Orbicular Peridotites of the Polar Urals: New Evidence of Magmatic Impregnation in Ophiolites

Peridotites of an unusual orbicular structure, attributed to the impregnated type of rocks, were found in ophiolites of the Voikar massif (Polar Urals). Orbicules in these rocks are composed of a secondary clinochlore–diopside aggregate containing grains of primary clinopyroxene and pargasite. The morphology and composition of orbicules make it possible to attribute them to segregations (globules) of the melt in the olivine matrix of peridotites that have experienced partial crystallization in situ. According to geochemical modeling results, these melts had characteristics transitional to boninites, corresponding to the suprasubduction conditions. The formation of orbicular peridotites was associated with blocking intergranular channels of the percolating basaltic melts.