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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 35 for “"Sr Isotope"”.
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Spatial analysis of the O-, H- and Sr- isotope composition of Cape Town groundwater
[Abstract has scientific formulas not accommodated by DSpace]
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Timing and Source of Alkali Enrichment at Mt. Etna, Sicily: Constraints from Clinopyroxene Geobarometry and In Situ SR Isotope Data
… (K, Rb, Cs) as well as elevated <sup>87</sup>Sr/<sup>86</sup>Sr in Etnean lavas. The source of this alkali-enrichment has been hotly debated, with end-member hypotheses involving mantle vs. crustal contributions. To further characterize the evolution of the subvolcanic magma storage and …
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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
… chemistry and can be tracked using the strontium isotope ratio of seawater, which can be faithfully captured by carbonate minerals. However, analysis of strontium isotopes in ancient carbonates can be complicated by diagenetic alteration. To ensure that the 87Sr/86Sr ratios generated in this study …
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Geochemical processes in the earth's mantle and the nature of crust-mantle interactions : evidence from studies of Nd and Sr isotope ratios in mantle-derived igneous rocks and lherzolite nodules
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980.
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Micro-geochemistry of the mantle and its volcanic rocks
… study investigates inter-grain trace element and Sr isotope variation in clinopyroxene (cpx), amphibole and melt from two spinel lherzolite xenoliths from the Middle Atlas Mountains, Morocco. These results support a multi-stage metasomatic process in which cpx and amphibole are recent additions to …
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The Role of Cumulate Plagioclase Entrainment in the Steens Basalt, SE Oregon: Insights from the Magma Chamber Simulator
… that more of the lower Steens plagioclase are in Sr isotope equilibrium with their groundmass compared to upper Steens plagioclase, where fewer plagioclase are in Sr isotope equilibrium with their groundmass. This led to the hypothesis that entrainment of a plagioclase-bearing cumulate into a …
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Dismantling the deep earth : geochemical constraints from hotspot lavas for the origin and lengthscales of mantle heterogeneity
… 1 presents the first published measurements of Sr-isotope variability in olivine-hosted melt inclusions. Melt inclusions in just two Samoan basalt hand samples exhibit most of the total Sr-isotope variability observed in Samoan lavas. Chapter 3 deals with the largest possible scales of mantle …
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Dismantling the deep earth : geochemical constraints from hotspot lavas for the origin and lengthscales of mantle heterogeneity
… 1 presents the first published measurements of Sr-isotope variability in olivine-hosted melt inclusions. Melt inclusions in just two Samoan basalt hand samples exhibit most of the total Sr-isotope variability observed in Samoan lavas. Chapter 3 deals with the largest possible scales of mantle …
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Physical and geochemical response in cave drip waters to recent drought, central Texas, USA : implications for drought reconstruction using speleothems
… conditions, including dripwater Mg/Ca, Sr/Ca, and Ba/Ca ratios, Sr isotope values, Ca concentrations, and oxygen isotope values. This lack of response indicates limited water-rock interaction (WRI) and/or prior calcite precipitation (PCP) affects these dripwaters. Intermediate drip sites …
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Mineralogical, Chemical, and Isotopic (Sr, Pb) Composition of Atmospheric Mineral Dusts in an Ombrotrophic Peat Bog, Southern South America
… of atmospheric dust and their radiogenic isotope compositions in the peat, provide important information about the mineralogical host phases of major and trace elements transported through the atmosphere, grain size fractionation during transport, and their possible source areas (PSAs). To …
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What are the biogeochemical consequences of heuweltjie formation?
… research has indicated ~95 000 years old. ⁸⁷/⁸⁶Sr isotope ratios of on-mound and off-mound soils indicate that the majority of the nutrients are exotically derived. However, it is important to note that there are various different sources which could have contributed to the mound and that it …
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The extinction of the rudist bivalves
… dating end Cretaceous strata by using strontium isotope stratigraphy. The method works by measuring the <sup>87</sup>Sr/<sup>86</sup>Sr of palaeo-seawater preserved in marine carbonate, such as the thick low-Mg calcite layer of rudist shells. The <sup>87</sup>Sr/<sup>86</sup>Sr of seawater was …
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The petrogenesis of the Pliocene Araral stratovolcano in the Andean Central Volcanic Zone, Northern Chile
… are compositionally heterogeneous with elevated Sr isotope ratios relative to mantle-derived lavas and the rest of the Andean Volcanic Arc. The lavas are produced by subduction-induced magmatism and magma differentiation processes, such as crustal assimilation as the magma ascends through the …
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Geodynamic Evolution of the Aegean Back-arc and its Implication for Associated Precious and Base Metal Mineralization
… geochemical, and isotopic analyses (Pb, Sr, δ34S and δ18O) of galena (PbS) and ore-associated hydrothermal barite (BaSO4). New galena Pb isotope data complemented by Pb isotope data of galena from the literature exhibit a range of isotopic ratios, with a resolvable geologic pattern. …
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Lithology and alteration assemblages of the Boss iron-copper deposit, Iron and Dent Counties, Southeast Missouri
… to a potassic alteration assemblage. A Rb-Sr isotope date of 1.136 Ga ± 0.170 Ga may represent the potassic alteration event. Granitic dikes post-date rhyolites and trachytes. The dikes lack potassium enrichment, suggesting that they were in equilibrium with, or post-dated, potassium …
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The Box Ankle and Ocmulgee shear zones of central Georgia: a study of geochemical response to Southern Appalachian deformation events
… age discordancy. Isotopic re-equilibration of Sr Isotopes did not occur on a cm whole rock scale during deformation. Porphyroclasts In the Ocmulgee shear zone retained partial Sr Isotopic signatures of the shear zone protolith. In contrast, Rb-Sr Isotope systems In the Box Ankle fault were …
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Geochemical Analysis of Mississippian Cherts and Devonian-Mississippian Novaculites, Southern Midcontinent Region
<p>This study uses trace elements and radiogenic isotopes (Pb, Sr, and Nd) to investigate the origin and mode of formation for the siliceous deposits in the Lower Mississippian Boone Formation and the Devonian-Mississippian Arkansas Novaculite in the southern midcontinent. Mississippi Valley-type …
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Mesozoic alkaline volcanism and mantle evolution of the southwestern São Francisco craton, Brazil
… (Almeida, 1977, Almeida et al., 1981). New Rb-Sr and Sm-Nd data are presented for both onand off-craton crustal rock sequences. The ultramafic greenstone association of the Rio das Velhas Supergroup yields 3.2 Ga Rb-Sr and Sm-Nd ages, in agreement with widespread 3.2 Ga old zircons from the …
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Trace metal applications in atmospheric and watershed dynamics: Case studies of mercury deposition in New England and bedrock groundwater-surface water mixing
… of two trace metals, mercury (Hg) and strontium (Sr). Both are naturally occurring and exist in the environment at trace levels.</p><p>Chapters II-IV of this dissertation focus on understanding the atmospheric chemistry of Hg and the wet and dry deposition of this toxic element. Chapter II …
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Mixed Carbonate-Siliciclastic Sequence Development and Chemostratigraphy On a Distal Foreland During Miocene Glaciation, Eastern Saudi Arabia
… in ∂¹³C beneath sequence boundaries. Positive C isotope excursions in the Lidam Miocene section can be tied to similar excursions in Qatar and UAE, where Sr isotope dates constrain the ages of the units. The overall C isotope profile at Lidam shows depleted values early in the Miocene to heavy …
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