Geochemistry, Age, and Geodynamic Setting of the Volcanic Rocks of the Indigirka Section of the Uyandina-Yasachnaya Volcanic Belt (Northeast Asia)

The Uyandina–Yasachnaya volcano-plutonic belt (UYVB) is one of the largest structures of this type in Northeast Asia. It strikes in the north-west direction for 900 km from the upper reaches of the Kolyma River to the upper reaches of the Selenyakh River. The belt is characterized by the strong facies variability and zoning, which is expressed in a change from mafic volcanic rocks (Ilin’-Tass zone) in the northeast to felsic volcanic rocks (Darpir zone) in the southwest. Poor knowledge of the UYVB results in an ambiguous interpretation of its geodynamic nature and volcanic evolution. The paper presents new detailed geochemical, isotopic, and geochronological data on the volcanic rocks of the Indigirka section of the Darpir zone of the UYVB. The U-Th-Pb SIMS zircon dating showed that volcanic rocks of the section previously attributed to the Oxfordian–Tithonian stages have the younger age within 150 ± 2–152 ± 2 Ma, which corresponds to the Tithonian. Andesites from the section base show Ta–Nb depletion, indicator element ratios Th/Nbpm, La/Nbpm, and La/Smpm > 1, and extremely low εNd = (–8), which may indicate a crustal contamination of mantle sources. Felsic volcanic rocks overlying the andesites have the postcollisional signatures. They are also characterized by the wide variations of εNd from –2.4 to –6.5 and model ages. The systematic position of the rocks in the section as well as upward increase of alkalinity and silica content from basaltic andesites to rhyolites in the upper parts of the section, which is typical of island-arc buildups, suggest that suprasubduction melts were generated beneath the collisional crust. Source of these melts could be a mantle domain that was enriched in fluid during previous subduction event.