Late jurassic–early cretaceous volcanic-plutonic assemblage of Oloy belt, Western Chukotka: U–Pb SIMS AND LA-ICPMS data

Abstract

U–Pb (SIMS and LA-ICP-MS) age estimates are obtained for the Egdygkychsky complex of rocks of hypabyssal intrusions of Nichansky and Vukneysky plutons and volcanic rocks and tuffs of host rocks of the Oloy volcanic belt in the Alazey-Oloy fold belt. The Oloy volcanic belt is overlapping for a number of island arc terranes of the Alazey-Oloy fold belt. Nichansky and Vukneysky plutons are located in the southwestern part of the 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 the Upper Jurassic–Lower Cretaceous periods. U–Pb SIMS zircon сoncordant age from three samples of rocks of the Nichansky pluton is 141,1 ± 0,4 Ma. The weighted mean zircon age of quartz monzodiorites was dated by U–Pb LA-ICP-MS as 140 ± 3 Ma.; this overlaps with the U–Pb SIMS age within error. U–Pb SIMS concordant zircon ages for the Vukneysky pluton is 142,6 ± 0,4 Ma.; dacite and felsic tuff from host strata— 147 ± 2 and 147 ± 3 Ma. Affinities of zircon morphology for all analyzed samples and Th/U ratios in them indicate their magmatic genesis. This makes it possible to consider obtained age estimates as the crystallization age of the 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 researchers to confidently distinguish a single volcanic-plutonic assemblage of Late Jurassic (Tithonian)–Early Cretaceous (Beriasian-Valanginian) age of the Oloy volcanic belt. Obtained data may be used for more distinct age limits of Au–Mo–Cu mineralization, located at the contacts between the Egdydkychsky compleх rocks and host volcanic-sedimentary rocks or at the contacts between separated intrusive phases of the complex.