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121.
Aluminous parageneses containing gedrite, cordierite, garnet, staurolite, biotite, sillimanite, kyanite, quartz or spinel plus corundum are found as dark colored lenses in the polymetamorphic, multideformed Archean complex at Ajitpura in northwest peninsular India. Staurolite, like kyanite, is a relict phase of earlier metamorphism and is excluded as a paragenetic mineral in view of its incompatibility with quartz and gedrite and its lower X
Mg values than for garnet of the assemblage. Its stability here is attributed to zinc content of up to 3 wt%. The XMg in other ferromagnesian minerals decreases in the order: cordierite, biotite, gedrite, garnet, as found elsewhere in high grade rocks.The textural criteria and systematic partitioning of Fe and Mg in the ferromagnesian phases, excluding staurolite, indicate attainment of equilibrium during the second metamorphism. From tie line configurations in the phase diagrams, X
Mg ratios in the constituent minerals, and other petrographic criteria, it is suggested that gedrite — cordierite-garnet — sillimanite — biotite assemblage has been produced by the reactions: Biotite+Sillimanite+Quartz = Cordierite+Garnet+K-feldspar+Vapor (1) and Biotite+Sillimanite+Quartz = Cordierite +Gedrite+K-feldspar+Vapor (2) which occurred during partial melting of the rocks at fixed P and T conditions.By isothermal P-X(Fe-Mg) sections it has been demonstrated that release of FeO, SiO2 and other components modified the composition of the reactant biotite presumably by the substitution FeSi2 Al, whereby reaction 1 was replaced by reaction 2. Cordierite with higher X
Mg was produced with gedrite instead of with garnet, whose X
Mg is less than X
Mg of gedrite. Reaction 2 has been tentatively located in T-P space from the intersection of some continuous loops in the P-X(Fe-Mg) diagram at 700°C and also by other constraints. The discontinuous reaction 2 is located about 1–2 kilobars higher than reaction 1, which implies that it is difficult to distinguish between effects of pressure and those of melting on the X
Mg ratios of the reaction phases.The P-T calibrations of garnet — cordierite, garnet — biotite and garnet — plagioclase equilibria and the calibrations from other dehydration curves give temperatures near 700°C and pressure (assuming
) about 6 kilobars. 相似文献
122.
Ram S. Sharma 《Lithos》1981,14(2):165-172
Electron-microprobe analyses of coexisting phases from a scapolite-garnet-epidote-calcite-plagioclase-hornblende-pyroxene (sphere-hematite-magnetite) rock of the Aravalli Group (Early Precambrian) at Karera, district Bhilwara, Rajasthan, reveal that chlorine is an important constituent of both scapolite (Me71.3 and hornblende, making the latter a dashkesanite variety. The amphibole also contains an unusually high K2O (3.7 wt.%), and is a chlor-potassium hastingsite. The epidote contains 41% pistacite and shows complete substitution of Al by Fe3+ in the Al-site and to some extent also in AIO and/or Al(OH) sites. The garnet is also rich in ferric iron and has a mol. composition Pyr23Alm8.5Gro13And54.5 Sp1.0. The pyroxene is dominantly a hedenbergite. The phase relations and textural as well as geological criteria exclude metasomatic processes and favour equilibrium recrystallization of the scapolite-bearing assemblage; the chlorine presumably derived from an evaporite component of the Aravalli metasediments. The geothermometry based on the fractionation of Na and Ca between scapolite (EqAn 43.3) and plagioclase (An85?90 yields metamorphic temperatures of around 700°C for the scapolite-bearing rock which are in agreement with those obtained by other mineral equilibria in the associated pelitic assemblages. 相似文献
123.
We present the results of a variability study of some H2O maser-emission components of Sgr B2, which is located in an active star-forming region. Our monitoring was conducted in 1982–2004 with the 22-m radio telescope of the Pushchino Radio Astronomy Observatory. We analyze brightness variations for the strongest groups of emission features in the H2O spectra, mainly during periods of maser flaring activity. Each of these groups contains many components, whose radial velocities and fluxes we determined. Most of the components displayed radial-velocity drifts. We detected a correlation between the flux and radial-velocity variations for some of the components. Variability of the emission can be explained in a model in which the maser spots form elongated chains and filaments with radial-velocity gradients. During H2O flares, the flux increases of some maser spots were accompanied by acceleration, while flux decreases were accompanied by deceleration of their motion in the dense circumstellar matter. Spectral groups of emission features are probably spatially compact structures. 相似文献
124.
125.
R Elangovan Kumar Krishna Neeraj Vishwakarma K R Hari M Ram Mohan 《Journal of Earth System Science》2017,126(7):92
Field and petrographic studies are carried out to characterize the interactions of mafic and felsic magmas from Pithora region of the northeastern part of the Bastar Craton. The MMEs, syn-plutonic mafic dykes, cuspate contacts, magmatic flow textures, mingling and hybridization suggest the coeval emplacement of end member magmas. Petrographic evidences such as disequilibrium assemblages, resorption textures, quartz ocelli, rapakivi and poikilitic textures suggest magma mingling and mixing phenomena. Such features of mingling and mixing of the felsic and mafic magma manifest the magma chamber processes. Introduction of mafic magmas into the felsic magmas before initiation of crystallization of the latter, results in hybrid magmas under the influence of thermal and chemical exchange. The mechanical exchange occurs between the coexisting magmas due to viscosity contrast, if the mafic magma enters slightly later into the magma chamber, then the felsic magma starts to crystallize. Blobs of mafic magma form as MMEs in the felsic magma and they scatter throughout the pluton due to convection. At a later stage, if mafic magma enters the system after partial crystallization of felsic phase, mechanical interaction between the magmas leads to the formation of fragmented dyke or syn-plutonic mafic dyke. All these features are well-documented in the study area. Field and petrographic evidences suggest that the textural variations from Pithora region of Bastar Craton are the outcome of magma mingling, mixing and hybridization processes. 相似文献
126.
Land surface temperature(LST) is the skin temperature of the earth surface. LST depends on the amount of sunlight received by any geographical area. Apart from sun light, LST is also affected by the land cover, which leads to change in land surface temperature. Impact of land cover change(LCC) on LST has been assessed using Landsat TM5, Landsat 8 TIRS/OLI and Digital Elevation Model(ASTER) for Spiti Valley, Himachal Pradesh, India. In the present study, Spiti valley was divided into three altitudinal zones to check the pattern of changing land cover along different altitudes and LST was calculated for all the four land cover categories extracted from remote sensing data for the years of 1990 and 2015. Matrix table was used as a technique to evaluate the land cover change between two different years. Matrix table shows that as a whole, about 2,151,647 ha(30%) area of Spiti valley experienced change in land cover in the last 25 years. The result also shows vegetation and water bodies increased by 107,560.2 ha(605.87%) and 45 ha(0.98%), respectively. Snow cover and barren land decreased by 19,016.5 ha(23.92%) and 88,589(14.14%), during the study period. A significant increase has been noticed in vegetation amongst all land cover types. Minimum, maximum and mean LST for three altitudinal zones have been calculated. The mean LST recorded was 11℃ in 1990 but it rose by 2℃ and reached to 13℃ in 2015. Changes in LST were obtained for each land cover categories. The mean temperature of different land cover types was calculated by averaging value of all pixels of a given land cover types. The mean LST of vegetation, barren land, snow cover and water body increased by 6℃, 9℃, 1℃, and 7℃, respectively. Further, relationships between LST, Normalized Difference Snow Index(NDSI), and Normalised Difference Vegetation Index(NDVI) were established using Linear Regression. 相似文献
127.
128.
129.
Over 200 earthquakes in the distance range 30°–90° and azimuthal range 0°–360°, recorded at Indian WWSSN stations, have been used in the present study. We have treated the four WWSSN recording stations i.e. New Delhi, Poona, Shillong and Kodai-Kanal, as Super Large Aperture Seismic Array (SLASA) Network with New Delhi being its cross-over point. Short period P-wave data as obtained from these stations have been analysed using a least square technique. Slowness and azimuthal anomalies have been computed for all these events. Relative time residuals have also been calculated. A velocity model has been derived on the basis of the slowness and travel-time data. The results do not indicate presence of any triplication in the travel-time curve. Variations in the relative residuals refer to the tectonic features beneath the recording stations. The P-wave velocity increases continuously in the lower mantle region and there is no indication for the presence of any appreciable velocity gradient. 相似文献
130.
Manas Ranjan Bhuyan Dhani Ram Rajak Markand Oza 《Journal of the Indian Society of Remote Sensing》2007,35(1):43-52
The Advanced WiFS sensor of RESOURCESAT- 1 satellite offers significantly improved specifications compared to the WiFS sensor
onboard IRS IC, P3 and ID satellites. The improvements are in terms of spatial resolution, radiometry (quantisation levels)
and number of spectral bands. In the present study, an attempt has been made to quantify the gains due to these enhanced specifications.
The study has been carried out in a predominantly agricultural area. For the study reported here, one set of overlapping data
acquired on the same day by WiFS and AWiFS sensors has been selected. This eliminates the need of atmospheric correction/
normalization for comparison. The effect of spatial resolution has been studied by applying ISODATA spectral clustering algorithm
with number of clusters set at three different levels, viz., 10, 20 and 30. They are assumed to mimic first, second and third
level classification, respectively. Output images were filtered using 3 × 3 majority filter. Homogeneous polygons having area
less than 1/2 and 1 pixel of WiFS were recorded. This indicates the minimum loss by using WiFS data. A relative gain of 10
– 15 % is observed due to improvement in spatial resolution. For comparison of radiometry, local variance measure was used.
It was observed that local variance is much larger for AWiFS data in comparison with WiFS data. This indicates presence of
enhanced local contrast, hence heterogeneity, in AWiFS data over WiFS data. Separability analysis has been carried out to
demonstrate improvements due to two additional spectral bands (Green and SWIR). 相似文献