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《Chemie der Erde / Geochemistry》2015,75(2):155-183
The howardite, eucrite and diogenite (HED) clan of meteorites are ultramafic and mafic igneous rocks and impact-engendered fragmental debris derived from a thoroughly differentiated asteroid. Earth-based telescopic observation and data returned from vestan orbit by the Dawn spacecraft make a compelling case that the asteroid (4) Vesta is the parent asteroid of HEDs, although this is not universally accepted. Diogenites are petrologically diverse and include dunitic, harzburgitic and noritic lithologic types in addition to the traditional orthopyroxenites. Diogenites form the lower crust of Vesta. Cumulate eucrites are gabbroic rocks formed by accumulation of pigeonite and plagioclase from a mafic magma at depth within the crust, while basaltic eucrites are melt compositions that likely represent shallow-level dikes and sills, and flows. Some basaltic eucrites are richer in incompatible trace elements compared to most eucrites, and these may represent mixed melts contaminated by partial melts of the mafic crust. Differentiation occurred within a few Myr of formation of the earliest solids in the Solar System. Evidence from oxygen isotope compositions and siderophile element contents favor a model of extensive melting of Vesta forming a global magma ocean that rapidly (period of a few Myr) segregated and crystallized to yield a metallic core, olivine-rich mantle, orthopyroxene-rich lower crust and basaltic upper crust. The igneous lithologies were subjected to post-crystallization thermal processing, and most eucrites show textural and mineral-compositional evidence for metamorphism. The cause of this common metamorphism is unclear, but may have resulted from rapid burial of early basalts by later flows caused by high effusion rates on Vesta. The observed surface of Vesta is covered by fragmental debris resulting from impacts, and most HEDs are brecciated. Many eucrites and diogenites are monomict breccias indicating a lack of mixing. However, many HEDs are polymict breccias. Howardites are the most thoroughly mixed polymict breccias, yet only some of them contain evidence for residence in the true regolith. Based on the numbers of meteorites, compositions of howardites, and models of magma ocean solidification, cumulate eucrites and their residual ferroan mafic melts are minor components of the vestan crust. 相似文献
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Kriging with imprecise (fuzzy) variograms. I: Theory 总被引：2，自引：0，他引：2
Imprecise variogram parameters are modeled with fuzzy set theory. The fit of a variogram model to experimental variograms is often subjective. The accuracy of the fit is modeled with imprecise variogram parameters. Measurement data often are insufficient to create good experimental variograms. In this case, prior knowledge and experience can contribute to determination of the variogram model parameters. A methodology for kriging with imprecise variogram parameters is developed. Both kriged values and estimation variances are calculated as fuzzy numbers and characterized by their membership functions. Besides estimation variance, the membership functions are used to create another uncertainty measure. This measure depends on both homogeneity and configuration of the data. 相似文献
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Kriging with imprecise (fuzzy) variograms. II: Application 总被引：2，自引：0，他引：2
The geostatistical analysis of soil liner permeability is based on 20 measurements and imprecise prior information on nugget effect, sill, and range of the unknown variogram. Using this information, membership functions for variogram parameters are assessed and the fuzzy variogram is constructed. Both kriging estimates and estimation variances are calculated as fuzzy numbers from the fuzzy variogram and data points. Contour maps are presented, indicating values of the kriged permeability and the estimation variance corresponding to selected membership values called levels. 相似文献
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A new family of planthoppers Fulgoromorpha from the Lower Jurassic of southern China is described to comprise Qiyangiricania cesta Lin, 1986. The new family differs in venation pattern from the other Jurassic representatives of Fulgoroidea, presenting particular model of tegmen venation, not found among extinct and recent planthoppers. The Mesozoic stage of Fulgoroidea evolution is discussed. The extinct taxon Ricaniites fulgens (Brodie, 1845) from the Purbeck of United Kingdom is excluded from the Hemiptera. 相似文献
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A new family of planthoppers Fulgoromorpha from the Lower Jurassic of southern China is described to comprise Qiyangiricania cesta Lin, 1986. The new family differs in venation pattern from the other Jurassic representatives of Fulgoroidea, presenting particular model of tegmen venation, not found among extinct and recent planthoppers. The Mesozoic stage of Fulgoroidea evolution is discussed. The extinct taxon Ricaniites fulgens (Brodie, 1845) from the Purbeck of United Kingdom is excluded from the Hemiptera. 相似文献
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《International Journal of Earth Sciences》1998,87(2):247-248
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Joe Alan Artz 《Geoarchaeology》1993,8(5):431-433