Genesis of alkaline and peralkaline syenite-granite series: the Kharitonovo Pluton (Transbaikalia, Russia)

The Kharitonovo pluton is located in the central part of the large Mongolian-Transbaikalian province of Late Paleozoic alkaline syenites and granites. It is made up of A-type granitoids forming two successive alkaline and peralkaline syenite-granite series. Rocks of both series are characterized by abundant mesoperthitic feldspar while plagioclase is almost absent. In the alkaline series coeval mafic rocks commonly occur which indicate at least two stages of mafic magma injection into the silicic magma chamber. Major and trace element data are used to test various petrogenetic models for the origin of the syenites and granites. Of the alternatives considered, it is most likely that each series resulted from crystal fractionation of syenite magma. It is suggested that the alkaline syenite magma originated via two possible petrogenetic schemes: 1) partial melting of deeply buried crustal rocks or 2) crystal fractionation of hybrid melt produced by mixing of subalkaline basaltic magma (80%) with about 20% of silicic lower crustal melt. -from Authors