Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Divakara Rao, V.

• Geochemistry of Komatiitic Basalt Dyke from Schirmacher Oasis, Queen Maud Land, East Antarctica

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Authors

S. H. Jafri ¹, S. Moeen ¹, V. Divakara Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 56, No 6 (2000), Pagination: 605-613

Abstract

Geochemistry of a Neoproterozoic/Phanerozoic basalt dyke of komatiitic affinity, in the Precambrian metamorphosed gneissic terrain of Schirmacher Oasis, Queen Maud Land, East Antarctica is reported here. The dyke is composed of olivine (Fo_87-90) which is largely pristine, clinopyroxene, magnesiochromite and devitrified glass. Clinopyroxene exhibits microspinifex texture. It has moderately high MgO (14.10-15.10 %), Cr (569-813 ppm), Ni (457-629 ppm) and low K₂O (0.46-0.68 9%) and TiO₂, (0.93-1.00 %) contents and high CaO/AI₂O₃ (1.11-1.22) ratios. The dyke shbws Al-depleted (low Al₂O₃, TiO₂, = 8.36-8.72, depleted HREE Gd_N = Yb_N = 1.66-1.96) signature. suggesting that the source magma was generated by low degree of partial melting of the mantle with garnet in the residue. LREE enrichment (La_N/Yb_N = 3.01-3.51) and negative Nb anomalies in the dyke samples further suggest crustal contamination of the source magma during ascent through the continental crust.

Keywords

Geochemistry, Basalt Dyke, Komatiitic Basalt, Mantle Plurne, Neoproterozoic/phanerozoic, East Antarctica.

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• Oxygen Isotope Values in Granulite Facies Rocks from the Eastern Ghats Granulite Belt, India

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Authors

A. T. Rao ¹, V. Divakara Rao ², M. Yoshida ³, M. Arima ⁴

Affiliations
1 Department of Geology, Andhra University, Visakhapatnam- 530 003, IN
2 National Geophysical Research Institute, Hyderabad - 500 007, IN
3 Department of Geosciences, Osaka City University, Osaka - 558, JP
4 Department of Geological Science, Yokhoma National University, Yokahoma, JP

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 56, No 4 (2000), Pagination: 445-452

Abstract

Oxygen isotope values in metapelites including garnet-sillimanite gneisses (khondalites), quartzo-feldspathic gneisses (leptynites), cordierite-sapphirine gneisses and the associated marbles, calc-silicates, quartzites, basic granulites and charnockites from the Eastern Ghats Granulite Belt are presented and their significance discussed. Metapefites show a wide variation in δ¹⁸O values (4.50 to 13.90‰) that is controlled largely by the mineralogy of the rocks. Coarse grained porphyritic charnockites have higher δ¹⁸O values (8.60-11.20‰) than that of medium grained ones (5.90-6.60‰) Basic granulites have the minimum δ¹⁸O values (∼5.0‰). Oxygen isotope values of different rock units in the granulite belt are constrained mostly by the composition of the source rocks of the sediments and of the protoliths in the case of charnockites. Post-depositional metamorphic and metasomatic fluids had little contribution to the δ¹⁸O variations in these rocks.

Keywords

O-Isotopes, Eastern Ghats Granulite Belt, Khondalites, Charnockites, Andhra Pradesh.

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• Petrological Studies in Parts of the Closepet Granite Pluton, Mysore State

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Authors

V. Divakara Rao ¹, U. Aswathanarayana ², M. N. Qureshy ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, IN
2 Centre of Advanced Study in Geology, UniversIty of Saugar, Sagar (M.P.), IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 13, No 1 (1972), Pagination: 1-12

Abstract

With the object of investigating the mode of origin of the Closepet granite, Mysore state, India, integrated geological, geochemical and geophysical studies have been made of the northern part of the pluton as also the adjacent Chitaldurg and Hosdurga granites and Penmsular gneiss. The Joints (post-emplacement'l) in the Closepet granite and the ratios of mineral pairs indicate that (i) the grey and the pink varieties of the Closepet granite and the Chitaldurg granite are comparable to many respects and might have had a common mode of origin, (ii) the Hosdurga granite is distinguishable from the above granites in having a lower amount of quartz and K-feldspar and higher amounts of plagioclase and mafics and (iii) the Peninsular gneiss markedly differs from the Closepet and Chitaidurg granites, and departs from them in the same direction as the Hosdurga granite but in a more accentuated way. A two-stage model for the origin of the Closepet granite is supported by the following petrological evidence presence of two generations of quartz, unzoned anhedral plagioclase, replacement of plagioclase by microcline and the presence of perthite and myrmekite along With K-feldspar and quartz. The Closepet granite was apparently formed by palingenesis (starting from the Peninsular  gneiss) and metasomatism involving enrichment in Si, K and Na, among other elements.

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• Geochemistry and Origin of the Peninsular Gneisses of Karnataka, India

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Authors

V. Divakara Rao ¹, S. M. Naqvi ¹, K. Satyanarayana ¹, S. M. Hussain ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 15, No 3 (1974), Pagination: 270-277

Abstract

Major and trace element analyses of gneisses from parts of the Karnataka State, reveal heterogeneity in their chemical, modal and normative compositions. On the basis of chemical differences it is suggested that the parent material for these gneisses was pelitic/arkosic in nature. Heterogeneity in their composition is attributed to their age difference, degree of granitisation and migmatisation to which the pelitic/arkosic parent material was subjected.

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• Isoconcentration Contours and Origin of the Closepet Granite, Karnataka, S. India

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Authors

V. Divakara Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, A.P., IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 16, No 2 (1975), Pagination: 221-225

Abstract

No Abstract.

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• Geochemistry of Subsurface Hornblendic Rocks from Kolar and the Archaean Crustal Composition of the Peninsular Shield

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Authors

V. Divakara Rao ¹, B. Venkatnarayana ¹, Y. V. Ramana ¹

Affiliations
1 National Geophysical Research Institute. Hyderabad, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 17, No 2 (1976), Pagination: 245-251

Abstract

Major and minor elemental analyses of the subsurface hornblendic schists, granulites and basalts from the Kolar schist belt, India (a Precambrian schist belt), suggest that the crust was mostly basic in the Archaean times and similar to tholeiitic basalt.

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• Geochemistry and Origin of Acidic Rocks from Jaspa and Rohtang, Himachal Pradesh

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Authors

V. Divakara Rao ¹, T. Radhakrishna ¹, S. V. Srikantia ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad-500007, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 19, No 12 (1978), Pagination: 563-570

Abstract

Geochemical investigations on the Jaspa granites and Rohtang gneisses from Himachal Pradesh indicate that the Rohtang gneisses are the migmatlsed/granltised products of the pre-existing metasediments and the Jaspa granite is an intrusive granite. Field relationship suggests that the Jaspa granite is a post-tectonic intrusive while the migmatisation/granltisation of the gneisses appear to be pre-and syntectonic and might have continued into the post-tectonic period.

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• Geochemistry and Origin of Acidic Rocks of Shimoga, Karnataka, India

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Authors

Syed Ali ¹, V. Divakara Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 21, No 2 (1980), Pagination: 91-96

Abstract

Acid igneous rocks of Shimoga which were earlier mapped as single granite unit actually consist of two distinct lithological units: an older tonalite and a younger granodiorite. Tonalite is highly disturbed, migmatised and appears to have been derived by partial melting of a basic crust. Younger granodiorite is coarse grained to often porphyritic with higher concentration of K, Ni, Cr and V. Its field relationship with tonalite suggests a different late stage intrusive mode of origin.

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• Physico-Chemical and Mineralogical Studies on Some of the Clay Mineral Deposits of Karnataka, India

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Authors

S. M. Ahmad ¹, V. Divakara Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad 500 007, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 27, No 3 (1986), Pagination: 298-302

Abstract

Physico-chemical properties such as EC and CEC along with X-ray diffraction studies, have been carried out on some of the clay mineral deposits of Karnataka. The results indicate that most of these deposits contain kaolinite as predominant clay mineral except Kurvi clay. Attapulgite is found to be the dominant mineral in the deposits from Kurvi.

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• A Note on the Significance of Uranium and Thorium Distribution in Granitoids from Joshimath-Badrinath of Central Crystalline Axis-Kumaun Himalaya

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Authors

Praveen Raj Saxena ¹, V. Divakara Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad 500 007, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 31, No 5 (1988), Pagination: 488-490

Abstract

Thorium and uranium concentrations in the pelitic-schists and granitic gneisses in Joshimath-Badrinath area of Central Crystalline Axis, show gradual decrease with increase in metamorphism up to anatectic stage. The leucogranites of anatectic origin show unusual increase in uranium. The distribution suggests that with increase in metamorphism these elements were expelled. At a late stage there was uranium enrichment as indicated by scattered distribution in the leucogranite, ranging from 5 ppm to 32ppm.

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• Precambrian Bimodal Volcanism in Weddell Sea, West Antarctica

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Authors

V. Divakara Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad-500 007, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 45, No 2 (1995), Pagination: 163-174

Abstract

Rhyolites and basalts constitute bulk of the bimodal volcanism in the Bertrab and Littlewood nunataks of Weddell Sea area, western Antarctica. Rhyolites with occasional granophyres from the two nunataks are compositionally similar except for high Ba in Littlewood. Basalts, of tholeiitic to calc-alkaline nature are mainly from the Bertrab nunatak and show compositional variation (basalt to basaltic-trachy-andesite) both in major (SiO₂, 45.82 to 53.81%, MgO, 4.67% to 11.20% Na₂O, 1.58 to 4.26%) and trace elements (V, Cr, Rb, Sr and Ba). The rare earth elemental abundances and their distribution patterns in the rhyolites from the two nunataks are broadly similar with comparable total REE (Bertrab 80.33; Littlewood 86.82), moderate LREE/HREE fractionation (Ce_N/Yb_N= 4.36 in Bertrab and 4.33 in Littlewood) and negative europium anomdies.

Overall major and trace elemental chemistry of the acid volcanics coupled with the systematic compositional variation from the basic to the acid end suggests a common source of origin for this bimodal volcanism. The source magma, a melt of the upper mantle appears to have evolved in a compressional tectonic regime and has intruded (extruded) in an extensional rift tectonic setting.

Keywords

Geochemistry, Volcanic Rocks, Antarctica, Precambrian.

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• Geochemistry of Polyphase Gneisses from Schirmacher Oasis, East Antarctica

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Authors

S. M. Hussain ¹, V. Divakara Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 47, No 3 (1996), Pagination: 303-312

Abstract

Gamet-biotite gneisses (GBG), augen gneisses (AG) and quartzo-feldspathic gneisses (QFG) constitute the main litho-units in the granulite terrain of Schirmacher Oasis, East Antarctica. The GBG and AG show chemical and mineralogical similarities. The QFG differs from GBG and AG both in major and trace elements. Overall composition of these different polyphase gneisses indicate increase in silica and alkalies from GBG to QFG and decrease in CaO, FeO and MgO. In trace elements Rb increases from GBG to QFG, while Sr and Ba increase in AG and decrease in QFG. The REE distribution patterns in GBG. AG and QFG differ in that, the total REE in GBG is 160.70, in AG 148.32 and the QFG 119.30. The LREE/HREE and Ce_n/Tb_n ratios of GBG and QFG are similar while in AG these differ slightly (GBG = 5.16 and 3.18; AG = 6.93 and 5.10; QFG = 5.62 and 3.90 respectively). Majority of the gneisses exhibit negative Eu anomaly (GBG = 0.55; AG = 0.35; QFG = 0.43) except two from AG having no anomaly. Overall major, trace and REE abundances in the garnet-biotite and augen gneisses suggest their origin by progressive metamorphism of a pelitic source. Partial melting of GBG locally appears to have formed quartzo-feldspathic gneisses. These gneisses resemble the metapelites of the Eastern Ghat granulite terrain and Kerala khondalite belt of India in their overall compositions.

Keywords

Geochemistry, Gneisses, East Antarctica.

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• Geochemistry, Age and Origin of Perur Granite, Chittoor District, Andhra Pradesh

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Authors

V. Divakara Rao ¹, M. V. Subba Rao ¹, P. Rama Rao ¹, G. V. C. Pantulu ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad-500 007, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 44, No 6 (1994), Pagination: 637-643

Abstract

The homophanous coarse-grained granite near Perur, Chittoor district, Andhra Pradesh ranges in composition from granite (normative) to granite-quartzmonzonite (chemical) and records a Rb-Sr whole rock isochron age of 2549 ± 39 Ma. Variation observed in the major and trace element concentrations (SiO₂ = 67.09-73.83%; Al₂O₃ = 12.76-14.51%; total iron = 2.31-4.97%; MgO = 1.03-3.66%; Cr = 7-102 ppm; Rb = 169-223 ppm and Sr = 128-423 ppm) and the low CaO (less than 2%) in the granite suggest that it is a crustal remelting (CR) type granite formed by the anatectic remelting of an intermediate source rock. The high total REB (201.38-245.63 ppm), their well fractionated nature (La_N/Yb_N= 17.83-22.32) and the negative Eu anomaly of the granite support that the source rock was intermediate in composition having hydroxyl-bearing minerals like biotite and hornblende.

The Rb-Sr whole rock age (2459 ± 39 Ma) of the granite is similar to that of Closepet, Lepakshi and Hyderabad granites suggesting that this granite has formed along with the other K-rich granites by extensive crustal remelting during the Archaean-Proterozoic Transition (APT).

Keywords

Geochemistry, Granites, Chittoor District, Andhra Pradesh.

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• Whole Rock and Mineral Chemistry of Aluminous Granulites From the Eastern Ghats Granulite Belt, Andhra Pradesh

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Authors

A. T. Rao ¹, V. Divakara Rao ², M. Yoshida ³, M. Arima ⁴

Affiliations
1 Department of Geology, Andhra University, Visakhapatnam-530 003, IN
2 National Geophysical Research Institute, Hyderabad- 500 007, IN
3 Department of Geosciences, Osaka City University, Osaka 558, JP
4 Department of Geological Sciences, Yokohama National University, Yokohama, JP

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 50, No 5 (1997), Pagination: 559-570

Abstract

The whole rock analyses confirm the basic to intermediate nature of the protolith (SiO₂, > 53% - < 67%) with high alumina (highest 22.18%) and high K₂O (∼ 4%). Metamorphic segregation as well as source rock compositions appear to have contributed -to the formation of high alumina granulites. The temperatures of metamorphism estimated using garnet - hypersthene/cordierite pairs range from 680-980°C, The gamet-cordierite reference temperatures with narrow range 700-750°C, indicate a pressure range of 5-7 kbar for the garnet-orthopyroxene-plagioclase-quartz assemblage in the aluminous granulites. Textural relationships of cordierite breakdown and reappearance of cordierite supplement the two generations of cordierite from aluminous granulites in the Eastern Ghats Granulites Belt.

Keywords

Geochemistry, Aluminous Granulites, P-T Estimates, Eastern Ghats Granulite Belt (EGGB), Andhra Pradesh.

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• Geochemical Prospecting for Copper in the Nuggihalli Schist Belt, Karnataka, India

Abstract Views :253  |  PDF Views:137

Authors

V. Divakara Rao ¹, S. M. Naqvi ¹, K. Satyanarayana ¹, S. M. Hussain ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 17, No 3 (1976), Pagination: 395-398

Abstract

Geochemical prospecting for copper in the Nuggihalli schist belt, Karnataka has indicated that the serpentinised dunites are moderately enriched in copper. The copper appears to have no structural control and the enrichment is not uniform in the dunite.

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• Reconnaissance Geochemical Exploration for Copper in the Central Part of the Chitradurga Schist Belt, Karnataka, India

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Authors

S. M. Naqvi ¹, V. Divakara Rao ¹, K. Satyanarayana ¹, S. M. Hussain ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 17, No 4 (1976), Pagination: 551-557

Abstract

An area of about 115 Sq km was sampled on a 0.4 km spacing grid. The samples, collected from the bed rock, after removing the thin soil cover, were analysed for Cu, Zn, Pb and Co by the emission spectrograph using indium as internal standard. The Cu concentration map of the area shows nine zones of anomalous Cu content, the highest giving a value of 4000ppm. Of these, four zones of highly anomalous Cu content (2000 ppm-4000 ppm) are very promising and are recommended for detailed geochemical exploration.

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• Occurrence of Quench Olivine Crystals in a Basaltic Dyke from Schirmacher Oasis, Queen Maud Land, East Antarctica

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Authors

S. H. Jafri ¹, S. Moeen ¹, N. Charan ¹, B. L. Narayana ¹, V. Divakara Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Source

Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 60, No 1 (2002), Pagination: 67-74

Abstract

Presence of several morphologies of quench olivine crystals, which provide important clues on cooling rate(s) of magma, are reported here in a basaltic dyke, from the Precambrian gneissic terrain of Schirmacher Oasis, Queen Maud Land, East Antarctica. The dyke, composed of plagioclase, clinopyroxene, olivine, magnetite and glass, shows intergranular texture. It is alkali basalt in composition with low silica (SiO₂ = 46.20-47.20) and negative Nb anomaly. The morphologies of quench olivine crystals suggcst rapid cooling of the basaltic magma approximately at 15-80°C/hour. Further, the delicate nature of these quench olivine crystals, confined mostly to the glassy margins of the dyke, also suggest in situ crystallisation.

Keywords

Basaltic Dyke, Quench Olivine Crystals, Petrography, Geochemistry, Schirmacher Oasis, East Antarctica.

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