The Chukotka Segment of the Uda–Murgal and Okhotsk–Chukotka Volcanic Belts: Age and Tectonic Environment

Abstract

Abstract —We present new data on the geology, geochronology, and geochemistry of volcanic complexes of the Uda–Murgal and Okhotsk–Chukotka belts that expose on the left bank of the Anadyr’ River in its middle course. The structural relationships between the stratons, supplemented by the U–Pb and 40Ar/39Ar dates of volcanics, indicate at least three compression events at this segment of the Pacific margin during the Cretaceous: pre-Aptian, early Albian, and late Turonian. The complexes of the Uda–Murgal and Okhotsk–Chukotka belts are separated by an early Albian unconformity, but the other two unconformities are also well pronounced. The studied segment of the Uda–Murgal belt evolved in the ensialic island arc setting till the Barremian. In the Aptian, after the accretion of the island arc to the continent, volcanism reactivated on the Andean-type margin. The main geochemical difference between the Uda–Murgal and Okhotsk– Chukotka belts is the different volume portions of silicic rocks. The less significant difference in the contents of trace elements indicates a change in the composition of the mantle protolith. The complexes of the Okhotsk–Chukotka belt show signs of geochemical zoning, both longitudinal and transverse relative to the strike of the continent–ocean boundary.