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Deformation History of the Kunavaram Complex, Eastern Ghats Belt, India: Implications for Alkaline Magmatism Along the Indo-Antarctica Suture 总被引：1，自引：0，他引：1
The Kunavaram alkaline complex is a NE-SW trending elongate body located along a major lineament, the Sileru Shear Zone (SSZ) that is regarded as a Proterozoic suture related to Indo-Antarctica collision. The complex is hosted within migmatitic quartzofeldspathic gneisses, mafic granulites retrogressed to amphibolites, and quartzites. The structural evolution of the country rocks and the alkaline complex are similar. The first phase of deformation, D1, produces a pervasive segregation banding (S1) in all rock units within and outside the complex. A second deformation phase D2 isoclinally folded S1 along subvertical axial planes with shallow plunging axes. F2 isoclinal folds are ubiquitous in the country rocks and the eastern extremity of the complex. In the interior of the alkaline body, D2 strain decreases and S1 is commonly subhorizontal. While amphibolite to granulite facies conditions prevailed during deformation, post-D2 annealing textures testify to persisting high grade conditions. In the west, a NNE-SSW trending dextral shear zone with strike-slip sense (D3) truncates the complex. Within this shear zone, quartzofeldspathic country rocks are plastically deformed, while hornblende-K-feldspar assemblages of the complex are retrogressed to biotite and plagioclase. Warping related to D3 shears also resulted in fold interference patterns on the subhorizontal S1 foliation in low D2 strain domains. Based on its steep dip, north-easterly trend, and non-coaxial nature with dextral strike-slip sense, the D3 shear zone can be correlated with the SSZ. Since this shear zone, i.e., the SSZ, is not associated with primary igneous fabrics and resulted in solid state deformation of the complex, it cannot be considered as a conduit for alkaline magmatism, but is probably responsible for the post-tectonic disposition of the pluton. 相似文献
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Shamik Ghosh Pankaj Jain Gopal Kashyap Rahul Kothari Sharvari Nadkarni-Ghosh Prabhakar Tiwari 《Journal of Astrophysics and Astronomy》2016,37(4):25
There currently exist many observations which are not consistent with the cosmological principle. We review these observations with a particular emphasis on those relevant for the Square Kilometre Array (SKA). In particular, several different data sets indicate a preferred direction pointing approximately towards the Virgo cluster. We also observe a hemispherical anisotropy in the Cosmic Microwave Background radiation (CMB) temperature fluctuations. Although these inconsistencies may be attributed to systematic effects, there remains the possibility that they indicate new physics and various theories have been proposed to explain them. One possibility, which we discuss in this review, is the generation of perturbation modes during the early pre-inflationary epoch, when the Universe may not obey the cosmological principle. Better measurements will provide better constraints on these theories. In particular, we propose measurement of the dipole in number counts, sky brightness, polarized flux and polarization orientations of radio sources. We also suggest test of alignment of linear polarizations of sources as a function of their relative separation. Finally we propose measurement of hemispherical anisotropy or equivalently dipole modulation in radio sources. 相似文献
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GEOFFREY STANO T. N. KRISHNAMURTI T. S. V. VIJAYA KUMAR ARUN CHAKRABORTY 《地球，A辑:动力气象学与海洋学》2002,54(4):370-381
This paper addresses the use of a satellite-based radar for obtaining the composite structure (from several monsoon depressions) of the distribution of precipitation elements in the horizontal and the vertical. This composting is based on the use of a simple elliptical layout of coordinates along the major and minor axes of each storm as it passed over north central India. This satellite, called the Tropical Rainfall Measuring Mission (TRMM), carries onboard a microwave instrument known as the Precipitation Radar (PR). The vertical structure of hydrometeors provided by the radar is somewhat of the same quality as the ground-based Doppler radar units. The PR could identify many features such as the melting layers, height of convection, extent of anvils and types of precipitation over different sections of the composited monsoon depression. Furthermore, the asymmetric nature of surface rainfall that intensifies around the composited monsoon depression has also been mapped, which could provide several more details than was possible from other satellite-based estimates. It is found that the most intense precipitation occurs in the south-southwest region of the monsoon depression. The preponderance of stratiform rain and the coverage of fewer deep convective elements, especially over the orographic upslope region, are some other noticeable features obtained using the TRMM PR. The stratiform rain was noted to arise where the melting layers (in the radar reflectivity signatures) were located near 5 km. In those few occasions where tall rain clouds were discernible, the cloud tops were seen to extend all the way from 12 to 15 km. Rainfall amounts across the composite monsoon depression range from 10 to 100 mm d−1 . The 3–4 d passage time of one of those disturbances resulted in local rainfall totals of the order of 200–300 min d−1 . 相似文献
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The metamorphic history of the Himalayas has been constrained mostly through studies of the ubiquitous metapelitic rocks. Non‐eclogitic metabasite rock lenses that occur intercalated with the metapelites have received little attention and it is not clear whether they share a common metamorphic history. This study reports the results of a petrological study of the metabasite lenses (dm3–m3) from the Lesser Himalayan (LH) and the Higher Himalayan (HH) domains in Sikkim. These have similar bulk chemical compositions and chemical affinities (sub‐alkaline tholeiitic basalts), with plagioclase and amphibole as the dominant mineralogical constituents. Garnet and clinopyroxene occur in some samples depending on small variations in bulk chemistry; and orthopyroxene is developed as a retrograde phase in some rocks. Minor phases are ilmenite, chlorite, titanite and rutile. The rocks were metamorphosed at similar conditions (～9–12 kbar, 800 °C). Minor differences in bulk chemical composition lead to different phase assemblages and mineral chemistry in adjacent metabasite lenses, a feature that is used to demonstrate that metamorphic conditions (peak P–T as well as retrograde P–T path) can be reliably retrieved through a combination of pseudosection analysis and kinetically constrained individual thermobarometry. The peak P–T conditions of the metabasites from this region are independent of the present geographic or tectonic (i.e. within the LH or HH) location of the samples and they differ from the conditions at which the regional metapelites (i.e. metapelites not immediately adjacent to the metabasite lenses) were metamorphosed. Metapelites that are immediately adjacent to the metabasite lenses differ in their appearance, phase assemblage and recorded P–T history from those of the regional metapelites, either because they were emplaced as slivers along with the metabasites, or because they were modified when they came in contact with the metabasites. The retrograde P–T paths of the LH and HH metabasites are different: the HH samples underwent steep decompression whereas the LH followed a more gentle exhumation path. The P–T conditions of peak metamorphism (9–12 kbar, 800 °C) are commensurate with a thermal perturbation at the base of a crust of average thickness and may be the signature of a widespread (samples found across different regions in the Himalaya) and long‐lasting (e.g. homogeneous garnet compositions) crustal underplating event that occurred during the early stages (?subduction) of the Himalayan orogeny, or earlier if the metamorphism was pre‐Himalayan. 相似文献
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Nishant Kumar Shamik Sarkar Nibir Mandal 《Journal of the Geological Society of India》2010,75(1):98-109
This paper presents results obtained from numerical model experiments to show different patterns of mantle flow produced by
lithospheric movement in subduction zones. Using finite element models, based on Maxwell rheology (relaxation time ∼ 1011S), we performed three types of experiments: Type 1, Type 2 and Type 3. In Type 1 experiments, the lithospheric slab subducts into the mantle by translational movement, maintaining a constant
subduction angle. The experimental results show that the flow perturbations occur in the form of vortices in the mantle wedge,
irrespective of subduction rate and angle. The mantle wedge vortex is coupled with another vortex below the subducting plate,
which tends to be more conspicuous with decreasing subduction rate. Type 2 experiments take into account a flexural deformation
of the plate, and reveal its effect on the flow patterns. The flexural motion induces a flow in the form of spiral pattern
at the slab edge. Density-controlled lithospheric flexural motion produces a secondary flow convergence zone beneath the overriding
plate. In many convergent zones the subducting lithospheric plate undergoes detachment, and moves down into the mantle freely.
Type 3 experiments demonstrate flow perturbations resulting from such slab detachments. Using three-dimensional models we
analyze lithospheric stresses in convergent zone, and map the belts of horizontal compression and tension as a function of
subduction angle. 相似文献
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Batch kinetic studies were carried out for the removal of safranin from aqueous solution using a biomatrix prepared from rice husk. The adsorption kinetic data were modeled using the pseudo‐first‐order and pseudo‐second‐order kinetic equations. The linear and non‐linear forms of these two widely used kinetic models were compared in this study. In order to determine the best‐fitting equation, the coefficient of determination (r2), the sum of the squares of the errors (SSE), sum of the absolute errors (SAE), average relative error (ARE), hybrid fractional error function (HYBRID), Marquardt's percent standard deviation (MPSD), and the Chi‐squared test (χ2) were used as error analysis methods. Results showed that the non‐linear forms of pseudo‐first‐order and pseudo‐second‐order models were more suitable than the linear forms for fitting the experimental data. Non‐linear method is thus more appropriate for estimating the kinetic parameters and should primarily be used to describe adsorption kinetics. 相似文献
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KAUSHIK DAS SANKAR BOSE SUBRATA KARMAKAR SUPRIYA CHAKRABORTY 《Journal of Earth System Science》2012,121(1):1-17
Granulite-facies rocks occurring north-east of the Chilka Lake anothosite (Balugan Massif) show a complex metamorphic and
deformation history. The M1–D1 stage is identified only through microscopic study by the presence of S1 internal foliation shown by the M1 assemblage sillimanite–quartz–plagioclase–biotite within garnet porphyroblasts of the aluminous granulites and this fabric
is obliterated in outcrop to map-scale by subsequent deformations. S2 fabric was developed at peak metamorphic condition (M2–D2) and is shown by gneissic banding present in all lithological units. S3 fabric was developed due to D3 deformation and it is tectonically transposed parallel to S2 regionally except at the hinge zone of the F3 folds. The transposed S2/S3 fabric is the regional characteristic structure of the area. The D4 event produced open upright F4 folds, but was weak enough to develop any penetrative foliation in the rocks except few spaced cleavages that developed in
the quartzite/garnet–sillimanite gneiss. Petrological data suggest that the M4–D4 stage actually witnessed reactivation of the lower crust by late distinct tectonothermal event. Presence of transposed S2/S3 fabric within the anorthosite arguably suggests that the pluton was emplaced before or during the M3–D3 event. Field-based large-scale structural analyses and microfabric analyses of the granulites reveal that this terrain has
been evolved through superposed folding events with two broadly perpendicular compression directions without any conclusive
evidence for transpressional tectonics as argued by earlier workers. Tectonothermal history of these granulites spanning in
Neoproterozoic time period is dominated by compressional tectonics with associated metamorphism at deep crust. 相似文献
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Shamik CHAKRABORTY YASUDA Hiroshi Abhik CHAKRABORTY NABETA Hajime KAWAI Takayuki ISHIYAMA Shun 《资源与生态学报(英文版)》2015,6(5):345-352
The Nile is one of the longest rivers on the planet and an important freshwater source for the arid regions of Africa. It is also a river that is extensively affected by anthropogenic impact. This paper aims to provide an account of the social drivers that combine to cause extensive changes in the Nilotic environments. This paper is based on extensive review of literature backed up by field research. The main focus is on the lower Nile, where the effects of anthropogenic disturbances are most prominent. We argue that the Nile Basin is characterized by interrelated and compound problems of resource management, and managing this river system effectively requires shifting the focus from water related problems to a basin wide management agenda. We contend that knowledge of environmental history is important for this agenda shift, and the idea of benefit sharing can alleviate the growing stress on this extremely sensitive arid river basin. 相似文献
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