The inregrated geological and geophysical studies carried out in recent years in the Lomonosov Ridge and at its junction with the Eurasian shelf revealed evidence for thinned (reduced) crust in the ridge (20–25 km) and its relationship with shelf structures. We compared the parameters of deep seismic cross-sections of the shelf and Lomonosov Ridge, thus proving the existence of continental crust in the latter. Also, we analyzed the deep structure of the junction between the Lomonosov Ridge and the shelf and established a genetic geologic relationship, with no evidence that the Lomonosov Ridge moved as a terrane with respect to the shelf. In addition, seismological studies independently confirm the relationship between the Lomonosov Ridge and the adjacent shelf.
The Lomonosov Ridge is a continental-crust block of a craton. The craton was reworked during the Caledonian tectonomagmatic activity with the formation of a Precambrian–Caledonian seismically unsegmented basement (upper crust) and an epi-Caledonian platform cover. Afterward, the block subsided to bathyal depths in the Late Alpine. This block and the adjacent areas of the Eastern Arctic shelf developed in the platform regime till the Late Mesozoic.
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.
New seismic research was carried out by JSC Marine Arctic Geological Expedition in 2006-2008, providing the first integrated geophysical grid (20 Â 30 km). The main purpose was to study the geological structure of the sedimentary cover of the north Barents shelf and investigate the structural-tectonic plan at different stratigraphic levels. The geological results yielded new information on the tectonic structure, depositional environments, palaeobasin geometry, bathymetry and regional history of geological development. The geological interpretation of the Lower Palaeozoic part of the section provided the most interesting results.
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