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51.
Guy Masters 《Geophysical Journal International》1979,57(2):507-534
Summary. The observations of the periods of free oscillation of the Earth provide direct constraints on the density distribution in the Earth. These in turn allow constraints to be placed on the size of departures from a state of adiabaticity and chemical homogeneity. These departures are quantified in terms of a stratification parameter '8' first introduced as an index of chemical homogeneity. The resolving power theory of Backus & Gilbert is used to determine the ability of the observed free oscillations to constrain η in the lower mantle and outer core. The results suggest that the outer core is not strongly chemically stratified although a significantly thermally stable core cannot be excluded. The free oscillations also apparently require a compositional difference between the inner and outer cores. 相似文献
52.
53.
Robert A. Watson Pedro Carreira Kieran Cleary Rod D. Davies Richard J. Davis Clive Dickinson Keith Grainge † Carlos M. Gutiérrez Michael P. Hobson Michael E. Jones Rüdiger Kneissl Anthony Lasenby Klaus Maisinger Guy G. Pooley Rafael Rebolo José Alberto Rubiño-Martin ‡ Ben Rusholme § Richard D. E. Saunders Richard Savage Paul F. Scott Ane Slosar Pedro J. Sosa Molina Angela C. Taylor David Titterington Elizabeth Waldram Althea Wilkinson 《Monthly notices of the Royal Astronomical Society》2003,341(4):1057-1065
54.
Calculation of the ionization state and consequent magnetic Reynolds number for the solar nebula shows that the presence of26Al will result in strong coupling of the gas to magnetic fields. In the absence of26Al,40K will still result in substantial ionization, but the degree of magnetic coupling is much more model dependent.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978.also Department of Astronomy. 相似文献
55.
56.
Corrigendum
Corrigendum 相似文献57.
58.
Guy D. H. Simpson 《Basin Research》2006,18(2):125-143
Interactions between fold and thrust belt deformation, foreland flexure and surface mass transport are investigated using a newly developed mathematical model incorporating fully dynamic coupling between mechanics and surface processes. The mechanical model is two dimensional (plane strain) and includes an elasto‐visco‐plastic rheology. The evolving model is flexurally compensated using an elastic beam formulation. Erosion and deposition at the surface are treated in a simple manner using a linear diffusion equation. The model is solved with the finite element method using a Lagrangian scheme with marker particles. Because the model is particle based, it enables straightforward tracking of stratigraphy and exhumation paths and it can sustain very large strain. It is thus ideally suited to study deformation, erosion and sedimentation in fold–thrust belts and foreland basins. The model is used to investigate how fold–thrust deformation and foreland basin development is influenced by the non‐dimensional parameter , which can be interpreted as the ratio of the deformation time scale to the time scale for surface processes. Large values of imply that the rate of surface mass transport is significantly greater than the rate of deformation. When , the rates of surface processes are so slow that one observes a classic propagating fold–thrust belt with well‐developed wedge top basins and a largely underfilled foreland flexural depression. Increasing causes (1) deposition to shift progressively from the wedge top into the foredeep, which deepens and may eventually become filled, (2) widespread exhumation of the fold–thrust belt, (3) reduced rates of frontal thrust propagation and possible attainment of a steady‐state orogen width and (4) change in the style and dynamics of deformation. Together, these effects indicate that erosion and sedimentation, rather than passively responding to tectonics, play an active and dynamic role in the development of fold–thrust belts and foreland basins. Results demonstrate that regional differences in the relative rates of surface processes (e.g. because of different climatic settings) may lead to fold–thrust belts and foreland basins with markedly different characteristics. Results also imply that variations in the efficiency of surface processes through time (e.g., because of climate change or the emergence of orogens above sea level) may cause major temporal changes in orogen and basin dynamics. 相似文献
59.
Gaston?GiulianiEmail author Anthony?Fallick Daniel?Ohnenstetter Guy?Pegere 《Mineralium Deposita》2009,44(2):221-231
Alluvial and colluvial gem sapphires are common in the basaltic fields of the French Massif Central (FMC) but sapphire-bearing
xenoliths are very rare, found only in the Menet trachytic cone in Cantal. The O-isotope composition of the sapphires ranges
between 4.4 and 13.9‰. Two distinct groups have been defined: the first with a restricted isotopic range between 4.4 and 6.8‰
(n = 22; mean δ18O = 5.6 ± 0.7‰), falls within the worldwide range defined for blue-green-yellow sapphires related to basaltic gem fields (3.0 < δ18O < 8.2‰, n = 150), and overlaps the ranges defined for magmatic sapphires in syenite (4.4 < δ18O < 8.3‰, n = 29). A second group, with an isotopic range between 7.6 and 13.9‰ (n = 9), suggests a metamorphic sapphire source such as biotite schist in gneisses or skarns. The δ18O values of 4.4–4.5‰ for the blue sapphire-bearing anorthoclasite xenolith from Menet is lower than the δ18O values obtained for anorthoclase (7.7–7.9‰), but suggest that these sapphires were derived from an igneous reservoir in
the subcontinental spinel lherzolitic mantle of the FMC. The presence of inclusions of columbite-group minerals, pyrochlore,
Nb-bearing rutile, and thorite in these sapphires provides an additional argument for a magmatic origin. In the FMC lithospheric
mantle, felsic melts crystallized to form anorthoclasites, the most evolved peraluminous variant of the alkaline basaltic
melt. The O-isotopic compositions of the first group suggests that these sapphires crystallized from felsic magmas under upper
mantle conditions. The second group of isotopic values, typified for example by the Le Bras sapphire with a δ18O of 13.9‰, indicates that metamorphic sapphires from granulites were transported to the surface by basaltic magma. 相似文献
60.
Guy Singleton Maria Fay Rola-Rubzen Kado Muir Deeva Muir Murray McGregor 《GeoJournal》2009,74(5):403-413
In spite of a ‘digital divide’, Aboriginal groups in Australia, as internationally, are increasingly using information and
communication technologies (ICTs) to maintain their cultures, communicate, archive knowledge, empower their communities, develop
skills and generate income. Each community uses the technologies differently in accordance with their particular needs and
the opportunities available. The use of ICTs in Aboriginal youth empowerment is illustrated through a case study of an initiative
undertaken by the Walkatjurra Cultural Centre in Leonora, remote Western Australia. A participatory process was used to engage
the Centre’s young people and they were given individual assistance to develop their ICT related capacity. The community conceives
this youth empowerment to be part of a broader youth participation process that will contribute to the Centre’s overall objectives. 相似文献