Metasomatism in Serpentinite Mélange Rocks from the High-Pressure Maksyutov Complex, Southern Ural Mountains, Russia

Abstract

Metasomatized basalts are enclosed in antigorite serpentine mélange of the Upper Unit of the Maksyutov Complex, southern Ural Mountains, Russia. The structurally Lower Unit of this complex consists predominantly of mafic eclogite and sedimentary gneiss metamorphosed at ultrahigh pressures; rocks of the Upper Unit underwent blueschist-facies conditions. The metasomatized rocks are fine-grained blocks, variably composed of chlorite, garnet, lawsonite, white-mica, epidote, and titanite. Partial rodingitization accompanied serpentinization of the surrounding peridotite, and predated the high-pressure metamorphism that led to the formation of lawsonite. Extensive Mg metasomatism followed rodingitization, leading to prevalent Mg-rich rims around the mafic blocks. Potassium metasomatism, although minor compared to the rodingitization and Mg metasomatism, contributed to the formation of muscovite pseudomorphs after lawsonite during exhumation.