Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 50 for “"Isotopic signature"”.
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Pedogenic gypsum of southern New Mexico: Genesis, morphology, and stable isotopic signature
… New Mexico were described and sampled for isotopic analysis. Gypsum soil morphology was expanded to include a new "snowball" morphology, as well as Stage I filaments and Stage II nodules, a classification scheme formerly only applied to carbonate morphology. A pedogenic origin for gypsum …
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Determining the concentration and source of lead in chocolate using lead isotopes
… to determine their lead concentrations and the isotopic composition of the lead. The lead isotope ratios were compared with published data from aerosols and volcanic rocks nearest to the cocoa growing regions. Samples from different countries and manufacturers were compared, and we conclude that …
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Mineralogical, chemical and isotopic diversity in plutonic rock suites from the Coastal Maine Magmatic Province:the role of source region heterogeneity, tectonic setting and magmatic processes
… effect of accessory minerals on the initial Pb isotopic signature of anatectic granites. Their initial Pb isotopic composition reflects (a) the age, type, modal distribution, and heterogeneity in the initial U and Th content of the accessory phase(s) present in the source, (b) variation in melt …
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The geochemistry of boron and lithium in mid -ocean ridge hydrothermal vent fluids
… processes. The B concentration and the Li isotopic signature of hydrothermal fluids from four areas on the mid-ocean ridge were examined in order to better constrain the physical and chemical controls on these elements.</p><p>The results for B suggest that water-rock reaction and phase …
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AN IMBRICATE MID CRUSTAL SUTURE ZONE: THE MOJAVE-YAVAPAI PROVINCE BOUNDARY IN GRAND CANYON, ARIZONA
… uncertain. This paper analyzes the U-Pb-Hf isotopic composition of zircons from both the oldest plutons and metasedimentary rocks in Grand Canyon. My results show that the Vishnu Schist does not support suturing. Paradoxically, plutons east and west of the Crystal shear zone support suturing …
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In situ mineral geochemistry as a guide to ore-forming processes
Isotopic and trace element analyses are essential to our understanding ore-forming processes, but traditionally these techniques have required bulk digestion of rocks and minerals. Recent advances in in situ microanalytical techniques permit us to analyse samples on a mineral-by mineral basis and …
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In situ mineral geochemistry as a guide to ore-forming processes
Isotopic and trace element analyses are essential to our understanding ore-forming processes, but traditionally these techniques have required bulk digestion of rocks and minerals. Recent advances in in situ microanalytical techniques permit us to analyse samples on a mineral-by mineral basis and …
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The Cretaceous to recent history of the southeastern Indian Ocean : the role of mantle plumes examined by geochronology and Sr, Nd, Pb and He isotopic geochemistry
… Plateau, 2) the geochronology and Sr-Nd-Pb-He isotopic characteristics of the olivinerich lavas of the Kerguelen Archipelago, and 3) Sr-Nd-Pb isotopic evidence for contamination of Southeast Indian Ridge basalts with melts from the Amsterdam-St. Paul and Kerguelen plumes. At Elan Bank of the …
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Using high resolution Sr isotope data from the Nama Group, South Africa, to constrain global stratigraphic relationships and continental weathering rates in the terminal Ediacaran
… collected in South Africa and Namibia. The isotopic signature of these rocks is consistent with other terminal Ediacaran age rocks, with typically slightly positive 13C and relatively high 87Sr/86Sr ratios (~0.7085). Correlation with other Ediacaran basins reveals a drop in 87Sr/86Sr from …
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Barium isotope cycling in the marine environment: Pathways of fractionation and implications for paleoceanographic applications
… the controls on the formation, cycling, and isotopic signature of the main particulate phase of marine barium, the mineral barite (BaSO₄) through its inception in the water column, during deposition, and ultimately into the rock record. To that end, I characterize the depth, spatial region, …
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Barium isotope cycling in the marine environment: pathways of fractionation and implications for paleoceanographic applications
… the controls on the formation, cycling, and isotopic signature of the main particulate phase of marine barium, the mineral barite (BaSO4) through its inception in the water column, during deposition, and ultimately into the rock record. To that end, I characterize the depth, spatial region, …
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In Situ Hydrogen Measurements in Garnet
… found in three textures. The water content and H isotopic composition was measured on traverses across garnet from all three texture types. The δD values of grains from each texture fall below the isotopic signature range for magmatic or carbonate source fluids indicating input of meteoric fluids. …
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Nutrient cycles across topography in drainage-impaired Corn Belt soils
… especially high after fertilization, when the isotopic signature of nitrate was consistent with a combination of mineralized soil nitrogen and recent fertilizer additions. When considered with the flooding-induced crop mortality in depressions during the study period, these results indicate …
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The Spatial Distribution of Terrestrial Stable Carbon Isotopes in North America, and the Impacts of Spatial and Temporal Resolution on Static Ecological Models
… on the modeling of terrestrial stable carbon isotopic landscapes (isoscapes). I model the distribution of leaf stable carbon isotope composition (delta<sup>13</sup>C) for the continent of North America at multiple temporal and spatial resolutions. I generate each delta<sup>13</sup>C isoscape …
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New insights into the marine oxygen cycle from manganese oxide minerals and reactive oxygen species
… atmosphere, oceans, and subsurface leave their isotopic fingerprints on the abundance of the three stable isotopes of O2 in the environment. In this thesis, I explore two aspects of the oxygen cycle in the past and present. First, I investigate the ability of manganese (Mn) oxide minerals to …
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The Marcona - Mina Justa District, South-Central Perú: Implications for the Genesis and Definition of the Iron Oxide-Copper (-Gold) Ore Deposit Clan
… of aqueous fluids with magmatic stable isotopic compositions. Subsequent, subeconomic chalcopyrite - pyrite - calcite ± pyrrhotite ± sphalerite assemblages were deposited from cooler fluids with similar δ34S, δ18O and δ13C values, but higher δD, which may record the involvement of both …
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A carbon and nitrogen isotopic analysis of Pleistocene food webs in North America: implications for paleoecology and extinction
Carbon and nitrogen isotopic reconstructions of North American Pleistocene trophic relationships were used to examine the extinction within terrestrial mammals ~10,000 years ago and distinguish between two potential causal mechanisms - human over-hunting and climate change. Additionally, individual …
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Reconstruction of the East Asian monsoon variability since the mid-Holocene from the Pearl River estuary, southern China
… a relatively new proxy of bulk organic carbon isotopic signature (δ13C). C/N ratios and trace elements are also employed to conduct a multi-proxy case study from the Pearl River estuary, southern China. Sources of sediments within an estuary include river-derived terrestrial/freshwater input, …
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The Maya Footprint: Soil Resources of Chunchucmil, Yucatan, Mexico
… Chunchucmil with vital raw materials. The carbon isotopic signature of ancient C4 crops was not detected suggesting that either maize was not extensively produced or that the mix of native C3 and C4 plants in the savanna hid the signature. There were no soil chemical or biomarker evidences of …
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Variations in δ56Fe during magma differentiation at Cedar Butte volcano: signatures of thermal diffusion?
… for producing the compositional zoning and isotopic signature is a top down crystallization-reaction process involving a downward moving temperature gradient zone as suggested by Lundstrom (2009). Such a process differentiates the magma by a moving thermal migration zone while thermal …
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