Subalkaline Basaltoids in Ultramafic Rocks of the Rai-Iz Massif (Polar Urals) and Their Petrogenetic Significance

The composition and age of subalkaline dolerites, localized in chromite-bearing ultramafic rocks of the Rai-Iz massif, were studied. Dolerites are traced along the tectonic zones inside ultramafic rocks and are not observed beyond their boundaries, spatially tending to deposits and occurrences of chromite ores. The studied dolerites are characterized by high concentrations of alkalis, TiO 2 , P 2 O 5 , enrichment in large-ion lithophilic elements and Th; the amount of REE varies from 103.3 to 164.2 ppm; (La/Sm) n = 1.3–1.7. The age of the subalkaline dolerites was determined by the method 40 Ar/ 39 Ar (402.7 ± 3.8 Ma). At this time, ultramafic rocks of most of the Rai-Iz massif were metamorphically processed with the formation of high-chromium chromitites and with the isolation of a vein series of subalkaline dolerites in the discharge zones.