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101.
Local modification of rock chemistry by deformation 总被引:1,自引:0,他引:1
R. Kerrich W. S. Fyfe B. E. German I. Allison 《Contributions to Mineralogy and Petrology》1977,65(2):183-190
Metabasalts subjected to progressive deformation in large-scale shear zones at Yellowknife display corresponding changes in major element abundances. Deformation, under conditions of greenschist facies metamorphism, has involved grain size reduction from 1200 m to <20 m, depletion of SiO2 (5%) and Na2O, together with hydration, and a decrease in specific gravity from 2.97 to 2.80. Chemical redistribution by deformation has been accomplished through a decrease in grain diameter of quartz and albite by intercrystalline diffusive mass transport (pressure solution), with concomitant transfer of material into extension veins. The degree of chemical modification is related to the finite strain. Deformation has involved a redistribution of 7.1015g of SiO2 over a volume of about 50km3.The microstructure of an adamellite deformed in a shear zone at higher temperature, under conditions of amphibolite facies metamorphism is indicative of dominant dislocation creep. A low degree of tectonic grain refinement is present. Constant values of major element abundances and specific gravity determined across the shear zone at increasing states of strain imply isochemical and isovolumetric deformation. These results are taken to support the precept that crustal deformation is characterised by a low temperature deformation regime dominated by pressure solution, with local changes of rock chemistry and volume; and a high temperature regime in which strain is accommodated principally by dislocation creep, an isochemical and isovolumetric deformation mechanism. 相似文献
102.
Lesley L. Rhodes Allison J. Haywood W. J. Ballantine A. Lincoln MacKenzie 《新西兰海洋与淡水研究杂志》2013,47(4):419-430
A raphidophyte‐dominated phytoplankton bloom extended discontinuously along the northeastern coastline of New Zealand, from Bream Tail, north of Leigh, to the western coast of the Coromandel Peninsula from late August until December 1992. The bloom was associated with an “El‐Niño” phase of the Southern Oscillation, resulting in unusually cold sea temperatures. The dominant bloom species in the north was Fibrocapsa japonica and in the south Heterosigma akashiwo. Associated species included the coccolithophorid Gephyrocapsa oceanica and the naked form of the silicoflagellate Dictyocha speculum. By December, numbers of the armoured form of D. speculum had increased, as those of raphidophytes and coccolithophorids declined. Bioassays to test for shellfish biotoxins were negative and Artemia salina bioassays, indicators of ichthyotoxicity, were negative except for Heterosigma akashiwo cultures, isolated from Coromandel water samples. 相似文献
103.
Allison E. Ray John R. Bargar Alice C. Dohnalkova Brent M. Peyton Timothy S. Magnuson 《Geochimica et cosmochimica acta》2011,75(10):2684-6510
Microbial reduction of hexavalent uranium has been studied widely for its potential role in bioremediation and immobilization of soluble U(VI) in contaminated groundwater. More recently, some microorganisms have been examined for their role in immobilization of U(VI) via precipitation of uranyl phosphate minerals mediated by microbial phosphate release, alleviating the requirement for long-term redox control. Here, we investigated the mechanism of U(VI) removal mediated by an environmental isolate, strain UFO1, that is indigenous to the Field Research Center (FRC) in Oak Ridge, TN and has been detected in U(VI)-contaminated sediments. Changes in U(VI) speciation were examined in the presence and absence of the electron-shuttling moiety, anthraquinone-2,6-disulfonate (AQDS). Cell suspensions were capable of nearly complete removal of 100 μM U(VI) from solution within 48 h; U(VI) removal was not dependent on the presence of an exogenous electron donor or AQDS, although AQDS increased the rate of U(VI) removal. X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopic measurements indicated that U(IV) was the predominant oxidation state of uranium in cell suspensions in both the absence and presence of 100 μM AQDS. Interestingly, 17% of the cell-associated precipitates in a U(VI)-treated suspension that lacked AQDS had spectral characteristics consistent with a uranyl phosphate solid phase. The potential involvement of phosphate was consistent with observed increases in soluble phosphate concentrations over time in UFO1 cell suspensions, which suggested phosphate liberation from the cells. TEM-EDS confirmed the presence of uranyl phosphate with a U:P ratio consistent with autunite (1:1). EXAFS analyses further suggested that U(IV) was bound to low-Z neighbors such as C or P, inferred to be present as functional groups on biomass. These results suggest that strain UFO1 has the ability to facilitate U(VI) removal from solution via reductive and phosphate precipitation mechanisms. Both mechanisms offer potential for the remediation of U-contaminated sediments at the FRC or elsewhere. 相似文献
104.
Eelgrass (Zostera marina) forms extensive beds in temperate coastal and estuarine environments worldwide and provides important ecosystem services, including habitat for a wide range of species as well as nutrient cycling and carbon storage. However, little is known about how eelgrass ecosystem structure and services differ naturally among regions. Using large-scale field surveys, we examined differences in eelgrass bed structure, carbon and nitrogen storage, community composition, and habitat services across three distinct regions in Eastern Canada. We focused on eelgrass beds with low anthropogenic impacts to compare natural differences. In addition, we analyzed the relationships of eelgrass bed structure with environmental conditions, and species composition with bed structure and environmental conditions, to elucidate potential drivers of observed differences. Our results indicate that regional differences in eelgrass bed structure were weakly correlated with water column properties, whereas differences in carbon and nitrogen storage were mainly driven by differences in eelgrass biomass. There were distinct regional differences in species composition and diversity, which were particularly linked to temperature, as well as eelgrass bed structure indicating differences in habitat provision. Our results highlight natural regional differences in ecosystem structure and services which could inform spatial management and conservation strategies for eelgrass beds. 相似文献
105.
Ian Kraucunas Leon Clarke James Dirks John Hathaway Mohamad Hejazi Kathy Hibbard Maoyi Huang Chunlian Jin Michael Kintner-Meyer Kerstin Kleese van Dam Ruby Leung Hong-Yi Li Richard Moss Marty Peterson Jennie Rice Michael Scott Allison Thomson Nathalie Voisin Tristram West 《Climatic change》2015,129(3-4):573-588
106.
107.
Laura Toran Jonathan E. Nyquist Allison C. Fang Robert J. Ryan Donald O. Rosenberry 《水文研究》2013,27(10):1411-1425
Time‐lapse geophysical surveys can map lingering hyporheic storage by detecting changes in response to saline tracer. Tracer tests were conducted in Crabby Creek, an urban stream outside Philadelphia, to examine the influence of stream restoration structures and variable sediment thickness. We compared electrical resistivity surveys with extensive well sampling (57 wells) in two 13.5‐m‐long reaches, each with a step drop created by a J‐hook. The two step drops varied in tracer behaviour, based on both the well data and the geophysical data. The well data showed more variation in arrival time where the streambed sediment was thick and was more uniform where sediment was thin. The resistivity in the reach with thin sediment showed lingering tracer in the hyporheic zone both upstream and downstream from the J‐hook. In the second reach where the sediment was thicker, the lingering tracer in the hyporheic zone was more extensive downstream from the J‐hook. The contrasting results between the two reaches from both methods suggested that sediments influenced hyporheic exchange more than the step at this location. Resistivity inversion differed from well data in both reaches in that it showed evidence for tracer after well samples had returned to background, mapping lingering tracer either upstream or downstream of a step. We conclude that resistivity surveys may become an important tool for hyporheic zone characterization because they provide information on the extent of slow moving fluids in the hyporheic zone, which have the potential to enhance chemical reactions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
108.
P.W. Gorham F.E. Baginski P. Allison K.M. Liewer C. Miki B. Hill G.S. Varner 《Astroparticle Physics》2011,35(5):242-256
We describe the scientific motivation, experimental basis, design methodology, and simulated performance of the ExaVolt Antenna (EVA) mission, and planned ultra-high energy (UHE) particle observatory under development for NASA’s suborbital super-pressure balloon program in Antarctica. EVA will improve over ANITA’s integrated totals – the current state-of-the-art in UHE suborbital payloads – by 1–2 orders of magnitude in a single flight. The design is based on a novel application of toroidal reflector optics which utilizes a super-pressure balloon surface, along with a feed-array mounted on an inner membrane, to create an ultra-large radio antenna system with a synoptic view of the Antarctic ice sheet below it. Radio impulses arise via the Askaryan effect when UHE neutrinos interact within the ice, or via geosynchrotron emission when UHE cosmic rays interact in the atmosphere above the continent. EVA’s instantaneous antenna aperture is estimated to be several hundred m2 for detection of these events within a 150–600 MHz band. For standard cosmogenic UHE neutrino models, EVA should detect of order 30 events per flight in the EeV energy regime. For UHE cosmic rays, of order 15,000 geosynchrotron events would be detected in total, several hundred above 10 EeV, and of order 60 above the GZK cutoff energy. 相似文献
109.
Michael A. O'Neal Nicholas T. Legg Brian Hanson Daniel J. Morgan Allison Rothgeb 《Geografiska Annaler: Series A, Physical Geography》2013,95(3):241-248
This study presents a growth curve developed from direct and indirect growth rates of Rhizocarpon geographicum lichens from study sites on Mounts Baker, Rainier, Adams, and Hood in the northern Cascade Range of the western USA. Our observations of direct growth rates are based on 31 measurements of 11 lichens growing on different surfaces. This direct growth rate dataset is complemented by indirect growth rates based on measurements of the largest lichen observed on 20 different surfaces over 24–33‐yr periods. The direct and indirect datasets produce statistically indistinguishable mean radial growth rates of 0.48 and 0.50 mm yr?1, respectively. Statistical analysis of zero and first order fits of our growth rate data suggests that lichen growth is best characterized by the average of our mean growth rate (zero order) models at 0.49 mm yr?1. Our revised growth curve for the study area extends the applicable range for dating rock surface in the study area to the seventeenth century, approximately 175 years longer than previous calibrated curves. 相似文献
110.
Allison Bent 《地震科学(英文版)》2022,35(1):19-21
I grew up in one of the most aseismic regions of the planet but decided as a child that I wanted to be a seismologist.Ignoring all the naysayers who claimed tha... 相似文献