• Volume 121, Issue 6

      December 2012,   pages  1365-1571

    • Ninety million years of orogenesis, 250 million years of quiescence and further orogenesis with no change in PT: Significance for the role of deformation in porphyroblast growth

      A A Shah T H Bell

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      In situ dating of monazite grains preserved as inclusions within foliations defining FIAs (foliation inflection/intersection axes preserved within porphyroblasts) contained within garnet, staurolite, andalusite and cordierite porphyroblasts provides a chronology of ages that matches the FIA succession for the Big Thompson region of the northern Colorado Rocky Mountains. FIA sets 1, 2 and 3 trending NE–SW, E–W and SE–NW were formed at 1760.5 ± 9.7, 1719.7 ± 6.4 and 1674 ± 11± Ma, respectively. For three samples where garnet first grew during just one of each of these FIAs, the intersection of Ca, Mg, and Fe isopleths in their cores indicate that these rocks never got above 4 kbars throughout the Colorado Orogeny. Furthermore, they remained around approximately the same depth for ∼250 million years to the onset of the younger Berthoud Orogeny at 1415 ± 16 Ma when the pressure decreased slightly as porphyroblasts formed with inclusion trails preserving FIA set 4 trending NNE–SSW. No porphyroblast growth occurred during the intervening ∼250 million years of quiescence, even though the PT did not change over this period. This confirms microstructural evidence gathered over the past 25 years that crenulation deformation at the scale of a porphyroblast is required for reactions to re-initiate and enable further growth.

    • Metallogenic epoch of the Jiapigou gold belt, Jilin Province, China: Constrains from rare earth element, fluid inclusion geochemistry and geochronology

      Zhixin Huang Wanming Yuan Changming Wang Xiangwei Liu Xiaotong Xu Liya Yang

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      The Jiapigou gold belt is located on the northern margin of the North China Craton, and is one of the most important gold-mining and production regions in the circum-Pacific metallogenic zone. Research has been conducted in this area since the 1960s, however, the timing of the gold mineralisation is still unresolved, and an ideal metallogenic model has not been well established. To address these questions, a systematic geological, geochemical and geochronological investigation was conducted. The study revealed that (i) the gold-bearing quartz veins can be divided into two groups, earlier and later gold-bearing quartz veins according to their occurrence and the geochemical characteristics, (ii) the geochemical characteristics of the ore bodies, while similar to granite, are clearly different from the altered rock, and (iii) the geochemical characteristics of the later gold-bearing quartz veins have more similarity to the altered rock than the earlier gold-bearing quartz veins do. Therefore, we conclude that two independent stages of metallogenesis within the Jiapigou gold deposit area are related to magmatic activity in the Palaeoproterozoic and the Yanshanian stage of the Mesozoic, that the ore-forming fluids are mainly of magmatic origin, and that magma contamination by the altered rock was stronger in the Mesozoic. Zircon LA–ICP–MS U–Pb data show that the age of the Palaeoproterozoic granite is ∼2426.0 Ma and that of the Mesozoic granite is ∼166.2 Ma; these ages can be interpreted as the maximum ages of the two periods of gold mineralisation. In addition to investigating the geotectonic and regional structure of the Jiapigou gold belt, this study also proposes that the WNW-trending zone of gold mineralization is a result of a magmatic event within the basement in the early Palaeoproterozoic, and that largescale sinistral strike-slip displacements of the Huifahe and Liangjiang Faults in the late Middle Triassic (Yanshanian epoch) controlled the later tectono-magmatic event and the NNE–ENE-trending zone of gold mineralisation.

    • Simultaneous estimation of earthquake source parameters and crustal 𝑄 value from broadband data of selected aftershocks of the 2001 $M_w$ 7.7 Bhuj earthquake

      A Saha S Lijesh P Mandal

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      This paper presents the simultaneous estimation of source parameters and crustal Q values for small to moderate-size aftershocks ($M_w$ 2.1–5.1) of the $M_w$ 7.7 2001 Bhuj earthquake. The horizontal-component S-waves of 144 well located earthquakes (2001–2010) recorded at 3–10 broadband seismograph sites in the Kachchh Seismic Zone, Gujarat, India are analyzed, and their seismic corner frequencies, long-period spectral levels and crustal 𝑄 values are simultaneously estimated by inverting the horizontal component of the S-wave displacement spectrum using the Levenberg–Marquardt nonlinear inversion technique, wherein the inversion scheme is formulated based on the 𝜔-square source spectral model. The static stress drops (𝛥 𝜎 ) are then calculated from the corner frequency and seismic moment.

      The estimated source parameters suggest that the seismic moment ($M_0$) and source radius (𝑟) of aftershocks are varying from 1.12 × 1012 to 4.00 × 1016 N-m and 132.57 to 513.20 m, respectively. Whereas, estimated stress drops (𝛥 𝜎) and multiplicative factor ($E_{mo}$) values range from 0.01 to 20.0 MPa and 1.05 to 3.39, respectively. The corner frequencies are found to be ranging from 2.36 to 8.76 Hz. The crustal S-wave quality factor varies from 256 to 1882 with an average of 840 for the Kachchh region, which agrees well with the crustal 𝑄 value of the seismically active New Madrid region, USA. Our estimated stress drop values are quite large compared to the other similar size Indian intraplate earthquakes, which can be attributed to the presence of crustal mafic intrusives and aqueous fluids in the lower crust as revealed by the earlier tomographic study of the region.

    • Multivariate erosion risk assessment of lateritic badlands of Birbhum (West Bengal, India): A case study

      Sandipan Ghosh Kamala Bhattacharya

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      Each geomorphic hazard involves a degree of risk which incorporates quantification of the probability that a hazard will be harmful. At present, the categorization of sub-watersheds into erosion risk is considered as the fundamental step to conserve the soil loss. Development of badlands over the laterites of Birbhum district is an indicative of excessive soil loss in the monsoonal wet-dry type of climate. Slope erosion and channel erosion have generated huge amount of sediment from the small watersheds during intense monsoonal rainfall (June–September). The adjoining areas of Rampurhat I Block, Birbhum (West Bengal) and Shikaripara Block, Dumka (Jharkhand) have lost the lateritic soil cover at a rate of 20–40 ton/ha/year (Sarkar et al. 2005). In order to estimate the progressive removal of soil particles from the gully-catchments of the above-mentioned area, different morphometric parameters, soil parameters, hydrologic parameters and empirical models are employed. Side by side, the study is carried out to categorize the gully-catchments into different magnitude of erosion risk using several multivariate statistical techniques.

    • Exploring deep potential aquifer in water scarce crystalline rocks

      Subash Chandra E Nagaiah D V Reddy V Ananda Rao Shakeel Ahmed

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      Characterization of the shear zone with pole–pole electrical resistivity tomography (ERT) was carried out to explore deep groundwater potential zone in a water scarce granitic area. As existing field conditions does not always allow to plant the remote electrodes at sufficiently far of distance, the effect of insufficient distance of remote electrodes on apparent resistivity measurement was studied and shown that the transverse pole–pole array affects less compared to the collinear pole–pole array. Correction factor have been computed for transverse pole–pole array for various positions of the remote electrodes. The above results helped in exploring deep aquifer site, where a 270 m deep well was drilled. Temporal hydro-chemical samples collected during the pumping indicated the hydraulic connectivity between the demarcated groundwater potential fractures. Incorporating all the information derived from different investigations, a subsurface model was synthetically simulated and generated 2D electrical resistivity response for different arrays and compared with the field responses to further validate the geoelectrical response of deep aquifer set-up associated with lineament.

    • Above-ground tree outside forest (TOF) phytomass and carbon estimation in the semiarid region of southern Haryana: A synthesis approach of remote sensing and field data

      Kuldeep Singh Pritam Chand

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      Trees outside forest (TOF) play an important role in global carbon cycling, since they are large pools of carbon as well as potential carbon sinks and sources to the atmosphere. In view of the importance of biomass estimates in the global carbon (C) cycle, the present study demonstrates the potential of the standwise tree outside forest inventory data and finer spatial resolution of IRS-P6 LISS-IV satellite data to classify TOF, to estimate above-ground TOF phytomass and the carbon content of TOF in a semiarid region of the southern Haryana, India. The study reports that above-ground TOF phytomass varied from 1.26 tons/ha in the scattered trees in the rural/urban area to 91.5 tons/ha in the dense linear TOF along the canal. The total above-ground TOF phytomass and carbon content was calculated as 367.04 and 174.34 tons/ha, respectively in the study area. The study results conclude that the classification of TOF and estimation of phytomass and carbon content in TOF can be successfully achieved through the combined approach of Remote Sensing and GIS based spatial technique with the supplement of field data. The present approach will help to find out the potential carbon sequestration zone in the semi-arid region of southern Haryana, India.

    • An assessment of the FlowCapt acoustic sensor for measuring snowdrift in the Indian Himalayas

      R K Das P Datt A Acharya

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      Wind caused snow drifting plays a dominant role in the redistribution of snow mass that restructures a snowpack. Strong wind activity at the mountain tops results in uneven distribution of snow with erosion on windward side and deposition on leeward areas. Such snowdrift events are responsible for the formation of cornices, increase in the loading of avalanche release zones on the leeward side and consequent increase in the level of avalanche hazard. In this paper, we present the results of snowdrift measurement using an acoustic snow-drift meter, the FlowCapt, built by IAV Engineering, which was used during winter seasons of 2007–2010 at a field research station of Snow and Avalanche Study Establishment (SASE) in the western Himalayas. The aim of the study was to evaluate the suitability of the instrument in measuring snowdrift in the Himalayan weather conditions. Results proved the utility of the instrument as a useful tool to study drifting snow in remote areas. However, in the absence of conventional snow gauges for validation, the quality of the absolute snow flux data could not be ascertained.

    • The assessment of geodiversity – a premise for declaring the geopark Buzăului County (Romania)

      Laura Comănescu Alexandru Nedelea

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      The geopark Buzăului County does not belong to the Geoparks European Network, as there are numerous governmental, legislative and scientific initiatives in this respect. The geopark is situated in the central-south-eastern part of Romania (in Buzau county) and it has a special potential of geological, geomorphological, biogeographical and anthropic nature, a potential which has to be developed and brought into value. The idea of creating a geopark in this area is relatively recent and it was realized by a series of actions carried on by local authorities in partnership with several institutions, a partnership within which it was accomplished the proposal of a general development framework of the geopark, as well as the launching of a promotion campaign. The scope of this work is to evaluate the geodiversity existing in this space as an important starting point in declaring it as a European geopark, being known that it represents a real “open air museum”. The high values of geodiversity and biodiversity represent special strong points in this respect. The method we used was taken from the specialised literature, suffering a series of adjustments to the specifics of the studied area.

      In the present format, the method is applied for the first time in the Geography literature, so the values obtained cannot be compared with those obtained by other calculation formulas. Thus, values between 0.20 and 1.91 which resulted cover the entire scale of variables proposed.

    • Prediction of monthly mean daily global solar radiation using Artificial Neural Network

      V Sivamadhavi R Samuel Selvaraj

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      In this study, a multilayer feed forward (MLFF) neural network based on back propagation algorithm was developed, trained, and tested to predict monthly mean daily global radiation in Tamil Nadu, India. Various geographical, solar and meteorological parameters of three different locations with diverse climatic conditions were used as input parameters. Out of 565 available data, 530 were used for training and the rest were used for testing the artificial neural network (ANN). A 3-layer and a 4-layer MLFF networks were developed and the performance of the developed models was evaluated based on mean bias error, mean absolute percentage error, root mean squared error and Student’s 𝑡-test. The 3-layer MLFF network developed in this study did not give uniform results for the three chosen locations. Hence, a 4-layer MLFF network was developed and the average value of the mean absolute percentage error was found to be 5.47%. Values of global radiation obtained using the model were in excellent agreement with measured values. Results of this study show that the designed ANN model can be used to estimate monthly mean daily global radiation of any place in Tamil Nadu where measured global radiation data are not available.

    • Tidal and gravity waves study from the airglow measurements at Kolhapur (India)

      R N Ghodpage Devendraa Siingh R P Singh G K Mukherjee P Vohat A K Singh

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      Simultaneous photometric measurements of the OI 557.7 nm and OH (7, 2) band from a low latitude station, Kolhapur (16.8°N, 74.2°E) during the period 2004–2007 are analyzed to study the dominant waves present in the 80–100 km altitude region of the atmosphere. The nocturnal intensity variations of different airglow emissions are observed using scanning temperature controlled filter photometers. Waves having period lying between 2 and 12 hours have been recorded. Some of these waves having subharmonic tidal oscillation periods 4, 6, 8 and 12 hours propagate upward with velocity lying in the range 1.6–11.3 m/s and the vertical wave length lying between 28.6 and 163 kms. The other waves may be the upward propagating gravity waves or waves resulting from the interaction of inter-mode tidal oscillations, interaction of tidal waves with planetary waves and gravity waves. Some times, the second harmonic wave has higher vertical velocity than the corresponding fundamental wave. Application of these waves in studying the thermal structure of the region is discussed.

    • Yearly variation and annual cycle of total column ozone over New Delhi (29°N, 77°E), India and Halley Bay (76°S, 27°W), British Antarctic Survey Station and its effect on night airglow intensity of OH(8, 3) for the period 1979–2005

      P K Jana D K Saha D Sarkar

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      A critical analysis made on the long-term monthly, seasonal, yearly variation and annual cycle of total column ozone (TCO) concentration at New Delhi (29°N,77°E), India and Halley Bay (76°S, 27°W), a British Antarctic Service Station reveals more decline in yearly mean ozone concentration at Halley Bay than at New Delhi from 1979 to 2005. The nature of variations of monthly mean TCO during the months of August and September was the most identical with that of yearly mean ozone values at New Delhi and Halley Bay, respectively, for the same period. Annual cycles of TCO over these stations are completely different for the above period. The effect of O3 depletion on night airglow emission of OH(8, 3) line at New Delhi and Halley Bay has been studied. Calculations based on chemical kinetics show that the airglow intensity of OH(8, 3) has also been affected due to the depletion of O3 concentration. The yearly variations and annual cycle of intensities of OH(8, 3) line for the above two stations are depicted and compared. It has been shown that the rate of decrease of intensity of OH(8, 3) line was comparatively more at Halley Bay due to dramatic decrease of Antarctic O3 concentration.

    • Subject Index

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    • Author Index

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    • Acknowledgements

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