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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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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