The crustal structure of central East Greenland - I: From the Caledonian orogen to the Tertiary igneous province

We present a regional crustal model of the East Greenland Fjord Region between 69°N and 74°N which spans the Caledonian fold belt and the adjoining Devonian and Mesozoic basins. The model is a compilation of existing seismic models that were partly reinterpreted and newly derived results from different modelling approaches. Remodelling of 33 stations on three deep seismic lines in the southern area yielded consistent P-wave velocity models for the entire Fjord Region. Seismic velocities, between 5.5 km s-1 near the surface and 6.9 km s-1 in the lower crust are typical for regions of Palaeozoic age. Moho depths up to 48 km in the seismic models suggest the existence of a crustal root beneath the Caledonian orogen. Shear wave modelling of 51 stations on six refraction seismic profiles resulted in S-wave velocities between 3.2 km s-1 in the upper crust, 4.0 km s-1 at the crust-mantle boundary and 4.2 km s-1 in the partial magmatic underplating of the lower crust in the northern area. Calculation of Poisson's ratio portrays a fairly homogeneous crust with only slight variations in Poisson's ratio of 0.26-0.30 for the uppermost crystalline crust and 0.22-0.24 for the middle crust. These values cannot be linked to lithological variations because they are either small-scale or span several tectonic provinces. Finite-difference modelling and amplitude analysis confirm models without magmatic underplating in the lower crust of the southern Hall Bredning, Scoresby Sund area.