The first evidence of UHP metamorphism in the Polar Urals (Russia)

A new ultrahigh-pressure (UHP) metamorphic terrane, the Marun-Keu eclogite–peridotite–gneiss complex was established in the Polar Urals (Russia). Owing to the P–T parameters of formation of garnet peridotites obtained for the first time, it was established that they experienced UHP metamorphism with a peak in the diamond stability field (39 kbar, 830oC) due to subduction of rocks of the Marun-Keu complex to the mantle (a depth of more than 100 km). Relics of plagioclase peridotites preserved in central parts of large peridotite bodies and petrochemical data are evidence that Marun-Key garnet peridotites cannot be of mantle origin. A basic-ultrabasic intrusion, which formed in the upper crust, can be considered as their protolith. Later, rocks of the massif plunged to the mantle along the subduction zone and metamorphosed under high-P to ultrahigh-P conditions.