The lower crust and upper mantle beneath the western Barents Sea and Svalbard: evidence from combined active source and array seismology.

Content Provider	Semantic Scholar
Author	Odden, Guri
Copyright Year	2015
Abstract	Svalbard is one of few places on Earth where an upwelling mantle flow associated with recently formed divergent plate boundary interacts with continental lithosphere. Seismic tomography studies, elevated heat flow and petrological data from upper mantle xenoliths indicate anomalously hot mantle and thin lithosphere (about 50 km). The Early Cretaceous opening of the Arctic Ocean and formation of the High Arctic Large Igneous Province resulted in abundant dolerite sills in the sedimentary cover and giant-like dike swarms cross-cutting the crystalline basement in the Svalbard region. Despite decent data coverage, velocity models obtained from wide-angle seismic data in the Svalbard region are often characterized by poor resolution in the upper mantle due to limited source-receiver offset. The datasets in this study originates from two wide-angle refraction surveys conducted in the vicinity of Kong Karl’s Land in 2008 and Hopen Island in 2014. Both surveys were shot with air guns with the total volume of about 80 l by the research vessel Håkon Mosby. The seismic line shot in 2008 was recorded with the seismological array on Spitsbergen (SPITS) and sampled crust and upper mantle in east-west direction, while the line shot in 2014 was recorded at SPITS, and the seismic stations at Hornsund (HSPB) and on Hopen Island (HOPEN) leading to sampling of crust and upper mantle in both north-south and east-west directions. Band-pass filtering, cutting, NEZ-LQT rotation, beamforming both at the source and receiver sides, and tau-p transformations have been performed on the data to enhance the signal-to-noise ratio for certain seismic phases and have resulted in clear mantle refractions at offsets up to 420 km. The travel-time data are inverted for a 1D P-wave velocity model, following Diebold and Stoffa (1981). Other 1D velocity models previously published by different authors will also be discussed. The 3D model Barents50 from Ritzmann et al. (2007) has been evaluated by ray tracing and travel-time modelling, and it has revealed some differences in travel times when compared to the data in this thesis. Full waveform modelling by a frequency-wavenumber integration method (Bouchon, 1981) has been performed in order to study offset dependent amplitude variations and the generation of converted S-waves. Discrepancies between the modelled travel-times from Barents50, Barents, Barey, Barez and Fennoscandia and the travel-times of the onsets from the data in this thesis was evident. The largest deviations between the previously published data and the data from this thesis was found in the crust. Previous depth and velocity estimates of the upper mantle are similar to the inverted 1D data. Some previous publications in this area supports magmatic underplating, however in this thesis no signs of magmatic underplating in the lower crust is evident and the largest P-wave velocity in the crust is 6.6 km/s. With this contribution new methodological developments that will allow for better imaging of the uppermost mantle from long-offset refraction data will be discussed.
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Language	English
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Resource Type	Article