Volcanism of the Nembonda Trough, Western Chukotka: Geochronology, Geochemistry, and Stratigraphy

At least three magmatic events have been identified in the Nembonda volcanic trough in Chukotka. The Early Aptian event (Ilguveem sequence of predominantly basaltic andesite‒andesite volcanic rocks with an age of 123 ± 1 to 120 ± 2 Ma) immediately follows the closure of the South Anyui suture zone (SAZ) and is subsynchronous with the formation of the Tytylveem volcano-plutonic belt north of the SAZ. During the second Upper Aptian‒Early Albian magmatic event, the Dirguveem dacite‒rhyolite sequence is formed (zircon U–Pb ages from 118 ± 1.5 to 112 ± 1 Ma), which is also synchronous with the Tytylveem belt. The final Albian stage of volcanism is marked by the formation of the predominantly trachybasaltic andesite–trachyandesite Teleneut volcanic sequence with an age of 108 ± 1 to 99 ± 1.5 Ma, which is assigned to the early stage of volcanism in the Anadyr sector of the Okhotsk‒Chukotka volcanic belt. The geochemical features of the studied calc-alkaline volcanic rocks allow us to interpret their geodynamic setting as pull-apart (early stages) and supra-subduction (late stages).