Mantle ultrabasites of ophiolite complexes in the Polar Urals: Petrogenesis and geodynamic environments

Abstract

Geological, mineralogical, and geochemical data on ultrabasites in the Polar Ural Ophiolite Zone in the Main Ural Fault zone indicate that the origin of the ultrabasites was controlled by the depletion process during the partial melting of mantle material, fluid-magmatic transformations, and subsequent metamorphism in various geodynamic environments. In a spreading environment above a subduction zone, the lherzolites and harzburgites of the older complex were produced by partial (10–25%) melting. The fluid-magmatic transformations were associated with the massive refertilization and enrichment in LREE, MREE, and incompatible trace elements. Along with this, the ultrabasites were affected by depyroxenization (dunitization) with the generation of a dunite-harzburgite complex in domains and zones of brittle-plastic deformations first in a spreading and then in an island-arc environment. The subsequent displacement of the ultrabasites to a crustal level was associated with their metamorphism without principal changes in their geochemistry.