FISSION-TRACK DATING OF DETRITAL ZIRCONS FROM SANDSTONE OF THE LESNAYA GROUP, NORTHERN KAMCHATKA

Abstract

Flyschoid deposits of the Lesnaya Group that are exposed within northern Kamchatka are almost barren of identifiable fossils. The group is considered to be of the Late Cretaceous age on the basis of geological correlation. Ages of detrital zircons from nine sandstone samples of the Lesnaya Group are determined using the fission-track dating. The youngest population of colorless idiomorphic zircon crystals, which experienced no secondary annealing, is from 43.7 ± 3.4 to 58.1 ± 4.2 Ma old. Morphological features of zircons allow us to relate their formation to the volcanic activity synchronous to accumulation of the Lesnaya Group flysch. Hypabyssal intrusions and blocks of older rocks that experienced rapid exhumation from the depth, where thermal parameters exceeded the blocking temperature, could be the source rocks for younger zircons. The age of the youngest zircon population can be interpreted as corresponding to sedimentation time of the Lesnaya Group that lasted, according to our data, until the mid-Middle Eocene.