Numerical study of mechanism of fold formation in a laminated rock

A set of large deformation experiments are presented to simulate folding pattern at various energy states during formation. In order to numerically simulate this phenomenon, a rectangular layer of shale is generated and compressed at various strain rates. The results reveal the variation in distribution of stress along the length of the bed. The stress distribution during elastic behaviour of shale bed at low compression rate and the change in stress distribution leading to rupture at high compression rates is discussed. Wavelength, limb length, bulk shortening, stress distribution, displacement of particles along the length of the bed is considered for comparative study of the fold pattern generated at various compression rates. The nature and position of crack generated during the formation of fold is also explained. After rupture in shale bed, the generation of fault and stress distribution in limbs of fold sliding over one another is also described.     

Determination of Thirteen Rare-Earth Elements by High-Performance Liquid Chromatography in Thirty and of K, Rb, Cs, Sr and Ba by Isotope Dilution Mass Spectrometry in Eighteen International Geochemical Reference Samples

This study reports the results of thirteen rare-earth elements in thirty geochemical reference samples. Three alkali (K, Rb, Cs) and two alkaline earth (Sr, Ba) elements were also determined in eighteen reference samples. The analytical procedure involved is based on spiked samples and later measurement of the rare-earth elements by high-performance liquid chromatography and the alkalies and alkaline earths by thermo-quartz mass spectrometric isotope dilution (THQ-MSID). Whenever possible, the results are compared with literature values.     

Tectonochemistry and p-t Conditions of Ramgarh and Almora Gneisses from Askot Klippe,Kumaun Lesser Himalaya

The chemical and petrological correlation of metamorphic nappes and klippes overlying the Proterozoic sedimentary units in the Kumaun Himalaya is still debated. The Ramgarh and Almora gneisses, not previously distinguished in the Askot Klippe, show distinct field, petrological and chemical signatures markedly similar to the tectonostratigraphic disposition of the Almora Nappe. A negative Eu anomaly in the Ramgarh granitic gneisses indicates lesser plagioclase fractionation while the Eu anomaly in the Almora pelitic gneisses is likely to have been controlled by feldspar crystallization in restites. During the anatexis at 776°C temperature and 6.6 kbar pressure, the melt moved slightly away to its crystallization sites. The Rb/Sr ratio ?0.54 and Nb ?10 ppm is consistent with the granodioritic composition. The negative Sr anomaly in the underlying Ramgarh granitic gneisses indicates a distinct mantle derived source/plagioclase fractionation with a notable correspondence to other late orogenic granites, particularly the basement Ulleri gneisses from the Nepal Himalaya. Ramgarh gneisses plot in the late-and post-COLG field. The Askot ensemble is likely to be the tectonometamorphically reworked basement, viz. the Ramgarh Group along with its metapelitic cover o f the Almora Group, together comprising southward thrust remnants of the leading edge of the Indian Plate that collided with Tibet during the Tertiary Himalayan orogeny.     

Efficient two-dimensional magnetotellurics modelling using implicitly restarted Lanczos method

This paper presents an efficient algorithm, FDA2DMT (Free Decay Analysis for 2D Magnetotellurics (MT)), based on eigenmode approach to solve the relevant partial differential equation, for forward computation of two-dimensional (2D) responses. The main advantage of this approach lies in the fact that only a small subset of eigenvalues and corresponding eigenvectors are required for satisfactory results. This small subset (pre-specified number) of eigenmodes are obtained using shift and invert implementation of Implicitly Restarted Lanczos Method (IRLM). It has been established by experimentation that only 15–20% smallest eigenvalue and corresponding eigenvectors are sufficient to secure the acceptable accuracy. Once the single frequency response is computed using eigenmode approach, the responses for subsequent frequencies can be obtained in negligible time. Experiment design results for validation of FDA2DMT are presented by considering two synthetic models from COMMEMI report, Brewitt-Taylor and Weaver (1976) model and a field data based model from Garhwal Himalaya.     

Prediction and error growth in the daily forecast of precipitation from the NCEP CFSv2 over the subdivisions of Indian subcontinent

This study investigates the forecast skill and predictability of various indices of south Asian monsoon as well as the subdivisions of the Indian subcontinent during JJAS season for the time domain of 2001–2013 using NCEP CFSv2 output. It has been observed that the daily mean climatology of precipitation over the land points of India is underestimated in the model forecast as compared to observation. The monthly model bias of precipitation shows the dry bias over the land points of India and also over the Bay of Bengal, whereas the Himalayan and Arabian Sea regions show the wet bias. We have divided the Indian landmass into five subdivisions namely central India, southern India, Western Ghat, northeast and southern Bay of Bengal regions based on the spatial variation of observed mean precipitation in JJAS season. The underestimation over the land points of India during mature phase was originated from the central India, southern Bay of Bengal, southern India and Western Ghat regions. The error growth in June forecast is slower as compared to July forecast in all the regions. The predictability error also grows slowly in June forecast as compared to July forecast in most of the regions. The doubling time of predictability error was estimated to be in the range of 3–5 days for all the regions. Southern India and Western Ghats are more predictable in the July forecast as compared to June forecast, whereas IMR, northeast, central India and southern Bay of Bengal regions have the opposite nature.     

AUTOMATIC INTERPRETATION OF GRAVITY ANOMALIES ASSOCIATED WITH TWO-DIMENSIONAL MASS DISTRIBUTIONS*

Several new features are described which facilitate an automatic, more meaningful, and more accurate interpretation of gravity anomalies associated with approximately two-dimensional mass distributions. These include a provision for fixed points on the bounds of a distribution, outward dipping boundaries, calculation of the gravity effect at individual elevations of stations, smoothing of models and end-corrections for distributions of limited strike length. It is possible to obtain distributions about a median plane; these distributions are sensitive to shape and allow estimates of optimum depths and minimum density contrasts for the anomalous masses.