First Data on the Isotopic Age of Zircons from Rocks of the Roseta Ultramafic Massif,Southern Margin of the São Francisco Craton (Brazil)

Doklady Earth Sciences - The results of isotope U–Pb dating of zircons from lherzolite and vein olivine orthopyroxenite composing the Roseta ultramafic massif are presented. The zircons...     

Influence of wind upon water quality in Liverpool Bay

Comprehensive distribution patterns of physical and chemical characteristics have been obtained from a series of cruises in Liverpool Bay. The marked feature of these distributions was their temporal variability, suggesting that the surface residual circulation is also temporally variable. The influence of wind stress upon the circulation pattern and hence water quality of this sea area is illustrated.     

Multidimensional statistical technique for detection of low contrast geochemical anomalies

In this article we propose an advanced technique for detecting low contrast geochemical anomalies using a set of features. There are three principal elements in this technique: (1) a statistical measure of the contrast of the anomaly, denoted as τ; (2) selection of a background population; and (3) reduction of the dimensionality of the feature space. In the frame of the model, which describes the statistical distribution of geochemical background as a multidimensional normal distribution of logarithms of concentrations, the index, τ, is a powerful test statistic for the hypothesis of abnormality of an observation. Maps of τ anomalies can be rigorously interpreted on the basis of statistical inferences. Under all equal conditions this technique allows the detection of geochemical anomalies with at least the same contrast (if the chemical elements in a background population are correlated, then even the better) as using selective extractions of metals from soil or other techniques for data processing. The advantages of the proposed technique are demonstrated both theoretically and on examples of rare-metal and copper–nickel mineral deposits.     

Data base management system for erosivity values

In order to check the premature siltation of the reservoirs and guard against the drop in the irrigation potential, the Government of India has launched the schemes of soil conservation and integrated watershed management in the catchments of RVPs and Flood Prone rivers. Owing to the large financial and manpower commitments needed to implement and execute soil conservation measures over vast catchment areas, a priority approach for treatment was identified. The methodology developed for prioritization of watersheds of a catchment area conceptualizes sedimentation of the reservoirs as a multiplicative function of erosivity value and the delivery ratio. This paper deals with the development of a computerized data base software module ‘WEIGHT’ for determination of erosivity values for the mapping units comprising assemblages of the varying combinations of climate, physiography and slope, land use and cover conditions, soil characteristics (texture, solumn thickness, permeability and pH) and the existing erosion and soil conservation measures. The WEIGHT software package is coded in FORTRON-4 for PDP 11/83 operating system. the data base comprises storage of the attributes of the different erosivity determinants of the mapping units with predetermined erosivity values sequentially on a disk and comparing the attributes of a new mapping unit to get the most probabilities erosivity value. The objective has been to eliminate the personal bias and bring about the objectivity in the process of assigning erosivity values to the different mapping units. The data base design, design logic and operational sequence of the data base are discussed in the paper.     

A robust algorithm for ellipse-based discrete element modelling of granular materials

With recent research indicating the importance of the rolling mechanism of deformation in granular systems consisting of perfectly round particles, it has become popular to use ellipse-shaped particles in the Discrete Element Method (DEM) numerical model. Inherent in this technique is the need for accurately computing ellipse to ellipse intersection, in order to properly detect contact formation and compute relative contact velocities. However, the commonly used algorithms for computing ellipse-ellipse intersection are generally poorly conditioned and can be inaccurate. An alternate method for computing ellipse-ellipse intersection is developed and presented which results in a well-conditioned, stable and accurate contact detection method. These modification are incorporated into the general DEM algorithm.     

Solubility of alumina in orthopyroxene plus spinel as a geobarometer in complex systems. Applications to spinel-bearing alpine-type peridotites

The addition of Fe and Cr to the simple system MgO-SiO₂-Al₂O₃ markedly affects the activities of phases involved in the equilibrium

Mantle(?) xenoliths in the carbonatites of northern Transbaikalia

The composition and nature of high-Cr minerals in lithic clasts from the carbonatites of the Veseloe occurrence, northern Transbaikalia, were considered. In order to determine their source, the Cr-bearing phases were compared with chromite, magnetite, and rutile from ultrabasic rocks, mantle xenoliths, and eclogites. It was suggested that the xenoclasts studied were formed at great depths, whereas the carbonatites were directly derived from the mantle rather than formed by the crustal differentiation of a silicate-carbonate melt.