Contrasting pressure–temperature–deformation history across a vestigial craton–mobile belt boundary: the western margin of the Eastern Ghats Belt at Deobhog, India     

S. Gupta  A. Bhattacharya  M. Raith  & J.K. Nanda 《Journal of Metamorphic Geology》2000,18(6):683-697

At Deobhog, migmatitic gneisses and granulites of the Eastern Ghats Belt are juxtaposed against a cratonic ensemble of banded augen gneiss, amphibolite and calcsilicate gneiss, intruded by late hornblende granite and dolerite. In the migmatitic gneiss unit, early isoclinal folds (syn‐D_1M and D_2M) are reoriented along N–S‐trending and E‐dipping shear planes (S_3M), with (S_1M–S_3M) intersection lineations having steep to moderate plunges. The near‐peak P–T condition was syn‐D_3M (≥900 °C, 9.5 kbar), as inferred from syn‐D_3M Grt+Opx‐bearing leucosomes in mafic granulites, and from thermobarometry on Grt (corona)–Opx/Cpx–Pl–Qtz assemblages. The P–T values are consistent with the occurrence of Opx–Spr–Crd assemblages in spatially associated high‐Mg–Al pelites. A subsequent period of cooling followed by isothermal decompression (800–850 °C, c. 7 kbar) is documented by the formation of coronal garnet and its decomposition to Opx+Pl symplectites in mafic granulites. Hydrous fluid infiltration accompanying the retrograde changes is manifested in biotite replacing Opx in some lithologies. The cratonic banded gneiss–granite unit also documents two phases of isoclinal folding (D_1B & D_2B), with the L_2B lineation girdle different from the lineation spread in the migmatitic gneiss unit. Calcsilicate gneiss (Hbl–Pl–Cpx–Scap–Cal) and amphibolite (Hbl–Pl±Grt±Cpx) within banded gneisses record syn‐D_2B peak metamorphic conditions (c. 700 °C, 6.5 kbar), followed by cooling (to c. 500 °C) manifested in the stabilization of coronal clinozoisite–epidote. The D_3B shear deformation post‐dates granite and dolerite intrusions and is characterized by top‐to‐the‐west movement along N–S‐trending, E‐dipping shear planes. Deformation mechanisms of quartz and feldspar in granites and banded gneisses and amphibole–plagioclase thermometry within shear bands in dolerites document an inverted syn‐D_3B thermal gradient with temperature increasing from 350 to 550 °C in the west to ≥700 °C near the contact with the migmatitic gneiss unit. The thermal gradient is reflected in the stabilization of chlorite after hornblende in S_3B shears to the west, and post‐D_2B neosome segregation along D_3B folds and shears to the east. The contrasting lithologies, early structures and peak metamorphic conditions in the two units indicate unconnected pre‐D₃P–T –deformation histories. The shared D₃ deformation in the two units, the syn‐D₃ inverted thermal gradient preserved in the footwall cratonic rocks and the complementary cooling and hydration of the hanging wall granulites across the contact are attributed to westward thrusting of ‘hot’ Eastern Ghats granulites on ‘cool’ cratonic crust. It is suggested that the Eastern Ghats migmatitic gneiss unit is not a reworked part of the craton, but a para‐autochthonous/allochthonous unit emplaced on and amalgamated to the craton.  相似文献   

Uniform anisotropic cosmological model with string source     

Sudeepto Bhattacharya  T. M. Karade 《Astrophysics and Space Science》1993,202(1):69-75

By adopting the comoving coordinate system, the axially symmetric models with string dust cloud source are obtained. Some of these models are singular free even at an initial epoch, where the geometric as well as thep-strings become singular.  相似文献   

Experimental p-y curves for liquefied soils from centrifuge tests     

Dash  Suresh R.  Bhattacharya  Subhamoy 《地震工程与工程振动(英文版)》2021,20(4):863-876

The present study aims to obtain p-y curves(Winkler spring properties for lateral pile-soil interaction) for liquefied soil from 12 comprehensive centrifuge test cases where pile groups were embedded in liquefiable soil. The p-y curve for fully liquefied soil is back-calculated from the dynamic centrifuge test data using a numerical procedure from the recorded soil response and strain records from the instrumented pile. The p-y curves were obtained for two ground conditions:(a) lateral spreading of liquefied soil, and(b) liquefied soil in level ground. These ground conditions are simulated in the model by having collapsing and non-collapsing intermittent boundaries, which are modelled as quay walls. The p-y curves back-calculated from the centrifuge tests are compared with representative reduced API p-y curves for liquefied soils(known as p-multiplier). The response of p-y curves at full liquefaction is presented and critical observations of lateral pile-soil interaction are discussed. Based on the results of these model tests, guidance for the construction of p-y curves for use in engineering practice is also provided.  相似文献   

Albedo-rainfall Feedback Over Indian Monsoon Region Using Long Term Observations Between 1981 to 2000     

Bimal Kumar Bhattacharya  Keshav R. Gunjal  Sushma Panigrahy  Jai Singh Parihar 《Journal of the Indian Society of Remote Sensing》2011,39(3):393-406

Albedo determines radiation balance of land (soil-canopy complex) surface and influence boundary layer structure of the atmosphere. Accurate surface albedo determination is important for weather forecasting, climate projection and ecosystem modelling. Albedo-rainfall feedback relationship has not been studied so far using observations on spatial scale over Indian monsoon region due to lack of consistent, systematic and simultaneous long-term measurements of both. The present study used dekadal (ten-day) composite of satellite (e.g. NOAA) based Pathfinder AVHRR Land (PAL) datasets between 1981 and 2000 over India (68–100°E, 5–40°N) at 8 km spatial resolution. Land surface albedo was computed using linear transformation of red and near infrared (NIR) surface reflectances. The cloud effects were removed using a smoothening filter with harmonic analysis applied to time series data in each year. The monthly, annual and long term means were computed from dekadal reconstructed albedo. The mean per year and coefficient of variation (CV) of surface albedo over seventeen years, averaged over Indian land region, were found to show a significantly decreasing (0.15 to 0.14 and 60 to 40%, respectively) trend between 1981 and 2000. Among all the land use patterns, the inter-annual variation of albedo of Himalayan snow cover showed a significant and the steepest reducing trend (0.42 – 0.35) followed by open shurbland, grassland and cropland. No significant change was noticed over different forest types.. This could be due to increase in snow melting period and snow melt area. A strong inverse exponential relation (correlation coefficient r = 0.95, n = 100) was found between annual rainfall and annual albedo over seven rainfall zones. The decreasing trend in snow-albedo of accumulation period (September to March) follows the declining trend in measured south-west monsoon rainfall between 1988 (980 mm) to 1998 (880 mm) over India. This finding perhaps suggests the possible reversal of reported coupling of increased snowfall followed by lower monsoon rainfall.  相似文献   

Morphostratigraphy and palaeoclimate appraisal of the Leh valley,Ladakh Himalayas,India     

Dhananjay A. Sant  Sudesh K. Wadhawan  Rajinder K. Ganjoo  Nathani Basavaiah  Prabhin Sukumaran  Sourabh Bhattacharya 《Journal of the Geological Society of India》2011,77(6):499-510

In the present paper we study morphology, occurrence and mutual interrelationship of erosional (amphitheaters) and depositional landforms belonging to glacial (moraines), fluvio-glacial (glacial out wash), mass wasting (alluvial fans), aeolian (obstacle dune and sand sheets) and lacustrine (palaeo-lake sediments) processes within the Leh valley. These landforms are the geomorphic expression of past deglaciation grouped into five Formative Stages of Landform (FSL 1 to FSL 5) development in the Leh valley. The broad age bracket for the formative stages are based on the empirical relationship of the landforms, available chronology and their correlation with comparable climate phases. The retreat of glaciers in the Leh valley, along the southern slopes of Ladakh hill range and their retention over the northern slopes and Karakoram is further explained.  相似文献   

Inferring the hydro-geochemistry of fluoride contamination in Bankura district, West Bengal: A case study     

S. Chakrabarti  H. N. Bhattacharya 《Journal of the Geological Society of India》2013,82(4):379-391

In view of the recent reports of fluorosis in many parts of Bankura district, West Bengal, a detailed hydrogeochemical monitoring was carried out in the different blocks of Bankura to find out the level and extent of affectation. It is observed that the sub-surface environment of Bankura is appreciably contaminated with the deadly poison of fluoride. Out of the 3617 tube wells surveyed in 10 affected blocks, 612 sources are detected with fluoride above the desirable limit of 1 mg/l. In addition, down-the-hole rock drilling was performed at 15 different locations in 8 worst affected blocks of Bankura. Nearly 75% of the drill-hole rock chip samples and 62% of sub-surface water samples collected from different depths is found to have fluoride equal to or above 4000 mg/kg and 1 mg/l respectively. Detailed microscopic examination of drill chip samples has indicated diverse rock units in close succession, such as Chotanagpur Gneissic Complex, Singhbhum Group of rocks, anorthosite suite and unclassified metamorphics of Archaean-Proterozoic age. All these rocks have been intruded later by granitic fluids causing mineralization of fluoride to take place. Besides, fluoride is also found derived, to lesser extent, from Older Alluvium which bears different fluoride bearing minerals. Preliminary health surveys have revealed that dental and skeletal fluorosis are prevalent in the study area, which further corroborates with the analytical findings.  相似文献   

Monitoring of River Center Line and Width—A Study on River Brahmaputra     

Aveedibya Dey  Rajib Kumar Bhattacharya 《Journal of the Indian Society of Remote Sensing》2014,42(2):475-482

Monitoring of river width and centerline is one of the most important activities in river engineering. Changes in the width and center line can be attributed to several reasons and monitoring these changes can be conveniently achieved with the aid of remote sensing images. In this study, digital image processing techniques have been implemented using the image processing tool-box available in MATLAB for studying temporal variations of width and centerline of the river Brahmaputra in its 300 Km reach in the state of Assam, India. The current study uses relatively high resolution imageries acquired from the LANDSAT series of satellites. Apart from the LANDSAT imageries, the low resolution imageries acquired by MODIS program is also used in order to see the variation in the obtained results. The evaluation of the results shows that the digital image processing technique is very handy and can be applied to obtain the centerline and width of a river. The evaluation also shows that the low resolution image can also be used for obtaining centerline of a river. However, it may give erroneous result when width of the river is narrow or very large.  相似文献   

Landuse classification for a part of kamiichi area,Japan, using visible,IR and thermal IR data     

T.J. Majumdar  B.B. Bhattacharya  S. Tanaka  A. Rikimaru 《国际地球制图》2013,28(2):39-44

Bendix 11 channel aerial MSS data have been used to generate landuse thematic classification using Image‐100 interactive image processing system for a part of Kamiichi area, Japan. Two different classification schemes were attempted, once with Visible and IR data using supervised classification technique and then with Thermal IR data using density slicing technique. Comparison of both the results shows that main features of interest are uniquely classified in both the cases. In addition, higher order classification could also be achieved using Visible, IR and Thermal IR data for each class of interest.  相似文献   

Usage of ERS SAR data over the Singhbhum Shear Zone,India for structural mapping and tectonic studies     

S. K. Pal  A. K. Bhattacharya 《国际地球制图》2013,28(4):285-295

The extraction of lineaments and anomalous patterns in the Singhbhum Shear Zone, Jharkhand, India, has multifaceted applications for mineral exploration as well as for geological interpretation of neotectonic movements. ERS-1 SAR data are very useful for such applications because of their structural information content. A comparative study has been attempted with ERS, Landsat and IRS images for the interpretation of various geological structures over the Singhbhum Shear Zone. The Rose diagram generated from this study has shown major trends that matched well with the geological map of the area and the associated tectonic boundary as well as with the results obtained from ground based studies.  相似文献   

Earthquake Source Zones in Northeast India: Seismic Tomography, Fractal Dimension and b Value Mapping     

Pankaj M. Bhattacharya  J. R. Kayal  Saurabh Baruah  S. S. Arefiev 《Pure and Applied Geophysics》2010,167(8-9):999-1012

We have imaged earthquake source zones beneath the northeast India region by seismic tomography, fractal dimension and b value mapping. 3D P-wave velocity (Vp) structure is imaged by the Local Earthquake Tomography (LET) method. High precision P-wave (3,494) and S-wave (3,064) travel times of 980 selected earthquakes, m _d ≥ 2.5, are used. The events were recorded by 77 temporary/permanent seismic stations in the region during 1993–1999. By the LET method simultaneous inversion is made for precise location of the events as well as for 3D seismic imaging of the velocity structure. Fractal dimension and seismic b value has been estimated using the 980 LET relocated epicenters. A prominent northwest–southeast low Vp structure is imaged between the Shillong Plateau and Mikir hills; that reflects the Kopili fault. At the fault end, a high-Vp structure is imaged at a depth of 40 km; this is inferred to be the source zone for high seismic activity along this fault. A similar high Vp seismic source zone is imaged beneath the Shillong Plateau at 30 km depth. Both of the source zones have high fractal dimension, from 1.80 to 1.90, indicating that most of the earthquake associated fractures are approaching a 2D space. The spatial fractal dimension variation map has revealed the seismogenic structures and the crustal heterogeneities in the region. The seismic b value in northeast India is found to vary from 0.6 to 1.0. Higher b value contours are obtained along the Kopili fault (~1.0), and in the Shillong Plateau (~0.9) The correlation coefficient between the fractal dimension and b value is found to be 0.79, indicating that the correlation is positive and significant. To the south of Shillong Plateau, a low Vp structure is interpreted as thick (~20 km) sediments in the Bengal basin, with almost no seismic activity in the basin.  相似文献