The Age of Granite of the Famous Thunder Stone, the Pedestal of the Bronze Horseman Monument to Peter the Great (St. Petersburg)

The U–Pb age of the Thunder Stone granite block, which is the pedestal of the Bronze Horseman monument to Peter the Great in St. Petersburg, is dated at ∼1595 Ma. This age was obtained from accessory zircons separated from the biotite flakes using a jeweler gravel. The study was carried out on an SIMS SHRIMP-IIe secondary ion microprobe (15 local U–Pb isotopic analyses, 12 zircon crystals) at the Center of Isotopic Research of the Karpinsky Institute (St. Petersburg). It is not yet possible to determine the source of the Thunder Stone, since granites of the same age have not yet been found either in the Vyborg batholith (1665–1615 Ma), in the Salmi batholith (1547–1535 Ma), or other granite intrusions located in the proximity of St. Petersburg. Thus, the Thunder Stone seems to confirm the historically established idea that it is unique and hints that it should be found among the manifestations of the yet unidentified phases of Early Riphean granitoid magmatism in the most closely located regions.