Mineralogical Study of Almandine-Hercynite-Muscovite-Ilmenite Hornblendite Dykes from the Southern Margin of the Gondwana Graben at Richughuta in Palamau District of the Eastern Indian Shield

正Introduction The rectangular block of Proterozoic formation lying between north of the Singhbhum Mobile Belt(SMB,2.3-2.4 Ga,Saha 1994),Neogene sediments of the Bengal basin and the Quaternary-Recent alluvium of the Ganga     

Petrogenetic study of Mesoproterozoic volcanic rocks of North Delhi fold belt,NW Indian shield: implications for mantle conditions during Proterozoic

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.     

Desertification status mapping in Muttuma Watershed by using Random Forest Model

Potential of the Random Forest Model on mapping of different desertification processes was studied in Muttuma watershed of mid-Murrumbidgee river region of New South Wales,Australia.Desertification vulnerability index was developed using climate,terrain,vegetation,soil and land quality indices to identify environmentally sensitive areas for desertification.Random Forest Model(RFM)was used to predict the different desertification processes such as soil erosion,salinization and waterlogging in the watershed and the information needed to train classification algorithms was obtained from satellite imagery interpretation and ground truth data.Climatic factors(evaporation,rainfall,temperature),terrain factors(aspect,slope,slope length,steepness,and wetness index),soil properties(pH,organic carbon,clay and sand content)and vulnerability indices were used as an explanatory variable.Classification accuracy and kappa index were calculated for training and testing datasets.We recorded an overall accuracy rate of 87.7%and 72.1%for training and testing sites,respectively.We found larger discrepancies between overall accuracy rate and kappa index for testing datasets(72.2%and 27.5%,respectively)suggesting that all the classes are not predicted well.The prediction of soil erosion and no desertification process was good and poor for salinization and water-logging process.Overall,the results observed give a new idea of using the knowledge of desertification process in training areas that can be used to predict the desertification processes at unvisited areas.     

Assessment and forecast of changes of reservoir volumes due to thermal settling in permafrost areas of Russia

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.     

Effect of Baroclinicity on Vortex Axisymmetrization.Part Ⅱ：Baroclinic Basic Vortex

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.     

Study of the spatial and historical distribution of sediment inorganic contamination in the Toulon bay (France)

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.     

The influences of various anthropogenic sources of deterioration on meiobenthos (Ostracoda) over the last 100 years in Suo-Nada in the Seto Inland Sea, southwest Japan

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.     

Baseline of organotin pollution in fishes, clams, shrimps, squids and crabs collected from the west coast of India

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.