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  • 1
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The intracrystalline diffusion rate of oxygen in diopside was constrained based on natural isotopic variations from a granulite facies marble from Cascade Slide, Adirondacks (New York, USA). The oxygen isotope compositions of the diopsides, measured as a function of grain size, are nearly constant (20.9 ± 0.3‰ vs. SMOW) over the entire measured size range (0.3–3.2 mm diameter). The δ18O values of the cores of calcite grains are 23.0‰. Temperature estimates based on the Δ18O(calcite-diopside) are 800d̀C, in agreement with the highest previous thermometric estimates for these rocks.The lack of isotopic variation in the diopsides as a function of grain size requires that the oxygen intracrystalline diffusion rate in diopside from the Adirondack samples was very slow. The maximum diffusion rates (D800d̀C parallel to the c-axis) were calculated with an infinite reservoir model (IRM) and a finite reservoir model (FRM) that incorporates mineral modal abundances and initial isotopic variations. For an assumed activation energy (Q) = 100 kJ/mol, the IRM diffusion rate estimate of 1.6 times 10-20cm2/s is two orders of magnitude faster than from the FRM; at Q=500kJ/mol, the D800d̀C estimate for both methods is c. 5.6 times 10-20 cm2/s. The present results require that a hydrothermal fluid significantly enhances the diffusion rate of oxygen in diopside if previous data are correct.The δ18O(SMOW) and δ13C(PDB) values of the calcite, measured in situ with a CO2 laser, are 22.9 ± 0.3, 0.1±0.3‰ in the grain cores, 22.1 ±0.3, 0.2 ±0.1‰ at the grain boundaries and 21.7 ±0.4, -0.6±0.1‰ abutting diopside grains. The δ18O and δ13δC values measured conventionally are: crystal cores, 22.96, -0.95‰; abutting diopside grains, 22.38, -0.93‰; bulk, 22.79, -0.95%. Use of the bulk δ18O(calcite) values for thermometry yields unreasonably high temperatures. The lower δ18O values at the calcite grain boundaries are not due to retrograde diffusional exchange with the diopside, they are thought to be a result of a late retrograde fluid infiltration.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Clay mineral crystallinity and crystallite (domain) size data determined by X-ray diffraction (XRD) are methods extensively used in the characterization of very low-grade metamorphic conditions. However, the lack of sufficient interlaboratory standardization has made comparisons between different research groups unreliable due to significant variations in numerical results obtained, a consequence of the different machine conditions, measurement methods and sample preparations used during analysis. A calibration approach to the standardization of data using rock chip standards is presented, which allows data sets produced by different research groups to be directly and quantitatively compared. A standardized scale, the crystallinity index standard (CIS), is proposed, with illite crystallinity anchizonal boundary limits of 0.25d̀Δ2θ and 0.42d̀Δ2θ, and equivalent illite crystallite sizes of 52 and 23 nm, respectively, determined by the Warren-Averbach method. Calibrating both old and new data will enable more reliable comparisons between similar and contrasting geological environments, and should improve the accuracy and reliability of correlations made between XRD data and other indicators of very low-grade metamorphism, hence increasing the value of such clay mineral studies.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The Chicago mineral-carbonate oxygen isotope fractionation curves have been combined with mineral-water fractionation data for jadeite, zoisite and rutile and new data for grossular-water to provide a set of self-consistent mineral-pair calibrations. The A coefficients in the equation 1000 In α=A× 106T-2 of the new mineral-pair fractionations areJadeite Zoisite Grossular RutileQuartz 1.69 2.00 3.03 5.02Jadeite 0.31 1.34 3.33Zoisite 1.03 3.02Grossular 1.99The isotopic fractionation properties of natural pyralspite garnet [(Ca, Fe, Mg, Mn)3Al2Si3O12] can be approximated by those of the grossular end-member. Appropriate substitutions also yield coefficients for the solid-solution minerals: sodic pyroxene and epidote, e.g. A quartz-sodic pyroxene= 2.75 - 1.06Xjd, A quartz-epidote= 2.00 + 0.75Xpswhere XJd and XPs are the mole fractions of the jadeite and pistacite components, respectively.The new data set is particularly suitable for the geothermometry of metamorphic rocks. δ18O data from minerals of the high-pressure metamorphic rocks of the Sesia Zone of Italy and Cyclades Complex of Greece yield well-constrained mean temperatures of 572 and 478d̀ C, respectively. Type III blueschist metabasalts of the Franciscan Formation of California give mean quartz-garnet temperatures of 354d̀ C.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Quantitative modelling of oxygen exchange by diffusion during slow cooling has been compared to the observed oxygen isotope distributions from high-grade metamorphic and granitic rocks of the High Himalayan Crystallines, Langtang Valley, central Nepal, in order to investigate the effect of retrograde diffusional exchange on the preservation of high-temperature, oxygen isotope systematics.Modelled fractionations, using water-present diffusion data reported in the literature, predict quartz-mica fractionations to be much larger than those at peak metamorphic and igneous conditions due to low closure temperatures for micas. Quartz-feldspar fractionations may be less than those at peak conditions, and in some samples may even be slightly negative.The observed oxygen isotope fractionations in the metamorphic rocks are small and largely appear to record equilibrations close to peak conditions determined by other methods. Hence these rocks clearly do not conform to predictions of fluid-present diffusional retrograde exchange. It is suggested that their retrograde history was therefore within an anhydrous closed system in which diffusion was slow and hence mineral closure temperatures were high. The granitic rocks record rather larger quartz-biotite fractionations, approaching those predicted by the diffusion modelling. However, quartz-feldspar fractionations are large and hence, although significant retrograde exchange has clearly occurred, simple diffusion alone is not sufficient to explain the observed data and open-system exchange may be required. The presence of fluids during the retrograde history of this part of the section is supported by petrographic evidence.The different retrograde oxygen exchange histories recorded between the regional metamorphic and magmatic regimes of the Langtang section would appear to support the importance of water on the kinetics of such exchange, and suggests that in its absence, diffusional exchange may become insignificant, allowing oxygen isotope thermometry to record meaningful high-temperature data.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The assemblages chlorite-pumpellyite-lawsonite-albite-quartz, chlorite-lawsonite-quartz-epidote and chlorite-epidote-albite-quartz occur in metabasaltic blocks and veins in a metamorphosed tectonic mélange in the structurally highest unit of the autochthonous and parautochthonous section underlying the Semail ophiolite in Saih Hatat, north-east Oman. The pre-Permian basement of this section contains mafic units characterized by the assemblage crossite-epidote-chlorite-quartz-albite /el actinolite. These assemblages indicate a down-section increase in metamorphic grade from ‘lawsonite-albite facies' conditions in the mélange to ‘epidote-blueschist’ facies conditions in the basement.Application of empirically and experimentally based thermobarometers as well as petrogenetic grids calculated for a model basaltic system indicates that the P-T conditions of metamorphism ranged from 3 to 6 kbar and 250 to 300d̀ C for the mélange and P 〉 6.8 kbar, T 〉 310d̀ C for the basement units. Textural relations interpreted in the context of petrogenetic grids indicate that these units followed clockwise P-T paths of evolution. The estimated P-T conditions and down-section increase in metamorphic grade in central, western and northern Saih Hatat are consistent with the hypothesis relating metamorphism to the Late Cretaceous tectonic loading of the continental margin by an ophiolite slab 〈 18 km in thickness. These results contrast with field and petrological observations documented for blueschists and eclogites exposed along the eastern coast of Saih Hatat which may have formed at an earlier stage in response to an Early Cretaceous collisional event.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Books reviewed in this article: Perspectives on Biodiversity: Case Studies of Genetic Resource Conservation and Development. Christopher S. Potter, foci 1. Cohen, and Dianne Janczewski, editors
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: To evaluate reclamation success on the Wooley Valley phosphate mine in southeastern Idaho, we compared vegetation structure and soil physical, chemical, and elemental properties of several different reclamation treatments with those of a nearby reference area (a native Artemisia tridentata vaseyana/Festuca idahoensis association) after 14 years. Vegetation data had been collected four years after reclamation, and we were able to compare differences in biomass and species composition between dates on the reclaimed area. Four years after reclamation there were no differences in total biomass between topsoil or spoil or between seed only, seed + mulch, or control treatments on the different soil types. Most treatments were dominated by seeded perennial grasses. Fourteen years after reclamation there were no differences in biomass or cover between spoil and topsoil plots, but on spoil plots the seeded and mulched treatment had higher total biomass and vegetation cover than on control or seed-only treatments. The seeded perennial legume Medicago sativa was codominant with the seeded forage grasses on all of the treatments. High initial fertilization rates probably facilitated the early establishment and dominance of the forage grasses; once nutrient levels, especially nitrogen, began to decline, the legume increased in abundance. Similarity between the reclaimed area and the reference or native area was low. Reclaimed treatments had higher biomass but lower species richness. The topsoil and spoil plots had similar soil texture, bulk density, pH, cation exchange capacity, electrical conductivity, and phosphorus. Differences in organic carbon, total nitrogen, carbon: nitrogen ratios, and available moisture were related more to treatments than to soil type. High biomass and, thus, litter input on the seed + mulch treatment on spoil plots resulted in both higher OC and TN than any on other soil/treatment combination. The reclaimed area had lower OC, TN, and available moisture than did the reference area on all but seed + mulch spoil plots. Bulk density was higher on reclaimed plots. The long-term differences observed between the reclaimed and reference areas parallel those obtained for other western reclamation sites. Although successional trajectories depend on the attribute measured, similarity to native reference areas depends on the initial reclamation methods. We discuss reclamation methods that would increase the structural and functional similarity of reclaimed and reference areas on the Wooley Valley phosphate mine.
    Materialart: Digitale Medien
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  • 10
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: In land restoration it is imperative to study the potential role of disturbances, biotic or abiotic, that may provide sites for colonization by specific plants. Disturbances can alter community composition by removing species or allowing others to become established. In communities where animal-generated disturbances open sites for seedling establishment, animals may have important indirect effects on several aspects of plant community structure. Animal disturbances in Quercus havardii communities of western Texas appear to open sites for colonization by herbaceous species. These animal disturbances vary in spatial distribution, density, and abiotic and biotic characteristics. The abundance of herbaceous plant seedlings is positively related to bare ground and the number of distinct disturbances. Thus, the density and the spatial distribution of these disturbances may be expected to have an important influence on the abundance and dispersion of plant species. Therefore, successful restoration efforts of sand shinnery oak communities and other similar habitats must consider the effects of animal disturbances and the role of plant-animal and plant-soil microbe interactions on plant community composition and the maintenance of plant species diversity.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The rates of seston elimination by zooplankton and primary production were measured in Funada-ike Pond, typical of human-made impoundments in Japan, from April to September in order to evaluate various treatments of the pond aimed at improving water quality by reducing seston abundance. The treatments included draining the pond water, dredging the bottom mud, eliminating the wastewater inflow, and biomanipulation through removal of all fish. After the treatment, seston abundance was reduced from more than 10 to 0.4–2.5 mg C/liter, and large daphnid species, Daphnia similis and D. magna, occurred and predominated in the zooplankton community. Seston abundance remained at a relatively low level from June to August but increased markedly in late August, while the biomass of zooplankton became high from June to mid-August and then decreased. A decrease in seston abundance was found when the elimination rate exceeded the primary production rate. The results indicate that the development of daphnid populations was effective in keeping seston abundance at a low level. The relationship between the rate of primary production and the zoo-plankton biomass required to offset this rate, however, suggests that biomanipulation aimed at increasing zooplankton biomass alone is less effective in a pond with a high primary production. The success in improving water quality in this pond seems to depend not only on the increase in biomass of large daphnid species that resulted mainly from the removal of fish, but also on the decrease in nutrient load that was realized by the other treatments.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 12
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: This essay reviews the recent attempts by the Northwest Power Planning and Conservation Council (NPPC) to conserve and restore wild salmon lost to hydroelectric development along the Columbia River and its tributaries. The restoration of the wild salmon is predicated on cooperation between myriad stakeholders in a planning process that includes the NPPC, 11 state and federal agencies, 13 Indian tribes, 8 utilities, and numerous interest groups. The two goals of the essay are (1) to review the recent amendments to the NPPC's fish and wildlife program, and (2) to describe the political barriers to restoration versus restocking of wild salmon in the Columbia River. The failure of political and administrative entities to deal with the problem of restoring wild salmon may result in drastic requirements being imposed by the imperatives of the Endangered Species Act.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: An environmental revolution is urgently needed that will lead to a post-industrial symbiosis between man and nature. This can be realized only if the present unrestrained biological impoverishment and neotechnological landscape degradation are replaced by the creation of healthy and attractive landscapes. Restorationists can fulfill a vital role in this process. They must broaden their scales from biodiversity restoration in small, protected nature islands to the large-scale restoration of natural and cultural landscapes. To achieve this they must restore not only the patterns of vegetation but also the processes that create these patterns, including human land uses. Their goal should be to restore the total biological, ecological, and cultural landscape diversity, or “ecodiversity,” and its intrinsic and instrumental values of highly valuable, endangered seminatural, agricultural and rural landscapes. For this purpose it is essential to maintain and restore the dynamic flow equilibrium between biodiversity, ecological, and cultural landscape heterogeneity, as influenced by human land uses, which occur at different spatial and temporal scales and intensities. Recent advances in landscape ecology should be utilized for broader assessment of ecodiversity, including proposed indices of ecodiversity, new techniques such as Intelligent Geographical Information Systems (IGIS), and Green Books for the holistic conservation and restoration of valuable endangered landscapes. Restoration ecology can make an important contribution to an urgently needed environmental revolution. This revolution should lead to a new symbiosis between man and nature by broadening the goal of vegetation restoration to ecological and cultural landscape restoration, and thereby to total landscape ecodiversity.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: A study of spider (Araneae) communities was conducted in rehabilitated bauxite mines at the Jarrahdale mine site of Alcoa of Australia Ltd. and in the nearby native jarrah (Eucalyptus marginata) forest in southwest Western Australia. The study was conducted from March to August 1993 in five rehabilitated sites of different age and method of rehabilitation and in two forest sites. A variety of collection methods was used, including pitfall trapping, litter sampling, sweep netting, tree beating, and visual searching. These methods were the same as those carried out in a previous study of some of these areas in 1983. We collected 151 spider species belonging to 102 genera and 34 families. We examined the relationship between various habitat features, including the age and method of rehabilitation, of the spider communities present. It was found that leaf litter depth and cover and vegetation density had a significant positive influence on recolonization by the various spider guilds. The age and method of rehabilitation were found to influence different vegetational and habitat features; these, in turn, influenced the spider communities. Thus, the older a rehabilitated site the greater the species richness of both plants and spiders. We compared these results with those of the 1983 study to determine the spider succession of the aging rehabilitation. The spider communities and guild composition were found to change as the vegetation matured, from a dominance of pioneer species to a community of species requiring less harsh conditions. By comparison with the pre-1983 rehabilitation, the latest method of rehabilitation increased the rate of recolonization by both plants and spiders.
    Materialart: Digitale Medien
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  • 15
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 16
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 17
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Peak flowering activity among woody species in the tropical dry forests of St. John, U.S. Virgin Islands, coincided with the brief spring rainy season but continued at moderate levels for six months, abating with the autumn rains. Fruit maturation showed a major peak in the long winter dry season and a minor crest during the summer dry season. Seeds of wind-dispersed species disseminated mainly during the winter dry season, while animal dispersal of seeds (74% of all woody species) followed the bimodal pattern (for wet and dry seasons) described for the community as a whole. Under shadehouse conditions, most dry forest tree species germinated well (〉 80%) and emerged promptly (within four weeks of planting) and synchronously (90% emergence within a four-week interval). Nine of 29 species tested in the shadehouse manifested dormancy of at least six weeks. Seed germinability varied among tree species, and the viability of most species began to decline following six months of dry storage. Few species retained high germinability after nine months of dry storage. The species composition of soil seed banks did not correspond closely with above-ground communities on three forested sites of varying stand age. In the youngest stand (35 years old), dominated by the weedy, arborescent legume Leucaena leucocephala, the soil seed bank was also dominated by this species, but no seeds of any other tree species were found in the soil samples. Seeds of native trees were scarcely encountered (only one indigenous species) in soil seed bank samples of three forest sites. Local seed rain from less disturbed forest may not be sufficient for prompt recovery of the dry forest community on degraded sites.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of economics & management strategy 3 (1994), S. 0 
    ISSN: 1530-9134
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Wirtschaftswissenschaften
    Notizen: I present an integrated survey of management strategy, which examines organizational design, competitive strategy, and public policy considerations. In addition, 1 offer suggestions on how economic analysis can be applied in unifying and developing management strategy as a field of study.
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  • 19
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of economics & management strategy 3 (1994), S. 0 
    ISSN: 1530-9134
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Wirtschaftswissenschaften
    Notizen: Under prospective pricing, payers for health care essentially use price regulation of hospitals as a way of indirectly regulating the provision of treatment intensity. This paper presents a theory of how a nonprofit hospital selects treatment intensities for its products given the payer's choice of prices and then determines how the payer should select prices in light of this theory. The main result is that, in equilibrium, the ratio of price to marginal cost will vary across products inversely with the elasticity of demand with respect to treatment intensity. This means that, generally, the hospital will earn positive (negative) accounting profit on products with low-(high-) intensity elasticities of demand.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of economics & management strategy 3 (1994), S. 0 
    ISSN: 1530-9134
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Wirtschaftswissenschaften
    Notizen: Legislation to create optional no-fault insurance (ONFL) programs has recently been enacted in Florida and Virginia. ONFI programs provide compensation to patients when certain medical complications arise, provided the patient agrees not to sue the doctor for additional damages. The optimal design of ONFI programs is explored in this paper, focusing on the incentive effects of ONFI programs. The question of whether ONFI programs should be funded entirely by participating doctors, or whether social subsidies are optimal, is examined.
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  • 21
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: When the transportation risk posed by shipments of hazardous chemical and radioactive materials is being assessed, it is necessary to evaluate therisks associated with both vehicle emissions and cargo-related risks. Diesel exhaust and fugitive dust emissions from vehicles transporting hazardous shipments lead to increased air pollution, which increases the risk of latent fatalities in the affected population along the transport route. The estimated risk from these vehicle-related sources can often be as large or larger than the estimated risk associated with the material being transported. In this paper, data from the U.S. Environmental Protection Agency's Motor Vehicle-Related Air Toxics Study are first used to develop latent cancer fatality estimates per kilometer of travel in rural and urban areas forall diesel truck classes. These unit risk factors are based on studies investigating the carcinogenic nature of diesel exhaust. With the same methodology, the current per-kilometer latent fatality risk factor used in transportation risk assessments for heavy diesel trucks in urban areas is revised and the analysis expanded to provide risk factors for rural areas and all diesel truck classes. These latter fatality estimates may include, but are not limited to, cancer fatalities and are based primarily on the most recent epidemiological data available on mortality rates associated with ambient air PM-10 concentrations.
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Risk assessors often use different probability plots as a way to assessthe fit of a particular distribution or model by comparing the plotted points to a straight line and to obtain estimates of the parameters in parametric distributions or models. When empirical data do not fall in a sufficiently straight line on a probability plot, and when no other single parametricdistribution provides an acceptable (graphical) fit to the data, the risk assessor may consider a mixture model with two component distributions. Animated probability plots are a way to visualize the possible behaviors of mixture models with two component distributions. When no single parametric distribution provides an adequate fit to an empirical dataset, animated probability plots can help an analyst pick some plausible mixture models for the data based on their qualitative fit. After using animations during exploratory data analysis, the analyst must then use other statistical tools, including but not limited to: Maximum Likelihood Estimation (MLE) to find the optimal parameters, Goodness of Fit (GoF) tests, and a variety of diagnostic plots to check the adequacy of the fit. Using a specific example with two LogNormal components, we illustrate the use of animated probability plots asa tool for exploring the suitability of a mixture model with two component distributions. Animations work well with other types of probability plots, and they may be extended to analyze mixture models with three or more component distributions.
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: For carcinogens, this paper provides a quantitative examination of the roles of potency and weight-of-evidence (WOE) in setting permissible exposure limits (PELs) at the U.S. Occupational Safety and Health Administration (OSHA) and threshold limit values (TLVs) at the private American Conference of Governmental Industrial Hygienists (ACGIH). On normative grounds, both of these factors should influence choices about the acceptable level of exposures. Our major objective is to examine whether and in what ways these factors have been considered by these organizations. A lesser objective is to identify outliers, which might be candidates for further regulatory scrutiny. Our sample (N=48) includes chemicals for which EPA has estimated a unit risk as a measure of carcinogenic potency and for which OSHA or the ACGIH has a PEL or TLV. Different assessments of the strength of the evidence of carcinogenicity were obtained from EPA, ACGIH, and the International Agency for Research on Cancer. We found that potency alone explains 49% of the variation in PELs and 62% of the variation in TLVs. For the ACGIH, WOE plays a much smaller role than potency. TLVs set by the ACGIH since 1989 appear to be stricter than earlier TLVs. We suggest that this change represents evidence that the ACGIH had responded to criticisms leveled at it in the late 1980s for failing to adopt sufficiently protective standards. The models developed here identify 2-nitropropane, ethylene dibromide, and chromium as having OSHA PELs significantly higher than predicted on the basis of potency and WOE.
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  • 24
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 25
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Much has been written about the development and application of quantitative methods for estimating under uncertainty the long-term radiological performance of underground disposal of radioactive wastes. Until recently, interest has been focused almost entirely on the technical challenges regardless of the role of the organization responsible for these analyses. Now the dialogue between regulators, the repository developer or operator, and other interested parties in the decision-making process receives increasing attention, especially in view of some current difficulties in obtaining approvals to construct or operate deep facilities for intermediate or high-level wastes. Consequently, it is timely to consider the options for regulators’review and evaluation of safety submissions, at the various stages in the site selection to repository closure process, and to consider, especially, the role for performance assessment (PA) within the programs of a regulator both before and after delivery of such a submission. The origins and broad character of present regulations in the European Union (EU) and in the OECD countries are outlined and some regulatory PA reviewed. The issues raised are discussed, especially in regard to the interpretation of regulations, the dangers from the desire for simplicity in argument, the use of regulatory PA to review and challenge the PA in the safety case, and the effects of the relationship between proponent and regulator. Finally, a very limited analysis of the role of PA in public hearings is outlined and recommendations are made, together with proposals for improving the mechanisms for international collaboration on technical issues of regulatory concern.
    Materialart: Digitale Medien
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  • 26
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: In this paper the problem of high-level nuclear waste disposal is viewed as a five-stage, cascaded decision problem. The first four of these decisions having essentially been made, the work of recent years has been focused on the fifth stage, which concerns specifics of the repository design. The probabilistic performance assessment (PPA) work is viewed as the outcome prediction for this stage, and the site characterization work as the information gathering option. This brief examination of the proposed Yucca Mountain repository through a decision analysis framework resulted in three conclusions: (1) A decision theory approach to the process of selecting and characterizing Yucca Mountain would enhance public understanding of the issues and solutions to high-level waste management; (2) engineered systems are an attractive alternative to offset uncertainties in the containment capability of the natural setting and should receive greater emphasis in the design of the repository; and (3) a strategy of “waste management” should be adopted, as opposed to “waste disposal,” as it allows for incremental confirmation and confidence building of a permanent solution to the high-level waste problem.
    Materialart: Digitale Medien
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  • 27
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 28
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 29
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Physiologically-based toxicokinetic (PBTK) models are widely used to quantify whole-body kinetics of various substances. However, since they attempt to reproduce anatomical structures and physiological events, they have ahigh number of parameters. Their identification from kinetic data alone is often impossible, and other information about the parameters is needed to render the model identifiable. The most commonly used approach consists of independently measuring, or taking fom literature sources, some of the parameters, fixing them in the kinetic model, and then performing model identification on a reduced number of less certain parameters. This results in a substantial reduction of the degrees of freedom of the model. In this study, we show that this method results in final estimates of the free parameters whose precision is overestimated. We then compared this approach with an empirical Bayes approach, which takes into account not only the mean value, but also the error associated with the independently determined parameters. Blood and breath 2H8- toluene washout curves, obtained in17 subjects, were analyzed with a previously presented PBTK model suitable for person-specific dosimetry. Model parameters with the greatest effect onpredicted levels were alveolar ventilation rate QPC, fat tissue fraction VFC, blood air partition coefficient Kb, fraction of cardiac output to fat Qa/co and rate of extrahepatic metabolismVmax.p. Differences in the measured and Bayesian-fitted values of QPC, VFc and Kb were significant (p 〈 0.05), andthe precision of the fitted values Vmax.p and Qa/co went from 11 ± 5% to 75 ± 170% (NS) and from 8 ± 2% to 9 ± 2% (p 〈 0.05) respectively. The empirical Bayes approach did not result in less reliable parameter estimates: rather, it pointed out that the precision of parameter estimates can be overly optimistic when other parameters in the model, eitherdirectly measured or taken from literature sources, are treated as known without error. In conclusion, an empirical Bayes approach to parameter estimation resulted in a better model fit, different final parameter estimates, and more realistic parameter precisions.
    Materialart: Digitale Medien
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  • 30
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: The US Department of Transportation was interested in the risks associated with transporting Hydrazine in tanks with and without relief devices. Hydrazine is both highly toxic and flammable, as well as corrosive. Consequently, there was a conflict as to whether a relief device should be used or not. Data were not available on the impact of relief devices on release probabilities or the impact of Hydrazine on the likelihood of fires and explosions. In this paper, a Monte Carlo sensitivity analysis of the unknown parameters was used to assess the risks associated with highway transport of Hydrazine. To help determine whether or not relief devices should be used, fault trees and event trees were used to model the sequences of events that could lead to adverse consequences during transport of Hydrazine. The event probabilities in the event trees were derived as functions of the parameters whose effects were not known. The impacts of these parameters on the riskof toxic exposures, fires, and explosions were analyzed through a Monte Carlo sensitivity analysis and analyzed statistically through an analysis of variance. The analysis allowed the determination of which of the unknown parameters had a significant impact on the risks. It also provided the necessary support to a critical transportation decision even though the values of several key parameters were not known.
    Materialart: Digitale Medien
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  • 31
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: During the modernization of the municipal waste incinerator (MWI, maximum capacity of 180,000 tons per year) of Metropolitan Grenoble (405,000 inhabitants), in France, a risk assessment was conducted, based on four tracerpollutants: two volatile organic compounds (benzene and 1,1,1 trichloroethane) and two heavy metals (nickel and cadmium, measured in particles). A Gaussian plume dispersion model, applied to maximum emissions measured at the MWI stacks, was used to estimate the distribution of these pollutants in the atmosphere throughout the metropolitan area. A random sample telephone survey (570 subjects) gathered data on time-activity patterns, according to demographic characteristics of the population. Life-long exposure was assessed as a time-weighted average of ambient air concentrations. Inhalation alone was considered because, in the Grenoble urban setting, other routes of exposure are not likely. A Monte Carlo simulation was used to describe probability distributions of exposures and risks. The median of the life-long personal exposures distribution to MWI benzene was 3.2 · 10−5μg/m3 (20th and 80th percentiles = 1.5 · 10−5 and 6.5 · 10−5μg/m3), yielding a 2.6 · 10−10 carcinogenic risk (1.2 · 10−10 - 5.4 · 10−10). For nickel, the corresponding life-time exposure and cancer risk were 1.8 ·10−4μg/m3 (0.9 ·10−4 - 3.6 ·10−4μg/m3) and 8.6 · 10−8 (4.3 · 10−8 - 17.3 ·10−8); for cadmium they were respectively 8.3 ·10−6μg/m3 (4.0 ·10−6 - 17.6 ·10−6) and 1.5 · (7.2 · 10−9 - 3.1. · 10−8). Inhalation exposure to cadmium emitted by the MWI represented less than 1% of the WHO Air Quality Guideline (5 ng/m3), while there was a margin of exposure of more than 109 between the NOAEL (150 ppm) and exposure estimates to trichloroethane. Neither dioxins nor mercury, a volatile metal, were measured. This could lessen the attributable life-long risks estimated. The minute (VOCs and cadmium) to moderate (nickel) exposure and risk estimates are in accord with other studies on modern MWIs meeting recent emission regulations, however.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 32
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Methods of quantitative risk assessment for toxic responses that are measured on a continuous scale are not well established. Although risk-assessment procedures that attempt to utilize the quantitative information in such data have been proposed, there is no general agreement that these procedures are appreciably more efficient than common quantal dose-response procedures that operate on dichotomized continuous data. This paper points out an equivalence between the dose-response models of the nonquantal approach of Kodell and West(1)) and a quantal probit procedure, and provides results from a Monte Carlo simulation study to compare coverage probabilities of statistical lower confidence limits on dose corresponding to specified additional risk based on applying the two procedures to continuous data from a dose-response experiment. The nonquantal approach is shown to be superior, in terms of both statistical validity and statistical efficiency.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 33
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: This paper discusses a successful public involvement effort that addressed and resolved several highly controversial water management issues involving environmental and flood risks associated with an electrical generation facility in British Columbia. It begins with a discussion of concepts for designing public involvement, summarizing research that indicates why individuals and groups may find it difficult to make complex choices. Reasons for public involvement, and the range of current practices are discussed. Next, four principles for designing group decision process are outlined, emphasizing decision-aiding concepts that include “value-focused thinking” and “adaptive management.” The next sections discuss the Alouette River Stakeholder Committee process in terms of objectives, participation, process, methods for structuring values and creating alternatives, information sources, and results. Discussion and conclusions complete the paper.
    Materialart: Digitale Medien
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  • 34
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: During the 1980s, seismic research suggested that Oregon and the City of Portland had a higher risk of a major earthquake than had previously been assumed. In 1993, the State of Oregon adopted a new version of the Oregon Structural Specialty Code, which changed the designation of western Oregon from seismic zone 2b to seismic zone 3. The City of Portland established a program and a Task Force on Seismic Strengthening of Buildings to recommend actions that would encourage upgrading of city buildings. A survey of adult city residents was conducted in April, 1996 to determine public attitudes and opinions about earthquake risks, management and mitigation of earthquake hazards, priorities for protection by strengthening buildings, evaluations of strategies for informing the public about earthquake risks, and support for specific options the city might take to protect citizens against earthquake events. Social and demographic information on individuals and households was also collected. Respondents provided ratings for a wide range of social and environmental risks, provided information on priorities for strengthening key buildings and infrastructure facilities, and answered hypothetical questions about voting for bond measures to pay for city earthquake mitigation programs. Respondents recognized significant risk from earthquakes and supported programs to protect people, especially vulnerable residents such as children and the sick. There was strong support for protecting emergency response capabilities. There was much less support for using public funds to reduce the risks associated with privately owned buildings. There were also some strong pockets of resistance to publicly funded mitigation programs in response to the hypothetical bond measures.
    Materialart: Digitale Medien
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  • 35
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: From a comprehensive search of the literature, the hormesis phenomenon was found to occur over a wide range of chemicals, taxonomic groups, and endpoints. By use of computer searches and extensive cross-referencing, nearly 3000 potentially relevant articles were identified. Evidence of chemical and radiation hormesis was judged to have occurred in approximately 10oO of these by use of a priori criteria. These criteria included study design features (e.g., number of doses, dose range), dose-response relationship, statistical analysis, and reproducibility of results. Numerous biological endpoints were assessed, with growth responses the most prevalent, followed by metabolic effects, reproductive responses, longevity, and cancer. Hormetic responses were generally observed to be of limited magnitude with an average maximum stimulation of 30 to 60 percent over that of the controls. This maximum usually occurred 4- to 5-fold below the NOAEL for a particular endpoint. The present analysis suggests that hormesis is a reproducible and generalizable biological phenomenon and is a fundamental component of many, if not most, dose-response relationships. The relatively infrequent observation of homesis in the literature is believed to be due primarily to experimental design considerations, especially with respect to the number and range of doses and endpoint selection. Because of regulatory considerations, most toxicologic studies have been carried out at high doses above the low-dose region where the hormesis phenomenon occurs.
    Materialart: Digitale Medien
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  • 36
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 37
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 38
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 39
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: As the use of digital computers for instrumentation and control of safety-critical systems has increased, there has been a growing debate over the issue of whether probabilistic risk assessment techniques can be applied to these systems. This debate has centered on the issue of whether software failures can be modeled probabilistically. This paper describes a “context-based” approach to software risk assessment that explicitly recognizes the fact that the behavior of software is not probabilistic. The source of the perceived uncertainty in its behavior results from both the input to the software as well as the application and environment in which the software is operating. Failures occur as the result of encountering some context for which the software was not properly designed, as opposed to the software simply failing “randomly.” The paper elaborates on the concept of “error-forcing context” as it applies to software. It also illustrates a methodology which utilizes event trees, fault trees, and the Dynamic Flowgraph Methodology (DFM) to identify “error-forcing contexts” for software in the form of fault tree prime implicants.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 40
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Australian state and federal agencies use a broad range of methods for setting conservation priorities for species at risk. Some of these are based on rule sets developed by the International Union for the Conservation ofNature, while others use point scoring protocols to assess threat. All of them ignore uncertainty in the data. In this study, we assessed the conservation status of 29 threatened vascular plants from Tasmania and New South Wales using a variety of methods including point scoring and rule-based approaches. In addition, several methods for dealing with uncertainty in the data were applied to each of the prioritysetting schemes. The results indicatethat the choice of a protocol for setting priorities and the choice of the way in which uncertainty is treated may make important differences to the resulting assessments of risk. The choice among methods needs to be rationalized within the management context in which it is to be applied. These methods are not a substitute for more formal risk assessment.
    Materialart: Digitale Medien
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  • 41
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: This paper describes a multi-stakeholder process designed to assess thepotential health risks associated with adverse air quality in an urban industrial neighborhood. The paper briefly describes the quantitative health risk assessment conducted by scientific experts, with input by a grassroots community group concerned about the impacts of adverse air quality on theirhealth and quality of life. In this case, rather than accept the views of the scientific experts, the community used their powers of perception toadvantage by successfully advocating for a professionally conducted community health survey. This survey was designed to document, systematically and rigorously, the health risk perceptions community members associated with exposure to adverse air quality in their neighborhood. This paper describes theinstitutional and community contexts within which the research is situated as well as the design, administration, analysis, and results of the community health survey administered to 402 households living in an urban industrial neighborhood in Hamilton, Ontario, Canada. These survey results served tolegitimate the community's concerns about air quality and tohelp broaden operational definitions of ‘health.’ In addition, the resultsof both healthrisk assessment exercises served to keep issues of air quality on the localpolitical agenda. Implications of these findings for our understanding of theenvironmental justice process as well as the ability of communitiesto influence environmental health policy are discussed.
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  • 42
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Psychometric data on risk perceptions are often collected using the method developed by Slovic, Fischhoff, and Lichtenstein, where an array of risk issues are evaluated with respect to a number of risk characteristics, such as how dreadful, catastrophic or involuntary exposure to each risk is. The analysis of these data has often been carried out at an aggregate level, where mean scores for all respondents are compared between risk issues. However, this approach may conceal important variation between individuals, and individual analyses have also been performed for single risk issues. This paper presents a new methodological approach using a technique called multilevel modelling for analysing individual and aggregated responses simultaneously, to produce unconditional and unbiased results at both individual and aggregate levels of the data. Two examples are given using previously published data sets on risk perceptions collected by the authors, and results between the traditional and new approaches compared. The discussion focuses on the implications of and possibilities provided by the new methodology.
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  • 43
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Retrograde exchange of oxygen isotopes between minerals in igneous and metamorphic rocks by means of diffusion is explored using a finite difference computer model, which predicts both the zonation profile of δ18O within grains, and the bulk δ18O value of each mineral in the rock. Apparent oxygen isotope equilibrium temperatures that would be observed in these rocks are calculated from the δ18O values of each mineral pair within the rock. In systems which cool linearly from a sufficiently high temperature or at a low enough cooling rate, such that the final oxygen isotope values are not dependent upon the initial oxygen isotope values (‘slow cooling’), the apparent oxygen isotope temperature derived for a rock composed of a single mineral pair can be shown to be simply related to the Dodson closure temperatures (Tc) for the two phases and the mode of the rock. Adding a third phase into a system which undergoes ‘slow’ cooling will cause the apparent temperature derived for the two minerals already present to differ from the simple relationship for a two-phase system. In some systems oxygen isotope reversals can be developed. If cooling is not ‘slow’, then the mineral δ18O values resulting from cooling will be partly dependent upon the initial temperature of the system concerned. The model successfully simulates the mineral δ18O values that are often observed in granitic rocks. Application of the model will help in assessing the validity of oxygen isotope thermometry in different geological settings, and allows quantitative prediction of the oxygen isotope fractionations that are developed in cooling closed systems.
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  • 44
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The highest grade pelitic and semipelitic rocks of the Ballachulish aureole are dominantly potash feldspar + cordierite + biotite hornfelses with widely variable amounts of quartz, plagioclase, andalusite, sillimanite and corundum (together with accessory phases). On a microscopic scale these hornfelses show textural evidence of the presence of melt, whilst on a mesoscopic scale they contain a variety of leucosomes. Oxygen isotope studies have been carried out on both whole rocks and mineral separates in order to: (1) assess the sources of molten and volatile constituents and (2) determine the extents of isotopic homogenization and equilibration. Data from localities with both restricted and extensive evidence of leucosomes and melt development are compared, as well as one locality with petrographic evidence of melt incursion from the igneous complex.The whole-rock δ18O values of the leucosomes (10.5–14.9%.) are in general similar to the immediately adjacent mesosomes (9.9–14.5%.) which are typically cordierite- and feldspar-rich hornfelses. Isotopic evidence is thus consistent with an in-situ partial melt origin for the leucosomes, without the substantial addition of externally derived components. In the area of extensive melt development, the ‘chaotic zone’, it is possible there was addition of an H2O-rich fluid phase (6-13 wt%) from the igneous complex which resulted in a slight lowering of δ18O values by 0.5–1.0%.Quartz mineral separates were used to assess the degree of local isotopic homogenization. In the extensively molten area (chaotic zone) there is extensive homogenization between rock layers (quartz δ18O usually within 1.0%), whilst in less molten areas δ18O quartz has a range of c. 3.0%. The greater homogenization in the chaotic zone is attributed to the increased degree of melting and infiltration of H2O-rich fluid from the igneous complex.
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  • 45
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The enderbites from Tromøy in the central, granulite facies part of the Proterozoic Bamble sector of southern Norway contain dominantly CO2 and N2 fluid inclusions. CO2 from fluid inclusions in quartz segregations in enderbites was extracted by mechanical (crushing) and thermal decrepitation and the δ13C measured. Measurement was also made on samples washed in 10% HCl, oxidized with CuO at high temperatures, and step-wise extracted with progressive heating. Results between the different techniques are systematic. The main results show δ13C of -4.5±1.5% for crushing and -7±2% for thermal decrepitation. δ13C is about constant for CO2 extracted at different temperatures and points to a homogeneous isotopic composition. Due to the presence of carbonate particles and/or induced contaminations for the extraction by thermal decrepitation, the results for the crushing experiments are assumed the most reliable for fluid-inclusion CO2. Very low values of δ13C have not been found in enderbite samples and δ13C combined with δ18O of the host quartzes (8-11%) indicates juvenile values. In addition, the fluid inclusions were examined by microthermometry and Raman analysis and host quartz by acoustic emission and cathodoluminescence. CO2 fluid inclusions have varying densities with a frequency maximum of 0.92 g cm-3 and generally do not concur with trapping densities at granulite conditions. Textures show that CO2 must have been trapped in fluid inclusions in one early event, but transformed to different extents during late isothermal uplift without important fractionation of isotope compositions. The present data support a model of intrusion and crystallization of a CO2-rich enderbitic magma at granuiite conditions.
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  • 46
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: High-grade exotic blocks in the Franciscan Complex at Jenner, California, show evidence for polydeformation/metamorphism, with eight distinct stages. Two parallel sets of mineral assemblages [(E) eclogite, and (BS) laminated blueschist] representing different bulk chemistry were identified. Stage 1, recorded by parallel aligned inclusions (S1) of crossite + omphacite + epidote + ilmenite + titanite + quartz (E), and glaucophane + actinolite + epidote + titanite (BS) in the central parts of zoned garnets, represents the epidote blueschist facies. The onset of a second stage (stage 2) is represented by a weak crenulation of S1 and growth of garnet. This stage develops a well-defined S2 foliation of orientated barroisite + epidote + titanite (E), or subcalcic actinolite + epidote + titanite (BS) at c. 90d̀ to S1, with syntectonic growth of garnet, defining the (albite-)epidote-amphibolite facies. A third stage, with aligned inclusions of glaucophane + (subcalcic) actinolite + phengite parallel to S2 in the outermost rims of large garnet grains, is assigned to the transitional (albite-)epidote-amphibolite/(garnet-bearing) epidote blueschist facies. The fourth stage represents the peak metamorphism, and was identified by unorientated matrix minerals in the least retrograded samples. In this stage the mineral assemblages garnet + omphacite + glaucophane + phengite (E) and garnet + winchite + phengite + epidote (BS) both represent the eclogite facies. Stage 5 is represented by the retrogression of eclogite facies assemblages to the epidote blueschist facies assemblages crossite/glaucophane + garnet + omphacite + epidote + phengite (E), and glaucophane + actinolite + epidote + phengite (BS), with the development of an S5 foliation subparallel to S2. Stage 6 represents a crenulation of S5, with the development of a well-defined S6 crenulation cleavage wrapping around relics of the eclogite facies assemblages. This crenulation cleavage is further weakly crenulated during a D7 event. Post-D7 (stage 8) is recorded by the growth of lawsonite + chlorite ± actinolite replacing garnet, and by veins of lawsonite + pumpellyite + aragonite and phengite + apatite. The different, yet coeval, mineral parageneses observed in rock types (E) and (BS) are probably due to differences in bulk chemistry.The metamorphic evolution from stage 1 to stage 8 seems to have been broadly continuous, following an anticlockwise P-Tpath: (1) epidote blueschist (garnet-free) to (2) (albite-)epidote-amphibolite to (3) transitional epidote blueschist (garnet-bearing)/(albite-)epidote-amphibolite to (4) eclogite to (5) epidote blueschist (garnet-bearing) to (6-7) epidote blueschist (garnet-free) facies to (8) lawsonite + pumpellyite + aragonite-bearing assemblages. This anticlockwise P-T path may have resulted from a decreasing geothermal gradient with time in the Mesozoic subduction zone of California at early or pre-Franciscan metamorphism.
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  • 47
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Rocks within the Zermatt-Saas ophiolite of the western Alps have undergone eclogite facies metamorphism during subduction prior to the Alpine collision. The metamorphic history of these rocks is well defined, with eclogitic assemblages being followed by the limited growth of blueschist assemblages of glaucophane and paragonite. Subsequent greenschist alteration occurs adjacent to faults, veins and metasediments. Away from such sources of water, retrogression is very limited. Sm-Nd isotopic analyses of an essentially unretrogressed eclogitic metabasalt suggest that eclogite facies metamorphism occurred at 52 ± 18 Ma. The large uncertainty is due to the presence of very small amounts of Nd-rich epidote present as inclusions within garnet. As the closure temperature of garnet to Sm & Nd is thought to be 〉600d̀C, resetting due to post-high-pressure diffusion is thought to be insignificant. Given the fine-grained protolith to the sample analysed, and its extensive deformation under eclogite facies conditions, incomplete homogenization of pre-metamorphic isotopic variations is also considered unlikely to be responsible for the young age. A Tertiary age of eclogitization means that models of early Alpine evolution based on the cessation of high-pressure metamorphism in the Cretaceous need to be revised.
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  • 48
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Porphyroblast inclusion fabrics are consistent in style and geometry across three Proterozoic metamorphic field gradients, comprising two pluton-related gradients in central Arizona and one regional gradient in northern New Mexico. Garnet crystals contain curved ‘sigmoidal’ inclusion trails. In low-grade chlorite schists, these trails can be correlated directly with matrix crenulations of an older schistosity (S1). The garnet crystals preferentially grew in crenulation hinges, but some late crenulations nucleated on existing garnet porphyroblasts. At higher grade, biotite, staurolite and andalusite porphyroblasts occur in a homogeneous S2 foliation primarily defined by matrix biotite and ilmenite. Biotite porphyroblasts have straight to sigmoidal inclusion trails that also represent the weakly folded S1 schistosity. Staurolite and andalusite contain distinctive inclusion-rich and inclusion-poor domains that represent a relict S2 differentiated crenulation cleavage. Together, the inclusion relationships document the progressive development of the S2 fabric through six stages. Garnet and biotite porphyroblasts contain stage 2 or 3 crenulations; staurolite and andalusite generally contain stage 4 crenulations, and the matrix typically contains a homogeneous stage 6 cleavage.The similarity of inclusion relationships across spatially and temporally distinct metamorphic field gradients of widely differing scales suggests a fundamental link between metamorphism and deformation. Three end-member relationships may be involved: (1) tectonic linkages, where similar P-T-time histories and similar bulk compositions combine to produce similar metamorphic and structural signatures; (2) deformation-controlled linkages, where certain microstructures, particularly crenulation hinges, are favourable environments for the nucleation and/or growth of porphyroblasts; and (3) reaction-controlled linkages, where metamorphic reactions, particularly dehydration reactions, are associated with an increase in the rate of fabric development. A general model is proposed in which (1) garnet and biotite porphyroblasts preferentially grow in stage 2 or 3 crenulation hinges, and (2) chlorite-consuming metamorphic reactions lead to pulses in the rate of fabric evolution. The data suggest that fabric development and porphyroblast growth may have been quite rapid, of the order of several hundreds of thousands of years, in these rocks. These microstructures and processes may be characteristic of low-pressure, first-cycle metamorphic belts.
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  • 49
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Incipient metamorphism accompanying thrusting, folding and cleavage development has been investigated in a varied sequence of Palaeozoic sediments near the Variscan front in SW Dyfed, Wales. The aim was to evaluate a critical stage in the progression from heterogeneous sediment, whose detrital phases are neither in equilibrium with one another, nor with pore fluids, through indurated sedimentary rock to metamorphic rock comprising newly formed crystals that equilibrated with one another as they grew.Quartz veins are widely developed in the area, especially in the more psammitic lithologies, while finer grained rocks became cleaved during tectonic deformation. Mineralogical constraints and fluid inclusion measurements suggest maximum temperatures around 200-310d̀ C (slightly higher in the Marloes-Musselwick Thrust Sheet than in other parts of the structural succession) at depths of the order of 6-13 km.Quartz veins yield distinctly heavier oxygen isotopic compositions than detrital quartz grains in the adjacent wall rocks, although care must be taken in interpreting the data because slivers of detrital grains may become incorporated into veins, while matrix detrital grains may incorporate veinlets or rims of newly formed quartz. It is concluded that vein quartz grew in isotopic equilibrium with a fluid phase whose isotopic composition was primarily controlled by exchange with phyllosilicates, not detrital quartz grains. Vein and matrix quartzes from the Marloes-Musselwick Thrust Sheet are distinctly lighter (δ18Oveins=+14 to +18% and δ18Omatrix=+11 to +14%) than those from other thrust sheets (δ18O =+17 to +20% and +14 to +17%, respectively).We conclude that vein quartz and phyllosilicate grains in cleavage domains probably attained equilibrium with a locally buffered pore fluid at the peak of metamorphism, but many relict grains of different chemical and isotopic composition remained elsewhere in the rock. Local fluid migration along veins and through cleavage lamellae facilitated the attainment of equilibrium, but there is little evidence for large-scale infiltration of externally derived fluids. With further metamorphism the quartz in these rocks would attain an isotopic composition intermediate between that of the heavy vein material and light detritus which coexist here.
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  • 50
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Fire is a common but poorly understood disturbance in the forested ecosystems of the Sierra Madre Occidental of Mexico. In this study, fire history, forest structure (density, species composition, regeneration, forest floor fuels, herbaceous cover, and age of pines), and the dendrochronological tree-ring record were measured at two unharvested 70-ha pine-oak sites near Ojito de Camellones, Durango, Mexico. Study sites were matched in slope, aspect, elevation, slope position, and plant composition, but they differed in fire history since 1945 and in forest structure. The long-term mean fire intervals (MFI) for all fires at both sites up to 1945 were similar—4.0 years at Site 1 (1744–1945) and 4.1 years at Site 2 (1815–1945)—but Site 1 burned only three times at the site margins since 1945 while Site 2 had 9 fires that scarred two or more sample trees and 15 total fires since 1945. Density measurements and age and diameter distributions showed that Site 1 was dominated by numerous, younger, smaller trees (mean total basal area of 23.4 m2/ha and 2730 trees/ha), while Site 2 had fewer, older, larger trees (basal area of 37.2 m2/ha, 647 trees/ha). Large, rotten fuel loading and duff depth were also greater at Site 1. Because regeneration averaged 6200 stems/ha at Site 1 and 8730 stems/ha at Site 2 (no significant difference), forest density at Site 2 was not limited by regeneration capability. The distributions of overstory diameter and pine age at both sites indicate that tree establishment occurred in pulses, with the largest cohort of trees establishing at Site 1 following the 1945 fire. The dense regeneration and heavy fuel accumulation at Site 1 are likely to support a switch from the former low-intensity fire regime to a high-intensity, stand-replacing fire across the site when the next suitable combination of ignition and weather occurs. Baseline quantitative information on fire frequency and ecological effects is essential to guide conservation or restoration of Madrean forests and may prove valuable for restoration of related fire-dependent ecosystems that have experienced extended fire exclusion elsewhere in North America.
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  • 51
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Food-related illness in the United States is estimated to affect over six million people per year and cost the economy several billion dollars. These illnesses and costs could be reduced if minimum infectious doses were established and used as the basis of regulations and monitoring. However, standard methodologies for dose-response assessment are not yet formulated for microbial risk assessment. The objective of this study was to compare dose response models for food-borne pathogens and determine which models were most appropriate for a range of pathogens. The statistical models proposed in the literature and chosen for comparison purposes were log-normal,(19) log-logistic,(17) exponential,(7,9,17)ß-Poisson(7,9,18) and Welbull-Gamma.(3) These were fit to four data sets also taken from published literature, Shigella fiexneri,(9,12,13)Shigella dysenteriae,(9,11)Campylobacter jejuni,(15,16) and Salmonella typhosa,(7,14) usingthe method of maximum likelihood. The Weibull-gamma, the only model with three parameters, was also the only model capable of fitting all the data sets examined using the maximum likelihood estimation for comparisons. Infectious doses were also calculated using each model. Within any given data set, the infectious dose estimated to affect one percent of the population ranged from one order of magnitude to as much as nine orders of magnitude, illustrating the differences in extrapolation of the dose response models. More data are needed to compare models and examine extrapolation from high to low doses for food-borne pathogens.
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  • 52
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Environmental managers are increasingly charged with involving the public in the development and modification of policies regarding risks to huma health and the environment. Involving the public in environmental decision making first requires a broad understanding of how and why the public perceives various risks. The Savannah River Stakeholder Study was conducted withthe purpose of investigating individual, economic, and social characteristics of risk perceptions among those living near the Savannah River Nuclear Weapons Site. A number of factors were found to impact risk perceptions among those living near the site. One's estimated proximity to the site and relative river location surfaced as strong determinants of risk perceptions among SRS residents. Additionally, living in a quality neighborhood and demonstrating a willingness to accept health risks for economic gain strongly abated heightened risk perceptions.
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  • 53
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Five atmospheric transport models were evaluated for use in Phase I1 ofthe Historical Public Exposures Studies at the Rocky Flats Plant. Models included a simple straight-line Gaussian plume model (ISCST2), several integrated puff models (RATCHET, TRIAD, and INPUFF2), and a complex terrain mode (TRAC). Evaluations were based on how well model predictions compared with sulfur hexafluoride tracer measurements taken in the vicinity of Rocky Flats in February 1991. Twelve separate tracer experiments were conducted, eac lasting 9 hr and measured at 140 samplers in arcs 8 and 16 km from the release point at Rocky Flats. Four modeling objectives were defined based on the endpoints of the overall study: (1) the unpaired maximum hourly average concentration, (2) paired time-averaged concentration, (3) unpaired time-averaged concentration, and (4) arc-integrated concentration. Performance measures were used to evaluate models and focused on the geometric mean and standard deviation of the predicted-to-observed ratio and the correlation coefficient between predicted and observed concentrations. No one model consistently outperformed the others in all modeling objectives and performance measures. About 75% of the maximum hourly concentration predictions were within a factor of 5 of the observations. About 64% of the paired and 80% of the unpaired time-averaged model predictions were within a factor of 5 of theobservations. The overall performance of the RATCHET model was somewhat better than the other models. All models appeared to experience difficulty defining plume trajectories, which was attributed to the influence of multilayered flow initiated by terrain complexities and the diurnal flow patterns characteristic of the Colorado Front Range.
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  • 54
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Calculation of accident dose-risk estimates with the RADTRAN code requires input data describing the population likely to be affected by the plumeof radioactive material (RAM) released in a hypothetical transportation accident. In the existing model, population densities within 1/2 mile (0.8 km)of the route centerline are tabulated in three ranges (Rural, Suburban, andUrban). These population densities may be of questionable validity since the plume in the RADTRAN analysis is assumed to extend out to 120 km from thehypothetical accident site. We present a GIs-based population model which accounts for the actual distribution of population under a potential plume, and compare accident-risk estimates based on the resulting population densities with those based on the existing model. Results for individual points along a route differ greatly, but the cumulative accident risks for a sample route of a few hundred kilometers are found to be comparable, if not identical. We conclude, therefore, that for estimation of aggregate accident risks over typical routes of several hundred kilometers, the existing, simpler RADTRAN model is sufficiently detailed and accurate.
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  • 55
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 56
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: This paper discusses a number of the key challenges to the acceptance and aplication of probabilistic risk analysis (PRA). Those challenges include:(a) the extensive reliance on subjective judgment in PRA, requiring the development of guidance for the use of PRA in risk-informed regulation, and possibly the development of “robust” or “reference” prior distributions to minimize the reliance on judgment; and (b) the treatment of human perfor-mance in PRA, including not only human errorperse but also management and organizational factors more broadly. All of these areas are seen as presentinginteresting research challenges at the interface between engineering and other disciplines.
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  • 57
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Rational decision making requires that the total uncertainty about a variate of interest (a predictand) be quantified in terms of a probability distribution, conditional on all available information and knowledge. Supposethe state-of-knowledge is embodied in a deterministic model, which is imperfect and outputs only an estimate of the predictand. Fundamentals are presented of two Bayesian methods for producing a probabilistic forecast via anydeterministic model. The Bayesian Processor of Forecast (BPF) quantifies the total uncertainty in terms of a posterior distribution, conditional on model output. The Bayesian Forecasting System (BFS) decomposes the total uncertainty into input uncertainty and model uncertainty, which are characterized independently and then integrated into a predictive distribution. The BFS is compared with Monte Carlo simulation and “ensemble forecasting” technique, none of which can alone produce a probabilistic forecast that quantifies the total uncertainty, but each can serve as a component of the BFS.
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  • 58
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: This article describes an application of a method for assessing risks associated with the introduction of an organism into a new environment. The test organism was a binucleate Rhizoctonia fungal isolate that has potential for commercial development as a biological control agent for damping-off diseases in bedding plants. A test sample of host plant species was selected using the centrifugal phylogenetic host range principles, but with an emphasis on economic species. The effect of the fungus on the plant was measured for each species and expressed on a logarithmic scale. The effects on weights of shoots and roots per container were not normally distributed, nor were the effects on the number of plants standing (those which survived). Statements about the effect on the number standing and the shoot weight per container involved using the observed (empirical) distribution. This is illustrated with an example. Problems were encountered in defining the population of species at risk, and in deciding how this population should be formally sampled. The limitations of the method are discussed.
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  • 59
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: The heuristic-systematic information processing model (HSM) holds that individuals will use one or both of these modes of information processing when attempting to evaluate information in order to arrive at a judgment. Systematic processing is defined by effortful scrutiny and comparison of information, whereas heuristic processing is defined by the use of cues to amve more easily at a judgment. Antecedents to the two processing modes include information sufficiency, motivation, and self-efficacy. Structural equation modeling is used to examine competing configuration of this model and to evaluate the model as appropriate for predicting risk judgment. The model also is evaluated across three groups that vary with respect to their level of concern. These analyses are executed within a case study involving an epidemiological investigation of a suspected cancer cluster. The analysis confirms the HSM's theoretically proposed structure and shows it to be a useful vehicle for evaluating risk judgment. In the overall analysis, antecedent variables generally function as specified by theory. Systematic processing is predicted by greater motivation. Heuristic processing is predicted by information sufficiency. Self-efficacy is a significant predictor of both processing modes. And heuristic processing is shown to be associated with judgment of less risk. However, when the analysis is contrasted across three groups (those concerned about cancer, not concerned and uncertain) it is shown that the model is significantly more robust for the uncertain group. This finding may have implications for the use of the HSM in risk research specifically, and in field research generally.
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  • 60
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: South Carolina has issued fish consumption advisories for the Savannah River based on mercury and radionuclide levels. We examine differences in fishing rates and fish consumption of 258 people interviewed while fishing along the Savannah River, as a function of age, education, ethnicity, employment history, and income, and test the assumption that the average consumption of fish is less than the recreational value of 19 kg/year assumed by risk assessors. Ethnicity and education contributed significantly to explaining variations in number of fish meals per month, serving size, and total quantity of fish consumed per year. Blacks fished more often, ate more fish meals of slightly larger serving sizes, and consumed more fish per year than did Whites. Although education and income were correlated, education contributed most significantly to behavior; people who did not graduate from high school ate fish more often, ate more fish per year, and ate more whole fish than people who graduated from high school. Computing consumption of fish for each person individually indicates that (1) people who eat fish more often also eat larger portions, (2) a substantial number of people consume more than the amount of fish used to compute risk to recreational fishermen, (3) some people consume more than the subsistence level default assumption (50 kglyear) and (4) Blacks consume more fish per year than Whites, putting them at greater risk from contaminants in fish. Overall, ethnicity, age, and education contributed to variations in fishing behavior and consumption.
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  • 61
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: The association between daily fluctuations in ambient particulate matter and daily variations in nonaccidental mortality have been extensively investigated. Although it is now widely recognized that such an association exists, the form of the concentration-response model is still in question. Linear, no threshold and linear threshold models have been most commonly examined. In this paper we considered methods to detect and estimate threshold concentrations using time series data of daily mortality rates and air pollution concentrations. Because exposure is measured with error, we also considered the influence of measurement error in distinguishing between these two completing model specifications. The methods were illustrated on a 15-year daily time series of nonaccidental mortality and particulate air pollution data in Toronto, Canada. Nonparametric smoothed representations of the association between mortality and air pollution were adequate to graphically distinguish between these two forms. Weighted nonlinear regression methods for relative risk models were adequate to give nearly unbiased estimates of threshold concentrations even under conditions of extreme exposure measurement error. The uncertainty in the threshold estimates increased with the degree of exposure error. Regression models incorporating threshold concentrations could be clearly distinguished from linear relative risk models in the presence of exposure measurement error. The assumption of a linear model given that a threshold model was the correct form usually resulted in overestimates in the number of averted premature deaths, except for low threshold concentrations and large measurement error.
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  • 62
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Facility-specific information on pollution was obtained for 36 coke plants and 46 oil refineries in the United States and matched with information on populations surrounding these 82 facilities. These data were analyzed to determine whether environmental inequities were present, whether they were more economic or racial in nature, and whether the racial composition of nearby communities has changed significantly since plants began operations. The Census tracts near coke plants have a disproportionate share of poor and nonwhite residents. Multivariate analyses suggest that existing inequities are primarily economic in nature. The findings for oil refineries are not strongly supportive of the environmental inequity hypothesis. Rank ordering of facilities by race, poverty, and pollution produces limited (although not consistent) evidence that the more risky facilities tend to be operating in communities with above-median proportions of nonwhite residents (near coke plants) and Hispanic residents (near oil refineries). Over time, the racial makeup of many communities near facilities has changed significantly, particularly in the case of coke plants sited in the early 1900s. Further risk-oriented studies of multiple manufacturing facilities in various industrial sectors of the economy are recommended.
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  • 63
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: We investigated the way results of human health risk assessments are used, and the theory used to describe those methods, sometimes called the “NAS paradigm.” Contrary to a key tenet of that theory, current methods have strictly limited utility. The characterizations now considered standard, Safety Indices such as “Acceptable Daily Intake,”“Reference Dose,” and so on, usefully inform only decisions that require a choice between two policy alternatives (e.g., approve a food additive or not), decided solely on the basis of a finding of safety. Riskis characterized as the quotient of one of these Safety Indices divided by an estimate of exposure: a quotient greater than one implies that the situation may be considered safe. Such decisions are very widespread, both in the U. S. federal government and elsewhere. No current method is universal; different policies lead to different practices, for example, in California's “Proposition 65,” where statutory provisions specify some practices. Further, an important kind of human health risk assessment is not recognized by this theory: this kind characterizes risk as likelihood of harm, given estimates of exposure consequent to various decision choices. Likelihood estimates are necessary whenever decision makers have many possible decision choices and must weigh more than two societal values, such as in EPA's implementation of “conventional air pollutants.” These estimates can not be derived using current methods; different methods are needed. Our analysis suggests changes needed in both the theory and practice of human health risk assessment, and how what is done is depicted.
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  • 64
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: The prominent role of animal bioassay evidence in environmental regulatory decisions compels a careful characterization of extrapolation uncertainties. In noncancer risk assessment, uncertainty factors are incorporated to account for each of several extrapolations required to convert a bioassay outcome into a putative subthreshold dose for humans. Measures of relative toxicity taken between different dosing regimens, different endpoints, or different species serve as a reference for establishing the uncertainty factors. Ratios of no observed adverse effect levels (NOAELs) have been used for this purpose; statistical summaries of such ratios across sets of chemicals are widely used to guide the setting of uncertainty factors. Given the poor statistical properties of NOAELs, the informativeness of these summary statistics is open to question. To evaluate this, we develop an approach to “calibrate” the ability of NOAEL ratios to reveal true properties of a specified distribution for relative toxicity. A priority of this analysis is to account for dependencies of NOAEL ratios on experimental design and other exogenous factors. Our analysis of NOAEL ratio summary statistics finds (1) that such dependencies are complex and produce pronounced systematic errors and (2) that sampling error associated with typical sample sizes (50 chemicals) is nonnegligible. These uncertainties strongly suggest that NOAEL ratio summary statistics cannot be taken at face value; conclusions based on such ratios reported in well over a dozen published papers should be reconsidered.
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  • 65
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: We compare the regulatory implications of applying the traditional (linearized) and exact two-stage dose-response models to animal carcinogenic data. We analyze dose-response data from six studies, representing five different substances, and we determine the “goodness- of-fit” of each model as well as the 95% confidence lower limit ofthe dose corresponding to a target excess risk of 10-5 (the target risk doseTRD). For the two concave datasets, we find that the exact model gives a substantially better fit to the data than the traditional model, and that the exact model gives aTRD that is an order of magnitude lower than that given by the traditional model. In the other cases, the exact model gives a fit equivalent to or better than the traditional model. We also show that although the exact two-stage model may exhibit dose-response concavity at moderate dose levels, it is always linear or sublinear, and never supralinear, in the low-dose limit. Because regulatory concern is almost always confined to the low-dose region extrapolation, supralinear behavior seems not to be of regulatory concern in the exact two-stage model. Finally, we find that when performing this low-dose extrapolation in cases of dose-response concavity, extrapolating the model fit leads to a more conservative TRD than taking a linear extrapolation from 10% excess risk. We conclude with a set of recommendations.
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  • 66
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: The characterization and treatment of uncertainty poses special challenges when modeling indeterminate or complex coupled systems such as those involved in the interactions between human activity, climate and the ecosystem. Uncertainty about model structure may become as, or more important than, uncertainty about parameter values. When uncertainty grows so large that prediction or optimization no longer makes sense, it may still be possible to use the model as a “behavioral test bed” to examine the relative robustness of alternative observational and behavioral strategies. When modelsmust be run into portions of their phase space that are not well understood, different submodels may become unreliable at different rates. A common example involves running a time stepped model far into the future. Several strategies can be used to deal with such situations. The probability of model failure can be reported as a function of time. Possible alternative “surprises” can be assigned probabilities, modeled separately, and combined. Finally, through the use of subjective judgments, one may be able to combine, and over time shift between models, moving from more detailed to progressively simpler order-of-magnitude models, and perhaps ultimately, on to simple bounding analysis.
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  • 67
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: In any model the values of estimates for various parameters are obtained from different sources each with its own level of uncertainty. When the probability distributions of the estimates are obtained as opposed to point values only, the measurement uncertainties in the parameter estimates may be addressed. However, the sources used for obtaining the data and the models used to select appropriate distributions are of differing degrees of uncertainty. A hierarchy of different sources of uncertainty based upon one's ability to validate data and models empirically is presented. When model parameters are aggregated with different levels of the hierarchy represented, this implies distortion or degradation in the utility and validity of the models used. Means to identify and deal with such heterogeneous data sourcesare explored, and a number of approaches to addressing this problem is presented. One approach, using Range/confidence Estimates coupled with an Information Value Analysis Process, is presented as an example.
    Materialart: Digitale Medien
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  • 68
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Risk analysis 19 (1999), S. 0 
    ISSN: 1539-6924
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik
    Notizen: Variability arises due to differences in the value of a quantity among different members of a population. Uncertainty arises due to lack of knowledge regarding the true value of a quantity for a given member of a population. We describe and evaluate two methods for quantifying both variability and uncertainty. These methods, bootstrapsimulation and a likelihood-based method, are applied to three datasets. The datasetsinclude a synthetic sample of 19 values from a Lognormal distribution, a sample of nine values obtained from measurements of the PCB concentration in leafy produce, and asample of five values for the partitioning of chromium in the flue gas desulfurization system of coal-fired power plants. For each of these datasets, we employ the two methods to characterize uncertainty in the arithmetic mean and standard deviation, cumulative distribution functions based upon fitted parametric distributions, the 95th percentile of variability, and the 63rd percentile of uncertainty for the 81st percentile of variability. The latter is intended to show that it is possible to describe anypoint within the uncertain frequency distribution by specifying an uncertainty percentile and a Variability percentile. Using the bootstrap method, we compare results based upon use of the method of matching moments and the method of maximum likelihood for fitting distributions to data. Our results indicate that with only 5-19 data pointsas in the datasets we have evaluated, there is substantial uncertainty based upon random sampling error. Both the boostrap and likelihood-based approaches yield comparable uncertainty estimates in most cases.
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  • 69
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Calc-silicate rocks occur as elliptical bands and boudins intimately interlayered with eclogites and high-pressure gneisses in the Münchberg gneiss complex of NE Bavaria. Core assemblages of the boudins consist of grossular-rich garnet, diopside, quartz, zoisite, clinozoisite, calcite, rutile and titanite. The polygonal granoblastic texture commonly displays mineral relics and reaction textures such as post kinematic grossular-rich garnet coronas. Reactions between these mineral phases have been modelled in the CaO-Al2O3-SiO2-CO2-H2O system with an internally consistent thermodynamic data base. High-pressure metamorphism in the calc-silicate rocks has been estimated at a minimum pressure of 31 kbar at a temperature of 630d̀ C with XH2, O ≥ 0.03. Small volumes of a CO2-N2-rich fluid whose composition was buffered on a local scale were present at peak-metamorphic conditions. The P-T conditions for the onset of the amphibolite facies overprint are about 10 kbar at the same temperature. XCo2 of the H2O-rich fluid phase is regarded to have been 〈0.03 during amphibolite facies conditions. These P-T estimates are interpreted as representing different stages of recrystallization during isothermal decompression. The presence of multiple generations of mineral phases and the preservation of very high-pressure relics in single thin sections preclude pervasive post-peak metamorphic fluid flow as a cause of a re-equilibration within the calc-silicates. The preservation of eclogite facies, very high-pressure relics as well as amphibolite facies reactions textures in the presence of a fluid phase is in agreement with fast, tectonically driven unroofing of these rocks.
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  • 70
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Mineral stable isotopic and trace element studies in 2 GPa banded eclogites of the Tauern Window, eastern Alps, record mm- to cm-scale heterogeneities that reflect compositional variations in the accompanying metamorphic fluids. A close correlation between dolomite mode and dolomite δ18O is consistent with equilibrium partitioning among coexisting minerals and fluids. Small variations in dolomite δ13C values correspond with δ18O variations, but an overall decrease in dolomite δ13C by c. 1%o across a 12-cm sample is a relict feature that pre-dates eclogite equilibration. Garnet, omphacite, and clinozoisite rims show little systematic mineral-mineral partitioning behaviour for Ti, V, Cr, Y, Sr, or Zr; major elements, however, are well equilibrated among these same minerals. Despite the apparent lack of mineral-mineral trace element equilibration, most of the trace elements vary systematically with water activity calculated in each layer. Trace element behaviour during the eclogite metamorphism thus appears to have been controlled largely by mineral-fluid interactions along grain boundaries.Shallow structural levels in other subduction complexes (c. 10-45 km) typically exhibit fracture-controlled permeability and extensive metasomatism, but there is no field or geochemical evidence for extensive fluid advection during high-pressure metamorphism in the Tauern eclogites. Because most dewatering and devolatilization during tectonic burial occurs prior to eclogite conditions, the volumetric fluid/rock ratio in eclogites should generally be low. Low fluid/rock ratios, coupled with the possible non-wetting nature of the fluids, permits the production and preservation of fine-scale chemical heterogeneities in deeply subducted eclogites and associated fluids. However, the eventual breakdown at greater depth of volatile-bearing dolomite, phengite, clinozoisite, zoisite, or amphibole could lead to renewed fracture-controlled fluid release from the subducted rocks to regions appropriate for arc magma generation.
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  • 71
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Metamorphism of the Gile Mountain Formation and Waits River Formation in the Strafford Dome and Townshend-Brownington Syncline in east-central Vermont records two nappe-style events, D1 and D2, followed by doming. D1 formed a muscovite + biotite ± ilmenite schistosity subparallel to compositional layering, SO, and was followed by heating to garnet grade. The temperature and pressure at the end of D1 are estimated to be c. 450d̀ C and 6-8 kbar. D2 variably crenulated and folded S1 during a nearly isothermal pressure increase of 1-2 kbar, calculated from compositions of garnet, which have inclusions trails with progressive crenulation and rotation of the S1 fabric. Similar P-T paths are computed for most of the area, suggesting that the later schistosity developed during emplacement of a regional nappe 3-6 km thick. There is a general lack of D3 (dome-stage) microstructures.Near the Strafford-Willoughby Arch, staurolite and kyanite overgrew S2 in pelites, and plagioclase with increasing XAn overgrew S2 in calcic pelites, reflecting post-D2 heating to a maximum of 550-600d̀ C. Metamorphic pressures at the end of D2 are fairly constant on the west side of the dome, indicating minor dome-stage uplift. In contrast, pressures at the thermal peak of metamorphism decrease by more than 4 kbar east of the dome. The observed pattern of isotherms and isobars is mainly the result of post-metamorphic, differential uplift and unroofing.Finally, a minor, retrograde metamorphism produced the assemblage albite + epidote + K-feldspar + muscovite + chlorite, with grade increasing east toward the Connecticut River.
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  • 72
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Grandite garnet-rich calcsilicate rocks from the Lower Calcsilicate Unit of the regionally metamorphosed Reynolds Range Group (central Australia) crop out along a strike-parallel section in which a transition zone from M22 amphibolite to granulite facies rocks is exposed. Across this transition the grandite-rich layers do not show systematic changes in mineral assemblages, compositions and modes, or stable isotope compositions. These layers are deformed by F22 folds that are associated with the peak of regional low-pressure/high-temperature metamorphism. Therefore, the grandite-rich layers appear to pre-date regional metamorphism and to have acted as closed chemical systems during prograde M22 metamorphism.Mineral assemblages in the grandite-rich layers are consistent with their formation through the infiltration of oxidized, water-rich fluids (Xco2 〈 0.1–0.3; log fo2 -16 to -14). The stable isotope values of calcite (Δ13C=-4.2 to -0.8%0 PDB; Δ18O = 10.5–14.0%0 V-SMOW) and bulk-silicate fractions (Δ18O = 6.1 to 10.8%) of the grandite-rich layers are most consistent with the infiltrating fluid being from a magmatic source. It is most likely that fluid infiltration occurred during the pre-M22 contact metamorphism (M21) that affected much of the Reynolds Range Group. The preservation of these assemblages is probably due to their high variance and little pervasive fluid-rock interaction having occurred during M22.The clinopyroxene- and feldspar-rich calcsilicate rocks that host the grandite-rich layers contain poikiloblastic grandite garnet that formed during prograde M22 metamorphism. Thin marbles that locally occur with the grandite-rich layers contain a third garnet generation that is post- or late M22. This grossular-rich garnet occurs in coronas around calcite, plagioclase, clinopyroxene, wollastonite and scapolite. These coronas are consistent with cooling and/or compression. However, because the marble assemblages are themselves overprinted by M21 grandite-rich layers the development of coronal garnet does not reflect a continuous P-T-t path. Rather, it more probably reflects the partial re-equilibration of M21 contact metamorphic assemblages to post-M22 conditions.
    Materialart: Digitale Medien
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  • 73
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Proterozoic granulite facies gneisses in MacRobertson Land, east Antarctica, are cut by numerous D5 mylonite-ultramylonite zones of probable Cambrian age. In garnet-absent mafic two-pyroxene gneisses and garnet-bearing charnockitic orthogneisses, the mylonite-ultramylonite zones are characterized by the growth of garnet at the expense of ilmenite, pyroxene and plagioclase. Textures within each mylonite zone can vary from protomylonitic to ultramylonitic. A range of mineral textures involving M5 garnet is developed corresponding to variations in deformation intensity. In protomylonites, garnet occurs as coronas on orthopyroxene-plagioclase and ilmenite-plagioclase boundaries, and as overgrowths on earlier garnet. In ultramylonites, fine-grained orthopyroxene-plagioclase-garnet ± quartz ± clinopyroxene intergrowths and poikilitic garnet are common. Garnet growth in all shear zones is accompanied by shifts in the compositions of neoblastic minerals occurring with garnet, consistent with local chemical equilibrium having been attained during recrystallization. Mylonitization is inferred to have occurred at P∼ 6.5 kbar. Temperature estimates for M5 vary between 550 and 797d̀ C, which may reflect variations and uncertainties associated with the calibrations used and/or partial re-equilibration during cooling. The presence of post-tectonic, coronate garnet in some mylonite zones indicates that garnet continued to form exclusively in the mylonite zones after movement had ceased and is interpreted to reflect the effects of localized strain heating.
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  • 74
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Transmission and scanning electron microscopy were utilized to investigate the nature and mechanisms of alteration of abundant detrital biotite of volcanic origin and progressive modification of phyllosilicate aggregates in a prograde sequence of pelitic rocks (illite crystallinity index = 0.19–0.58d̀λ2θ) from the Gaspé Peninsula in Quebec.Detrital biotite has been diagenetically altered to form corrensite and chlorite through two mechanisms; (1) layer-by-layer replacement gave rise to interstratification of packets of layers and complex mixed layering via several kinds of layer transitions between biotite and chlorite, corrensite or smectite; (2) dissolution-transport-precipitation resulted in the formation of relatively coarse-grained aggregates of randomly orientated, corrensite-rich flakes and fine-grained corrensite intergrown with chlorite and illite in the matrix.The data show that stacks consisting of alternating packets of trioctahedral and dioctahedral phyllosilicates originated during early diagenesis when lenticular fissures in strained altering biotite were filled by dioctahedral clays. Subsequent prograde evolution of dioctahedral clays occurred through deformation, dissolution and crystallization, and overgrowth. Illite evolved to muscovite, with K in part provided through biotite alteration, and corrensite/chlorite to homogeneous chlorite. The alteration of detrital biotite is closely related to the formation of titanite and magnetite in diagenetic rocks, and pyrite, calcite and anatase or rutile in the higher grade rocks.The observations demonstrate that detrital biotite of volcanic origin may be the principal precursor of chlorite in chlorite-rich metapelites originating in marginal basins. The mineral parageneses suggest that the transitions from corrensite to chlorite and illite to muscovite may be a function of local chemistry and time.
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  • 75
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: A fluid dynamic model for a rigid spherical porphyroblast growing in a viscous fluid matrix undergoing simple shear deformation predicts an arrangement of captured inert inclusions that is remarkably similar to the spiral pattern observed in synkinematic ‘rolled’ garnets. The model assumes only creeping (Stokes) flow of the matrix and a kinetic model for the growth of the porphyroblast of the form rm=kmΩ, where r is the crystal radius, Ω is the amount of shear-induced rotation, and m and k are kinetic parameters. For rotation less than 18d̀, J. B. Thompson and J. L. Rosenfeld's simple ring-model provides a surprisingly accurate description of the three-dimensional geometry of the central inclusion surface in the simulated porphyroblasts. Although marker planes, originally parallel to the shear plane, are deflected around the porphyroblast, their intersections with its surface remain approximately circular for much larger amounts of rotation than anticipated by Rosenfeld. The polar coordinate equation, T(r, θ), of the double spiral formed by the trace of the central inclusion surface in a section through the centre of simulated porphyroblasts, is also surprisingly simple, as follows: rm∼ (6/5k)mθ. This relationship was observed over the complete range of rotation angles investigated, 0-720d̀, and could form a reasonable basis for estimating the growth-rotation history of rolled garnets from the shape of their spiral inclusion trails. Two-dimensional sections through the simulated porphyroblasts, parallel to the rotation axis, yield ‘clamshell’ (Rosenfeld's term) inclusion geometries similar to the controversial ‘millipede’ patterns observed in many natural porphyroblasts.
    Materialart: Digitale Medien
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  • 76
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Detailed textural and chemical data for mineral assemblages on a regional scale are presented for the metaandesitic Eocene-Oligocene Taveyanne greywacke of the Glarus Alps, Eastern Switzerland. Presented data indicate an increase of metamorphic grade from zeolite facies to prehnite-pumpellyite and pumpellyite-actinolite facies. Low-grade outcrops contain laumontite, minor corrensite and pumpellyite (assemblage type 1), whereas outcrops of higher metamorphic grade contain prehnite and two populations of pumpellyite (type 2), prehnite—pumpellyite-(Al)—white mica (type 3), a single outcrop shows pumpellyite-actinolite facies (type 4). From the zeolite to prehnite-pumpellyite/pumpellyite-actinolite facies there are indications for an increase of the chemical equilibrium domain size for the critical paragenesis from a single detrital grain ≤1 mm) in type 1, to a few millimetres in type 2, and to a whole thin section in type 3. Metamorphic P-T conditions were determined by a combination of chlorite thermometry, fluid inclusion and vitrinite reflectance data. Peak temperatures range from 170-190d̀ C for zeolite facies to 270-310d̀ C for prehnite-pumpellyite and pumpellyite-actinolite facies. For the higher temperature range, pressures of 2-3 kbar are derived indicating a geothermal gradient of 24-32d̀ C km-1. The well-constrained temperature estimations derived for the assemblages provide a useful test of the different empirical calibrations of chlorite thermometers recently proposed. The best correspondence to the temperatures determined here is for the Cathelineau calibration. In addition, in the lower grade samples differences in textures and calculated temperatures provide a mean to distinguish between detrital and newly formed chlorites.
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  • 77
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Discordant andalusite-biotite-quartz-bearing veins occur in the contact aureole of the Vedrette di Ries pluton (Italian Eastern Alps), never outside the area of contact metamorphic andalusite development. Andalusite veins are found only within andalusite-bearing hornfelses, and vein biotite occurs wherever host-rock garnet is partially replaced by biotite. Veins formed during contact metamorphism, synchronously with the crystallization of andalusite and biotite within host rocks. Their pegmatitic structure and their orientation suggest that vein parageneses crystallized within fluid-filled cavities that opened by hydraulic fracturing.A mechanism of synmetamorphic veining is proposed to explain rock failure and subsequent mineral deposition within veins. During hydrofracturing induced by dehydration reactions in response to heating in the aureole, fissures were immediately filled with locally derived fluids. The lack of large-scale flux, together with high fluid pressures required by hydrofracturing, suggest fluid in the cavities was a virtually stagnant, passive medium, and that mass-transport toward fractures was driven by intergranular diffusion. Because temperature and Pf values within veins are similar to those in the host rock, vein assemblages are interpreted as the stable, high-T side of reactions taking place within pelitic schists, at the time when fractures opened. Once nucleation of product phases occurred, chemical components released by dissolution of reactant minerals were driven to precipitation sites by chemical potential gradients. Since nucleation was favoured at the strained grains of vein walls, andalusite and biotite simultaneously grew in vein and host rock.The proposed genetic model contrasts with generally adopted metasomatic mechanisms for the genesis of Al2SiO5-bearing veins, in not requiring large fluid/rock ratios or a highly ‘aggressive’ fluid composition. The mechanism of synmetamorphic veining may be particularly useful in the interpretation of vein occurrences in medium- and deep-crustal rocks which have undergone extensive devolatilization.
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  • 78
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Mineral and isotope studies were undertaken on migmatites from the Schwarzwald, Moldanubian zone of the Variscan belt. The aims of the study were to date the migmatite formation and to determine the processes involved in migmatization in order to evaluate their influence on isotopic resetting. Textural evidence and the comparison of mineral compositions from leucosomes and mesosomes of two centimetre-scale migmatite profiles, respectively, suggest that migmatitic textures and mineral assemblages were formed by metamorphic segregation (deformation-enhanced mass transport) rather than by partial melting (anatexis). The results of Rb-Sr thin-slab dating on these profiles indicate that Sr isotopes were not completely reset during migmatization. No true isochron ages, but ages of approximate isotopic homogenization were obtained on the thin slabs by calculating 87Sr/86Sr ratios back to various stages in their evolution. The coincidence of these Rb-Sr data with U-Pb ages of monazites from migmatites and non-migmatitic gneisses shows that gneisses and migmatites were formed during the same high-temperature event in the Carboniferous (330-335 Ma). The observation that high-temperature metamorphism failed to equilibrate Sr isotopes on the centimetre-scale imposes limitations on the use of conventional whole-rock isochron techniques in dating migmatites.
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  • 79
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 80
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: In the inner aureole of the Bufa del Diente alkali syenite (north-east Mexico), thin calcareous argillite bands horizontally embedded in impure marbles acted as contact-metamorphic aquifers for hypersaline brines of magmatic origin. Thick-bedded marbles were largely impervious. From 180 m up to the intrusion contact, argillites were completely decarbonated, resulting in melilite + wollastonite + phlogopite + perovskite-bearing parageneses. In marbles, this assemblage is confined to a narrow 7-12-m-wide infiltration zone adjacent to the contact. Up to this distance, calcite + wollastonite + diopside + alkali feldspar + titanite was stable, indicating that the fluid evolution in these marbles was internally buffered.Brine infiltration from the metaargillite aquifer into the marbles occurred perpendicular to the marble-metaargillite boundaries and was confined to a zone 4-6 cm wide above the boundaries. This is documented by the three reactionsCc + Di = Mel + CO2, (1)Cc + Kfs + Di + H2O = Phl + Wo + CO2, (2)Cc + Ttn = Prv + Wo + CO2, (3)Melilites (Ak32-45Gh13-32Sm32-40 to Ak52-72Gh0-1Sm28-48) occur as rims around diopsides and become continuously thicker towards the metaargillite beds. Fluid inclusion observations suggest that the infiltrating brine was hypersaline (NaCl + KClcq∼ 65 wt%) and that the reactions took place at the water-rich side of the H2O-CO2-salts immiscibility field at about 600d̀ C (2, 3) and 660 to 680d̀ C (1) at P∼ 1200 bar and Xco2∼ 0.02.Mass balance calculations show that the amount of brine infiltrated from the aquifer into the marble was very low and decreased continuously with increasing distance from the boundary. The maximum width of brine infiltration was about 6 cm. This confirms that brine flow was largely parallel to the aquifer, not perpendicular to it. The CO2 produced by the decarbonation reactions probably escaped as an immiscible low-density H2O-CO2 fluid of Xco2≤ 0.5 into overlying marble via grain-edge flow. The metaargillite-marble boundary acted as a semipermeable membrane 6 cm in thickness keeping back the brine in the aquifer and losing the in-situ produced low-density CO2-rich fluid.
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  • 81
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: During the Alice Springs Orogeny, deformation at Ormiston Gorge, central Australia, occurred under lower- to middle-greenschist facies conditions. Dolomites of the Bitter Springs Formation and quartzites. metagreywackes, and metapelites of the Heavitree Quartzite contain abundant early-, syn-, and post-tectonic veins. However, though vein densities locally approach 15%, the distribution of veins and the oxygen isotope geochemistry of wallrocks and veins suggest that fluid movement was on a local scale. The Heavitree Quartzite contains quartz veins that, even along the main thrust plane, have similar δ18O values (13.5–16.9%o) to those of their wallrocks (13.6–16.9%o), with Δ18O(vein-wallrock) values of -0.6 to 0.4%o. In contrast, the Bitter Springs Formation contains predominantly dolomite veins that have δ18O values of 23.4 to 27.7%o. These differences are observed even at the boundary between the Heavitree and Bitter Springs rocks, implying that significant fluid exchange between these rocks has not occurred, or that fluid flow was channelled through areas outside those sampled for this study. By contrast with the Heavitree Quartzite, δ18O values of wallrocks in individual samples of the Bitter Springs Formation are significantly higher (23.3–29.1%o) than those of the veins, with δ18O(vein-wallrock) values up to -4%o (average of -2.1%o). These systematic differences in δ18O values most likely result from oxygen isotope fractionation caused by fluid immiscibility or disequilibrium dissolution. Smaller differences in δ13C values between some dolomite veins and wallrocks [δ13C(vein-wallrock) up to -1.9%o, average of -0.5%o] are also explained by these processes. This study indicates that large volumes of veins may be produced by repeated fracturing and fluid migration within particular rock units, without involving large volumes of externally derived fluids.
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  • 82
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Calcite and quartz veins have formed, and are forming, in steeply dipping fissures in the actively rising Alpine Schist metamorphic belt of New Zealand. The fluids that deposited these minerals were mostly under hydrostatic pressure almost down to the brittle-ductile transition, which has been raised to 5-6 km depth by rapid uplift. Some fluids were trapped under lithostatic pressures. Fluids in the fissure veins were immiscible H2O + NaCl-CO2 mixtures at 200-350d̀ C. Bulk fluid composition is 15-20 mol% CO2 and 〈4.3 total mol CH4+ N2+ Ar/100mol H2O. Water hydrogen isotopic ratio δDH2O in the fissure veins spans -29 to -68‰, δ18OH2O -0.7 to 8.5‰, and bulk carbon isotopic ratio δ13C ranges from -3.7 to -11.7‰. The oxygen and hydrogen isotopic data suggest that the water has a predominantly meteoric source, and has undergone an oxygen isotope shift as a result of interaction with the host metamorphic rock. Similar fluids were present during cooling and uplift. Dissolved carbon is not wholly derived from residual metamorphic fluids; part may be generated by oxidation of graphite.
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  • 83
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: In the central Minto Block of northern Québec, the Lake Minto and Goudalie domains are dominated, respectively, by orthopyroxene-bearing plutonic suites (granite-granodiorite and diatexite) and a tonalitic gneiss complex, both of which contain scattered remnant paragneisses. Two main granulite-grade mineral assemblages are observed in the paragneiss: garnet (Grt)-orthopyroxene (Opx)-plagioclase-quartz (GOPQ) and garnet (Grt)-cordierite (Crd)-sillimanite-plagioclase-quartz (GCSPQ). These show distinct lithological associations, with the GCSPQ assemblages occurring exclusively within the diatexite in the Lake Minto domain. Petrogenetic grid considerations demonstrate that the GOPQ rocks are higher grade than the GCSPQ rocks. Maximum temperatures for GOPQ rocks, obtained from equilibria based on Al solubility in orthopyroxene in equilibrium with garnet, range from 950 to 1000d̀ C, significantly higher than garnet-orthopyroxene Fe-Mg exchange temperatures of 700 ± 50d̀ C, the latter probably representing a closure temperature below peak conditions. The Al temperatures were corrected for late cation exchange by adjusting the Fe/(Fe + Mg) ratios in garnet and orthopyroxene, to achieve internal consistency between the GOPQ thermometers and barometers. Grt-Crd thermometry records temperatures of 750±50d̀ C. Peak P-T conditions range from 5-6 kbar and 750-800d̀ C in the Goudalie and eastern Lake Minto domains, to 7-10 kbar and 950-1000d̀ C in the western and central Lake Minto domain. This variability contrasts with the uniform crustal pressures of 5 ± 1 kbar recorded by the GCSPQ assemblages in the diatexites and the hornblende granodiorites (c. 4-5 kbar) across the same area. The GOPQ rocks are inferred to record earlier P-T conditions that prevailed before the formation of GCSPQ assemblages and the intrusion of the granodiorites. Partial P-T paths in GOPQ rocks from both domains, based on net transfer equilibria corrected for Fe-Mg resetting, document cooling of 100-250d̀ C from thermal-peak conditions, concomitant with a modest pressure decrease of 2-3 kbar. Although textures diagnostic of isobaric cooling are not developed, the paths are consistent with a tectonic model in which granulite metamorphism and crustal thickening in the Minto Block were consequences of magmatic underplating. The progression from higher P-T conditions recorded by GOPQ assemblages to lower P-T conditions recorded by GCSPQ assemblages is attributed to variable amounts of synmagmatic uplift and cooling in a single, continuous thermal event in the Minto crust, associated with protracted crustal magmatism. In the Goudalie and eastern Lake Minto domains, where GOPQ and GCSPQ rocks and Hbl granodiorites have similar P-T conditions of equilibration, the crust may not have been thickened as much as further west, where GOPQ P-T conditions are significantly higher than those of the hornblende granodiorites and the GCSPQ rocks.
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  • 84
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: A sequence of regional metamorphic isograds indicating a range from prehnite-pumpellyite to lower amphibolite facies was mapped in metabasites near Flin Flon, Manitoba. The lowest grade rocks contain prehnite + pumpellyite and are cut by younger brittle faults containing epidote + chlorite + calcite. Isobaric temperature-XCO2 and pressure-temperature (constant XCO2) diagrams were calculated to quantify the effects of CO2 in the metamorphic fluid on the stability of prehnite-pumpellyite facies minerals in metabasites containing excess quartz and chlorite. Prehnite and, to a lesser extent, pumpellyite are stable only in fluids with Xco2 〈0.002. For Xco2〉0.002, epidote + chlorite + calcite assemblages are stable. Our calculated phase relations are consistent with regional metamorphism in the Flin Flon area in the presence of an H2O-rich fluid and a more CO2-rich fluid in the later fault zones. We believe that the potential effects of small amounts of CO2 in the metamorphic fluid should be assessed when considering the pressure-temperature implications of mineral assemblages in low-grade metabasites.
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  • 85
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The Palghat Gap region is located near the centre of the large southern Indian granulite terrane. at the northern edge of the Kodaikanal charnockite massif. The dominant rock types in the region are hornblende-biotite ± orthopyroxene gneisses and charnockites along with minor amounts of intercalated mafic granulite, metapelite and calc-silicate. The P-T estimates from garnetiferous mafic granulites and metapelite samples are generally in the range 9-10 kbar and 800-900d̀ C using both conventional thermobarometric methods and the TWEEQU thermobarometry program. These P-T estimates, which should be taken as minimum values, are among the highest yet reported for South Indian and Sri Lankan granulites. The occurrence of orthopyroxene + plagioclase symplectites around embayed garnet grains in the mafic granulites and cordierite rims around garnet grains in metapelite suggest an isothermal decompression-type path. Similarly, a core-rim P-T trajectory indicates c. 3 and 7 kbar decompression at high temperature in the mafic granulites and metapelite, respectively. In both rock types, the key to the determination of the retrograde P-T path was the recognition of small amounts of second generation plagioclase with a more anorthitic composition than the matrix plagioclase. The preservation of high garnet-pyroxene temperatures in the mafic granulites (despite small garnet grain size) suggests rapid cooling of the terrane. Calculated minimum cooling rates range from 8 to 80d̀ C Ma-1. Such cooling rates are more rapid than those associated with normal isostatic processes and suggest that the terrane was tectonically exhumed at high temperature.
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  • 86
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Microstructural timing relationships indicate that the Rosebery massive sulphide ore, western Tasmania, Australia, formed by metasomatic replacement of ‘sericite’ schist during a Devonian deformation event (D3). This interpretation is contrary to earlier volcanogenic-based interpretations, but accords with the discordant position and inferred structurally controlled emplacement of the orebody. The main timing criteria are: overprinting of S3 by the late ore minerals, replacement textures in undeformed mineral parageneses, and a D3 structural control from the microscopic to the macroscopic scales. The consistent observation of these criteria in the orebody and the complete lack of pre-D3 ore argue against in situ dissolution of a primary orebody and local redeposition of sulphides by replacement.D3 deformation at Rosebery is inferred to have been characterized by heterogeneous cleavage-parallel extension, which resulted in localized microfracturing and selective replacement of zones of maximum strain rate. Continuous shifts in the strain-rate distribution pattern during progressive mineralization led to the compositional ore banding.Published Pb-isotope data point towards a Cambrian source rock for the orebody. This suggests a metamorphogenic origin by regional-scale dissolution of dispersed volcanogenic metals, focused solution transfer and concentrated redeposition in a structural trap.
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  • 87
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Granulite facies metasedimentary gneiss exposed on Jetty Peninsula, east Antarctica, contains assemblages involving garnet-sillimanite-biotite-cordierite-spinel-ilmenite-rutile and garnet-orthopyroxene-cordierite-biotite, as well as quartz and K-feldspar. Peak assemblages involve garnet + sillimanite + ilmenite (±rutile) and garnet + orthopyroxene. P-T calculations suggest formation conditions of approximately 800d̀ C at 7-7.5 kbar. Cooling from peak conditions is suggested by biotite + garnet (±sillimanite) overprinting some peak assemblages. A subsequent increase in temperature is inferred from the formation of cordierite + garnet + biotite + ilmenite, garnet + sillimanite + cordierite + ilmenite and cordierite + orthopyroxene assemblages during D2. In slightly zincian bulk compositions, hercynitic spinel + cordierite + sillimanite constitutes the peak D2 assemblage. Average pressure calculations indicate peak pressures of 5.9 ±0.4 kbar at 700d̀ C for the cordierite-bearing D2 assemblages. Available radiometric data suggest that peak metamorphism occurred at c. 1000 Ma and D2 occurred after 940 ± 20 Ma. The following two possibilities exist for the metamorphic evolution. (1) The formation of the lower pressure cordierite-bearing assemblages is associated with a separate metamorphic event (M2), unrelated to the peak assemblage (M1), and the lower pressure assemblages have no relevance in terms of a single tectonothermal event. (2) The cordierite-bearing assemblages formed during a progression from peak conditions. In this case, the lower pressure assemblages reflect a broadly decompressional metamorphic evolution, during which temperatures fluctuated. Comparison with P-T paths from granulites of similar age in adjacent areas suggests that the second possibility should be preferred. The cooling interval between peak conditions and the development of cordierite-bearing coronas and symplectites suggests affinities with isobarically cooled granulites of similar age immediately to the west, and the low-P/high-T post-peak conditions are similar to the later stages of decompressional paths recognized in much of east Antarctica.
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  • 88
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: A petrogenetic grid is presented for the system KFMASH (K2O-FeO-MgO-Al2O3-SiO2-H2O), including biotite, muscovite, K-feldspar, chlorite, chloritoid, staurolite, cordierite, garnet, orthoamphibole, orthopyroxene, spinel, andalusite, sillimanite, kyanite, quartz and corundum with H2O in excess, which was calculated using the computer program THERMOCALC and the Powell and Holland internally consistent thermodynamic dataset. By removing the normal constraint of having quartz in excess, both quartz-bearing and quartz-absent equilibria are shown. Quartz-absent equilibria are particularly relevant at high-T and low-P conditions, because of their common occurrence at these conditions. The calculated mineral assemblage and mineral compositional variations in terms of FeMg-1 and (Fe, Mg)SiAl-2 exchange vectors are broadly compatible with observations on natural rocks, particularly when non-KFMASH components are taken into account.
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  • 89
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Vein-controlled retrograde infiltration of H2O-CO2 fluids into Dalradian epidote amphibolite facies rocks of the SW Scottish Highlands under greenschist facies conditions resulted in alteration of calcite-rich marble bands to dolomite and spatially associated 18O enrichment of about 10%. on a scale of metres. Fluid inclusion data indicate that the retrograde fluid was an H2O-salt mixture with a low CO2 content, and that the temperature of the fluid was about 400d̀ C. Detailed petrographic and textural (backscattered electron imaging) studies at one garnet-grade locality show that advection of fluid into marbles proceeded by a calcite-calcite grain edge flow mechanism, while alteration of non-carbonate wall-rock is associated with veinlets and microcracks.Stable isotopic analysis of carbonates from marble bands provides evidence for advection of isotopic fronts through carbonate wall-rocks perpendicular to dolomite veins, and fluid fluxes in the range 2.4–28.6 m3/m2 have been computed from measured advection distances. Coincidence of isotope and reaction fronts is considered to result from reaction-enhanced kinetics of isotope exchange at the reaction front. Front advection distances are related to the proportion of calcite to quartz in each marble band, with the largest advection distance occurring in nearly pure calcite matrix. This relationship indicates that fluid flow in carbonates is only possible along fluid-calcite-calcite grain edges. However, experimental constraints on dihedral angles in calcite-fluid systems require that pervasive infiltration occurred in response to calcite dissolution initiated at calcite-calcite grain junctions rather than to an open calcite pore geometry.The regional extent of the retrograde infiltration event has been documented from the high δ18O of dolomite-ankerite carbonates from veins and host-rocks over an area of least 50 × 50 km in the SW Scottish Highlands. Isotopically exotic 18O-rich retrograde fluids have moved rapidly upwards through the crust, inducing isotopic exchange and mineral reaction in wall-rocks only where lithology, pore geometry or mineral solubilities, pressure and temperature have been appropriate for pervasive infiltration to occur.
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  • 90
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The role of volatiles in the stabilization of the lower (granulite facies) crust is contentious. Opposing models invoke infiltration of CO2-rich fluids or generally vapour-absent conditions during granulite facies metamorphism. Stable isotope and petrological studies of granulite facies metacarbonates can provide constraints on these models. In this study data are presented from metre-scale forsteritic marble boudins within Archaean intermediate to felsic orthogneisses from the Rauer Group, East Antarctica.Forsteritic marble layers and associated calcsilicates preserve a range of 13C- and 18O-depleted calcite isotope values (δ13C= -9.9 to -3.0% PDB, δ18O = 4.0 to 12.1% SMOW). A coupled trend of 13C and 18O depletion (∼2%, ∼5%, respectively) from core to rim across one marble layer is inconsistent with pervasive CO2 infiltration during granulite facies metamorphism, but does indicate localized fluid-rock interaction. At another locality, more pervasive fluid infiltration has resulted in calcite having uniformly low, carbonatite-like δ18O and δ13C values. A favoured mechanism for the low δ18O and δ13C values of the marbles is infiltration by fluids that were derived from, or equilibrated with, a magmatic source. It is likely that this fluid-rock interaction occurred prior to high-grade metamorphism; other fluid-rock histories are not, however, ruled out by the available data. Coupled trends of 13C and 18O depletion are modified to even lower values by the superposed development of small-scale metasomatic reaction zones between marbles and internally folded mafic (?) interlayers. The timing of development of these layers is uncertain, but may be related to Archaean high-temperature (〉1000d̀C) granulite facies metamorphism.
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  • 91
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The effects of high-strain deformation and fluid infiltration during Alpine eclogite facies metamorphism have been studied across ductile shear zones in relatively undeformed metagranitoids at Monte Mucrone (Sesia Zone, Western Alps, Italy). Microfabrics together with bulk rock and stable isotope data indicate that the mineralogical and chemical variations are related to the degree of deformation, rather than to changes in P-T conditions or tectonic position. Transformation of meta-quartz diorite to recrystallized eclogitic mylonites involved the breakdown of biotite and plagioclase and required the influx of H2O. Bulk-rock geochemical data show that ductile deformation to form eclogitic mylonites involved an increase in volume with a weight percent gain in H2O and Si and variable loss of K, Na, Ca and Al. δ18O changes systematically across ductile shear zones into the undeformed country rocks. Constant values in shear zone centres indicate advection parallel to the shear zone and within 10 cm of the mylonites. A dominant component of diffusive oxygen exchange perpendicular to the shear zones produced isotopic fronts, evident from a gradual increase in δ18O values to the reference values of the country rocks. The degree of isotopic shift within the shear zones reflects increasing deformation and degree of reaction progress.Multiple phases of Alpine deformation and mineral growth are recognized in the Monte Mucrone metagranitoids, and in some cases, eclogite facies shear zones were reactivated under greenschist facies conditions. The results of this study suggest that high-strain deformation provided pathways for both synkinematic and post-kinematic metamorphic fluids which were necessary for complete reactions. Relict igneous fabrics, as well as the presence of corona textures around biotite and pseudomorphs after primary igneous plagioclase in the least deformed rocks, indicate a paucity of hydrous fluids and support the conclusion that fluid movement was channelled rather than pervasive.
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  • 92
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Granulite facies anorthosites on Holsenøy Island in the Bergen Arcs region of western Norway are transected by shear zones 0.1–100 m wide characterized by eclogite facies assemblages. Eclogite formation is related to influx of fluid along the shears at temperatures of c. 700d̀C and pressures in excess of 1.7 GPa. Combined carbon and nitrogen stable isotope, 40Ar/36Ar, trace-element and petrological data have been used to determine the nature and distribution of fluids across the anorthosite-eclogite transition.A metre-wide drilled section traverses the eclogitic centre of the shear into undeformed granulite facies garnet-clinopyroxene anorthosite. Clinozoisite occurs along grain boundaries and microcracks in undeformed anorthosite up to 1 m from the centre of the shear and clinozoisite increases in abundance as the edge of the shear zone is approached. The eclogite-granulite transition, marked by the appearance of sodic pyroxene and loss of albite, occurs within the most highly sheared section of the traverse. The jadeite-in reaction coincides with increased paragonite activity in mica. The separation between paragonite and clinozoisite reaction fronts can be semiquantitatively modelled assuming advective fluid flow perpendicular to the shear zone. The inner section of the traverse (0.25 m wide) is marked by retrogressive replacement of omphacite by plagioclase + paragonite accompanied by veins of quartz-phengite-plagioclase.C-N-Ar characteristics of fluid inclusions in garnet show that fluids associated with precursor granulite, eclogite and retrogressed eclogite are isotopically distinct. The granulite-eclogite transition coincides with a marked change in CO2 abundance and δ13C (〈36ppm, δ13C=-2% in the granulite; 〈180 ppm, δ13C=-10% in the eclogite). The distribution of Ar indicates mixing between influxed fluid (40Ar/36Ar 〉 25 times 103) and pre-existing Ar in the granulite (40Ar/36Ar 〈 8 times 103). δ15N values decrease from +6% in the anorthosite to +3% within the eclogite shear. The central zone of retrogressed eclogite post-dates shearing and is characterised by substantial enrichment of Si, K, Ba and Rb. Fluids are CO2-rich (δ13C ∼ -5%) with variable N2 and Ar abundances and isotopic compositions.Both Ar and H2O have penetrated the underformed granulite fabric more than 0.5m beyond the granulite/eclogite transition during eclogite formation. Argon isotopes show a mixing profile consistent with diffusion through an interconnecting H2O-rich fluid network. In contrast, a carbon-isotope front coincides with the deformation boundary layer, indicating that the underformed anorthosite was impervious to CO2-rich fluids. This is consistent with the high dihedral angle of carbonic fluids, and may be interpreted in terms of evolving fluid compositions within the shear zone.
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  • 93
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Ultramafic blocks that themselves contain eclogite lenses in the Triassic Su-Lu ultrahigh-P terrane of eastern China range in size from hundreds of metres to kilometres. The ultramafic blocks are enclosed in quartzofeldspathic gneiss of early Proterozoic age. Ultramafic rocks include garnetiferous lherzolite, wehrlite, pyroxenite, and hornblende peridotite. Garnet lherzolites are relatively depleted in Al2O3 (〈3.8wt%), CaO (〈3.2%) and TiO2 (〈0.11 wt%), and are low in total REE contents (several p.p.m.), suggesting that the rocks are residual mantle material that was subjected to low degrees of partial melting. The eclogite lenses or layers within the ultramafic rocks are characterized by higher MgO and CaO, lower Al2O3 and TiO2 contents, and a higher CaO/Al2O3 ratio compared to eclogites enclosed in the quartzofeldspathic gneiss. Scatter in the plots of major and trace elements vs. MgO, REE patterns and La, Sm and Lu contents suggest that some eclogites were derived from melts formed by various degrees (0.05–0.20) of partial melting of peridotite, and that other eclogites formed by accumulation of garnet and clinopyroxene ± trapped melt in the upper mantle.Both ultramafic and eclogitic rocks have experienced a complex metamorphic history. At least six stages of recrystallization occurred in the ultramafic rocks based on an analysis of reaction textures and mineral compositions. Stage I is a high temperature protolith assemblage of Ol + Opx + Cpx + Spl. Stage II consists of the ultrahigh-pressure assemblage Ol + Cpx + Opx + Grt. Stage III is manifested by the appearance of fine-grained garnet after coarse-grained garnet. Stage IV is characterized by formation of kelyphitic rims of fibrous Opx and Cpx around garnet, and replacement of garnet by spinel and pargasitic-hornblende. Stage V is represented by the assemblage Ol + Opx + Prg-Hbl + Spl. The mineral assemblages of stages VIA and VIB are Ol + Tr-Amp + Chl and Serp + Chl ± talc, respectively. Garnet and orthopyroxene all show a decrease in MgO with retrogressive recrystallization and Na2O in clinopyroxene also decreases throughout this history. Eclogites enclosed within ultramafic blocks consist of Grt + Omp + Rt ± Qtz ± Phn. A few quartz-bearing eclogites contain rounded and oval inclusion of polycrystalline quartz aggregates after coesite in garnet and omphacite. Minor retrograde features include thin symplectic rims or secondary amphiboles after Cpx, and ilmenite after rutile. P-T estimates indicate that the ultrahigh-metamorphism (stage II) of ultramafic rocks occurred at 820-900d̀ C and 36-41 kbar and that peak metamorphism of eclogites occurred at 730-900d̀ C and 〉28 kbar. Consonant with earlier plate tectonic models, we suggest that these rocks were underplated at the base of the continental crust. The rocks then underwent ultrahigh-pressure metamorphism and were tectonically emplaced into thickened continental crust during the Triassic collision between the Sino-Korean and Yangtze cratons.
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  • 94
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Jadeitites from Guatemala are found as weathered blocks in tectonized serpentinite in a 15-km zone north of the Motagua Fault Zone. Rock types found with jadeitite include albitites, albite-mica rocks, omphacite/taramitic amphibole-bearing metabasites, chlorite-actinolite schists, talc-carbonate rocks and antigorite schists. In addition to the predominant jadeitic (Jd93_100) pyroxene, common phases in jadeitite include micas (paragonite and/or phengite ± rarer phlogopite), omphacite, albite, titanite /Pm zircon, apatite and graphite. Conditions of jadeitite formation are 100-400d̀ C, 5-11 kbar with 0.0 〉 log10asio2≥= 0.7. Fluid inclusions, coarse textures, vein structures, and rhythmic zoning of pyroxene indicate an aqueuos fluid was involved. Jadeitites are either (1) metasomatic modifications of former felsic-to-pelitic inclusions that have undergone silica depletion plus efficient soda exchange and enrichment, or (2) solution precipitations derived from such a source. The close spatial relationship of faults and shear zones, serpentinites, and jadeitites suggests jadeitites form in a relatively high-P/T setting with substantial flow of sodic fluid in a tectonized zone.Most Guatemalan jadeitites are extensively altered to analcime, albite, taramitic amphibole, (clino)zoisite ± nepheline and preiswerkite. This alteration reflects depressurization /Pm heating to below the jadeite + fluid = analcime reaction at high aNa. With progressive alteration, analcime and nepheline are replaced by albite; the increase in silica content may result from fluid flowing up a tectonized zone reaching saturation with an albite assemblage. Albitite phases, albite, actinolite, zoisite, /Pm chlorite, phengite, K-feldspar and quartz, record conditions of c. 3-8 kbar at T 〈 400d̀ C, indicating a clockwise P-T trajectory of the blocks.Barium aluminosilicates—banalsite, celsian, cymrite and hyalophane—are common minor late-stage phases in jadeitites and albite-rich rocks. Barian phengite is common in albite-mica rocks.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 95
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: Mineral assemblages in metapelites of the contact aureole of the Tono granodiorite mass, northeast Japan, change systematically during progressive metamorphism along an isobaric path at 2-3 kbar. The bulk rock compositions of metapelites are aluminous with A′ values on an AFM projection larger than that of the chlorite join. The metapelites commonly contain paragonite in the low-grade zone. With increasing temperatures, andalusite is formed by the breakdown of paragonite. The importance of pyrophyllite as a source of Al2SiO5 polymorphs is limited in typical pelitic rocks.The most common type of metapelite in the study area has FeO/(FeO + MgO) = 0.5–0.6, and develops assemblages involving chlorite, andalusite, biotite, cordierite, K-feldspar, sillimanite and almandine, with paragenetic changes similar to other andalusite-sillimanite type aureoles. Rocks with FeO/(FeO + MgO) 〉 0.8 progressively develop chloritoid-bearing assemblages from Bt-Chl-Cld, And-Bt-Cld, to And-Bt at temperatures between the breakdown of paragonite and the appearance of cordierite in the more common pelitic rocks in the aureole. The paragenetic relations are explained by a KFMASH univariant reaction of Chl + Cld = And + Bt located to the low-temperature side of the formation of cordierite by the terminal equilibrium of chlorite. A P-T model depicting the relative stability of chloritoid and staurolite at low- and medium-pressure conditions, respectively, is proposed, based on the derived location of the Chl + Cld = And + Bt reaction combined with the theoretical phase relations among biotite, chlorite, chloritoid, garnet and staurolite.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The objective of this study was to evaluate seven woody plant species on four growth media for their potential contribution to moose habitat and establishment of viable plant communities on a proposed mine site in southcentral Alaska. Populus balsamifera (balsam poplar), Salix alaxensis (feltleaf willow), S. barclayi (Barclay willow), S. bebbiana (Bebb willow), Alnus tenuifolia (thinleaf alder), Betula papyrifera (paper birch), and Picea glauca (white spruce) were selected for their functions in moose habitat, ease of propagation, and presence in the existing native vegetation. Three native soils were selected for biological characteristics such as different potential to form mycorrhizae and to regenerate local plant species, both of which are governed partly by existing vegetation. The fourth growth medium, glacial till or overburden, was expected to have little or no biological activity. A mining disturbance was simulated on three sites by removing existing vegetation from the plots, stripping the native soils, and then spreading these soil materials over the respective study plots. Rooted cuttings of the Salicaceae and nursery seedlings of the other species were planted in each of the four growth media. Height and survival of all plant species were greater on the three soil media than on the glacial till during the second and third years. Percentage of ectomycorrhizal infection on transplants was similar among growth media, although lower ectomycorrhizal infection occurred on volunteers in grassland soils than in the other growth media. Browsable plants were produced within three years on the disturbed native soils but not on the glacial till.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Seagrass transplanting experiments were conducted in Back Sound, Carteret County, North Carolina, and Tampa Bay, Pinellas County, Florida. In Florida, we compared three planting methods (cores, stapled bare root, and peat-pot plugs) for shoot addition rate coverage, and labor cost (harvest, fabrication, and deployment) using Halodule wrightii. Only planting methods and development rates were recorded for Syringodium filiforme. Fertilizer additions were made to peat-pot plantings of H. wrightii and Zostera marina in both North Carolina and Florida. Exclosure cages were tested to attempt to minimize bioturbation of H. wrightii and Z. marina in both North Carolina and Florida. Recovery from harvesting impacts to existing, natural beds of S. filiforme and H. wrightii were assessed in Florida. The peat-pot method was about 35% and 63% less expensive in work time than staples and core tubes, respectively. Response to fertilizer additions was masked by inconsistent release properties of the fertilizer, although some indication of positive response to phosphorus fertilizer in sediments with low carbonate content, and nitrogen in general, was detected. Complete loss of peat pots, largely ascribed to bioturbation, occurred in a large planting (Tampa Bay) but not in nearby smaller ones where exclosure cages were used. Cages did not affect planting unit survival in North Carolina but did improve number of shoots per planting unit in one of three experiments. No detrimental effects of cages were noted. Existing natura beds used to harvest transplanting stock in Tampa Bay recovered from excavations as large as 0.5 m2 in one year. Significant cost savings were found to be possible through methodological improvement, including planting techniques, bioturbation exclusion, and possibly fertilizer additions.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Land rehabilitation is proposed as a management strategy to reverse the negative consequences of tropical deforestation and land degradation. We first define the concepts associated with ecosystem modification—conversion, damage, and degradation—and those associated with ecosystem repair—restoration, rehabilitation, and reclamation. We then present a scheme of sustainable land use in the tropics, with illustrations of how rehabilitation and restoration activities fit into the overall scheme of the use of land. Because damaged lands cannot contribute effectively to sustained economic development, land rehabilitation is a necessary step for increasing the chances of attaining sustainability. Approaches for rehabilitating ecosystems are discussed, including the management of stressors and subsidies in relation to their point of interaction in the ecosystem. Finally, we illustrate the concepts of ecosystem rehabilitation of damaged, degraded, and derelict lands with examples of case studies from dry to humid life zones in island and continental situations throughout the tropics. The case studies demonstrate that opportunities for success exist, even with severely degraded lands, but a considerable amount of research remains to be done before we have a full understanding of the complexity of the task facing us.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The foundation of a successful revegetation or restoration program is quality native seed. This requires careful collection, processing, and storage. Mature seed should be collected from healthy, local stands with a sufficiently broad genetic base. Careful identification of the site characteristics and seed-lot tracking are essential. Yearly variation in seed production and seed quality can be very high, and an early determination of seed quality can prevent expensive failures. Nondestructive evaluation using X-rays is effective and economical, but techniques such as staining, inspection, and germination tests can also be helpful. Cleaning, dewinging, and upgrading seed before storage can (1) reduce weight and bulk, (2) improve storage life, (3) increase germination, and (4) make greenhouse production and field planting easier and more economical. The seeds of many native plants can lose their viability quickly if they are not stored under controlled conditions. Seeds in storage must also be protected from rodents, pests, and disease. Dormancy is common in the seeds of many native species, and experimentation is often necessary to determine the best way to break seed dormancy. This can be complicated by year-to-year and plant-to-plant variation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Restoration ecology 2 (1994), S. 0 
    ISSN: 1526-100X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The performance of woody plants was analyzed in 15 successional seres starting at bare ground in central European manmade habitats. The total cover of woody species after 10 years of succession was significantly related neither to initial soil moisture nor to nitrogen (expressed using Ellenberg indicator values). But the comparison of seres indicates that establishment of woody plants was easier under moderate environmental conditions and retarded in extreme habitats (dry, nutrient-poor, or acid). The arrival of the first woody plants was delayed in dry sites. No significant differences were found between primary and secondary seres, either with respect to the total cover of woody plants reached after 10 years of succession or considering the time of their arrival. In total, 24 woody species (10 shrubs and 14 trees) appeared in the series investigated. Their successional performance (in terms of the number of seres in which the species occurred and maximum cover reached in any sere) was not related to species traits (life strategy, type of mycorrhizae, mode of dispersal, diaspore weight), except for the regeneration strategy, species with seasonal regeneration by seeds were capable of creating higher cover. Betula pendula (European birch) was the most successful species in spontaneous succession, especially on moist sites. Practical suggestions for the management of particular habitats (sites disturbed by mining, sites reclaimed after acid rain deforestation, urban sites, abandoned fields) are provided regarding the establishment of woody plants.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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