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Aeromagnetic anomalies over Bastar craton and Pranhita-Godavari (P-G) basin in the south of central India could be attributed
to NW-SE striking mafic intrusives in both the areas at variable depths. Such intrusions can be explained considering the
collision of the Bastar and Dharwar cratons by the end of the Archaean and the development of tensile regimes that followed
in the Paleoproterozoic, facilitating intrusions of mafic dykes into the continental crust. The P-G basin area, being a zone
of crustal weakness along the contact of the Bastar and Dharwar cratons, also experienced extensional tectonics. The inferred
remanent magnetization of these dykes dips upwards and it is such that the dykes are oriented towards the east of the magnetic
north at the time of their formation compared to their present NW-SE strike. Assuming that there was no imprint of magnetization
of a later date, it is concluded that the Indian plate was located in the southern hemisphere, either independently or as
part of a supercontinent, for some span of time during Paleoproterozoic and was involved in complex path of movement and rotation
subsequently. The paper presents a case study of the utility of aeromagnetic anomalies in qualitatively deducing the palaeopositions
of the landmasses from the interpreted remanent magnetism of buried intrusive bodies. 相似文献
14.
Magnetic anomalies of offshore Krishna-Godavari basin,eastern continental margin of India 总被引:1,自引:0,他引:1
K. V. Swamy I. V. Radhakrishna Murthy K. S. Krishna K. S. R. Murthy A. S. Subrahmanyam M. M. Malleswara Rao 《Journal of Earth System Science》2009,118(4):405-412
The marine magnetic data acquired from offshore Krishna-Godavari (K-G) basin, eastern continental margin of India (ECMI),
brought out a prominent NE-SW trending feature, which could be explained by a buried structural high formed by volcanic activity.
The magnetic anomaly feature is also associated with a distinct negative gravity anomaly similar to the one associated with
85°E Ridge. The gravity low could be attributed to a flexure at the Moho boundary, which could in turn be filled with the
volcanic material. Inversion of the magnetic and gravity anomalies was also carried out to establish the similarity of anomalies
of the two geological features (structural high on the margin and the 85°E Ridge) and their interpretations. In both cases,
the magnetic anomalies were caused dominantly by the magnetization contrast between the volcanic material and the surrounding
oceanic crust, whereas the low gravity anomalies are by the flexures of the order of 3–4 km at Moho boundary beneath them.
The analysis suggests that both structural high present in offshore Krishna-Godavari basin and the 85°E Ridge have been emplaced
on relatively older oceanic crust by a common volcanic process, but at discrete times, and that several of the gravity lows
in the Bay of Bengal can be attributed to flexures on the Moho, each created due to the load of volcanic material. 相似文献
15.
Hemchandra Chaulagain Hugo Rodrigues Enrico Spacone Ramesh Guragain Radhakrishna Mallik Humberto Varum 《地震工程与工程振动(英文版)》2014,13(3):455-470
Most current seismic design includes the nonlinear response of a structure through a response reduction factor(R). This allows the designer to use a linear elastic force-based approach while accounting for nonlinear behavior and deformation limits. In fact, the response reduction factor is used in modern seismic codes to scale down the elastic response of a structure. This study focuses on estimating the actual ‘R' value for engineered design/construction of reinforced concrete(RC) buildings in Kathmandu valley. The ductility and overstrength of representative RC buildings in Kathmandu are investigated. Nonlinear pushover analysis was performed on structural models in order to evaluate the seismic performance of buildings. Twelve representative engineered irregular buildings with a variety of characteristics located in the Kathmandu valley were selected and studied. Furthermore, the effects of overstrength on the ductility factor, beam column capacity ratio on the building ductility, and load path on the response reduction factor, are examined. Finally, the results are further analyzed and compared with different structural parameters of the buildings. 相似文献
16.
Experiments have been performed to study the thermal performance of a backfilled disposal vault in which the waste containers are emplaced in boreholes and surrounded by a bentonitesand buffer.
The near-field thermal regime in a buffer-backfill disposal vault in which the nuclear fuel waste is emplaced in canisters, is studied by one-eight scale experimental models. The thermal performance of the buffer and backfill are examined in a thermal drying environment prior to the ground water recharge of the disposal vault.
The formation of shrinkage cracks in the buffer due to drying and the response of these shrinkage cracks to the rewetting condition and their influence on the near-field thermal regime are assessed. 相似文献
17.
18.
T. Radhakrishna D. G. Pearson John Mathai 《Contributions to Mineralogy and Petrology》1995,121(4):351-363
Agali–Coimbatore dolerite dykes constitute an important Proterozoic magmatic event that affected the south Indian shield.
Rb-Sr whole rock isotope data yield an “errorchron” of 2369±400 Ma (2σ error) which is within error of the reported 2030±65 Ma
K-Ar age. The dyke magmas were evolved Fe-rich tholeiitic melts produced by fractionation of clinopyroxene, orthopyroxene
and olivine in the initial stages. Plagioclase became a fractionation phase during the latter stages of crystallization. The
dykes characteristically have high 87Sr/86Sri (0.703–0.706) and are enriched in large-ion lithophile and light rare earth elements relative to primordial mantle values
and show negative Nb anomalies. These compositional characteristics are interpreted as source mantle characteristics whereas
some crustal effects are visible in some samples with high initial 87Sr/86Sr. Peridotite with minor hydrous metasomatic phases like amphibole (and phlogopite) within the shallow lithospheric mantle
could be a potential source material for the dykes. However, at this stage we cannot convincingly differentiate whether the
source of the parent magmas is solely lithospheric or a product of asthenosphere-lithosphere mixing. The δ18O values of the dykes range from +5.2 to +7.2 per mil (vs standard mean oceanic water). Initial Nd isotope values at the time
of dyke intrusion (ɛNd at t=2.0 Ga) range from −2.3 to −4.8. Whole rocks define a correlation on an Sm-Nd isochron plot with a slope equivalent to an
age of 3.15±0.53 Ga (2σ error); Sm-Nd crustal residence ages average at 2.87 Ga. The isochron age does not appear to be the
result of systematic mixing with an older crustal component. These results together with trace element geochemistry suggest that the south Indian
mantle lithosphere developed by addition of enriched melts/fluids at about 3.0 Ga synchronously with major crustal gene- ration
in the south Indian shield.
Received 20 June 1994/Accepted: 17 May 1995 相似文献
19.
I. V. Radhakrishna Murthy 《Pure and Applied Geophysics》1969,73(1):43-46
Summary A simple transformation called pseudo-magnetic transformation is introduced in which the horizontal derivatives of the observed gravity anomalies of any body will be calculated. These horizontal derivatives, called the pseudo-magnetic anomalies, are proportional to the vertical magnetic anomalies of the same body assumed to be polarised horizontally. It is shown that the interpretation of gravity anomalies of dykes is not unique except by computing the pseudo-magnetic anomalies, which will be interpreted by the logarithmic curve fitting technique indicated earlier [5]2). 相似文献
20.
B. S. R. Rao I. V. Radhakrishna Murthy S. Jeevananda Reddy 《Pure and Applied Geophysics》1970,80(1):5-26
Summary Second derivative coefficients for various grid systems are derived followingPeters' andElkins' approaches. Two simple formulae, one for three dimensional bodies and the other for two dimensional bodies are also suggested. These utilise the average of the anomalies around a single circle and the anomaly at the central point.All the coefficient sets and the proposed simple formulae are applied to gravity fields of spheres and cylinders. Coefficients ofElkins' type derived with a weightage of 1/r
4 to all the circles gave excellent results in both the cases of spheres and cylinders, whereasPeters' coefficients without any weightage to the circles gave reliable results in case of cylinders only. The simple formulae suggested gave more accurate results than any of the above coefficient sets. 相似文献