Ectasian 40Ar/39Ar Age of Phlogopite from Apopicritic Metasomatites in the Structure of the Bashkirian Meganticlinorium, South Urals

The central part of the Bashkirian Meganticlinorium hosts abundant bodies of mafic intrusive rocks of the low-Ti (LTi) type (<1 wt % TiO2), which include picrites, picrodolerites, and metasomatic rocks (carbonate–talc and chlorite–quartz rocks with phlogopite, calcite, and dolomite) after picrites. Phlogopite was extracted from metasomatic rocks. According to the 40Ar/39Ar studies, phlogopite shows a plateau with an age of 1356 ± 16 Ma. The picrites most likely underwent metasomatosis related to early magmatic processes almost synchronous with intrusion of picrites. Similar age values are known for a series of intrusive bodies in the north of the Bashkirian Meganticlinorium, which belong to the high-Ti (HTi) type. Our data indicate in favor of the possibility that the intrusions with LTi and HTi rocks formed synchronously, at least, at the late stage of the Mesoproterozoic magmatic activity.