Cobalt‐Bearing Grunerite in the Metamorphosed Banded Iron Formation in Orissa,India

Banded iron formation (BIF) comprising high grade iron ore are exposed in Gorumahisani‐Sulaipat‐Badampahar belt in the east of North Orissa Craton, India. The ores are multiply deformed and metamorphosed to amphibolite facies. The mineral assemblage in the BIF comprises grunerite, magnetite/martite/goethite and quartz. Relict carbonate phases are sometimes noticed within thick iron mesobands. Grunerite crystals exhibit needles to fibrous lamellae and platy form or often sheaf‐like aggregates in linear and radial arrangement. Accicular grunerite also occur within intergranular space of magnetite/martite. Grunerite needles/accicules show higher reflectivity in chert mesoband and matching reflectance with that of adjacent magnetite/martite in iron mesoband. Some grunerite lamellae sinter into micron size magnetite platelets. This grunerite has high ferrous oxide and cobalt oxide content but is low in Mg‐ and Mn‐oxide compared to the ones, reported from BIFs, of Western Australia, Nigeria, France, USA and Quebec. The protolith of this BIF is considered to be carbonate containing sediments, with high concentrations of Fe and Si but lower contents of cobalt and chromium ± Mg, Mn and Ni. During submarine weathering quartz, sheet silicate (greenalite) and Fe‐Co‐Cr (Mg‐Mn‐Ni)‐carbonate solid solution were formed. At the outset of the regional metamorphic episode grunerite, euhedral magnetite and recrystalized quartz were developed. Magnetite was grown at the expense of carbonate and later martitized under post‐metamorphic conditions. With the increasing grade of metamorphism greenalite transformed to grunerite.     

气候变化对喜马拉雅中部甘达基河流域濒危物种的影响预测（英文）

甘达基河流域位于喜马拉雅山脉中部,是众多濒危野生物种的重要栖息地。然而气候变化使该流域的生态环境变得愈发脆弱。本研究利用最大熵物种分布模型(Max Ent)评估气候变化对喜马拉雅黑熊(Ursus thibetanus laniger)和印度花豹(Panthera pardus fusca)等濒危物种空间分布变化的潜在影响。研究基于物种出没地点、生物气候和地形(海拔、坡度和坡向)等数据拟合模拟并预测物种在目前与未来的潜在分布情况。研究结果显示,目前喜马拉雅黑熊的高度适宜区面积约为1642 km²,占流域面积的5.01%,预计至2050年,其高度适宜区面积在甘达基河流域内将会增加约51 km²;印度花豹的高度适宜区面积约为3999 km²,占流域面积的12.19%,预计至2050年可能会增加到4806 km²。喜马拉雅黑熊的栖息地面积可能会在研究区域的东部(伯塞里、塔托潘尼和班塞以北)增加,而在东部(颂当、切坎帕)、西部(布尔提邦和波邦)和北部(桑波切、玛南、切坎帕)减少;印度花豹的栖息地面积则将在研究...     

Tunneling in lesser Himalaya,Jammu and Kashmir,India with special emphasis on tectonic mélange

Himalayan fold belt has full of geological surprises, ‘mélange’ is one of them which create difficulties during tunneling. Such mélange completely went unnoticed during surface mapping and geotechnical investigation preceding the construction of the Udhampur railway tunnel (URT). During the construction, the mélange zone has encountered across the tunnel, which occurs along the Tanhal thrust (equivalent to MBT) that separates the Murree Group and the Shiwalik Group. The mélange was characterized by a chaotic, heterogeneous geological mixture of stronger blocks (scale independence) and weaker sheared fine-grained matrix, often termed as “block-in-matrix rocks” or bimrocks, which enforced mixed face tunneling. The heterogeneity in a tectonic mélange led to stress concentrations in the rock blocks, and there were relatively high deformations within the matrix also. Release of stress from the blocks due to excavation, with unfavorable joint and thrust orientations enforced brittle failure of the blocks (face and crown collapses) while matrix deformation (time dependent) caused convergence of primary support later. Additionally, the clay minerals with high swelling potential within the matrix swelled and created pressure on the primary support. Due to the geomechanical heterogeneity in mélange, homogenizing the rock-mass by the commonly used quantitative systems might have lead to an inappropriate design and construction. The adopted New Austrian Tunneling Method (NATM) proved to be an useful tool for tunneling.     

2D Numerical Simulations of Soil Nail Walls

In practice, numerical simulations of soil nail walls are often carried out to assess the performance and stability. In the present study, implications of the use of advanced soil models, such as hardening soil model and hardening soil with small-strain stiffness model to simulate the behavior of in situ soil on the overall response of simulated soil nail wall have been studied, and compared with respect to the analysis using conventional and most prevalently used Mohr-Coulomb soil model. Further, influence of the consideration of bending stiffness of soil nails on the simulation results has been examined. Results of the simulations indicated that the use of advanced models is desirable for cases of soil nail walls constructed in soft soils and when lateral wall displacements are critical to the adjoining structures. Incorporation of bending stiffness of nails is found important from the consideration of facing failure modes of soil nail walls.     

A note on the applicability of log-Gumbel and log-logistic probability distributions in hydrological analyses: I. Known pdf

Abstract

Two probability density functions (pdf), popular in hydrological analyses, namely the log-Gumbel (LG) and log-logistic (LL), are discussed with respect to (a) their applicability to hydrological data and (b) the drawbacks resulting from their mathematical properties. This paper—the first in a two-part series—examines a classical problem in which the considered pdf is assumed to be the true distribution. The most significant drawback is the existence of the statistical moments of LG and LL for a very limited range of parameters. For these parameters, a very rapid increase of the skewness coefficient, as a function of the coefficient of variation, is observed (especially for the log-Gumbel distribution), which is seldom observed in the hydrological data. These probability distributions can be applied with confidence only to extreme situations. For other cases, there is an important disagreement between empirical data and theoretical distributions in their tails, which is very important for the characterization of the distribution asymmetry. The limited range of shape parameters in both distributions makes the analyses (such as the method of moments), that make use of the interpretation of moments, inconvenient. It is also shown that the often-used L-moments are not sufficient for the characterization of the location, scale and shape parameters of pdfs, particularly in the case where attention is paid to the tail part of probability distributions. The maximum likelihood method guarantees an asymptotic convergence of the estimators beyond the domain of the existence of the first two moments (or L-moments), but it is not sensitive enough to the upper tails shape.     

Simulation of infiltration from porous clay pipe in subsurface irrigation

Abstract

Advances in the traditional method of subsurface porous clay pipe irrigation rely on knowledge of the distribution of water in the soil. Knowing the relationships among the hydraulic and physical parameters in the system is important for both the design and management of the system. To simulate the infiltration from the porous clay pipe and predict the wetted zone geometry in the soil, a computer model is developed herein. Laboratory experiments were conducted on soil samples representing two different soil textures in a specially designed bin to understand the flow phenomenon and to validate the developed model. In a given soil texture, the installation depth of the pipe and the volume of water applied in the soil are the major factors affecting the wetted zone. The relationships among various parameters, namely lateral spacing, installation depth, irrigation run time, hydraulic conductivity of the body of the pipe, and hydraulic head in the system, were established using the developed model.     

EFFECTS OF DATA ERRORS AND ACCURACY IN SECOND DERIVATIVE COMPUTATION BY RATIONAL APPROXIMATION*

The effects of systematic (constant) and random errors in the observed data have been investigated analytically for rational approximation method of computing second derivative involving a summation of the products of the averages of the gravity field with the corresponding weight coefficients, both in numerator as well as in denominator. A theoretical gravity anomaly over three spheres has been analyzed to demonstrate the high accuracy in the approximation. Since the sums of the weight coefficients in numerator and denominator are zero and one respectively, the regional gravity anomaly, even though approximated by a constant value over the entire area under computation, can produce substantially large error in the calculated derivative value. This is happening because of the contribution of the regional field in the denominator. Thus, inspite of the high accuracy in rational approximation, the method has limited application to field cases where a combined gravity field consisting of regional and residual anomalies is usually used. Master curves are presented for the constant and random errors by which a rough estimate of the percentage of error in second derivative computation can be made provided one has some idea of the magnitudes of the regional field and random error.     

Orthopyroxene-Bearing Rocks of Charnockitic Affinities in the South Savanna--Kanuku Complex of British Guiana

Orthopyroxene-bearing rocks of the South Savanna—Kanukucomplex of British Guiana vary in composition from basic toacid types. They include basic granulites; acid, orthopyroxene-bearingbiotite gneisses; orthopyroxene-bearing acid granulites; orthopyroxene-bearinggranites, and orthopyroxene-bearing xenoliths contained in theSouth Savanna Granite. The field, petrographic, and chemicalcharacters of the rocks bear strong resemblances to charnockitesdescribed from other parts of the world, but the origins formany charnockites are inconsistent with evidence advanced forthe evolution of the South Savanna—Kanuku rocks. Fieldand petrographic criteria indicate that the basic granuliteswere originally intrusive basic rocks and have suffered regionalmetamorphism of Granulite Facies grade, which induced the conversionof clinopyroxene to orthopyroxene. The orthopyroxene-bearing,acid biotite gneisses and acid granulites have resulted fromcontamination by enclosed basic granulites which occur as boudins,bands, and lenses. The orthopyroxene-bearing granites and xenolithsare related to the assimilation of intruded orthopyroxene-bearingcountry rocks by the South Savanna Granite and its apophyses. The chemistry of the rocks appears to support the conclusionsreached from field and petrographic studies by indicating consistentenrichment of Ca, Mg, Fe, and Na in the orthopyroxene-bearingrocks compared with their non-orthopyroxene-bearing equivalents.Variation diagrams also indicate slightly anomalous plots forthe orthopyroxene-bearing rocks of the complex.     

Weathering potential index for rocks based on density and porosity measurements

Rock samples belonging to ten lithological types under different stages of weathering, were collected from different stratigraphical horizons at Bhagalpur. Their densities and porosities were determined experimentally and the data obtained were fitted empirically in a linear equation for each lithological type. The slopes of the curves, which were negative in each case, showed that the increase in porosity for the same decrease in density were in the order, white sandstone > ferruginous sandstone > white claystone > porphyritic gneiss > quartzite > pegmatite > amphibolite ≅ biotite gnejss > basalt ≅ dolerite. A new weathering potential index based on the density-porosity data was proposed and the values for a specific stage of weathering for all the lithological types studied fall within the same range.