• N A Vemban

      Articles written in Proceedings – Section A

    • A chemical and petrological study of some dyke rocks in the pre-cambrian (Cuddapah traps)

      N A Vemban

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    • Differentiation trends in the Deccan traps

      N A Vemban

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      In this study the author has critically reviewed the existing literature on the Deccan traps, brought together all the published analyses (55 in number) and studied their petro-chemical relationships. The material under study has come from four regions,viz., the Central Provinces, Pavagad Hills, the Bombay Coast and Kathiawar. The analyses are first grouped according to the major rock types which they represent and the peculiarities in each group studied. A regional grouping of the rocks is adopted for studying the differentiation trends graphically using the variation diagram as also Prof. Niggli’s QLM diagram. It is deduced from these studies that the original magma is probably an ultrabasic (essexitic or picritic) type which proceeds during differentiation towards both the calc-alkaline and alkaline fields, the former predominating. There does not seem to be much evidence for the existence of two separate primary basic magmas (tholeiitic and olivine-basaltic) as advocated by Kennedy. A single magma-type more basic than plateau basalts would appear to be adequate for the evolution of rocks in the Deccan trap assemblage, as shown by Kuno.

      The study reveals also that much more petrological and chemical work should be done on some of the differentiated groups and attention should be focussed on the solution of the mechanism of differentiation and the localisation of the resultant products in certain regions.

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