New data on the Early Cenozoic volcanism of the Kolyuchinskii-Mechigmen graben, Chukotka Peninsula

The isotopic-geochemical composition of the Late Paleocene-Early Eocene basalts in the central part of the Kolyuchinskii-Mechigmen graben on the east of the Chukotka Peninsula is studied. The distribution of major and trace elements and the elemental ratios point to the formation of basalts under conditions of marginal-continental rifting. The basalts of Mount Otdel’naya are characterized by a combination of depleted, intraplate, and suprasubduction geochemical features, which differentiates them both from the rocks of suprasubduction volcanic belts and tholeiites and alkaline lavas of the continental rifts and oceanic island arcs. The specific peculiarities of basalts of Mount Otdel’naya are extremely high, relative to similar basalts of spreading zones of the region and the 87 Sr/ 86 Sr ratios, which reflect the involvement of carbonate material in the magma generation zone.