International Geologiical Congress - Oslo 2008

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MPI-02 Integrated perspectives on the accretion of oceanic crust

 

Geochemical features of magmatic evolution at Spitsbergen island and the Knipovich ridge (Polar Atlantic)

 

Nadezhda Sushchevskaya, Vernadsky Insitute of Geochemestry RAS (Russian Federation)
Boris Belyatsky, VNIIOkeangeologia (Russian Federation)
 

 

Magmatic activity at Spitsbergen Island is in close connection with general evolution of Norway-Greenland basin which developed in pulses with possible repeated jumping of the spreading axis, the main one was in Neogene when the present position of the Knipovich ridge was fixed near the western margin of Spitsbergen (Mosar et al., 2002). Shifting of the Knipovich ridge spreading axis and the subsequent extension coincide in time with the pulse of magmatic activity in the region of the Svalbard Archipelago (about 20 Ma ago), frequently developed in the form of plateau basalts. The magmatic process continued till 10 Ma ago. In the Quaternary time this process caused formation of three volcanoes with mainly alkaline lavas situated at the northern edge of Breibogen fault.
The origin of the modern Knipovich ridge according the model (Crane et al., 1991) is connected with formation of a series of faults ("detachment fault") which involved the western part of Spitsbergen as well. These faults could serve as channels for the asthenospheric melts upwelling within the Arctic basin and cause the formation of the Knipovich ridge and the continental mantle melting in the western part of Spitsbergen (Czuba et al., 2004). The melting of continental mantle itself beneath the island could be caused by formation of deep rupture cracks or by rising of higher temperature asthenospheric oceanic mantle.
The carried out study of tholeiitic magmatism of the Knipovich ridge, Neogene trap magmatism and Quaternary alkaline magmatism of Spitsbergen has demonstrated that during generation of primary magmas of different genesis there was involved an enriched substance which was similar to primary melts met in the form of veinlets in ultrabasic mantle xenolithes from Quaternary lavas at Spitsbergen (Ionov et al., 2002). These enrich component has characteristics resembling Ne-basalt with enrichment of Pb and Sr radiogenic isotopes and depleting of neodymium: 207Pb/204Pb=15.50-15.55, 206Pb/204Pb=18.4-18.6, 208Pb/204Pb= 38.4-38.6 and 87Sr/86Sr= 0.7038-0.7048, that considerably exceed isotope signatures for alkaline basalts of the Quaternary Spitsbergen volcanoes (Sushchevskaya et al., 2008). In the process of development of Norway-Greenland basin, at the early stages of its evolution, near the continental slope of the Svalbard Archipelago there could be formed the enriched oceanic mantle due to penetration into its upper levels of deep alkaline melts generated in subcontinental lithosphere of Spitsbergen. While the Neogene trap magmatism could reflects the recycled crust substance melting without considerable involvement of mantle peridotite. The increasing of peridotite component share accompanied by regular changing in Sr and Nd isotope composition associates with decreasing of magmatism age but its influence on the composition of the modern Knipovich ridge lavas is negligible.

 

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