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791.
Roger Guérin 《Hydrogeology Journal》2005,13(1):251-254
792.
Martian Topography: Scaling, Craters, and High-Order Statistics 总被引:1,自引:0,他引:1
The high-order structure functions of Mars topography reveal three specific ranges of scales: (1) scaling range at small scales where the structure functions exhibit scaling behavior; (2) transition range where the structure functions continue to grow but do not reveal scaling; and (3) saturation range at large scales where the structure functions saturate. The scaling and saturation ranges are explored in detail in respect to scaling and intermittency. Analysis of the Mars Orbiter Laser Altimeter (MOLA) data and computer simulations suggest that there are two potential contributors to the small-scale scaling: (i) scale-invariant surface formation; and (ii) effects of discrete morphological forms such as craters. The crater effect also provides an explanation for the large-scale intermittency revealed using the normalized structure functions within the saturation range, which cannot be explained by the ‘scale-invariant’ concept. Overall, the obtained results suggest that the “crater” contribution to the structure function behavior often dominates over the effect of the scale-invariant surface formation. 相似文献
793.
We have used a first-principle approach based on the calculation of generalised stacking faults (GSF) to study the influence
of pressure on the mechanical properties of forsterite. Six cases corresponding to [100] glide over (010), (021) and (001),
and [001] glide over (100), (010) and (110) have been considered. The relaxed energy barriers associated with plastic shear
have been calculated by constraining the Si atoms to move perpendicular to the fault plane and allowing Mg and O atoms to
move in every direction. These conditions, which preserve dilations as a relaxation process, introduce Si–O tetrahedral tilting
as an additional relaxation mechanism. Relaxed GSF show little plastic anisotropy of [100] glide over different planes and
confirms that [001] glide is intrinsically easier than [100] glide. The GSF are affected by the application of a 10 GPa confining
pressure with a different response for each slip system that cannot be explained by sole elastic effect. In particular, [100](010)
is found to harden significantly under pressure compared to [001](010). Our results give the first theoretical framework to
understand the pressure-induced change of dominant slip systems observed by Couvy et al. (in Eur J Mineral 16(6):877–889,
2004) and P. Raterron et al. (in GRL, submitted). It appears necessary to account for the influence of pressure on the mechanical
properties of silicates in the context of the deep Earth. 相似文献
794.
795.
Derek Blundell Nicholas Arndt Peter R. Cobbold Christoph Heinrich 《Ore Geology Reviews》2005,27(1-4):333
Metallogenic provinces in Europe range in age from the Archaean to the Neogene. Deposit types include porphyry copper and epithermal Cu–Au, volcanic-hosted massive sulphide (VMS), orogenic gold, Fe-oxide–Cu–Au, anorthosite Fe–Ti-oxide and sediment-hosted base-metal deposits. Most of them formed during short-lived magmatic events in a wide range of tectonic settings; many can be related to specific tectonic processes such as subduction, hinge retreat, accretion of island arcs, continental collision, lithosphere delamination or slab tear. In contrast, most sediment-hosted deposits in Europe evolved in extensional, continental settings over significant periods of time. In Europe, as elsewhere, ore formation is an integral part of the geodynamic evolution of the Earth's crust and mantle. Many tectonic settings create conditions conducive to the generation of water-rich magma, but the generation of ore deposits appears to be restricted to locations and short periods of change in temperature and stress, imposed by transitory plate motions. Crustal influence is evident in the strong structural controls on the location and morphology of many ore deposits in Europe. Crustal-scale fault–fracture systems, many involving strike-slip elements, have provided the fabric for major plumbing systems. Rapid uplift, as in metamorphic core complexes, and hydraulic fracturing can generate or focus magmatic–hydrothermal fluid flow that may be active for time spans significantly less than a million years. Once a hydrologically stable flow is established, ore formation is strongly dependent on the steep temperature and pressure gradients experienced by the fluid, particularly within the upper crust. In Europe, significant fracture porosity deep in the crystalline basement (1%) is not only important for magmatic–hydrothermal systems, but allows brines to circulate down through sedimentary basins and then episodically upward, expelled seismically to produce sediment-hosted base-metal deposits and Kupferschiefer copper deposits. Emerging research, stimulated by GEODE, can improve the predicting power of numerical simulations of ore-forming processes and help discover the presence of orebodies beneath barren overburden. 相似文献
796.
An understanding of the Okcheon Metamorphic Belt (OMB) in South Korea is central to unraveling the tectono-metamorphic evolution of East Asia. Amphibole-bearing rocks in the OMB occur as calcsilicate layers and lenses in psammitic rocks, in the psammitic rocks themselves, and in the mafic volcanic layers and intrusives. Most amphiboles fail to show 40Ar/39Ar plateau ages; those that do have ages ranging from 132 to 975 Ma. The disturbed age pattern and wide variation in 40Ar/39Ar ages can be related to metamorphic grade, retrograde chemical reactions, excess Ar and amphibole composition. The oldest age (975 Ma) can be interpreted either as an old igneous or metamorphic age predating sedimentation or a false age caused by excess Ar. The youngest age of 132 Ma and the disturbed age pattern found in amphiboles from rocks located close to Jurassic granitoids are the result of retrograde thermal metamorphic effects accompanying intrusion of the granitoids. Some medium- or coarse-grained amphiboles in the calcsilicates are aggregates of fine-grained crystals. As a result, they are heterogeneous and prove to be readily affected by excess Ar. A disturbed age pattern in amphiboles from the calcsilicates occurring in the high-grade metamorphic zone may also be the product of excess Ar. On the other hand, the disturbed pattern of amphiboles present in the calcsilicates from the low-grade metamorphic zone could arise from both excess Ar and mixed ages. However, amphiboles from psammitic rocks and some calcsilicates in the high-grade metamorphic zone and in intrusive metabasites display real plateau ages of 237 to 261 Ma. The temperature conditions in the high-grade metamorphic zone were higher than the argon closing temperature for amphibole, and the amphiboles in this zone give plateau ages only when they are homogeneous in composition, lack excess Ar, and have not been thermally affected by intrusion of the granitoids. The unmodified 40Ar/39Ar ages prove rather younger than the age of the Late Paleozoic metamorphic event of 280 to 300 Ma, but they are close to muscovite K-Ar ages of 263 to 277 Ma. These 40Ar/39Ar amphibole ages are interpreted as the time of cooling that followed the main regional, intermediate-P/T metamorphic climax. The results demonstrate that interpretation of 40Ar/39Ar amphibole ages in an area subjected to several metamorphic events can be accomplished only by undertaking a thorough tectono-metamorphic study, accompanied by detailed chemical analysis of the amphiboles. 相似文献
797.
Naïma AbouAli Mohamad Hafid El Hassane Chellaï Mohamed Nahim Mahmoud Zizi 《Comptes Rendus Geoscience》2005,337(14):1267-1276
Seismic reflection profiles from the Ifni/Tan-Tan Atlantic margin of southern Morocco, interpreted in the light of well data and field geology from the Western Anti-Atlas, allowed us to establish the seismostratigraphic framework of the syn-rift series and to reveal (i) a compressional structural style in the pre-Triassic basement similar to that established in the adjacent outcropping onshore basement but with an opposed western vergence, (ii) the importance of inherited anterior structures in the formation of Triassic-Liassic rift structures and (iii) an east–west propagation of these rift structures. To cite this article: N. AbouAli et al., C. R. Geoscience 337 (2005). 相似文献
798.
我国公路泥石流病害严重,泥石流淤埋公路构建筑物是一类常见的公路泥石流病害类型。泥石流衰减动力学是防治泥石流淤埋病害的重要关键技术,也是泥石流运动学、动力学研究的核心问题之一。本文作者运用泥沙运动力学及流体力学原理,初步建立了泥石流固相颗粒和液相浆体的能量衰减条件,把泥石流衰减模式概化为两类,即能量抑制衰减和能量自由衰减;通过泥石流沉积模型试验,得到了不同粘度泥石流体的沉积扇变化形态,随着泥石流体粘度的增大,沉积扇边缘变陡、扩展范围变小、纵轴线长度减小等结论与实际情况吻合;初步建立了泥石流能量衰减速率计算方法。研究成果为防治公路泥石流病害奠定了基础。 相似文献
799.
Using CRD method for quantification of groundwater recharge in the Gaza Strip, Palestine 总被引:1,自引:0,他引:1
Husam Baalousha 《Environmental Geology》2005,48(7):889-900
Rainfall is the main source of groundwater recharge in the Gaza Strip area in Palestine. The area is located in the semi-arid
zone and there is no source of recharge other than rainfall. Estimation of groundwater recharge from rainfall is not an easy
task since it depends on many uncertain parameters. The cumulative rainfall departure (CRD) method, which depends on the water
balance principle, was used in this study to estimate the net groundwater recharge from rainfall. This method does not require
much data as is the case with other classical recharge estimation methods. The CRD method was carried out using optimisation
approach to minimise the root mean square error (RMSE) between the measured and the simulated groundwater head. The results
of this method were compared with the results of other recharge estimation methods from literature. It was found that the
results of the CRD method are very close to the results of the other methods, but with less data requirements and greater
ease of application. Based on the CRD method, the annual amount of groundwater recharge from rainfall in the Gaza Strip is
about 43 million m3.
An erratum to this article can be found at 相似文献
800.
Experimental evidences and numerical modelling of debris flow initiated by channel runoff 总被引:1,自引:1,他引:1
Debris flow initiation by channel bed mobilization is a common process in high mountainous areas. Initiation is more likely
to occur at the outlet of small, steeply sloping basins where concentrated overland flow feeds an ephemeral channel incised
in slope deposits. Such geological conditions are typical of the Dolomite region (Italian Alps), which is characterized by
widespread debris flow activity triggered by severe summer thunderstorms. Real-time data and field observations for one of
these catchments (Acquabona catchment, Belluno, Italian Alps) were used to characterize the hydrological response of the initiation
area to rainfalls of varying intensity and duration. The observed behaviour was then reproduced by means of a simple hydrological
model, based on the kinematic wave assumption, to simulate the generation of channel runoff. The model is capable of predicting
the observed hydrological response for a wide range of rainfall impulses, thus providing a physical basis for the understanding
of the debris flow triggering threshold. 相似文献