Poland
Projects
Project Name and Acronym:
Continent-ocean-transition across a rifted shear-margin: off Bear Island, Barents Sea (BIS-2008)
The experiment was done in the framework of the 4th International Polar Year Panel "Plate Tectonics and Polar Gateways", the international project "The Dynamic Continental Margin Between the Mid-Atlantic-Ridge System (Mohns Ridge, Knipovich Ridge) and the Bear Island Region".
A 410 km long Ocean Bottom Seismometer profile from the Bear Island, Barents Sea to oceanic crust formed along the Mohns Ridge have been modelled by use raytracing with regard to observed P-waves. The northeastern part of the model represents typical continental crust, thinned from c. 30 km thickness beneath the Bear Island to c. 13 km within the Continent-Ocean-Transition.
Principal Contacts for Data
Project Scientists
Aleksander GUTERCH, Polish Academy of Sciences, Warsaw, Poland, adgip@igf.edu.pl
Marek GRAD, University of Warsaw, Warsaw, Poland, mgrad@mimuw.edu.pl
Rolf MJELDE, University of Bergen, Bergen, Norway Rolf.Mjelde@geo.uib.no
Project Locations
European Arctica
Project Activities
The seismic refraction experiment between Mohns Ridge and Bear Island was done in August 2008 with use of two ships: Norwegian R/V Håkon Mosby and Polish R/V Horyzont II. Geographical coordinates of BIS-2008 profile are: 72.114oN, 9.600oE and 74.460oN, 19.263oE. The sources of seismic waves were airgun and chemical shots performed in the sea. Offshore airgun shooting along the whole profile length, was done by R/V Håkon Mosby with use a system of four airguns of 1200 in3 each and total volume of 4800 in3 (78.66 l). Altogether 1914 airgun shots were performed with distance interval of 200 m (corresponding to 1 minute time interval), at the depth of approximately 10 m. A total of 104 chemical shots (25 kg of TNT each) were done by R/V Horyzont II along the northeastern part of the profile (distance along profile 176.4-385.5 km), with average interval of 2 km.
Principal Science Objectives
Between the Hornsund FZ and the Knølegga Fault, a 3-4 km thick sedimentary basin, dominantly of Permian/ Carboniferous age, is modelled beneath the c. 1.5 km thick layer of volcanics (Vestbakken Volcanic Province). The P-wave velocity in the 3-4 km thick lowermost continental crust is significantly higher than normal (c. 7.5 km/s). We interpret this layer as a mixture of mafic intrusions and continental crystalline blocks, dominantly related to the Paleocene-Early Eocene rifting event. The crystalline portion of the crust within the south-western part of the COT consists of a c. 30 km wide and c. 6 km thick high-velocity (7.3 km/s) body. We interpret the body as a ridge of serpentinized peridotites. The magmatic portion of the ocean crust accreted along the Knipovich Ridge from continental break-up at c. 35 Ma until c. 20 Ma is 3-5 km thicker than normal. We interpret the increased magmatism as a passive response to the bending of this southernmost part of the Knipovich Ridge. The thickness of the magmatic portion of the crust formed along the Mohns Ridge at c. 20 Ma decreases to c. 3 km, which is normal for ultra slow spreading ridges.
Research Highlights
The experiment targeted the lithospheric structure of the transition between continent and ocean using high resolution seismic refraction technique. Results are important for the tectonic development of the Northern Atlantinc, particularly for the opening of the ocean in the Arctica.
Published Papers
submitted to Geophysical Journal International Continent-ocean-transition across a rifted shear-margin: off Bear Island, Barents Sea
Institutes / Agencies that provided project support
Norwegian Research Council (NFR Project number 176069/S30)
PGNiG (Polish Oil and Gas Company SA)
Ministery of Science and Higher Education in Poland
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