Evolution of Aptian and Albian magmatism of Western and Northern Chukotka (Northeast Russia) based on zircon U-Pb geochronology and rock geochemistry

Across western and northern Chukotka, a region spanning 400 000 km(2), we have defined three different tectono-magmatic systems that were active during the Aptian-Albian (123-100 Ma) time span: (1) the Tytylveem post-collisional belt (123-105 Ma); (2) the Chaun province of extension-related magmatism (109-100 Ma); and (3) the earliest eruptive units (106-100 Ma) of the subduction-related Okhotsk-Chukotka volcanic belt (OCVB). The observed tectono-magmatic systems are characterized by their location and by their different chemical and isotopic compositions. The general enrichment of magma sources successively increases from the OCVB to the Tytylveem belt and then to the Chaun province. While the Tytylveem belt was active, the volcanic loci shifted northwest along the strike of the belt, perhaps because of diachronous delamination of the lithosphere of the once present, but extinct, South Anyui ocean. On the scale of the entire region of NE Asia, the tectonic re-arrangement that controlled magmatism in the Early Cretaceous was marked by the extinction of major subduction zones on the periphery of the closing Oimyakon and South Anyui oceanic basins followed by magmatic events likely caused by lithospheric delamination and/or extension. Along the Pacific margin of Asia, subduction-related volcanism was nearly continuous during the entire Cretaceous.