Peculiarities of roughness and thickness of oceanic crust in the Eurasian Basin, Arctic Ocean

The Gakkel Ridge, northern boundary of the American and Eurasian plates, has the slowest spreading rate of the global ridge system. Therefore, it provides an excellent opportunity to study any dependence of crustal fabric on spreading rate. Two parameters, crustal surface roughness and crustal thickness: at the super-slow-spreading Gakkel Ridge (<20 mm yr(-1) full rate) are the subject of the following study. Seismic and gravity data acquired across the Gakkel Ridge and the adjacent Nansen and Amundsen basins during the ARCTIC'91 expedition are used. The surface of the basement, imaged along the seismic multichannel profiles, is very rough and varies in its topography from several hundreds of metres up to 1000 m. Its RMS-roughness ranges from 450 m in the central Amundsen Basin to 584 m in the southern Eurasian Basin. These values agree reasonably well with RMS-roughness values derived by an empirical model from spreading rates. The gravity models reveal a 5-6 km thick oceanic crust (density of 2900 kg m(-3)) in the central part of the Amundsen Basin, increasing to 9 km towards the Gakkel Ridge. At the southwestern end of the Eurasian Basin, the oceanic crust is only 2-5 km thick and thickens towards the Gakkel Ridge. In our model the ridge is composed of a 2 km thick upper layer with a density of 2600 kg m(-3), underlain by an 8 km thick zone with a density of 2900 kg m(-3). The increase of crustal thickness does not confirm theoretical models for the I-elation between spreading rate and crustal thickness. The results indicate that the super-slow spreading rate of the Gakkel Ridge may have caused lateral variations in the crustal thickness of the Eurasian Basin.