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排序方式： 共有72条查询结果，搜索用时 69 毫秒
1.
Rao G. Srinivasa Kumar Manish Radhakrishna M. 《International Journal of Earth Sciences》2018,107(6):2191-2207
International Journal of Earth Sciences - The continental breakup history at the northwest continental margin of India remained conjectural due to lack of clearly discernable magnetic anomaly... 相似文献
2.
S. K. G. Krishnamacharyulu Bh. V. V. Gopalarao I. V. Radhakrishna Murthy 《Pure and Applied Geophysics》1990,132(4):719-731
Magnetic anomaly profiles over two thin sheets separated by a small distance resemble those of dykes andvice versa. Interpretation of anomalies over a pair of sheets based on the magnetic properties of dykes predicts a dyke whose centre lies midway between the positions of the sheets. The dyke, on the other hand, is magnetically equivalent to a pair of sheets, both lying at the same depth and having the same magnetization.The magnetic anomalies due to a pair of sheets can be interpreted by framing linear equations between the anomalies and their distances measured from an arbitrary reference. Application of this method to anomalies of dipping sheets with a finite depth extent is indicated. 相似文献
3.
B. S. R. Rao I. V. Radhakrishna Murthy C. Visweswara Rao 《Pure and Applied Geophysics》1973,110(1):2056-2065
Summary A common computer program for the interpretation of vertical magnetic anomalies of spheres and horizontal cylinders has been developed. The input consists of the observed anomalies noted against their distances measured from an arbitrary point in the profile and a code number for each model. The program is written so that the positions and magnitudes of the maximum and minimum anomalies are located and their ratios and signs are used to define the initial parameters of the model under consideration. The errors resulting from these approximate values are derived and are solved for the increments to be given to the initial values. The process is repeated until the sum of the squares of the errors is less than 0.25% of the sum of the squares of the observed anomalies. The method has been tested on various theoretical examples and the results justify the validity of the programme. 相似文献
4.
Approximately 1650-Ma-old NW/SE and NE/SW-trending dolerite dykes in the Tiruvannamalai (TNM) area and approximately 1800-Ma-old NW/SE-trending dolerite dykes in the Dharmapuri (DP) area constitute major Proterozoic dyke swarms in the high-grade granulite region of Tamil nadu, southern India. The NW- and NE-trending TNM dykes are compositionally very similar and can be regarded as having been formed during a single magmatic episode. The DP dykes may relate to an earlier similar magmatic episode. The dolerites are Fe-rich tholeiites and most of the elemental variations can be explained in terms of fractional crystallisation. Clinopyroxene and olivine are the inferred ferromagnesian fractionation phases followed by plagioclase during the late fractionation stages. All the studied dykes have, similar to many continental flood basalts (CFB), large-ion lithophile element (LILE) and light rare-earth element (LREE) enrichment and Nb and Ta depletion. The incompatible element abundance patterns are comparable to the patterns of many other Proterozoic dykes in India and Antarctica, to the late Archaean (～2.72 Ga) Dominion volcanics in South Africa and to the early Proterozoic (～2.0 Ga) Scourie dykes of Scotland. The geochemical characteristics of the TNM and DP dykes cannot be explained by crustal contamination alone. Instead, they are consistent with derivation from an enriched lithospheric mantle source which appears to have been developed much earlier than the dyke intrusions during a major crustal building event in the Archaean. The dyke magmas may have been formed by dehydration melting induced by decompression and lithospheric attenuation or plume impingement at the base of the lithosphere. These magmas, compared with CFB, appear to be the minor partial melts from plume heads of smaller diameter and of shallow origin (650 km). Therefore, the Proterozoic thermal events could induce crustal attenuation and dyke intrusions in contrast to the extensive CFB volcanism and continental rifting generally associated with the Phanerozoic plumes of larger head diameter (>1000 km) and of deeper origin (at crust mantle boundary). 相似文献
5.
The first set of full resolution images have been made using the Mauritius Radio Telescope (MRT) for the Right Ascension range
18:00 to 19:00 hours and the declination range -70° to -10°.This is a part of the southern sky survey at 151.5 MHz being carried out using the MRT. To minimise the effect of bandwidth
decorrelation, the images are made from the visibilities recorded with four different delay settings. This paper discusses
three key issues of data analysis for the survey: Selection of good data for the survey, detection and removal of interference
in the images and, preliminary analysis of these images.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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7.
T. Radhakrishna 《Journal of the Geological Society of India》2009,73(1):131-142
South Indian granulite terrain had witnessed significant part of Precambrian mafic igneous activity in the form of episodic
mafic dyke intrusions of the Palaeoproterozoic period. Strike trends of these dykes are not uniform over the region and the
dykes are generally fresh, massive, black dolerites except in the Bhavani shear zone bordering the southern fringes of Nilgiri
massif. In Agali-Coimbatore area of our study in the western Bhavani shear zone, the dykes appear to be penecontemporaneous
with shearing. Isotopic data place age of Agali-Coimbatore dyke intrusions at about 2.1 Ga. The age of these dykes is significant
to constrain an early Palaeoproterozoic age for major shearing event in the Bhavani shear zone. Other dyke emplacement ages
are placed at about 1.8 Ga and 1.65 Ga based on the Ar/Ar and K-Ar isotopic results of dykes in Dharmapuri and Tiruvannamalai
areas. Older ages comparable to those of the Dharwar craton are not known and in this respect future isotopic dating is vital.
Geochemically, these dykes are quartz/hypersthene normative subalkalic tholeiites. An attempt is made here to provide insights
into the general petrogenetic history of the Precambrian dykes. Compositional trends are explained by the fractional crystallization
of ferromagnesian phases and plagioclase control is conspicuous at the advanced stages of fractionation. Geochemical characteristics
suggest that the dykes have tapped Fe-rich non-pyrolite mantle sources with LIL and LREE enrichment as in many continental
basalts. The data suggest that role of crustal contamination is limited in petrogenesis; crustal signatures are noticed in
the more mafic end members formed in early stage of evolution suggesting that contamination was temperature controlled with
most primitive high temperature magmas being most vulnerable to the process. Nd-Sr isotopic data, at present restricted to
Agali-Coimbatore dykes, suggest that Palaeoproterozoic magmas tapped subcontinental lithosphere that may have stabilized in
the Archaean times at about 3 Ga during the major crustal building activity in the shield region. Further work coupled with
isotopic and mineral chemistry will improve our knowledge on the petrological evolution of the dyke magmas and mafic magmatism
in general. 相似文献
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