Separation of Palaeogene and Neogene uplift on Nuussuaq, West Greenland

摘要

The geological record exposed on Nuussuaq, central West Greenland, shows that uplift in the Palaeocene, probably caused by impact of the Iceland plume head, was followed by kilometre-scale subsidence. Analysis of apatite fission-track and vitrinite-reflectance data from borehole samples down to 3 km depth reveals that the samples cooled from maximum palaeotemperatures between 40 and 30 Ma followed by two further cooling episodes beginning in the intervals 11–10 and 7–2 Ma. When the first cooling episode began, the samples from the neighbouring Gro-3 and Gane-1 boreholes were buried 1500–2000 m deeper than at the present day, and the palaeogeothermal gradient was 40–48 °C km–1. It is not clear whether this cooling involved exhumation or if it was due solely to reduction in heat flow and a drop in surface temperature. The two later episodes definitely involved exhumation because by then the palaeogeothermal gradient had declined to a value close to the assumed present value of 30 °C km–1, which agrees with estimates from offshore wells. The most recent cooling episode corresponds to the incision of the present-day relief (c. 1100 m) below the summits around the two boreholes. We conclude that the present-day high mountains of West Greenland were not uplifted during the Palaeogene, but are erosional remnants of a landmass uplifted during the Neogene.