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Crustal Structure of the East Greenland Volcanic Margin - II: Alongstrike Variations Between the Jan Mayen and Greenland Fracture Zones

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Schmidt-Aursch, M. C. , Voss, M. and Jokat, W. (2006): Crustal Structure of the East Greenland Volcanic Margin - II: Alongstrike Variations Between the Jan Mayen and Greenland Fracture Zones , EGU General Assembly, 02-07 April, Vienna, Austria, Geophys. Res. Abs. .
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Beside wide-angle seismic data acquired for the EUROMARGINS project, twoadditional seismic refraction profiles were gathered further north acrossthe East Greenland rifted margin during an expedition in 2003. This datasetprovides new insights into the formation of the entire continental marginsegment between the Jan Mayen and the Greenland fracture zones.A total of 25 ocean bottom seismometers (OBS) were deployed from theGreenland shelf into the Greenland basin along the 330 km long northernmostprofile, AWI-20030200. The transect near the Greenland Fracture Zonecrosses an area with very thick sedimentary basins. These continentalsediments on the shelf show uniformly high seismic velocities in the upperlayers (2.2 km/s), which is the result of glacial compaction. Theoccurrence of low velocity zones and a large basin thickness leads to theabsence of seismic signals from the crystalline continental crust. Typicalseismic velocities and thicknesses were found for deep sea sediments (1.6 -2.4 km/s, 1 - 1.5 km) and oceanic crust (4.8 - 7.0 km/s, 6 km) furtheroffshore. In contrast to the southern profiles, no evidence for massiveunderplating could be found.The second profile, AWI-20030300, was acquired in the prolongation of theArdencaple Fjord south of Shannon Island with 25 OBS and six REFTEKlandstations. P-wave modelling reveals a slightly different crustalstructure than that on the two southern profiles. While the 30 km thickcontinental crust shows strong structural variations, a diffuse (~70 kmwide) transition zone leaves the lower crust ambiguous. The middle crust ofthe continent-ocean transition (COT) is characterised by an increasedvelocity gradient compared to normal continental crust. In the ~100 km wideregion, between magnetic spreading anomalies C24 and C22, the lower oceaniccrust has high velocities of 7.0 - 7.3 km/s. The oceanic crust consists ofa thin layer 2A (4.3 km/s), a layer 2B (4.7-6.7 km/s) and a layer 3A/B (6.8- 7.3 km/s) whose thickness increases from 5 km at the eastern end of theprofile to almost 16 km near the COT. Seaward dipping reflectors (SDRs) canbe inferred from multi channel seismic (MCS) data and from slow p-wavevelocities in the upper oceanic crust between anomalies C24 and C23.An overall view of all four seismic refraction profiles shows significantvariations in the crustal structure along the margin. These include adecrease in the thicknesses of the magmatic underplate towards the north,and a widening of the COT in the south. These variations may indicatevariable rift processes along the rifted continental margin between the JanMayen and the Greenland fracture zones.

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