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61.
A trace-gas climatology above Zotino, central Siberia 总被引:1,自引:1,他引:1
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STEPHAN WEINBRUCH HEINZ BÜTTNER ASTRID HOLZHEID MATTHIAS ROSENHAUER ROGER H. HEWINS 《Meteoritics & planetary science》1998,33(1):65-74
Abstract— Dynamic crystallization experiments performed with different container materials (Fe crucible, pure Pt wire loop, presaturated Pt wire loop) demonstrate the strong influence of Fe loss on texture, mineralogy and chemical zoning in olivine. The use of pure Pt wire loops results in severe Fe loss and prevents the development of strong Fe/Mg zoning in olivine in slower cooled runs (≤ 100 °C/h). Presaturated Pt wire loops reduce Fe loss to some extent but not completely. If severe Fe loss from the melt is avoided by the use of Fe crucibles, then cooling rates between 2000 and 1.2 °C/h yield textures, modal mineral abundances and Fe/Mg zoning in olivine comparable to natural porphyritic olivine chondrules. However, Fe gain from the crucible may possibly enhance Fe/Mg zoning in olivine for cooling rates < 10 °C/h. Therefore, it is concluded that the lower limit of cooling rates of porphyritic olivine chondrules derived from dynamic crystallization experiments is 10 °C/h, perhaps it is even lower, on the order of a few degrees Celsius per hour. This value is not significantly different from estimates for subsolidus temperatures based on the microstructure of chondrule minerals (Weinbruch and Müller, 1995). The lower limit of chondrule cooling rates of 100 °C/h advocated by Hewins (1988) and Radomsky and Hewins (1990) seems to be an artifact of the experimental technique, as their samples were crystallized in pure Pt wire loops. 相似文献
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Abstract Internal waves at high altitudes are greatly damped by the drastic increase in molecular viscosity and thermal diffusivity, resulting in important heating and other effects at those altitudes. Here we consider the case where this increase in viscosity is very rapid, idealized as an interface with inviscid flow in the lower layer and constant viscosity in the upper layer. The results show that waves are partially reflected by this interface, with a reflection coefficient that increases monotonically with an increase in the viscosity of the upper layer. This mechanism would have a significant impact on the vertical distribution of thermal energy at high altitudes. 相似文献
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ROGER F. AUCH DARRELL E. NAPTON STEVEN KAMBLY THOMAS R. MORELAND JR. KRISTI L. SAYLER 《Geographical review》2012,102(1):53-75
Driving forces facilitate or inhibit land‐use / land‐cover change. Human driving forces include political, economic, cultural, and social attributes that often change across time and space. Remotely sensed imagery provides regional land‐change data for the Northern Piedmont, an ecoregion of the United States that continued to urbanize after 1970 through conversion of agricultural and forest land covers to developed uses. Eight major driving forces facilitated most of the land conversion; other drivers inhibited or slowed change. A synergistic web of drivers may be more important in understanding land change than individual drivers by themselves. 相似文献
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ROGER MASON 《Journal of Metamorphic Geology》1984,2(2):77-82
Abstract At Sulitjelma, Norway, there is a major inversion of metamorphic isograds beneath an inverted but undisrupted ophiolite. The flysch-like Furulund schist in which the inverted isograds occur is also inverted and the early folds in it are downward facing. The isograds cut across the axial surfaces of early folds and across the schistosity. These relationships are explained as the consequence of metamorphism during the progressive development of a large overfold. The inverted limb of the overfold is regarded as a major, thick, gently-dipping shear zone, separating the lower-grade, lower part of the Caledonian allochthon below from the higher-grade upper part of the allochthon above. The association between stratigraphical inversion, downward-facing of syn-schistosity folds and metamorphic inversion is explained by the progressive development of the shear zone. It is suggested that the presence of such shear zones is a common feature of orogenic belts formed by continental collision. 相似文献
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The equilibrium thermodynamics of the reaction:
And the equilibrium constant is composed of activities formulated using ideal mixing on sites. Consideration is given to the evaluation of uncertainties in pressures calculated using the geobarometer. Preliminary testing suggests that the geobarometer has considerable potential. Much wider testing is now required. 相似文献
And the equilibrium constant is composed of activities formulated using ideal mixing on sites. Consideration is given to the evaluation of uncertainties in pressures calculated using the geobarometer. Preliminary testing suggests that the geobarometer has considerable potential. Much wider testing is now required. 相似文献