POSTPALEOZOIC COOLING AND UPLIFT OF THE BRABANT MASSIF AS REVEALED BYAPATITE FISSION-TRACK ANALYSIS

A fission track study has been carried out on apatite from the igneous rock belt running along the southern border of the Brabant Massif. Th e study includes age determinations and a length analysis of both surf ace tracks and confined tracks. Apatite fission track ages vary betwee n 146 Ma and 209 Ma. Confined track length distributions and the proje cted length age spectra indicate that the rocks cooled relatively rapi dly from above 100-degrees-C to ambient temperatures. The fission trac k ages therefore date a cooling phase of the Brabant Massif which is i nterpreted as reflecting an important uplift during the major part of the Jurassic, related to the Cimmerian tectonism which affected the No rth Sea basin and adjacent areas. Two apatite samples from the souther ly Dinant Basin yield fission track ages around 200 Ma, similar to the oldest ages observed in the Brabant Massif, and with comparable track length characteristics. This indicates that the uplift was not limite d to the Brabant region but also affected the Hercynian basement to th e south.