THE AGE OF VOLCANIC TUFFS FROM THE BASU AND ZIGAN FORMATIONS OF THE VENDIAN (EDIACARAN) ASHA GROUP IN THE SOUTHERN URALS: RESULTS OF U–Th–Pb (SIMS and La–ICP–MS) DATING OF ACCESSORY ZIRCON

Abstract

For accessory zircon from ash tuffs of the Basu and Zigan Fms of the Asha Vendian (Ediacaran) Group of the Southern Urals obtained isotopic U–Pb age (SIMS (SHRIMP II) и La–ICP–MS). The compositions of rare-metal enriched tuffs correspond to rhyolites, comendites, trachytes, trachyandesites. The concordant value of the U–Pb age of zircon from the tuffs of the Basu Formation is 578 ± 7, 577 ± 7 and 568 ± 5 Ma (SHRIMP II). The age of the zircon from the other two points of the Basu Formation is 573 ± 4 and 574 ± 3 Ma (La–ICP–MS). The age of zircons from the tuffs of the Zigan Formation is 566 ± 5 Ma (SHRIMP II). Tuffs accumulated in the hinterland of the marginal continental volcanic belt.