Th—U—Pb-dating of monazite from the metamorphic rocks of the Itkul formation of the Sysert Complex (Middle Urals)

Abstract

New data were obtained on the age of metamorphism of the rocks of the Itkul formation of the Sysert Metamorphic Complex (Middle Urals). Amphibole-chlorite rocks from the Glubochinskoye deposit of the garnet were studied, which was partially worked by several mines. The investigated rocks are composed of chlorite (clinochlore), amphibole (sodic-ferrozhedrite, sodic-zhedrit), garnet (Alm78-65), staurolite, plagioclase (An4-18), ilmenite, fluorapatite and monazite-(Ce). We performed a microprobe study of the chemical composition of monazite and determined the age of the mineral using the Th—U—Pb dating method. The age of the monazite is from 273 to 314 Ma, a weighted average of 297 ± 12 Ma and isochrone of 293 ± 26 Ma (MSWD = 0.23). The age of accessory monazite shows that the formation of amphibole-chlorite rocks occurred in the early Permian times. Probably, the transformation of metamorphic rocks in the northern part of the Sysert metamorphic complex occurred at the Permian and Carboniferous boundary under the influence of a powerful thermal event. At present, this is the subject of discussions. Some researchers believe that metamorphic rocks were formed as a result of a thermal event associated with suprasubduction tonalite-granodiorite magmatism, while others posit that the Sysert complex was formed as a suprasubduction accretion prism.