Aeromagnetic signatures of Precambrian shield and suture zones of Peninsular India   总被引：2，自引：1，他引：1  

Mita Rajaram  S.P.Anand 《地学前缘(英文版)》2014,5(1):3-15

In many Precambrian provinces the understanding of the tectonic history is constrained by limited exposure and aeromagnetic data provide information below the surface cover of sediments,water,etc.and help build a tectonic model of the region.The advantage of using the aeromagnetic data is that the data set has uniform coverage and is independent of the accessibility of the region.In the present study,available reconnaissance scale aeromagnetic data over Peninsular India are analyzed to understand the magnetic signatures of the Precambrian shield and suture zones thereby throwing light on the tectonics of the region.Utilizing a combination of differential reduction to pole map,analytic signal,vertical and tilt derivative and upward continuation maps we are able to identify magnetic source distribution,tectonic elements,terrane boundaries,suture zones and metamorphic history of the region.The magnetic sources in the region are mainly related to charnockites,iron ore and alkaline intrusives.Our analysis suggests that the Chitradurga boundary shear and Sileru shear are terrane boundaries while we interpret the signatures of Palghat Cauvery and Achankovil shears to represent suture zones.Processes like metamorphism leave their signatures on the magnetic data:prograde granulites(charnockites)and retrograde eclogites are known to have high susceptibility.We fnd that charnockites intruded by alkali plutons have higher magnetization compared to the retrogressed charnockites.We interpret that the Dharwar craton to the north of isograd representing greenschist to amphibolite facies transition,has been subjected to metamorphism under low geothermal conditions.Some recent studies suggest a plate tectonic model of subductionecollisioneaccretion tectonics around the Palghat Cauvery shear zone(PCSZ).Our analysis is able to identify several west to east trending high amplitude magnetic anomalies with deep sources in the region from Palghat Cauvery shear to Achankovil shear.The magnetic high associated with PCSZ may represent the extruded high pressureeultra high temperature metamorphic belt(granulites at shallow levels and retrogressed eclogites at deeper levels)formed as a result of subduction process.The EW highs within the Madurai block can be related to the metamorphosed clastic sediments,BIF and mafc/ultramafc bodies resulting from the process of accretion.  相似文献   

Stability of the magnetopause     

G. L. Kalra  J. N. Tandon  Ramaswamy Rajaram 《Astrophysics and Space Science》1976,43(2):433-448

The Magnetosphere-Solar Wind boundary is treated as a tangential discontinuity between collisionless plasma described by C.G.L. equations. An estimate is made, analytically, of the minimum shear speed required to render the interface unstable for propagation in any arbitrary direction. It is found that even systems, which are, for all shear speeds, stable towards propagation parallel to the field, are rendered unstable by propagation away from the field, in some velocity domain. Numerical evaluations for parameters characteristic of the Solar wind-Magnetosphere boundary show that the interface could be unstable even under relatively quiet conditions.  相似文献   

Determination of the orbital parameters of binary pulsars     

Bhaswati Bhattacharyya  Rajaram Nityananda 《Monthly notices of the Royal Astronomical Society》2008,387(1):273-278

We present a simple method for determination of the orbital parameters of binary pulsars, using data on the pulsar period at multiple observing epochs. This method uses the circular nature of the velocity space orbit of Keplerian motion and produces preliminary values based on two one-dimensional searches. Preliminary orbital parameter values are then refined using a computationally efficient linear least-squares fit. This method works for random and sparse sampling of the binary orbit. We demonstrate the technique on (i) the highly eccentric binary pulsar PSR J0514−4002 (the first known pulsar in the globular cluster NGC 1851) and (ii) 47 Tuc T, a binary pulsar with a nearly circular orbit.  相似文献   

Worldwide distribution of polyclyclic aromatic hydrocarbons in urban road dust     

D. Majumdar  B. Rajaram  S. Meshram  P. Suryawanshi  C. V. Chalapati Rao 《International Journal of Environmental Science and Technology》2017,14(2):397-420

Polycyclic aromatic hydrocarbons (PAHs) are considered as one of the most important groups of organic environmental contaminants due to their toxicity, persistence and ubiquity. PAHs have been monitored in urban road dust at various locations worldwide in about last three decades. Resuspension of road dust containing PAHs is an important route of human exposure to PAHs. This paper collates the available information on reported concentrations of PAHs in urban road dust at various worldwide locations classified as industrial, residential, traffic, city and commercial and other areas, reported sources of PAHs and related interpretations. The available information has been reviewed and documented country-wise. Variation in PAHs concentrations over various worldwide locations have been scrutinized, and interestingly, most of the reported average PAHs concentrations were found to be distributed within a very narrow range of values, implying only little variation in average PAH concentrations in spite of great distances between locations, climatic variation and differences in anthropogenic activities.  相似文献   

Comparison of an algebraic multigrid algorithm to two iterative solvers used for modeling ground water flow and transport   总被引：1，自引：0，他引：1  

Detwiler RL  Mehl S  Rajaram H  Cheung WW 《Ground water》2002,40(3):267-272

Numerical solution of large-scale ground water flow and transport problems is often constrained by the convergence behavior of the iterative solvers used to solve the resulting systems of equations. We demonstrate the ability of an algebraic multigrid algorithm (AMG) to efficiently solve the large, sparse systems of equations that result from computational models of ground water flow and transport in large and complex domains. Unlike geometric multigrid methods, this algorithm is applicable to problems in complex flow geometries, such as those encountered in pore-scale modeling of two-phase flow and transport. We integrated AMG into MODFLOW 2000 to compare two- and three-dimensional flow simulations using AMG to simulations using PCG2, a preconditioned conjugate gradient solver that uses the modified incomplete Cholesky preconditioner and is included with MODFLOW 2000. CPU times required for convergence with AMG were up to 140 times faster than those for PCG2. The cost of this increased speed was up to a nine-fold increase in required random access memory (RAM) for the three-dimensional problems and up to a four-fold increase in required RAM for the two-dimensional problems. We also compared two-dimensional numerical simulations of steady-state transport using AMG and the generalized minimum residual method with an incomplete LU-decomposition preconditioner. For these transport simulations, AMG yielded increased speeds of up to 17 times with only a 20% increase in required RAM. The ability of AMG to solve flow and transport problems in large, complex flow systems and its ready availability make it an ideal solver for use in both field-scale and pore-scale modeling.  相似文献   

Wave-coupling at the magnetopause     

Ramaswamy Rajaram  G. L. Kalra  J. N. Tandon 《Astrophysics and Space Science》1974,31(1):143-153

The paper considers wave coupling for an arbitrary direction of propagation on the basis of single fluid hydromagnetic equations appropriate for a rarefied plasma. The analysis is used to study the transfer of solar wind momenta into the magnetosphere. It is found that wave refraction is significant only during disturbed conditions for waves travelling with the wind. Enhanced reflection of waves might be important even under quiet conditions in the flanks of the magnetosphere.  相似文献   

Induction by long period geomagnetic variations in the Indian sub-continent     

Mita Rajaram  B P Singh  S Y Waghmare 《Journal of Earth System Science》1982,91(1):79-83

In the present paper storm time variations and 27-day geomagnetic periodicity have been analysed to estimate the depth of the substitute conductor, assuming an infinitely (super) conducting core model of the earth. The advantage of using data from a restricted longitude range is that the uncertainties arising from lateral contrasts in the upper mantle and contributions from Sq current systems are considerably reduced. The result of the present analysis, which has been done in the time domain, gives a value of 522 km for the depth of the substitute conductor in case of storm time variations which rises to 870 km for 27-day recurrent storms. A higher value of the depth for 27-day variations indicate that the rise in conductivity inside the earth is not like a step function rather is a gradual one. The value of 522 km for storm time variations for the Indian region is smaller than the global average. This is natural to expect because the Indian sub-continent is known to be a tectonically active region.  相似文献   

An application of complex demodulation technique to geomagnetic data and conductivity anomaly studies     

A. K. Agarwal  B. P. Singh  N. Nityananda 《Journal of Earth System Science》1980,89(1):67-77

The method of complex demodulation has been used here to compute the amplitude and phase of a signal present in a geomagnetic series using, Banks’ method. It is found that the results are quite accurate when four or more continuous cycles of the signal of interest are present. The same limitations have also been observed when band-pass filters are used to isolate a signal. The information on phase is always correct. It is concluded that complex demodulation will give correct results for periodic variations like 11-year, 27-day, Sq or pulsations; but will give small values of amplitude for signals like sudden impulses or bays. The latter is not a limitation in conductivity studies where ratios likeZ/H, Z/D orH/D are mostly used in calculations. It has been shown that even with the records of one magnetic storm the cause of anomalies can be accurately identified which otherwise would need a large number of events.  相似文献   

Petrology and sedimentation of the middle siwalik clays at dholkhand,saharanpur district,U.P., India     

Nityananda Bhattacharya  Sarada Saran Misra 《Contributions to Mineralogy and Petrology》1963,9(2):139-147

The Middle Siwalik clays at Dholkhand, Saharanpur district, U. P., in India were studied to investigate the nature of Siwalik (middle Miocene to lower Pleistocene) sedimentation in relation to the tectonism associated with the Himalayan orogenesis. The clays are reddish brown to buff in color containing montmorillonite, expandable mixed-layers, degraded chlorite, and illite. The clays were studied byX-ray diffractometry using standard techniques with copper radiation. The clay mineral distribution of the Middle Siwaliks indicates that the material was deposited under continental conditions in stream channels during periods of minimum current activity. The clays were deposited by slow sedimentation and are little affected by diagenesis. Further work in this area and elsewhere are now under progress to establish the relation of Siwalik sedimentation with the uplift of the Himalayas in the Tertiary period.  相似文献   

"Making Place": The "Pacific Solution" and Australian Emplacement in the Pacific and on Refugee Bodies     

Prem Kumar Rajaram 《Singapore journal of tropical geography》2003,24(3):290-306

In September 2001, Australia effected a "Pacific Solution" to its "refugee problem": the interception and transfer of "unauthorised boat arrivals" to processing centres in the Pacific Third World. These centres were agreed to by poor countries that were approached precisely because of their vulnerability and dependence upon Australia, in exchange for increases in aid. Australia thereby created a regional refugee problem and, in so doing, Australian seignorage also demands that the laws of those sovereign countries be placed in stasis so that people not convicted of a crime may be detained indefinitely. The Pacific region, in effect, came to be mapped in terms of its utility to Australia, both downplaying and concealing complex economic, social and political issues. This essay studies the Pacific Solution as a means of Australian "emplacement" in the Pacific and on refugee identity/bodies. Both refugee identity and the Pacific Third World are assessed in terms of their utility in serving as sites for Australian emplacement, whereby and wherein the borders of Australia are reinforced, to the detriment of extant "local" emplacements.  相似文献