Crustal structure in Central-Eastern Greenland: Implications for topography

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 from the TopoGreenland programme, 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 (BB) onshore stations, partly on the ice cap, 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.

Our two-dimensional velocity model of the crust is constrained by tomographic inversion and forward ray tracing modelling. It 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. High lower crustal velocities (Vp 6.8 – 7.3 km/s) in the western part of the profile may result from past collision tectonics or it may be related to the passage of the Iceland mantle plume. Crustal receiver functions based on data from the BB stations, indicates pronounced, relatively sharp variation in crustal thickness around the mountains at the edge of the ice cap. The variation is from thick crust at the low topography below the ice cap, and the high mountains at its edge, to very thin crust below elevated topography close to the coast.

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 Scoresby Sund in Eastern Greenland, is unknown. Our new results on the crustal structure demonstrate that crustal isostasy alone cannot explain the topographic variation in central-eastern Greenland, and other phenomena, including possible dynamic processes must be active in the area.