Heterogeneity of Mantle Peridotites from the Polar Urals (Russia): Evidence from New LA-ICP-MS Data

Abstract

To discuss the nature of the compositional heterogeneity of the peridotite massifs of the Polar Urals (Russia), the geochemical study by LA-ICP-MS of pyroxenes and amphiboles from these mantle formations was performed. The trace element compositions in clinopyroxenes indicate the existence of the mantle protolith of two types. The first protolith type, represented by lherzolites and diopside harzburgites, was originated from the partial melting (5%-10%) under the spinel facies conditions, while the second one, represented by diopside harzburgites, was formed under the polybaric partial melting (17%-19%) under garnet and spinel facies conditions. Subsequently, the mantle peridotite protolith was subject to fluidinduced partial melting in the suprasubduction setting that was resulted in the formation of harzburgites. Being affected by penetrating melts and fluids peridotites experienced the refertilization (LREE enrichment of clinopyroxenes) and high-temperature hydratation with subsequent development of pargasite and Mg amphibole. The high-T fluid-induced metamorphism at the subduction zone was accompanied by the formation of metaperidotites with clinochlore and REE-depleted tremolite.