HR: 0800h
AN: V31B-1432    [Abstracts]
TI: Late magmatic underplating of oceanic crust at the outer V{\o}ring margin, Norway, Euromargins 2003 OBS experiment
AU: * Breivik, A J
EM: a.j.breivik@geo.uio.no
AF: Department of Geosciences, University of Oslo, PO Box 1047 Blindern, Oslo, N-0316 Norway
AU: Faleide, J I
AF: Department of Geosciences, University of Oslo, PO Box 1047 Blindern, Oslo, N-0316 Norway
AU: Mjelde, R
AF: Department of Earth Science, University of Bergen, Allegt. 41, Bergen, N-5007 Norway
AB: The V{\o}ring margin off mid-Norway is a volcanic passive margin where large volumes of magmatic rocks were emplaced during the breakup of the Norwegian-Greenland Sea during the earliest Eocene. In 2003, an ocean bottom seismometer/hydrophone survey was acquired on the V{\o}ring and Lofoten margins. One profile crosses the V{\o}ring Plateau and a bathymetric high northeast of the East Jan Mayen Fracture Zone (EJMFZ). The P-wave data were modeled by a combined forward ray-tracing and inversion procedure, giving a 2D velocity model. The model shows a rapid transition from continent to oceanic crust (COT) located under the zone of seaward dipping reflectors, similar to earlier results. Maximum igneous crustal thickness was found to be 17.5 km, but the thickness is in general 5 km lower than found by previous studies nearby. From the COT the igneous crustal thickness decreases from 17.5 to 9 km over a distance of 90 km, indicating abating magmatism over 4-5 Ma after continental breakup. West of that, the bathymetric high is supported by increased (12-15 km) crustal thickness. P-wave velocity is well constrained to be 7-7.25 km s$^{-1}$ in the lower crust of the high, indicating a gabbroic composition. The sedimentary pattern over the high seen on recent single or multi-channel reflection seismic profiles, show that the high is not a primary feature, but was created through later uplift.To explain later magmatic underplating of oceanic crust, magmatic and plate kinematic development of the Norway Basin around the extinct spreading axis of the Aegir Ridge is investigated. V-shaped lineations seen in the satellite gravity field indicate NE migrating asthenosphere zones with increased melt production potential, delivering to the Aegir Ridge. Due to low magnetic track coverage, the EJMFZ was reinterpreted from the satellite gravity field. Comparing the new interpretation to published spreading poles, spreading appears more asymmetric than previously believed: East of the Aegir Ridge, spreading followed Greenland vs. Eurasia up to about A13 time. After that, the spreading followed published poles located southeast of Iceland. The latter poles can, however, now be applied to the whole opening history on the western side of the ridge. The revised flowlines show that the V-shaped lineations are reasonably symmetric with respect to spreading direction, even if they are not symmetric with respect to the ridge trend. Estimated asthenospheric transport velocity along the Aegir Ridge is 0.35 cm/a or lower for the Paleogene. It is suggested that partially melted asthenosphere was transported northeastwards when spreading in the Norway Basin ceased, and released through episodic ascent northeast of the EJMFZ. However, there is a need to speed up the transport in the Neogene to cover the distance during the available time, which could be related to the increased activity on the Iceland hot-spot.
DE: 8434 Magma migration
DE: 7220 Oceanic crust
DE: 3035 Midocean ridge processes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting