Uranium-lead age of zircons from granites and the substrate of the Mazara massif (Southern Urals)

摘要

The U-Pb dating of zircons from the Mazara granite massif (Southern Urals) by means of the SHRIMP II technique resulted in the conclusion that the zircons were constituted of two key generations belonging, respectively, to the substrate and to the intrusion proper. The age of the granite substrate presented by zircon cores is estimated at 1527-1548 Ma; the final stage of the substrate evolution is characterized by a concordant date of 1388 +/- 16 Ma. The latter estimate is much closer to the Mesoproterosoic stage of magmatism. The information on the formation of granites of the Mazara intrusion is mainly contained in the outer parts of the crystals, with two stages distinguished within the formation history. The early and final stages are determined by the datings of 746.6 +/- 24.3 and 709.1 +/- 5.2 Ma, respectively (both estimates conform to the Neoproterozoic).