Paper No. 13
Presentation Time: 9:00 AM-6:30 PM
CRUSTAL STRUCTURE IN CENTRAL-EASTERN GREENLAND FROM THE TOPOGREENLAND REFRACTION PROFILE
SHULGIN, Alexey1, THYBO, Hans2, KAIP, G.3, GRESCHKE, B.3, CHEMIA, Z.3, REICHE, S.3 and BRUUN, A.3, (1)Department of Geography and Geology, University of Copenhagen, Oester Voldgade 10, Copenhagen, 1350, Denmark, (2)Geology Section, IGN, University of Copenhagen, Oester Voldgade 10, Copenhagen, 1350, Denmark, (3)Topogreenland Refraction Seismic Field Team, c/o University of Copenhagen, Dept. of Geography & Geology, Oester Voldgade 10, Copenhagen, 1350, Denmark, thybo@geo.ku.dk
We present the results of the first measurements of seismic structure in the interior of Greenland by the seismic refraction/wide angle reflection method. Acquisition of geophysical data onshore Greenland is logistically complicated by the presence of an up to 3.4 km thick ice sheet, permanently covering most of the land mass. Previous seismic surveys have only been carried out offshore and near the coast of Greenland, where the crustal structure is affected by oceanic break-up and may not be representative of the interior of the island. The seismic data was acquired by a team of six people during a two-month long experiment in summer of 2011 on the ice cap in the interior of central-eastern Greenland along an EW-trending profile, extending 310 km inland from the approximate edge of the stable ice cap near Scoresby Sund across the centre of the ice cap. 350 Reftek Texan receivers recorded high-quality seismic data from 8 equidistant shots along the profile. Explosive charge sizes were 1 ton at the ends and ca. 500 kg along the profile, loaded with about 100 kg at 35-85 m depth in individual boreholes. The planned extension of the profile by use of OBSs and air gun shooting in Scoresbysund Fjord to the east coast of Greenland was unfortunately cancelled, because navigation was prevented by ice drift.
Based on forward ray tracing modelling, a two-dimensional velocity model show a decrease of crustal thickness from 50 km below the centre of Greenland in the western part to 42 km in the eastern part of the profile. It is known that crustal thickness further decreases eastward to ca. 30 km below the fjord system, but details of the changes are unknown. Relatively high lower crustal velocities (Vp 6.8 – 7.3) in the western part of the model may indicate past collision tectonics or may be related or to the passage of the Iceland mantle plume. The origin of the pronounced circum-Atlantic mountain ranges in Norway and eastern Greenland is unknown. Average elevation is well above 1500 m with peak elevations of more than 3.5 km close to Scoresby Sund in Eastern Greenland. The new results will provide data for assessment of the isostatic balance of the crust in Greenland, as well as for insight into possible links between crustal composition, rifting history and present-day topography of the North Atlantic Region.
