Main Stages of Magmatism in the Uda–Murgal Arc and Okhotsk–Chukotka Belt (the Okhotsk–Pyagin Segment)

The composition and age of magmatism in the Okhotsk–Pyagin segment of the Uda-Murgal magmatic arc (UM) on the northern coast of the Sea of Okhotsk are studied. U‒Pb dating of zircons from igneous rocks, in addition to rare Permian granitoids, identified three main stages of igneous activity: Late Jurassic (Oxfordian–Tithonian) 160‒145 Ma, Early Cretaceous (Valanginian–Aptian) 139‒122 Ma, and Early-Late Cretaceous (Albian–Cenomanian) 108‒92 Ma. A distinct magmatic lull has been identified in the interval from 122 to 108 ± 2 Ma, which corresponds to the boundary between the UM and the Okhotsk–Chukotka volcanic belt (OCVB). Judging by their geochemical characteristics, the Cretaceous igneous complexes in the frontal zone of the UM formed in an ensialic island arc environment and differ from the overlying Albian-Campanian volcanics of the back-arc zone of the continental-marginal OCVB in lower potassium contents, positive εNd values, and lower concentrations of incompatible trace elements, particularly Nb, Ta, and LREE. Albian–Cenomanian granitoid intrusions and rare coastal volcanics with ages ranging from 108 to 95 Ma belong to the OCVB, as they are synchronous with early magmatism there. The spatial distribution of the OCVB complexes of different ages indicates that igneous activity shifted 50‒100 km inland approximately 90 Ma ago, or these complexes were eroded.