New Data on the Age and Composition of Volcanogenic–Tuffogenic Rocks of the Upper Pegtymel Depression, Chukotka Terrane

Volcanogenic–tuffogenic rocks of the Upper Pegtymel depression on the southern edge of the Chukotka terrane were studied. Dolerites and acid tuffs yielded a Late Cretaceous age (86–88 Ma). The chemical composition of the studied rocks shows that they accumulated within the active margin in a suprasubduction environment, but they differ in composition from coeval volcanic complexes of the Okhotsk–Chukotka volcanic belt (OChVB) and Upper Jurassic–Early Cretaceous formations. The data obtained allow us to suggest that the mafic volcanics we studied formed from another magmatic source less enriched compared to coeval volcanics of the OChVB and was probably associated with extension in the rear part of the volcanic belt.