To drive an atmospheric general circulation model (AGCM), land surface boundary conditions like albedo and morphological roughness, which depend on the vegetation type present, have to be prescribed. For the late Quaternary there are some data available, but they are still sparse. Here an artificial neural network approach to assimilate these paleovegetation data is investigated. In contrast to a biome model the relation between climatological parameters and vegetation type is not based on biological knowledge but estimated from the available vegetation data and the AGCM climatology at the corresponding locations. For a test application, a data set for the modern vegetation reduced to the amount of data available for the Holocene climate optimum (about 6000 years B.P.) is used. From this, the neural network is able to reconstruct the complete global vegetation with a kappa value of 0.56. The most pronounced errors occur in Australia and South America in areas corresponding to large data gaps. 相似文献
In this paper, we have analyzed neutron spectroscopy data gathered by the High Energy Neutron Detector (HEND) instrument onboard Mars Odyssey for comparison of polar regions. It is known that observation of the neutron albedo of Mars provides important information about the distribution of water-ice in subsurface layers and about peculiarities of the CO2 seasonal cycle. It was found that there are large water-rich permafrost areas with contents of up to ∼50% water by mass fraction at both the north and south Mars polar regions. The water-ice layers at high northern latitudes are placed close to the surface, but in the south they are covered by a dry and relatively thick (10-20 cm) layer of soil. Analysis of temporal variations of neutron flux between summer and winter seasons allowed the estimation of the masses of the CO2 deposits which seasonally condense at the polar regions. The total mass of the southern seasonal deposition was estimated as 6.3×1015 kg, which is larger than the total mass of the seasonal deposition at the north by 40-50%. These results are in good agreement with predictions from the NASA Ames Research Center General Circulation Model (GCM). But, the dynamics of the condensation and sublimation processes are not quite as consistent with these models: the peak accumulation of the condensed mass of CO2 occurred 10-15 degrees of Ls later than is predicted by the GCM. 相似文献
Low pressure partial melting of basanitic and ankaramitic dykes gave rise to unusual, zebra-like migmatites, in the contact aureole of a layered pyroxenite–gabbro intrusion, in the root zone of an ocean island (Basal Complex, Fuerteventura, Canary Islands). These migmatites are characterised by a dense network of closely spaced, millimetre-wide leucocratic segregations. Their mineralogy consists of plagioclase (An32–36), diopside, biotite, oxides (magnetite, ilmenite), +/− amphibole, dominated by plagioclase in the leucosome and diopside in the melanosome. The melanosome is almost completely recrystallised, with the preservation of large, relict igneous diopside phenocrysts in dyke centres. Comparison of whole-rock and mineral major- and trace-element data allowed us to assess the redistribution of elements between different mineral phases and generations during contact metamorphism and partial melting.
Dykes within and outside the thermal aureole behaved like closed chemical systems. Nevertheless, Zr, Hf, Y and REEs were internally redistributed, as deduced by comparing the trace element contents of the various diopside generations. Neocrystallised diopside – in the melanosome, leucosome and as epitaxial phenocryst rims – from the migmatite zone, are all enriched in Zr, Hf, Y and REEs compared to relict phenocrysts. This has been assigned to the liberation of trace elements on the breakdown of enriched primary minerals, kaersutite and sphene, on entering the thermal aureole. Major and trace element compositions of minerals in migmatite melanosomes and leucosomes are almost identical, pointing to a syn- or post-solidus reequilibration on the cooling of the migmatite terrain i.e. mineral–melt equilibria were reset to mineral–mineral equilibria. 相似文献
The Mordor Alkaline Igneous Complex (MAIC) is a composite intrusion comprising a body of syenite and a funnel-shaped layered
mafic–ultramafic intrusion of lamprophyric parentage, the Mordor Mafic–Ultramafic Intrusion or MMUI. The MMUI is highly unusual
among intrusions of lamprophyric or potassic parentage in containing primary magmatic platinum-group element (PGE)-enriched
sulfides. The MMUI sequence consists largely of phlogopite-rich pyroxenitic cumulates, with an inward dipping conformable
layer of olivine-bearing cumulates divisible into a number of cyclic units. Stratiform-disseminated sulfide accumulations
are of two types: disseminated layers at the base of cyclic units, with relatively high PGE tenors; and patchy PGE-poor disseminations
within magnetite-bearing upper parts of cyclic units. Sulfide-enriched layers at cycle bases contain anomalous platinum group
element contents with grades up to 1.5 g/t Pt+Pd+Au over 1-m intervals, returning to background values of low parts per billion
(ppb) on a meter scale. They correspond to reversals in normal fractionation trends and are interpreted as the result of new
magma influxes into a continuously replenished magma chamber. Basal layers have decoupled Cu and PGE peaks reflecting increasing
PGE tenors up-section, due to increasing R factors during the replenishment episode, or progressive mixing of between resident PGE-poor magma and more PGE-enriched
replenishing magma. The presence of PGE enriched sulfides in cumulates from a lamprophyric magma implies that low-degree partial
melts do not necessarily leave sulfides and PGEs in the mantle restite during partial melting.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
文章通过详细的野外地质调查和系统的岩石化学、稀土元素、微量元素及硅、氧同位素等研究,探讨了羊蹄子山-磨石山钛矿区无矿白色硅质岩和富钛硅质岩的成因及形成地质构造环境。研究结果表明,呈厚层状产出的无矿白色硅质岩具较高的SiO2、Al2O3含量及Al/(Al Fe Mn)、Al2O3/(Al2O3 Fe2O3)比值,稀土元素总量很低,其北美页岩标准化配分模式为向右倾的曲线,无明显铈异常和铕异常,表明其形成于受陆源影响的大陆边缘构造环境;赋矿岩系中薄层状富钛硅质岩的TiO2、Fe2O3、Cu、V含量较高,但Al/(Al Fe Mn)、Al2O3/(Al2O3 Fe2O3)比值较低,稀土元素总量较高,北美页岩标准化曲线为明显左倾型-平坦型,具弱的负铈异常,表明其形成于洋脊及附近环境。两种硅质岩的δ30Si值为变化较小的负值,与热水沉积和某些生物成因硅质岩的硅同位素组成相似,两者的δ18O值范围和平均值均相似。两类硅质岩的成因及形成构造环境不同,富钛硅质岩的地球化学特征表明,该矿床的形成与本区元古宙海底火山热液喷流作用有关。 相似文献