Abstract: Based on the U–Th–Pb (SIMS) dating of zircons from magmatic bodies of trachytes and trachydolerites of the Upper Agyndzha complex located within the Rassokha island arc and Argatass oceanic terranes, we have reached a conclusion about the Valanginian age of its formation. In terms of the age and composition, the Valanginian volcanics of the Rassokha and Argatass terranes are close to those of the base of the Alazeya–Indigirka zone. The spatial position of Valanginian trachytes and trachydolerites does not allow us to consider them as suprasubduction formations of the Andean-type margin. This is due to the distance of these bodies from the main field of the Alazeya–Indigirka zone. It can be concluded that the formation of these bodies was associated with the extension within this zone. The tectonic position of the Valanginian magmatic bodies allows us to interpret them as complexes that amalgamated two geodynamically different terranes.