Rheological Properties of Partially Molten Lherzolite   总被引：2，自引：1，他引：2  

ZIMMERMAN  MARK E.; KOHLSTEDT  DAVID L. 《Journal of Petrology》2004,45(2):275-298

Lherzolite samples synthesized from fine-grained powders preparedfrom a natural xenolith were deformed at P = 300 MPa and 1373  相似文献   

Computer program for presentation of grain-size data by the graphic method     

ROGER M. SLATT  DAVID E. PRESS 《Sedimentology》1976,23(1):121-131

A computer program is described for a Hewlett-Packard desk-top Calculator (Model 9820A)-Plotter (Model 9862A) which plots a histogram, frequency polygon and/or cumulative curve, as well as standard statistical parameters and percentages of gravel, sand, silt, and clay from raw weight data from a sediment grain-size analysis. The program utilizes the graphic method for calculating statistical parameters in contrast to other commonly used computer programs derived for the method of moments. This program is advantageous because (1) it is rapid, (2) it allows direct comparison with grain-size data in the literature which have been computed by the graphic method, (3) either a complete presentation of a distribution can be obtained on one sheet of paper or a series of cumulative curves or frequency polygons can be prepared on a single graph which is ready for publication photocopying, (4) automatic extrapolation of data points from a cumulative curve eliminates inconsistencies arising from manual extrapolation, and (5) the desk-top calculator is more convenient to use, eliminates punching of data cards, and can be operated by someone without a knowledge of computers and programming. Disadvantages of the program are: (1) some authors feel critical percentiles are more accurately read off cumulative curves plotted on a probability ordinate than on an arithmetic ordinate, (2) the cumulative curve is a series of straight-line segments, (3) the frequency polygon is not as accurate a representation of grain-size distribution as a frequency curve and (4) size class intervals for the histogram and frequency polygon are standardized at 0.5φ, even though gravel and mud fractions are analysed at whole φ intervals. For most studies, the advantages of the program outweigh the disadvantages.  相似文献   

Evolution of Low-Al Orthopyroxene in the Horoman Peridotite, Japan: an Unusual Indicator of Metasomatizing Fluids     

MORISHITA  TOMOAKI; ARAI  SHOJI; GREEN  DAVID H. 《Journal of Petrology》2003,44(7):1237-1246

Unusually alumina-poor orthopyroxene is found in a spinel peridotitefrom the Horoman Peridotite Complex, Japan. Al₂O₃, Cr₂O₃ andCaO contents in the low-Al orthopyroxene (named Low-Al OPX hereafter)are <0·25 wt %, <0·04 wt % and <0·3wt %, respectively, and are distinctively lower than those inorthopyroxene porphyroclasts. The Low-Al OPX occurs in two modes,both at the margin of olivine. The first mode of occurrenceis as the rim of a large orthopyroxene porphyroclast in contactwith olivine. This type of Low-Al OPX occurs only locally (15µm x 45 µm), and the orthopyroxene rim in contactwith olivine more commonly has normal Al₂O₃ contents (>2wt %). In the second mode of occurrence, the Low-Al OPX occursas a thin film, 5 µm x 50 µm in dimension, at agrain boundary between olivine and clinopyroxene. Trace elementcompositions of porphyroclast clinopyroxene in the sample indicatethat the sample having the Low-Al OPX underwent metasomatismalthough there are no hydrous minerals around the Low-Al OPX.Petrographic observations and trace element compositions ofclinopyroxene combined with an inferred P–T history ofthe Horoman peridotite suggest that the Low-Al OPX was formedthrough a very local reaction between peridotite and invasivefluids, probably formed by dehydration of a subducted slab,in a late stage of the history of the Horoman peridotite. Crystallizationof orthopyroxene, representing addition of silica to mantlelherzolite via a CO₂ + H₂O-bearing fluid phase, is a mechanismfor metasomatic alteration of mantle wedge peridotite. KEY WORDS: Horoman Peridotite Complex; low-Al orthopyroxene; metasomatism; mantle wedge  相似文献   

The Great Australian Wind Rush and the Devaluation of Landscape Amenity     

DAVID MERCER 《The Australian geographer》2003,34(1):91-121

Up until very recently--and in marked contrast to such countries as Spain, Denmark and Germany--Australia generated hardly any electricity from the wind. Driven largely by the mandatory targets embodied in the Renewable Energy (Electricity) Act 2000 (Commonwealth) this situation is now changing. Australia has several operational small- to medium-sized wind energy power stations in Western Australia, Victoria, New South Wales and Queensland. But--in the face of often strong local opposition--the Australian Wind Energy Association is keen to increase the number and scale of such projects. This paper outlines recent overseas developments in wind energy and then focuses on the environmental and planning dilemmas posed by this form of electricity production. Particular attention is focused on a highly controversial wind energy proposal in south-western Victoria, the Portland Wind Energy Project (PWEP). The argument presented is that wind is only one of a number of possible renewable energy options, that coastal landscapes are an 'endangered species', and that it is time for geographers to revisit methodologies concerned with evaluating landscape beauty and debating the place of landscape values within the ecologically sustainable development paradigm.  相似文献   

AMERICAN NATIONAL IDENTITY AND THE PROGRESS OF THE NEW SOUTH IN NATIONAL GEOGRAPHIC MAGAZINE*     

DAVID R. JANSSON 《Geographical review》2003,93(3):350-369

ABSTRACT. This article examines how National Geographic Magazine's coverage of the U.S. South contributed to the production of an exalted American national identity. The framework of internal orientalism is employed to explain the role of the South as an internal other in the national discourse and to show how even positive representations of the South are often implicated in this othering. In the pages of National Geographic, the New South's progress is measured by the steps it takes away from the Old South. In highlighting the improvements made within the South, the articles provide subtle hints that the legacy of segregation, intolerance, racism, and poverty continues to haunt the region. The articles set up a spatial distinction that construes these evils as inherently southern problems, which implies that however far the New South moves away from the problematic legacy of the Old South, it will never quite reach the American ideal.  相似文献   

Comparison of methods for calculating annual solute exports from six forested appalachian watersheds     

BRYAN R. SWISTOCK  PAMELA J. EDWARDS  FREDERICA WOOD  DAVID R. DEWALLE 《水文研究》1997,11(7):655-669

Six methods were compared for calculating annual stream exports of sulfate, nitrate, calcium, magnesium and aluminum from six small Appalachian watersheds. Approximately 250–400 stream samples and concurrent stream flow measurements were collected during baseflows and storm flows for the 1989 water year at five Pennsylvania watersheds and during the 1989–1992 water years at a West Virginia watershed. Continuous stream flow records were also collected at each watershed. Solute exports were calculated from the complete data set using six different scenarios ranging from instantaneous monthly measurements of stream chemistry and stream flow, to intensive monitoring of storm flow events and multiple regression equations. The results for five of the methods were compared with the regression method because statistically significant models were developed and the regression equations allowed for prediction of solute concentrations during unsampled storm flows. Results indicated that continuous stream flow measurement was critical to producing exports within 10% of regression estimates. For solutes whose concentrations were not correlated strongly with stream flow, weekly grab samples combined with continuous records of stream flow were sufficient to produce export estimates within 10% of the regression method. For solutes whose concentrations were correlated strongly with stream flow, more intensive sampling during storm flows or the use of multiple regression equations were the most appropriate methods, especially for watersheds where stream flows changed most quickly. Concentration–stream flow relationships, stream hydrological response, available resources and required level of accuracy of chemical budgets should be considered when choosing a method for calculating solute exports. © 1997 John Wiley & Sons, Ltd.  相似文献   

The Quaternary history of the subtidal central Wash,eastern England     

DAVID S. BREW 《第四纪科学杂志》1997,12(2):131-141

The history of Quaternary sedimentation in the subtidal Wash is described using high-resolution seismic profiles. The Pleistocene sequence is divided into three depositional units, comprising Anglian till overlain by possible Late Devensian subglacial scour fill and lacustrine sediments. These latter sediments may provide further evidence for a lake in the Wash impounded by ice along the Lincolnshire–Norfolk coast. The Holocene sequence is divided into six depositional units, each truncated by the one above. Estuarine sediment resting on a marine flooding surface forms the earliest unit. This sediment was partially eroded by migration of the shoreface as the marine flooding progressed landward. The following four units comprise sand and gravel banks deposited on the erosion surface. Bank deposition was followed by an episode of tidal scour caused either by increased tidal current velocities following reclamation of the Fenland or by breakdown of postulated former offshore barriers. The youngest and most extensive Holocene unit rests on the scoured surface and comprises several types of deposit. These are: large sand banks around the periphery of the subtidal area with sediment extending seawards into two NE–SW aligned troughs; low sand banks on a central ridge dividing the troughs and partially covering the sediments in the troughs; thick gravels towards the mouth of the Wash; muddy sediments forming drapes over the sand in the centre of the Wash. The data provide information on the variety of processes related to the advance and retreat of Pleistocene ice sheets in eastern England and the subsequent Holocene marine flooding of the Wash–Fenland embayment. The Holocene sequence reveals periods of widespread sedimentation separated by periods of both local and regional erosion, with possible implications for climatic and hydrodynamic change. © 1997 John Wiley & Sons, Ltd.  相似文献   

GROUNDWATER SAPPING AND VALLEY DEVELOPMENT IN THE HACKNESS HILLS,NORTH YORKSHIRE,ENGLAND     

DAVID J. NASH 《地球表面变化过程与地形》1996,21(9):781-795

This paper describes evidence for the role of groundwater sapping and seepage erosion processes in the development of valleys which cut the southern edge of the Hackness Hills plateau in North Yorkshire, England. The development of drainage in this region has previously been suggested to relate to erosion by Late Devensian sub-aerial glacial meltwater channels. The role of groundwater erosion is investigated through a combination of geomorphological studies, lithological logging and X-ray diffraction (XRD) analyses. The geology of the region consists of a series of permeable Middle and Upper Jurassic lithologies (the Corallian sequence and Lower Calcareous Grit) which overlie the impermeable Upper Oxford Clay. The rocks dip gently to the south at between 1° and 4° and are relatively unfolded. Valleys exhibit many characteristic features of groundwater sapping networks. They rise abruptly at the edge of the plateau with amphitheatre-like valley heads, alcoves in headwalls, steep bedrock side walls, flat floors, spring sites and seepage zones in many valley flanks. Lithological logging indicates that sites of groundwater emergence usually occur either at or slightly above the boundary of the Upper Oxford Clay and Lower Calcareous Grit. XRD analyses of bedrock samples indicate that seepage occurs within siltstones which contain no clay but a variable percentage of calcite. The cause of groundwater emergence is attributed to decreasing grain size and increasing calcite cementation within bedrock which combine to reduce permeability. Development of valleys in the Hackness Hills is suggested to have occurred by a combination of headward erosion by groundwater sapping processes operating in an up-dip direction superimposed onto a valley morphology shaped by surface fluvial erosion.  相似文献   

CONTROLS ON SURFACE WATER CHEMISTRY IN THE UPPER MERCED RIVER BASIN,YOSEMITE NATIONAL PARK,CALIFORNIA     

DAVID W. CLOW  M. ALISA MAST  DONALD H. CAMPBELL 《水文研究》1996,10(5):727-746

Surface water draining granitic bedrock in Yosemite National Park exhibits considerable variability in chemical composition, despite the relative homogeneity of bedrock chemistry. Other geological factors, including the jointing and distribution of glacial till, appear to exert strong controls on water composition. Chemical data from three surface water surveys in the upper Merced River basin conducted in August 1981, June 1988 and August 1991 were analysed and compared with mapped geological, hydrological and topographic features to identify the solute sources and processes that control water chemistry within the basin during baseflow. Water at most of the sampling sites was dilute, with alkalinities ranging from 26 to 77 μequiv. l⁻¹. Alkalinity was much higher in two subcatchments, however, ranging from 51 to 302 μequiv. l⁻¹. Base cations and silica were also significantly higher in these two catchments than in the rest of the watershed. Concentrations of weathering products in surface water were correlated to the fraction of each subcatchment underlain by surficial material, which is mostly glacial till. Silicate mineral weathering is the dominant control on concentrations of alkalinity, silica and base cations, and ratios of these constituents in surface water reflect the composition of local bedrock. Chloride concentrations in surface water samples varied widely, ranging from <1 to 96 μequiv. l⁻¹. The annual volume-weighted mean chloride concentration in the Merced River at the Happy Isles gauge from 1968 to 1990 was 26 μequiv. l⁻¹, which was five times higher than in atmospheric deposition (4–5 μequiv. l⁻¹), suggesting that a source of chloride exists within the watershed. Saline groundwater springs, whose locations are probably controlled by vertical jointing in the bedrock, are the most likely source of the chloride. Sulphate concentrations varied much less than most other solutes, ranging from 3 to 14 μequiv. l⁻¹. Concentrations of sulphate in quarterly samples collected at the watershed outlet also showed relatively little variation, suggesting that sulphate may be regulated to some extent by a within-watershed process, such as sulphate adsorption.  相似文献   

RELATIONSHIPS BETWEEN CATCHMENT ATTRIBUTES AND HYDROLOGICAL RESPONSE CHARACTERISTICS IN SMALL AUSTRALIAN MOUNTAIN ASH CATCHMENTS     

DAVID A. POST  ANTHONY J. JAKEMAN 《水文研究》1996,10(6):877-892

Sixteen small catchments in the Maroondah region of Victoria, Australia were analysed using rainfall, temperature and streamflow time series with a rainfall–runoff model whose parameters efficiently characterize the hydrological response of a catchment. A set of catchment attributes for each of these catchments was then compared with the associated set of hydrological response characteristics of the catchments as estimated by the model. The time constant governing quickflow recession of streamflow (τ_q) was related to the drainage network and catchment area. The time constant governing slowflow recession of streamflow (τ_s) was related to the slope and shape of the catchment. The parameter governing evapotranspirative losses ( f ) was related to catchment gradient and vegetative water use. Forestry activities in the catchments changed evapotranspirative losses and thus total volume of streamflow, but did not affect the rate of streamflow recession.  相似文献