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921.
922.
923.
Mesoproterozoic North Delhi fold belt of NW Indian shield comprises three volcano-sedimentary basins viz. Bayana, Alwar and Khetri aligned parallel to each other from east to west. Each basin contains excellent exposures of mafic volcanic rocks. Major, trace and rare earth element abundances of volcanic rocks of the three basins are significantly diverse. Bayana and Alwar volcanics are tholeiites bearing close similarity with low Ticontinental flood basalts. However, Bayana volcanics are characteristically enriched in incompatible trace elements and REEs while Alwar volcanics display least enriched incompatible trace element abundances and flat REE patterns. The Khetri volcanics exhibit a transitional composition between tholeiite and calc-alkaline basalts. REE based source modeling suggests that Bayana suite was formed from the melts derived from 1 % to 10 %(avg.4 %) of the partial melting of a spinel lherzolite source giving a residual mineralogy of 56 % Olv, 25 % Opx and19 % Cpx. Whereas Alwar suite evolved through 12 %–20 %(avg. 15 %) partial melting of the same source with a residual mineralogy 61 % Olv, 25 % Opx and 14 % Cpx.Khetri volcanics are exposed at two localities Kolihan and Madhan–Kudhan. The Kolihan volcanics were derived from 1 % to 6 %(avg. 4 %) partial melting with residualmineralogy 56 % Olv, 25 % Opx and 19 % Cpx whereas the magma of Madhan Kudhan volcanic suite was generated by 15%–30 % partial melting of the same source leaving behind 64 % Olv, 25 % Opx and 11 % Cpx as residual mineralogy. This source modeling proves that melts of Bayana and Alwar tholeiites were generated by partial melting of a common source within the spinel stability field under the influence of mantle plume. During the course of ascent, Bayana melts were crustally contaminated but Alwar melts remained unaffected. There was two tier magma production in Khetri region, one from the partial melting of the mantle wedge overlying the subducted oceanic plate which formed Kolihan suite and two the melting of the subducted plate itself generating Madhan–Kudhan volcanics. It is interpreted that during Mesoproterozoic(1,800 Ma), the continental lithosphere of NW Indian shield suffered stretching, attenuation and fracturing in response to a rising plume. Consequently, differential crustal extension coupled with variable attenuation brought the asthenosphere to shallower setting which led to the production of tholeiitic melts. These melts enroute to the surface suffered variable lithospheric contamination depending upon the thickness of traversed crust. The Khetri basin attained maturity which resulted in the generation of true oceanic crust and its subsequent destruction through subduction. The spatial existence of three suites of mafic volcanics of diverse chemical signatures is best example of subduction–plume interaction. It is therefore, proposed that the Mesoproterozoic crust of NW Indian shield has evolved through the operation of a complete Wilson cycle at about1,832 Ma, the age of mafic volcanics of Khetri basin. 相似文献
924.
This paper presents the results of data analyses and assessments of field and theoretical researches on reservoir bed relief transformation due to thermal settling in the permafrost regions of Russia.The resulting changes(increases) of the total volumes of large and small reservoirs are quantified,of which information will be of great use in future reservoir design and exploitation. 相似文献
925.
The effect of baroclinicity on vortex axisymmetrization is examined within a two-layer dynamical model.Three basic state vortices are constructed with varying degrees of baroclinicity:(i) barotropic,(ii) weak baroclinic,and (iii) strong baroclinic.The linear and nonlinear evolution of wavenumber-2 baroclinic disturbances are examined in each of the three basic state vortices.The results show that the radial propagating speed of the vortex Rossby wave at the lower level is larger with the stronger baroclinicity,resulting in a faster linear axisymmetrization process in the stronger baroclinic vortex.It is found that the nonlinear axisymmetrization process takes the longest time in the strongest baroclinic vortex among the three different basic vortices due to the weaker kinetic energy transfer from asymmetric to symmetric circulations at the lower level.A major finding in this study is that the same initial asymmetric perturbation can have different effects on symmetric vortices depending on the initial vortex baroclinicity.In numerical weather prediction models,this implies that there exists a sensitivity of the subsequent structural and intensity change solely due to the specification of the initial vertical shear of the tropical cyclone vortex. 相似文献
926.
Study of the spatial and historical distribution of sediment inorganic contamination in the Toulon bay (France) 总被引:4,自引:0,他引:4
Tessier E Garnier C Mullot JU Lenoble V Arnaud M Raynaud M Mounier S 《Marine pollution bulletin》2011,62(10):2075-2086
This study presents trace elements levels in surface and deep sediments of the Toulon bay (SE France) subjected to anthropogenic inputs (navy base, harbors, etc.). The studied elements (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) are defined as priority contaminants in aquatic systems. Fifty-five points scattered on the entire bay were sampled, allowing the determination of contaminants distribution with a high resolution. Several approaches were used to assess the degree of contamination and the potential toxicity of the Toulon bay sediments: comparison to the French legislation, surface-weighted average metal concentrations, enrichment factors (EF), geoaccumulation indices (Igeo), trace element stock calculation and comparison to sediment quality guidelines. A principal component analysis was performed to reveal common behavior of the studied contaminants. Results demonstrated the very high contamination of the small bay, especially in Hg (EF up to 1500), Cu, Pb and Zn, with export to the large bay further governed by hydrodynamics. 相似文献
927.
Irizuki T Takimoto A Sako M Nomura R Kakuno K Wanishi A Kawano S 《Marine pollution bulletin》2011,62(10):2030-2041
This study focuses on the relationships of water and sediment quality with meiobenthos (Ostracoda) over the past 100 years, using a sediment core obtained from Suo-Nada in the Seto Inland Sea, Japan. We compared high-resolution ostracode results with geochemical and sedimentological data obtained from the study core as well as with rich environmental monitoring data that are available. R-mode cluster analysis revealed two bioassociations (BC, KA). Until the1960s, assemblages continued to show high diversity. They changed in approximately 1970, when excessive nutrients and organic matter began to be supplied, and most species decreased in number. All species of bioassociation BC were dominant again by the mid-1990s; however, those of bioassociation KA containing infaunal species did not increase and have been absent or rare since the 1970s because organic pollution of sediments has continued to date. This study provided robust baseline for ostracode-based long-term environmental monitoring in East Asia. 相似文献
928.
Organotins, especially tributyltins (TBT) are highly toxic to many marine organisms. These compounds are introduced in marine waters by ship trafficking, ship scrapping activities, as antifouling compounds and sewage disposal. Marine fishes, crustaceans and molluscans are easily prone to organotins contamination. In view of this, a baseline monitoring study was conducted in order to establish the levels of organotins in edible marine fishes, bivalves, shrimps, squids and crabs collected from Mumbai, Goa and Karwar on the west coast of India. At these locations average organotin concentration found in fishes, clams, shrimps, squids and crabs was 108, 852, 179, 70 and 89 ng Sn g−1 dw, respectively. In all the samples butyltins dominated over phenyltins. The levels of organotins suggest that all the organisms were contaminated with organotins and their consumption may pose health problems to humans. 相似文献
929.
Agusa T Yasugi SY Iida A Ikemoto T Anan Y Kuiken T Osterhaus AD Tanabe S Iwata H 《Marine pollution bulletin》2011,62(5):963-975
Body distribution and growth- and nutritional status-dependent accumulation of 21 trace elements were investigated in harbor seals (Phoca vitulina) stranded in the North Sea coast in 2002. Higher concentrations and burdens of Mn, Se, Mo, Ag, Sn, Hg, and Bi in the liver, Cd in the kidney, As in the blubber, and Co, Sr, and Ba in the bone were observed. Significant positive correlations of hepatic Se, Mo, Ag, Cd, Sn, Hg, Tl, and Bi with standard body length were found, while significant negative relationships were detected for Mn, As, Rb, Sr, and Sb in the liver. Concentrations of Co, Se, Sr, Sn, Hg, and Bi in the liver, V, Sr, Ag, Sn, and Hg in the kidney, V, Mn, Co, Rb, Sr, Sn, Ba, and Pb in the blubber increased with decreasing blubber thickness of harbor seals, indicating enrichment of these elements in the target tissue by emaciation. 相似文献
930.
Brooks S Harman C Zaldibar B Izagirre U Glette T Marigómez I 《Marine pollution bulletin》2011,62(2):327-339
The biological impact of a treated produced water (PW) was investigated under controlled laboratory conditions in the blue mussel, Mytilus edulis. Mussel health status was assessed using an integrated biomarker approach in combination with chemical analysis of both water (with SPMDs), and mussel tissues. Acyl-CoA oxidase activity, neutral lipid accumulation, catalase activity, micronuclei formation, lysosomal membrane stability in digestive cells and haemocytes, cell-type composition in digestive gland epithelium, and the integrity of the digestive gland tissue were measured after 5 week exposure to 0%, 0.01%, 0.1%, 0.5% and 1% PW. The suite of biomarkers employed were sensitive to treated PW exposure with significant sublethal responses found at 0.01-0.5% PW, even though individual chemical compounds of PW were at extremely low concentrations in both water and mussel tissues. The study highlights the benefits of an integrated biomarker approach for determining the potential effects of exposure to complex mixtures at low concentrations. Biomarkers were integrated in the Integrative Biological Response (IBR/n) index. 相似文献