Article révisé par les pairs
Résumé : Rb/Sr isochron ages recorded by Ashgillian ignimbrites from Deerlijk and Harelbeke and the Caradocian quartz rhyolites from Quenast and Bierghes significantly post-date their emplacements. At Quenast, two isochrons (372 + or - 13 and 375 + or - 14 m.y.) show that the Brabant branch of the Caledonian belts was affected by a post-Siegenian, pre-Tournaisian event, contemporaneous with the Oudenaarde-Bierghes fault zone at 373-379 m.y. This approx 375 m.y. cluster of events is interpreted as representing late Givetian stresses in strike-slip movements, the Brabant massif thus apparently being affected by successive crustal extension and shortening in the Middle Devonian. Petrological evidence for the very low-grade metamorphism of the metasediments on both sides of the fault zone indicated that Sr isotopic homogenization of whole-rock ignimbrite and the loss of radiogenic Sr from biotite and K-feldspar could be operative even at <250oC.-R.A.H.