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21.
Osumilite is reported in Palaeoproterozoic Al–Mg‐rich granulites from the Khanfous area (Tekhamalt, In Ouzzal, Hoggar, Algeria). The main peak assemblages are osumilite + sapphirine + biotite + orthopyroxene + sillimanite and osumilite + orthopyroxene + sillimanite + quartz ± biotite (±K‐feldspar) in silica‐deficient and silica‐saturated granulites respectively. Osumilite coexists with F‐rich biotite (XF ≈ 0.6). The observed microstructures, the mass balance of metamorphic reactions and P–T pseudosections modelled for bulk‐rock and reaction‐microdomain compositions indicate a clockwise P–T metamorphic evolution at ultrahigh temperatures, without substantial post‐peak deformation. The peak P–T conditions recorded by the osumilite‐bearing assemblages are 8.5–9.0 kbar and 930–980 °C. During retrogression, osumilite was partially or totally replaced by fine‐grained pseudomorphs of cordierite + orthopyroxene + K‐feldspar + quartz at ~7 kbar and ~850 °C. This study confirms that osumilite can occur only in Mg‐rich metamorphic rocks that experienced ultrahigh‐temperature metamorphism under anhydrous conditions. In the presence of a hydrous fluid, it is replaced, even at high temperatures, by cordierite‐bearing assemblages. This important feature explains the rarity of osumilite in granulite facies rocks and its common replacement by cordierite + orthopyroxene + K‐feldspar + quartz pseudomorphs. The peak conditions suggest that a delamination of the lithospheric mantle underneath the In Ouzzal crust brought the asthenosphere close to the Mohorovi?i? discontinuity. 相似文献
22.
One way to address the assessment of strategies to control wave overtopping at seawalls and related coastal defence structures is to make use of Cost-Benefit Analysis. The institutional context in which Cost-Benefit Analysis takes place influences decisions on the types of values that are taken into consideration and the subsequent selection of valuation methods. We suggest to consider Cost-Benefit Analysis in a broad institutional framework when decisions are to be made on coastal defence strategies. It is argued that the institutional context provides the rules of the game on how a balance can be found between social, economic and ecologic functions of projects that protect societies against overtopping. 相似文献
23.
The Law of the Sea Convention constrains regional environmental regimes, especially with respect to navigation beyond the territorial sea. Existing soft-law institutions, notably the Arctic Council, have already strengthened environmental governance in the region by (1) improving the knowledge base; (2) preparing practical guidance on risk reduction; (3) highlighting in broader regulatory fora the Arctic dimension of problems like long-range transported hazardous compounds; and (4) supporting the capacity of Arctic states to implement existing commitments. None of those functions would be much enhanced by a legally binding Arctic environmental regime. The political impediments to reaching circumpolar agreement on a single comprehensive legal regime would suggest a flexible approach to norm building that seeks productive interplay with existing institutions. 相似文献
24.
H. M. Tovmassian R. KH. Hovhannessian R. A. Epremian D. Huguenin Yu. M. Khodjayants M. N. Krmoyan A. L. Kashin A. P. Alexandrov Yu. V. Romanenko 《Astrophysics and Space Science》1992,188(2):217-231
The results of observations of 159 stars at 1640 Å in Puppis made with the space telescope Glazar are presented. It is shown that the observed stars are members of different groups of stars situated at distances of about 120, 370, 700, 1250, 2400, and 4000 pc. The last two groups belong to the Pup OB1 and the Pup OB2 stellar associations.There is relatively little absorption in the observed region. The absorbing matter is mainly concentrated in small clouds.It is suggested that three stars — CP –27°4197, HD 60479, and HD 61672-are embedded in a dust envelope and that the star HD 60057 has a hot subdwarf companion.Forty-four of the observed stars are new OB or early A-type stars, spectral types of which were not known. 相似文献
25.
介绍梅山铁矿、凤凰山铁矿的尾矿特征,探讨利用澳大利亚新型重选设备进行铁矿尾矿再选的可能途径。对于降低铁矿山尾矿库存量,保护环境,合理利用资源,具有一定的意义。 相似文献