Propagation of plane relativistic shock waves in a slowly moving medium

Similarity solutions for the propagation of plane relativistic shock waves in a slowly moving medium, where the nucleon number density obeys an exponential law ofx/t, is obtained in this paper. The shock surface moves with constant velocity and the total energy of the disturbance is dependent on time. The solutions are applicable only to an isothermal medium.     

Morphological characteristics and emplacement mechanism of the seamounts in the Central Indian Ocean Basin

The morphotectonic features of the Central Indian Ocean Basin (CIOB) provide information regarding the development of the basin. Multibeam mapping of the CIOB reveals presence of abundant isolated seamounts and seamount chains sub-parallel to each other and major fracture zones along 73° E, 79° E and 75°45′ E. Morphological analyses were carried out for 200 seamounts that occur either as isolated edifies or along eight sub-parallel chains. The identified eight parallel seamount chains that trend almost north–south and reflecting the absolute motion of the Indian plate, probably originated from the ancient propagative fractures. Inspite of the differences in their height, the seamounts of these eight chains are morphologically correlatable. In the study area the seamounts are clustered north and south of 12° S latitude. Interestingly, in the area north of 12° S (area II: 9°–12° S) the seamounts are distinctly smaller (≤ 400 m height) whereas, the area south of 12° S (area I: 12°–15° S) has a mixed population of seamounts. The normalized abundance of the CIOB seamount is 976 seamounts/10⁶ km² but on a finer scale this value varies from 500 to 1600 seamounts/10⁶ km², which is less than the seamount concentrations of the Pacific and Atlantic oceans (9000 to 16,000 seamounts/10⁶ km²). Three categories of seamounts are present in the CIOB e.g. (1) single-peaked (2) multi-peaked and (3) composite. The study indicate that single-peaked seamounts are dominant (89%) while multi-peaked is less (8%) and composite ones are rare (3%) in the CIOB.The progressive northward movement of the Indian continent caused collision between India and Asia at around 62 Ma ago. A majority of the near-axis originated seamounts in the CIOB seemed to have formed as a consequence of the temporally widespread (Cretaceous  65 Ma to late Eocene < 49 Ma) collision between India and Eurasia. The regional stress patterns in the Indian plate vary N to NE in the continent and N to NW in Indian Ocean areas. The combined effect of the regional stress patterns maintained the orientation of the seamount chains and the local stress regime helped in the upwelling of magma and formation of seamounts. The low heat flow, morphological features and geochemical signature indicate that the morphotectonic structures formed contemporaneously with the oceanic crust.     

Record of Leaf and Pollen cf. <Emphasis Type="Italic">Sloanea</Emphasis> (Elaeocarpaceae) from the Middle Siwalik of Darjeeling sub-Himalaya,India and its Palaeobiogeographic Implications

Fossil leaf impressions and pollen grains comparable to modern Sloanea sp. of Elaeocarpaceae collected from the middle part of the Siwalik sediments (Geabdat Sandstone Formation; Pliocene) in Darjeeling foothills of eastern Himalaya are reported in the present communication. On the basis of macro morphological features, leaf remains are described as a new species Sloanea siwalika sp. nov. This is the first authentic record of the occurrence of leaf and pollen grains comparable to the genus Sloanea L. from the Cenozoic sediments of India and Asia as well. The recovery of this species and other earlier-described evergreen taxa from the same formation, suggests the existence of a tropical, warm and humid climatic conditions during the depositional period. The present study further suggests that after Pliocene the taxon might have shifted from Darjeeling Himalayan region to the adjoining southeast Asian land masses, due to possible climate change caused by post-Pliocene orogenic movement of the Himalaya.     

Phosphate minerals as a recorder of P-T-fluid regimes of metamorphic belts: example from the Palaeoproterozoic Singhbhum Shear Zone of the East Indian shield

The Arcuate Singhbhum Shear Zone (SSZ) forms an integral part and occurs at the southern fringe of the Palaeoproterozoic North Singhbhum Fold Belt (NSFB) of the East Indian Shield. Repeated folding, ductile shearing, and accompanying hydrothermal activities in the SSZ during the late Palaeoproterozoic (ca. 1.66–1.60 Ga) orogeny resulted in a highly tectonized ensemble of rocks including a suite of peraluminous kyanite-rich quartzite (KQR). Near Kanyaluka village, the KQR shows millimetre- to decimetre-thick alternation of kyanite- and quartz-rich bands. The banded rock is intensely sheared and is cross-cut by weakly deformed to undeformed kyanite-quartz veins. In many places, kyanite-rich bands show sea-green coloured pods rich in lazulite. Textural studies reveal that deformed kyanite and quartz grains are sequentially replaced by augelite and lazulite (X_Mg > 0.97) at the terminal phase of shearing in the SSZ. Modelling of observed textures and mineral compositions with the C-Space program shows the following augelite- and lazulite-forming reactions:

1. 1.829Kyanite + 0.998P + 1.5H₂O + 0.001Ca = 1Augelite + 1.666Al + 0.001 Mg + 1.822SiO₂ + 0.002Fe + 0.0002Na

2. 1.778Kyanite + 0.667Augelite + 1.294P + 1.011 Mg + 0.011Fe + 0.0001Na = 1Lazulite + 2.833Al + 1.78SiO₂ + 0.001 Ca

Stoichiometry of the balanced chemical reactions suggests that a significant amount of P, Mg, and H₂O were added to, and Al and SiO₂ were subtracted from, the host kyanite-rich rock to produce augelite and lazulite. Experimental studies in the system Al₂O₃-SiO₂-FeO-MgO-P₂O₅-H₂O and the results of quantitative geothermobarometry suggest that lazulite and augelite were formed in a narrow temperature (440 ± 40°C) and pressure (~6.3 ± 1 kbar) range. Ductile shearing along the SSZ channelized the P- and Mg-rich fluids that metasomatized the kyanite-rich bands and veins to produce lazulite. The inferred P-T conditions can be explained by burial of the studied rock under an ~25 km-thick thrust sheet of NSFB during the Palaeoproterozoic orogenesis.     

Petrogenesis of ultramafic-mafic to felsic plutonic rock associations from southern portion of Chhotanagpur Gneissic Complex in Central India: A multi-stage crust-mantle interaction process

A granite-granodiorite-gabbro-ultramafic rock association occurs in the southern sector of Chhotanagpur Gneissic Complex in Central India. Field relations show mingling and mixing of mafic and granodioritic magmas along the contacts of the intrusives. Petrographic studies, coupled with analyses of phase compositions and bulk rock major and trace element compositions favor origin of mafic magma from partial melting of sub-continental hybridized lithospheric mantle and subsequent two stage emplacement. Initial ponding of mafic magma at basal crust elevated the geothermal gradient so as to cause partial melting of lower crustal materials and generation of granodioritic melt. Simultaneous emplacement of granodioritic and mafic magmas tapped from basal crustal reservoir at mid-crustal depth resulted in restricted mingling-mixing along the contacts of the contrasting magma types locally producing rocks of dioritic composition. The mode of evolution of this cogenetic mafic-felsic association, when combined with available geochronological data, has important implications in demarcation of the extent of Grenvellian orogen that resulted in amalgamation of the Southern Crustal Province of India (SCP) with the Bundelkhand Craton or Northern Crustal Province (NCP).     

Metal distributions in seawater,sediment and marine benthic macroalgae from the South Australian coastline

Algal species which are ubiquitous along the coastlines of many countries reflect the environmental conditions of the coastal seawater and may serve as useful biomonitors of anthropogenic pollution. Heavy metal concentrations of ten elements (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) of potential environmental concern were determined in seawater, sediments and twelve species of benthic marine macroalgae from four locations (Glenelg, Port Adelaide, Port Broughton and Port Pirie) along the South Australian coastline. The four sites chosen represented varying degrees of metal contamination, where the capacity for benthic macroalgae to accumulate heavy metals from the environment was evaluated. Spatial differences in heavy metal concentration in both seawaters and sediments were observed at all sites with the highest concentrations of heavy metals including Cd (125 μg g^?1), Pb (2,425 μg g^?1) and Zn (7,974 μg g^?1) found in the finer sediment fractions (<250 μm) of Port Pirie. While all algal species studied (Acrosorium polyneurum, Anotrichium tenue, Cystophora Cephalornithos Cystophora monillifera, Cystophora monilliformis, Dictyopteris australis, Gelidium micropterum, Gracilaria, Hormophysa Cuneiformis, Sargassum cinctum, Scaberia agardhii and Ulva lactuca) accumulated metals to varying degrees, Blindigia marginata was a good biomonitor species for a number of metals including Cd, Co, Cr, Fe, Pb and Zn, exhibiting both relatively high total metal concentrations and significant concentration factors.     

Cyclic Thermo-Mechanical Analysis of Wellbore in Underground Compressed Air Energy Storage Cavern

The compressed air energy storage (CAES) method is a viable method of storing surplus energy underground when there is a mismatch between energy generation and demand. Wellbores embedded in rock are an integral part of energy storage structures, and are used for injecting and extracting the compressed air. During injection and production cycles, the storage reservoir and wellbore are subjected to cyclic change in external pressure and temperature, which may cause failure of the wellbore. In this paper, cyclic thermo-mechanical analysis of a horizontal wellbore in an underground CAES cavern is performed using finite element analysis. The rock behavior is simulated using the Mohr-Coulomb constitutive law. The reduction in the yield strength of rock with increase in the number of loading cycles is taken into account in the analysis. Parametric sensitivity studies are carried out to study the effects of dilation and friction angles of rock, the ratio of in situ horizontal and vertical stresses, loading frequency, and the magnitude of the temperature cycles in the cavern on the wellbore performance for different types of rock. The thermo-mechanical cyclic behavior leads to plastic strains that are greater than those obtained by performing mechanical analysis only. Significantly large deformation is generated in rock for large dilation angle and high loading frequencies.     

Cosmological evolution across phantom crossing and the nature of the horizons

Recent observational evidences demand that the universe is going through an accelerating phase and hence in the frame work of Einstein gravity the matter should be exotic in nature. In the present work, we study the evolution of the apparent and event horizons across phantom barrier (a cosmological constant) and examine the validity of the generalized second law of thermodynamics (GSLT) for the universe bounded by the horizons.     

Particle motion in the field of a five-dimensional charged black hole

In this paper, we have investigated the geodesics of neutral particles near a five-dimensional charged black hole using a comparative approach. The effective potential method is used to determine the location of the horizons and to study radial and circular trajectories. This also helps us to analyze the stability of radial and circular orbits. The radius of the innermost stable circular orbits have also been determined. Contrary to the case of massive particles for which, the circular orbits may have up to eight possible values of specific radius, we find that the photons will only have two distinct values for the specific radii of circular trajectories. Finally we have used the dynamical systems analysis to determine the critical points and the nature of the trajectories for the timelike and null geodesics.     

Early Permian xiphosurid trackways from india

Present work is the first report of Early Permian xiphosurid trackways from India. Surface trackways and undertracks, preserved within ice-marginal storm-affected, shoreface sediments of the Talchir Formation, Jayanti coalbasin closely resemble Kouphichnium Nopsca 1923. Trackways reveal distinct heteropody with foliate pusher impressions, paired series of semi-circular, oval, V- or Y-shaped chilate (walking) leg impressions. Varied ventral impressions also include telson drag marks and telson dents; spine drag marks, book -gills impression, genal gouges as well as symmetric, paired lateral genal furrows, partial cubichnial impressions of prosoma and spinose opisthosoma. A tentative early Permian age (Asselian/Sakmarian) and marginal marine facies association points towards a paleolimuloidae affinity for the trace makers, which is in conformity with their inferred widths of exoskeleton, sub-rounded prosoma and subtriangular spinose opisthosoma with predictable movable spines. Flexed pusher impressions and co-dominant pincer impressions as well as, other ventral impressions in abundance, confirm crawling as their dominant mode of locomotion. Inferred presence of juvenile crawlers in the community suggests a probable shoreline or marginal marine ecospace.