ВАЛЕНТНОЕ СОСТОЯНИЕ ЖЕЛЕЗА И РАСПРЕДЕЛЕНИЕ FE2+ И FE3+ В СТРУКТУРЕ МИНЕРАЛОВ МАНТИЙНЫХ КСЕНОЛИТОВ ИЗ ЩЕЛОЧНЫХ БАЗАЛЬТОВ МОНГОЛИИ (ПО ДАННЫМ МЁССБАУЭРОВСКОЙ СПЕКТРОСКОПИИ)

Abstract

The Mössbauer spectroscopy techniques have been used to study pyroxenes, spinels and olivines from upper mantle xenoliths in alkaline basalts of Central (Tariat depression) and Southeast Mongolia (Dariganga pla-teau) - South-Hangaue and Dariganga volcanic regions. The data on Fe"+ distribution between nonequivalent M\ and Ml sites in structure of orthorhombic pyroxenes allow to estimate the temperatures of intracrystalline equilibrium of cations by the refined intraphase orthopyroxene thermometer. The calculated temperatures are high (900-1300 °C) and close to equilibrium temperatures of garnet-orthopyroxene and twopyroxenes assemblages (1080-1280 °C) in mantle peridotites and pyroxenites. This indicates the high-speed export of xenoliths from zone of their crystallization up to surface. Remained normal distribution of iron cations in spinel structure (λFe = 0) confirms the high temperature of the xenoliths formation and the high speed exporting. The oxidation degree is higher for clynopyroxenes and spinels from xenoliths in Dariganga plateau basalts than for the same minerals from xenoliths in basalts of Tariat depression. The higher Fe31 contents in pyroxenes and spinel structures from xenoliths of Dariganga plateau correlate with higher fO2 values for the upper mantle in this region as compared with Tariat region. Those facts allow to suppose that the studied xenoliths were not altered by any superimposed processes during their way up to surface