Elevated, passive continental margins: Long-term highs or neogene uplifts? New evidence from West Greenland

It is commonly assumed that elevated, passive continental margins have remained uplifted since the time of rifting. In many areas, e.g. Scandinavia, the timing and extent of uplift movements are difficult to determine because the uplifted area consists almost exclusively of ancient metamorphic rocks. However, the preserved Mesozoic-Cenozoic sedimentary and volcanic record of West Greenland makes this a key area for studying the uplift of passive continental margins. We have combined apatite fission-track analysis data with landform analysis to investigate the development of West Greenland landscapes across areas with substantially different geology. We show that the present-day mountains of West Greenland (65-71°N) are the end result of three Cenozoic phases of uplift and erosion. The first phase that began between 36 and 30 Ma led to the formation of a planation surface during the Oligocene-Miocene. This surface was offset by reactivated faults, resulting in megablocks that were tilted and uplifted to present-day altitudes of up to 2 km in two phases that began between 11 and 10 and between 7 and 2 Ma. These late Neogene uplift phases postdate rifting by c. 50 million years and sea-floor spreading west of Greenland by c. 30 million years, while the first of these phases predates onset of glaciation in Greenland by c. 3 million years. The similarity in morphology between West Greenland and other rifted continental margins suggests that uplift of rift flanks to present-day elevations may often post-date rifting significantly. The regional nature of the uplift movements along passive margins and their considerable distance from active plate boundaries suggest that the causal mechanisms must be located in the deep crust or the upper mantle where the thickness of the crust and lithosphere changes substantially over a short distance.