New findings on the course of river sarasvati     

A. K. Gupta  J. R. Sharma  G. Sreenivasan  K. S. Srivastava 《Journal of the Indian Society of Remote Sensing》2004,32(1):1-24

Numerous studies have been carried out during last 20-25 years by different agencies to trace the courses of palaeo river Sarasvati. Varying number of courses of river Sarasvati have been suggested by the different workers in the north-western region. Taking advantage of the developments in satellite/ sensor and digital image processing technologies an attempt has been made to rediscover the course of river Sarasvati and solve the controversy regarding its exact course, in the sand covered Thar desert region. Data available from a variety of ground investigations carried out by different agencies working in this area have been analyzed in support of confirmation of palaeo channels, along the courses mapped under the present study. The results indicate that the river Sarasvati had its course through river Ghaggar and did not drain along the Aravalli hills. Also it did not shift its course drastically and continuously from east to west, as suggested by earlier workers. The image anomalies indicate that river Sarasvati flowed parallel to the river Indus as an independent river system (closer to the north-western Indian border) and did not flow through present course of river Nara. The findings raise the doubt that ‘Rise along Delhi-Hardwar ridge’ as suggested by earlier workers was the main cause for west-ward shift of Sarasvati river and ultimate drainage desiccation in the northwestern region. The analysis indicates towards rise in Himalayas/ Siwaliks and consequent displacements in the Siwaliks and its foot hills region (in the form of Yamuna and Satlej tear faults) as the main cause for drainage desiccation and disappearance of river Sarasvati.  相似文献   

The Neoproterozoic Malani magmatism of the northwestern Indian shield: implications for crust-building processes   总被引：1，自引：0，他引：1  

Kamal K. Sharma 《Journal of Earth System Science》2004,113(4):795-807

Malani is the largest event of anorogenic felsic magmatism (covering ∼50, 000 km²) in India. This magmatic activity took place at ∼750 Ma post-dating the Erinpura granite (850 Ma) and ended prior to Marwar Supergroup (680 Ma) sedimentation. Malani eruptions occurred mostly on land, but locally sub-aqueous conditions are shown by the presence of conglomerate, grits and pillow lava. The Malani rocks do not show any type of regional deformation effects. The Malanis are characterised by bimodal volcanism with a dominant felsic component, followed by granitic plutonism and a terminal dyke phase. An angular unconformity between Malani lavas and basement is observed, with the presence of conglomerate at Sindreth, Diri, and Kankani. This indicates that the crust was quite stable and peneplained prior to the Malani activity. Similarly, the absence of any thrust zone, tectonic mélange and tectonised contact of the Malanis with the basement goes against a plate subduction setting for their genesis. After the closure of orogenic cycles in the Aravalli craton of the northwestern shield, this anorogenic intraplate magmatic activity took place in a cratonic rift setting under an extensional tectonic regime.  相似文献   

Silica-poor,mafic alkaline lavas from ocean islands and continents: Petrogenetic constraints from major elements     

Shantanu Keshav  Gudmundur H Gudfinnsson 《Journal of Earth System Science》2004,113(4):723-736

Strongly silica-poor (ne-normative), mafic alkaline lavas generally represented by olivine nephelinites, nephelinites, melilitites, and olivine melilitites have erupted at various locations during Earth's history. On the basis of bulk-rock Mg#, high concentrations of Na₂O, TiO₂, and K₂O, and trace element geochemistry, it has been suggested that these lavas represent low-degree melts that have undergone little crystal fractionationen route to the surface. Many of these lavas also carry high-pressure mantle material in the form of harzburgite, spinel lherzolite, and variants of websterite xenoliths, and rare garnet-bearing xenoliths. However, phenocryst phases instead indicate that these magmas cooled to variable extents during their passage. We note subtle, yet important, differences in terms of CaO, Al₂O₃, CaO/AlP₂O3, and CaO/MgO. High-pressure experimental melting studies in CMAS-CO₂ (3-8 GPa) and natural lherzolitic systems (3GPa) demonstrate that at an isobar increasing F leads to a moderate decrease in CaO + MgO, whereas CaO/MgO and CaO/Al₂O₃ sharply decrease. Relatively high CaO/Al₂O₃ indicates melting in the presence of garnet (>- 85 km). Studies also demonstrate that CO₂-bearing lherzolitic systems, when compared with anhydrous ones, also have higher CaO content in the coexisting melt at a given P and T. Comparison of the bulk-rock major-element chemistry of silica-poor, mafic alkaline lavas with experimentally determined high-pressure melts indicates that melting of anhydrous mantle lherzolite or garnet pyroxenite is not able to explain many of the major element systematics of the lavas. However, high-pressure partial melts of carbonated lherzolite have the right major element trends. Among ocean islands, lavas from Samoa and Hawaii are perhaps the products of very low degree of partial melting. Lavas from Gran Canaria and Polynesia represent products of more advanced partial melting. On continents, lavas from South Africa and certain localities in Germany are the products of a very low degree of partial melting, and those from Texas and certain other localities in Germany are products of a slightly more advanced degree of partial melting of a carbonated lherzolite. Lavas from Deccan, Czech Republic, and Freemans Cove are the products of even more advanced degree of partial melting. The mere presence of mantle xenoliths in some of these lavas does not necessarily mean that the erupted lavas represent direct mantle melts.  相似文献   

Himalayan Collision Tectonics   总被引：1，自引：0，他引：1  

R.S. Sharma 《Gondwana Research》2003,6(4):950-951

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Estimation of Seismic Hazard Parameters for the Himalayas and its Vicinity from Complete Data Files     

D. Shanker  M. L. Sharma 《Pure and Applied Geophysics》1998,152(2):267-279

—The maximum likelihood estimation of earthquake hazard parameters has been made in the Himalayas and its surrounding areas on the basis of a procedure which utilizes data containing complete files of the most recent earthquakes. The entire earthquake catalogue used covers the period from 1900–1990. The maximum regional magnitude M _max?, the activity rate of the seismic event λ, the mean return period R of earthquakes with a certain lower magnitude M _max≥ m along with their probability of occurrence, as well as the parameter b of of Gutenberg Richter magnitude-frequency relationship, have been determined for six different seismic zones of the Himalayas and its vicinity. It is shown that in general the hazard is higher in the zone NEI and BAN than the other four zones. The high difference of the b parameter and the hazard level from zone to zone reflect the high seismotectonic complexity and crustal heterogeneity.  相似文献   

Tropical-middle latitude interactions viewed via wave energy flux in the frequency domain     

T. N. Krishnamurti  M. C. Sinha  Vasubandhu Misra  O. P. Sharma 《Dynamics of Atmospheres and Oceans》1998,27(1-4)

Over the upper troposphere of the polar latitudes the zonal flows exhibit a large variance on the time scale of the Madden-Julian oscillation, i.e. roughly 30–50 days. The other prominent regions for these intraseasonal oscillations are the Asian and Australian monsoon belts. These two regions are separated by the so-called critical latitude, to the south of which easterlies generally prevail and westerlies are prevalent to the north. A perplexing issue is that of possible tropical-middle latitude interactions across the critical latitude. The notion of the critical latitude emerged from the linear theories for the wave energy flux which assume a constancy in time for the zonal flows. This same problem, viewed in its full non-linear context, can be cast in a frequency domain. Such a formulation does not assume a constancy of the zonal flows in time but does permit the intraseasonal variations of the zonal flows to be present. The computation of the wave energy flux, from the more complete non-linear system in the frequency domain, requires the handling of linear, quadratic and triple product terms via use of Hayashi's co-spectral method. These results of the present study, based on 6 years of daily global data sets, show that wave energy flux clearly passes from the latitudes of the monsoon to the polar latitudes. A strong convergence of wave energy flux in the polar latitudes suggests the tropical-middle latitude convergence interactions across the so-called critical latitude—when the problem is viewed in the frequency domain.  相似文献   

Input-output model for runoff-sediment yield processes     

T.C. Sharma  W.G.S. Hines  W.T. Dickinson 《Journal of Hydrology》1979,40(3-4):299-322

Runoff (log-transformed) and sediment yield (log-transformed) sequences on a monthly or daily basis can be regarded as input and output for the watershed fluvial system. These sequences are nonstationary in general in different hydrological environments. Frequency and time domain analyses have shown that a parsimonious model can be built directly in terms of these nonstationary input-output sequences on a monthly and daily basis. A first-order dynamic model was found adequate to model the monthly runoff-sediment yield process; a second-order model adequately modeled the daily runoff-sediment yield process. The noise component in both cases possessed the characteristics of a white-noise sequence.  相似文献   

Electrical conductivity of some Indian basalts under various temperature conditions     

Mohan L. Gupta  S.R. Sharma 《Physics of the Earth and Planetary Interiors》1978,17(1):14-21

Electrical conductivity of nineteen samples of the Deccan Traps, collected from the Pawagarh area and two boreholes drilled at Koyna, has been measured in the temperature range from 475 K to about 1100 K. The results indicate the change of the conduction mechanism from impurity to electronic/ionic conduction as the temperature increases. Few samples show the normal behaviour, i.e. the increase of conductivity with temperature, while some samples show an anomalous behaviour between the temperatures 600 and 1000 K. This anomalous behavior may be due to either the dehydration of OH^? ions or/and the oxidation of Fe²⁺ to Fe³⁺.  相似文献   

Closing temperatures of different fission track clocks     

Y. P. Sharma  N. Lal  K. D. Bal  R. Parshad  K. K. Nagpaul 《Contributions to Mineralogy and Petrology》1980,72(3):335-336

The fission track closing temperatures of the minerals which are found to be suitable for fission track geochronology have been calculated for various cooling rates using the stepwise cooling. Biotite is found to have the lowest closing temperature whereas the sphene is having the highest. The closing temperature falls with decrease in cooling rate.  相似文献   

Plane failure analysis of rock slopes   总被引：1，自引：0，他引：1  

S. Sharma  T. K. Raghuvanshi  R. Anbalagan 《Geotechnical and Geological Engineering》1995,13(2):105-111

Summary Hoek and Bray (1981) gave an analytical approach for plane failure analysis for rock slopes that is limited to those slopes in which the upper slope surface is horizontal and the tension crack is vertical. An analysis is presented here which can take these factors into account. It is found that varying the angle of the upper slope from 0° to 30° causes a significant reduction in the factor of safety. Varying the tension crack from vertical to 70° only has an effect when the upper slope angle is less than 20°.  相似文献