Arrested charnockite formation in southern India and Sri Lanka   总被引：7，自引：3，他引：7  

E. C. Hansen  A. S. Janardhan  R. C. Newton  W. K. B. N. Prame  G. R. Ravindra Kumar 《Contributions to Mineralogy and Petrology》1987,96(2):225-244

Arrested prograde charnockite formation in quartzofeldspathic gneisses is widespread in the high-grade terrains of southern India and Sri Lanka. Two major kinds of orthopyroxene-producing reactions are recognized. Breakdown of calcic amphibole by reaction with biotite and quartz in tonalitic/granitic gray gneiss produced the regional orthopyroxene isograd, manifest in charnockitic mottling and veining of mixed-facies exposures, as at Kabbal, Karnataka, and in the Kurunegala District of the Sri Lanka Central Highlands. Chemical and modal analyses of carefully chosen immediately-adjacent amphibole gneiss and charnockite pairs show that the orthopyroxene is produced by an open system reaction involving slight losses of CaO, MgO and FeO and gains of SiO₂ and Na₂O. Rb and Y are depleted in the charnockite. Another kind of charnockitization is found in paragneisses throughout the southern high-grade area, and involves the reaction of biotite and quartz±garnet to produce orthopyroxene and K-feldspar. Although charnockite formation along shears and other deformation zones at such localities as Ponmudi, Kerala is highly reminiscent of Kabbal, close pair analyses are not as suggestive of open-system behavior. This type of charnockite formation is found in granulite facies areas where no prograde amphibole-bearing gneisses exist and connotes a higher-grade reaction than that of the orthopyroxene isograd. Metamorphic conditions of both Kabbaltype and Ponmudi-type localities were 700°–800° C and 5–6 kbar. Lower P(H₂O) in the Ponmudi-type metamorphism was probably the definitive factor.CO₂-rich fluid inclusions in quartz from the Kabbaltype localities support the concept that this type of charnockite formation was driven by influx of CO₂ from some deep-seated source. The open-system behavior and high oxidation states of the metamorphism are in accord with the CO₂-streaming hypothesis. CO₂-rich inclusions in graphitebearing charnockites of the Ponmudi type, however, commonly have low densities and compositions not predictable by vapor-mineral equilibrium calculations. These inclusions may have suffered post-metamorphic H₂ leakage or some systematic contamination.Neither the close-pair analyses nor the fluid inclusions strongly suggest an influx of CO₂ drove charnockite formation of the Ponmudi type. The possibility remains that orthopyroxene and CO₂-rich fluids were produced by reaction of biotite with graphite without intervention of fluids of external origin. Further evidence, such as oxygen isotopes, is necessary to test the CO₂-streaming hypothesis for the Ponmudi-type localities.  相似文献   

Dispersion of waves in a continuously stratified elastic medium     

Ravi Ravindra 《Pure and Applied Geophysics》1969,72(1):17-21

Summary It is shown that the waves travelling at normal incidence in a continuously stratified elastic medium in which the longitudinal and the transverse wave velocities increase linearly are appreciably dispersed. Dispersion curves are given showing the variation of phase and group velocities, with frequency and different laws of increase in density. The results are relevant to seismology and underwater acoustics.A part of this paper was presented at the meetings of the Canadian Association of Physicists held in Toronto in June 1967  相似文献   

Usual assumptions in the treatment of wave propagation in heterogeneous elastic media     

Ravi Ravindra 《Pure and Applied Geophysics》1968,70(1):12-17

Summary Several assumptions are usually made in seismology in the treatment of wave propagational problems in heterogeneous elastic media. These assumptions are pointed out and some of them are critically examined.This paper was presented in a modified form at the meetings of the Canadian Association of Physicists in Toronto in June, 1967.The author was formerly known asRavindra N. Gupta  相似文献   

The petrology and geochemistry of massif anorthosites and gabbros of the Bavali fault zone,North Kerala     

G R Ravindra Kumar 《Journal of Earth System Science》1986,95(1):117-130

The massif anorthosites and gabbros occurring in the north Kerala region are localised along the Bavali fault. Several other bodies of granophyres and syeites also occupy this fault. All these bodies are considered to be a continuous graduating igneous series. This paper aims at delineating the field relations, petrochemistry and origin of massif anorthosites and gabbros occurring in the vicinity of the fault. Anorthosites (An 70-55) are nonlayered and highly deformed with no igneous structure present. Gabbros show relict poikilitic texture with a mineralogy of plagioclase, clinopyroxene, hornblende and biotite. Geochemical study suggests dominantly calc-alkaline characteristics for both anorthosites and gabbros. However, their chemical variation is not transitional to indicate evolution by continuous differentiation from a single parent magma. The rock types seem to be chemically unrelated and appear to have evolved independently from discreet magma sources and the magma migration might have only been promoted by the Bavali lineament.  相似文献   

Model tank experiments for resistivity measurements on sloping and vertical non conducting dykes     

Jagdeo Singh  Ravindra Prakash Gupta 《Pure and Applied Geophysics》1970,81(1):192-201

Summary Model resistivity experiments over sloping and vertical, non-conducting dykes have been carried out and reported in this paper. The results of vertical dykes as compared to the sloping dykes are very interesting and not so far reported in the available literature. Of particular interest is distinct resistivity high in the centre of the two vertical dykes, followed by lows over the dykes and again by highs on either side. As expected the curves are symmetrical. As against this, in the cases of sloping dykes, there is a distinct low, in between the dykes, followed by highs over the dykes, the curves being asymmetrical.  相似文献   

Deformation of the rocks of Simla Hills     

Ravindra Kumar  I. C. Pande 《International Journal of Earth Sciences》1972,61(2):430-441

Simla Hills form a part of Lesser Himalaya. Metamorphic rocks of this area (Pre-Cambrian), forming Chail-Jutogh nappe, are thrust over a series of mostly unfossiliferous rock formations ranging in age from Palaeozoic to Eocene. The rocks of the area are characterised by meso-structures belonging to three phases of deformation. The second phase structures, both in the allochthon as well as in the para-autochthon units are synchronous with the nappe formation. The third structure in the para-autochthon unit has been related with the movement of nappe. A model explaining the probable kinematics of thrusting in the Simla Hills has been suggested.

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Zusammenfassung Die Simla-Berge sind ein Teil des Lesser Himalaya. Metamorphe Gesteine dieses Gebietes (Präkambrium), die die Chail-Jutogh-Decke bilden, sind über einer Serie vorwiegend fossilfreier Formationen (Paläozoikum bis Eozän) überschoben. Die Gesteine dieses Gebietes sind durch Meso-Strukturen, die zu drei Phasen der Deformation gehören, gekennzeichnet. Die Strukturen der zweiten Phase, zu der allochthone sowie para-autochthone Einheiten gehören, sind gleichaltrig mit der Anlage der Deckenbildung. Die Strukturen der dritten Phase in der para-autochthonen Einheit hängen mit der weiteren Bewegung der Decke zusammen. Ein Modell, das die wahrscheinliche Kinematik der Überschiebung in den Simla-Bergen erklärt, wird vorgeschlagen.

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Résumé Les monts Simla représentent une partie du « Lesser Himalaya ». Les roches métamorphiques de cette région (Précambrien), formant la nappe du « Chail-Jutogh », ont glissé par-dessus une série de formations (du Paléozoique à l'Eocène) en majorité dépourvues de fossiles. Les roches de cette région sont caractérisées par des interstructures appartenant à trois phases de la déformation. Les structures de la 2^e phase, auxquelles appartiennent les unités allochtones et para-autochtones se sont formées en même temps que la nappe. Les structures de la 3^e phase, dans l'unité para-autochtone, sont en rapport étroit avec le déplacement postérieur de la nappe. Une possibilité d'explication de la cinématique probable du glissement dans les monts Simla est proposée.

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Simla Lesser Himalaya. — —, Chail-Jutogh, , - . -, . - , - , . - . , , , .

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Theoretical Love wave dispersion in a single layer model     

Ravindra N. Gupta  Fraser S. Grant 《Pure and Applied Geophysics》1963,55(1):16-20

Summary From a study of the Love wave dispersion in a single layer model it is shown that the shape of the dispersion curves is very insensitive to the changes in the density ratio. The bilogarithmic grids giving dispersion curves for different shear velocity ratios and a mean density ratio of 1.20 should be sufficient for interpretation by the method of curve matching. Such grids and the numerical data are given both for the phase velocity and the group velocity. An example is given illustrating the use of these grids.  相似文献   

Examining the Effect of Ancillary and Derived Geographical Data on Improvement of Per-Pixel Classification Accuracy of Different Landscapes     

Uttam Kumar  Anindita Dasgupta  Chiranjit Mukhopadhyay  T. V. Ramachandra 《Journal of the Indian Society of Remote Sensing》2018,46(3):407-422

Effective conservation and management of natural resources requires up-to-date information of the land cover (LC) types and their dynamics. Multi-resolution remote sensing (RS) data coupled with additional ancillary topographical layers (both remotely acquired or derived from ground measurements) with appropriate classification strategies would be more effective in capturing LC dynamics and changes associated with the natural resources. Ancillary information would make the decision boundaries between the LC classes more widely separable, enabling classification with higher accuracy compared to conventional methods of RS data classification. In this work, we ascertain the possibility of improvement in classification accuracy of RS data with the addition of ancillary and derived geographical layers such as vegetation indices, temperature, digital elevation model, aspect, slope and texture, implemented in three different terrains of varying topography—urbanised landscape (Greater Bangalore), forested landscape (Western Ghats) and rugged terrain (Western Himalaya). The study showed that use of additional spatial ancillary and derived information significantly improved the classification accuracy compared to the classification of only original spectral bands. The analysis revealed that in a highly urbanised area with less vegetation cover and contrasting features, inclusion of elevation and texture increased the overall accuracy of IKONOS data classification to 88.72% (3.5% improvement), and inclusion of temperature, NDVI, EVI, elevation, slope, aspect, Panchromatic band along with texture measures, significantly increased the overall accuracy of Landsat ETM+ data classification to 83.15% (7.6% improvement). In a forested landscape with moderate elevation, temperature was useful in improving the overall accuracy by 6.7 to 88.26%, and in a rugged terrain with temperate climate, temperature, EVI, elevation, slope, aspect and Panchromatic band significantly improved the classification accuracy to 89.97% (10.84% improvement) compared to the classification of only original spectral bands, suggesting selection of appropriate ancillary data depending on the terrain.  相似文献   

A Geospatial Approach to Understand the Dynamics of Shifting Cultivation in Champhai District of Mizoram,North-East India     

Pentile Thong  Rocky Pebam  Uttam Kumar Sahoo 《Journal of the Indian Society of Remote Sensing》2018,46(10):1713-1723

The dynamics of crop-fallow rotation cycles of shifting cultivation has been poorly understood in northeastern part of the country although it is one of the major land use systems in the hilly states of this region. The present study was conducted to understand the dynamics of shifting cultivation through the use of Landsat time-series data from 1999 to 2016 in Champhai district of Mizoram. We mapped the current jhum fields and abandoned areas of each imagery of the study period and performed a post classification comparison to assess the crop-fallow rotation cycle/jhum cycle. The chrono-sequential change of slash and burn area over the past 17 years showed a decreasing trend with the greater part of the shifting cultivation area being occupied by 2nd year crop fields, covering 48.81% of total jhum land. On average, 114.46 km² area were annually slashed for current jhum, out of which 33.41% continued with current jhum 2nd year cropping and only 3.27% of jhumias continued with 3rd year cropping. The shifting cultivation patches were mostly confined to moderately steep slopes (15°–30°). East facing aspect was mostly preferred and North facing aspect was least preferred. During the study period, 10 years jhum cycle covered the maximum area followed by 9 years and 11 years jhum cycle. The end result of this study proved that the prevalent jhum cycle in Champhai district is 8–11 years with a fallow period of 6–9 years.  相似文献   

Science Communication: Part II Techniques of Presentation     

G.R. Ravindra Kumar 《Gondwana Research》1999,2(2):300-305

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