The study area in the Arctic Ocean comprises the Eurasia Basin, Lomonosov Ridge, Podvodnikov and Makarov basins adjacent to the Amerasia Basin, and a system of the Alpha and Mendeleev ridges. It is widely accepted that slow spreading, the axis of which corresponded to the Gakkel Ridge, was responsible for the formation of the Eurasia Basin during the entire Cenozoic. Thereby the Lomonosov Ridge is considered a fragment of the former Barents-Kara continental margin that separated from it at the Late Cretaceous-Cenozoic boundary. However, numerous geophysical and bathymetric data come into direct conflict with this concept. Asymmetry in depth distribution, asymmetrical magnetic and gravity anomalies in the eastern part of the Eurasia Basin, and peculiarities in the spatial distribution and thickness of a number of seismic units-these all testify to a more complex geological history of the region. The analysis of geophysical and bathymetric information is aimed at the reconstruction of the consecutive processes that resulted in the present-day structures of the Eurasia Basin and Lomonosov Ridge. The study included amplitude-frequency analysis of potential field anomalies with application of two-dimensional Fourier spectra, correlation of magnetic anomalies and bottom topography, and model calculations along profiles transecting deep-sea structures. As a result, it has been established that the Eurasia Basin segment located east of 75° E was formed in the pre-Miocene time, because the spreading axis was localized substantially closer to the Lomonosov Ridge than the present-day Gakkel Ridge. The Gakkel Ridge, 160-200 km wide, is a structure superimposed on the pre-Miocene basement after a jump of the spreading axis. Normal continental crust underlies the Lomonosov Ridge near the Eurasian continental margin, whereas the basement of the central ridge segment is mainly composed of basic igneous rocks. The basement beneath the Alpha-Mendeleev ridge system incorporates bodies of mafic and ultramafic rocks. The upper part of the Alpha Ridge section probably contains flood-basalt members similar in their magnetic properties to flood basalts of Franz Josef Land. Original Russian Text