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

V. Chandrasekaran ¹, R. K. Srivastava ², M. P. Chawade ¹

Affiliations
1 Geological Survey of India, Jhalana Dungri, Jaipur 302004, IN
2 Department of Geology, University of Rajasthan, Udaipur, IN

Abstract

The alkaline suite of Sarnu-Dandali (comprising ultrabasic alkaline rocks, ijolite, foidal syenite, phonolite and carbonatite) is one of the few occurrences of carbonatite-nephelinite association reported in India. The suite is intrusive into the Lower Cretaceous sedimentaries. The rocks show a continuous gradation from alkali pyroxenite to feldspathic ijolite through micro-melteigite and ijolite, Foidal syenite and phonolite mark the end phase of ijolitic series and phonolites are the last to be emplaced. Carbonatites include sovitic alvikite and ferro-carbonatite varieties. The suite shows a progressive increase in Al₂O₃, Na₂O and K₂O and decrease in MgO, CaO, total Iron, MnO and TiO₂ with increasing SiO₂. Fractional crystallisation has played a dominant role in the evolution of the suite, the major fractional phases being pyroxene and iron oxide mineral.

Keywords

Alkaline Rocks, Geochemistry, Sarnu-Dandali, Rajasthan.

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V. Chandrasekaran ¹, R. K. Srivastava ²

Affiliations
1 Geological Survey of India, Operation TNKP, Madras 600032, IN
2 Department of Geology, M.S. University, Udaipur 313 001, IN

Abstract

The Sarnu-Dandali carbonatites of Western Rajasthan are some of the few occurrences of a typical carbonatit-nephelinite magmatic association known from India. They occur as dykes and dykelets of sovitic-alvikite and ferrocarbonatite showing distinct variation in their chemistry. The sovitic-alvikites have high contents of BaO (up to 3.42%) and SrO (up to 1 %). Fractionation trend is marked by decreasing concentration of SrO from sovitic-alvikite (1.00%) to ferrocarbonatite (0.06%). Trace element contents reveal pronounced preference of Ce and other rare earth elements for sovitic-alvikites. Their oxygen and carbon isotope values are that of typical primary igneous carbonatites. The chemical and isotopic data reveal that the Sarnu-Dandali carbonatites are magmatic, fractionated and have originated from a mantle-derived nephelinitic magma.

Keywords

Carbonatite, Geochemistry, Sarnu-Dandali, Rajasthan.

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V. Chandrasekaran ¹, R. k. Srivastava ²

Affiliations
1 Geological Survey of India, J.L. Nehru Road, Madras-600032, IN
2 Department of Geology, M. S. University, Udaipur-313001., IN

Abstract

Applying multivariate Linear Regression and Principal Component analyses, the petrogenetic aspects of the polyphase igneous rocks of the Malani Igneous Province, Western Rajasthan were dealt with and inferences arrived. The various rocks of the province belong to different magmatic activities unrelated to each other. Normal and peralkaline rhyolites of the province are not co-genetic. Siwana and Jalor granites are distinct and generated at different stages. The acid dykes represent the end phases of the Jalor granite activity, crystallising from the same melt. Fractional crystallisation has played a major role in the development of the mildly alkaline and hyperalkaline rock series. Pyroxene, iron oxide minerals, feldspathoid and alkali feldspar play a major role in the development of the alkaline rocks, whereas pyroxene, iron oxide minerals and plagioclase playa dominant role in the development of the mildly alkaline rocks. The rocks of different groups fall on different liquid lines of descent in the Latent vector variation diagrams.

Keywords

Correlation and Principal Component Analyses, Malani Igneous Province, Petrogenesis, Samu-Dandali, Rajasthan.

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M. P. Chawade ¹, V. Chandrasekaran ²

Affiliations
1 97 Ambazari Layout, Nagpur, IN
2 Geological Survey of India, Madras-600 018, IN

Abstract

Anorthosite occurs as a discontinuous ENE-WSW trending lensoidal (300 m x 1500 m) discordant body within biotite granite and gneisses of pre-Malani age and lies to the SSW of the intersection of the Jaisalmer-Barwani and Lathi-Rajkot lineaments. It is a coarse-grained greenish grey rock with no banding or mineral lineation. It comprises of 92% plagioclase (An 70-78) and 7% hornblende. It is characterised by low SiO₂, K₂O, Ba and Rb and high Sr and has normative olivine, nepheline and corundum.

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