High-level landscapes along the margin of southern East Greenland-A record of tectonic uplift and incision after breakup in the NE Atlantic

Elevated plateaux and deeply incised valleys characterise the large-scale landscapes along the East Greenland margin as in many elevated, passive continental margins around the world. The absence of syn- or post-rift rocks in, for example, the mountains of Norway, hampers the assessment of the age of these landscapes and of the present-day elevation. The mountains of southern East Greenland (68-71°N), however, expose thick basalts that were extruded onto a largely horizontal lava plain near sea level during breakup of the NE Atlantic at the Paleocene-Eocene transition. We take advantage of these favourable geological conditions to investigate the uplift history after continental breakup. In particular, it is clear that present-day elevations of these basalts up to 3.7. km above sea level (a.s.l.) were reached after breakup. We have mapped regional erosion surfaces and integrated the information about the landscape with the stratigraphic record (i.e. stratigraphic landscape analysis). The analysis led to the following relative denudation chronology for southern East Greenland: At breakup, the margin subsided and underwent km-scale burial. Around the Eocene-Oligocene transition, the first phase of uplift, tilting and subsequent erosion led to the formation of an extensive, low-relief erosion surface (the Upper Planation Surface, UPS) that was graded towards the base level of the adjacent ocean before the eruption of Miocene lavas onto that surface. A second uplift that most likely occurred after the Miocene produced a new erosion surface (the Lower Planation Surface, LPS) by incision below the UPS. Finally, a third event in the late Cenozoic lifted the UPS and the LPS to their present elevations of up to 3 and 2. km. a.s.l., respectively and shaped the present-day valleys and fjords by incision of rivers and glaciers below the LPS. The general picture of landscape development is highly similar to West Greenland and the common characteristics between the stepped landscapes in East Greenland and those on the conjugate margin in Scandinavia lead us to conclude that the mountains of Norway also formed after the North Atlantic breakup.