EVIDENCE OF ULTRAHIGH-PRESSURE EVOLUTION OF GARNET PERIDOTITES IN THE POLAR URALS

Abstract

In garnet peridotites of the Marunkeu eclogite-gneiss complex (Polar Urals), segregations of carbonates in association with chlorapatite were first established. They contain relics of dolomite, which is “replaced” by calcite with symplectite (graphic) intergrowths of brucite and hydrocarbonate. The formation of peridotites with unusual carbonate structures is the result of the evolution of this complex at different depths. During deep subduction and progressive with the formation of garnet peridotites, segregated dolomite experienced a solid-phase breakdown into aragonite and magnesite at the pressure peak (≥5 GPa). During exhumation and retrograde metamorphism, garnet peridotites, together with segregations, underwent low-temperature transformations; aragonite was replaced by calcite, and magnesite by brucite and hydrocarbonate. The presence of carbonates with deep-seated structures confirms that the garnet peridotites and eclogites of the Polar Urals belong to ultrahigh-pressure complexes.