Composition of micas from rocks and melt inclusions in quartz of Li-F granites of the Orlovka massif in Eastern Transbaikalia as a genetic indicator

Abstract

Based on the study of the chemical composition of rock-forming micas and micas from melt inclusions in quartz of a full range of differentiates of the Li-F granite Orlovka massif in Eastern Transbaikalia, possible mechanisms of formation of the massif are considered. An early stage with a mica evolution trend in rocks (biotite — Li-rich aluminous annite — Li-rich phengite-muscovite), manifested in the synchronous accumulation of Li and F in the melt, mica from the rock and melt inclusions (an ongonite trend of the melt evolution), culminated in the formation of specific porphyroblast microcline-albite granites with Li-rich phengite-muscovite and snow-ball quartz. It was this melt that served as the basis for all its subsequent transformations (repeated manifestation of silicate-salt liquid immiscibility, post-magmatic metasomatism), which determined the development of the “apogranite process”. The crystallization of exclusively lithium-free high-alumininous muscovite in the melt inclusions of microcline-albite granites and the subsequent series of amazonite-bearing rocks with a high content of Li and F in the homogenized glass of these inclusions allows us to assume the crystallization of this mineral from the depleted melt, coexisting with the isolated Li-F hydrosalt phase. The obtained results indicate the convergence of the mechanism of formation of Li-Fe micas, which allows the probability of their crystallization from a fluid-saturated melt and as a result of metasomatic reworking at the different stages of formation of the Orlovka massif.