Ultra-calcic Magmas Generated from Ca-depleted Mantle: an Experimental Study on the Origin of Ankaramites   总被引：3，自引：1，他引：3  

SCHMIDT  MAX W.; GREEN  DAVID H.; HIBBERSON  WILLIAM O. 《Journal of Petrology》2004,45(3):531-554

Ultra-calcic ankaramitic magmas or melt inclusions are ubiquitousin arc, ocean-island and mid-ocean ridge settings. They areprimitive in character (X_Mg > 0·65) and have highCaO contents (>14 wt %) and CaO/Al₂O₃ (>1·1). Experimentson an ankaramite from Epi, Vanuatu arc, demonstrate that itsliquidus surface has only clinopyroxene at pressures of 15 and20 kbar, with X_CO2 in the volatile component from 0 to 0·86.The parental Epi ankaramite is thus not an unfractionated magma.However, forcing the ankaramite experimentally into saturationwith olivine, orthopyroxene and spinel results in more magnesian,ultra-calcic melts with CaO/Al₂O₃ of 1·21–1·58.The experimental melts are not extremely Ca-rich but high inCaO/Al₂O₃ and in MgO (up to 18.5 wt %), and would evolve tohigh-CaO melts through olivine fractionation. Fractionationmodels show that the Epi parent magma can be derived from suchultra-calcic experimental melts through mainly olivine fractionation.We show that the experimental ultra-calcic melts could formthrough low-degree melting of somewhat refractory mantle. Thelatter would have been depleted by previous melt extraction,which increases the CaO/Al₂O₃ in the residue as long as someclinopyroxene remains residual. This finding corrects the commonassumption that ultra-calcic magmas must come from a Ca-richpyroxenite-type source. The temperatures necessary for the generationof ultra-calcic magmas are  相似文献   

ENVIRONMENT RECONSTRUCTION FOR A PART OF THE GLEN ROSE LIMESTONE, CENTRAL TEXAS     

E. WILLIAM BEHRENS 《Sedimentology》1965,4(1-2):65-111

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New Zealand in the Post Cold-War World     

WILLIAM W. HARRIS 《New Zealand geographer》1993,49(2):7-12

Abstract. The paper examines political and economic aspects of New Zealand's position in the world in the aftermath of the Cold War. It stresses the need for a balanced approach to the country's connections with the major power centres of the capitalist West, in an emerging multipolar geopolitical environment. It warns against disproportionate enthusiasms for particular places or concepts. New Zealand's national identity and interests have a distinctive South Pacific bicultural context, and this has a strong relevance for New Zealand's international profile, especially in relation to Australia.  相似文献   

FIGHTING FIRE WITH A BROKEN TEACUP: A COMPARATIVE ANALYSIS OF SOUTH AFRICA'S LAND‐REDISTRIBUTION PROGRAM*     

WILLIAM G. MOSELEY  BRENT McCUSKER 《Geographical review》2008,98(3):322-338

ABSTRACT. Since the rise of its first democratically elected government in 1994, South Africa has sought to redress its highly inequitable land distribution through a series of land‐reform programs. In this study we examine land‐redistribution efforts in two of South Africa's provinces, the Western Cape and Limpopo. By analyzing a cross‐section of projects in these two locales we develop a political ecology of stymied land‐reform possibilities to explain the limited progress to date. Given South Africa's ambitious goal of redistributing 30 percent of its white‐owned land by 2014 and the incremental and flawed nature of its redistribution program, we argue that the process is like trying to put out a fire with a broken teacup. Our results are based on interviews with policymakers, commercial farmers, and land‐redistribution beneficiaries, as well as on an analysis of land‐use change in Limpopo Province.  相似文献   

Late Quaternary environmental history of central Prins Karls Forland, western Svalbard   总被引：1，自引：0，他引：1  

TORBJÖRN ANDERSSON  STEVEN L. FORMAN  ÓLAFUR INGÓLFSSON  WILLIAM F. MANLEY 《Boreas: An International Journal of Quaternary Research》1999,28(2):292-307

This paper presents the results from stratigraphic and geomorphologic investigations in the Poolepynten area, Prins Karls Forland, western Svalbard. Field mapping, soil profile development and ¹⁴C dating reveal the existence of at least two generations of raised beach deposits. Well-developed raised beaches rise to the Late Weichselian marine limit at 36 m a.s.l. Discontinuous pre-Late Weichselian beach deposits rise from the Late Weichselian marine limit to approximately 65 m a.s.l. Expansion of local glaciers in the area during the Late Weichselian is indicated by a till that locally overlies pre-Late Weichselian raised beach deposits. Stratigraphic data from coastal sections reveal two shallow marine units deposited during part of oxygen isotope stage 5. The two shallow marine units are separated by a subglacially deposited till that indicates an ice advance from Prins Karls Forland into the Forlandsundet basin some time during the latter part of stage 5. Discontinuous glaciofluvial deposits and a cobble-boulder lag could relate to a Late Weichselian local glacial advance across the coastal site. Late Weichselian/early Holocene beach deposits cap the sedimentary succession. Palaeotemperature estimates derived from amino acid ratios in subfossil marine molluscs indicate that the area has not been submerged or covered by warm based glacier ice for significant periods of time during the time interval ca. 70 ka to 10 ka.  相似文献   

INCORPORATING RADIATION INPUTS INTO THE SNOWMELT RUNOFF MODEL     

KAYE BRUBAKER  ALBERT RANGO  WILLIAM KUSTAS 《水文研究》1996,10(10):1329-1343

Process-based, distributed-area snowmelt runoff models operating at small scales are essential to understand subtle effects of climate change, but require data not commonly available. Temperature index models operating over large areas provide realistic simulations of basin runoff with operationally available data, but lack rigorous physically based algorithms. A compromise between the two types of models is required to provide realistic evaluations of basin response to environmental changes in cold regions. One adaptation that is uniformly required for snowmelt models is the use of remotely sensed data, either as input or in model validation. At a minimum, snowmelt forecasting models need to incorporate snowcover extent information, which is currently obtained operationally. As more remote sensing capabilities come on line, models should accept upgraded information on snow water equivalent; additional remotely sensed information on landcover, frozen soil, soil moisture, cloudiness and albedo would also be useful. Adaptations to the semi-distributed snowmelt runoff model (SRM) are underway to make it more physically based for use in large area studies. A net radiation index has been added to the model, which formerly used only a temperature (degree–day) index to melt snow from a basin's elevation zones. The addition of radiation to the SRM allows the basin to be subdivided into hydrological response units by general aspect (orientation) as well as elevation. Testing of the new radiation-based SRM with measured radiation from a small research basin is the first step towards large scale simulations. Results from the W-3 research basin in Vermont, USA are promising. In the radiation version, the factor that multiplies the degree–day index is estimated independently of model output and is held constant throughout the season, in contrast with the degree–day version, where the corresponding factor is allowed to increase throughout the season. Without calibrating or optimizing on this important parameter, the goodness-of-fit measure R² is improved in two out of six test years when the radiation version of the SRM is used in place of the degree–day version in melt season simulations. When the accumulation of error is eliminated with periodic updating of streamflow, more significant improvement is noted with radiation included.  相似文献   

Variations in the discharge and organic matter content of stalagmite drip waters in Lower Cave,Bristol     

ANDY BAKER  WILLIAM L. BARNES  PETER L. SMART 《水文研究》1997,11(11):1541-1555

Six drip waters, which were actively depositing stalagmites in Lower Cave, Bristol, were analysed both for discharge and luminescence properties. Drip discharges were determined for two different years, and show a complex response to surface precipitation variations. Inter annual variability in drip discharge is demonstrated to be significantly higher than intra-annual variability, and discharge was demonstrated both to increase and decrease non-linearly with increased precipitation. Drip waters demonstrate a correlation between their luminescence intensity and drip discharge, with increased luminescence in winter as more organic matter is flushed through the aquifer. The strength of the relationship between luminescence intensity and discharge increases with increased discharge. The results presented here have implications for the palaeoenvironmental interpretation of annual growth laminae and the growth rates of stalagmite samples. © 1997 John Wiley & Sons, Ltd.  相似文献   

LAND-USE IMPACT ON WATERSHED RESPONSE: THE INTEGRATION OF TWO-DIMENSIONAL HYDROLOGICAL MODELLING AND GEOGRAPHICAL INFORMATION SYSTEMS     

WILLIAM W. DOE III  BAHRAM SAGHAFIAN  PIERRE Y. JULIEN 《水文研究》1996,10(11):1503-1511

The integration of a two-dimensional, raster-based rainfall–runoff model, CASC2D, with a raster geographical information system (GIS), GRASS, offers enhanced capabilities for analysing the hydrological impact under a variety of land management scenarios. The spatially varied components of the watershed, such as slope, soil texture, surface roughness and land-use disturbance, were characterized in GRASS at a user-specified grid cell resolution for input into the CASC2D model. CASC2D is a raster-based, single-event rainfall–runoff model that divides the watershed into grid cell elements and simulates the hydrological processes of infiltration, overland flow and channel flow in response to distributed rainfall precipitation. The five-step integration of CASC2D and GRASS demonstrates the potential for analysing spatially and temporally varied hydrological processes within a 50 square mile semi-arid watershed. By defining possible land-use disturbance scenarios for the watershed, a variety of rainfall–runoff events were simulated to determine the changes in watershed response under varying disturbance and rainfall conditions. Additionally, spatially distributed infiltration outputs derived from the simulations were analysed in GRASS to determine the variability of hydrological change within the watershed. Grid cell computational capabilities in GRASS allow the user to combine the scenario simulation outputs with other distributed watershed parameters to develop complex maps depicting potential areas of hydrological sensitivity. This GIS–hydrological model integration provides valuable spatial information to researchers and managers concerned with the study and effects of land-use on hydrological response.  相似文献   

Climbing‐ripple successions in turbidite systems: depositional environments,sedimentation rates and accumulation times     

DONALD R. LOWE  WILLIAM R. MORRIS 《Sedimentology》2012,59(3):867-898

Climbing‐ripple cross‐lamination is most commonly deposited by turbidity currents when suspended load fallout and bedload transport occur contemporaneously. The angle of ripple climb reflects the ratio of suspended load fallout and bedload sedimentation rates, allowing for the calculation of the flow properties and durations of turbidity currents. Three areas exhibiting thick (>50 m) sections of deep‐water climbing‐ripple cross‐lamination deposits are the focus of this study: (i) the Miocene upper Mount Messenger Formation in the Taranaki Basin, New Zealand; (ii) the Permian Skoorsteenberg Formation in the Tanqua depocentre of the Karoo Basin, South Africa; and (iii) the lower Pleistocene Magnolia Field in the Titan Basin, Gulf of Mexico. Facies distributions and local contextual information indicate that climbing‐ripple cross‐lamination in each area was deposited in an ‘off‐axis’ setting where flows were expanding due to loss of confinement or a decrease in slope gradient. The resultant reduction in flow thickness, Reynolds number, shear stress and capacity promoted suspension fallout and thus climbing‐ripple cross‐lamination formation. Climbing‐ripple cross‐lamination in the New Zealand study area was deposited both outside of and within channels at an inferred break in slope, where flows were decelerating and expanding. In the South Africa study area, climbing‐ripple cross‐lamination was deposited due to a loss of flow confinement. In the Magnolia study area, an abrupt decrease in gradient near a basin sill caused flow deceleration and climbing‐ripple cross‐lamination deposition in off‐axis settings. Sedimentation rate and accumulation time were calculated for 44 climbing‐ripple cross‐lamination sedimentation units from the three areas using TDURE, a mathematical model developed by Baas et al. (2000) . For T_c divisions and T_bc beds averaging 26 cm and 37 cm thick, respectively, average climbing‐ripple cross‐lamination and whole bed sedimentation rates were 0·15 mm sec^?1 and 0·26 mm sec^?1 and average accumulation times were 27 min and 35 min, respectively. In some instances, distinct stratigraphic trends of sedimentation rate give insight into the evolution of the depositional environment. Climbing‐ripple cross‐lamination in the three study areas is developed in very fine‐grained to fine‐grained sand, suggesting a grain size dependence on turbidite climbing‐ripple cross‐lamination formation. Indeed, the calculated sedimentation rates correlate well with the rate of sedimentation due to hindered settling of very fine‐grained and fine‐grained sand–water suspensions at concentrations of up to 20% and 2·5%, respectively. For coarser grains, hindered settling rates at all concentrations are much too high to form climbing‐ripple cross‐lamination, resulting in the formation of massive/structureless S₃ or T_a divisions.  相似文献   

Submarine mass-transport facies: new perspectives on flow processes from cores on the eastern North American margin     

EFTHYMIOS K. TRIPSANAS  DAVID J. W. PIPER  KIMBERLEY A. JENNER  WILLIAM R. BRYANT† 《Sedimentology》2008,55(1):97-136

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