The role of heterogeneous strain in the development and preservation of a polymetamorphic record in high-P granulites, western Canadian Shield   总被引：1，自引：0，他引：1  

K. H. MAHAN  P. GONCALVES  R. FLOWERS  M. L. WILLIAMS  D. HOFFMAN-SETKA 《Journal of Metamorphic Geology》2008,26(6):669-694

Mafic rocks in the Chipman domain of the Athabasca granulite terrane, western Canadian Shield, provide the first well‐documented record of two distinct high‐P granulite facies events in the same domain in this region. Textural relations and the results of petrological modelling (NCFMASHT system) of mafic granulites are interpreted in terms of a three‐stage tectonometamorphic history. Stage 1 involved development of the assemblage Grt + Cpx + Qtz ± Pl (M₁) from a primary Opx‐bearing igneous precursor at conditions of 1.3 GPa, 850–900 °C. Field and microstructural observations suggest that M₁ developed synchronously with an early S₁ gneissic fabric. Stage 2 is characterized by heterogeneous deformation (D₂) and synkinematic partial retrogression of the peak assemblage to an amphibole‐bearing assemblage (M₂). Stage 3 involved a third phase of deformation and a return to granulite facies conditions marked by the prograde breakdown of amphibole (Amph₂) to produce matrix garnet (Grt_3a) and the coronitic assemblage Cpx_3b + Opx_3b + Ilm_3b + Pl_3b (M_3b) at 1.0 GPa, 800–900 °C. M₁ and M_3b are correlated with 2.55 and 1.9 Ga metamorphic generations of zircon, respectively, which were dated in a separate study. Heterogeneous strain played a crucial role in both the development and preservation of these rare examples of multiple granulite facies events within single samples. Without this fortuitous set of circumstances, the apparent reaction history could have incorrectly led to an interpretation involving a single‐cycle high‐grade event. The detailed P–T–t–D history constructed for these rocks provides the best evidence to date that much of the east Lake Athabasca region experienced long‐term lower crustal residence from 2.55 to 1.9 Ga, and thus the region represents a rare window into the reactivation and ultimate stabilization processes of cratonic lithosphere.  相似文献   

Three-dimensional discontinuous deformation analysis (3-D DDA) using a new contact resolution algorithm     

S. Amir Reza Beyabanaki  Roozbeh Geraili Mikola  Kianoosh Hatami   《Computers and Geotechnics》2008,35(3):346-356

This paper presents a new contact calculating algorithm for contacts between two polyhedra with planar boundaries in the three-dimensional discontinuous deformation analysis (3-D DDA). In this algorithm, all six type contacts in 3-D (vertex-to-face, vertex-to-edge, vertex-to-vertex, face-to-face, edge-to-edge, and edge-to-face) are simply transformed into the form of point-to-face contacts. The presented algorithm is a simple and efficient method and it can be easily coded into a computer program. In this paper, formulations of normal contact, shear contact and frictional force submatrices based on the new method are derived and the algorithm has been programmed in VC⁺⁺. Examples are provided to demonstrate the new contact rule between two blocks.  相似文献   

Using ALSM to map sinkholes in the urbanized covered karst of Pinellas County,Florida—1, methodological considerations   总被引：1，自引：0，他引：1  

Larry D. Seale  Lee J. Florea  H. L. Vacher  Robert Brinkmann 《Environmental Geology》2008,54(5):995-1005

Comparison of a database of interpreted sinkholes made using airborne laser swath mapping (ALSM) with databases of sinkholes made from interpretation of aerial photographs reveals substantial disagreement. The discrepancies involve the location, number, areas, and circularity of interpreted sinkholes. Methodological factors that contribute to the discrepancies include blockage of ALSM laser returns in thick vegetation, multi-path reflections, and misrepresentation of the true extent of sinkholes. Comparison of two ALSM-derived databases made (1) independently from versus (2) in combination with earlier air photo analysis in undeveloped regions had the following result: one-fourth of the sinkholes interpreted by using the composite method were missed by the independent analysis, and one-third of the sinkholes that were interpreted from the independent analysis were not interpreted as sinkholes using the composite method. Subjective interpretation leads to a high level of uncertainty such that the results of the remote sensing studies are suspect, if not invalid.  相似文献   

Hydrochemical characteristics and the effects of irrigation on groundwater quality in Harran Plain,GAP Project,Turkey     

M. Irfan Yesilnacar  M. Said Gulluoglu 《Environmental Geology》2008,54(1):183-196

Improper design, faulty planning, mismanagement and incorrect operation of irrigation schemes are the principle reasons for the deterioration of groundwater quality in a large number of countries, in particular in semi-arid and arid regions. The aim of this study is to determine the dimensions of groundwater quality after surface irrigation was begun in the semi-arid Harran Plain. Physical and chemical parameters of the groundwater including pH, temperature, electrical conductivity (EC), sodium, potassium, calcium, magnesium, chloride, bicarbonate, sulphate, nitrate, nitrite, ammonium, total phosphorus, total organic carbon and turbidity were determined monthly during the 2006 water year. The quality of the groundwater in the study area was assessed hydrochemically in order to determine its suitability for human consumption and agricultural purposes. In the general plain, the EC values measured were considerably above the guide level of 650 μS/cm, while nitrate in particular was found in almost all groundwater samples to be significantly above the maximum admissible concentration of 50 mg/l for the quality of water intended for human consumption as per the international and national standards. Total hardness reveals that a majority of the groundwater samples fall in the very hard water category. Interpretation of analytical data shows that Ca–HCO₃ and Ca–SO₄ are the dominant hydrochemical facies in the study area.  相似文献   

Delineation of groundwater protection zones by the backward particle tracking method: theoretical background and GIS-based stochastic analysis   总被引：1，自引：0，他引：1  

Konstadinos N. Moutsopoulos  Alexandra Gemitzi  Vassilios A. Tsihrintzis 《Environmental Geology》2008,54(5):1081-1090

The backward particle tracking method, an effective and powerful tool that can be used to delineate groundwater protection zones, is presented. The theoretical background and insights on the applicability of this method are provided. Moreover, the present work enriches the backward particle tracking method with an uncertainty analysis concerning the porosity values, applying a Monte Carlo (MC) approach, coupled with the use of geographical information systems (GIS). As an application example, a wellfield in the Komotini area, Greece, is investigated. The present study may serve as a potential guideline for wellfield delineation, particularly in areas like Greece where lack of data related to the hydrogeological system is often a problem.  相似文献   

Multivariate analysis of heavy metal contents of sediments from Gumusler creek, Nigde, Turkey   总被引：2，自引：0，他引：2  

M. Gurhan Yalcin  Ibrahim Narin  Mustafa Soylak 《Environmental Geology》2008,54(6):1155-1163

In this study, heavy metal contents of samples from Gumusler creek in Turkey were studied and the metal contamination characteristics were investigated. In this respect, considering the pollutant sites in the area, systematic sediment samples were collected in a zone starting from the manifestation part of the water to the entrance of the Karasu creek in Gumusler town. Samples were taken from lower section of the river bed at 30 stations along Gumusler creek, 13 km in length and their heavy metal contents were analyzed with XRF Spectrometer. Correlation coefficients, element coefitic coefficient correlation, dendogram hierarchical cluster, model summary and Annova analysis statistical methods were applied to data. Strong positive correlations were determined for some elements which are believed to have possibly the same origin. In addition, mineralizations in the area are thought to cause variation in metal contents. Results of chemical analysis show that soil limit values and clark values were exceeded. The heavy metal accumulation in the creek is believed to be derived from non-operated Sb-Hg-W and Fe quarries.  相似文献   

Upcoming international events     

Anne Marie de Grosbois 《Environmental Geology》2008,54(5):1121-1126

  相似文献   

Case history of controlling a landslide at Panluo open-pit mine in China     

Zuoan Wei  Guangzhi Yin  Ling Wan  Louyan Shen 《Environmental Geology》2008,54(4):699-709

Controlling of landsides safely and economically is a great challenge to mine operators because landslides are major geological problems especially in open-pit mines. In this paper, a case history at Panluo open-pit mine is presented in detail to share the experiences and lessons with mine operators. Panluo open-pit mine is located in the southwestern Fujian province of China. It is the largest open-pit iron mine in the Fujian province and was planned in 1965 and is in full operation from 1978. In July 1990, an earthquake of magnitude 5.3 in Taiwan Strait and big rainstorms impacted the mine slope, causing tension cracks and rather large-scale failures, and forming a U-shaped landslide. Total potential volume was estimated to be up to 1.0 × 10⁶ m³. This directly threatened the mine production. In order to protect the mine production and the dwellers’ safety around, a dynamic comprehensive method was implemented including geotechnical investigations, in-situ testing and monitoring, stability analysis, and many mitigation and preventive measures. These measures slowed down the development and further occurrence of the landslide. The results showed that the landslides were still active, it was slowed with the control measures and moved rapidly with rainfall and mining down. However, no catastrophic accidents occurred and the pit mining was continued till it was closed at the elevation of 887 m in 2000. As a successful case of landslide control at an open-pit mine for 10 years, this paper reports the controlling measures in details. These experiences of landslide control may be beneficial to other similar mines for landslide control.  相似文献   

The largest karst cave discovered in a tunnel during motorway construction in Slovenia’s Classical Karst (Kras)   总被引：1，自引：0，他引：1  

Martin Knez  Tadej Slabe  Stanka Šebela  Franci Gabrovšek 《Environmental Geology》2008,54(4):711-718

Karst researchers of the Karst Research Institute ZRC SAZU are regularly consulted during the planning of Slovenia’s motorways and invited to observe and monitor construction in the karst areas. More than 350 caves have been discovered in the course of building 60 km of new motorways over the past decade. Access to the most important caves is preserved by concrete tubes closed with metal covers at the roadside. The largest cave system in a tunnel, named LC-S647, is almost entirely preserved. The protection of this cave will serve as a good example for the preservation of natural heritage in the future. Construction work for the motorway uncovered a high degree of karstification. In particular, the discovery of this cave in the Kastelec tunnel LC-S647 showed the existence of a major cave system in the geological and speleological past. A number of unconnected passages have also been found. Caves discovered during highway construction have brought new knowledge about the cavernosity and the geological history of this part of the karst.  相似文献   

GIS-based colour composites and overlays to delineate heavy metal contamination zones in the shallow alluvial aquifers, Ankaleshwar industrial estate, south Gujarat, India     

Suyash Kumar  K. D. Shirke  N. J. Pawar 《Environmental Geology》2008,54(1):117-129

In an attempt to delineate heavy metal contamination precincts and to evaluate the extent and degree of toxic levels, besides their possible sources, 38 water samples from Ankaleshwar Industrial Estate, south Gujarat, India were analyzed. By clutching geochemical analyses and GIS-based colour composites areas depicting anomalously high concentration of heavy metals (Mo, Zn, Pb, Ni, Co, Cd, etc.) in the groundwater were revealed. The multicomponent overlays in grey-scale facilitated in identifying situates of heavy metal ‘hot spots’, and lateral protuberances of the contamination plume around defile stretch of the main stream Amla Khadi flowing through the area. The multiple pollution plumes emerging from other parts of the area further coincide with effluent laden streams and small channels indicating industrial establishments as major sources of groundwater contamination. Influent nature of the streams, accelerated infiltration process, high mass influx and shallow groundwater table are the factors conducive for easy access of heavy metals to the phreatic aquifers affecting over 20 km² area. On the basis of P/U ratios (concentration of metals in polluted water to unpolluted water), geogenic and anthropogenic sources have been identified. Very high levels of technogenic elements present in the ground water raise concerns about possible migration into food crops, as the area is an important horticultural locale and is highly cultivated.  相似文献