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The Global ETD Search service is a free service for researchers
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Showing 81 to 90 of 143 (0.031 seconds)Spelling suggestions: "subject:"than"" "subject:"han""
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Zircon (U-Th)/He Dates from Radiation Damaged Crystals: A New Damage-He Diffusivity Model for the Zircon (U-Th)/He ThermochronometerGuenthner, William Rexford January 2013 (has links)
Zircon (U-Th)/He (zircon He) dating has become a widely used thermochronologic method in the geosciences. Practitioners have traditionally interpreted (U-Th)/He dates from zircons across a broad spectrum of chemical compositions with a single set of ⁴He diffusion kinetics derived from only a handful of crystals (Reiners et al., 2004). However, it has become increasingly clear that a "one-size-fits-all" approach to these kinetics is inadequate, leading to erroneous conclusions and incongruent data. This dissertation develops a more grain-specific approach by showing the fundamental role that intracrystalline radiation damage plays in determining the He diffusivity in a given zircon. I present three appendices that seek to quantify the radiation damage effect on He diffusion in zircon, explain how this effect manifests in zircon He dates, and show how to exploit such manifestations to better constrain sample thermal histories. Of particular importance, this dissertation represents the first comprehensive study to concentrate on the entire damage spectrum found in natural zircon and also the first to show that two different mechanisms affect He diffusion in zircon in different ways across this spectrum. In the first appendix, I and my fellow co-authors describe results from a series of step-heating experiments that show how the alpha dose of a given zircon, which we interpret to be correlated with accumulated radiation damage, influences its He diffusivity. From 1.2 × 10¹⁶ α/g to 1.4 × 10¹⁸ α/g, He diffusivity at a given temperature decreases by three orders of magnitude, but as alpha dose increases from ~2 × 10¹⁸ α/g to 8.2 × 10¹⁸ α/g, He diffusivity then increases by about nine orders of magnitude. We parameterize both the initial decrease and eventual increase in diffusivity with alpha dose with a function that describes these changes in terms of increasing abundance and size of intracrystalline radiation damage zones and resulting effects on the tortuosity of He migration pathways and dual-domain behavior. This is combined with another equation that describes damage annealing in zircon. The end result is a new model that constrains the coevolution of damage, He diffusivity, and He date in zircon as a function of its actinide content and thermal history. The second and third appendices use this new model to decipher zircon He datasets comprising many single grain dates that are correlated with effective uranium (eU, a proxy for the relative degree of radiation damage among grains from the same sample). The model is critical for proper interpretation of results from igneous settings that show date-eU correlations and were once considered spurious (appendix B). When applied to partially reset sedimentary rocks, other sources of date variability, such as damage and He inheritance, have to be considered as well (appendix C).
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| 82 |
Die erste Stadt an der äußersten Grenze. / Die historische Entwicklung der Stadt Tengchong im Prozeß der Entstehung und Konsolidierung des Grenzgebietes im Westen der chinesischen Provinz Yunnan. / The first town at the far frontier. / The historical development of Tengchong and the consolidation of the chinese border region in Western Yunnan.Kott, Diana 10 July 2003 (has links)
No description available.
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| 83 |
Cenozoic tectonic deformation, thermochronology and exhumation of the Diancang Shan metamorphic massif along Ailao Shan-Red River shear zone, southeastern Tibet, China / Känozoischen tektonischen Deformationen, Thermochronologie und Exhumierung der Diancang Shan metamorphen Massiv entlang Ailao Shan-Red River Scherzone, Südost-Tibet, ChinaCao, Shuyun 03 November 2010 (has links)
No description available.
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| 84 |
Fluid Histories During HP and UHP Metamorphism in Dabie Shan, China: Constraints from Trace Elements, Fluid Inclusions, and Stable IsotopesXiao, Yilin 23 January 2001 (has links)
No description available.
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| 85 |
Tao Fong Shan Christian Centre a sustainable landscape development /Fan, Tak-lai, Terry. January 1995 (has links)
Thesis (M.L.A.)--University of Hong Kong, 1995. / Includes special study report entitled : Solar applications to landscape design. Includes bibliographical references. Also available in print.
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| 86 |
A youth oriented activities space in our urban areaMa, Hoi-yin, Claris. January 2001 (has links)
Thesis (M.L.A.)--University of Hong Kong, 2002. / Includes bibliographical references. Also available in print.
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| 87 |
Die Gräberfelder in Samad al Shan (Sultanat Oman) : Materialen zur einer Kulturgeschichte /Yule, Paul, January 2001 (has links)
Habilitationsschrift--Fakultät für orientalische Sprachen und Altertumswissenschaften--Heidelberg--Ruprecht-Karls-Universität, 1995. / Résumé en anglais et en arabe. Bibliogr. vol. 1, p. 409-438. Index.
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| 88 |
Behaviour of the Sm-Nd isotopic system during metamorphism : examples from the HT-LP metamorphic terrane of the Limpopo Belt, South Africa and the UHP metamorphic terrane of Dabieshan, Central China /Chavagnac, Valérie. January 1999 (has links)
Th. doct.--Rennes 1, 1998. / Bibliogr. p. 319-355. Notes bibliogr. Résumé en anglais et français.
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| 89 |
Palaeoglaciology of the central Tibetan PlateauMorén, Björn January 2010 (has links)
The glacial history of the Tibetan Plateau has long been a contentious topic with widely different reconstructions. For Tanggula Shan, an extensive mountain range on the central Tibetan Plateau, multiple glacial reconstruc- tions and studies on the glacial chronology have been presented. However, the glacial geomorphological record has been sparse resulting in insufficient data to fully infer the area’s palaeoglaciology. Focussing on four landform categories, glacial valleys, marginal moraines, hummocky terrain, and glacial lineations; a glacial geomorphological map was produced, using Landsat 7 ETM+ satellite imagery, SRTM digital elevation model, and Google Earth. This map, together with GIS analyses and available cosmogenic exposure and electron spin reso- nance ages from the study area, was used to investigate the extent of former glaciations. Cosmogenic exposure and electron spin resonance ages range from 18.4 ± 1.6 to 203.4 ± 33.2 ka (recalculated using the CRONUS calculator). The extent of the glacial footprint is restricted to the high mountain areas, and is similar in extent to earlier glacial reconstructions. This glacial footprint can tentatively be explained by a monsoonal influence in the southeast, with the influence diminishing to the northwest. Alternatively, the precipitation gradient might have resulted in cold-based ice in the west and warm-based ice in the east. These variations in ice regime could have left fewer traces of glaciation in the west, than in the east. There is no evidence supporting an ice sheet covering the entire Tibetan Plateau. Rather, the available data support a smaller ice field in the high mountain areas, with a maximum extent well before the Last Glacial Maximum.
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| 90 |
Central Asian ice-marginal moraines of the global last glacial maximum : An analysis of topographic features affecting the glaciation pattern in the Tian Shan and Altai mountainsSandström, Sonja January 2018 (has links)
Glacial runoff from the Tian Shan and Altai Mountains is an important water resource, especially for people living in the arid areas of Central Asia. Measured water volumes from glaciers have decreased, and glacier area have shrunk with 50-90% since the Little Ice Age. Lack of knowledge regarding glaciers in high mountain areas, and the impact from climate change makes this an important field to investigate. This thesis focuses on topographic features and their impact on spatial glaciation patterns; today and during the global last glacial maximum, 19-30 thousand years ago (ka). From selected marginal moraines in the Tian Shan and Altai mountains, with a deglaciation age between 19-30 ka, an analysis was created in ArcMap (GIS, Geographic Information System) with 1 arc second resolution ASTER GDEM2 (Digital Elevation Model) and in Google Earth. An elevation profile, hypsometry and mapping were created for the analysis. The interpretations made from the limited dataset resulted in topographic features affecting the glaciation extension today and percentage of decreasing glacier area since 19-30 ka, to be connected to north/south-facing direction of the drainage area and the elevation. Drainage areas experiencing the highest percentage of glacial shrinkage were southfacing and/or at elevation below 3961 m a.s.l. / Central Asia Paleoglaciology Project
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