Uranium-lead zircon geochronology, hafnium isotope and trace element geochemistry of a unique lower crustal- upper mantle section of a dying slow-spreading mid-ocean ridge (Macquarie Island, Southern Ocean) PDF Download
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Author: Charles Ryan Jeffcoat
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Charles Ryan Jeffcoat
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Charles Ryan Jeffcoat
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 96
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Author: John M. Hanchar
Publisher: Walter de Gruyter GmbH & Co KG
ISBN: 1501509322
Category : Science
Languages : en
Pages : 520
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Volume 53 of Reviews in Mineralogy and Geochemistry covers the most important aspects of zircon-related research over the past twenty-years and highlight possible future research avenues. The chapters review the structure of zircon and other mineral (and synthetic) phases with the zircon structure; the minor and trace element compositions of igneous, metamorphic and hydrothermal zircons; the study of melt inclusions in zircon; experimental and natural studies of zircon saturation and the use of zircon saturation thermometry for natural rocks; cation diffusion and oxygen diffusion in zircon; the historical development of zircon geochronology from the mid-1950s to the present; ID-TIMS, SIMS and ICP-MS; the application of zircon chronology in constraining sediment provenance and the calibration ofthe geologic time-scale; other isotopic systematics; the spectroscopy of zircon, both crystalline and metamict and an atlas of internal textures of zircon.
Author: Marvin A. Lanphere
Publisher:
ISBN:
Category : Cosmochronology
Languages : en
Pages : 404
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Author: Gwen Margaret Linde
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 360
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This dissertation investigated Neoproterozoic–Devonian units of the western Laurentian passive margin and Roberts Mountains allochthon (RMA) and determined U-Pb detrital ages and Hf isotope zircon analyses that provide new insights into the early Paleozoic tectonics of western Laurentia. The three chapters investigate several difficult questions and contradictions in the understanding of early Paleozoic tectonism in western Laurentia through analysis of sedimentary units. The provenance, depositional histories, and tectonic evolution of the lower Paleozoic sedimentary strata of north-central Nevada have long been subjects of speculation and debate. Detrital zircon U-Pb geochronology and Hf-isotope analyses indicate the provenance, sedimentary distribution patterns, and tectonic evolution of Upper Neoproterozoic–Cambrian passive margin strata and Ordovician–Devonian strata of the RMA, with a special emphasis on the enigmatic Harmony Formation. The study reported in Chapter 1 uses detrital zircon U-Pb geochronology to determine whether or not the Upper Neoproterozoic–Lower Cambrian Osgood Mountain Quartzite and the Upper Cambrian–Lower Ordovician Preble Formation in the Osgood Mountains of northern Nevada were units of the western Laurentian passive margin. Within the Osgood Mountain Quartzite, U-Pb age populations of the detrital zircons shift with stratal age. This shift indicates that the zircons were shed in different proportions from the source terranes, which suggests a change in provenance within the Osgood Mountain Quartzite. These changes are consistent across a Great Basin transect of coeval passive margin strata. The change in provenance is due to a shift in sedimentary transport patterns, which was caused by the Late Neoproterozoic-Early Cambrian uplift of the Transcontinental Arch. This study provided independent corroboration of the existence of the Transcontinental Arch and better precision for the timing at which the Arch uplifted. The study also recorded the impact of the uplifted Arch on continent-wide sediment dispersal patterns—the change in predominant source terranes—and confirmed the Arch as a sediment source for passive-margin strata. Regional coeval changes in detrital zircon U-Pb age patterns provide a correlative tool in unfossiliferous sediments and could be useful in future studies. Chapter 2 describes how detrital zircon U-Pb geochronology and Hf-isotope analyses were used to determine the provenance, sedimentary transport, and tectonic evolution of RMA strata. Workers have speculated for decades, with little agreement, on the origin, depositional basin(s), and subsequent tectonic transport of the RMA. Zircon grains from six Ordovician to Devonian arenite samples were analyzed for U-Pb ages; approximately one-quarter of these grains were further analyzed for Hf isotope ratios. Five of the studied units have similar U-Pb age populations and Hf-isotope ratios, while the U-Pb ages and Hf-ratios of the Ordovician lower Vinini Formation are significantly different. Comparison of these data with known analyses of igneous basement rocks and other sedimentary units of Laurentia reveals that the lower Vinini Formation originated in the north-central Laurentian craton. The other five units, as well as Ordovician passive margin sandstones of the western Laurentian margin, had a common source in the Peace River Arch region of western Canada. All of the RMA strata were deposited near the Peace River Arch region and subsequently tectonically transported south along the Laurentian margin, from where they were emplaced onto the craton during the Antler orogeny. This study determined the origin, location of the depositional basin, and proposed a subsequent tectonic evolution that accounts for origin, deposition, and current location of the RMA strata. Chapter 3 describes the origin, age, and tectonic development of the Harmony Formation. The Harmony Formation has always been difficult to explain—it is mostly an immature feldspathic arenite, which would argue for minimal transport from origin to deposition. However, its general position as the top thrust plate in the RMA stack argues for deposition oceanward of other more texturally mature RMA strata. The age of the Harmony Formation is equally contentious—published age determinations range from Cambrian to Mississippian. Zircon grains from ten arenite samples were analyzed for U-Pb ages; grains from eight of these samples were further analyzed for Hf-isotope ratios. Seven of the arenite units have similar U-Pb age peaks and Hf isotope ratios, whereas three differ significantly. The data confirmed the subdivision of the Harmony Formation into two petrofacies, quartzose (Harmony A) and feldspathic (Harmony B). Harmony A originated in the central Laurentian craton. Harmony B had a common source in eastern Alberta–western Saskatchewan, north of the source of the Harmony A. All of the Harmony Formation strata were deposited near eastern Alberta in Late Neoproterozoic through Cambrian time and subsequently tectonically interleaved with the Roberts Mountains allochthon strata. The entire package was tectonically transported south along the Laurentian margin. Subsequently, it was emplaced eastward onto the craton during the Late Devonian to Early Mississippian Antler orogeny. This study proposed a reasonable solution to one of the longest enduring and most puzzling conundrums of the western Cordillera—the origin, age, and transport of the Harmony Formation. These three studies demonstrated the utility of detrital zircon U-Pb geochronology and Hf-isotope analyses in better understanding difficult sedimentary and tectonic problems. The studies also provided new insights into the Early Paleozoic tectonic evolution of western Laurentian.
Author: Heinrich D Holland
Publisher: Academic Press
ISBN: 0080967094
Category : Science
Languages : en
Pages : 539
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The history of Earth in the Solar System has been unraveled using natural radioactivity. The sources of this radioactivity are the original creation of the elements and the subsequent bombardment of objects, including Earth, in the Solar System by cosmic rays. Both radioactive and radiogenic nuclides are harnessed to arrive at ages of various events and processes on Earth. This collection of chapters from the Treatise on Geochemistry displays the range of radioactive geochronometric studies that have been addressed by researchers in various fields of Earth science. These range from the age of Earth and the Solar System to the dating of the history of Earth that assists us in defining the major events in Earth history. In addition, the use of radioactive geochronometry in describing rates of Earth surface processes, including the climate history recorded in ocean sediments and the patterns of circulation of the fluid Earth, has extended the range of utility of radioactive isotopes as chronometric and tracer tools. Comprehensive, interdisciplinary and authoritative content selected by leading subject experts Robust illustrations, figures and tables Affordably priced sampling of content from the full Treatise on Geochemistry
Author: Jason Duff
Publisher:
ISBN:
Category : Hafnium
Languages : en
Pages : 222
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Author: Bethany S. Murphy
Publisher:
ISBN:
Category : Geochronometry
Languages : en
Pages : 131
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Crystal-rich (40-50 vol.%) intermediate lava has been the primary eruptive product of several recent hazardous eruptions: Mt. Pinatubo, Philippines (1991), Soufriere Hills, Montserrat (1995-present), and Unzen, Japan (1990-1995). Despite this association with such devastating eruptions, the formation, timing, and evacuation of such magma is not well understood: do such eruptions tap a long-lived, multi-cycle crystal mush, or, is it generated in a single magmatic cycle prior to eruption? This thesis explores this question through research at the Unzen Volcanic Complex (UVC), southwestern Japan, where a 500 ka history of crystal-rich dacitic dome eruptions has built the Unzen Volcanic Complex. Previous studies (e.g. Nakamura, 1995) have demonstrated the role of mafic recharge in rejuvenating crystal mush zone a few months prior to the most recent eruptions, but - until now - its formation and evolution have not been investigated using detailed geochronology. Now, this gap has been addressed through U/Th zircon geochronology and zircon chemistry studies (zircon chronochemistry) on several eruptions, spanning in age from the most recent (Heisei-Shinzan; 1990-1995) to lavas of the Older Unzen period ([greater than or equal to]200 ka). Zircon geochronology has revealed the protracted history and evolution of the crystal mush zone at the Unzen Volcanic Complex. Individual zircon surface-interior age pairs, together with zircon age spectra, suggest that portions of this crystal mush have been present in the crust since at least the late Older Unzen period ([greater than or equal to]200 ka). Significant zircon growth appears to occur throughout the eruptive hiatus (200-100 ka), suggesting that magmatic activity continued uninterrupted through this period. Zircon chemistry shows that UVC crystals are typical of unaltered, igneous zircon, and - overall - zircon crystals show a restricted range in trace element chemistry in all eruption samples. Ti-in-zircon temperatures show that zircon crystalizes from a low temperature ([less than or equal to]790°C) magma, in agreement with previous temperatures estimates for UVC upper-crustal magma (e.g. Venezky and Rutherford 1999). Subtle variations in trace element chemistry are observed in titanium and hafnium content through time: titanium contents show a moderate negative correlation with time, while hafnium shows a moderate positive correlation. This suggests that the crystal mush zone has evolved towards a more mature, heterogeneous system. Additionally, Older Unzen eruption samples show restricted chemistry, suggesting that crystallization occurred in a more homogenous, less evolved and possibly warmer crystal mush, compared to zircon of Younger Unzen (100 ka - present) that record variable storage conditions skewed towards a more evolved, poorly-mixed crystal mush. Complex age populations, particularly from samples of the Younger Unzen period, suggest that localized regions within the crystal mush may have different thermal histories. These results lead to the conclusion that eruptions at Unzen are tapping a mature and long-lived, multi-cycle mush of significant longevity.
Author: P. van den Haute
Publisher: Springer Science & Business Media
ISBN: 9401591334
Category : Science
Languages : en
Pages : 344
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Since 1980, progress in research on the fission-track dating method and its applications to earth and related sciences has been evaluated during an International Workshop that takes place every four years. This volume contains a selection of papers presented at the International Workshop held in Gent (Belgium) from 26 to 30 August, 1996. Primarily the articles will be of interest to the active fission-track scientists but the combination of research papers and critical reviews that is presented may also provide the interested non-specialist reader with a valuable insight into the fission-track dating method and its role in the earth sciences. This reader will undoubtedly note the evolution that the method has undergone during the last fifteen years, from a technique that was debated in most of its facets to an established chronometric tool with unique qualities in geothermochronology.
Author: Christopher T. Harper
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 496
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