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.
Results
Showing 1 to 20 of 178 for “"U-Pb"”.
-
U-Pb geochronology of the Acasta Gneiss Complex in Northwest Canada
… in age from 4.03-3.6 Ga, as determined by U-Pb dating of zircons (Bowring and Williams 1999). U-Pb dating of xenocrystic cores in these zircons indicates a cryptic record of continental crust older than 4.0 Ga. In this study, zircons were selected and characterized from thirteen samples of …
-
High-precision U/Pb dating of the Cenomanian-Turonian boundary Kaiparowits Plateau, Utah
… the Kaiparowits Plateau, Utah were dated using U/Pb geochronology. The Cenomanian-Turonian boundary is constrained to be 94.040 ± 0.029/0.098/0.14 Ma, in agreement with recent astrochronologic studies of the same time period. This research will help improve the calibration of the astronomical time …
-
Integrating high-precision U-Pb geochronologic data with dynamic models of earth processes
… behavior and/or initial conditions of the U-Pb system and provides an effective means of exploring the parameters that influence a calculated date. The record provided by geochronologic data is then coupled with models to quantitatively determine rates of geologic process on Earth. This …
-
U-Pb dating of granites from the Charlotte belt of the southern Appalachians
New U-Pb zircon ages from plutons in the Charlotte belt of the southern Appalachians have provided evidence of Cambro-Ordovician and Siluro-Devonian magmatic activity. Several U-Pb zircon ages of Cambro-Ordovician plutons predate their Rb-Sr whole rock ages by as much as 60 m.y., suggesting a post …
-
U-Pb calcite dating of fossil eggshell and its impact on continental terrestrial sedimentology
… a non-traditional geochronometer, ergo U-Pb calcite age dating of fossil eggshell. Within Data Chapter One, we evaluated the reliability of elemental mapping coupled with LA-ICP-MS U-Pb calcite age dating of dinosaur eggshell recovered from Tel Ulaan Chaltsai against dinosaur eggshell from …
-
Zircon crystallization patterns from U-Th dates inform U-Pb estimates of volcanic eruption ages
U-Pb dating of zircons provides time constraints on events from 4.5 Ga to < 1Ma by measuring the timing of zircon crystallization. Absolute uncertainties on U-Pb zircon dates are significant enough to obscure zircon crystallization and complicate estimating the relationship between zircon …
-
Paleogeography of Western North America: Insights from Detrital Zircon U-Pb Geochronology and Hf Isotope Geochemistry
… using modern analytical techniques including U-Pb geochronology and Hf isotope geochemistry of detrital zircons, as well as, geologic mapping and paleocurrent analysis. The Neoproterozoic through Pennsylvanian Yukon-Tanana terrane (YTTs) in the Coast Mountains of southeastern Alaska, the …
-
High-precision U/Pb geochronology of large igneous provinces and mass extinctions : testing coincidence and causation
… are coupled with the latest techniques in U/Pb geochronology to generate highprecision age models which are used to evaluate the relative timing of (1) the end- Permian mass extinction, which is the most severe in the Phanerozoic, and the Siberian Traps LIP, which is the largest continental …
-
High-Precision ID-TIMS U-Pb Zircon Geochronology of Three Cenomanian Bentonites from the Western Canada Foreland Basin
… and dated using high-precision U-Pb ID-TIMS geochronology techniques. The Pb/ U weighted-mean ages are: 95.87±0.10 Ma for the X-bentonite, 95.67±0.15 Ma for the A-X bentonite, and 94.29±0.13 Ma for the Bighorn River Bentonite (2a confidence level). These new ages establish a more …
-
Recalibrating the breakup history of SW Gondwana: the first U-Pb chronostratigraphy for the Uitenhage Group, South Africa
… By integrating field observations with U-Pb geochronology of over 4000 detrital and primary volcanic zircons from pyroclastic, mixed-origin volcaniclastic and sedimentary rocks by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS), this thesis presents the first …
-
U-Pb geochronological constraints on the tectonic and thermal evolution of paleoproterozoic crust in the Grand Canyon, Arizona
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996.
-
⁴⁰Ar/³⁹Ar and U-Pb geochronological constraints on the thermal and tectonic evolution of the Connemara Caledonides, Western Ireland
… was inferred based on a >75 Ma spread in U-Pb, Rb-Sr, and K-Ar mineral dates. Such a history is inconsistent with field observations which suggest a simple relationship between metamorphism and syntectonic magmatism. This study was designed to explore the significance of the large spread in …
-
Statistical considerations in high precision U-Pb geochronology, with an application to the tectonic evolution of the North Cascades, Washington
… of geologic problems that may be addressed by U-Pb geochronology is governed by the precision to which U-Pb dates can be measured, expressed as their estimated uncertainties. Accurate and precise knowledge of both the value and uncertainty of an isotopic date are imperative to its correct …
-
Exhumation, rift-flank uplift, and the thermal evolution of the Rwenzori Mountains determined by combined (U-Th)/He and U-Pb thermochronometry
… study combining (U-Th)/He and U-Pb analysis of apatite, titanite, and zircon separated from crystalline basement rocks was conducted across the Rwenzori block to characterize the timing and rate of rift-flank exhumation related to continental extension in east-central Africa. The …
-
Early Laramide Magmatism in Southern Arizona U-Pb Geochronology of Key Igneous Units and Implications for the Timing of Regional Porphyry Copper Mineralization
… This investigation presents new U-Pb in zircon ages on key igneous units across southern Arizona to constrain the onset of early Laramide magmatism and to compare the timing of mineralization in several key mining districts with these early events. The objectives of this …
-
U/Pb Zircon Ages of Plutons from the Central Appalachians and GIS-Based Assessment of Plutons with Comments on Their Regional Tectonic Significance
… region. SIMS (secondary ion mass spectrometry) U/Pb ages of zircons were obtained for ten plutons (Leatherwood, Rich Acres, Melrose, Buckingham, Diana Mills, Columbia, Poore Creek, Green Springs, Lahore and Ellisville) within Virginia. These plutons are distinct chemically, isotopically, and show …
-
Timing and drivers of exhumation in the hinterland of the North American Cordillera from detrital zircon U-Pb and (U-Th)/He double-dating
… A total of 2,163 new detrital zircon U-Pb ages were obtained from 16 samples to confirm the published provenance of the sandstones and/or recover new grain-age populations. The U-Pb ages reveal the major sources for zircons: Permian-Triassic, Jurassic, and Cretaceous arc rocks, the …
-
Palaeoenvironments and position of the Precambrian–Cambrian boundary within the lower Vanrhynsdorp Group of South Africa: sedimentary facies analysis, U-Pb series zircon geochronology and micropalaeontology
… discovered in the Vanrhynsdorp Group. Through U-Pb dating of detrital zircons using LA-ICP-MS, radiometric ages for the middle part of the Vanrhynsdorp Group (Besonderheid Formation) were obtained in a preliminary study of this project. The radiometric data, yielding a maximum depositional age of …
Page 1 of 9