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11.
Garnets from recrystallized, staurolite- and kyanite-bearing mica schists from the central Saualpe basement, representing the host rocks of the type-locality eclogites, give concordant Sm–Nd garnet–whole-rock isochron ages between 88.5±1.7 and 90.9±0.7 Ma. The millimetre-sized, mostly inclusion-free grains show fairly homogeneous element profiles with pyrope contents of 25–27%. Narrow rims with an increase in Fe and Mn and a decrease in Mg document minor local re-equilibration during cooling. According to phengite geothermobarometry, peak metamorphic conditions at 90 Ma were close to 20 kbar and 680 °C and similar to those recorded by the eclogites. The garnet rims record about 575 °C/7 kbar for the final stages of metamorphism. A phengitic garnet–mica schist, sampled at the immediate contact with the Gertrusk eclogite, gave a garnet–whole-rock Sm–Nd age of 94.0±2.7 Ma.
Garnet porphyroclasts separated from a pegmatite–mylonite of the Koralpe plattengneiss near Stainz are unzoned and show spessartine contents of 15%. Composition and Sm–Nd ages of close to 260 Ma point to a magmatic origin for these garnets.
The garnet data from the Saualpe document an intense Alpine metamorphism for this part of the Austroalpine basement. The mica schists recrystallized during decompression and rapid exhumation, at the final stages of and immediately following a high- P event. The Koralpe data show that high Alpine temperatures did not reopen the Sm–Nd isotope system, implying a closure temperature in excess of c . 600 °C for this isotopic system in garnet. 相似文献
Garnet porphyroclasts separated from a pegmatite–mylonite of the Koralpe plattengneiss near Stainz are unzoned and show spessartine contents of 15%. Composition and Sm–Nd ages of close to 260 Ma point to a magmatic origin for these garnets.
The garnet data from the Saualpe document an intense Alpine metamorphism for this part of the Austroalpine basement. The mica schists recrystallized during decompression and rapid exhumation, at the final stages of and immediately following a high- P event. The Koralpe data show that high Alpine temperatures did not reopen the Sm–Nd isotope system, implying a closure temperature in excess of c . 600 °C for this isotopic system in garnet. 相似文献
12.
CH. HEMON 《Geophysical Prospecting》1969,17(2):165-181
In the case of simple time series it is shown that prediction operators can be considered as deconvolution operators which are easily obtained. These operators possess the special feature of having a minimum phase, and their spectrum modulus represents, with a good dynamic range, the reciprocal of the square root of the modulus of the original autocorrelation spectrum. A generalization of the simple time series theory to the functions of two independent variables is possible in as much as, on a given section, the application of the multiple time series method enables the function of time and distance variables to have well-defined statistical properties; it is necessary, in particular, that the processes involved are stationary with respect to the two independent variables. In the case of multiple time series the application of the Prediction Theory permits greater uniformity of the traces because it enhances the events which show a good correlation between traces and, on the other hand, tends to minimize the random events which cannot be correlated between traces. The signal-to-noise ratio is thus increased to a great extent. 相似文献
13.
Metallogenesis of the late Pan-African gold-bearing East Ouzzal shear zone (Hoggar, Algeria) 总被引：1，自引：0，他引：1
CH. MARIGNAC A. SEMIANI S. FOURCADE M.-C. BOIRON J.-L. JORON J.-R. KIENAST J.-J. PEUCAT 《Journal of Metamorphic Geology》1996,14(6):783-801
In the W Hoggar (Algeria), the major transcurrent N–S East Ouzzal shear zone (EOSZ) hosts several world-class gold deposits over a 100-km length. The late Pan-African EOSZ separates two contrasting Precambrian domains: the Archaean In Ouzzal block to the west (orthogneisses with subordinate metasediments, reworked and granulitized in the c. 2 Ga Eburnean event) and a Middle Proterozoic block to the east (again orthogneisses and metasediments, involved in the c. 600 Ma Pan-African event). The EOSZ is a mylonite belt, 1–3 km wide, with a 50-m-wide ultramylonite belt hosting numerous quartz veins and lenses (giant hydrothermal quartz system) associated with a quartz-sericite-pyrite-carbonate (beresite) alteration. These hydrothermal events occurred under ductile (evolving towards brittle) conditions, between 500 and 300 MPa, at 500–300°C, with aqueous-carbonic fluids derived both from underlying devolatilized metamorphic rocks and a mantle source, as recorded by stable (C, O) isotope data. No gold mineralization was associated with these typical mesothermal events. Following a pressure drop (to 130 MPa), related to the inception of extensional tectonics, the EOSZ was later percolated by a new set of hydrothermal fluids, evolved from basinal waters that deeply penetrated into the In Ouzzal basement. These fluids were Ca-bearing brines (up to 25% wt. eq. NaCl), characterized by high δD (-9 to + 18‰ range), mobilized by the thermal energy released by the late Pan-African granite magmatism (Taourirt granites). As demonstrated by Pb isotope data, the brines leached Au from the In Ouzzal granulites (which contain 3 ppb Au). Fluid inclusion studies indicate that gold was deposited from these brines in the EOSZ at a depth of c. 5 km, due to mixing and cooling with descending diluted fluids. 相似文献
14.
15.
为验证 CFRP板条嵌入式加固方法对提升十字形 RC框架节点抗震性能的有效性,开展了1 个 CFRP板条嵌入式加固节点和1个对比节点的拟静力试验研究.试验结果表明:在核心区及相邻梁端嵌入 CFRP板条可起到类似箍筋的抗剪作用,使得节点由核心区剪切破坏转变为梁端受弯破坏,且梁铰得到转移;构件抗震性能明显提升,承载力和延性分别提高了16．3%和13．7%.同时, 利用 ABAQUS建立试验数据验证的有限元模型,并对节点主要加固设计参数进行影响分析.结果表明,节点承载力随着 CFRP板条面积的增大、板条间距的减小和基体混凝土强度的提高而提高.所提节点加固方法体现出塑性铰转移的抗震设计理念,同时提高核心区抗剪强度和梁端的抗弯强度,可用于 RC节点的抗震加固. 相似文献
16.
N. Voglis M. Harsoula CH. Efthymiopoulos 《Celestial Mechanics and Dynamical Astronomy》2000,78(1-4):265-278
As it is known, a good number of galaxies are observed to have counterrotating cores. A popular scenario to explain the formation of such galaxies is based on a secondary process of merging of galaxies with their satellites, or gas infall, or merger events between galaxies. An alternative mechanism, proposed by Voglis et al., 1991, and by Harsoula and Voglis 1998, could also be responsible for the formation of these galaxies directly from cosmological initial conditions (direct scenario). The novel mechanism was demonstrated by using quiet cosmological initial conditions in N-body simulations. In the present paper we extend our N-body simulations using clumpy initial conditions and show that this mechanism still works to create counterrotating galaxies. Counterrotation is a result of the considerable amount of memory of initial conditions surviving for times comparable to the Hubble time, despite the large degree of instability of individual orbits and the dramatic redistribution and mixing of the particles in phase space. We show, for example, that the particles remember, in a statistical sense, not only their distance from the center of mass (memory of energy), but also the initial orientation of their position relative to the direction of an external tidal field, which determines the sign and the amount of angular momentum that is transferred to the particles of the system. 相似文献
17.
ABSTRACT From data obtained at stations set up in Chad, the Central African Republic and Congo-Brazzaville, stretching from the desert to the equatorial zone, it has been possible to compare measurements of evapotranspiration and of evaporation with results obtained by using the energy-balance method. Several difficulties arise in these comparisons since the scale of the measurements (small evaporating surfaces) is generally different from that of the climatic characteristics on which evaporation is dependent. After proposing a model to resolve this problem and fitting the empirical coefficients of Penman's formula, the author has applied this formula to some results derived for stations in Congo-Brazzaville; the potential evapotranspiration calculated in this way is in good agreement with water balance data. At these stations the evapotranspiration energy may be a constant percentage of global short-wave radiation. Finally, the energy-balance method has been used at Brazzaville to measure the actual evapotranspiration over grass during the dry season. The result is that actual and potential evapotranspiration were found to be closely related. These results indicate the importance of solar readiation in the field of hydrometeorology. 相似文献
18.
R T RATHEESH KUMAR TANMAY K MAJI SURESH CH KANDPAL D SENGUPTA RAJESH R NAIR 《Journal of Earth System Science》2011,120(3):447-458
Global estimates of the elastic thickness (Te) of the structure of passive continental margins show wide and varying results
owing to the use of different methodologies. Earlier estimates of the elastic thickness of the North Atlantic passive continental
margins that used flexural modelling yielded a Te value of ~20–100 km. Here, we compare these estimates with the Te value
obtained using orthonormalized Hermite multitaper recovered isostatic coherence functions. We discuss how Te is correlated
with heat flow distribution and depth of necking. The E–W segment in the southern study region comprising Nova Scotia and
the Southern Grand Banks show low Te values, while the zones comprising the NE–SW zones, viz., Western Greenland, Labrador,
Orphan Basin and the Northern Grand Bank show comparatively high Te values. As expected, Te broadly reflects the depth of
the 200–400°C isotherm below the weak surface sediment layer at the time of loading, and at the margins most of the loading
occurred during rifting. We infer that these low Te measurements indicate Te frozen into the lithosphere. This could be due
to the passive nature of the margin when the loads were emplaced during the continental break-up process at high temperature
gradients. 相似文献
19.
It is usually believed that we know everything to be known for any separable Hamiltonian system, i.e. an integrable system
in which we can separate the variables in some coordinate system (e.g. see Lichtenberg and Lieberman 1992, Regular and Chaotic Dynamics, Springer). However this is not always true, since through the separation the solutions may be found only up to quadratures,
a form that might not be particularly useful. A good example is the two-fixed-centers problem. Although its integrability
was discovered by Euler in the 18th century, the problem was far from being considered as completely understood. This apparent
contradiction stems from the fact that the solutions of the equations of motion in the confocal ellipsoidal coordinates, in
which the variables separate, are written in terms of elliptic integrals, so that their properties are not obvious at first
sight. In this paper we classify the trajectories according to an exhaustive scheme, comprising both periodic and quasi-periodic
ones. We identify the collision orbits (both direct and asymptotic) and find that collision orbits are of complete measure
in a 3-D submanifold of the phase space while asymptotically collision orbits are of complete measure in the 4-D phase space.
We use a transformation, which regularizes the close approaches and, therefore, enables the numerical integration of collision
trajectories (both direct and asymptotic). Finally we give the ratio of oscillation period along the two axes (the ‘rotation
number’) as a function of the two integrals of motion.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
In order to evaluate the use of satellite (moderate resolution imaging spectroradiometer: MODIS) and ground-measured (hyperspectral spectrometer and broadband micrometeorological sensors) normalized difference vegetation index (NDVI), this study compares NDVI derived from five experimental (FLUXNET) field sites (grassland, winter wheat, corn, spruce, and beech) in Germany in June 2006 and April-September 2007. In addition, the spatial variability of ground radiation measured within one specific land-use class (for grass and winter wheat) was investigated to analyze the accuracy of the FLUXNET tower values. Furthermore, the angular dependence of spectrometer values on viewing angles was determined in order to enhance the spatial representativeness of spectrometer measurements which, especially above trees, are affected by soil parts and the tower structure when measured in nadir. The best agreement between the satellite- and ground-measured NDVI was found for winter wheat (2006) with values from 0.79–0.88 followed by grass (2006), showing NDVI values between 0.71 and 0.86. The spatial variability of NDVI within one land-use type was lower than the differences caused by the different NDVI determination methods. Above more open canopies (corn, beech), spectrometer measurements with 60° viewing angle in solar plane direction were found to better correspond to satellite-derived NDVI. Together with broadband NDVI, our ground-based results can complement satellite-derived NDVI. 相似文献