Sphene bearing gneisses of Madhugiri area, Karnataka State, India

Abstract

Sphene fleck granitic rocks (Titanitflecken-gesteine) composed of biotite and migmatitic gneisses are frequently found in the granitic terrain between Madhugiri and Koratagere. The detailed field and thin section studies of these rocks indicate that sphene is formed during the migmatization and feldspathization of the amphibolites, which has resulted in the recrystallization of plagioclase and in the breakdown of hornblende and biotite. The released lime, titania and iron have resulted in the formation of sphene, seen in the gneissic rocks as trains, patches and discrete crystals. Mineralogical, petrological and petrochemical evidences are given in support of the above conclusion.