COMPOSITION OF MAFIC ROCK-FORMING MINERALS IN THE ROCKS OF THE BURPALA ALKALINE MASSIF (Northern Baikal area)

Abstract

Petrographic and mineralogical studies have been carried out for major varieties of rocks composing the Burpalа massif: peralkaline (nepheline), alkali, and quartz syenites. The emphasis was put on the major and trace element composition of mafic minerals present in all types of rocks: clinopyroxenes, micas, and amphiboles. The studies have shown that the compositions of mafic minerals fractionate within each group of rocks but do not form a single trend of evolution in the groups of peralkaline, alkali, and quartz syenites. This suggests the formation of the massif under pulsed intrusion of variably differentiated magma, the contamination of the first portion of magma, and the subsequent formation of quartz syenites.