Age of Detrital Zircons from Sandstones of the Mesozoic Flysch Formation in the South Anyui Suture Zone (Western Chukotka)

摘要

The South Anyui fold zone (western Chukotka) is considered a suture zone related to closure of the South Anyui oceanic basin and collision of Eurasia with the Chukotka-Arctic Alaska microcontinent in the Early Cretaceous. The existence of a compensatory sedimentation basin (foredeep) during folding in the terminal Jurassic-initial Cretaceous remains debatable. This work presents first data on age estimates of detrital zircons from Upper Mesozoic terrigenous sequences of the South Anyui suture zone obtained by the fission-track method. The distal flysch of presumably Late Jurassic age and the proximal flysch of probably Late Triassic age were sampled in the Uyamkanda River basin. The fission-track dating showed that sandstones from the flysch sections contain detrital zircons of two different-age populations. Young zircon populations from sandstones of distal turbidites in the upper course of the Uyamkanda River (two samples) are 149 +- 10.2 and 155.4 +- 9.0 Ma old (Late Jurassic), whereas those from coarse-grained proximal turbidites sampled in the lower course of the Uyamkanda River (one sample) is 131.1 +- 7.5 Ma old (Early Cretaceous). The data obtained indicate that the Late Mesozoic folding in the South Anyui suture zone was accompanied by the formation of a marginal sedimentary basin. Sediments accumulated in this basin compose tectonic nappes that constitute a fold-thrust structure with the northern vergence.