Structure and formation mechanism of the Nizhny Tagil dunite-clinopyroxenite massif, Central Urals

The results of the structural study of the Nizhny Tagil platiniferous massif in the Central Urals are presented. This is a classic massif of the Ural-Alaskan-type zonal dunite-clinopyroxenite complexes. The massif is characterized by a nearly concentric vertical planar internal structure conformable to petrographic zoning (layering). The primary ultramafic rocks are distinguished by adcumulative protogranular structure with relict euhedral olivine protocrysts and distinct linear orientation of minerals, which was formed as a result of magmatic flow. The deformational linear and planar structures conformable to the early structural elements were formed in the process of subsequent coaxal high-temperature ductile flow. At this stage, dynamometamorphic zoning is formed, expressed in the change of the protogranular microstructure typical of the inner portion of the massif by porphyroclastic and mosaic microstructures in its marginal part. The country rocks underwent conjugate high-temperature metamorphism with the formation of hornfels and kytlymite. The structure of the massif is considered to be a result of dynamic differentiation in the course of magmatic flow followed by high-temperature coaxal flow during intrusive and diapiric ascent of rocks to the crustal level.