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351.
It is presently widely accepted that the solar low p modes show asymmetric profiles when their power spectrum is analysed and that the fact of fitting symmetric profiles yields systematic effects in the obtained frequencies which could affect the results of inversions. In this paper the low p-mode profiles are analysed using wavelets to denoise the power spectra of the modes. This denoising method is applied both to artificial data generated by Kosovichev (the Hare and Hound exercise) and to real data obtained with the GOLF instrument. The asymmetries as well as the frequencies obtained are studied in both cases. The results show that although the obtained p-mode profiles present a slightly negative asymmetry, the use of symmetric profiles to fit the power spectra does not introduce any systematic effect in the obtained frequencies. 相似文献
352.
Sanz Pérez E 《Ground water》2001,39(2):203-209
Specific functions of distribution of the number of springs and of their contributions according to flow for each of nine lithological groups are established. These functions confirm the suitability of a general type of distribution (Sanz 1996), which is a borderline case of the lognormal distribution. The statistical methods proposed for the lithological types presented can be applied to any region if data on flow and lithology of the aquifers drained by springs are available. These methods have been applied to Spain, a representative region with varied geology, climate and topography; 71.2% of spring flow is supplied by limestones, 19.17% by alluvial sediments and marls, 6.7% by conglomerates and sandstones, and 3% by slates, plutonic rocks, quartzites, and other groups. Springs with discharge rates exceeding 2000 L/s exist only in limestones. The majority of springs with low flow occur in marls. If we consider springs with flow greater than 0.5 L/s, alluvial sediments, sandstones, marls, and limestones have the greatest density of springs per surface area, although the average flow varies greatly from one lithology to the next. The cumulative estimated discharge and the estimated number of springs depend upon the definition of the lower limit of flow. For example, total discharge is reduced by 30% if we eliminate all springs with flow lower than 0.5 L/min. 相似文献
353.
M. Déqué R. G. Jones M. Wild F. Giorgi J. H. Christensen D. C. Hassell P. L. Vidale B. Rockel D. Jacob E. Kjellström M. de. Castro F. Kucharski B. van den Hurk 《Climate Dynamics》2005,25(6):653-670
Four high resolution atmospheric general circulation models (GCMs) have been integrated with the standard forcings of the
PRUDENCE experiment: IPCC-SRES A2 radiative forcing and Hadley Centre sea surface temperature and sea-ice extent. The response
over Europe, calculated as the difference between the 2071–2100 and the 1961–1990 means is compared with the same diagnostic
obtained with nine Regional Climate Models (RCM) all driven by the Hadley Centre atmospheric GCM. The seasonal mean response
for 2m temperature and precipitation is investigated. For temperature, GCMs and RCMs behave similarly, except that GCMs exhibit
a larger spread. However, during summer, the spread of the RCMs—in particular in terms of precipitation—is larger than that
of the GCMs. This indicates that the European summer climate is strongly controlled by parameterized physics and/or high-resolution
processes. The temperature response is larger than the systematic error. The situation is different for precipitation. The
model bias is twice as large as the climate response. The confidence in PRUDENCE results comes from the fact that the models
have a similar response to the IPCC-SRES A2 forcing, whereas their systematic errors are more spread. In addition, GCM precipitation
response is slightly but significantly different from that of the RCMs. 相似文献
354.
355.
Julien Berger Olivier Féménias Nicolas Coussaert Jean-Claude C. Mercier Daniel Demaiffe 《Contributions to Mineralogy and Petrology》2007,153(5):557-575
Ultramafic and mafic xenoliths of magmatic origin, sampled in the Beaunit vent (northern French Massif Central), derive from
the Permian (257 Ma) Beaunit layered complex (BLC) that was emplaced at the crust-mantle transition zone (∼1 GPa). These plutonic
xenoliths are linked to a single fractional crystallisation process in four steps: peridotitic cumulates; websteritic cumulates;
Al-rich mafic cumulates (plagioclase, pyroxenes, garnet, amphibole and spinel) and finally low-Al mafic cumulates. This sequence
of cumulates can be related to the compositional evolution of hydrous Mg basaltic magma that evolved to high-Al basalt and
finally to andesitic basalt. Sr and Nd isotopic compositions confirm the co-genetic character of the various magmatic xenoliths
and argue for an enriched upper mantle source comparable to present mantle wedges above subduction zones. LILE, LREE and Pb
enrichment are a common feature of all xenoliths and argue for an enriched sub-alkaline transitional parental magma. The existence
of a Permian magma chamber at 30 km depth suggests that the low-velocity zone observed locally beneath the Moho probably does
not represent an anomalous mantle but rather a sequence of mafic/ultramafic cumulates with densities close to those of mantle
rocks. 相似文献
356.
Thermochemistry and melting properties of basalt 总被引:1,自引:0,他引:1
M. A. Bouhifd P. Besson P. Courtial C. Gérardin A. Navrotsky P. Richet 《Contributions to Mineralogy and Petrology》2007,153(6):689-698
The heat capacities of the liquid, glassy and crystalline phases of an alkali basalt have been determined from relative enthalpies
measured between 400 and 1,800 K. Values given by available models of calculation generally agree to within 2% of these results.
As derived from the new data and the enthalpy of vitrification measured at 973 K by oxide-melt drop solution calorimetry for
the same sample, the enthalpy of fusion of this basalt increases from 15.4 kJ/mol at 1,000 K to 33.6 kJ/mol at 1,800 K. Comparisons
between the enthalpies of fusion of basalt and model compositions confirm the small magnitude of the enthalpy of mixing between
the molten mineral components of the liquids. Minor variations in the chemical composition have only a small effect in the
heat capacity and the enthalpy of melting of basalt. The enthalpies of formation at 298 K from the oxides of the crystallized
and glass phases of this alkali basalt are −112.2 and −98.5 kJ/mol, respectively, for a gram formula weight based on one mole
of oxide components. 相似文献
357.
358.
André Strasser 《Swiss Journal of Geoscience》2007,100(3):407-429
Detailed investigation of facies and sedimentary structures reveals that, during the Middle Oxfordian to Late Kimmeridgian,
the shallow carbonate platform of the Swiss and French Jura Mountains recorded high-frequency sea-level fluctuations quite
faithfully. The cyclostratigraphic analysis within the established biostratigraphic and sequence-chronostratigraphic framework
implies that the resulting hierarchically stacked depositional sequences formed in tune with the orbital cycles of precession
(20 kyr) and eccentricity (100 and 400 kyr). The astronomical time scale presented here is based on the correlation of 19
platform sections and 4 hemipelagic sections from south-eastern France where good biostratigraphic control is available. The
cyclostratigraphic interpretation suggests that the interval between sequence boundaries Ox4 and Kim1 (early Middle Oxfordian
to earliest Kimmeridgian) lasted 3.2 myr and that the Kimmeridgian sensu gallico has a duration of 3.2 to 3.3 myr. The astronomical time scale proposed here is compared to time scales established by other
authors in other regions and the discrepancies are discussed. Despite these discrepancies, there is a potential to estimate
the durations of ammonite zones and depositional sequences more precisely and to better evaluate the rates of sedimentary,
ecological and diagenetic processes.
Editorial handling: Hanspeter Funk, Helmut Weissert, Stefan Bucher 相似文献
359.
360.
Hugues Raimbourg Bruno Goffé Laurent Jolivet 《Contributions to Mineralogy and Petrology》2007,153(1):1-28
Caledonian eclogite-facies metamorphism partially reworking Grenvillian granulite-facies anorthosite allows us to study the processes of garnet reequilibration at high pressure and to reconstruct the evolution of the unit near metamorphic peak conditions. Our results indicate that eclogite-facies metamorphism happened in two successive phases: first, inherited granulitic garnet was fractured and reequilibrated from their boundaries (crystal or fracture rims); then eclogite-facies minerals were crystallised in the fractures as overgrowths on inherited garnets. The reequilibration of inherited garnets is achieved through Fe2+Mg−1 exchange, whereas eclogite-facies garnets crystallised during the subsequent phase are notably richer in Ca than un- and re-equilibrated granulitic garnet. Pseudosection construction shows that this lack in Ca reequilibration cannot be related to variations in thermodynamic conditions (a
H2O, reacting system composition) between the two phases. From the compilation of the available data, the reequilibration of granulitic garnet seems to be controlled by the inefficient intra- and inter-granular transport properties of Ca compared to Fe2+ and Mg. While these kinetic factors confine garnet reequilibration to Fe2+Mg−1 exchange, the extent of reequilibration along this exchange vector is controlled by partitioning with adjacent omphacite. On the contrary to the diffusional reequilibration of granulitic garnet that lasted for several My according to our modelling of the diffusional relaxation, the strong compositional gradients between eclogite-facies and reequilibrated garnets, which are almost unaffected by diffusional reequilibration, provide evidence that rapid exhumation followed the crystallisation of eclogite-facies minerals. We propose that the movement reversal itself, from burial to exhumation, and associated deformation and fluid flow, triggered this crystallisation event. The resulting evolution near metamorphic peak conditions is therefore strongly asymmetrical: on the one hand, the prograde diffusional relaxation profiles indicate slow movement during the last stages of burial, whereas the unaffected retrograde overgrowth indicates fast exhumation rates. 相似文献