Neoproterozoic granitoids and rhyolites of Wrangel Island: Geochemical affinity and geodynamic setting in the Eastern Arctic region

New results from the study of zircon U–Pb ages by SIMS SHRIMP and LA–ICP–MS, Nd isotopy and the geochemistry of granitic plutonism and felsic volcanism of Wrangel Island are considered. Granitic intrusions are confined to the Wrangel Complex in the Southern tectonic zone, cropping out in the core of a latitudinally extending anticlinorium and representing the metamorphic basement of the Eastern Arctic shelf. Felsic and basic volcanic rocks form a belt of scattered outcrops in the Central tectonic zone. The obtained U–Pb data form two Neoproterozoic age clusters in the Wrangel Complex at ~680–720 and ~590–600Ma corresponding to the times of granitic plutonism and felsic volcanism, respectively. Granites that are 680–720Ma old contain inherited zircons of Meso-, Palaeoproterozoic, and Neoarchaean ages, implying the existence of ancient rocks in the basement of Wrangel Island and their participation in partial melting during granite magma formation. The negative εNd(Т) (−2.97 to −4.46) values obtained for granites suggest the contribution of a crustal component to their petrogenesis, and their model ages indicate possible Palaeo-Mesoproterozoic ages of crustal protoliths. The geochemical affinities of granites are similar to those of highly fractionated peraluminous I-type granites, and their association with clastic and volcanic rocks of felsic, intermediate, and basic compositions provides grounds for assuming their formation on an active continental margin. Similar formation settings above subduction zones are also proposed for Neoproterozoic (600–700Ma) granites and orthogneisses of the Seward Peninsula (Amato et al., 2009, 2014). The close association of ~590–600-Ma-old felsic volcanic rocks with geochemical affinities of A-type granites and coeval enriched basalts (Moiseev et al., 2015) makes them similar to a bimodal rift-related assemblage. The moderate positive εNd(Т) (1.21; 1.1) values and Mesoproterozoic model T(DM) and T(DM-2) ages obtained for felsic volcanic rocks lead us to assume a heterogeneous source of magmas, which included both crustal and mafic mantle components. Similar rift-related geodynamic settings were proposed for orthogneisses (565Ma) and gabbro (540Ma) of the Seward Peninsula, Alaska (Amato et al., 2009, 2014) and orthogneisses (656 and 574Ma) of the Koolen gneiss dome, Chukotka, which indicate intense rifting. The rocks also exhibit some analogies with Neoproterozoic volcano-plutonic complexes of the Timanides grouped into I- and A-types (Kuznetsov et al., 2006; Pease et al., 2004). I-type granitoids are 700–515Ma old and represent constituents of the volcanic–plutonic series of an active continental margin. A-type granitoids have isotopic ages of 565–500Ma and are associated with volcanic rocks of the bimodal basalt–rhyolite series formed in extensional environments.