Geology of Pulikonda and Dancherla alkaline complexes,Andhra Pradesh     

G. Suresh  R. Ananthanarayana  R. C. Hanumanthu  Subhasish Ghosh  A. Anil Kumar  K. V. S. Reddy 《Journal of the Geological Society of India》2010,75(4):576-595

Geological studies on saturated to oversaturated and subsolvus aegirine-riebeckite syenite bodies of the Pulikonda alkaline complex and Dancherla alkaline complex were carried out. The REE distribution of the Dancherla syenite shows a high fractionation between LREE and HREE. The absence of Eu anomaly suggests source from garnet peridotite. The Pulikonda syenite shows moderate fractionation between LREE and HREE as reflected by enrichment of HREE and moderate enrichment of LREE. The negative Eu anomaly indicates role of plagioclase fractionation.Three distinct co-eval primary magmas i.e. mafic syenite-, felsic syenite- and alkali basalt magmas — all derived from low-degrees of partial melting of mantle differentiates and enriched metasomatised lower crust played a major role in the genesis and emplacement of the syenites into overlying crust along deep seated regional scale trans-lithospheric strike-slip faults and shear zones following immediately after late-Archaean calc-alkaline arc magmatism at different time-space episodes i.e. initially at craton margin and later on into the thickened interior of the Eastern Dharwar craton. The ductile sheared and folded Pulikonda alkaline complex was evolved dominantly from the magmas derived from partial melting of lower crust and minor juvenile magmas from mantle. Differentiation and fractionation by liquid immiscibility of mafic magma and commingling-mixing of intermediate and felsic magmas followed by fractionational crystallisation under extensional tectonics during waning stages of calc-alkaline arc magmatism nearer to the craton margin were attributed as the main processes for the genesis of Pulikonda syenite complex. Commingling and limited mixing of independent mantle derived mafic and felsic syenitic magmas and accompanying fractionation resulting into soda rich and potash rich syenite variants was tentatively deduced mechanism for the origin of Dancherla, Danduvaripalle, Reddypalle syenites and other bodies belonging to Dancherla alkaline complex at the craton interior. The Peddavaduguru syenite was formed by differentiation of alkali mafic magma (gabbro to diorite) and it’s simultaneous mingling with fractionated felsic syenitic magma under incipient rift. Vannedoddi and Yeguvapalli syenites were derived due to desilicification and accompanying alkali feldspar mestasomatism of younger potash rich granites along Guntakal-Gooty fault and along Singanamala shear zone respectively.  相似文献   

Nagaur — tertiary interface under Punjab-Haryana semi-desertic plains in western India     

R. C. Dey 《Journal of the Geological Society of India》2009,74(1):131-137

The subsurface Nagaur Basin in northwest Haryana and southwest Punjab hosts evaporite sequence, conformably overlain by Nagaur red beds and grey beds. A polymictic conglomerate intervenes the Nagaur sequence and the overlying Tertiary sequence. The focus is on the new finds of (i) distinctive ‘grey beds’ overlying ubiquitous red beds, (ii) ‘Malout conglomerate and grit’ horizon (Palaeocene-Miocene) marking an unconformity over the Nagaur Group (early Cambrian) and (iii) ‘entrapped gas and dried-up leaves/carbonaceous flakes’ in the conglomerate unit and succeeding Tertiary rocks. Palaeoenvironmental significance has been discussed. The Nagaur ‘red beds’ has been likened to ‘continental red beds’ of Schreiber (1978) and ‘reworked red beds’ of Krynine (1949). The ‘grey beds’ are channel fillings, fresh material having been derived from fresh cuttings by streams/rivers following structural grains in the Aravalli landscape where the interfluves provided weathered (oxidised) materials for the red beds. Association of continental red beds and grey beds is known in the Newark Series (Triassic) of the Eastern United States and the Keweenawan ‘late Precambrian’ of the Lake Superior region.  相似文献   

TeV neutrinos and gamma-rays from pulsars     

A. Bhadra  R. K. Dey 《Monthly notices of the Royal Astronomical Society》2009,395(3):1371-1375

Recent studies suggest that pulsars could be strong sources of TeV muon neutrinos provided positive ions are accelerated by pulsar polar caps to PeV energies. In such a situation, muon neutrinos are produced through the Δ-resonance in interactions of pulsar-accelerated ions with its thermal radiation field. High-energy gamma-rays should also be produced simultaneously in pulsar environment as both charged and neutral pions are generated in the interactions of energetic hadrons with the ambient photon fields. Here, we estimate TeV gamma-ray flux at the Earth from a few nearby young pulsars. When compared with the observations, we find that proper consideration of the effect of polar cap geometry in flux calculation is important. Incorporating such an effect, we obtain the (revised) event rates at the Earth due to a few potential nearby pulsars. The results suggest that pulsars are unlikely to be detected by the upcoming neutrino telescopes. We also estimate TeV gamma-ray and neutrino fluxes from pulsar nebulae for the adopted model of particle acceleration.  相似文献   

Vibroseis deconvolution: a comparison of cross-correlation and frequency-domain sweep deconvolution   总被引：3，自引：0，他引：3  

K.F. Brittle  L.R. Lines  A.K. Dey 《Geophysical Prospecting》2001,49(6):675-686

Ideally, traditional vibroseis processing produces a band-limited zero-phase Klauder wavelet through cross-correlation of the sweep with the recorded signal. An alternative wavelet processing method involves deconvolving the sweep from the recorded vibroseis trace. This deconvolution can be achieved through frequency-domain division. We compare and contrast the advantages and disadvantages of sweep deconvolution versus cross-correlation on synthetic and real data.  相似文献   

INITIATION OF SHELL MOTION ON SAND BEDS: AN EXPERIMENTAL STUDY     

Subhasish DEY  Alok KUMAR 《国际泥沙研究》2002,17(4)

1 INTRODUCTION Bivalve shells are found in biologically productive coastal regions encompassing the surf zone, tidal entrance and estuarine waters near the entrances. An example of a beach composed exclusively of shells (about 97% of the surficial sedimentary material) is the beach at John o'Groats in Scotland (Raymond and Hutchins, 1932; Komar, 1976). Southern Gulf Coast of Florida in USA (Runsak et al., 1966; Austin, 1971) and the banks of Lower Medway estuary in England (Kirby,…  相似文献   

Variations In Upper Mantle Structure Under Northern Australia     

S. C. Dey  B. L. N. Kennett  J. R. Bowman  A. Goody 《Geophysical Journal International》1993,114(2):304-310

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Morphological signatures of fault lines in an earthquake prone zone of southern Baromura hill,north-east India: a multi sources approach for spatial data analysis   总被引：3，自引：2，他引：1  

Sudip Dey  Prasamita Sarkar  Chandrani Debbarma 《Environmental Earth Sciences》2009,59(2):353-361

This paper aims to assess the morphological signatures of tectonic features (faults) on the basis of multi sources spatial data analysis. For that purpose, the present authors selected the southern part of Baromura hill of Tripura, which has been discussed very little in the scientific literatures. An extensive field work was done in the assumed faulted areas to understand the geomorphic signatures of faulting. In the field, GPS was used for fixing the ground control points. Scanned Survey of India (SOI) topographical sheets, SPOT PAN and Land sat band-5 was used for digital analysis. An old DEM on IRS LISS-III FCC was also consulted for final mapping. Two clear lineaments (Faults) were detected from field observation on southern Baromura hill. Apart from these, another one was found in the outer part of this hill range. An attempt was made to explain the morphological signatures of those faults by density slicing on radiometric data based on emittance of different physical components. Finally a geomorphic map with main tectonic features of Baromura was prepared for future disaster management planning.  相似文献   

A new cache of Eoarchaean detrital zircons from the Singhbhum craton,eastern India and constraints on early Earth geodynamics     

Bulusu Sreenivas  Sukanta Dey  Y.J.Bhaskar Rao  T.Vijaya Kumar  E.V.S.S.K.Babu  Ian S.Williams 《地学前缘(英文版)》2019,10(4):1359-1370

The dominant geodynamic processes that underpin the formation and evolution of Earth’s early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei.Here,we present U-Pb ages and Hf isotopic compositions of detrital zircon grains from^2.9 Ga old quartzites and magmatic zircon from a 3.505 Ga old dacite from the Iron Ore Group of the Singhbhum craton,eastern India.The detrital zircon grains range in age between 3.95 Ga and 2.91 Ga.Together with the recently reported Hadean,Eoarchean xenocrystic(up to 4.24 Ga)and modem detritus zircon grains from the Singhbhum craton,our results suggest that the Eoarchean detrital zircons represent crust generated by recycling of Hadean felsic crust formed at^4.3-4.2 Ga and^3.95 Ga.We observe a prominent shift in Hf isotope compositions at^3.6-3.5 Ga towards super-chondritic values,which signify an increased role for depleted mantle and the relevance of plate tectonics.The Paleo-,Mesoarchean zircon Hf isotopic record in the craton indicates crust generation involving the role of both depleted and enriched mantle sources.We infer a short-lived suprasubduction setting around^3.6-3.5 Ga followed by mantle plume activity during the Paleo-,Mesoarchean crust formation in the Singhbhum craton.The Singhbhum craton provides an additional repository for Earth’s oldest materials.  相似文献   

REVIEW ON LOCAL SCOUR DUE TO JETS   总被引：1，自引：0，他引：1  

ArindamSARKAR SubhasishDEY 《国际泥沙研究》2004,19(3):210-238

The safety of an apron of the energy dissipator is threatened by the large-scale scour in the downstream of the apron due to the erosive action of a horizontal jet issuing from a sluice opening. Also, large-scale deposition of the scoured sediments due to an impinging jet in a plunging pool type energy dissipator affects the passage of flow adversely in the downstream channels. Owing to the significant practical importance, the problem of local scour due to jets has been studied by many investigators, In this paper, a comprehensive review of the up-to-date investigations on local scour due to horizontal and impinging jets is presented including all possible aspects, such as scouring process, parameters affecting scour, time variation of scour velocity distribution on the apron and within the scour hole, development of boundary layer thickness, bed shear stress, scour estimation formulas and protection works.  相似文献   

Geochemistry and Origin of Neoproterozoic Granitoids of Meghalaya, Northeast India: Implications for Linkage with Amalgamation of Gondwana Supercontinent   总被引：2，自引：1，他引：2  

Subhasish Ghosh  A.E. Fallick  D.K. Paul  P.J. Potts 《Gondwana Research》2005,8(3):421-432

Many granitic bodies intrude the basement gneisses in Meghalaya Plateau, Northeast India. Rb-Sr whole-rock isotopic ages of the granitoids range from 881 to 479 Ma while the ages of the basement orthogneisses vary from 1714 to 1150 Ma. All the plutons are dominantly metaluminous and show geochemical variation. Oxygen isotopic compositions in the granitoids and gneisses are concordant (d¹⁸O: + 5.78% to + 8.70%). However, the gneisses from high-grade terrain have low d¹⁸O value of +2.52% to +5.31%. Initial ⁸⁷Sr/⁸⁶Sr (I_Sr) ratios of the plutons vary from 0.70459 to 0.71487 and tend to increase with progressive younging in age. The geochemical characters suggest derivation of the granites from lower crustal source. The fractionated rare earth patterns observed in the granitoids can be obtained by partial melting of gneisses or diorites. Some gneiss samples have experienced interaction with hydrothermal fluids resulting in lowering d¹⁸O. The isotopic ages of granite plutonism in Meghalaya are similar to the plutonic and tectonothermal events in other parts of India, southwestern Australia and document final amalgamation events of the Gondwana Supercontinent.  相似文献