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In 1995–2006 FSUE ‘Sevmorgeo’ within the framework of the Federal Program of state survey baselines network development performed geophysical works in the Barents and Kara seas along four regional profiles: 1-AR (Kola Peninsula–Heysa Island of Franz-Joseph Land Archipelago); 2-AR (Central part of the Barents region–Novaya Zemlya – Yamal Peninsula); 3-AR (White Sea–Severnaya Zemlya Archipelago); and 4-AR (Taimyr Peninsula–Franz-Joseph Land Archipelago). Geophysical surveys included works using seismic refraction–deep seismic sounding technique, seismic reflection–common-depth point technique, seismic acoustic profiling and gravimetric and magnetic measurements. Integrated geophysical surveys along the regional profiles enabled more exact definition of the Earth deep crustal structure and the sedimentary cover of the main tectonic elements.

Consolidated crust in the North Barents basin with sediments 16–18 km thick is attenuated approximately by two times. The normal faults in the basin basement ensure only 10–15% stretching, which caused the deposition of 2–3 km sediments during the early evolution of the basin. The overlying 16 km of sediments have accumulated since the Late Devonian. Judging by the undisturbed reflectors to a depth of 8 s, crustal subsidence was not accompanied by any significant stretching throughout that time. Dramatic subsidence under such conditions required considerable contraction of lithospheric rocks. The contraction was mainly due to high-grade metamorphism in mafic rocks in the lower crust. The metamorphism was favored by increasing pressure and temperature in the lower crust with the accumulation of a thick layer of sediments. According to gravity data, the Moho in the basin is underlain by large masses of high-velocity eclogites, which are denser than mantle peridotites. The same is typical of some other ultradeep basins: North Caspian, South Caspian, North Chukchi, and Gulf of Mexico basins. From Late Devonian to Late Jurassic, several episodes of rapid crustal subsidence took place in the North Barents basin, which is typical of large petroleum basins. The subsidence was due to metamorphism in the lower crust, when it was infiltrated by mantle-source fluids in several episodes. The metamorphic contraction in the lower crust gave rise to deep-water basins with sediments with a high content of unoxidized organic matter. Along with numerous structural and nonstructural traps in the cover of the North Barents basin, this is strong evidence that the North Barents basin is a large hydrocarbon basin.

The magnetic properties of polycrystalline samples of isotopically enriched iron with the content of isotope 56 Fe 99.945±0.002 at. % were investigated. The samples of monoisotopic iron were preliminarily melted in the environment of argon and annealed in hydrogen. For the sake of comparison the same measurements were carried out on the samples of iron with natural isotopic composition. The quantity and composition of impurities in the samples of natural and monoisotopic iron were equal. The measurements were conducted by the method of vibration magnetometry with the use of the method of automatic vibro-magnetometer VSM-250 (China) using IDAW-2000D VSM test software as well as by induction-pulse method with the use of automated measuring set МK-3E (the Russia) with automatic processing of the obtained data according to GOST 8.377-80 and GOST 12119.1-98. It was found that the value of saturation intensity Js in 56 Fe is by 4.6% higher than in nat Fe. There is actually no difference in saturation intensity Bs of monoisotopic 56 Fe and natural iron within the error in limits of detection of analysis. The difference in the values of coercitive force Нс, residual magnetic induction Br and maximum magnetic permittivity µmax in natural iron and 56 Fe can be explained by the difference in structure and content of impurities in the studied samples.

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