Alkaline basic intrusives of Elchuru,Prakasam District,Andhra Pradesh,India |
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| Authors: | Sattrajit Nag T E Smith P S Chakravorty |
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| Institution: | 1. Department of Geological Sciences, Jadavpur University, 700 032, Calcutta, India
2. Department of Geology, University of Windsor, N9B 3P4, Ontario, Canada
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| Abstract: | The igneous alkaline rocks at Elchuru start from a parent ijolite-melteigite association to basic malignite, melalusitanite and shonkinite followed by nepheline syenites and then biotite lamprophyres (as dykes) at the waning phase of the evolutionary course of the complex. The distinct alkalinity of the rocks is manifested by the development of modal nepheline and calcic amphibole (kaersutite). For both the basic rocks,i.e. alkali gabbro and biotite lamprophyre, the percentages of normative nepheline are always higher than modal nepheline, indicating silica deficiency and alkali enrichment of the mafics. It is evident from detailed petrological and geochemical studies that the two basic members are very much akin to each other and there is no major deviation in their bulk chemistry. |
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