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Alkaline basic intrusives of Elchuru, Prakasam District, Andhra Pradesh, India

  • Sattrajit Nag
  • T E Smith
  • P S Chakravorty
Article
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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.

Keywords

Alkaline complex ijolite-melteigite malignite melalusitanite biotite lamprophyre 

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Copyright information

© Indian Academy of Sciences 1983

Authors and Affiliations

  • Sattrajit Nag
    • 1
  • T E Smith
    • 1
    • 2
  • P S Chakravorty
    • 1
  1. 1.Department of Geological SciencesJadavpur UniversityCalcuttaIndia
  2. 2.Department of GeologyUniversity of WindsorCanada

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