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161.
P. C. Rickwood M. Mathias J. C. Siebert 《Contributions to Mineralogy and Petrology》1968,19(4):271-301
The chemical compositions of garnets from 58 eclogite, 72 peridotite and 4 pyroxenite xenoliths in kimberlites have been estimated from their unit cell edge length and refractive indices. The samples studied were obtained from 17 kimberlite occurrences and include all those of known source which remain in the famous Williams (1932) collection which is stored at the University of Cape Town. Every suitable sample available to the authors has been examined.A gap in the range of garnet volume percentages occurs in the samples studied between approximately 15 and 30%. Garnet peridotites characteristically have <15% garnet and eclogites >30% garnet. Very rare exceptions occur. Our collection contains no eclogites with olivine and only one with orthopyroxene. All but two of the peridotite-pyroxenite group contain orthopyroxene. The garnets from the peridotites and pyroxenites plot on a pyrope-almandine-uvarovite triangle in a narrow band with a remarkably constant almandine/uvarovite ratio. Garnets from the eclogites are plotted on a pyrope-almandine-grossularite triangle and have a wide spread of compositions. These fall into 4 groups viz. eclogite I, eclogite II, kyanite eclogite and corundum eclogite.The reasons for the differences in garnet chemistry are considered and a tentative evolutionary scheme suggested by partial melting of the garnet peridotite which is assumed to occur in the upper mantle. Recent models of upper mantle composition and the genesis of garnet-bearing xenoliths in kimberlite are briefly and critically examined.S.A. UMP Publication No. 9. 相似文献
162.
Full-scale observations from two urban sites in Basel, Switzerland were analysed to identify the magnitude of different processes
that create, relocate, and dissipate turbulent kinetic energy (TKE) in the urban atmosphere. Two towers equipped with a profile
of six ultrasonic anemometers each sampled the flow in the urban roughness sublayer, i.e. from street canyon base up to roughly
2.5 times the mean building height. This observational study suggests a conceptual division of the urban roughness sublayer
into three layers: (1) the layer above the highest roofs, where local buoyancy production and local shear production of TKE
are counterbalanced by local viscous dissipation rate and scaled turbulence statistics are close to to surface-layer values;
(2) the layer around mean building height with a distinct inflexional mean wind profile, a strong shear and wake production
of TKE, a more efficient turbulent exchange of momentum, and a notable export of TKE by transport processes; (3) the lower
street canyon with imported TKE by transport processes and negligible local production. Averaged integral velocity variances
vary significantly with height in the urban roughness sublayer and reflect the driving processes that create or relocate TKE
at a particular height. The observed profiles of the terms of the TKE budget and the velocity variances show many similarities
to observations within and above vegetation canopies. 相似文献
163.
Summary The land surface model SEWAB (Surface Energy and Water Balance) is designed to be coupled to both, atmospheric and hydrological
models. Its application in mid and high latitudes requires the inclusion of freezing and thawing processes within the soil
and the accumulation and ablation of a snow cover. These winter processes are parameterised with a minimum number of empirical
formulations in order to assure reasonable computation times for an application in climate and sensitivity studies yet accounting
for all important processes. Meteorological forcing data and measurements of snow depth, soil temperature and liquid soil
water content at two locations in the mid-west of North America are used to test the model. Generally the simulated snow depth
matches the measurements, remaining differences in snow depth can be explained by uncertainties in snow density, blowing snow
and errors in precipitation measurements. The simulated soil temperature and liquid soil water content compare well with the
measurements, showing the isolating effect of the snow cover.
Received August 25, 2000 Revised January 19, 2001 相似文献