The "Zone Houillere Brianconnaise" (ZHB) is the westernmost continuous unit of the Pennine domain that overlies the Pennine Front. The ZHB comprises Namurian and Westphalian formations locally overlain by Permian and Triassic cover rocks. As with other basements of the Pennine domain (Brianconnais id France, Grand Saint Bernard in Italy and Switzerland), the ZHB comprises gneissic units, whose age, origin and tectonic significance have been discussed for a long time. This study deals with the Sapey gneisses, defined near Modane (Savoie), and the Costa Citrin metagranites (Valle d'Aosta, Italy). The alpine tectonic evolution of the ZHB involves an early thrusting event that produced a non-penetrative foliation in the Carboniferous formations. This foliation occurs only in the vicinity of tectonic contacts between individual slices. The thrusting event is overprinted by a regional large-scale, eastward-verging, deformation event and then by a partly extensional event. Pre-alpine relict amphibolite-facies mineral assemblages found in the Sapey gneisses confirm that they belong to a poly-metamorphic basement. Ages from U-Pb geochronology on zircons (three samples of different lithology and from different regions) confirm this interpretation. Concordia diagrams evidence that zircons have a Proterozoic inheritance and that minimum ages are older than 360 Ma (lower intercepts with the concordia). By contrast, two samples of the Costa Citrin metagranite yielded well-defined Visean-Namurian ages at 324 +/- 17 MA and 323 +/- 8 Ma. This old basement age (early Hercynian or older) associated with evidences for a Visean-Namurian magmatic event in the ZHB are consistent with the recent reappraisal of the age of the sedimentary formations of the ZHB (now dated of Namurian to Westphalian). These data support the possible "exotism" of a "Brianconnais" terrane with respect to external domains of the Alps. The ages of the basement (pre-Carboniferous), of the sediments (Visean-Namurian) and of the recorded magmatic event (Visean-Namurian) of the ZHB cannot be related to the late orogenic basin formation and magmatic evolution of the Eastern Massif Central or of the External Basement Massifs during Stephanian times. The significance of the Visean-Namurian plutonism of the Costa Citrin is discussed with respect to other parts of the european hercynian belt. It is interpreted either to be a consequence of a late Hercynian "eastern" subduction or rather, to relate to an early extensional stage during the orogeny.