PRELIMINARY PETROGRAPHIC INVESTIGATIONS OF PERIDOTITE XENOLITHS FROM THE VITIM VOLCANIC FIELD, SIBERIA, RUSSIA

The Vitim volcanic field near the Baikal rift zone in Russia originated in the early Paleozoic. The field has undergone several tectonic collisions, oogenesis, and volcanism since then. The most active magmatic episode was during the Miocene to Pleistocene, and the most recent episode was from the Pleistocene to the Holocene. The major rock types are basalt/picro-basalt, trachybasalt/tephrite basanite, with minor amounts of andesite and basaltic andesite. Peridotite xenoliths were exhumed during volcanic activity and provide an opportunity to study the underlying mantle.

Six basalt-hosted peridotite xenolith samples from this location were examined, primarily using petrographic microscopy, whilst some geochemical data (major, minor and trace elements) from previously unpublished work was also examined. The samples were collected 200 km east of Lake Baikal and initially examined by Ionov et al. (1993). The peridotite shows evidence of recrystallization and have a high modal abundance of olivine, with lower modal percentages of garnet, orthopyroxene, clinopyroxene, and spinel. The presence of both garnet and spinel in some samples provides a unique opportunity to explore the mantle in the spinel/garnet transition region of 2-3 GPa. We will present preliminary findings based on the initial investigation of the samples.