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121.
122.
Robert J. Allison 《地球表面变化过程与地形》1991,16(5):473-476
In a previous publication (Allison, 1989), a non-destructive method for indirectly determining rock strength by measuring Dynamic Young's Modulus was described. Data were presented to assess the Grindosonic apparatus in relation to standard laboratory techniques. A further Short Communication (Allison, 1990) evaluated the non-destructive test as a field technique, in part achieved by comparing the Grindosonic results with data collected using the Schmidt hammer. The Schmidt hammer is a widely used field technique in geomorphology for determining rock strength (see for example Day and Goudie, 1977; Day, 1981). Allison (1989, 1990) also suggested that the elastic properties of materials are becoming increasingly important in geomorphological studies. The opportunity to provide additional information and comments here is appreciated. 相似文献
123.
The East Antarctic sea ice zone: Ice characteristics and drift 总被引:2,自引:0,他引:2
Dr. Ian Allison 《GeoJournal》1989,18(1):103-115
Results from studies of the surface energy balance and the ocean structure in the presence of fast ice near Mawson on the Antarctic coast are used to illustrate the important ways in which sea ice interacts with the ocean and atmosphere. Away from the coast, ship and drifting buoy observations are used to characterize the E Antarctic sea ice zone in a study area between 60° E and 120° E and S of 61° S. Divergent drift over most of the region plays a dominant role in expanding the ice extent in autumn and in determining the characteristics of the pack. Much of the sea ice in the region is young thin ice which forms in leads and polynyas, and in late spring in the study area, the ice thickness averaged over the total ocean surface within the ice edge less than 0.4 m. Even in winter the majority of ice floes off E Antarctica are probably less than 1 m thick. 相似文献
124.
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
125.
A mathematical model is developed describing the shape of H218O and HDO depth profiles which result from evaporation of water from dry soil under quasi-steady state conditions. Typically, isotope concentrations rise from a minimum at the soil surface to a maximum a short distance beneath the surface, and then decrease approximately exponentially to constant concentrations at depth. The model predicts that for isothermal conditions, the slope of the relationship between 18O and deuterium δ-values of samples of the soil water will be 30% lower for a dry soil than for a wet soil evaporating under the same conditions. It is concluded that low slopes should be indicative of soil water or groundwater recharged under arid or semi-arid conditions. Using the shape of the 18O and deuterium profiles, three independent methods for estimating evaporation for dry soils are developed. When water loss occurs by both transpiration and evaporation, the slope of the 18O-D relationship should be slightly lower than that for a site where water loss occurs by evaporation alone. 相似文献
126.
The use of natural tracers as indicators of soil-water movement in a temperate semi-arid region 总被引:12,自引:0,他引:12
In a semi-arid area of southern Australia a change in land use from Eucalyptus scrub to cropping with wheat is shown to have caused considerable change in the mechanism of the movement of soil water and the amount of deep drainage. Chloride concentrations of soil water have been used to show the mean annual amount of deep drainage increases from less than 0.1 to 3 mm yr.−1 following clearing of the native vegetation.
The concentration of environmental tritium in soil water beneath the native vegetation is consistent with the hypothesis that some relatively recent water (post 1960) has penetrated to depths of at least 12m along channels occupied by living roots. Where the native vegetation has been cleared, no water which fell as rain since 1960 was found at depths greater than 2.5 m.
18O and deuterium concentrations suggest that some water movement to the roots of the native vegetation is in the vapour phase. 相似文献
127.
Robert Kerrich Iain Allison Robert L. Barnett Stephen Moss John Starkey 《Contributions to Mineralogy and Petrology》1980,73(3):221-242
At Miéville, in the Aiguilles-Rouges Massif, granitic rocks of the basement are deformed into mylonites within a major subvertical shear zone. The ambient temperature during translation is estimated at 250° C±30° C from fluid inclusion filling temperatures in syntectonic microveins, from
18O quartzilmenite of+15%, and from mineralogical criteria. Porphyroclasts of both oligoclase and orthoclase feldspar decrease from initial diameters of 20 mm and assume elliptical shapes during progressive deformation, due to recrystallisation of the margins to ultra-fine polygonal grains which extend out from the porphyroclasts in thin trails: the final stable grain size is <5 . The recrystallised feldspar has a composition of the parent porphyroclast,+albite, requiring relative gains of Na and losses of K+Ca compared to the precursor, and implying short range redistribution of the components during deformation. Decrease of free energy associated with the deformation catalysed change in feldspar composition, coupled with stored strain energy in the porphyroclasts may account for recrystallisation to a stable aggregate of ultrafine grain size. The long trails imply exceptionally high ductility, which, coupled with microstructural criteria, and admixture of quartz from neighbouring pure quartz aggregates by grain boundary sliding, is interpreted in terms of superplastic flow. Estimated temperatures of T/T
m0.2 for the inferred superplastic deformation is lower by a factor of 2 than previously recorded for this flow michanism in silicates. The feldspar and quartz probably accomodated grain boundary sliding by intercrystalline diffusion.Biotite responds to deformation by bendgliding, kinking, and recrystallisation in mantles. The reaction of high-Ti parent grains to low-Ti biotite+Fe-muscovite+ ilmenite+chlorite is catalysed at all of these microstructural sites. Progressive deformation of the fine-grained products in the mantles is coupled with steady reaction to low-Fe muscovite+epidote+ sphene+rutile resulting in exceptionally ductile trails, as for the case of feldspar.Biotite grains have pervasive networks of nondisplacive intragranular fractures. At the fracture tips increase of the stress intensity has catalysed the reaction of high-Ti parent grains to low-Ti biotite+muscovite+ ilmenite which occupy the fractures. The fractures propagate and coalesce resulting in mechanical breakdown of the parent grains: these microstructures are believed to be examples of natural stress corrosion cracking. These features are also abundant in feldspar porphyroclasts where at fracture tips orthoclasesecondary orthoclase+albite, and oligoclasesecondary oligoclase+albite. Stress corrosion cracking may be significant in the steady state deformation of crustal rocks at low temperatures when intracrystalline plasticity is not generally dominant.Two way mass balance calculations utilising major and selected trace element data, reveal that deformation of the granite was essentially isochemical, involving average additions of <1 % H2O+CO2, at approximately constant specific gravity. The parameters Fe2+/Fe and 18Owhole rock maintain relatively constant values across the shear zone, and this also implies limited participation of fluids in the deformation. Alkali elements and titanium display the largest percentage variation during progressive deformation, whereas SiO2, Al2O3, and P2O5, together with V, Ni, Cr,Y,Zr, and Nb remain relatively constant. All variations decrease at increasing states of deformation and this is interpreted in terms of mechanical mixing of chemical inhomogeneities of the granite precursor within the shear zone. Constraints imposed by variations in abundance of the relatively immobile elements imply that volume changes accompanying deformation in the shear zone were less than ±10%. 相似文献
128.
A small maar lake, known as the Blue Lake, set in a karstic region of southeastern Australia, provides the municipal water supply for a population of 20,000. The lake has a volume of 3.6·107m3, of which 10–15% is pumped from it each year. The lake is recharged almost entirely from groundwater and the main objective of this study was to estimate the total groundwater inflow and outflow rates. Estimation of groundwater throughflow in a lake is difficult to assess using classical hydrological techniques and an alternative method involving measurement of the concentrations of the environmental isotopes 3H, 18O, 2H and 14C in the lake water and in the recharging groundwater was used to establish the lake-water balance. The water-balance calculations indicated a total groundwater inflow to Blue Lake of between 5.0·106 and 6.5·106m3yr.−1, corresponding to a residence time of water in the lake of 6 yr. It was not possible to derive the relative proportions of inflow to the lake from the two possible source aquifers, using these isotopes, because their concentrations did not show a sufficiently large contrast to distinguish the two water sources. 相似文献
129.
Lain Allison 《Journal of Structural Geology》1984,6(3):331-333
The pole of a Mohr diagram, for the two-dimensional case, is a unique point on the Mohr circle which permits any point on the Mohr circle to be related to the direction in the physical plane associated with that point. A Mohr diagram can be constructed for any second rank tensor. To illustrate the simplicity of this geometrical construction two examples of the use of the pole are presented, one for the strain tensor and the other for the stress tensor. 相似文献
130.
An efficient methodology is presented which uses modal analysis implemented in the frequency domain to obtain the structural response of a system with soil-structure interaction. The interaction effects are represented using a free-field ground motion modification factor, derived for each mode of vibration and used in the determination of structural response. Applying this algorithm, the advantages of the modal superposition method are fully exploited, and the interaction problem can be solved easily and effectively within the framework of the conventional frequency domain analysis for a fixed-base structure. In addition, this method produces accurate approximation with less computational effort due to consideration of only the first few vibration modes of the structure. 相似文献