Early Cretaceous Adakite and High-Potassium Granitoids as Indicators of the Post-Subduction Environment for the Formation of Porphyry Copper Deposits in the Baim Ore Zone of Chukotka

The article presents new petrological and geochemical data on the rocks of the Egdegkych and Vesenninsky plutonic and hypabyssal complexes in the Baim ore zone located in the Oloy zone of the Alazeya–Oloy fold system, Chukotka. Rocks of the Egdegkych Complex are Early Cretaceous (Berriasian–Valanginian) in age and form ore-bearing intrusions associated with porphyry copper deposits and occurrences. The granitoids of the Egdegkych and Vesenninsky complexes are moderately alkaline rocks and include both high-potassium and adakite varieties. Based on some geochemical parameters, the granitoids of both complexes are similar to high-silica adakites, slab-failure granitoids, and magmatic rocks of transform margins, the formation of which was related to the impact of the asthenospheric mantle on slab-failure zones, and differ from the Late Jurassic supra-subduction rocks of the Oloy zone. The Egdegkych and Vesenninsky complexes formed in the course of collision between the Kolyma–Omolon and Chukotka microcontinents; they are post-subduction and syncollisional, not suprasubduction granitoids, as previously thought. Adakite granitoids of these complexes can be considered as an indicator of possible porphyry copper mineralization in the Oloy zone.