Current geoscientific knowledge on the High Arctic submarine Alpha-Mendeleev complex

Today Alpha-Mendeleev Ridge is the largest single submarine feature in the Arctic Ocean, which geological origin is still unknown. A better understanding of the evolution of the ridge complex in relation to the opening of the Canada Basin would have profound consequences for Arctic geodynamic models. Currently models in which Alpha Ridge represents a former spreading centre or "hot spot" trail are favoured. In this contribution the state of knowledge will be reviewed.The ridge was discovered by the US ice station Alpha during its drift in the years 1957-1958, which acquired the first information on the ridges topography and sedimentary thickness. The largest single-channel seismic data set was gathered during the drift of the US ice station T-3 from February 1967 to June 1970. The width of Alpha Ridge ranges from 250 to 800 km. In bathymetric cross sections it is roughly symmetrical with greatest elevation at the centre. The existing single channel seismic reflection lines acquired from ice stations Alpha, T-3 and CESAR and ship based seismic experiments show that Alpha-Mendeleev Ridge is mainly covered by a sedimentary sequence, which can reach up to 1000 m in thickness. Along most of the profiles the sediments lie conformably on the basement. Deep seismic experiments of Canadian and Russian researchers indicate that the crust beneath the ridge has a thickness well above 30 km, and high seismic velocities above 7.0 km/s are present at lower crustal levels.The most important and complete geophysical data sets in that area are aeromagnetic and aerogravity data acquired by US and Russian researchers. The magnetic data across the Alpha Ridge indicate the presence of mostly irregular magnetic anomalies up to 2000 nT. No clear evidence of magnetic seafloor spreading anomalies has been obtained. Based on the existing geophysical data various researchers suggested that the ridge must have been formed during the Cretaceous positive polarity chron from 124 to 83 Ma, if the irregular magnetic anomalies are due to oceanic basalts. At three locations Cretaceous and Early Cenozoic sediments were recovered from western part of Alpha-Mendeleev Ridge. Two volcanic rock samples were dredged from the Alpha-Mendeleev Ridge. One of them could be dated to 83 Ma. So far, all existing geoscientific data support a formation of this complex in Cretaceous times. However, details on the responsible processes and the plate movements during this period are rather hypothetical