Long-term exhumation of a Palaeoproterozoic orogen and the role of pre-existing heterogeneous thermal crustal properties: a fission-track study of SE Baffin Island

<p>New apatite fission-track data from SE Baffin Island exhibit central ages that range from just under 200 Ma to 440 Ma, and mean track lengths that vary between <em>c</em>. 12 and 13.3 µm. First-order analysis of the data (a plot of central age v. mean track length) reveals an approximate ‘boomerang’ trend, typical of samples that have experienced contemporaneous cooling from an array of initial temperatures. One-dimensional inverse thermal modelling of single samples suggests that cooling through the partial annealing zone (<em>c</em>. 120–60 °C) occurred over discrete periods ranging from 100 to 300 Ma. Modelling the 3D exhumation of a heterogeneous crust with flat topography demonstrates that some of the variability in observed fission-track ages could be attributed to heterogeneity in crustal heat production and thermal conductivity. The remaining variability in the observed dataset is attributed here to differential erosion from a variable initial topography. However, age discontinuities over short distances require other explanations such as faulting and/or unidentified compositional effects. Collectively, these results suggest that the observed data are consistent with a simple exhumation scenario where the present-day high topography is a remnant of that created during Palaeoproterozoic orogenies. The new data do not require any recent (Cenozoic) periods of exhumation. </p>