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

Naresh Kochhar ¹

Affiliations
1 Centre for Advanced Study in Geology, Panjab University, Chandigarh, IN

Abstract

No Abstract.

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Naresh Kochhar ¹

Affiliations
1 Department of Geology, Panjab University, Chandigarh, IN

Abstract

No Abstract.

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Naresh Kochhar ¹

Affiliations
1 Department of Geology, Panjab University, Chandigarh, IN

Abstract

No Abstract.

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Naresh Kochhar ¹

Affiliations
1 Department of Geology, Panjab University, Chandigarh 160014, IN

Abstract

The trans-Aravalli igneous activity of Malani suite of western Rajasthan comprising non-orogenic peraluminous (Jalore and Tusham) to peralkaline (Siwana) granites with the cogenetic carapace of acid volcanics are characterized by ring structures. This alkaline (as opposed to subduction related calc-alkaline) magmatism which was due to hot-spot activity in the region is interpreted as the final tectono-magmatic event that marked the cratonization (stabilization) of the northern part of the Indian shield after the closure of Aravalli-Delhi orogenic cycles. The alkaline to subalkaline magmatism in the form of ring shaped intrusions of nepheline syenites, carbonatites and kimberlites is indicative of tensional environments which existed in the region prior to the emplacement of Malani suite of rocks. The nucleus of the Indo-Gangetic rift was probably formed some 1000 Ma ago. The cratonization was completed with the deposition of Vindhya Platform sediments. The scope of tin mineralization in the region is also discussed in the light of trace element data.

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Naresh Kochhar ¹

Affiliations
1 Department of Geology, Panjab University, Chandigarh 160014, IN

Abstract

Two periods of hot-spot related alkaline magmatism temporally and spatially confined to Aravalli-Delhi mobile belts at 1500-1100 Ma, and at 950-750 Ma have been recognised. The third period is related to the Deccan volcanic province. These three periods of alkaline magmatism correspond with three periods of widespread rifting events in most of the continents.

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G. Nelson Eby ¹, Naresh Kochhar ²

Affiliations
1 Department of Earth Sciences, University of Lowell, Lowell, MA01854, US
2 Department of Geology, Panjab University, Chandigarh 160 014, IN

Abstract

Major and trace element data have been obtained for the ca. 730 Ma granites of the Siwana and Jalor complexes, Rajasthan and the Tosham complex, Haryana. On the basis of geologic, geochronologic and chemical data these granites are classified as anorogenic, and are believed to have been formed during a wide-spread thermal event centered around 800 Ma. All of the complexes show evidence of differentiation at high levels through fractionation of alkali feldspar, plagioclase, and amphibole. The granite from the Siwana complex is peralkaline and Shows high rare-earth (REE) contents with little fractionation between LREE and HREE. This granite may have been derived as a high temperature melt from an anhydrous granulitic source region from which a previous melt had been extracted or by melting of a metasomatized lower crustal source. The Jalor quartz syenites and granites are more primitive, metaluminous and have more fractionated REE patterns. These rocks are most likely differentiates of a mantle-derived magma. The Tosham granites are metaluminous to peraluminous and show isotopic and chemical characteristics typical of magmas derived from a high-grade metasedimentary source, These observations indicate that a variety of granite types can be formed during a period of anorogenic magmatism.

Keywords

Geochemistry, Petrology Igneous) Malani Igneous Suite, Siwana and Jalore Complexes, Rajasthan.

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Naresh Kochhar ¹, G. Vallinayagam ¹, L. N. Gupta ¹

Affiliations
1 Department of Geology, Panjab University, Chandigarh, IN

Abstract

Zircons are hydrothennal or late-magmatic. The high UO₂ contents of the Tosham zircons reflect the high UO₂ of the host rocks. The Siwana granites, though high in Zr values, have very poor zircon yield. This is probably due to the pcralkalinity of the Si wana magma.

Keywords

Malani Igneous Suite, Zircon, Siwana Granite, Geochemistry, Rajasthan.

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Sunil Dhar ¹, Robert Frei ², Jan D. Kramers ², Thomas F. Nagler ², Naresh Kochhar ³

Affiliations
1 Post Graduate Department of Geology, Govt College, Dharamsala, Himachal Pradesh - 176 215, IN
2 Isotope Geology Group, Mineralogical-Petrographical Institute, University of Bern, Erlachstr. 9A, CH-3012 Bern, CH
3 Department of Geology, Panjab University, Chandigarh - 160 014, IN

Abstract

The Jalor and Siwana complexes belong to the Malani igneous suite, Rajasthan, India and are characterised by within - plate, A - type granites associated with coeval felsic and mafic volcanism. Sr, Pb and Nd isotopic compostions of the two complexes have been determined. Sr isotopic studies reveal an isochron age of 725±7 Ma for the felsic rocks of the Jalor Complex, with an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7062±0.0020. Three highly differentiated granites from Siwana plot on the same near-isochron, indicating that the complexes are coeval. The Pb and Nd isotopic ratios range between (²⁰⁶Pb/²⁰⁴Pb = 18.52-21.28, ²⁰⁷Pb²⁰⁸Pb = 15.58-15.98, ²⁰⁴Pb/²⁰⁴Pb/²⁰⁶Pb = 38.53-40.8) and (¹⁴³Nd/¹⁴⁴Nd = 0.5122-0.5127, ¹⁴⁷Sm/¹⁴⁴Nd = 1.1260-0.157) respectively. Pb and Nd isotopic compositions of the Siwana samples show that the magma is mantle derived; for the Jalor complex the combined Sr, Nd and Ph data indicate primary mantle derivation with a variable degree of crustal contamination. with the assimilated crust being most likely of Archaean age.The petrogenesis of the two complexes is interpreted as an effect of fractionation of a primary mantle derived magma, simultaneous with assimilation of rocks from the lower crust. The data further document the presence of Archaean crust in the area.

Keywords

Geochronology, Petrology, Malani Igneous Suite, Rajasthan.

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Ramanathan Baskar ¹, Naresh Kochhar ²

Affiliations
1 Department of Environmental Sciences & Engineering, Guru Jambheshwar University, Hisar 125 001, IN
2 Department of Geology, Panjab University, Chandigarh 160 014, IN

Abstract

Compositional characteristics and substritutional schemes of the amphiboles and pyroxenes of the alkali granites and the associated volcanics around Goliya Bhaylan area are studied. In the alkali granite, the amphiboles evolve from ritchterite to arfvedsonite, in trachytes from winchite to riebeckite and in the case of rhyolites from ritchterite through arfvedsonite to riebeckite with dominant substitution of the type Na^M4 +R³⁺ for Ca + R²⁺. The pyroxenes in alkali granite evolve from hedenbergite to degirine through Aegirine-Augite representing the acmitic hedenbergite trend with dominant NaFe³⁺= Ca(Mg,Fe)²⁺substitution and a minor amount of NaAl = CaFe²⁺substitution , whereas the pyroxenes in the acid volcanics are aegirine representing the acmitic trend, with the same substitution characteristics as those found in the alkali granites. The occurrence of TI aegrine and aenigmatite is also reported. The chemical trends of the pyroxenes and amphiboles indicate that they are formed from a highly evolved peralkaline residual melt.

Keywords

Pyroxenes, Amphiboles, Peralkaline, Alkali Granite, Siwana, Rajasthan.

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L. N. Gupta ¹, Naresh Kochhar ¹

Affiliations
1 Centre of Advanced Study in Geology, Panjab University, Chandigarh - 160014, IN

Abstract

No Abstract.

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Naresh Kochhar ¹

Affiliations
1 Chandigarh, IN

Abstract

No Abstract.

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Sunil Dhar ¹, Naresh Kochhar ², Rajni Sharma ³, L. N. Gupta ²

Affiliations
1 PG Department of Geology, H.P. University, Regional Centre, Dharamsala, (H.P.) - 176 2 15, IN
2 Department of Geology, Panjab University, Chandigarh, 160 014, IN
3 HCC Ltd., C-1 Works, Tala Hydroelectric Project, PB# 390, Phuentsholing, BT

Abstract

This paper describes mineral chemistry of biotites from Jalor, Tosham and Jhunjhunu ring complexes of Malani igneous suite, India. The chemistry reveals iron enrichment trend in all the biotite samples of the three complexes. FeO*/MgO ratio is the highest (6.72) in Jalor samples whereas lower values of (4.08) and (3.72) have been observed in Tosham and Jhunjhunu samples respectively. Higher MgO has not affected the enhanced proportions of FeO in the biotites of Tosham and Jhunjhunu. Mg ⇌ Fe and 2A1 ⇌ 3Fe²⁺ substitution is dominant in Jalor samples whereas, influence of 3M ⇌ Al is deciphered in the Tosham and Jhunjhunu samples. Most of the biotites fall in the anorogenic (A-type) suites, representing extensional tectonic environment for their host rocks.

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