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961.
Geostatistical regionalization of glacial aquitard thickness in northwestern Germany, based on fuzzy kriging 总被引:1,自引:0,他引:1
In many instances hydrogeological parameters obtained by conventional methods for selected localities within an aquifer or an aquitard are not sufficient for adequate regionalization at the scale of the entire layer. Here, we demonstrate an application of the fuzzy kriging method in regionalization of hydrogeological data, in which the set of conventional, crisp values is supplemented by imprecise information subjectively estimated by an expert. It is believed that such an approach eventually may reflect the real-world conditions more closely than a traditional crisp-value approach, because the former does not impose exactness artificially on phenomena which are diffuse by their nature. Spatial interpolation was done for the thickness of one of the major aquitards (till and glaciolacustrine clay) in northwestern Germany. The dataset consists of 329 crisp values from boreholes supplemented by 172 imprecise values defined as fuzzy numbers. It is demonstrated that the reliability of regionalization was higher, compared to regionalization performed with the crisp dataset only. Fuzzy kriging was performed with FUZZEKS (Fuzzy Evaluation and Kriging System) developed at the Ecosystem Research Center at the University of Kiel. 相似文献
962.
Using surface charts at 0330GMT, the movement of the monsoon trough during the months June to September 1990 at two fixed
longitudes, namely 79°E and 85°E, is studied. The probability distribution of trough position shows that the median, mean
and mode occur at progressively more northern latitudes, especially at 85°E, with a pronounced mode that is close to the northern-most
limit reached by the trough. A spectral analysis of the fluctuating latitudinal position of the trough is carried out using
FFT and the Maximum Entropy Method (MEM). Both methods show significant peaks around 7.5 and 2.6 days, and a less significant
one around 40–50 days. The two peaks at the shorter period are more prominent at the eastern longitude. MEM shows an additional
peak around 15 days. A study of the weather systems that occurred during the season shows them to have a duration around 3
days and an interval between systems of around 9 days, suggesting a possible correlation with the dominant short periods observed
in the spectrum of trough position. 相似文献
963.
964.
The Banded Hematite Jasper Formation within the Iron Ore Supergroup of the Singhbhum Craton in eastern India comprises fine alternating layers of jasper and specularite. It was deposited at 3000 Ma and deformed by a mobile episode at 2700 Ma. Hematite pigment (<1 μm) mixed with cryptocrystalline silica and specularite (> 10 μm) is chiefly responsible for red to brown rhythmic bands in the hematite jasper facies although thermomagnetic study also shows that minor amounts (1–2%) of magnetite are present. Palaeomagnetic study identifies a dual polarity remanence resident in hematite (D/I = 283/60°, α95 = 12°) which predates deformation. Studies of the fabric of magnetic susceptibility and rock magnetic results suggest a diagenetic origin for this magnetisation with the hematite formed from oxidation of primary magnetite. The palaeopole (32°E, 24°N, dp/dm = 14/18°) records the earliest post-metamorphic magnetisation event in the Orissa Craton. A minimum apparent polar wander motion of the Orissa-Singhbhum craton of through 80° is identified during Late Archaean times (2900-2600 Ma). 相似文献
965.
966.
Time-dependent behaviour of deep clays 总被引:1,自引:0,他引:1
The time-dependent behaviour of deep saturated clays is related both to the effects of hydraulic diffusion and of viscosity. In this paper, we present first, by means of an experimental approach, the main features of the mechanical properties of deep clays. Then, we study the effects of these specific behaviours on the time-dependent behaviour of underground structures. We present theoretical and numerical investigations of the effects of pore pressure diffusion resulting from a tunnel excavation in a poroplastic or poroviscoplastic medium. Finite-element calculations show that the time-dependent convergence of the tunnel wall is non negligible. Then, we focus on the behaviour of a cylindrical thermal source buried in a deep clay.
Coupling effects between thermal, hydraulic and mechanical behaviours are very important in soft and low permeable deep clays (saturated compressible clays with high porosity). We show in particular that the displacements and the stresses are very sensitive to the constitutive model. Irreversible behaviour may be traduced by appearance of residual stresses within the rockmass. 相似文献
967.
Kusuma G. Rao V. N. Lykossov A. Prabhu S. Sridhar E. Tonkacheyev 《Journal of Earth System Science》1996,105(3):227-260
An attempt has been made here to study the sensitivity of the mean and the turbulence structure of the monsoon trough boundary
layer to the choice of the constants in the dissipation equation for two stations Delhi and Calcutta, using one-dimensional
atmospheric boundary layer model withe-ε turbulence closure. An analytical discussion of the problems associated with the constants of the dissipation equation is
presented. It is shown here that the choice of the constants in the dissipation equation is quite crucial and the turbulence
structure is very sensitive to these constants. The modification of the dissipation equation adopted by earlier studies, that
is, approximating the Tke generation (due to shear and buoyancy production) in theε-equation by max (shear production, shear + buoyancy production), can be avoided by a suitable choice of the constants suggested
here. The observed turbulence structure is better simulated with these constants. The turbulence structure simulation with
the constants recommended by Aupoixet al (1989) (which are interactive in time) for the monsoon region is shown to be qualitatively similar to the simulation obtained
with the constants suggested here, thus implying that no universal constants exist to regulate dissipation rate.
Simulations of the mean structure show little sensitivity to the type of the closure parameterization betweene-l ande-ε closures. However the turbulence structure simulation withe-ε. closure is far better compared to thee-l model simulations. The model simulations of temperature profiles compare quite well with the observations whenever the boundary
layer is well mixed (neutral) or unstable. However the models are not able to simulate the nocturnal boundary layer (stable)
temperature profiles. Moisture profiles are simulated reasonably better. With one-dimensional models, capturing observed wind
variations is not up to the mark. 相似文献
968.
The age and thermal history of Cerro Rico de Potosi, Bolivia 总被引:1,自引:0,他引:1
C. G. Cunningham R. E. Zartman E. H. McKee R. O. Rye C. W. Naeser O. Sanjinés V G. E. Ericksen F. Tavera V 《Mineralium Deposita》1996,31(5):374-385
Cerro Rico de Potosi, Bolivia, is the world’s largest silver deposit and has been mined since the sixteenth century for silver,
and for tin and zinc during the twentieth century, together with by-product copper and lead. The deposit consists primarily
of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and
explosion breccia. The deposit is compositionally and thermally zoned, having a core of cassiterite, wolframite, bismuthinite,
and arsenopyrite surrounded by a peripheral, lower-temperature mineral assemblage consisting principally of sphalerite, galena,
lead sulfosalt, and silver minerals. The low-temperature assemblage also was superimposed on the high-temperature assemblage
in response to cooling of the main hydrothermal system. Both the dacite dome and the ore fluids were derived from a larger
magmatic/hydrothermal source at depth. The dome was repeatedly fractured by recurrent movement on the fault system that guided
its initial emplacement. The dome was extruded at 13.8±0.2 Ma (2σ), based on U-Th-Pb dating of zircon. Mineralization and
alteration occurred within about 0.3 my of dome emplacement, as indicated by a 40Ar/39Ar date of 13.76±0.10 Ma (1σ) for sericite from the pervasive quartz-sericite-pyrite alteration associated with the main-stage,
high-temperature, mineralization. The last thermal event able to reset zircon fission tracks occurred no later than 12.5±1.1 Ma
(1σ), as indicated by fission-tract dating. Minor sericite, and magmatic-steam alunite veins, were episodically formed around
11 Ma and between 8.3 and 5.7 Ma; the younger episodes occurring at the time of extensional fracturing at Cerro Rico and widespread
volcanism in the adjacent Los Frailes volcanic field. None of these younger events appear to be significant thermal/mineralizing
events; the exceptionally flat thermal release pattern of 39Ar from sericite and the results of the fission-tract dating of zircon show that none of the younger events was hot enough,
and lasted long enough, to cause significant loss of Ar or annealing of zircon fission tracks. U-Th-Pb dating of zircon cores
indicates a Precambrian progenitor for some zircons, and REE analyses of dated samples of hydrothermally altered dacite show
the presence of a prominent positive Eu anomaly, which constrains interpretations of the origin and evolution of the magmatic/hydrothermal
system.
Received: 14 October 1995/Accepted: 29 January 1996 相似文献
969.
Ordering and exsolution processes in Or-rich alkali feldspar megacrysts from the Eldzhurtinskiy granite (Caucasus) 总被引:3,自引:0,他引:3
G. Witt-Eickschen C. Evangelakakis H. A. Seck H. Kroll A. G. Gurbanov 《Contributions to Mineralogy and Petrology》1996,124(1):71-81
The extremely young (2.5 Ma) I-type Eldzhurtinskiy granite complex (Central Caucasus) is uniform with respect to modal composition,
major and trace element chemistries of bulk rocks and mineral phases. In contrast, it reveals two types of alkali feldspar
megacrysts differing in tetrahedral Al-content (2t1) and exsolution microtextures:
1. Alkali feldspar megacrysts (Or70An2Ab28) from the top of the body consist of ideally coherent intergrowths of fine-scale regular Or- and Ab-rich lamellae. The exsolved
K-feldspar host is monoclinic (2t1=0.7), the exsolved Na-rich phase consists of Albite- and/or Pericline-twinned albite.
2. Megacrysts from greater depths have the same bulk composition, but the exsolved Ab-rich phase occurs in the form of optically
visible, broad lamellae and patches of low albite. In addition, the K-rich host yields a higher degree of (Al, Si) ordering
(2t1=0.8). The evolution of the distinct types of megacrysts reflects differences in the cooling history within the upper and
lower part of the granite body. The occurrence of the coherent lamellae in the megacrysts from the top of the body is attributed
to exsolution under dry conditions during fast cooling, whereas coarsening of lamellae and formation of albite patches in
the megacrysts from the lower part are caused by fluid-feldspar interaction. The transition zone in the body between the two
types of megacrysts is sharp (in a depth interval of 100–200 m) and not related to shear zones.
Received: 12 June 1995 / Accepted: 29 January 1996 相似文献
970.
Trace element and isotope geochemistry of depleted peridotites from an N-MORB type ophiolite (Internal Liguride,N. Italy) 总被引:6,自引:0,他引:6
E. Rampone A. W. Hofmann G. B. Piccardo R. Vannucci P. Bottazzi L. Ottolini 《Contributions to Mineralogy and Petrology》1996,123(1):61-76
Mantle peridotites of the Internal Liguride (IL) units (Northern Apennines) constitute a rare example of the depleted lithosphere
of the Jurassic Ligurian Tethys. Detailed chemical (ICP-MS and SIMS techniques) and isotopic investigations on very fresh
samples have been performed with the major aim to constrain the timing and mechanism of their evolution and to furnish new
data for the geodynamic interpretation. The data are also useful to discuss some general geochemical aspects of oceanic-type
mantle. The studied samples consist of clinopyroxene-poor spinel lherzolites, showing incipient re-equilibration in the plagioclase-facies
stability field. The spinel-facies assemblage records high (asthenospheric) equilibration temperatures (1150–1250° C). Whole
rocks, and constituent clinopyroxenes, show a decoupling between severe depletion in highly incompatible elements [light rare
earth elements (LREE), Sr, Zr, Na, Ti] and less pronounced depletion in moderate incompatible elements (Ca, Al, Sc, V). Bulk
rocks also display a relatively strong M(middle)REE/H(heavy)REE fractionation. These compositional features indicate low-degree
(<10%) fractional melting, which presumably started in the garnet stability field, as the most suitable depletion mechanism.
In this respect, the IL ultramafics show strong similarity to abyssal peridotites. The Sr and Nd isotopic compositions, determined
on carefully handpicked clinopyroxene separates, indicate an extremely depleted signature (87Sr/86Sr=0.702203–0.702285; 143Nd/144Nd=0.513619–0.513775). The Sm/Nd model ages suggest that the IL peridotites melted most likely during Permian times. They
could record, therefore, the early upwelling and melting of mid ocean ridge basalt (MORB) type asthenosphere, in response
to the onset of extensional mechanisms which led to the opening of the Western Tethys. They subsequently cooled and experienced
a composite subsolidus evolution testified by multiple episodes of gabbroic intrusions and HT-LP retrograde metamorphic re-equilibration, prior to their emplacement on the sea floor. The trace element chemistry of IL peridotites
also provides useful information about the composition of oceanic-type mantle. The most important feature concerns the occurrence
of Sr and Zr negative anomalies (relative to “adjacent” REE) in both clinopyroxenes and bulk rocks. We suggest that such anomalies
reflect changes in the relative magnitude of Sr, Zr and REE partition coefficients, depending on the specific melting conditions.
Received: 15 February 1995/Accepted: 4 August 1995 相似文献