Interactions of marine plankton with transuranic elements. II. Influence of dissolved organic compounds on americium and plutonium accumulation in a diatom     

Nicholas S Fisher  Poul Bjerregaard  Lang Huynh-Ngoc  George R Harvey 《Marine Chemistry》1983,13(1):45-56

To assess the significance of naturally occurring dissolved organic matter (DOM) on complexation of transuranic elements in seawater, a series of bioassay experiments was conducted in which the effect of DOM on the accumulation of ²⁴¹ Am, ²³⁷Pu (III–IV), and ²³⁷Pu (V–VI) by the marine diatom Thalassiosira pseudonana was measured. EDTA at 0.3μM complexed both metals substantially, resulting in reduced radio-isotope uptake by the diatom; the greatest effect was on Pu (III–IV). In contrast, there was no apparent complexation of either element by equimolar concentrations of marine fulvic (MFA) or humic acids (MHA), naturally occurring photooxidizable DOM (uncharacterized), or diatom exudates, as none of these materials reduced isotope uptake; on the contrary, there were indications that some of this DOM enhanced transuranic bioaccumulation in the diatom slightly. Subsequent experiments showed this enhancement was probably due to complexation of transition metals by the DOM, leading to fewer ambient ions ‘competing’ for binding sites on the cells; ²⁴¹ Am uptake rates were negatively correlated (r =? 0.846, P < .01) with Σ ASV-labile Cu + Zn + Cd + Pb. These experiments suggest that naturally occurring DOM may not appreciably complex Am or Pu or greatly affect their bioavailability in the sea.  相似文献   

Matrix analysis of metamorphic mineral assemblages and reactions   总被引：1，自引：0，他引：1  

George W. Fisher 《Contributions to Mineralogy and Petrology》1989,102(1):69-77

Assemblage diagrams are widely used in interpreting metamorphic mineral assemblages. In simple systems, they can help to identify assemblages which may represent equilibrium states; to determine whether differences between assemblages reflect changes in metamorphic grade or variations in bulk composition; and to characterize isograd reactions. In multicomponent assemblages these questions can be approached by investigating the rank, composition space (range) and reaction space (null-space) of a matrix representing the compositions of the phases involved. Singular value decomposition (SVD) provides an elegant way of (1) finding the rank of a matrix and detemining orthonormal bases for both the composition space and the reaction space needed to represent an assemblage or pair of assemblages; and (2) finding a model matrix of specified rank which is closest in a least squares sense to an observed assemblage. Although closely related to least squares techniques, the SVD approach has the advantages that it tolerates errors in all observations and is computationally simpler and more stable than non-linear least squares algorithms. Models of this sort can be used to interpret multicomponent mineral assemblages by straightforward generalizations of the methods used to interpret assemblage diagrams in simpler systems. SVD analysis of mineral assemblages described by Lang and Rice (1985) demonstrates the utility of the approach.  相似文献   

Weichselian before 15,000 years B.P. at Jæren-Karmø in southwestern Normay     

BJøRN G.ANDERSEN  REIDAR NYDAL  OLE P. WANGEN  SVEIN R. øSTMO 《Boreas: An International Journal of Quaternary Research》1981,10(4):297-314

On the basis of studies of many stratigraphical profiles, together with radiocarbon dates, Thorium-Uranium dates and amino-acid dates, the following preliminary stratigraphy is proposed: (1)Late Weichselian. Stavanger Stadial. The glacier covered the coast and deposited the upper drift sheet. - (2) Middle Weichselian.(a)Sandnes Interstadial (30,000?-39,000 years B.P.). Thick units of marine deposits underlie the Stavanger Stadial drift. The lithology, the foraminiferal fauna, the molluscan fauna and the pollen flora all record cold, partly near-ice environment during their deposition. Elements of a boreal type foraminiferal fauna suggest that certain phases of the Sandnes Interstadial could have been slightly warmer. The shore level was very high. (b) Jæren Stadial (40,000? 1000 years B.P.). Tills and glaciomarine deposits at several locailites are correlated with a Jæren Stadial. (c) Nygaard Interstadial (41,000–50,000? years B.P.). Marine deposits representing a low shore-level phase, record cool to cold conditions. - (3)Early Weichselian. (a) Karmøy Stadial (older than 47,000 years B.P.). Gravelly and very bouldery tills at low stratigraphical levels in several prifles are correlated with a Karmøy Staidial.(b) Older deposits. Marine deposits which lie below the Karmøy Stadial till and on top of Eemian deposits at Bø II on Karmøy are being studies.  相似文献   

Rate laws in metamorphism   总被引：1，自引：0，他引：1  

George W. Fisher 《Geochimica et cosmochimica acta》1978,42(7):1035-1050

Once a new mineral has nucleated in a metamorphic rock, further growth generally involves three mechanisms, operating simultaneously: (1) diffusion of components; (2) supply of heat needed for chemical reactions; and (3) precipitation on the nucleus. The resulting structure can grow no faster than is permitted by the slowest mechanism, the rate-determining step. During growth, the relative rates of these mechanisms change systematically, so that metamorphic structures pass through a definite sequence of stages, each characterized by a different rate-determining step. Spherical structures tend to pass through three successive stages: (1) an initial reaction-controlled stage, in which growth is linearly proportional to time; (2) an intermediate diffusion-controlled stage, in which growth is proportional to the square root of time; and (3) a final heat-flow-controlled stage, with growth proportional to the cube root of time. Planar reaction zones follow a two-stage sequence beginning with either a reaction-controlled or a heat-flow-controlled stage, both characterized by linear growth laws; and culminating with a diffusion-controlled stage, in which growth is proportional to the square root of time.Estimated values of the kinetic coefficients governing each of these steps suggest that in most metamorphic processes the reaction-controlled stage will end long before the structure is large enough to detect, and that most growth will occur by either a heat-flow-controlled or diffusion-controlled mechanism. Increasing distance between the initial nuclei, increasing grain size, decreasing diffusion coefficients, and increasing heat flow rates all tend to favor diffusion control over heat-flow control. The rate-determining step can be expected to vary both with local and regional changes in these variables; and attempts to delineate domains in which different mechanisms constitute the ratedetermining step may provide valuable insight into the scale on which these parameters vary in metamorphism.  相似文献   

A New Zealand test of the track-etch® method of prospecting for geothermal steam     

N.E. Whitehead  J.E. Gingrich  J.C. Fisher 《Journal of Volcanology and Geothermal Research》1983,15(4):339-354

The Track Etch® system for radon detection was evaluated as a geothermal exploration technique in a known geothermal resource area in New Zealand called the Craters of the Moon (previously known as “Karapiti”). Very strong radon anomalies spaced along mapped fault traces were detected using 60-m sample spacings. Such radon anomalies may indicate good areas to drill for steam. The anomalies detected in these tests were located inside a larger area known to have above-back-ground concentrations of radon and thought to be a generally favourable area for finding shallow steam. Track Etch® radon cups with an improved type of detector were found to be usable in ground temperatures as high as 60°C. There was no direct correlation of radon concentrations with resistivity measurements, but a moderate correlation with near-surface temperature measurements. Varying vegetation cover had no significant effect on the results but there was an apparent correlation with superficial pumice deposits. It is concluded from the tests that the Track Etch method shows promise in vapour-dominated areas for improving drill-hole siting and thus reducing the economic loss of drilling non-productive holes.  相似文献   

Comment on “rejection of palaeomagnetic observations” by P.L. McFadden     

Nicholas I. Fisher  Toby Lewis  Mary E. Willcox 《Earth and Planetary Science Letters》1983,64(2):316-317

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Multi-mineral geochronology: insights into crustal behaviour during exhumation of an orogenic root     

Crystal?LaFlammeEmail author  Christopher?R.?M.?McFarlane  Christopher?M.?Fisher  Christopher?L.?Kirkland 《Contributions to Mineralogy and Petrology》2017,172(2-3):9

Under rare conditions, reworked cratons and their margins preserve the orogenic roots of ancient mountain-building events. However, based on the preservation of high-temperature (~?800?°C), middle and lower crustal metamorphic assemblages, present day exposure of these terrains is not simply a result of protracted denudation, but also must reflect a multifaceted exhumational history. In situ analysis within thin section preserves the textural setting of target minerals that can be used as thermochronometers such as U-Pb of zircon, monazite, titanite and apatite, and Sm-Nd of apatite. In situ analyses of these chronometers has the potential to provide critical timing constraints on exhumation processes related to decompression, melting and cooling across large metamorphic terrains. The Repulse Bay block of the Rae craton preserves a large composite amphibolite–granulite area (50,000 km²) of Archean orthogneiss, migmatite, and slivers of Proterozoic metasediments that underwent high-grade metamorphism, partial melting, ductile flow and finally exhumation during the Paleoproterozoic Trans-Hudson Orogeny. The granulite domain preserves dry granitoid assemblages, whereas the amphibolite domain is dominated by hydrated migmatites and orthogneiss. Metasediments occur in both domains and preserve mineral assemblages that are consistent with having undergone tectonometamorphic conditions of ~?9 kbar/800?°C during burial. U-Pb thermochronometers document identical cooling histories of the granulite and amphibolite domains through the U-Pb closure temperatures of titanite (~?650?°C) and apatite (~?450?°C). This suggests that melt-loss from the underlying granulite domain and melt-gain to the amphibolite domain prior to cooling through 650?°C are a controlling factor of the metamorphic assemblages across the composite granulite–amphibolite terrains such as the Repulse Bay block, rather than significant differences in burial history, cooling history, and/or reorganization of the crust.  相似文献