The crustal structure of central East Greenland: results from combined land-sea seismic refraction experiments

Abstract

We present results from the first combined marine-land seismic refraction survey in the area of the East Greenland Caledonides, together with gravimetric measurements. The seismic and gravimetric models show a consistent picture of the crustal structures. In the western area, which is part of the Caledonian mountains of East Greenland, crystalline rocks with P-wave velocities of about 5.5 km s-1 occur at the surface. Seismic velocities increase continuously with depth and reach values of 6.6 km s-1 at 12km. The total thickness of the crust as revealed by the seismic measurements reches high values of up to 48km in the southwestern part of the region (28°W). Gravity data, which also cover the region west of the seismic lines, indicate a possible further increase of the crustal thickness. These high values raise questions about whether they represent a Caledonide crustal root, which would stand in strong contrast to the findings in the Caledonian areas of Europe, or whether the crustal thickening represents a pre-Caledeonian structure and is affine rather to the older regions west of the Caledonides and adjacent to the Greenland inland ice. Towards the east crustal thickness decreases rapidly. It reaches a minimum of 22km under the Late Palaeozoic-Mesozoic sedimentary basin of Jameson Land. The crustal thinning is the result of the stretching of East Greenland which was produced by a general extensional tectonic regime and the collapse of the Caledonian mountain chain from Devonian time onwards. In the area of transition from thick to thin crust, the seismic data indicate a layered structure at the Moho. This region is interpreted as a zone of extensive intrusion or underplating during the rifting in the Tertiary.