Mineral-chemical and isotopic studies of Namaqualand granulites,South Africa: A grenville analogue     

Tom N. Clifford  Eugen F. Stumpfl  Alwyn J. Burger  Terence S. McCarthy  David C. Rex 《Contributions to Mineralogy and Petrology》1981,77(3):225-250

The northwestern part of South Africa and southern South-West Africa/Namibia is amongst the most extensive granulite terranes in Africa. This work reports the results of electron microprobe studies of minerals from two-pyroxene, cordieriteorthopyroxene (-gedrite) (-sapphirine) and garnet and/or cordierite parageneses from Namaqualand, in the N.W. Cape Province of South Africa. Determined PT conditions of prograde metamorphism based on thermodynamic calculations are 800°–900° C and ca. 6–7 Kb; and it is argued that rocks of unusual composition, notably cordierite-orthopyroxene rocks, are restites after the extraction of granitic liquid from former argillites. This interpretation is consistent with previously published data on similar rocks, and with McCarthy's (1976) suggestion of extensive partial melting in the quartzofeldspathic rocks in the area. U-Pb isotopic studies of some 50 zircon fractions have been carried out and confirm an age of 1,200 m.y. for the high-grade regional metamorphism; but certain zircon populations record inherited ages greater than 1,700 m.y. Garnet-sillimanite rocks that contain retrograde kyanite reflect PT conditions of 550°–650° C and ca. 7–8 Kb; and constituent biotite has yielded a K-Ar age of ca. 950 m.y. These data, the regional stratigraphy and structure, and the mineralisation are compared with data from the Grenville Province of Canada. Notable similarities are the possible basement-cover relationships, and the calendar of tectonothermal events, while differences include the important stratiform base-metal mineralisation in the supracrustal sequence in Namaqualand, and the Cu-mineralisation in hypersthenebearing intrusives, emplaced some 1,100 m.y. ago, that are areally, and believed to be genetically, related to the granulite facies metamorphic regime.  相似文献   

Impacts of hydrological changes on phytoplankton succession in the Swan River, Western Australia   总被引：2，自引：0，他引：2  

Terence U. Chan  David P. Hamilton  Barbara J. Robson  Ben R. Hodges  Chris Dallimore 《Estuaries and Coasts》2002,25(6):1406-1415

The Swan River estuary, Western Australia, has undergone substantial hydrological modifications since pre-European settlement. Land clearing has increased discharge from some major tributaries roughly 5-fold, while weirs and reservoirs for water supply have mitigated this increase and reduced the duration of discharge to the estuary. Nutrient loads have increased disproportionately with flow and are now approximately 20-times higher than pre-European levels. We explore the individual and collective impacts of these hydrological changes on the Swan River estuary using a coupled hydrodynamic-ecological numerical model. The simulation results indicate that despite increased hydraulic flushing and reduced residence times, increases in nutrient loads are the dominant perturbation producing increases in the incidence and peak biomass of blooms of both estuarine and freshwater phytoplankton. Changes in salinity associated with altered seasonal freshwater discharge have a limited impact on phytoplankton dynamics.  相似文献   

CHAOS—a model of the Earth's magnetic field derived from CHAMP, Ørsted, and SAC-C magnetic satellite data     

Nils Olsen  Hermann Lühr  Terence J. Sabaka  Mioara Mandea  Martin Rother  Lars Tøffner-Clausen  Sungchan Choi 《Geophysical Journal International》2006,166(1):67-75

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Modification of the Natural Slake Test and Assessment of Slaking Behavior of a Shale from Malaysia Under Rainfall     

Lai  Teck Yew  Loo  Vera Hui  Wong  Vun Ket  Wong  Kwong Soon 《Geotechnical and Geological Engineering》2022,40(6):3169-3190

Geotechnical and Geological Engineering - The durability of clay-bearing rocks has been a concern to the construction industry. Extensive research have been conducted to determine the durability of...  相似文献   

An intelligent expert system shell for knowledge-based Geographical Information Systems: 1. The tools     

Yee Leung  Kwong Sak Leung 《International journal of geographical information science》2013,27(3):189-199

Abstract

An intelligent expert system shell for the development of knowledge-based geographical information systems (GIS) is examined in this two-part article. Basic concepts and the overall architecture of the shell are discussed in the present part. Fuzzy logic and expert systems technology are demonstrated to be appropriate methods for approximating human reasoning and enhancing the level of intelligence in GIS. The shell can be employed as an effective and efficient tool for developing knowledge-based GIS.  相似文献   

Environmental refugees in sub-Saharan Africa: a review of perspectives on the trends,causes, challenges and way forward     

Terence Epule Epule  Changhui Peng  Laurent Lepage 《GeoJournal》2015,80(1):79-92

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Climate-induced fluvial dynamics in tropical Africa around the last glacial maximum?     

Katherine Pingree  Max Lurie  Terence Hughes 《Quaternary Research》2011,75(3):417-429

The Greenland and East and West Antarctic ice sheets are assessed as being the source of ice that produced an Eemian sea level 6 m higher than present sea level. The most probable source is total collapse of the West Antarctic Ice Sheet accompanied by partial collapse of the adjacent sector of the East Antarctic Ice Sheet in direct contact with the West Antarctic Ice Sheet. This conclusion is reached by applying a simple formula relating the “floating fraction” of ice along flowlines to ice height above the bed. Increasing the floating fraction lowered ice elevations enough to contribute up to 4.7 m to global sea level. Adding 3.3 m resulting from total collapse of the West Antarctic Ice Sheet accounts for the higher Eemian sea level. Partial gravitational collapse that produced the present ice drainage system of Amery Ice Shelf contributes 2.3 m to global sea level. These results cast doubt on the presumed stability of the East Antarctic Ice Sheet, but destabilizing mechanisms remain largely unknown. Possibilities include glacial surges and marine instabilities at the respective head and foot of ice streams.  相似文献   

Hydrogen peroxide dimers and the production of O₂ in icy satellite surfaces     

Paul D. Cooper  Terence I. Quickenden 《Icarus》2003,166(2):444-446

Oxygen is seen in the reflectance spectra of the icy surfaces of Ganymede and Europa via absorption bands at 627 and 573 nm. Here we show that the trapped O₂ associated with these spectral features can be produced via radiation-induced decomposition of hydrogen peroxide dimers contained in hydrogen peroxide inclusions in these icy satellite surfaces.  相似文献   

A Detailed Study on the Equal Arrival Time Surface Effect in Gamma-Ray Burst Afterglows     

Yong-Feng Huang Ye Lu Anna Yuen Lam Wong Kwong Sang Cheng 《中国天文和天体物理学报》2007,7(3):397-404

Due to the relativistic motion of gamma-ray burst remnant and its deceleration in the circumburst medium, the equal arrival time surfaces at any moment are not spherical, rather, they are distorted ellipsoids. This will leave some imprints in the afterglows. We study the effect of equal arrival time surfaces numerically for various circumstances, i.e., isotropic fireballs, collimated jets, density jumps and energy injection events. For each case, a direct comparison is made between including and not including the effect. For isotropic fireballs and jets viewed on axis, the effect slightly hardens the spectra and postpones the peak time of the afterglows, but does not change the shapes of the spectra and light curves significantly. In the cases of a density jump or an energy injection, the effect smears out the variations in the afterglows markedly.  相似文献   

Uncertainties in real‐time flood forecasting with neural networks     

Dawei Han  Terence Kwong  Simon Li 《水文研究》2007,21(2):223-228

Although artificial neural networks (ANNs) have been applied in rainfall runoff modelling for many years, there are still many important issues unsolved that have prevented this powerful non‐linear tool from wide applications in operational flood forecasting activities. This paper describes three ANN configurations and it is found that a dedicated ANN for each lead‐time step has the best performance and a multiple output form has the worst result. The most popular form with multiple inputs and single output has the average performance. In comparison with a linear transfer function (TF) model, it is found that ANN models are uncompetitive against the TF model in short‐range predictions and should not be used in operational flood forecasting owing to their complicated calibration process. For longer range predictions, ANN models have an improved chance to perform better than the TF model; however, this is highly dependent on the training data arrangement and there are undesirable uncertainties involved, as demonstrated by bootstrap analysis in the study. To tackle the uncertainty issue, two novel approaches are proposed: distance analysis and response analysis. Instead of discarding the training data after the model's calibration, the data should be retained as an integral part of the model during its prediction stage and the uncertainty for each prediction could be judged in real time by measuring the distances against the training data. The response analysis is based on an extension of the traditional unit hydrograph concept and has a very useful potential to reveal the hydrological characteristics of ANN models, hence improving user confidence in using them in real time. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献