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S. P. Venkata Dasu ¹, T. M. Ramakrishnan ¹, B. Mahabaleswar ²

Affiliations
1 Geological Survey of India, A.M.S.E. Wing, Church Street, Bangalore-560001, IN
2 Department of Geology, Bangalore University, Bangalore-560056, IN

Abstract

New geological and preliminary geochemical data presented here from J ayachamarajapura (JC Pura) reinforce the idea of orogenic separation of two sequences across a deformed angular un confonnity . The JC Pura belt forms a major structural dome linking a trail of enclaves to the north and south. Its main lithology is altered komatiites preserving excellent polyhedral joints, pillows, ocelli and spinifex texture. These peridotitic komatiites are closely associated with the basaltic komatiites now represented by dark shiny amphibolites.Cherty quartzites and BIF form minor units. This association is typical of the older greenstones (Sargur Group) of Kamataka. These lithologies are overlain unconformably by the basal quartz-pebble conglomerate and associated amygdular metabasalt - crossbedded quartz arenite alternations constituting the Bababudan Group in the Kibbanahalli arm of Chitradurga schist belt. Kibbanahalli volcanics are mainly tholeiites as distinct from the dominant komatiites of the JC Pura belt. Such chemical distinction, but of a different kind, is reported recently from the Kalasapura area of Bababudan belt. JC Pura area therefore offers yet another spectacle of Sargur-Dharwar orogenic discrimination in Kamataka.

Keywords

Jayachamarajapura Greenstone Belt, Kibbanahalli, Komatiites, Angular Unconformity, Sargur-Dharwar Relationship, Geochemistry, Geochronology, Kamataka.

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S. P. Venkata Dasu ¹

Affiliations
1 PPOD Division, AMSE Wing, Geological Survey of India, Bangalore-560082, IN

Abstract

No Abstract.

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T. R. Anantharamu ¹, K. N. Nagarna Rao ², Manjunatha ³, Shafeeq Ahmed ⁴, T. K. Gandhi Prasad ⁵, T. Gopal Reddy ⁵, S. P. Venkata Dasu ⁶, E. B. Sugavanam ⁷

Affiliations
1 No.53, 9th 'E' Cross, S.B.I. Colony, J.P. Nagar I Phase. Bangalore -560078, IN
2 No. 693, Yelahanka, Bangalore- 560064, IN
3 No. 60, II main road, B.S.K. III Stage, III Phase, Bangalore-560085., IN
4 No.45/J, Marappa bLock,J. C. Nagar, Bangalore-560006, IN
5 Flat 202, Sandhyagiri Apartments, Kalyan Nagar, Hyderabad-500068, IN
6 7th Main, Padmanabhanagar, Bangalore- 560070, IN
7 54F, Venkatapuram, Shankernagar, Salem -636007, IN

Abstract

Several lensoid bodies of carbonatite occur within a wide zone of fenitisation in the granulite terrain of Kollegal taluk, Karnataka. These are emplaced along deep NNE-SSW fracture system and are associated with pyroxenite, talc-tremolite schist showing varying degree of fenitisation. The sovite and beforsite varieties show high percentage of SiO₂ due to contamination during emplacement The Fe₂0 ₃ , MnO and MgO values of Ajjipuram carbonatites broadly compare with the Koratti carbonatites occurring on the eastern part ofthe mobile belt with similar tectonic history.

Keywords

Carbonatites, Kollegal Taluk, Karnataka.

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M. Ramakrishnan ¹, S. P. Venkata Dasu ², A. Kroener ³

Affiliations
1 Geological Survey of India, Training Institute, Hyderabad, IN
2 Geological Survey of India, AMSE Wing, Bangalore, IN
3 Institut fuer Geowissenschaften, Johannes Gutenberg-Universitaet, 55099 Mainz, DE

Abstract

The middle Archaean J. C. Pura greenstone belt of Sargur Group underlies the Dharwar angular unconformity along the Kibbanahalli arm of Chitradurga schist belt. It consists essentially of periodotitic komatiite (serpentinite), basaltic komatiite (dark amphibolite), rare BIF and minor metaquartzite. In view of the ongoing debate on the origin of Sargur quartzite as to whether it is a chemogenic, biogenic or detrital-rich chert or quartz arenite, the study of J. C. Pura metaquartzite is important as it will have a direct bearing on the depositional setting of the metaquartzite in particular, and the Sargur association in general. In the absence of primary sedimentary structures, accessory zircons in the metaquartzite provide the main clue to its origin. Euhedral zircons with minor rounding of pyramidal terminations in the metaquartzite suggest little mechanical corrosion and negligible sedimentary transport. These zircons are interpreted as detrital grains and the host rock as siliciclastic in origin. Geochemical parameters like Al₂O₃ vs TiO₂, SiO₂ and K₂O, trace element spider plots, REE patterns and La/Sc ratio indicate a significant continental contribution, low Fe and Mn content, low TiO₂-normalised values and variable Co/Zn and Ni/Zn ratios preclude major sea water hydrothermal activity. The proximal provenance indicated by euhedral zircons did not apparently have a significant felsic volcanic component since such rocks are neither present witnin the schist belt nor found as enclaves in the surrounding gneisses. Furthermore, the Sr, Zn, Y, Yb values of the metaquartzite are lower than that of felsic volcanics and pyroclastics, thereby ruling out their prevalence in the source area. The most likely source would therefore be the widespread early Archaean continental crust of southern India made up of granitoids. The metaquartzite was probably deposited as quartz arenite in shallow marine enviroment close to the continent. The associated pillowed komatiite also lends support to this environmental interpretation.

Euhedral zircons from J. C. Pura metaquartzite were dated by single grain evaporation technique which yielded a Pb-Pb age of 3230 ± 5 Ma. This date representing the maximum age of the Sargur metaquartzite is fully in accord with previous Sm-Nd model ages and SHRIMP U-Pb zircon ages (ca 3200 Ma) of Sargur rocks from nearby areas. The Sargur Group is pervasively intruded by gneisses and granites around 3000 Ma. Still older gneisses seen in the neighbourhood such as the Gorur gneiss of 3300 Ma age may constitute a possible basement to the Sargur supracrustals and represent widespread early Archaean granitic crust of the Dharwar craton.

Keywords

Geochronology, Geochemistry, Metamorphic Petrology, J. C. Pura/Sasivala Greenstone Belt, Sargur Group, Dharwar Craton, Kanataka.

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S. P. Venkata Dasu ¹

Affiliations
1 Geological Survey of India, AMSE Wing, Bangalore, IN

Abstract

No Abstract.

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S. P. Venkata Dasu ¹

Affiliations
1 PPOD Division, AMSE Wing Geological Survey of India Bangalore - 560 078, IN

Abstract

No Abstract.

Full Text

   

S. P. Venkata Dasu ¹

Affiliations
1 PPOD Division, AMSE Wing Geological Survey of India Bangalore - 560 078, IN

Abstract

No Abstract.

Full Text

   

S. P. Venkata Dasu ¹

Affiliations
1 PPOD Division, AMSE Wing, Geological Survey of India, Bangalore - 560 078, IN

Abstract

No Abstract.

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S. P. Venkata Dasu ¹

Affiliations
1 AMSE Wing, Central zone, Geological Survey of India, Nagpur, IN

Abstract

No Abstract.

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S. P. Venkata Dasu ¹

Affiliations
1 Airborne Mineral Surveys and Exploration Wing, Geological Survey of India, Bangalore - 560 078, IN

Abstract

No Abstract.

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S. P. Venkata Dasu ¹

Affiliations
1 AMSE Wing, Geological Survey of India, Bangalore, IN

Abstract

No Abstract.

Full Text