Tectonic Evolution of the Svalbard Continental Margin - Results from Seismic Refraction Experiments -

In 1997 and 1999 the western and northern continental margins of Svalbard were geophysically explored by a German/Polish/Japanese scientific team. Main target of the surveys was the determination of the crustal seismic velocity structure. Therefore four seismic refraction profiles, with a total length of 1300 km were carried out across the continental margin. On the northernmost profile across the southern Yermak Plateau stretched continental crust is present up to 81 N. Seismic velocities vary between 5.1-6.9 km/s, therefore we exclude a rifted-volcanic evolution for the southern part, as supposed for the origin of the entire Yermak Plateau. The E-W striking profiles from Knipovich Ridge across the western continental margin of Svalbard show local zones with slightly elevated seismic velocities up to 7.2 km/s in various depths within continent-ocean transition zone (COT). The structure of the adjacent continental crust is similar to that on Yermak Plateau. Thinned oceanic crust with a thickness of 2-4 km is oberserved westwards of the COT. The deeper structure within the COT shows strong variations along the western margin. A 180 km broad COT is found at 79.8 N (northern Svalbard). Approximately 100 km further to the south at 79.0 N (Kongsfjord) the COT narrows to 40 km followed by the abrupt termination of continental crust to the adjacent oceanic crust. We interprete this part of the margin as a sheared continental margin. Off Van Mijenfjord at 77.8 N the width of the COT broadens again to 80 km and forms a normal stretched non-sheared part of the margin, as observed in the north. It seems that the Spitsbergen Fracture Zone of the complex Fram-Strait MOR-system was active while to the north and south normal stretching of continental crust occurred. The occurence of bodies of higher seismic velocity between 77.8 N and 79.8 N might be explained by the close distance of the newly developing margin to active spreading center segments. A limited amount of mantle derived melts was injected into the COT.