Publication Date:
2009-10-06
Description:
Apatite fission-track (AFT) analyses were performed on 13 Late Palaeozoic samples in order to unravel the late- to post-Variscan evolution of the Ardennes. The dated AFT ages cover a range from 290{+/-}33 Ma to 168{+/-}12 Ma, and the mean confined track lengths correspond to a unimodal distribution, with means varying between 13.1{+/-}0.1 {micro}m and 11.7{+/-}0.3 {micro}m. These ages for the sedimentary rocks are clearly younger than the respective stratigraphic ages, indicative of a cooling through the apatite partial annealing zone after post-depositional complete annealing. All available AFT data (290-146 Ma) from this region might be classified as three groups, that is 290-229 Ma, 218-198 Ma and 190-146 Ma, at least in correlation with three exhumation events. Using an inverse model, four major cooling episodes are identified from the modelled temperature-time (T-t) paths. The first rapid cooling (4.2-5.4 {degrees}C Ma-1, 320-300 Ma) corresponds to the late-Variscan rapid thrusting that ceased at about 300 Ma. The second cooling episode (0.2-4.0 {degrees}C Ma-1, up to 230 Ma) activated differentially, and was probably controlled by the post-Variscan transtension. The third cooling regime (0.1-0.3 {degrees}C Ma-1, 230-45 Ma) in the Ardennes Allochthon is slow, and represents a long-term and slow exhumation. In the Brabant Parautochthon, however, it is subdivided into 0.7 {degrees}C Ma-1 (225-110 Ma) and 0.2 {degrees}C Ma-1 (110-45 Ma). The last accelerated cooling (0.7-1.1 {degrees}C Ma-1, since 45 Ma) that affected the whole Ardennes is associated with a south-north compression during the Pyrenean phase.
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