Ediacarenian-middle Cambrian basic volcanism of Wrangel Island: Age and geodynamic setting (Russian East Arctic region)

Abstract

New results from the study of zircon U-Pb ages by SIMS and the geochemistry of basic volcanism of Wrangel Island's central part are considered. Volcanites are represented by rhyolites and spilitized basalts. For a long time, the age of rocks was considered early Carboniferous, since they are discordantly overlapped by late Carboniferous limestones. Recently, the age of rhyolites was estimated at ~590-610 million years; their compositions were compared with A-type granites. For basic volcanites, there is a large spread of U-Pb SIMS ages of zircon grains. The age of crystallization corresponds to the Ediacaran-middle Cambrian time (~510-608 million years). The volcanic rocks' compositions have high concentrations of TiO2 up to 3.4 wt. %. Chondrite-normalized rare earth element pattern exhibit pronounced enrichment of light REE in respect to medium (La/Sm)n = 1.4-2.4 and heavy (La/Yb)n = 2.2-6.1 REE. Primitive-mantle normalized spidergrams show negative Nb-Ta anomaly, significant enrichment with LILEs and most HFSE. The geochemical characteristics of the basic volcanic rocks of Wrangel Island indicate the similarity to traps of the Noril'sk area in northen Central Siberia and intraplate environment. The geological observations and the obtained ages suggest that the basic volcanic rocks are comagmatic with rhyolites having the geochemical features of A-type granites. It is assumed that this bimodal association was formed within the continental rift zone. It is assumed that the rocks were formed in a one single rift system with the coeval orthogneisses and gabbroids of the Alaskan Seward Peninsula.