Amphiboles of Alkaline-Ultrabasic Rocks from North-Western Part of the Ukrainian Shield

Abstract

Different magnesian amphiboles — pargasites, Ca-Na- and alkaline ones (richterites, Mg-kathophorites, Mg-taramites, Mg-riebeckites, Mg-arfvedsonites and intermediate varieties) of alkaline-ultrabasic rocks (hypabyssal intrusions and dikes) from North-Western part of the Ukrainian Shield are studied and analyzed (mainly microbe method). Some pargasites and richterites are characterized by increased or high TiO2 contents (2.9-3.2%). In studied region more enriched in iron and titanium amphiboles (ferri-kaersutites) rarely occur too in veins rocks of essexite composition. Chemistry of amphiboles depends on types of rocks and erosion of their intrusions. Low aluminian and alkaline amphiboles are characteristic for at least eroded intrusions (dikes) whereas in more eroded and more crystallized hypabysal intrusions amphiboles with higher aluminium of pargasite composition form. Such diversity of studied amphiboles is caused by composition of alkaline-ultrabasic melts and some different depth of their crystallization.