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

T. P. Srinivasan ¹, R. Natarajan ²

Affiliations
1 Department of Geology, Osmania University, Hyderabad 500 007, IN
2 National Geophysical Research Institute, Uppal, Hyderabad 500 039, IN

Abstract

The Fayalite syenites of Gokanakonda in Andhra Pradesh, India, are mineralogically divided into two types: (1) fayalite-clinopyroxene syenites (FC-syenites) and (2) fayalite-quartz syenites (FQ-syenites). The olivine composition ranges from Fa_90-95 and the petrochemistry suggests their successive evolution in that order. The assemblage (fayalite+magnetite+quartz) in these syenites suggests a pressure of 11.5 kb and a temperature of 900°C under constant fo_2.

Keywords

Petrology (Igneous), Fayalite-Syenite, Prakasarn District, Andhra Pradesh.

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T. P. Srinivasan ¹, N. V. Chalapathi Rao ²

Affiliations
1 Bhavan's New Science College, Narayanguda, Hyderabad - 500 029, IN
2 Department of Geology, Osmania University, Hyderabad-500 007, IN

Abstract

The Settupalle igneous complex is characterised by syenitic variants with distinct mineralogic assemblages. The variable perthitic patterns, nature of plagioclase, fayalite-quartz assemblage in Settupalle syenites clearly suggest that the Settupalle igneous complex has evolved under fluctuating pressure and temperature conditions. The mineral chemistry of K-feldspar and plagioclase suggests that K-feldspar assemblage in these rocks indicates their subsolvus nature. The probable crystallization sequence of rocks is fayalite clinopyroxene syenite (FC-Syenite) - fayalite quartz syenite (FQ-Syenite)-hornblende syenite - quartz syenite - nepheline syenite in that order.

Keywords

Mineralogy, Syenites, Settupalle, Prakasarn District, Andra Pradesh.

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