Abstract

The East Sikhote-Alin volcanic belt extending for ~1500 km is commonly considered a single tectonomagmatic structure formed during the Late Cretaceous subduction and the Cenozoic oceanic-slab breakup and active asthenospheric diapirism under transform plate sliding. Based on analysis of the published geological information and the new data on the age and trace-element and isotope compositions of the igneous rocks of the Late Cretaceous Bol’ba Formation, it is shown that the initial stages of volcanism in the southern and northern Sikhote-Alin took place in different geodynamic settings. In contrast to the coeval suprasubductional volcanics of the southern sector (Primorye), the volcanic section of the Bol’ba Formation is dominated by magnesian (Mg# = 26–40) adakites (La/Yb = 19–34) and high-Nb basalts. This igneous rock association and the lead (Δ8/4Рb = 30–46) and neodymium (0.51279–0.51281) isotope ratios of the studied rocks suggest the influence of the “hot” oceanic asthenosphere on magma genesis. The earlier slab breakup north of 48–49 °N was due to the oblique convergence of oceanic and continental lithospheric plates in the Late Cretaceous, accompanied by sinistral shears. The results obtained indicate that the lateral zonation of the eastern Sikhote-Alin is due to different geodynamic settings of formation of its northern and southern sectors rather than variations in its basement composition. In theoretical aspect, the performed research is important for the correct reconstruction of the geologic events in zones of convergence of oceanic and continental plates. It is necessary to take into account not only the general direction of the convergence but also the configuration of the plate boundary.

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