We provide a brief description of the main structures in the Eastern Arctic, in the evolution of which two major stages have been distinguished and considered: the late Paleozoic-early Mesozoic and the Late Jurassic-Early Cretaceous. We have established the synchronicity of tectonic events on the Arctic margins of Northeast Asia and Arctic Alaska and within the structures of the Amerasia Basin, indicating the existence of a cause-and-effect relation between the compression (fold-and-thrust structures) and extension (rifting and spreading in the Canada Basin). We have proposed the tectonic models of the formation of fold-and-thrust structures in Chukotka and Arctic Alaska and have determined their similarities and differences. Paleotectonic reconstructions have been performed for 160 and 120 Ma. We present a critical review of the concepts about the formation of the structures in the Amerasia Basin and provide a subduction-convection geodynamic model according to the analysis of seismic tomography of the mantle and regional geology and tectonics data. This model was previously used to describe the Cretaceous and Cenozoic evolution of the Arctic lithosphere at a qualitative level. The model is based on the idea of the existence of a two-tier subduction system: a horizontally extended convection cell in the upper mantle, coupled with a conveyor mechanism of subduction of the Pacific lithosphere. As a result, there is a convergence of the "outer" Pacific subduction zone and the "inner" subduction zone located inside the South Anyui and Angayucham oceanic basins, which provides their closure and subsequent collision. Under the influence of the reverse upper mantle flow, scattered deformations of the Amerasia lithosphere occur, caused by viscous dragging with flows beneath the lithosphere, which is the reason for the diversity of the structures in the Amerasia Basin and the Canada Basin in particular. In addition, the developed geodynamic model is supplemented by a tectonic and magmatic mechanism of crustal subsidence and the formation of sedimentary basins.
The Laptev Sea is an area of active exploration for hydrocarbons; however, estimations of its hydrocarbon potential vary significantly, both in terms of total hydrocarbon quantities and their phase composition. This variability is due to the absence of a unified geological framework and, consequently, the use of different analogous basins in calculations. Based on a comprehensive interpretation of geological and geophysical data, as well as seismic facies analysis, a reliable geological model was created. Paleogeographic conditions for the formation of major sedimentary cover complexes were reconstructed, including the Aptian-Upper Cretaceous, Paleocene-Eocene, Oligocene, and Miocene-Quaternary periods. It was shown that, within the modern shelf of the Laptev Sea, a marine basin existed since the second half of the Cretaceous, the boundaries of which are determined based on outcrop data from adjacent islands and onshore, wells, and seismic patterns. The main factors controlling the formation of the sedimentary cover and the change of paleogeographic conditions along the modern Laptev Sea continental margin were global tectonic events, including the opening of the Makarov-Podvodnikov Basin, rifting, and post-rift subsidence in the Eurasian Basin.
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.
Dating of the modern seafloor massive sulfides (SMS) is a complex task largely due to the multistage deposition of ore-forming minerals and the influence of changing physicochemical conditions on the isotope geochemistry during the interaction of hydrothermal fluids with host rocks and near-bottom seawater. Based on data obtained for the sulfide ores of the Semenov-5 field at the Mid-Atlantic Ridge (MAR), the possibilities and limitations of the 230Th/U method are demonstrated, particularly concerning the formation of the radiometric system in environment above and below the paleo-seafloor level. New ages obtained for surface ores range from 60 to 8 thousand years. However, dating of subsurface sulfides was impossible due to the minimal input of near-bottom seawater within mound and its influence on the deposition of the sulfides. The study indicates that massive sulfides formed beneath the seafloor are of metasomatic origin, suggesting that the sulfide mineralization is not limited only by paleo-seafloor but also extends to the greater depths. This finding has significant implications for other sulfide deposits within the MAR as well and may lead to the revision of their resource potential. The established long-term character of hydrothermal discharge within the Semenov-5 field is comparable with longevity of other hydrothermal fields within the Semenov ore cluster. Obtained data indicate a long and complex evolution of hydrothermal systems related to the ultramafic rocks of the ocean core complexes in slow-spreading mid-ocean ridges.
The Longqi-1 hydrothermal field (LQ-1 HF), the first active high-temperature vent field discovered along the ultraslow-spreading Southwest Indian Ridge (SWIR), provides a valuable setting for studying seafloor sulfide mineralisation. However, spatially resolved constraints on physicochemical gradients during chimney growth remain limited. This study presents mineralogical, trace element, and sulfur isotopic analyses of Cu-rich, Zn-Ferich, and Zn-rich chimneys from the LQ-1 HF, revealing systematic mineral zonation and metal enrichment across sulfide chimney walls. The Cu-rich chimney displays well-developed zonation, transitioning from anhydrite, pyrite, or marcasite with minor sphalerite at the exterior to massive chalcopyrite at the interior. The presence of bornite, covellite, and digenite suggests episodic seawater infiltration and oxidation during chimney evolution. Pyrite from outer zones is enriched in Mn, Mo, Tl, U, and V due to low-temperature precipitation from seawater mixing, while increasing Co in pyrite and Se in chalcopyrite toward the interior reflect higher temperatures and conditions favouring the stability of Cu-rich sulfides. In contrast, the Zn-Fe-rich and Zn-rich chimneys exhibit colloform to dendritic pyrite, marcasite, and sphalerite with minor chalcopyrite, consistent with lower-temperature, seawater-influenced precipitation conditions. Sulfur isotope gradients (delta 34S: 4.5-9.9 parts per thousand) reflect a mixed sulfur source from seawater sulfate and host rocks, with early-formed zones more seawater influenced. Elevated Sn and low Cd/Zn ratios are consistent with metal inputs from a heterogeneous lithological source, potentially involving ultramafic components and possibly facilitated by deep detachment faults. These results reveal the influence of host-rock composition, temperature, redox state, and seawater mixing on sulfide mineralisation at the detachment fault-controlled LQ-1 HF on the ultraslow-spreading SWIR.
