Sedimentational,structural and migmatitic history of the Archaean Dharwar tectonic province,southern India     

K. Naha  R. Srinivasan  S. Jayaram 《Journal of Earth System Science》1991,100(4):413-433

The earliest decipherable record of the Dharwar tectonic province is left in the 3.3 Ga old gneissic pebbles in some conglomerates of the Dharwar Group, in addition to the 3.3–3.4 Ga old gneisses in some areas. A sialic crust as the basement for Dharwar sedimentation is also indicated by the presence of quartz schists and quartzites throughout the Dharwar succession. Clean quartzites and orthoquartzite-carbonate association in the lower part of the Dharwar sequence point to relatively stable platform and shelf conditions. This is succeeded by sedimentation in a rapidly subsiding trough as indicated by the turbidite-volcanic rock association. Although conglomerates in some places point to an erosional surface at the contact between the gneisses and the Dharwar supracrustal rocks, extensive remobilization of the basement during the deformation of the cover rocks has largely blurred this interface. This has also resulted in accordant style and sequence of structures in the basement and cover rocks in a major part of the Dharwar tectonic province. Isoclinal folds with attendant axial planar schistosity, coaxial open folds, followed in turn by non-coaxial upright folds on axial planes striking nearly N-S, are decipherable both in the “basement” gneisses and the schistose cover rocks. The imprint of this sequence of superposed deformation is registered in some of the charnockitic terranes also, particularly in the Biligirirangan Hills, Shivasamudram and Arakalgud areas. The Closepet Granite, with alignment of feldspar megacrysts parallel to the axial planes of the latest folds in the adjacent schistose rocks, together with discrete veins of Closepet Granite affinity emplaced parallel to the axial planes of late folds in the Peninsular Gneiss enclaves, suggest that this granite is late-tectonic with reference to the last deformation in the Dharwar tectonic province. Enclaves of tonalite and migmatized amphibolite a few metres across, with a fabric athwart to and overprinted by the earliest structures traceable in the supracrustal rocks as well as in a major part of the Peninsular Gneiss, point to at least one deformation, an episode of migmatization and one metamorphic event preceding the first folding in the Dharwar sequence. This record of pre-Dharwar deformation and metamorphism is corroborated also by the pebbles of gneisses and schists in the conglomerates of the Dharwar Group. Volcanic rocks within the Dharwar succession as well as some of the components of the Peninsular Gneiss give ages of about 3.0 Ga. A still younger age of about 2.6 Ga is recorded in some volcanic rocks of the Dharwar sequence, a part of the Peninsular Gneiss, Closepet Granite and some charnockites. These, together with the 3.3 Ga old gneisses and 3.4 Ga old ages of zircons in some charnockites, furnish evidence for three major thermal events during the 700 million year history of the Archaean Dharwar tectonic province.  相似文献   

Prediction of downward flux of atmospheric radiation from clear skies     

J. Srinivasan 《Boundary-Layer Meteorology》1981,21(2):173-181

At present, there are two approaches to the prediction of downward flux of atmospheric radiation at the earth's surface. One can use either empirical correlations or radiation charts. The empirical correlations, being very elementary, do not always agree with observations made under different conditions. The radiation charts on the other hand require detailed knowledge of temperature and water vapour profiles. In the present paper, a semi-empirical approach is advocated. The emissivity of water vapour measured in the laboratory is used to predict the atmospheric downward radiation. Since the laboratory data are based on a homogeneous atmosphere, suitable pressure scaling is employed to take into account the non-homogeneity in the earth's atmosphere. The atmospheric downward radiation is obtained as a function of local temperature, water vapour scale height, and temperature lapse rate. It is shown that the resulting predictions agree somewhat better with observations than do the predictions based on empirical correlations.  相似文献   

Kr and Xe isotopes from spontaneous fission of ²⁴⁸Cm and ²⁵⁰Cf: Comparison with noble gases in carbonaceous chondrites     

B. Srinivasan  K.F. Flynn 《Earth and Planetary Science Letters》1980,47(2):235-242

Relative yields of Kr and Xe isotopes from the spontaneous fission of ²⁴⁸Cm and ²⁵⁰Cf have been determined mass spectrometrically. The yields are as follows: ⁸³Kr/⁸⁴Kr/⁸⁵Kr/⁸⁶Kr = 0.223/0.458/0.596/ ≡ 1.00 and 0.306/0.582/0.793/ ≡ 1.00;¹³¹Xe/¹³²Xe/¹³⁴Xe/¹³⁶Xe = 0.486/0.819/1.075/ ≡ 1.00 and 0.343/0.506/0.851/ ≡ 1.00 from ²⁴⁸Cm and ²⁵⁰Cf, respectively. The Xe yields from ²⁴⁸Cm agree with an earlier determination by Leich et al. [24]. Neither of these yield patterns matches that of “fissiogenic” Kr and Xe in carbonaceous chondrites and hence ²⁴⁸Cm and ²⁵⁰Cf are ruled out as progenitors of the meteoritic Kr and Xe. In general, none of the spontaneously fissioning nuclides of actinide elements can be identified as a possible progenitor. Even the mixtures of actinides, including a combination of ²⁴⁸Cm and ²⁵⁰Cm, are unsuitable. The origin of “anomalous” Kr and Xe in carbonaceous chondrites must then be traced either to the spontaneous fission of a superheavy element or to peculiarities in specific nucleosynthetic reactions.  相似文献   

Gamma rays from millisecond pulsars     

D. Bhattacharya  G Srinivasan 《Journal of Astrophysics and Astronomy》1991,12(1):17-25

We estimate the contribution of millisecond pulsars to the diffuse gamma-ray background of the Galaxy, and show that a significant fraction of the Galactic background may originate from them. A small number of the unidentified COS-B point sources may, in fact, be millisecond pulsars. It is argued that several hundred millisecond pulsars may be detectable as point sources by the GRO satellite A preliminary version of these results was presented at the NATO Advanced Study Institute on Neutron stars, AGNs and Jets, Erice, September 5–17, 1988. On leave from Raman Research Institute, Bangalore, India.  相似文献   

On the supernova remnants produced by pulsars     

Srinivasan  G.  Bhattacharya  D.  Dwarakanath  K. S. 《Journal of Astrophysics and Astronomy》1984,5(4):403-423

We conclude that pulsar-driven supernova remnants (SNRs) are extremely rare objects. Indeed an analysis of the known sample of plerions suggests a very low birthrate ∼ 1 in 240 years. Long-lived and bright plerions like the Crab nebula are likely to be produced only when the pulsar has an initial period ∼ 10–20 milliseconds and a field ∼ 10¹² G. Such pulsars inside rapidly expanding shell remnants should also produce detectable plerions. The extreme rarity of SNRs with such hybrid morphology leads us to conclude that these pulsars must have been born with an initial period larger than ∼ 35–70 milliseconds. Joint Astronomy Program, Department of Physics, Indian Institute of Science, Bangalore 560012.  相似文献   

GMRT observations of interstellar clouds in the 21cm line of atomic hydrogen     

Rekhesh Mohan  K. S. Dwarakanath  G. Srinivasan  Jayaram N. Chengalur 《Journal of Astrophysics and Astronomy》2001,22(1):35-50

Nearby interstellar clouds with high (|ν|≥10km s⁻¹) random velocities although easily detected in NaI and CaII lines have hitherto not been detected (in emission or absorption) in the HI 21cm line. We describe here deep Giant Metrewave Radio Telescope (GMRT) HI absorption observations toward radio sources with small angular separation from bright O and B stars whose spectra reveal the presence of intervening high random velocity CaII absorbing clouds. In 5 out of the 14 directions searched we detect HI 21cm absorption features from these clouds. The mean optical depth of these detections is ∼0.09 and FWHM is ∼10km s⁻¹, consistent with absorption arising from CNM clouds.  相似文献   

The global gas and dust budget of the Large Magellanic Cloud: AGB stars and supernovae, and the impact on the ISM evolution     

M. Matsuura  M. J. Barlow  A. A. Zijlstra  P. A. Whitelock  M.-R. L. Cioni  M. A. T. Groenewegen  K. Volk  F. Kemper  T. Kodama  E. Lagadec  M. Meixner  G. C. Sloan  S. Srinivasan 《Monthly notices of the Royal Astronomical Society》2009,396(2):918-934

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Comparison of small scale soil maps prepared by conventional methods and air photo-interpretation procedure     

G. Krishnamurti  T. R. Srinivasan 《Journal of the Indian Society of Remote Sensing》1974,2(2):47-52

A small scale soil map for a part of Barnagar Tehsil prepared by the adoption of a systematic air photo-interpretation procedure has been compared with the soil map for the same area resulting from a previous reconnaissance soil survey using toposheets as base maps. Tt has been shown that the soil boundaries of the photo-interpretation map are both more accurate and natural in shape; delineation of gullied lands has been achieved more accurately by the A.P.I. procedure; soil erosion could be mapped more consistently and accurately through photo-interpretation. Additionally. the photo-internretation procedure achieves accurate delineation of distinctive facets of land forms because of the advantages arising from the viewing of a stereo model of the landscape; this paves the way for easier and better soil mapping in view of the correlation between landscape elements and soil patterns. Apart from the increased accuracy and diminished costs the photo-interpretation procedure will be helpful in modernising previously prepared reconnaissance soil maps.  相似文献   

Monitoring and modelling of hydrological processes in the semiarid region of Brazil: The Cariri experimental basins     

Vajapeyam S. Srinivasan  Hugo M. de Alcântara  Carlos de O. Galvão  Ulisses A. Bezerra  John E. de Brito Leite Cunha 《水文研究》2021,35(5):e14194

Catchments have highly variable yields of runoff and soil erosion. The size, land use and the surface cover play a significant role and influence the catchment response and parameter values of simulation models. Two experimental basins—the Cariri basins—were equipped in a semi-arid region of Brazil, for obtaining runoff and sediment yield at different catchment scales, as well as, to evaluate the influence of the land use and surface cover. In the first basin, located in the municipality of Sumé, the field studies were carried out at two different scales: four micro-catchments with an area of around 0.5 ha and nine standard Wischmeier-type erosion plots of 100 m². The experimental units had varied vegetation and management. They were subjected only to natural rainfall events, and were monitored from 1982 to 1991. The total runoff and total sediment yield were determined for each of the events. The installations in the second basin, in the municipality of São João do Cariri, from 1999, include two erosion plots, three micro-catchments, and two sub-catchments of a small basin. These basins are still being monitored for runoff and sediment production. Among the micro-catchments two are nested to detect any scale effect at the micro-catchment level. Nearly 600 events of precipitation, that produced runoff in at least one of the experimental units, have been registered. These data have been used to evaluate the influence of various factors, including cultivation practices and to calibrate hydrological models for plots and micro-catchments. Parameters have been tested by means of cross validations among micro-catchments and sub-catchments. The data sets are made available to all the catchment hydrology researchers and others at https://doi.org/10.5281/zenodo.4690886 .  相似文献   

Time‐lapse pre‐stack seismic data registration and inversion for CO2 sequestration study at Cranfield     

Rui Zhang  Xiaolei Song  Sergey Fomel  Mrinal K Sen  Sanjay Srinivasan 《Geophysical Prospecting》2014,62(5):1028-1039

Pre‐stack seismic data are indicative of subsurface elastic properties within the amplitude versus offset characteristic and can be used to detect elastic rock property changes caused by injection. We perform time‐lapse pre‐stack 3‐D seismic data analysis for monitoring sequestration at Cranfield. The time‐lapse amplitude differences of Cranfield datasets are found entangled with time‐shifts. To disentangle these two characters, we apply a local‐correlation‐based warping method to register the time‐lapse pre‐stack datasets, which can effectively separate the time‐shift from the time‐lapse seismic amplitude difference without changing the original amplitudes. We demonstrate the effectiveness of our registration method by evaluating the inverted elastic properties. These inverted time‐lapse elastic properties can be reliably used for monitoring plumes.  相似文献