The Spitsbergen archipelago is at the junction of the northern segment of the Norwegian-Greenland Basin and the western part of the Arctic Ocean, which makes it a key area for deciphering the formation history and geological structure of the region. Crystalline basement rocks and sedimentary cover units outcrop here, including those that constitute the petroleum-bearing complexes of the shelf. There is a clear need to substantiate the presence of evidence for the Baikalian (Timanian) tectono-magmatic activation within the Earth’s crust of the Spitsbergen archipelago, as well as to determine the conditions of its manifestation. To address this objective, a comprehensive description of the Trollheimen volcanogenic formation – whose rocks are known within Oscar II Land – is provided for the first time, based on the authors’ own data. We examine geotectonic features, material composition, age, and geodynamic interpretations of the formation settings. The authors identified that the sedimentary-volcanogenic complex described in the mountainous glacial part of Oscar II Land was formed during the Vendian (574-558 Ma) as a result of tectono-magmatic activation of the epi-Grenvillian paraplatform. They provide the petrographic and petro‑geochemical profile of the identified metabasalts, metaandesites, and metatuffs. The results of studying the petrochemical features of the Trollheimen volcanogenic formation indicate magma generation at great depths; the rift-related nature of these formations is determined. The authors carry out a correlation with the previously identified sedimentary-volcanogenic complex of the Chamberlaindalen Series in the northern part of Wedel Jarlsberg Land. The presented data confirm the previously proposed arguments for the Vendian-Baikalian, Timanian intraplate activation in the archipelago, as well as the widespread development of these complexes within the cover of the epi-Grenvillian paraplatform of Spitsbergen.

Data on the content and distribution of trace and rare-earth elements (SIMS method) in sectors and growth zones of a large zircon crystal from miaskite pegmatites of the Vishnegogorsky massif are presented. The morphology of the zircon crystal is a combination of a dipyramid {111} and prism {010}. It has been established that the growth sector of dipyramid {111} is characterized by almost one order of magnitude higher contents of Y, Nb, REE, Th; higher Th/U and Eu/Eu* values; REE distribution spectra are flatter compared to prism {010} growth sector. A regular decrease in the content of trace and rare-earth elements in the direction from the central zone to the marginal zone of crystal growth was revealed. A smooth regression of zircon crystallization temperature of zircon from 960 °C in the central zone to 740 °C in the marginal zone of the dipyramid sector and 700-650 °C in the prism sector has been revealed, which may be a reflection of thermal evolution of the crystallization process. It is assumed that crystallization of the central zone of zircon occurred at early stages from a relatively trace-еlement-rich melt. The crystallization was completed at lower temperatures, probably, simultaneously with the formation of REE-concentrating minerals, which resulted in natural decrease of content of trace and rare-earth elements in the melt and, consequently, in zircon crystallizing from it.

The article presents original data of chemical composition of tholeiitic basaltoids and andesites, dredged from the Shaka Ridge (South Atlantic) in the course of field research in spring 2016 on the scientific expedition vessel “Akademik Fedorov”. The analytical part of the work on estimating the contents of petrogenic, trace and rare-earth elements was carried out using the classical method (“wet chemistry”), X-ray fluorescence analysis (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). The studied samples demonstrate elevated concentrations of large-ion lithophile elements, or LILE, (Ba, Rb, Pb) and light rare earth elements, or LREE, (La, Ce, Nd, Sm) relative to high field strength elements, or HFSE, (Nb, Ta) and heavy rare earth elements, or HREE, (Dy, Yb, Lu). The specifics of trace element geochemistry suggest a significant contribution of crustal or subduction components to the magmas of the Shaka Ridge. Discrimination diagrams of basaltoids and allied rocks with fields of different geodynamic settings indicate that they were formed in the setting of the mid-ocean ridge basalt (MORB). The reason behind the appearance of subduction and crustal marks in the rocks is possibly associated with assimilation of crustal matter by magmas or lies in their inheritance from the mantle source.