Late Cretaceous Okhotsk‒Penzhina‒Anadyr Small Oceanic Basin (Northeast Eurasia): Geological Evidence and Geodynamic Evolution

The modern structure of the Eurasian margin combines suprasubduction Upper Cretaceous volcanic formations—the marginal continental Okhotsk–Chukotka volcanic belt and the accreted Nemuro‒Olyutor intraoceanic arc that formed during Pacific oceanic crust subduction. We consider the formation of the Okhotsk–Chukotka volcanic belt, separated by the Nemuro–Olyutor intraoceanic arc from the Pacific, in conditions of a paleoceanic basin that was being existed for ~20 Ma. As a result of the conducted paleogeodynamic analysis, it was found that in the Late Cretaceous in northeastern Eurasia, between the Eurasian continent and tectonic blocks of the Sea of Okhotsk, Western Kamchatka, and Northern Koryak located south and southeast of it, a small pull-apart oceanic basin developed in transtension conditions, which can be called the Okhotsk‒Penzhina‒Anadyr Basin, which formed as a result of a major strike-slip fault when tectonic terranes escaped from the eastern part of the closing Mongol‒Okhotsk Ocean. The progressive opening of the Okhotsk‒Penzhina‒Anadyr spreading basin subducted from the southwest to the northeast under the Eurasian continent, which caused a corresponding delay in the onset of suprasubduction volcanism in the Okhotsk‒Chukchi volcanic belt. The geodynamic evolution of the southwestern and northeastern parts of the Okhotsk‒Penzhina‒Anadyr Basin differed in that the Iruney (West Kamchatka) island arc arose and developed in the southwestern part of it, earlier in its formation time, near the West Kamchatka continental block. In the northeast, the arc was bounded by a transform fault that stretched southeast, delimiting not only the Kamchatka terrane from the North Koryak and Uchkhichkhil, but also the Valaga (East Kamchatka) and Olyutor intraoceanic island arcs. In the Cenozoic stage of development, this fault was transformed into the Palana‒Ozernovsky translithospheric zone, which is the boundary between the accreted Olyutor and East Kamchatka terranes of the Nemuro–Olyutor island arc system. A geodynamic model of the prearc, the Albian‒Turonian stage of intraoceanic subduction, which lasted until the beginning of the formation of the Early Nemuro arc in the Coniacian, was applied the Olyutor island arc system. The duration of the prearc stage of intraoceanic subduction corresponds to the time of the same stage of the geodynamic evolution of Izu‒Bonin‒Mariana island-arc system. This allows us to confirm expansion of the Pacific since the Albian due to subduction in Nemuro‒Olyutor island arc system.