黑土的水土流失及其保育治理   总被引：10，自引：2，他引：10  

王其存  齐晓宁  王洋  刘兆永  鲍强 《地理科学》2003,23(3):361-365

黑土因其肥沃而闻名，但其退化和水土流失问题往往易被忽略。虽然在人类影响下的现代环境过程开始较晚，但黑土区的环境已发生了较大的变化。对黑土水土流失的现状进行了评价，指出了黑土保育治理的必要性与紧迫性，提出了治理保育措施。  相似文献   

Jurassic Dextral and Cretaceous Sinistral Movements Along the Hida Marginal Belt     

Kazuhiro Tsukada 《Gondwana Research》2003,6(4):687-698

The Hida marginal belt (HMB), which consists of various kinds of fault-bound blocks, is located between the continental massif of the Hida belt and the Mesozoic accretionary complex of the Mino belt in Central Japan. Detailed field investigation reveals that the HMB had grown through the two different movements, i.e., Jurassic dextral and Cretaceous sinistral movements. The Jurassic dextral ductile shear zones run in the southern marginal part of the Hida belt and the northern part of the HMB, whereas the Cretaceous sinistral cataclastic shear zones occur in the southern part of the HMB and the northern marginal part of the Mino belt. Geologic map and field evidence seem to suggest that the Jurassic dextral movement form the fault-bound blocks of the HMB to form the basic structure of the Hida marginal belt, i.e., formation of the ‘proto-HMB.’ Following the dextral movement, the sinistral one restructured the ‘proto-HMB’ to complete the present feature of the Hida marginal belt. The Cretaceous sinistral movement might result in the sinistral collision between the proto-HMB and the Mino belt.  相似文献   

Preliminary Rock-Slope-Susceptibility Assessment Using GIS and the SMR Classification   总被引：1，自引：1，他引：1  

Irigaray  C.  Fernández  T.  Chacón  J. 《Natural Hazards》2003,30(3):309-324

This paper aims to examine the impact of large-scale structuraladjustments (like the Greater Dhaka Flood Protection Project, GDFPP) on local living environment.It focuses the importance of environmental factors in flood hazard mitigation, and examines theenvironmental attitudes of the floodplain residents arising from the large-scale structural adjustments.Based on `perceived natural hazard research perspectives', this paper examines: (i) the reasons for persistentfloodplain occupation, and (ii) the importance of environmental factors in the choice, motivations and decision-makingof floodplain residents.This research used data collected from 300 households situated inthe eastern part of Dhaka. The face-to-face household survey data provided individuals' responses to a structuredquestionnaire on hazards and environment. Survey concerned urban floodplains, and looked fordata on housing, household characteristics, and residents' attitudes. Results of interview surveys wereused to: (i) explore the reasons of floodplain occupation, and (ii) residents' attitudes to tolerable levelof flood risk and willingness to accept environmental change resulting from the proposed structural embankments inthe eastern perimeter of Dhaka City, Bangladesh.Findings revealed that floodplain occupation (by theindividuals' decision-making) was a result of overall reaction to the Government's structuraladjustment policies that resulted from institutional, locational and socio-economic factors. The attitude survey results provided residents' perception to hazards and environment to be dependenton the socio-economic factors – but in a complex manner, many factors are interrelated.In addition to support for structural embankments, the study sample displayed a common concernand widespread environmental awareness. In terms of any `trade-off' between thebenefits (resources) from the embankments and costs (hazards) due to the detrimental impact on environment, the residents of Dhaka, despite some concern forsacrificing embankments for environment, tended to show a generalconsensus for embankments.  相似文献   

Geomechanical Properties of Shear Zones in the Eastern Aar Massif,Switzerland and their Implication on Tunnelling     

S. Laws  E. Eberhardt  S. Loew  F. Descoeudres 《Rock Mechanics and Rock Engineering》2003,36(4):271-303

Summary ¶Rock zones containing a high fracture density and/or soft, low cohesion materials can be highly problematic when encountered during tunnel excavation. For example in the eastern Aar massif of central Switzerland, experiences during the construction of the Gotthard highway tunnel showed that heavily fractured areas within shear zones were responsible for overbreaks in the form of chimneys several metres in height. To understand and estimate the impact of the shear zones on rock mass behaviour, knowledge concerning the rock mass strength and deformation characteristics is fundamental. A series of laboratory triaxial tests, performed on samples from granite- and gneiss-hosted shear zones revealed that with increasing degree of tectonic overprint, sample strength decreases and rock behaviour shows a transition from brittle to ductile deformation. These trends may be explained by increasing fracture densities, increasing foliation intensity, increasing thickness of fine-grained, low cohesion fracture infill, and increasing mica content associated with the increasing degree of tectonic overprint. As fracture density increases and the influence of discrete, persistent discontinuities on rock mass strength decreases, behaviour of the test samples becomes more and more representative of rock mass behaviour, i.e. that of a densely fractured continuum. For the purpose of numerical modeling calculations, the shear zones may be subdivided with respect to an increasing fracture density, foliation intensity and mica content into a strongly foliated zone, a fractured zone and a cohesionless zone, which in turn exhibit brittle, brittle-ductile and ductile rock mass constitutive behaviour, respectively.Received December 17, 2001; accepted January 9, 2003 Published online April 29, 2003  相似文献   

Simulation of marine boundary layer characteristics using a 1-D PBL model over the Bay of Bengal during BOBMEX-99     

N. V. Sam  U. C. Mohanty  A. N. V. Satyanarayana 《Journal of Earth System Science》2003,112(2):185-204

The characteristic features of the marine boundary layer (MBL) over the Bay of Bengal during the southwest monsoon and the factors influencing it are investigated. The Bay of Bengal and Monsoon Experiment (BOBMEX) carried out during July–August 1999 is the first observational experiment under the Indian Climate Research Programme (ICRP). A very high-resolution data in the vertical was obtained during this experiment, which was used to study the MBL characteristics off the east coast of India in the north and south Bay of Bengal. Spells of active and suppressed convection over the Bay were observed, of which, three representative convective episodes were considered for the study. For this purpose a one-dimensional multi-level PBL model with a TKE-ε closure scheme was used. The soundings, viz., the vertical profiles of temperature, humidity, zonal and meridional component of wind, obtained onboard ORV Sagar Kanya and from coastal stations along the east coast are used for the study. The temporal evolution of turbulent kinetic energy, marine boundary layer height (MBLH), sensible and latent heat fluxes and drag coefficient of momentum are simulated for different epochs of monsoon and monsoon depressions during BOBMEX-99.The model also generates the vertical profiles of potential temperature, specific humidity, zonal and meridional wind. These simulated values compared reasonably well with the observations available from BOBMEX.  相似文献   

Determination of Halogens (F, Cl, Br, I), Sulfur and Water in Seventeen Geological Reference Materials   总被引：5，自引：0，他引：5  

Agnès Michel  Benoît Villemant 《Geostandards and Geoanalytical Research》2003,27(2):163-171

Fluorine, chlorine, bromine, iodine and sulfur were determined in seventeen geological reference materials after extraction by pyrohydrolysis. Fluorine, Cl and S (as sulfate ions) were determined in the extraction solution by ion chromatography with detection limits of around 0.2 mg l⁻¹. Bromine and I were measured by ICP-MS with detection limits of 1 μg l⁻¹ for Br and 0.1 μg l⁻¹ for I. For rock samples, using normal extraction conditions (500 mg of sample and 100 ml of final solution) detection limits were 40 mg kg⁻¹ for F and Cl, 15 mg kg⁻¹ for S, 0.2 mg kg⁻¹ for Br and 0.02 mg kg⁻¹ for I. These detection limits may be improved by increasing the amount of sample and hence the concentration of the final solution. Water was also determined using an extraction technique based on H₂O degassing, reduction on zinc at 1000 °C and H₂ manometry. Our results for fluorine, chlorine, sulfur and water are in good agreement with literature data. Very few reference materials have recommended values for bromine and especially for iodine. Among the analysed samples, three are new reference materials: BHVO-2, BCR-2 and AGV-2.  相似文献   

Origin and tectonic significance of a Mesozoic multi-layer over-thrust system within the Yangtze Block (South China)   总被引：21，自引：0，他引：21  

Dan-Ping Yan  Mei-Fu Zhou  Hong-Lin Song  Xin-Wen Wang  John Malpas 《Tectonophysics》2003,361(3-4):239-254

In the Yangtze Block (South China), a well-developed Mesozoic thrust system extends through the Xuefeng and Wuling mountains in the southeast to the Sichuan basin in the northwest. The system comprises both thin- and thick-skinned thrust units separated by a boundary detachment fault, the Dayin fault. To the northwest, the thin-skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast. The former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines. Thrust detachments occur along Silurian (Fs) and Lower Cambrian (Fc) strata and are dominantly associated with the anticlines. To the southeast, this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along Silurian (Fs), Cambrian (Fc) and Lower Sinian (Fz) strata. There are, however, numerous secondary back thrusts. Therefore, the thin-skinned belt is like the Valley and Ridge Province of the North American Applachian Mountains. The thick-skinned belt structurally overlies the thin-skinned belt and is characterized by a number of klippen including the Xuefeng and Wuling nappes. It is thus comparable to the Blue Ridge Province of Appalachia.The structural pattern of this thrust system in South China can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution. The system was developed through a northwest stepwise progression of deformation with the earliest delamination along Lower Sinian strata (Fz). Analyses of balanced geological cross-sections yield about 18.1–21% (total 88 km) shortening for the thin-skinned unit and at least this amount of shortening for the thick-skinned unit. The compressional deformation from southeast to northwest during Late Jurassic to Cretaceous time occurred after the westward progressive collision of the Yangtze Block with the North China Block and suggests that the orogenic event was intracontinental in nature.  相似文献   

The anisotropy of magnetic susceptibility in biotite, muscovite and chlorite single crystals     

Ftima Martín-Hernndez  Ann M. Hirt 《Tectonophysics》2003,367(1-2):13-28

The anisotropy of magnetic susceptibility (AMS) of single crystals of biotite, muscovite and chlorite has been measured in order to provide accurate values of the magnetic anisotropy properties for these common rock-forming minerals. The low-field AMS and the high-field paramagnetic susceptibility are defined. For the high-field values, it is necessary to combine the paramagnetic deviatoric tensor obtained from the high-field torque magnetometer with the paramagnetic bulk susceptibility measured from magnetization curves of the crystals. This leads to the full paramagnetic susceptibility ellipsoid due to the anisotropic distribution of iron cations in the silicate lattice. The ellipsoid of paramagnetic susceptibility, which was obtained for the three phyllosilicates, is highly oblate in shape and the minimum susceptibility direction is subparallel to the crystallographic c-axes. The anisotropy of the susceptibility within the basal plane of the biotite has been evaluated and found to be isotropic within the accuracy of the instrumental measurements. The degree of anisotropy of biotite and chlorite is compatible with previously reported values while for muscovite the smaller than previously published values. The shape of the chlorite AMS ellipsoid for all the samples is near-perfect oblate in contrast with a wide distribution of oblate and prolate values reported in earlier studies. Reliable values are important for deriving models of the magnetic anisotropy where it reflects mineral fabrics and deformation of rocks.  相似文献   

Early formed regional antiforms and synforms that fold younger matrix schistosities: their effect on sites of mineral growth     

T. H. Bell  A. P. Ham  K. A. Hickey 《Tectonophysics》2003,367(3-4):253-278

In the metamorphic cores of many orogenic belts, large macroscopic folds in compositional layering also appear to fold one or more pervasive matrix foliations. The latter geometry suggests the folds formed relatively late in the tectonic history, after foliation development. However, microstructural analysis of four examples of such folds suggests this is not the case. The folds formed relatively early in the orogenic history and are the end product of multiple, near orthogonal, overprinting bulk shortening events. Once large macroscopic folds initiate, they may tighten further during successive periods of sub-parallel shortening, folding or reactivation of foliations that develop during intervening periods of near orthogonal shortening. Reactivation of the compositional layering defining the fold limbs causes foliation to be rotated into parallelism with the limbs.Multiple periods of porphyroblast growth accompanied the multiple phases of deformation that postdated the initial development of these folds. Some of these phases of deformation were attended by the development of large numbers of same asymmetry spiral-shaped inclusion trails in porphyroblasts on one limb of the fold and not the other, or larger numbers of opposite asymmetry spirals on the other limb, or similar numbers of the same asymmetry spirals on both limbs. Significantly, the largest disparity in numbers from limb to limb occurred for the first of these cases. For all four regional folds examined, the structural relationships that accompanied these large disparities were identical. In each case the shear sense operating on steeply dipping foliations was opposite to that required to originally develop the fold. Reactivation of the folded compositional layering was not possible for this shear sense. This favoured the development of sites of approximately coaxial shortening early during the deformation history, enhancing microfracture and promoting the growth of porphyroblasts on this limb in comparision to the other. These distributions of inclusion trail geometries from limb to limb cannot be explained by porphyroblast rotation, or folding of pre-existing rotated porphyroblasts within a shear zone, but can be explained by development of the inclusion trails synchronous with successive sub-vertical and sub-horizontal foliations.  相似文献   

闪长岩强风化带做高层建筑天然地基的可行性研究   总被引：1，自引：0，他引：1  

尚敏  王清  樊祜传 《岩土力学》2003,(Z1)

借助于中国工商银行山东省分行营业办公楼的工程实践,将常规勘察与原位测试相结合,运用野外钻探、室内试验、原位测试多种手段,对闪长岩强风化带的物理力学性质进行了测试分析和深入地研究,并通过对承载力、沉降变形的验算,得出其作为高层建筑的天然地基是可行的。实践证明,与桩基础处理方案相比,节省资金近200万元,大大加快了施工进度,减少了基础施工难度,取得了巨大的经济效益与社会效益;同时,也提出了研究岩石风化带所遇到的问题:由于采取原状试样及制样难,导致对其物理力学性质了解不够。  相似文献