岩石扩散蠕变及其地质意义   总被引：3，自引：1，他引：3  

王永锋  金振民 《地质科技情报》2001,20(4):5-11

总结了近十年来岩石扩散蠕变显微构造鉴别特征，研究方法的最新进展，矿物颗粒大小和流体（包括熔体和水）等是影响扩散蠕变的重要因素。扩散蠕变与位错蠕变和超塑性变形有密切关系，它的研究对大陆裂谷化过程，大陆碰撞带中岩石圈地幔强度弱化，中下地壳韧性剪切应变局限化以及与相变有关的矿物粒度细小化作用的分布有重要应用意义。  相似文献   

Do reduction spots predate finite strain? A magnetic diagnosis of Cambrian slates in North Wales     

Norihiro Nakamura  Graham Borradaile 《Tectonophysics》2001,340(3-4):133-139

The purple Cambrian slates of North Wales contain green-colored, irregular patches drawn out along cleavage and the more familiar ellipsoidal reduction spots that are parallel to cleavage. Because parallelism of pre-strain ellipsoids could only be produced by extremely high strain, we reject the hypothesis that these are strain markers. Here, we use magnetic methods to resolve this argument. The magnetic analysis reveals that the magnetic fabric of purple slate differs from the green variety of the slate only in the oxidation state, and indicates that the reduction process postdates cleavage. This suggests that the shape of reduction spots reflects the anisotropy of diffusion during reduction, not finite strain and alignment of an initially ellipsoidal object in the slates.  相似文献   

一个模拟SO2浓度分布的数值模式研究   总被引：1，自引：0，他引：1  

佟华  肖静玢  陈万隆  邵德民  谈建国  曾智华 《南京气象学院学报》2001,24(3):371-377

初步发展了一个空气污染准业务数值模式，该模式将修改过的二维Mass风场模式预报的风场据实测风廓线推广到三维，用有限元法求解欧位平流扩散方程，在此基础上，预报上海地区SO2指数和浓度分布。通过半年的试验，其结果与实测值基本一致，初步可用于业务预报使用。通过模拟表明，上海市的浓度高值区一般位于市区和郊区宝山，一天中早晨的浓度最大，傍晚次之，中午最小。  相似文献   

Comment on `Footprint Analysis: A Closed Analytical Solution Based on Height-Dependent Profiles of Wind Speed and Eddy Viscosity'     

T. W. Horst 《Boundary-Layer Meteorology》2001,101(3):435-447

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Groundwater recharge: an overview of processes and challenges   总被引：11，自引：13，他引：11  

Jacobus J. de Vries  Ian Simmers 《Hydrogeology Journal》2002,10(1):5-17

Since the mid-1980s, a relative explosion of groundwater-recharge studies has been reported in the literature. It is therefore relevant to assess what is now known and to offer further guidance to practitioners involved in water-resource development. The paper summarizes current understanding of recharge processes, identifies recurring recharge-evaluation problems, and reports on some recent advances in estimation techniques. Emphasis is accorded to (semi-)arid regions because the need for information is greatest in those areas – groundwater is often the only water source, is vulnerable to contamination, and is prone to depletion. Few studies deal explicitly with groundwater recharge in temperate and humid zones, because recharge is normally included in regional groundwater investigations as one component of the water balance. The resolution of regional water-balance studies in (semi-)arid areas is, in contrast, often too low to quantify the limited recharge component with sufficient precision. Despite the numerous studies, determination of recharge fluxes in (semi-)arid regions remains fraught with uncertainty. Multiple tracer approaches probably offer the best potential for reliable results in local studies that require 'at-point' information. However, many investigations indicate that these approaches are not straightforward, because in some cases preferential flow contributes as much as 90% of the estimated total recharge. Tracer results (e.g. Cl^–, ³H) must therefore be interpreted with care in areas with multi-modal flow in the vadose zone. Moreover, accurate estimation of total chloride deposition is essential, and tritium may be influenced by vapour transport at low flux rates. In addition, paleoclimatic and paleohydrological conditions may cause discrepancies between measured actual processes and calculated long-term averages. The frequently studied issues of localized recharge and spatial variability need not be a problem if concern is with regional estimates. The key for practitioners is the project objective, which dictates whether 'at-point' or area-/groundwater-based estimation methods are appropriate. Many indirect (wadi) recharge studies reported in the literature are site specific; the relationship between 'at point' hydraulic properties and channel-reach losses demands further investigation. Electronic Publication  相似文献   

Constraints on the duration of high-pressure metamorphism in the Tauern Window from diffusion modelling of discontinuous growth zones in eclogite garnet   总被引：4，自引：0，他引：4  

E. Dachs  A. Proyer 《Journal of Metamorphic Geology》2002,20(8):769-780

An eclogite sample from the Grossgockner region of the Hohe Tauern, Austria contains garnet with a pronounced compositional discontinuity between a Mn‐rich core and an Fe‐rich rim. This jump in composition was caused by a garnet‐consuming reaction followed by growth of the garnet rim + omphacite and marks the prograde transition from epidote–amphibolite to eclogite facies metamorphism. Garnet growth ended at peak metamorphic conditions of 570 °C, 17 kbar, but intracrystalline diffusion continued until about 450 °C, 4 kbar on the retrograde path. This garnet overgrowth texture represents a natural diffusion couple and a time span of 1 Myr was calculated from the diffusion profile developing out of the original sharp compositional step. For typical crustal densities, this time corresponds to a minimum average velocity in the range 4.6–7.4 cm yr^?1 (for vertical movement), which is one of the fastest exhumation rates reported. The diffusion of all divalent cations of four profiles was modelled, both analytically and numerically. Both approaches gave comparable results, but the times computed for each element were always discrepant up to a factor of 2. Variations of diffusion coefficients within 2 in analytical calculations remedied this and gave consistent upper time limits. Numerical modelling does not require the simplifications introduced in the analytical approach. On the other hand, error propagation was computationally unfeasible with this method.  相似文献   

Interpretation of single-well tracer tests using fractional-flow dimensions. Part 2: A case study     

Kornelius Riemann  Gerrit van Tonder  Panganai Dzanga 《Hydrogeology Journal》2002,10(3):357-367

Generalized equations using fractional-flow dimensions were derived to estimate the Darcy and groundwater-flow velocities obtained from the point-dilution and the single-well injection-withdrawal field tests. Flow velocities can only be estimated from single-well tests if the kinematic porosity or the hydraulic conductivity and hydraulic gradient are known a priori. A pumping test performed on the boreholes will yield an estimate of the fractional-flow dimension and the extent of the flow region by applying the generalized radial flow (GRF) model of Barker [Barker JA (1988) A generalized radial flow model for hydraulic tests in fractured rock. Water Resour Res 24(10):1796–1804]. These parameters are used in the generalised equations for the single-well tracer tests to estimate the flow-through area and, therewith, the Darcy or flow velocity. The generalized procedure, described in detail in Part 1 of this paper, is applied to two boreholes on the Campus Test Site located at the University of the Free State, Bloemfontein, South Africa, and it is shown that the two independent tests (i.e. the point-dilution and the single-well injection-withdrawal tests) yield similar estimates of the natural-seepage velocity in the aquifer. The estimated natural-flow velocity obtained by using fractional dimensions is about two times higher than the velocity estimated by using the standard method (i.e. flow dimension n=2, flow thickness equal to length of the sealed-off section of the borehole). Electronic Publication  相似文献   

A stochastic approach to model bottom boundary conditions and compute efficiency in a settling tank     

J. Ph. Chancelier  M. Cohen de Lara  F. Pacard 《Stochastic Environmental Research and Risk Assessment (SERRA)》1997,11(6):449-457

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冈底斯岩带热演化史的MDD模式新证据Ⅰ   总被引：2，自引：0，他引：2  

陈文寄  李齐  郝杰  周新华  孙敏 《地球学报》1997,18(Z1):86-88

本文首次报道在我国实验室利用特定的40Ar/39Ar阶段加热程序和MDD械处理得到的钾长石冷却曲线，加之黑云母和磷灰石的年龄测定结果进一步讨论了冈底斯岩带的热演化史。  相似文献   

GEOGRAPHY AS MELODY IN MUTTUSVAMI DIKSHITA'sINDIAN MUSICAL WORKS*     

CHANDRA S. BALACHANDRAN  SURINDER M. BHARDWAJ 《Geographical review》2001,91(4):690-701

ABSTRACT. The life and works of Muttusvami Dikshita (1775–1834), a luminary of South Indian Karnatak classical music, abound in spatiocultural symbolisms of integration and harmony. Dikshita'speregrinations symbolize a cultural circuit of Hindu pilgrimage. His studies of North Indian Hindustani music at Varanasi (formerly Benares), and his transplantation of them throughout South India, make him an active agent of cultural diffusion, harmonizing cultural traditions through spatiosymbolic anchors. The religious expression of his musical genius, his songs, and his melodies contributed to linking linguistically and politically disparate regions of eighteenth‐ and nineteenth‐century India. The works of Dikshita affirm India'scultural continuity and underscore its enduring cultural empathies and similarities.  相似文献