THE ST-ETIENNE STEPHANIAN COAL-BASIN IS N OT THE RESULT OF A LATE-HERCYNIAN OVERALL EXTENSION BUT IS A PULL-APART BASIN RELATED TO A DEXTRAL STRIKE-SLIP-FAULT

The St-Etienne area (Stephanian coal-basin and Mt Pilat metamorphic ma ssif) has been taken as one of the examples of late orogenic extension in the Variscan belt. The key structure was the Mt Pilat ductile norm al fault which was considered as the southern boundary of the St-Etien ne coal basin. We show with precise field observations and taking into account the old subsurface data obtained from coal exploitation that this structural interpretation must be modified. The Stephanian coal-b asin is a pull apart basin on a NE-SW strike-slip fault, which is dist inct from the Mt Pilat detachment. We compare the latter to the North Himalayan normal fault and we discuss the evolution of this part of th e Hercynian belt from the Monts du Lyonnais to the Cevennes at lithosp heric scale.