoic metasedimentary rocks including sandy marbles and biotite schist replace the metavolcanic pendants. The foothill blocks are identical to the Sierras in composition.
\r\n\r\nBelow the foothills coalescing alluvial fans grade a few km east to the alluvium and lacustrine sediments of the Owens River and Owens Lake. These sediments have been shown in geophysical studies to mask a second escarpment as high as the one of the range front, and the total bedrock relief from the Sierra crest to the floor of the graben is as much as 6 km.
\r\n\r\nDuring the Quaternary Period the southeastern Sierra Nevada was characterized by the down-faulting of Owens Valley along two zones, one a series of normal faults along the range front (Independence Fault) and the other a series of faults along the center of the valley (Owens Valley fault zone). This same period has seen the cutting of deep canyons through the 2-km-high escarpment. During repeated glaciations these canyons were widened and deepened. Traces of at least seven glaciations were found during this study. Moraines and other deposits left during these glaciations could be distinguished based on the degree of weathering of granitic clasts, vegetative cover, and morphologic characteristics. Absolute age limits were obtained for two of the Pleistocene glaciations by radiometric dating of basalt flows interfingered with the moraines.
\r\n\r\nThree of the recognized glaciations, probably corresponding to the Matthes, Recess Peak, and Hilgard neoglaciations found by J.H. Birman in the central Sierra Nevada, occurred during the Holocene Epoch. The youngest glaciers (Matthes glaciation) left unconsolidated and unvegetated till in stagnant rock glaciers and moraines in cirques on high peaks. Some rock glaciers are still ice-cored. Extending out from the cirques and into the upper reaches of the canyons are moraines correlating to the Recess Peak glaciation. Till is generally consolidated and supports heavy lichen growth and bushes but few trees. The oldest Holocene glaciation (Hilgard) left few large moraines in the study area. Hilgard glaciers extended much farther down-canyon than the younger Holocene glaciers, sometimes within one or two km of the Tioga terminal moraines. Those Hilgard terminal moraines which were found have been barely breached by streams. Moraines tend to be heavily forested, and lakes are largely unsedimented. The Hilgard glaciation may have simply been the last stade of the Tioga glaciation from the evidence found in this study.
\r\n\r\nAt least four Pleistocene glaciations occurred in the southeastern Sierra Nevada. All four postdate most of the significant incision of streams through the escarpment. The three youngest probably correlate with the Tioga, Tenaya, and Tahoe stages (in order of increasing age) recognized throughout the Sierra. In each case, moraine morphology has been well preserved. Tioga moraines were found down to about 2200 m elevation. Nested sets of moraines were common. The terminal moraines of the youngest of these were sometimes intact. lakes were rare; one (Sawmill Meadow) was completely sedimented. Granitic boulders in the moraines were largely unweathered. Weathering of boulders in Tenaya moraines was similar, but a small fraction of granitic boulders were grusy. Boulders from Tahoe moraines were conspicuously weathered, and the moraines themselves were rounded and gullied.
\r\n\r\nThe oldest group of moraines probably significantly predates the Tahoe glaciation. It is nevertheless post-Sherwin. Moraines in this group were found in five of the eight canyons studied. While obviously eroded, these moraines still retained their original shape. All surficial boulders were heavily weathered, but some exposed in road cuts were fresh. No moraines of Sherwin age were identified, although Sherwin till is widespread only a few km to the north. However, on plateaus and ridges 200 to 300 m above the modern canyons near the Sierra crest were found ancient diamictons, some of which could be till. Remnants of U-shaped valleys preserved as high passes across the crest or as cols between canyons east of the crest may be testimonials to ancient glaciers of Sherwin age or older.
\r\n\r\nRadiometric dating (40Ar - 39Ar) of basalts interfingered with moraines in Sawmill Canyon provided a new upper limit of 0.12 my for a moraine of the Tahoe glaciation, and a range of 0.13 - 0.46 my for one pre-Tahoe glaciation. These results confirm that the Tahoe glaciation occurred during the Wisconsin stage of the continental ice age, and conclusively demonstrate the existence of pre-Wisconsin glaciers in the southern Sierra. Relative dating based on acoustic wave speeds through weathered boulders on the moraines indicates the age of the pre-Wisconsin moraine may be close to the upper limit.
\r\n\r\nAlluvial fans appear to have aggraded early in the Wisconsin glaciation (Tahoe glaciation). Subsequently, the fan heads have been incised and the locus of deposition has moved eastward down the fans. The Tenaya and Tioga glaciers during the late Wisconsin stage left outwash plains and terraces along streams cut into the older fans, but aggradation during these events was considerably less than earlier.
\r\n\r\nThree ages of fans were found. The oldest fanglomerate probably is pre-Wisconsin and is exposed in regions protected from later deposition. The heavily weathered fan deposits of this group overlie basalts which appear to be contemporaneous with dated 1.1 - 1.2 my-old basalts nearby. In the middle elevations of the fans, roughly 10 m of fanglomerate was deposited over the old fanglomerate, probably during the Tahoe glaciation. Deposition rates probably are about 0.1 mm/y for the late Pleistocene Epoch. The extent and distribution of the youngest fans (Tenaya-Tioga) are variable, but they are generally found downstream from the incised Tahoe fan heads.
\r\n\r\nFaulting along the range front appears to have been dip-slip only. The offset rate along the range-front faults was determined at several canyons where the fault crossed dated moraines or lava flows. At least during the Wisconsin glaciation faulting on this zone appears to have been erratic, with rates ranging from zero to 0.5 mm/y or more. Offset moraines and terraces at Independence Creek indicated a faulting rate of 0.1 mm/y. Only a few km to the north, Tahoe moraines of both forks of Oak Creek were not offset at all, although scarps could be seen on adjacent hillsides. At Sawmill Creek an offset lava flow gave a lower limit of 0.5 mm/y. It seems that during the late Pleistocene Epoch, offset on the range front faults has been less than on the mid-valley faults east of the study area. Geodetic studies have suggested modern strain rates of 2.2 mm/y for the Owens Valley fault zone.
\r\n\r\nBasalts found in canyons through the escarpment and on terraces and ridges in the foothills to the east document stream erosion during the Pleistocene Epoch. Ridgetop basalts, dated at 1.2 my, stand at least 125 m above the modern streams through the foothills. This indicates an erosion rate of ~ 0.1 mm/y. A comparable rate of ~ 0.15 mm/y for the last 0.46 my was found for Sawmill Creek within the Sierra Nevada. Thus at least during the late Pleistocene Epoch erosion rates in the Sierra and in the foothills have been similar.
\r\n\r\nPatches of boulders and gravels atop the basalt show that some time after 1.2 my BP the foothill block was submerged by alluvial fans. Incision may have begun in response to the inception or renewal of subsidence of the graben along the Owens Valley fault zone.
\r\n\r\nExtensive volcanism in the Big Pine Volcanic field appears to have begun at least 1.2 my ago, and has continued sporadically up to perhaps 0.05 my ago. Minor eruptions may have occurred more recently.
\r\n\r\nThe eastern escarpment of the Sierra Nevada consists of two zones of truncated ridges. Within the study area, the upper zone is about 950 m high; the lower is about 750 m high. Triangular facets of the upper zone have a gradient of only ~ 24\u00b0, lower than slopes of ~ 29\u00b0 in the lower zone. This could be explained if subsidence of Owens Valley along the range-front faults occurred in two great pulses.
\r\n\r\nBoth absolute and relative dating methods were refined for this study. Absolute dating of the K-poor basaltic lavas was done indirectly, by 40Ar - 39Ar analysis of K-rich granitic xenoliths found in the lava. These ancient xenoliths were partially degassed of their accumulated 40Ar during heating in the magma, and it proved possible to date this heating event.
\r\n\r\nIn addition to conventional relative dating methods, a new quantitative approach based on the speed of acoustic waves through individual clasts in a deposit was investigated. This method had been used only once before, on terrace deposits. The technique proved to be very useful, and was capable of discriminating moraines successfully in well-studied canyons in the central Sierra. Acoustic wave speeds may be controlled by the abundance of intergranular cracks in granitic boulders. If this is the case, then this technique relies on different processes than those exploited by conventional methods of relative dating. The successful application to moraines in this study enhances our ability to analyse glacial sequences and complements conventional semi-quantitative methods of relative dating.
", "doi": "10.7907/GNES-QH83", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:1324", "collection": "thesis", "collection_id": "1324", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04102003-122837", "primary_object_url": { "basename": "gillespie_ar_1982.pdf", "content": "final", "filesize": 50336898, "license": "other", "mime_type": "application/pdf", "url": "/1324/14/gillespie_ar_1982.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Quaternary Glaciation and Tectonism in the Southeastern Sierra Nevada, Inyo County, California", "author": [ { "family_name": "Gillespie", "given_name": "Alan Reed", "clpid": "Gillespie-Alan-Reed" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" }, { "family_name": "Sharp", "given_name": "Robert P.", "clpid": "Sharp-R-P" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Clark", "given_name": "M. M.", "clpid": "Clark-M-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The southeastern Sierra Nevada consists of three geographic regions. From west to east, they are: an upland region across the crest, a steep east-facing escarpment along which Owens Valley has partly subsided, and foothill blocks intermediate to the Sierra Nevada and Owens Valley. Farther east, Owens Valley is a deep graben separating the Sierra Nevada and the Inyo Range.
\r\n\r\nThe main goals of this thesis were the detailed mapping of Quaternary glacial and other deposits in these regions, dating of critical events, and geomorphic analysis of the range front. The focus was on Pleistocene moraines near the range front. The motivation of this research was to improve our understanding of the chronology of Pleistocene events, to characterize details of the tectonic history of the Sierra, to infer faulting, erosion, and deposition rates, and to provide a basis for the comparison of the Quaternary geology in the southeastern Sierra and in more intensively studied regions in the central and northern Sierra and elsewhere.
\r\n\r\nThe study area extended from the alluvial fans of Owens Valley west to the Sierra crest from latitude 36\u00b045' N to 37\u00b000' N. It included the southern part of the Big Pine volcanic field, an eruptive center for basaltic lavas for most of the Pleistocene Epoch. Elevations within the study area ranged from about 1000 m (Owens Valley) to about 4000 m (peaks along the crest).
\r\n\r\nThroughout the study area the principal rocks are granodiorite and quartz monzonite of Cretaceous age. Plutons are rather small, and individual drainages generally include more than one. In the southern part of the study area, Jurassic-Triassic metavolcanic rocks are found as roof pendants. These rocks, originally ranging in composition from basalt to rhyolite, are most common near the Sierra crest. In the northern canyons of the study area, Paleozoic metasedimentary rocks including sandy marbles and biotite schist replace the metavolcanic pendants. The foothill blocks are identical to the Sierras in composition.
\r\n\r\nBelow the foothills coalescing alluvial fans grade a few km east to the alluvium and lacustrine sediments of the Owens River and Owens Lake. These sediments have been shown in geophysical studies to mask a second escarpment as high as the one of the range front, and the total bedrock relief from the Sierra crest to the floor of the graben is as much as 6 km.
\r\n\r\nDuring the Quaternary Period the southeastern Sierra Nevada was characterized by the down-faulting of Owens Valley along two zones, one a series of normal faults along the range front (Independence Fault) and the other a series of faults along the center of the valley (Owens Valley fault zone). This same period has seen the cutting of deep canyons through the 2-km-high escarpment. During repeated glaciations these canyons were widened and deepened. Traces of at least seven glaciations were found during this study. Moraines and other deposits left during these glaciations could be distinguished based on the degree of weathering of granitic clasts, vegetative cover, and morphologic characteristics. Absolute age limits were obtained for two of the Pleistocene glaciations by radiometric dating of basalt flows interfingered with the moraines.
\r\n\r\nThree of the recognized glaciations, probably corresponding to the Matthes, Recess Peak, and Hilgard neoglaciations found by J.H. Birman in the central Sierra Nevada, occurred during the Holocene Epoch. The youngest glaciers (Matthes glaciation) left unconsolidated and unvegetated till in stagnant rock glaciers and moraines in cirques on high peaks. Some rock glaciers are still ice-cored. Extending out from the cirques and into the upper reaches of the canyons are moraines correlating to the Recess Peak glaciation. Till is generally consolidated and supports heavy lichen growth and bushes but few trees. The oldest Holocene glaciation (Hilgard) left few large moraines in the study area. Hilgard glaciers extended much farther down-canyon than the younger Holocene glaciers, sometimes within one or two km of the Tioga terminal moraines. Those Hilgard terminal moraines which were found have been barely breached by streams. Moraines tend to be heavily forested, and lakes are largely unsedimented. The Hilgard glaciation may have simply been the last stade of the Tioga glaciation from the evidence found in this study.
\r\n\r\nAt least four Pleistocene glaciations occurred in the southeastern Sierra Nevada. All four postdate most of the significant incision of streams through the escarpment. The three youngest probably correlate with the Tioga, Tenaya, and Tahoe stages (in order of increasing age) recognized throughout the Sierra. In each case, moraine morphology has been well preserved. Tioga moraines were found down to about 2200 m elevation. Nested sets of moraines were common. The terminal moraines of the youngest of these were sometimes intact. lakes were rare; one (Sawmill Meadow) was completely sedimented. Granitic boulders in the moraines were largely unweathered. Weathering of boulders in Tenaya moraines was similar, but a small fraction of granitic boulders were grusy. Boulders from Tahoe moraines were conspicuously weathered, and the moraines themselves were rounded and gullied.
\r\n\r\nThe oldest group of moraines probably significantly predates the Tahoe glaciation. It is nevertheless post-Sherwin. Moraines in this group were found in five of the eight canyons studied. While obviously eroded, these moraines still retained their original shape. All surficial boulders were heavily weathered, but some exposed in road cuts were fresh. No moraines of Sherwin age were identified, although Sherwin till is widespread only a few km to the north. However, on plateaus and ridges 200 to 300 m above the modern canyons near the Sierra crest were found ancient diamictons, some of which could be till. Remnants of U-shaped valleys preserved as high passes across the crest or as cols between canyons east of the crest may be testimonials to ancient glaciers of Sherwin age or older.
\r\n\r\nRadiometric dating (40Ar - 39Ar) of basalts interfingered with moraines in Sawmill Canyon provided a new upper limit of 0.12 my for a moraine of the Tahoe glaciation, and a range of 0.13 - 0.46 my for one pre-Tahoe glaciation. These results confirm that the Tahoe glaciation occurred during the Wisconsin stage of the continental ice age, and conclusively demonstrate the existence of pre-Wisconsin glaciers in the southern Sierra. Relative dating based on acoustic wave speeds through weathered boulders on the moraines indicates the age of the pre-Wisconsin moraine may be close to the upper limit.
\r\n\r\nAlluvial fans appear to have aggraded early in the Wisconsin glaciation (Tahoe glaciation). Subsequently, the fan heads have been incised and the locus of deposition has moved eastward down the fans. The Tenaya and Tioga glaciers during the late Wisconsin stage left outwash plains and terraces along streams cut into the older fans, but aggradation during these events was considerably less than earlier.
\r\n\r\nThree ages of fans were found. The oldest fanglomerate probably is pre-Wisconsin and is exposed in regions protected from later deposition. The heavily weathered fan deposits of this group overlie basalts which appear to be contemporaneous with dated 1.1 - 1.2 my-old basalts nearby. In the middle elevations of the fans, roughly 10 m of fanglomerate was deposited over the old fanglomerate, probably during the Tahoe glaciation. Deposition rates probably are about 0.1 mm/y for the late Pleistocene Epoch. The extent and distribution of the youngest fans (Tenaya-Tioga) are variable, but they are generally found downstream from the incised Tahoe fan heads.
\r\n\r\nFaulting along the range front appears to have been dip-slip only. The offset rate along the range-front faults was determined at several canyons where the fault crossed dated moraines or lava flows. At least during the Wisconsin glaciation faulting on this zone appears to have been erratic, with rates ranging from zero to 0.5 mm/y or more. Offset moraines and terraces at Independence Creek indicated a faulting rate of 0.1 mm/y. Only a few km to the north, Tahoe moraines of both forks of Oak Creek were not offset at all, although scarps could be seen on adjacent hillsides. At Sawmill Creek an offset lava flow gave a lower limit of 0.5 mm/y. It seems that during the late Pleistocene Epoch, offset on the range front faults has been less than on the mid-valley faults east of the study area. Geodetic studies have suggested modern strain rates of 2.2 mm/y for the Owens Valley fault zone.
\r\n\r\nBasalts found in canyons through the escarpment and on terraces and ridges in the foothills to the east document stream erosion during the Pleistocene Epoch. Ridgetop basalts, dated at 1.2 my, stand at least 125 m above the modern streams through the foothills. This indicates an erosion rate of ~ 0.1 mm/y. A comparable rate of ~ 0.15 mm/y for the last 0.46 my was found for Sawmill Creek within the Sierra Nevada. Thus at least during the late Pleistocene Epoch erosion rates in the Sierra and in the foothills have been similar.
\r\n\r\nPatches of boulders and gravels atop the basalt show that some time after 1.2 my BP the foothill block was submerged by alluvial fans. Incision may have begun in response to the inception or renewal of subsidence of the graben along the Owens Valley fault zone.
\r\n\r\nExtensive volcanism in the Big Pine Volcanic field appears to have begun at least 1.2 my ago, and has continued sporadically up to perhaps 0.05 my ago. Minor eruptions may have occurred more recently.
\r\n\r\nThe eastern escarpment of the Sierra Nevada consists of two zones of truncated ridges. Within the study area, the upper zone is about 950 m high; the lower is about 750 m high. Triangular facets of the upper zone have a gradient of only ~ 24\u00b0, lower than slopes of ~ 29\u00b0 in the lower zone. This could be explained if subsidence of Owens Valley along the range-front faults occurred in two great pulses.
\r\n\r\nBoth absolute and relative dating methods were refined for this study. Absolute dating of the K-poor basaltic lavas was done indirectly, by 40Ar - 39Ar analysis of K-rich granitic xenoliths found in the lava. These ancient xenoliths were partially degassed of their accumulated 40Ar during heating in the magma, and it proved possible to date this heating event.
\r\n\r\nIn addition to conventional relative dating methods, a new quantitative approach based on the speed of acoustic waves through individual clasts in a deposit was investigated. This method had been used only once before, on terrace deposits. The technique proved to be very useful, and was capable of discriminating moraines successfully in well-studied canyons in the central Sierra. Acoustic wave speeds may be controlled by the abundance of intergranular cracks in granitic boulders. If this is the case, then this technique relies on different processes than those exploited by conventional methods of relative dating. The successful application to moraines in this study enhances our ability to analyse glacial sequences and complements conventional semi-quantitative methods of relative dating.
", "doi": "10.7907/GNES-QH83", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:4399", "collection": "thesis", "collection_id": "4399", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11042002-153232", "primary_object_url": { "basename": "Watson_k_1964.pdf", "content": "final", "filesize": 4070255, "license": "other", "mime_type": "application/pdf", "url": "/4399/1/Watson_k_1964.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "I. The Thermal Conductivity Measurements of Selected Silicate Powders in Vacuum from 150\u00b0 to 350\u00b0 K. II. An Interpretation of the Moon's Eclipse and Lunation Cooling as Observed through the Earth's Atmosphere from 8-14 Microns", "author": [ { "family_name": "Watson", "given_name": "Kenneth", "clpid": "Watson-Kenneth" } ], "thesis_advisor": [ { "family_name": "Brown", "given_name": "Harrison", "clpid": "Brown-Harrison" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "thesis_committee": [ { "family_name": "Press", "given_name": "Frank", "clpid": "Press-F" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Sharp", "given_name": "Robert P.", "clpid": "Sharp-R-P" }, { "family_name": "Brown", "given_name": "Harrison", "clpid": "Brown-Harrison" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "An apparatus was constructed to measure the thermal conductivity of powders in vacuum from 150\u00b0 to 350\u00b0K. It was found that the conductivity of selected silicate powders can be adequately represented, within the experimental errors, by a temperature independent term related to the contact conduction plus a temperature cube term which is due to radiative transfer between and through the grains. The conductivity for glass spheres approximately suggests an inverse grain size dependence and does not appear to be related in any simple manner to the elastic contact area between the spheres. The effects of angular grains, produced by crushing, and limited chemical composition range are not significant when compared with the experimental errors. The radiative transfer term which is grossly independent of chemical composition and grain texture is dominated by radiation between the grains for grain sizes > 300 \u03bc. Radiation through the grains is significant for grain sizes < 100 \u03bc.
\r\n\r\nPrevious interpretations of the eclipse observations of Pettit and Nicholson indicate that homogeneous constant thermal property models provide an adequate fit. The recent lunation observations of Murray and Wildey cannot be adequately explained by homogeneous models with either constant thermal properties or with thermal properties which are based on the results of this experimental investigation and existing specific heat data. It is suggested that the possibility of layering can best be examined in the region of the morning terminator.
\r\n", "doi": "10.7907/7HDE-1M52", "publication_date": "1964", "thesis_type": "phd", "thesis_year": "1964" } ]