Peculiarities of Knipovich Ridge Magmatism in the Vicinity of Svalbard Archipelago

Generation of primary magmatic melts at the Knipovich Ridge takes place under conditions of the least deep regions of slow-spreading rifts. According to geochemical data the basalts developed here belong to weakly enriched tholeiites with K2O/TiO2 ratio and (La/Sm)n in the limits 0.1-0.4 and 1.0-1.8, respectively. Nevertheless, they differ from tholeiites formed under Kolbeinsey and Mohns Ridges by the conditions of primary magmas generation; such features as the enrichment by lithophile elements (including water) and isotope composition show their closeness to the same geochemical province. Enriched component of the Arctic province tholeiites differs by higher values of 87Sr/86Sr (0.7035), 208Pb/206Pb (38.5), 206Pb/204Pb (19.0) and lower values of 143Nd/144Nd (0.5129) and is close to those of the basalts of Iceland, Jan Mayen F.Z. and Western Greenland, and alkaline lavas of Quaternary volcanoes on Spitsbergen as well. All these evidence that the contamination process for melts formed at different depths is similar for different parts of Arctic province from Iceland to the Knipovich Ridge. Knipovich Ridge (KR) consists of the succession of magmatic and amagmatic zones with oblique orientation to the spreading zone and can be an example of lithospheric rupture and appearance of the partial melting zone beneath it (pull-apart structure). Distribution of tectonic zones on the eastern flank could inherit more ancient structure which is seen in the form of abnormal magnetic field of N-E direction. Bathymetric and seismo-acoustic data evidence that formation of the KR is connected with young overprinted tectonic processes. Supposed jumping of KR axis and the following spreading coincides in time with the high magmatic activity (abundant basalt flows) within Svalbard Archipelago (about 20 m.y. ago) and about 1 m.y. ago caused appearance of three alkaline volcanoes. Formation of Norwegian-Greenland basin took place in cycles with replacement of tectonic and magmatic stages of activity for long periods of rest, which is reflected in its abnormal geological structure. We suppose that spreading activity in the basin could stimulate magmatic activity within continental margin of Svalbard Archipelago also. During the Arctic opening the old and newly formed rupture zones within the eastern part of Spitsbergen could be activated several times and serve as channels for alkaline melts. These melts were formed from the enriched, saturated in fluids, continental mantle and in their composition were close to the strongly enriched melts discovered in the form of veins in mantle xenoliths of Spitsbergen Quaternary volcanoes [Ionov et al., 2002]. Such melts could migrate not only within the continental mantle, but in the apical parts of ancient oceanic depleted (asthenospheric) mantle as well. Similar process which took place in pre-Miocene time could cause formation of suboceanic enriched mantle. The shift of spreading axis in Miocene from the Norwegian Sea to the region along Spitsbergen continental margin resulted in the involvement of suboceanic enriched mantle into the melting process and formation of melts with isotope characteristics close to alkaline basalt melts at Spitsbergen. Isotope-geochemical features of Knipovich Ridge basalts could be caused by addition of some substance (first percents) of enriched source to the substance of typical depleted mantle source.