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981.
The Mohorovičić discontinuity is the boundary between the Earth’s crust and mantle. Several isostatic hypotheses exist for
estimating the crustal thickness and density variation of the Earth’s crust from gravity anomalies. 相似文献
982.
Mohammad Amir Hossain Bhuiyan M. Julleh Jalalur Rahman Samuel B. Dampare Shigeyuki Suzuki 《Journal of Geochemical Exploration》2011,111(3):113-137
This present study describes the elemental geochemistry of fluvial sediments in the Kurigram (upstream) to Sirajganj–Tangail (downstream) section of the Brahmaputra–Jamuna River, Bangladesh, with the aim of evaluating their provenance, weathering and tectonic setting. Petrographically, the sediments are rich in quartz (68%), followed by feldspars (8.5%) and lithic grains (7%). The bulk sediment chemistry is influenced by grain size. Concentrations of TiO2, Fe2O3, MgO, K2O, P2O5, Rb, Nb, Cr, V, Y, and, Ce, Th and Ga slightly decrease with increasing SiO2/Al2O3 and grain size, suggesting clay matrix control. In contrast, concentrations of CaO, Na2O, Sr and Pb increase with increasing SiO2/Al2O3 and grain size, suggesting residence of these substances in feldspar. Decrease in Zr as grain size increases is likely controlled both by clay matrix and heavy minerals. In addition, heavy minerals' sorting also influences Ce, Th, Y and Cr abundances in some samples. The sediments are predominantly quartzose in composition with abundant low-grade metamorphic and sedimentary lithics, low feldspars and trace volcanic detritus, indicating a quartzose recycled orogen province as a source of the sediments. Discriminant diagrams together with immobile element ratio plots show that, the Brahmaputra–Jamuna River sediments are mostly derived from rocks formed in an active continental margin. Moreover, the rare earth element ratios as well as chondrite-normalized REE patterns with flat HREE, LREE enrichment, and negative Eu anomalies indicate derivation of the sediments of Brahmaputra–Jamuna River from felsic rock sources of upper continental crust (UCC). The chemical indices of alteration suggest that Brahmaputra–Jamuna River sediments are chemically immature and experienced low chemical weathering effects. In the A–CN–K ternary diagram, most of the samples close to the plagioclase–K-feldspar join line and to the UCC plot, and in the field of various lithologies of Higher Himalayan Crystalline Series, suggesting that rocks in these series are likely source rocks. Therefore, the elemental geochemistry of the Brahmaputra–Jamuna River sediments is controlled mostly by mechanical breakdown of lithic fragments and subsequent preferential attrition of muscovite > albite > quartz. 相似文献
983.
Mohammad Tahsin Karimi Nezhad Manijeh Ghahroudi Tali Mohammad Hashemi Mahmoudi Ebrahim Pazira 《Environmental Earth Sciences》2011,64(5):1203-1213
The aim of this study was to investigate the influences of land use, parent materials (rock types) and soil properties on total arsenic and cadmium concentrations in the agricultural soils. A total of 87 surface (0–20 cm) soil samples were collected from four types of land use: irrigated farming, rangeland, dry farming and orchard. The average concentrations of the analyzed elements in topsoil were 84.426 mg As/kg and 3.289 mg Cd/kg. In addition, the pH, organic matter (OM), cation exchange capacity (CEC), soil grain sizes and CaCO3 were measured for each sample. The results indicated that land use had no significant effect on As and Cd concentrations. Our findings indicated that the Cd concentrations were influenced by bedrock composition, but for As there were no significant differences between various soil parent materials (bedrocks). Soil pollution was assessed on the basis of pollution index (PI), comprehensive pollution index (P n ) and geoaccumulation index (I geo). Calculated indices showed high-pollution levels for As and low- to moderate-pollution levels for Cd. 相似文献
984.
Mohsen Safari Reza Kakaei Mohammad Ataei Mohammad Karamoozian 《Arabian Journal of Geosciences》2011,5(5):1011-1019
Site selection for the mineral processing is the most important decision made by owner that has a significant impact on the efficiency of the whole process. This is a critical decision which involves considering a number of criteria and finding the best location among feasible alternatives. Therefore, a multicriteria decision-making method is necessary to apply site-selection process to find the best location that meet desired conditions set by the selection criteria. This paper presents an application of TOPSIS method based on fuzzy sets (fuzzy TOPSIS), which is one of the broader multicriteria decision making means, used to select an appropriate site for mineral processing plant for Sangan iron ore mine (phase 2). For this purpose, at first considering the geological, technical, economical, and environmental factors, three feasible alternatives were selected for the processing plant using Geographical Information System. Then, based on the technical and experimental experiences and through judgment of the decision makers and experts, 14 criteria were established and these alternatives were evaluated. Finally, the alternatives were ranked and the best location was recommended. 相似文献
985.
This research makes use of the remote sensing, simulation modeling and field observations to assess the non-point source pollution
load of a Himalayan lake from its catchment. The lake catchment, spread over an area of about 11 km2, is covered by different land cover types including wasteland (36%), rocky outcrops (30%), agriculture (12%), plantation
(12.2%), horticulture (6.2%) and built-up (3.1%) The GIS-based distributed modeling approach employed relied on the use of
geospatial data sets for simulating runoff, sediment, and nutrient (N and P) loadings from a watershed, given variable-size
source areas, on a continuous basis using daily time steps for weather data and water balance calculations. The model simulations
showed that the highest amount of nutrient loadings are observed during wet season in the month of March (905.65 kg of dissolved
N, 10 kg of dissolved P, 10,386.81 kg of total N and 2,381.89 kg of total P). During the wet season, the runoff being the
highest, almost all the excess soil nutrients that are trapped in the soil are easily flushed out and thus contribute to higher
nutrient loading into the lake during this time period. The 11-year simulations (1994–2004) showed that the main source areas
of nutrient pollution are agriculture lands and wastelands. On an average basis, the source areas generated about 3,969.66 kg/year
of total nitrogen and 817.25 kg/year of total phosphorous. Nash–Sutcliffe coefficients of correlation between the daily observed
and predicted nutrient load ranged in value from 0.80 to 0.91 for both nitrogen and phosphorus. 相似文献
986.
An assessment of marine pollution due to metals was made in the Caspian Sea based on coastal sediment collected in Azerbaijan, Iran, Kazakhstan, Russia and Turkmenistan. Despite the high carbonate content, the distribution of most metals was largely controlled by terrigenous inputs. Several metals (As, Cr, Ni) exhibited concentrations that exceed sediment quality guidelines. Such metals have a high natural background but anthropogenic activities, notably mining, may further enhance concentrations. This would explain hot spots for Cu and Zn in Azerbaijan and Iran, and Cr at the mouth of the Ural River in Kazakhstan. Contamination by Hg was observed to the south of Baku Bay, Azerbaijan. Some anomalously high concentrations of Ba in the central Caspian are probably from offshore drilling operations, but the elevated U concentrations (up to 11.1 microg g(-1)) may be natural in origin. Several metals (Ag, Cd, Pb) have relatively low levels that pose no environmental concerns. 相似文献
987.
High-Cr podiform chromitites hosted by upper mantle depleted harzburgite were investigated for PGM and other solid inclusions from Faryab ophiolitic complex, southern Iran. Chemical composition of the chromian spinels, Cr#[100*Cr/(Cr+Al) = 77–85], Mg# [100*Mg/(Mg+Fe2+) = 56–73], TiO2≤0.25wt%, and the presence of abundant primary hydrosilicates included in the chromian spinels indicate that the deposits were formed from aqueous melt generated by high degree of partial melting in a suprasubduction zone setting. Solid phases hosted by chromian spinel grains from the Faryab ophiolitic chromitites can be divided into three categories: PGM, base-metal minerals and silicates. Most of the studied PGM occurred as very small (generally less than 20 μm in size) primary single or composite inclusions of IPGE-bearing phases with or without silicates and base metal minerals. The PGM were divided into the three subgroups: sulfides, alloys and sulfarsenides. Spinel-olivine geothermometry gives the temperatures 1,131–1,177 °C for the formation of the studied chromitites. At those temperatures, fS2 values ranged from 10?3 to 10?1 and provided a suitable condition for Ru-rich laurite formation in equilibrium with Os-Ir alloys. Progressive crystallization of chromian spinel was accompanied by increase of fS2 in the melt. The formation of Os-rich laurite, erlichmanite and then sulfarsenides occurred by increase of fS2 and slight decrease in temperature of the milieu. The compositional and mineralogical determinations of PGM inclusions respect to their spatial distribution in chromian spinels show that the minerals regularly distributed within the chromitites, reflecting cryptic variation consistent with magmatic evolution during host chromian spinel crystallization. 相似文献
988.
989.
Hossein Bari Abarghouei Mohammad Reza Kousari Mohammad Amin Asadi Zarch 《Arabian Journal of Geosciences》2013,6(5):1417-1433
Drought is one of the most important natural hazards in Iran. It is especially more prevalent in arid and hyper arid regions where there are serious limitations in regard to providing sufficient water resources. On the other hand, drought modeling and particularly its prediction can play important role in water resources management under conditions of lack of sufficient water resources. Therefore, in this study, drought prediction in a hyper arid location of Iran (Ardakan region) has been surveyed based on the abilities of artificial neural. Standardized Precipitation Index (SPI) in different time scales (3, 6, 9, 12, and 24 monthly time series) computed based on the data gathered from four rain gauge stations. After evaluation and testing of different artificial neural networks (ANN) structures, gradient descent back propagation (traingd) network showed higher abilities than others. Then, the predictions of SPI time series with different monthly lag times (1:12 months) were tested. Generally, drought prediction by ANNs in the Ardakan region has shown considerable results with the correlation coefficient (R) more than 0.79 and in the most cases and it rises more than 0.90, which indicates the ANN’s ability of drought prediction. 相似文献
990.
Dipankar Chakraborti Mohammad Mahmudur Rahman Bhaskar Das Bishwajit Nayak Arup Pal Mrinal Kumar Sengupta Md. Amir Hossain Sad Ahamed Manabendranath Sahu Kshitish Chandra Saha Subhash Chandra Mukherjee Shyamapada Pati Rathindra Nath Dutta Quazi Quamruzzaman 《Environmental Earth Sciences》2013,70(5):1993-2008
The authors’ survey of the Ganga–Meghna–Brahmaputra (GMB) plain (area 569,749 km2; population >500 million) over the past 20 years and analysis of more than 220,000 hand tube-well water samples revealed groundwater arsenic contamination in the floodplains of the Ganga–Brahmaputra river (Uttar Pradesh, Bihar, Jharkhand, West Bengal, and Assam) in India and the Padma–Meghna–Brahmaputra river in Bangladesh. On average, 50 % of the water samples contain arsenic above the World Health Organization guideline value of 10 μg/L in India and Bangladesh. More than 100 million people in the GMB plain are potentially at risk. The authors’ medical team screened around 155,000 people from the affected villages and registered 16,000 patients with different types of arsenical skin lesions. Arsenic neuropathy and adverse pregnancy outcomes have been recorded. Infants and children drinking arsenic-contaminated water are believed to be at high risk. About 45,000 biological samples analyzed from arsenic-affected villages of the GMB plain revealed an elevated level of arsenic present in patients as well as non-patients, indicating that many are sub-clinically affected. In West Bengal and Bangladesh, there are huge surface water in rivers, wetlands, and flooded river basins. In the arsenic-affected GMB plain, the crisis is not over water scarcity but about managing the available water resources. 相似文献