Upper mantle and crustal structure in Central-Eastern Greenland: Results from the TopoGreenland project

English Abstract:

Until present, seismic surveys in Greenland have mainly been carried out offshore and near the coasts, where the crustal structure is affected by oceanic break-up. We present models of the seismic structure of the upper mantle and crust in the interior of Greenland, based on new seismological data, including the only existing seismic refraction/wide-angle reflection profile in the interior of Greenland. The seismic data was acquired in central-eastern Greenland by 24 broadband onshore stations over a period of 3 years and as a refraction seismic profile on the ice cap by a team of six people during a two-month long experiment in summer of 2011, mainly on the ice cap.

Using tomographic inversion and forward ray tracing modelling we have obtained a two-dimensional velocity model of the crust. The model shows a decrease of crustal thickness from 47 km below the centre of Greenland in the western part of the profile to 40 km in its eastern part. Relatively high lower crustal velocities (Vp 6.8 – 7.3 km/s) in the western part of the TopoGreenland profile may result from past collision tectonics or, alternatively, may be related to the speculated passage of the Iceland mantle plume.

Models of the structure of the upper mantle and transition zone under central-eastern Greenland based on the teleseismic P and S receiver functions, including estimates of the velocity structure and upper mantle discontinuities show strong signals from the 410-km and 660-km discontinuities. Their delay times suggest a thinner transition zone compared to IASP91, mainly caused by a depression of the 410-km discontinuity, in major parts of the region. On several stations we see a conversion, which might originate from a mid-lithospheric discontinuity, whereas the lithosphere-asthenosphere boundary does not seem to be resolved.

The origin of the pronounced circum-Atlantic mountain ranges in Norway and eastern Greenland, which have average elevation above 1500 m with peak elevations of more than 3.5 km near the Scoresby Sund in Eastern Greenland, is unknown. Our new results on the crustal structure provide constraints for assessment of the isostatic balance of the crust in Greenland, as well as for examining possible links between crustal composition, rifting history and present-day topography of the North Atlantic Region.