Late jurassic-early cretaceous volcanic-plutonic assemblage of Oloy Belt, Western Chukotka: U-Pb SIMS and LA-ICP-MS data

Abstract

U-Pb (SIMS and LA-ICP-MS) age estimates are obtained for Egdygkychsky complex rocks of hypabyssal intrusions of Nichansky and Vukneysky plutons and volcanic rocks and tuffs of host rocks of Oloy volcanic belt, Alazey-Oloy fold belt. Oloy volcanic belt is overlapping for a number of island arc terranes of Alazey-Oloy fold belt. Nichansky and Vukneysky plutons are located in the southwestern part of Yarakvaamsky terrane and are composed of rocks of Early Cretaceous Egdygkychsky gabbro-monzonite-syenite and Vesenninsky granodiorite-diorite complexes. Host strata for both plutons are volcanic-terrigenous and volcanic rocks of Upper Jurassic – Lower Cretaceous. U-Pb SIMS zircon сoncordant age from three samples of rocks of Nichansky pluton is 141.1±0.4 Ma. The weighted mean zircon age of quartz monzodiorites, dated by U-Pb LA-ICP-MS, 140±3 overlaps with U-Pb SIMS age within error. U-Pb SIMS concordant zircon ages for Vukneysky pluton is 142.6±0.4, these for dacite and felsic tuff from host strata, 147±2 and 147±3 Ma. Affinities of zircons morphology for all analyzed samples and Th/U ratios in them indicate their magmatic genesis. It allows considering obtained age estimates as the crystallization age of Egdygkychsky complex of Nichansky and Vukneysky plutons and the time interval of host strata (volcanic rocks and tuffs) formation. New U-Pb geochronological data allow confidently distinguishing a single volcanic-plutonic assemblage of Late Jurassic (Tithonian) – Early Cretaceous (Beriasian-Valanginian) age of Oloy volcanic belt. Obtained data may be used for more distinct age limits of Au-Mo-Cu mineralization, located at the contacts between Egdydkychsky compleх rocks and host volcanic-sedimentary rocks or at the contacts between separated intrusive phases of the complex.