NOBLE GASES IN THE UNIQUE CHONDRITE,KAKANGARI     

B. Srinivasan  Edward Anders 《Meteoritics & planetary science》1977,12(4):417-424

The Kakangari chondrite has a cosmic-ray exposure age of 5.4 m.y. and a K-Ar age near 4 g.y. Its high cosmogenic ³He/²¹Ne ratio of 7.5 indicates a small preatmospheric mass. The He and Ne are largely of solar-wind origin, presumably implanted during exposure in the regolith of its parent body. The heavy gases Ar, Kr, Xe are largely of planetary origin. Taken together, the low ¹²⁹Xe/¹³²Xe (1.07), low ³⁶Ar/¹³²Xe (225), and high ¹³²Xe content (45 × 10^?10 cc STP/g) are more similar to the values for unequilibrated ordinary chondrites or even C1, C2 chondrites than to enstatite chondrites, and suggest that Kakangari has the same gas-bearing mineral assemblage as the former, in spite of its high degree of reduction (Fa_4.9).  相似文献   

Weathering impact on the colour of building stones of the ‘Gateway of India’ monument     

L. B. Tiwari  C. J. Jahagirdar  V. D. Deshpande  R. Srinivasan  G. Parthasarathy 《Environmental Geology》2005,48(6):788-794

To understand the effect of monsoon and marine environment on the colour of building stones of the ‘Gateway of India’ monument, 133 samples from different areas were assessed. Colour changes were evaluated using Microflash 200d colour spectrophotometer over a period of 1 year. The alteration in the stones effecting the colour change was studied by petrographic thin section, which shows that the colour change is associated with weathering of the feldspars.  相似文献   

Superposed folding in the Honakere arm of the Chitradurga-Karighatta schist belt in the Dharwar tectonic province,southern India,and its bearing on the Sargur-Dharwar relation     

K. Naha  A. Rai Choudhuri  V. Ranjan  R. Srinivasan 《Journal of Earth System Science》1995,104(3):327-347

The supracrustal enclave within the Peninsular Gneiss in the Honakere arm of the Chitradurga-Karighatta belt comprises tremolite-chlorite schists within which occur two bands of quartzite coalescing east of Jakkanahalli(12°39′N; 76°41′E), with an amphibolite band in the core. Very tight to isoclinal mesoscopic folds on compositional bands cut across in the hinge zones by an axial planar schistosity, and the nearly orthogonal relation between compositional bands and this schistosity at the termination of the tremolite-chlorite schist band near Javanahalli, points to the presence of a hinge of a large-scale, isoclinal early fold (F₁). That the map pattern, with an NNE-plunging upright antiform and a complementary synform of macroscopic scale, traces folds 'er generation (F ₂),is proved by the varying attitude of both compositional bands (S₀) and axial pranar schistosity (S ₁), which are effectively parallel in a major part of the area. A crenulation cleavage (S ₂) has developed parallel to the axial planes of theF ₂ folds at places. TheF ₂ folds range usually from open to rarely isoclinal style, with theF ₁ andF ₂ axes nearly parallel. Evidence of type 3 fold interference is also provided by the map pattern of a quartzite band in the Borikoppalu area to the north, coupled with younging directions from current bedding andS ₀ -S ₁ inter-relation. Although statistically theF ₁ andF ₂ linear structures have the same orientation, detailed studies of outcrops and hand specimens indicate that the two may make as high an angle as 90°. Usually, in these instances, theF ₁ lineations are unreliable around theF ₂ axes, implying that theF ₂ folding was by flexural slip. In zones with very tight to almost isoclinalF ₂ folding, however, buckling attendant with flattening has caused a spread of theF ₁ lineations almost in a plane. Initial divergence in orientation of theF ₁ lineations due to extreme flattening duringF ₁ folding has also resulted in a variation in the angle between theF ₁ andF ₂lineations in some instances. Upright later folding (F₃) with nearly E-W strike of axial planes has led to warps on schistosity, plunge reversals of theF ₁ andF ₂ axes, and increase in the angle between theF ₁ andF ₂ lineations at some places. Large-scale mapping in the Borikoppalu sector, where the supposed Sargur rocks with ENE ‘trend’ abut against the N-‘trending’ rocks of the Dharwar Supergroup, shows a continuity of rock formations and structures across the hinge of a large-scaleF ₂ fold. This observation renders the notion, that there is an angular unconformity here between the rocks of the Sargur Group and the Dharwar Supergroup, untenable.  相似文献   

The nature of the basement in the Archaean Dharwar craton of southern India and the age of the Peninsular Gneiss     

K Naha  R Srinivasan  K Gopalan  GVC Pantulu  M V Subba Rao  A B Vrevsky  Ye S Bogomolov 《Journal of Earth System Science》1993,102(4):547-565

The Archaean Peninsular Gneiss of southern India is considered by a number of workers to be the basement upon which the Dharwar supracrustal rocks were deposited. However, the Peninsular Gneiss in its present state is a composite gneiss formed by synkinematic migmatization during successive episodes of folding (DhF₁, DhF_1a and DhF₂) that affected the Dharwar supracrustal rocks. An even earlier phase of migmatization and deformation (DhF_*) is evident from relict fabrics in small enclaves of gneissic tonalites and amphibolites within the Peninsular Gneiss. We consider these enclaves to represent the original basement for the Dharwar supracrustal rocks. Tonalitic pebbles in conglomerates of the Dharwar Supergroup confirm the inference that the supracrustal rocks were deposited on a gneissic basement. Whole rock Rb-Sr ages of gneisses showing only the DhF₁ structures fall in the range of 3100–3200 Ma. Where the later deformation (DhF₂) has been associated with considerable recrystallization, the Rb-Sr ages are between 2500 Ma and 2700 Ma. Significantly, a new Rb-Sr analysis of tonalitic gneiss pebbles in the Kaldurga conglomerate of the Dharwar sequence is consistent with an age of ～2500 Ma and not that of 3300 Ma reported earlier by Venkatasubramanian and Narayanaswamy (1974). Pb-Pb ages based on direct evaporation of detrital zircon grains from the metasedimentary rocks of the Dharwar sequence fall into two groups, 3300–3100 Ma, and 2800–3000 Ma. Stratigraphic, structural, textural and geochronologic data, therefore, indicate that the Peninsular Gneiss of the Dharwar craton evolved over a protracted period of time ranging from > 3300 Ma to 2500 Ma.  相似文献   

Middle to late Archaean geology of the eastern Baltic shield,with a note on its similarity and contrast with the Archaean of southern India     

R Srinivasan  K Naha  Y J Bhaskar Rao  A B Vrevsky  S I Rybakov  A I Golubev  M Efimov 《Journal of Earth System Science》1993,102(4):567-585

The middle to late Archaean rocks of Kola and Karelia in the eastern Baltic shield consist of the Infracomplex overlain by the Saamian complex, and the Lopian greenstone belts. The Infracomplex which forms the basement is a polymigmatite, parts of which are at least 3100 Ma old. The Saamian in the central Belomorian region comprises granite gneiss, amphibolite, garnet-kyanite gneiss and high alumina gneisses which belong to the Keret, Hetolombina and Chupa suites. The Lopian greenstone belts ranging in age from 3000 to 2700 Ma are composed of peridotitic, pyroxenitic and basaltic komatiites, tholeiitic basalts, andesites, dacites and rhyolites, together with tuffs, graywackes and iron formations. Whereas there is a dominance of volcanic over sedimentary rocks in the greenstone belts of the Baltic shield, a significant proportion of detrital and chemogenic sedimentary rocks characterizes the Dharwar succession of approximately the same time span in the southern Indian shield. Association of mature and immature detrital sedimentary rocks with bimodal volcanic assemblages points to a back-arc setting for the Dharwar belts. This contrasts with the association of immature sediments with calc-alkaline volcanic rocks in the greenstone belts of the eastern Baltic shield, suggesting an island arc environment there.  相似文献   

Low frequency variation of tropical convergence zones     

Dr. S. Gadgil  J. Srinivasan 《Meteorology and Atmospheric Physics》1990,44(1-4):119-132

Summary Intraseasonal variation of tropical convergence zones (TCZ) is studied focussing on the three major features of the TCZ over the Indian longitudes during the summer monsoon viz. (i) the oscillation between active and weak spells, (ii) the occurrence of two favourable zones — one over the equatorial oceans and another over the heated continent and (iii) poleward propagations of the oceanic TCZ onto the heated continent. An observational study of the intraseasonal variation over different parts of the tropics has shown that the first feature may be an ubiquitous feature of the TCZ variations, the second occurs only over the Asian summer and winter monsoon zones, and the third only over the Asian summer monsoon. Analysis of a simple monsoon model has revealed that poleward propagation occurs in the presence of a meridional surface temperature gradient because the convective heating is asymmetric, with more heating on the poleward side. Preliminary analysis of the T-21 version of the ECMWF model has shown that it is capable of simulating the three major features of the intraseasonal variation of the TCZ over the Indian longitudes during the summer monsoon.With 16 Figures  相似文献   

Use of remote sensing techniques for detailed hydrogeological investigations in parts of Narmada Sagar command area,MP     

P. Srinivasan 《Journal of the Indian Society of Remote Sensing》1988,16(1):55-62

Of late, airphoto interpretation and Landsat imagery analysis play a vital role in geological mapping for detailed hydrogeological investigations for ground water prospecting. Certain obscure features like lineaments/fracture zones which are masked by surface soil and cultivated lands are easily visible. In hard rocks like granites and basalts the occurrence and movement of ground water are controlled by the fracture pattern. Delineation of potential zones of ground water for successful exploration is possible by the study and analysis of aerial photographs, visual interpretation of Landsat imagery and interactive data analysis system through computer techniques and applications. These techniques constitute for data integration with conventional methods of hydrogeological investigations and exploratory drilling. As a case study an area of 1500 sq km in part of the Narmada river basin of Madhya Pradesh and also forming a portion of Narmada Sagar area covered under topo sheets 46 N/12 and 46 N/16 was taken up. Aerial photographs pertaining to the area of study and Landsat imagery of band 5 and 7 in scale blown upto 1∶250,00 were scanned and analysed. It was observed that the successful artesian wells are located in pominent lineament/fractured zones in the study area. It is also recommended after through analysis different hyddromorphic zonations for future exploration of ground water.  相似文献   

Prediction of inversion strengths and heights from A 1-D nocturnal boundary layer model     

Swati Basu  Nirupama Raghavan 《Boundary-Layer Meteorology》1986,35(1-2):193-204

A 1-D numerical model for the nocturnal boundary layer is developed which is capable of predicting inversion heights and strengths successfully. The model uses two distinct length scales for the dissipation of turbulent energy and for transfer of heat and momentum within the Planetary Boundary Layer (PBL). The wind and potential temperature profiles obtained from the present model are compared with observations and the agreement is found to be good, viz., the RMSE for inversion height is found to be 71 m and that for inversion strength is found to be 2.0 °C.  相似文献   

Fortran 77 programs for preliminary summarisation of lineament patterns     

Venkatesh Raghavan  P. V. Panchanathan 《Journal of the Indian Society of Remote Sensing》1989,17(4):31-38

Fortran 77 programs have been developed for summarisation of lineament pattern and fracture traces on MS-DOS based micro-computer system. Two menu driven programmes CLAFY and HIST perform the above task. CLAFY reads the X, Y co-ordinates of lineament and points from an input file and produces an output file containing azimuth frequency, total length and average length for 18 predefined azimuth classes at 10 degree interval. HIST reads the output generated by CLAFY and offers an option to generate histograms of azimuth frequency/total length/average length on a dot matric printer. CLAFY and HIST were tested using digitised lineament co-ordinates derived from lineament maps of parts of Central Kerala region, southwestern, India which were prepared based on Landsat imagery interpretation. The programmes afford repetitive manipulation of large quantities of lineament data without ignoring short and /or faint lineaments which have geologic significance.  相似文献   

Impact of climate change on Indian agriculture: a review     

R. K. Mall  Ranjeet Singh  Akhilesh Gupta  G. Srinivasan  L. S. Rathore 《Climatic change》2007,82(1-2):225-231

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