The post-orogenic evolution of the Northeast Greenland Caledonides constrained from apatite fission track analysis and inverse geodynamic modelling
Résumé
We present new apatite !ssion track (AFT) data from the Northeast Greenland passive margin, between 75.8 and 81°N, where elevations reach over 1000 m and no signs of magmatism related to the opening of the North Atlantic exist. The AFT ages are old, ranging from just less than 200 Ma up to more than 350 Ma, and the length distributions are predominantly narrow unimodal, with c-axis projected mean track lengths between 13.3 and 15.0 !m. The passive margin of Northeast Greenland differs from other studied passive margins in terms of AFT age trends, as we observe no correlation with elevation or characteristic trends relative to mean track length. Using these new data and inverse geodynamic modelling, we constrain the evolution in the area since the orogenic collapse of the Caledonides. Exhumation histories are inferred using a uniform stretching model, incorporating variable rates of erosion or deposition, and thermal histories are found by solving the onedimensional transient conduction-advection heat equation. These thermal histories are used with the observed !ssion track data to constrain acceptable strain rate histories and exhumation paths. The results suggest that rifting has been focused mainly in the now offshore regions since ~300 Ma, or in minor local areas onshore, not affecting the sampled areas signi!cantly. The present-day high topography is therefore suggested simply to represent remnants of the original Caledonian topography, modi!ed during early rifting and, other than the "exural isostatic response to erosional unloading, we !nd no need for introducing post-rift related uplift mechanisms.