Zirconology of ultramafic rocks from the Vostochnotagilskii massif (Middle Urals)

Abstract

441 The Vostochnotagilskii massif (VTM; also known as Krasnoural’skii) is one of the largest in the Middle and North Urals [1]. This massif occurs in the merid ian direction for >300 km (Fig. 1, the southern part of massif) and controls the Serovsko–Maukskii ophiolite complex separating the Tagil and Magnitogorsk paleo island arc zones. The massif is composed of dunite and harzburgite serpentinized to various degrees. Chrysotile serpentinite prevails in the central part intruded by gabbro diabase and granitoid dykes, whereas antigorite serpentinite predominates in the marginal zones. The exocontact zones of dykes are characterized by bimetasomatic zoning with the for mation of vermiculite, chlorite–actinolite, talc, and talc–carbonate rocks. The freshest rock varieties are preserved in the central part of massif. Poor exposure does not provide unambiguous evidence for relation ships between dunite and harzburgite; according to the composition of chrome spinellids, ultramafic rocks form a continuous series [2]. At the same time, transi tional varieties between dunite and harzburgite were not found in the largest Kutuzovskii mine located at the latitude of Krasnoural’sk.