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:6705", "collection": "thesis", "collection_id": "6705", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10042011-103334484", "primary_object_url": { "basename": "Sheng_yj_1992.pdf", "content": "final", "filesize": 53319949, "license": "other", "mime_type": "application/pdf", "url": "/6705/1/Sheng_yj_1992.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Origin of plagioclase-olivine inclusions", "author": [ { "family_name": "Sheng", "given_name": "Yuntai Jack", "clpid": "Sheng-Y-J" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Plagioclase-Olivine Inclusions (POIs) are an abundant group of chondrule-like objects found in carbonaceous chondrites. Despite textural evidence of a molten or partially molten origin, approximately half of the POls studied exhibited variations in Mg isotope composition of up to 11 %/amu between spinel and coexisting silicates. Equilibrium crystallization experiments performed to study the crystallization behavior of melts of POI compositions showed that the phase assemblages predicted on the basis\r\nof phase equilibria are generally consistent with those observed in POIs. Spinel is the liquidus phase for most of the inclusions that contain spinel with fractionated Mg\r\nisotopes, and therefore these spinels could be preserved if melting was below the liquidus temperature for the bulk composition of the inclusion. The presence of resorbed spinels in some inclusions whose bulk composition does not permit spinel in its phase assemblage requires that these spinels were relict. The petrographic and chemical properties of POIs indicate that they are not condensates or evaporative residues, but formed by melting or partial melting of pre-existing solids that had originated from isotopically distinct reservoirs. The presence of isotopically heterogeneous spinel in the POIs requires that\r\nthe maximum temperature experienced by these objects was low enough, the duration of heating short enough, and the subsequent cooling rate fast enough to prevent\r\nhomogenization of Mg isotopes by diffusive transport. The self-diffusion rate of Mg was measured in spinel and coexisting melt using isotope tracers. For spinel, the activation energy of 384\u00b17 kJ for Mg and pre-exponential factor of 7791.9\u00b11.3 cm^2/s is obtained. The temperatures of melting of POIs is estimated to be in the range of 1350-1500\u00b0C, the duration of the heating events were < 2 hr, and the initial cooling rate was > 25\u00b0/hr. The melting occurred after most ^(26)Al had decayed and possibly subsequent to the extensive oxygen isotopic exchange between solids and nebula gas. The melting of POIs\r\nis probably by flash heating or impact melting in a hot parcel or region of the nebula. These refractory objects (including CAIs) are believed to be the result of repetitive\r\nheating events that had frequently generated or reprocessed refractory residues over a prolonged timescale of very early solar system history.\r\n", "doi": "10.7907/cjkd-xe14", "publication_date": "1992", "thesis_type": "phd", "thesis_year": "1992" }, { "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: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: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:16283", "collection": "thesis", "collection_id": "16283", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01242024-233510543", "primary_object_url": { "basename": "Jacobsen_SB_1980.pdf", "content": "final", "filesize": 95874903, "license": "other", "mime_type": "application/pdf", "url": "/16283/1/Jacobsen_SB_1980.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Study of Crust and Mantle Differentiation Processes from Variations in Nd, Sr, and Pb Isotopes", "author": [ { "family_name": "Jacobsen", "given_name": "Stein Bj\u00f8rnar", "clpid": "Jacobsen-Stein-Bj\u00f8rnar" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This study discusses two simple transport models for the evolution of the mantle and the crust. In Model I, the continents grow by extraction of melts over the history of the earth from undepleted mantle; the residue forms a depleted mantle, which today is the source of mid-ocean ridge basalts. In Model II, new additions to the continents are derived from a mantle reservoir which becomes increasingly depleted through time by repeated extraction of melts. In developing these models, I solved the transport equations for stable, radioactive, and daughter isotopes for arbitrary crustal growth curves. For both models the isotopic composition and concentrations of trace elements reduce to simple mathematical expressions which readily permit calculations of basic evolutionary parameters from new and published data.
\r\n\r\nNew measurements of \u00b9\u2074\u00b3Nd/\u00b9\u2074\u2074Nd in chondrites yield a range in values of 3.4 \u03f5-units (0.511767 to 0.511845), which correlates with the variation of 2.6% in \u00b9\u2074\u2077Sm/\u00b9\u2074\u2074Nd (0.1920 to 0.1969). From these data a new set of reference values for CHUR (\"chondritic uniform reservoir\") have been selected. The evolution of \u00b9\u2074\u00b3Nd/\u00b9\u2074\u2074Nd in CHUR can be described by a self-consistent set of present-day values of (\u00b9\u2074\u00b3Nd/\u00b9\u2074\u2074Nd)\u00b0_(CHUR) = 0.511836 and (\u00b9\u2074\u2077Sm/\u00b9\u2074\u2074Nd)\u00b0_(CHUR) = 0.1967. Some terrestrial samples of Archean age show clear deviations from the new CHUR curve. If the CHUR curve is representative of undifferentiated mantle then it demonstrates that some Archean rocks were formed from depleted sources. This may indicate that the depleted source of present-day mid-ocean ridge basalts (MORB) originated very early in the earth's history.
\r\n\r\nTwo Sm-Nd internal isochrons for pyroxene-gabbros of the Bay of Islands Ophiolite Complex give well-defined ages of 508\u00b16 m.y. and 501\u00b113 m.y. with initial \u00b9\u2074\u00b3Nd/\u00b9\u2074\u2074Nd of \u03f5_(Nd) = +7.9\u22130.1 and \u03f5_(Nd) = +7.7\u22130.2, respectively. Total rock samples from pillow basalts, sheeted dikes, trondhjemites, hornblende gabbros, pyroxene gabbros, and an orthopyroxenite layer from the harzburgite give initial \u03f5_(Nd) in the range from +6.7 to +8.3 with an average value of +7.8. However, the initial \u2078\u2077Sr/\u2078\u2076Sr within the different phases of the complex is found to be highly variable(~52 \u03f5-units) and shows the effect of seawater alteration. The magnitude of the initial \u03f5_(Nd) values (+7.8) are somewhat smaller than for typical present-day mid-ocean ridge basalts (+10). This is most likely due to differential evolution over the past 0.5 AE of the oceanic mantle relative to the bulk earth.
\r\n\r\nSm-Nd and Rb-Sr data for the Oslo Rift demonstrate that this province which is strongly enriched in large ion lithophile (LIL) elements is derived from depleted.to undepleted mantle materials. A source with a long history of light rare earth (LREE) enrichment can clearly be ruled out.
\r\n\r\nSm-Nd data for the Archean granulite and amphibolite facies migmatites of Lang\u00f8y and Hinn\u00f8y in Vester\u00e5len indicate that their protoliths formed ~2.6 AE ago. Rb and U loss during a granulite facies metamorphism at ~1.8 AE caused serious disturbance of total rock U-Pb and Rb-Sr systems. Therefore these systems do not provide any precise age information for the granulite facies migmatites. For the amphibolite facies migmatites of Vester\u00e5len both Sm-Nd, Rb-Sr, and Pb-Pb total rock systems give model ages of ~2.6 AE.
\r\n\r\nSm-Nd and Rb-Sr isotopic data for continental crust, depleted and undepleted mantle, have been used to evaluate both models and yield young mean ages for the mass of the continental crust of 1.8 AE and 1.5 AE for Model I and Model II, respectively. Both models also suggest that the rate of growth of the continents for the last 0.5 AE is much less than the average growth rate. The young mean age of the continents implies either rapid refluxing of crustal materials to the mantle in the period from 4.5 AE to 3.6 AE or that very little early crust ever formed. Mass balance calculations for both models show that the continents were only formed from ~30% of the total mantle leaving 70% of the mantle as undepleted. The major difference in the two models lies in the difference in the compositions of newly derived crust. For Model I the trace element concentrations in new additions to the crust is constant and the isotopic values are those of the undepleted mantle reservoir in agreement with recent Nd isotopic studies. Model II implies that new additions to the continents have the isotopic characteristics of the depleted mantle and that the concentrations of Rb, U, Ba and other highly incompatible trace elements in newly added material have changed by a factor of ~10 through time. There is no evidence, however, for such a large change in the concentration of these elements with time.
", "doi": "10.7907/q5z7-d408", "publication_date": "1980", "thesis_type": "phd", "thesis_year": "1980" }, { "id": "thesis:16244", "collection": "thesis", "collection_id": "16244", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11152023-171559514", "primary_object_url": { "basename": "McCulloch_MT_1980.pdf", "content": "final", "filesize": 107341101, "license": "other", "mime_type": "application/pdf", "url": "/16244/1/McCulloch_MT_1980.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Part I. Sm-Nd and Rb-Sr Chronology of Crustal Formation. Part II. Ba, Nd and Sm Isotopic Anomalies in the Allende Meteorite", "author": [ { "family_name": "McCulloch", "given_name": "Malcolm Thomas", "clpid": "McCulloch-Malcolm-Thomas" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis is divided into two parts. The first part has as its theme the chronology of crustal formation. The times at which new segments of crust were formed has been ascertained by using Sm-Nd and Rb-Sr isotopic systematics, together with plausible assumptions regarding the geochemical evolution of the crust and mantle. The general approach that has been used is to assume that the differentiation processes which produce magmatic rocks occur with a marked chemical fractionation of the Sm/Nd and Rb/Sr ratios relative to the source region. It is then the time of this chemical fractionation which has been dated. This approach is valid insofar as the dominant contribution to the crust comes from the emplacement of magmatic rocks derived from a \"uniform\" mantle reservoir.
\r\n\r\nSm-Nd studies of early Archean complexes from the Minnesota River Valley, Labrador, and the Pilbara of Western Australia have shown that these rocks were derived at ~ 3.6 AE from a mantle with a time\u00ad average Sm/Nd ratio approximately equal to that in chondrites (CHUR). These results, together with a 3.6 AE Sm-Nd model age from a tonalitic gneiss in northern Michigan, confirm that this time period marks one of the earliest episodes of major continental crustal formation on the earth.
\r\n\r\nIn contrast to the apparent uniformity of Sm/Nd in the mantle of the earth, many lunar magmatic rocks have initial \u00b9\u2074\u00b3Nd/\u00b9\u2074\u2074Nd ratios which indicate variability in the Sm/Nd ratios of their source reservoirs of up to 60%. These highly fractionated reservoirs must have formed within about 200 m.y. after the accretion of the moon. The Sm-Nd data on highland breccias and KREEP samples indicate a low Sm/Nd ratio for these samples which was also plausibly established early in lunar history and is complementary to the early production of high Sm/Nd mare basalt source regions. The contrast between the lunar and terrestrial Nd isotopic data implies a grossly different early differentiation history for these two planets.
\r\n\r\nA study of the Nd, Sr, and O isotopic characteristics of the Samail Ophiolite is also presented. This complex represents oceanic crust that was abducted onto the Arabian continental margin during late Cretaceous times. Using the Sm-Nd method, internal isochrons were obtained from three gabbros establishing a Cretaceous crystallization age for the Samail Ophiolite. These results appear to be highly consistent in spite of extensive hydrothermal exchange which has altered the primary \u2078\u2077Sr/\u2078\u2076Sr and \u00b9\u2078O/\u00b9\u2076O ratios. Gabbros from Ibra give an age of 130 \u00b1 12 m.y., and a gabbro in the northern part of Oman gives an age of 100 \u00b1 20 m.y. These results show that the Sm-Nd technique can be used to determine crystallization ages and initial Nd ratios of relatively young, Mesozoic and Cenozoic mafic complexes.
\r\n\r\nIn part two of this thesis, isotopic anomalies are reported for Ba, Nd, and Sm in two inclusions from the Allende meteorite. These inclusions are typical Ca-Al-rich objects associated with early condensates from the solar nebula but have distinctive O and Mg isotopic anomalies of the FUN type. Sample Cl shows \u00b9\u2074\u2074Sm enrichments and a depletion in \u00b9\u00b3\u2075Ba of 2 parts in 10\u2074 and normal Nd. Sample EKl-4-1 shows large positive excesses in the unshielded isotopes \u00b9\u00b3\u2075Ba and \u00b9\u00b3\u2077Ba of 13.4 and 12.3 parts in 10\u2074, respectively, The Nd and Sm isotopic composition in EKl-4-1 is highly aberrant in at least five isotopes The Ba, Sm, and Nd anomalies in EKl-4-1 can be explained by a model of r-process addition. From the observations of \u00b9\u2074\u2074Sm isotopic anomalies in Cl, it is inferred that the p-processes is decoupled from the r-process. All these anomalies are found to be uniform between coexisting mineral phases. These observations show the existence of substantial isotopic anomalies in refractory elements in the neighborhood of Xe and extend the range of elements showing isotopic effects to O, Ne, Si, Mg, Ca, Sr, Kr, Xe, Ba, Sm, and Nd. These observations, in conjunction with the presence of \u00b9\u2070\u2077Pd (\u03c4\u00bd = 6.5 x 10\u2076 yrs) and \u00b2\u2076Al (\u03c4\u00bd = 7 x 10\u2075 yrs), are interpreted as the result of a nearby supernova explosion which produced elements over a wide mass range and injected them into the early solar nebula shortly before condensation.
", "doi": "10.7907/hnt7-9586", "publication_date": "1980", "thesis_type": "phd", "thesis_year": "1980" }, { "id": "thesis:9537", "collection": "thesis", "collection_id": "9537", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01212016-132933875", "primary_object_url": { "basename": "Smith_sp_1979.pdf", "content": "final", "filesize": 128702631, "license": "other", "mime_type": "application/pdf", "url": "/9537/1/Smith_sp_1979.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Studies of Noble Gases in Meteorites and in the Earth", "author": [ { "family_name": "Smith", "given_name": "Stephen Pritchard", "clpid": "Smith-Stephen-Pritchard" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The isotopic and elemental abundances of noble gases in the solar\r\nsystem are investigated, using simple mixing models and mass-spectrometric\r\nmeasurements of the noble gases in meteorites and terrestrial rocks and\r\nminerals.
\r\n\r\n\r\nPrimordial neon is modeled by two isotopically distinct components\r\nfrom the interstellar gas and dust. Neon from the gas dominates solar neon,\r\nwhich contains about ten times more 20Ne than 22Ne. Neon from the dust is\r\nrepresented in meteorites by neon-E, with 20Ne/22Ne less than 0.6. Isotopic\r\nvariations in meteorites require neon from both dust and gas to be present.\r\nMixing dust and gas without neon loss generates linear correlation lines\r\non three-isotope and composition-concentration diagrams. A model for solar\r\nwind implantation predicts small deviations from linear mixing, due to preferential\r\nsputtering of the lighter neon isotopes.
\r\n\r\n\r\nNeon in meteorites consists of galactic cosmic ray spallation neon\r\nand at least two primordial components, neon-E and neon-S. Neon was measured\r\nin several meteorites to investigate these end- members. Cosmogenic\r\nneon produced from sodium is found to be strongly enriched in\r\n22Ne. Neon measurements on sodium-rich samples must be interpreted with care so not to\r\nconfuse this source of 22Ne with neon-E, which is also rich in 22Ne.
\r\n\r\nNeon data for the carbonaceous chondrite Mokoia show that the end member composition of neon-Si in meteorites is 20Ne/22Ne = 13.7, the same as\r\nthe present solar wind. The solar wind composition evidently has remained\r\nconstant since before the compaction of Mokoia.
\r\n\r\nCa, Al-rich inclusions from the Allende meteorite were examined for\r\ncorrelation between neon-E and oxygen or magnesium isotopic anomalies.\r\n22Ne and 36Ar enrichments found in some inclusions are attributed to cosmic-\r\nray-induced reactions on Na and Cl, not to a primordial component. Neon-E\r\nis not detectably enriched in Allende.
\r\n\r\nMeasurements were made to determine the noble gas contents of various\r\nterrestrial rocks and minerals, and to investigate the cycling of noble\r\ngases between different terrestrial reservoirs. Beryl crystals contain a\r\ncharacteristic suite of magmatic gases including nucleogenic 21Ne and 22Ne\r\nfrom (\u03b1,n) reactions, radiogenic 40Ar, and fissiogenic 131-136Xe from the\r\ndecay of K and U in the continental crust. Significant concentrations of\r\natmospheric noble gases are also present in beryl.
\r\n\r\nBoth juvenile and atmospheric noble gases are found in rocks from\r\nthe Skaergaard intrusion. The ratio 40Ar/36Ar (corrected for in situ decay\r\nof 40K) correlates with \u03b418O in plagioclase. Atmospheric argon has been\r\nintroduced into samples that have experienced oxygen-isotope exchange with\r\ncirculating meteoric hydrothermal fluids. Unexchanged samples contain\r\njuvenile argon with 40Ar/36Ar greater than 6000 that was trapped from the\r\nSkaergaard magma.
\r\n\r\nJuvenile and atmospheric gases have been measured in the glassy\r\nrims of mid-ocean ridge (MOR) pillow basalts. Evidence is presented that\r\nthree samples contain excess radiogenic 129Xe and fission xenon, in addition\r\nto the excess radiogenic 40Ar found in all samples. These juvenile gases\r\nare being outgassed from the upper-mantle source region of the MOR magma.\r\nNo isotopic evidence has been found here for juvenile primordial noble\r\ngases accompanying the juvenile radiogenic gases in the MOR glasses. Large\r\nargon isotopic variations in a single specimen provide a clear indication\r\nof the late-stage addition of atmospheric argon, probably from seawater.
\r\n\r\nThe Skaergaard data demonstrate that atmospheric noble gases dissolved\r\nin ground water can be transferred into crustal rocks. Subduction\r\nof oceanic crust altered by seawater can transport atmospheric noble gases\r\ninto the upper mantle. A substantial portion of the noble gases in mantle\r\nderived rocks may represent subducted gases, not a primordial component\r\nas is often assumed.
\r\n\r\n", "doi": "10.7907/x4b9-m132", "publication_date": "1979", "thesis_type": "phd", "thesis_year": "1979" }, { "id": "thesis:3204", "collection": "thesis", "collection_id": "3204", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08232006-154851", "type": "thesis", "title": "Study of Magma Sources, Mantle Structure and the Differentiation of the Earth from Variations of \u00b9\u2074\u00b3Nd/\u00b9\u2074\u2074Nd in Igneous Rocks", "author": [ { "family_name": "DePaolo", "given_name": "Donald James", "clpid": "DePaolo-Donald-James" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The decay of 147Sm to 143Nd allows 143Nd/144Nd to be used to trace Sm/Nd fractionation in long time-scale geologic processes. Since Sm/Nd is a sensitive indicator of many aspects of the overall chemistry of rocks, the Sm-Nd system provides an excellent tool for the study of the chemical evolution of the earth's crust and mantle.
\r\n\r\n143Nd/144Nd has been measured in terrestrial rock samples of different ages to establish the characteristics of Nd isotopic evolution in the crust and mantle. The evolution of 143Nd/144Nd in the mantle indicates Sm/Nd equal to that of chondrites, and implies a chondritic REE distribution for the earth. Young basalts show a significant dispersion in 143Nd/144Nd indicating the existence of distinct mantle reservoirs with characteristic 143Nd/144Nd. 143Nd/144Nd in average crustal rocks today is much lower than in mantle samples and reflects their age and low Sm/Nd. Continental flood basalts and mid-ocean ridge (MOR) tholeiitic basalts have distinctly different 143Nd/144Nd which may permit a priori distinction between \"continental\" and \"oceanic\" igneous rocks. Ocean island basalts have 143Nd/144Nd intermediate between MOR and continental flood basalts. Initial 143Nd/144Nd of many continental igneous rocks through time fall on a Sm/Nd evolution curve with chondritic REE abundance ratio. Oceanic igneous rocks are derived from a different ancient reservoir which has Sm/Nd higher than chondritic. These observations indicate that many continental igneous rocks are derived from a reservoir with chondritic REE pattern which may represent primary undifferentiated material remaining since the formation of the earth, while oceanic igneous rocks are derived from highly differentiated reservoirs. The mantle beneath the oceans appears to be more depleted in crustal components than is the mantle which is subjacent to the continental crust. In general, basalts are not derived from mantle reservoirs which have been light REE-enriched for long times.
\r\n\r\nInitial 143Nd/144Nd and 87Sr/86Sr in young basalts from both oceans and continents show a strong correlation suggesting that Sm-Nd and Rb-Sr fractionation events in the mantle may be correlative and caused by the same process. From this correlation Rb/Sr for the earth is inferred to be 0.029.
\r\n\r\nInitial 143Nd/144Nd in lunar igneous rocks show much more dispersion than in terrestrial rocks of similar age. The data suggest that the earth, unlike the moon, did not undergo an early differentiation event which greatly fractionated the rare earth elements, or if it did, a mixing process operated during the subsequent AE to erase the variation of Sm/Nd produced in this event.
\r\n\r\nNd and Sr isotopes indicate that if the earth is made of a mixture of achondrites (low Rb/Sr) and chondrites (high Rb-Sr) that these two components must have been thoroughly mixed. The present-day isotopic heterogeneity of the earth's mantle is unrelated to accretional heterogeneity.
\r\n\r\nTransport calculations and material balance considerations for simple models of formation of the continental crust indicate that only a small portion of the earth's total budget of Sm and Nd are found in the crust. Highly differentiated mantle reservoirs such as those from which MOR basalts are derived must represent only a small portion of the mantle, perhaps one-fourth to one-sixth or less. The data are consistent with the existence of large volumes of undifferentiated (possibly undegassed) material in the mantle. The data also suggest that the continental crust has a low Rb/Sr (less than 0.10) implying a highly layered structure for the crust, with the lower crust having a much lower Rb/Sr than the upper crust.
\r\n\r\nIsland arc lavas from New Britain and the Marianas have 143Nd/144Nd similar to other oceanic basalts and distinctly different from continental flood basalts and thus appear to be derived from a high Sm/Nd, light-REE-depleted reservoir. Consideration of both Nd and Sr isotopes suggests seawater involvement in the generation of some island arc lavas and thus indicates that they may be derived from altered subducted oceanic crust. Other island arc lavas show no evidence of seawater involvement and may be derived from mantle reservoirs with affinities to the sources of ocean island basalts. Nd and S in some basaltic and ultrapotassic continental lavas and in some Andean volcanics indicate that some magmas in continental regions may be derived from old low-Sm/Nd reservoirs or are heavily contaminated with old continental crustal material. Fish debris from the ocean floor provides an estimate of 143Nd/144Nd in seawater and indicates that light-REE in the marine environment are derived mainly from continents.
", "doi": "10.7907/YBQ5-4B95", "publication_date": "1978", "thesis_type": "phd", "thesis_year": "1978" }, { "id": "thesis:2817", "collection": "thesis", "collection_id": "2817", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07062006-115658", "primary_object_url": { "basename": "Gancarz_aj_1976.pdf", "content": "final", "filesize": 23952103, "license": "other", "mime_type": "application/pdf", "url": "/2817/1/Gancarz_aj_1976.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "I: Isotopic Systematics in Archean Rocks, West Greenland. II: Mineralogic and Petrologic Investigations of Lunar Rock Samples", "author": [ { "family_name": "Gancarz", "given_name": "Alexander John, Jr.", "clpid": "Gancarz-Alexander-John" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Pb isotopic abundances and U-Th-Pb concentrations are reported for feldspar megacrysts from the 3.59 AE old Amitsoq Gneiss, Godthaab District, West Greenland. The distinctive Pb in the feldspars is the most primitive terrestrial Pb so far observed. It is observed in feldspars which are from different geographic localities and which exhibit varying degrees of deformation and recrystallization. This appears to be either the initial Pb in the Amitsoq Gneiss or the initial Pb only slightly modified by subsequent metamorphism in a low 238U/204Pb environment. 238U/204Pb in the feldspars is low and the corrections for in situ produced Pb are only 0.4 per cent for 207Pb/206Pb and 0.6 per cent for 204Pb/206Pb. The mean corrected isotopic abundances are 204Pb/206Pb=0.08720, 207Pb/206Pb = 1.1513, and 208Pb/206Pb = 2.7309. The feldspars contain a very small amount of easily leachable radiogenic Pb which is strongly correlated with U and which indicates the formation of U-rich phases at about 2.7 AE. The matrix surrounding the feldspar megacrysts contains Pb which is much evolved relative to the megacrysts and this matrix does not appear to have behaved as a simple closed system. Element redistribution and open system behavior at about 2.7 AE is also suggested by Pb in feldspar from a dyke cutting across the gneiss. Assuming that the Amitsoq Gneiss feldspar Pb corrected for in situ U decay was the initial Pb in the gneiss at 3.59 AE (Baadsgaard, 1973), a single-stage \"age of the earth\" is determined as 4.47 +/- 0.05 AE and \u00b5 is 8.5. This is indistinguishable from the single-stage age for modern rocks and is distinctly younger than the age of some meteorites. If we assume that the earth originally formed at 4.6 AE and assume that it underwent major, large-scale differentiation at a time T(D), we use the same observed data to calculate that the time of differentiation is approximately 4.4 AE and that \u00b5 for the total earth is approximately 1.6 while \u00b5 for the mantle and crustal rocks is approximately 9.5.\r\n\r\nPb and Sr isotopic data and K-Rb-Sr-U-Th-Pb concentration data are presented for three anorthosite complexes in West Greenland. The three complexes are the Majorqap Qava outcrop of the Fiskenaesset Anorthosite Complex, the Storo Anorthosite Complex, Godthaab District, and the Ivnajaugtoq Anorthosite Complex, Godthaab District. The Pb isotopic data yield an age of 2.8 AE for the Majorqap Qava Anorthosite and Storo Anorthosite. The Ivnajaugtoq data are consistent with a 2.8 AE age. We interpret this as the time of igneous crystallization and metamorphic recrystallization. U-Pb data indicate substantial U redistribution within the last ~100 m.y. These three complexes have very different initial Sr isotopic abundances. These differences indicate that either the anorthosites crystallized at 2.8 AE from melts with different \u00b5's which were derived and fractionated at ~3.6AE from \"normal\" (i.e. \u00b5~9) mantle material and remained isolated until 2.8 AE or the anorthosites crystallized at 2.8 AE from melts derived at 2.8 AE from \"normal\" mantle material and which were variably contaminated during emplacement with Pb like that in the Amitsoq Gneiss.\r\n\r\nIncluded are a series of published articles which are primarily concerned with the mineralogic and petrographic characterization of lunar highland samples.\r\n", "doi": "10.7907/S5C5-9E60", "publication_date": "1976", "thesis_type": "phd", "thesis_year": "1976" }, { "id": "thesis:603", "collection": "thesis", "collection_id": "603", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02112004-095253", "primary_object_url": { "basename": "Wolfe_sh_1972.pdf", "content": "final", "filesize": 21263845, "license": "other", "mime_type": "application/pdf", "url": "/603/1/Wolfe_sh_1972.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Part I. Geology of the Manicouagan-Mushalagan Lakes Structure. Part II. Geochronology of the Manicouagan-Mushalagan Lakes Structure", "author": [ { "family_name": "Wolfe", "given_name": "Stephen Howard", "clpid": "Wolfe-Stephen-Howard" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe Manicouagan-Mushalagan Lakes structure is an area of anomalous geological features in the Grenville Province terrain of northeastern Canada. Three features of this structure have been revealed by geological studies:\r\n\r\n(1) The Grenville gneisses and anorthosites which outcrop in the area between the arcuate lakes have been shock metamorphosed.\r\n\r\n(2) The shocked Grenville gneisses are covered by a thin, discontinuous layer of shock breccia and thin outcrops of Ordovician limestone.\r\n\r\n(3) An annular-shaped body of Permo-Triassic, igneous, andesitic rock, which shows no signs of shock metamorphism, overlies the shocked gneisses, the shock breccia and the Ordovician limestone. This rock (monzonite) is 800 feet thick at a maximum.\r\n\r\nThe shocked basement rocks in the structure were most probably caused by the impact of an extraterrestrial body, but the origin of the igneous rock unit is not completely understood. This latter unit has been hypothesized to be either (1) a shock-melted breccia or (2) a later, secondary igneous event occurring at the crater site due to disruptions of the earth's thermal regime around the impact site. A geochronological study of this structure was made to determine which, if either, of the above modes of formation for the igneous material is likely.\t\t\r\n\r\n[...] data for the igneous material and rock units related to it yield a well-defined crystallization age of [...]. [...] data for this unit indicate that it has experienced no subsequent metamorphism. Argon isotopic ages obtained for a series of shock-sequence anorthosites do not indicate a well-defined time of shock metamorphism; the ages could characterize a system shocked at anytime between 320 and 210 m.y. ago which then suffered a secondary gas loss. It is shown that anorthosites yielding ages between 280 and 320 m.y. probably underwent complete or nearly complete outgassing at the time of shock. These latter ages should therefore yield a good impact age. The time interval within which the impact took place is thought to be 280-320 m.y. ago.\r\n\r\nThe [...] data show unexpected evidence for the occurrence of a secondary event at about 100-110 m.y. which affected the anorthosites in the crater but not the igneous monzonite.\r\n\r\nSince it is not possible to say with certainty when the meteoritic impact took place, the difference between the monzonite formation time and the impact time is unclear. The suggested impact time is, however, significantly earlier than the crystallization time of the igneous material. This suggests that a secondary formation mode for this material is more likely than an impact melt formation mode. A secondary mode is also compatible with evidence that the monzonite formed in a subsurface environment with [...].", "doi": "10.7907/YB0X-BZ53", "publication_date": "1972", "thesis_type": "phd", "thesis_year": "1972" }, { "id": "thesis:11049", "collection": "thesis", "collection_id": "11049", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06082018-102752217", "primary_object_url": { "basename": "Schramm_DN_1971.pdf", "content": "final", "filesize": 74441872, "license": "other", "mime_type": "application/pdf", "url": "/11049/1/Schramm_DN_1971.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Isotopic Composition of Mg and the Implied Limits on \u00b2\u2076Al in the Early Solar System. Nucleosynthesis of \u00b2\u2076Al. And Nucleosynthetic Chronologies for the Galaxy", "author": [ { "family_name": "Schramm", "given_name": "David Norman", "clpid": "Schramm-David-Norman" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "A particular isotope pair of astrophysical interest, 26Al-26Mg, was investigated in detail. A high precision mass spectrometric technique was developed whereby Mg isotopic compositions could be analyzed to better than five parts in 104.
\r\n\r\nFeldspar (high Al, low Mg) mineral separates were carried out on several meteoritic and lunar samples. No anomalous 26Mg values were found. Thus, there is no evidence for the existence of 26 Al at the formation of the solar system.
\r\n\r\nUpper limits on the possible amount of 26Al at solidification in the extraterrestrial samples were calculated. These limits were used to estimate the maximum change in central temperature of a planetary object which could be produced by the 26Al decay.
\r\n\r\nA review is given of the production mechanisms for 26Al and it has been shown that a flux of at least 4 x 1018 protons/cm2 is required to produce enough 26 Al to melt the cores of planetary objects.
\r\n\r\nThe general problem of nucleosynthetic chronologies has been\r\ninvestigated. Nucleochronologies for the galaxy have been calculated using235U;238U,232Th/238U, 244Pu/238U (or preferably 244Pu/232Th),and 129I/127I. The systematics of the nucleochronologic equations are derived and it has been found that the mean age of the elements can be found from long-lived radioactive nucleii in a manner which is independent of the time dependent production rate. It has also been found that the interval between the termination of nucleosysthesis and the time of formation of solid bodies in the solar system can be determined model independently from the short~lived\r\nnucleii. In addition, some information on the time dependent shape of the production function can also be determined model independently.
\r\n", "doi": "10.7907/J2VA-1S31", "publication_date": "1971", "thesis_type": "phd", "thesis_year": "1971" }, { "id": "thesis:908", "collection": "thesis", "collection_id": "908", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03092009-160704", "primary_object_url": { "basename": "Papanastassiou_da_1970.pdf", "content": "final", "filesize": 5585882, "license": "other", "mime_type": "application/pdf", "url": "/908/1/Papanastassiou_da_1970.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Determination of Small Time Differences in the Formation of Planetary Objects", "author": [ { "family_name": "Papanastassiou", "given_name": "Dimitri Anastassios", "clpid": "Papanastassiou-Dimitri-Anastassios" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA new solid source single focusing, sector magnet mass spectrometer was developed with a programmable magnetic field analyzer of stability [...]. Digital data are obtained during a completely automatic sequence and include the real time at which an intensity measurement is made. An on line computer analyses the data and returns the results to the operator throughout a run. The precision obtained in measuring isotopic ratios is increased by an order of magnitude over conventional similar instruments and is documented for the strontium isotopes. The [...] ratio is measured to better than [...] 0.007% over the extended time of the experiments.\r\n\r\nCa-rich achondritic meteorites having a total spread of 0.2% in [...] were studied and appear to define an identical initial abundance of 0.698983 [...] 0.000032. The samples lie on a well defined isochron with slope 0.0642 [...] 0.0034, corresponding to an age of 4.47 [...] 0.24 x [...] years. The maximum deviation of data points from the isochron is 6 x [...] and shows that these samples were formed over a time interval of 1.6 x [...] years if they were derived from an environment of solar Rb/Sr abundance. The Angra dos Reis achondrite has the distinctly lower inital Sr composition of 0.69884 [...] 0.00004 and is, therefore, derived from more primitive material than any other meteorite measured. Angra dos Reis may have formed 5.4 x [...] years earlier than the other achondrites (from a solar Rb/Sr environment). The Angra dos Reis initial Sr isotopic composition should be considered as the best estimate of the primordial Sr isotopic abundance in the solar system.\r\n\r\nMeasurements on the chondrite Guarena yield an age 4.56 [...] 0.08 x [...] years and precise Sr initial composition of 0.69995 [...] 0.00015. This is evidence for either a late formation of Guarena or a metamorphic event taking place 74 x [...] years after the time of formation of the Ca-rich achondrites. These measurements may yield a time index for the classification of meteorites.\r\n\r\nMeasurements on Apollo XI lunar samples are presented and discussed.", "doi": "10.7907/D5S4-JN64", "publication_date": "1970", "thesis_type": "phd", "thesis_year": "1970" }, { "id": "thesis:10792", "collection": "thesis", "collection_id": "10792", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04052018-084913740", "primary_object_url": { "basename": "O'Connell_RJ_1969.pdf", "content": "final", "filesize": 137893985, "license": "other", "mime_type": "application/pdf", "url": "/10792/1/O'Connell_RJ_1969.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Part 1. Dynamic Response of Phase Boundaries in the Earth to Surface Loading. Part 2. Pleistocene Glaciation and the Viscosity of the Lower Mantle", "author": [ { "family_name": "O'Connell", "given_name": "Richard John", "clpid": "O'Connell-Richard-John" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Anderson", "given_name": "Don L.", "clpid": "Anderson-D-L" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Part 1. Analytic approximate solutions have been found for the response of a phase change to pressure loading. These solutions allow the behavior of the system to be analyzed in terms of simple parameters of the system. Different characteristic types of behavior are shown to obtain for short times and long times, and criteria for defining these characteristic time scales are given in\r\nterms of known parameters. The distribution of heat sources and convective heat transport are shown to generally have only minor influence on the solution, and may be neglected in many cases. The important parameters are the latent heat of the phase change, and the difference between the Clapeyron slope and the temperature gradient at the phase boundary; in addition the long term behavior is governed by the boundary conditions at the surface and at depth,\r\nand the relative positions of the surface, the phase boundary, and the lower boundary. The effect of thermal blanketing from sediments is included in the solution, and it depends primarily on the depth of the phase boundary and the average temperature gradient in the sediments. The effect of isostasy in conjunction with a phase change is shown to be of major importance; the existence of instabilities where the water depth increases with sedimentation are demonstrated. These solutions allow the history of a sedimentary basin to be calculated, and characterized in terms of certain types of behavior. The existence of oscillatory behavior is demonstrated, where repeated cycles of sedimentation and erosion take place.\r\nThese oscillations can either decay or grow in amplitude, and expressions are given for their frequency and damping or growth constants. A phase change mechanism can account for thicknesses of sediments which exceed the depth of the basin in which they were deposited by a factor of twenty or more. These solutions allow the discussion of the geological implications of phase changes in a quantitative manner. The consequences of a phase change can be\r\naccurately calculated. This will allow the more complete investigation of the role of phase changes in geologic processes.
\r\n\r\nPart 2. The non-tidal acceleration of the earth, revealed by astronomical observations and records of eclipses in antiquity, is attributed to the change in the earth's moment of inertia resulting from isostatic response to the most recent deglaciation and rise in sea level. The isostatic response time for a spherical harmonic deformation\r\nof degree two is calculated on this basis to be either ~2000\r\nyears or ~100,000 years. A correlation of the geopotential with the potential that would have existed following de glaciation indicates that any large scale anomalies resulting from deglaciation have already decayed. This rules out the 100,000 relaxation time; thus the relaxation time of the earth is ~2000 years for degree two. Calculations of the relaxation time spectrum of a layered, gravitating spherical viscous earth model indicates that a model with a uniform mantle viscosity of ~10^(22) poise, except for fine structure in the upper few hundred kilometers, can satisfy the relaxation time of 3000 years for degree two as well as the relaxation time of ~4000\r\nyears for degree twenty which results from studies of uplift in Fennoscandia. A zone of high viscosity in the lower 800 km. of the mantle has a significant effect on the degree two relaxation time. This rules out any substantial increase in viscosity in the lower mantle. The calculated viscosity permits rapid polar wandering and convection in the lower mantle.
\r\n", "doi": "10.7907/3JGM-5Q68", "publication_date": "1969", "thesis_type": "phd", "thesis_year": "1969" }, { "id": "thesis:10795", "collection": "thesis", "collection_id": "10795", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04052018-144537140", "primary_object_url": { "basename": "Henyey_TL_1968.pdf", "content": "final", "filesize": 113926434, "license": "other", "mime_type": "application/pdf", "url": "/10795/1/Henyey_TL_1968.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Heat Flow near Major Strike-Slip Faults in Central and Southern California", "author": [ { "family_name": "Henyey", "given_name": "Thomas Louis", "clpid": "Henyey-Thomas-Louis" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Seventeen heat flow measurements have been made near the\r\nSan Andreas, San Jacinto, and Garlock faults of California in regions representative of several levels of seismic activity. Data from these measurements in conjunction with results of other heat flow investigations in central and southern California show no maxima directly attributable to the fault zones. This negative result along with stress-drop\r\nresults from earthquakes suggests an upper bound of the order of 200 bars for the absolute stress in the vicinity of the San Andreas fault. In addition, the average heat flow in the four regions investigated (San Bernardino Mountains - Lake Hughes, Anza, Hollister, and Tehachapi\r\nMountains) is the same; the mean value of 23 determinations is 1.7 \u03bccal/cm2/sec \u00b1 0.1 s.d.
\r\n\r\nIn the region between Lake Hughes and San Bernardino, presently seismically inactive but in the zone of rupture from the ~8 magnitude Fort Tejon earthquake, six measurements show no correlation with distance from the San Andreas fault. Near the San Jacinto fault in an area characterized by frequent medium magnitude earthquakes, determinations at 1 and 4 km from the fault are equal\r\nbut 20 per cent higher than a measurement 13 km to the west, but not appreciably different from a probable regional average 25 km to the east. Near Hollister where the San Andreas is actively creeping at a rate of several centimeters per year, a measurement 8 km east of the fault yields a flux twice as great as one 30 km to the west, but\r\nvalues at intermediate points suggest that this anomaly may reflect more the regional geology than the San Andreas fault alone. Finally, measurements across the historically inactive Garlock fault exhibit high fluxes near the fault in comparison with a determination 8 km to the north, but do not differ significantly from determinations in the\r\nMojave Block to the south.
\r\n\r\nIn California, the major fault systems appear to lie in transition zones between blocks of crust characterized by Basin and Range heat flows -- Mojave Block and Salton Trough -- and blocks representative of normal continental heat flows -- Central Valley and the crustal strip between the San Jacinto-San Andreas fault system and the Pacific continental margin.
\r\n", "doi": "10.7907/Z153-RH23", "publication_date": "1968", "thesis_type": "phd", "thesis_year": "1968" }, { "id": "thesis:10152", "collection": "thesis", "collection_id": "10152", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05032017-084934764", "primary_object_url": { "basename": "Naylor_RS_1967.pdf", "content": "final", "filesize": 39381081, "license": "other", "mime_type": "application/pdf", "url": "/10152/1/Naylor_RS_1967.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "A Field and Geochronologic Study of Mantled Gneiss Domes in Central New England", "author": [ { "family_name": "Naylor", "given_name": "Richard Stevens", "clpid": "Naylor-Richard-Stevens" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "New information on the origin of mantled gneiss domes comes\r\nfrom a study of these structures in Central New England. The domes\r\nhave cores of massive granite and gneiss encircled by concordant\r\nmantles of well-stratified metamorphic rocks, and appear to originate\r\nthrough intense metamorphism of rock sequences in which massive,\r\nchiefly quartzo-feldspathic rocks are overlain by less competent\r\nstrata. Contrary to previous hypotheses, the new work indicates that\r\nneither unconformable separation of the core and mantle nor re-mobilization\r\nor anatexis of the core rocks are essential elements in\r\nthe formation of mantled gneiss domes. Two contrasting types of\r\ngneiss domes have been identified in central New England.
\r\n\r\n\r\nExamples of the first type are domes of the Chester Dome group\r\nin southeastern Vermont. Formation of these domes involved kyanite-staurolite\r\ngrade metamorphism of Precambrian gneissic basement overlain\r\nunconformably by Paleozoic strata. The angular relationships at\r\nthe unconformity have been obscured by differential movement of the\r\ncore-rocks relative to the mantling strata. The Precambrian rocks in\r\nthe cores of the Chester Dome and the nearby Green Mountain Anticlinorium\r\nhave been badly disturbed by Paleozoic metamorphism, but\r\ngenerally yield Precambrian zircon and Rb-Sr whole-rock ages.
\r\n\r\n\r\nThe second type of gneiss dome is exemplified by the Mascoma\r\nand Lebanon (Oliverian) Domes exposed about thirty miles to the east\r\nin central New Hampshire. No Precambrian rocks have been identified\r\nin the cores of these domes. Fieldwork indicates that the core of\r\nthe Mascoma Dome can be subdivided into two major units: (1) massive\r\ngneiss of intermediate igneous composition lying stratigraphically\r\nbeneath the Ordovician Ammonoosuc Volcanics, and (2) a sub-central\r\npluton of granite and quartz monzonite which crosscuts the massive\r\ngneiss and probably the Ammonoosuc Volcanics, but which lies\r\nunconformably beneath the Late Lower Silurian Clough Formation.\r\nWithin limits imposed by analytical uncertainty and the metamorphic\r\ndisturbance of the rocks, a common age of 440 \u00b1 40 million years\r\n(initial Sr87/Sr86 = 0.706 \u00b1 0.002) is determined for whole-rock\r\nsamples of the granitic sub-cores of the Lebanon and Mascoma Domes,\r\nand for whole-rock samples of the Ammonoosuc Volcanics. Zircon\r\nseparates from both the gneissic and granitic units within the core\r\nof the Mascoma Dome yield Pb207/Pb206 ages of 450 \u00b1 25 million years.\r\nThe data indicate that these domes formed in the following stages:\r\n(1) Ordovician volcanism followed by intrusion of granitic rocks,\r\n(2) uplift and local unroofing followed by deposition of Lower\r\nSilurian through Lower Devonian strata, and (3) garnet- to staurolite-\r\ngrade post-Lower Devonian metamorphism and deformation. Most of\r\nthe crosscutting relationships were established by Ordovician\r\nplutonic activity and not by post-Lower Devonian plutonic activity or\r\nanatexis. The core-rocks of these domes appear to be the result of\r\nvolcanic and intrusive activity towards the end of the Ordovician,\r\nand not the result of in-place remobilization or anatexis of Pre-\r\ncambrian basement subsequent to deposition of the mantling strata.\r\nThe other Oliverian Domes, particularly those in New Hampshire,\r\nresemble the Mascoma Dome, and probably originated in much the\r\nsame manner.
", "doi": "10.7907/7TWJ-DJ70", "publication_date": "1967", "thesis_type": "phd", "thesis_year": "1967" }, { "id": "thesis:9610", "collection": "thesis", "collection_id": "9610", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03102016-141714720", "primary_object_url": { "basename": "Aronson_jl_1966.pdf", "content": "final", "filesize": 39574661, "license": "other", "mime_type": "application/pdf", "url": "/9610/1/Aronson_jl_1966.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Geochronology of the Plutonic and Metamorphic Rocks of New Zealand", "author": [ { "family_name": "Aronson", "given_name": "James Louis", "clpid": "Aronson-James-Louis" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Extensive Rubidium-Strontium age determinations on both mineral\r\nand total rock samples of the crystalline rocks of New Zealand, which\r\nalmost solely crop out in the South Island, indicate widespread plutonic\r\nand metamorphic activity occurred during two periods, one about \r\n100-118 million years ago and the other about 340-370 million years ago.\r\nThe former results date the Rangitata Orogeny as Cretaceous. They\r\nassociate extensive plutonic activity with this orogeny which uplifted\r\nand metamorphosed the rocks of the New Zealand Geosyncline,\r\nalthough no field association between the metamorphosed geosynclinal\r\nrocks and plutonic rocks has been found. The Cretaceous plutonic\r\nrocks occur to the west in the Foreland Province in Fiordland, Nelson,\r\nand Westland, geographically separated from the Geosynclinal\r\nProvince. Because of this synchronous timing of plutonic and high\r\npressure metamorphic activity in spatially separated belts, the Rangitata\r\nOrogeny in New Zealand is very similar to late Mesozoic orogenic\r\nactivity in many other areas of the circum-Pacific margin (Miyashiro,\r\n1961).
\r\n\r\nThe 340-370 million year rocks, both plutonic and metamorphic,\r\nhave been found only in that part of the Foreland Province north of the\r\nAlpine Fault. There, they are concentrated along the west coast over \r\na distance of 500 km, and appear scattered inland from the coast.\r\nProbably this activity marks the outstanding Phanerozoic\r\nstratigraphic gap in New Zealand which occurred after the Lower\r\nDevonian.
\r\n\r\nA few crystalline rocks in the Foreland Province north of the\r\nAlpine Fault with measured ages intermediate between 340 and 120\r\nmillion years have been found. Of these, those with more than one\r\nmineral examined give discordant results. All of these rocks are\r\ntentatively regarded as 340-370 million year old rocks that have been\r\nvariously disturbed during the Rangitata Orogeny, 100-120 million\r\nyears ago.
\r\n\r\nIn addition to these two periods, plutonic activity, dominantly\r\nbasic and ultrabasic, but including the development of some rocks of\r\nintermediate and acidic composition, occurred along the margin of the\r\nGeosynclinal Province at its border with the Foreland Province during\r\nPermian times about 245 million years ago, and this activity possibly\r\nextended into the Mesozoic.
\r\n\r\nEvidence from rubidium-strontium analyses of minerals and a\r\ntotal rock, and from uranium, thorium, and lead analyses of uniform\r\neuhedral zircons from a meta-igneous portion of the Charleston\r\nGneiss, previously mapped as Precambrian, indicate that this rock\r\nis a 350-370 million year old plutonic rock metamorphosed 100 million\r\nyea rs ago during the Rangitata Orogeny. No crystalline rocks with\r\nprimary Precambrian ages have been found in New Zealand. However,\r\nPb207/Pb206 ages of 1360 million years and 1370 million years have\r\nbeen determined for rounded detrital zircons separated from each of\r\ntwo hornfels samples of one of New Zealand's olde st sedimentary units,\r\nthe Greenland Series. These two samples were metamorphosed 345-\r\n370 million years ago. They occur along the west coast, north of the\r\nAlpine Fault, at Waitaha River and Moeraki River, separated by 135\r\nkm. The Precambrian measured ages are most likely minimum ages\r\nfor the oldest source area which provided the detrital zircons because\r\nthe uranium, thorium and lead data are highly discordant. These\r\nresults are of fundamental importance for the tectonic picture of the\r\nSouthwest Pacific margin and demonstrate the existence of relatively\r\nold continental crust of some lateral extent in the neighborhood of New\r\nZealand.
", "doi": "10.7907/GZ9M-GP33", "publication_date": "1966", "thesis_type": "phd", "thesis_year": "1966" }, { "id": "thesis:7278", "collection": "thesis", "collection_id": "7278", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11202012-153218336", "primary_object_url": { "basename": "Zartman_re_1963.pdf", "content": "final", "filesize": 27444384, "license": "other", "mime_type": "application/pdf", "url": "/7278/1/Zartman_re_1963.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "A Geochronological Study of the Lone Grove Pluton from the Llano Uplift, Texas", "author": [ { "family_name": "Zartman", "given_name": "Robert Eugene", "clpid": "Zartman-Robert-Eugene" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A detailed geological study of the Lone Grove granitic pluton and surrounding rocks from the Llano Uplift, Texas, was made. Field and petrologic evidence suggests that this intrusive has had a simple history of emplacement with no later metamorphism. Samples of granite, aplite, pegmatite, rhyolite, and metamorphic rocks were investigated geochronologically in order to determine the consistency in Rb87\u2013Sr87 and K40\u2013Ar40 ages between various minerals and between different localities. Refined chemical and mass spectrometric methods of analysis are described and the limits of precision are established. It is found possible to determine ages on most highly radiogenic minerals to a precision of \u00b1 1 1/2% or better. All ages were calculated with the following decay constants: Rb87, \u03bb\u03b2=1.47x10(-11)yr(-1); K40, \u03bb\u03b2=4.72x10(-10)yr(-1) and \u03bbe= 0.585x10(-10)yr(-1). The distribution of ages on most of the minerals from these rocks show a spread commensurate with the experimental error. The average Rb87-Srv age on microclines,muscovites and biotites is 1015 million years and the average K40\u2013Ar40 age on muscovites, biotites, and hornblendes is 1045 million years. A total rock Rb87-Sr87 age on one of the granites gives no indication of having an older age than the constituent minerals. The only rock to show an apparently real different age is a rhyolite porphyry,\r\nwhich gives an average Rb87-Sr87 microcline age of 910 million years. K40-Ar40 determinations on several microclines and plagioclases give ages which are 5-20% too low, presumably due to argon diffusion from the feldspar. Anomalously low Rb87\u2013Sr87 ages occur on several biotites from fresh pegmatites and granite. Evidence is presented for radiogenic strontium migration from these rocks although the exact nature of the process is not known. Somewhat low K40\u2013Ar40 ages also are obtained on the pegmatitic biotites. A study of the effects of weathering on the geochronologic systems is made on two obviously altered granites. The only mineral to suffer any decrease in age from such surface alteration is biotite by the Rb87-Sr87 method. The isotopic composition of the common strontium incorporated into the minerals of the granite is determined on several minerals having low Rb/Sr ratios. The Sr87/Sr88 ratio is found to be 0.0843 \u00b1 0.0002 (normalized to make Sr866/Sr88 = 0.1194). A discussion of the distribution of rubidium, potassium, and normal strontium throughout the pluton is given and several partitioning factors for the rubidium to potassium concentrations between different mineral species are calculated.
\r\n", "doi": "10.7907/SXVC-R234", "publication_date": "1963", "thesis_type": "phd", "thesis_year": "1963" }, { "id": "thesis:6598", "collection": "thesis", "collection_id": "6598", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08182011-145051903", "primary_object_url": { "basename": "Lanphere_ma_1962.pdf", "content": "final", "filesize": 39207754, "license": "other", "mime_type": "application/pdf", "url": "/6598/3/Lanphere_ma_1962.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "I. Geology of the Wildrose Area, Panamint Range, California. II. Geochronologic Studies in the Death Valley-Mojave Region, California", "author": [ { "family_name": "Lanphere", "given_name": "Marvin Alder", "clpid": "Lanphere-Marvin-Alder" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Jahns", "given_name": "Richard H.", "clpid": "Jahns-R-H" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The bedrock in the Wildrose area is predominantly a sequence\r\nof metamorphosed sedimentary and possible volcanic rocks that is more than 15,000 feet thick. All the metamorphic rocks are Precambrian in age on stratigraphic evidence. The rocks are divided into three age groups, early Precambrian, later Precambrian, and Precambrian (?), that are separated by unconformities. The early Precambrian Panamint metamorphic complex has been divided into two series that are separated by a profound unconformity. Small stocks\r\nand dikes of granitic rocks, which are presumably Cretaceous in age, intrude the metamorphic rocks. Tertiary sedimentary rocks and Quaternary alluvium are also present in the area.\r\n\r\nThe structural features of the area are ascribed to four periods of deformation. The large folds in the early Precambrian rocks and associated minor folds were produced during the first two periods of deformation of early Precambrian age. Low angle faults are evidence\r\nof the third deformation which is considered to be Cretaceous in age. The fourth period of deformation produced high angle faults. Movement\r\nalong the high angle faults began in late Tertiary time and has continued to the present.\r\n\r\nAll the Precambrian rocks of the area have been affected by\r\nmiddle or lower middle grade metamorphism. Even though structural evidence suggests that metamorphism must have accompanied the earlier periods of deformation, the present mineral assemblages reflect the third period of deformation which, on the basis of mineral age measurements, was Cretaceous in age. Narrow contact metamorphic\r\naureoles surround the larger masses of granite.\r\n\r\nRadioactive ages were measured in five areas in the Death\r\nValley-Mojave Desert region. The rocks are Precambrian in age on stratigraphic evidence in three areas, the Wildrose area of the Panamint Range, the Mountain Pass district, and the Marble Mountains. The rocks in Joshua Tree National Monument and the Kilbeck Hills are presumably Precambrian, but no stratigraphic evidence of their age has been found. The geochronologic studies in the five areas indicate three distinct groups of K - Ar and Rb-Sr ages. Ages of\r\napproximately 1650 million years are obtained on metamorphic rocks and associated pegmatite s in the Mountain Pass district. Younger igneous rocks at Mountain Pass and in the Marble Mountains have age patterns that are interpreted to indicate intrusion in the 1350\r\nto 1450 million year interval. Metamorphic rocks in the Wildrose area, Joshua Tree National Monument , and the Kilbeck Hills have ages in the 75 to 85 million year interval which are interpreted as the age of regional metamorphism related to the Cretaceous Nevadan\r\norogeny. An age of 73 million years was obtained on a post-metamorphic granite.\r\n", "doi": "10.7907/VKKA-P510", "publication_date": "1962", "thesis_type": "phd", "thesis_year": "1962" } ]