SIGNIFICANCE OF LATEST-VARISCAN AND ALPINE DEFORMATION FOR THE EVOLUTION OF MONTAGNE DE PORMENAZ (SOUTHWESTERN AIGUILLES-ROUGES MASSIF, WESTERN ALPS)

The polymetamorphic basement of the Montagne de Pormenaz (including th e Pormenaz granite) is covered by autochthonous and parautochthonous U pper Carboniferous and Triassic rocks and by allochthonous Morcles nap pe. Starting in the Late Westphalian, black shales were deposited in a n intramontanous basin. Brittle tectonic activity probably caused the forming of conglomerates in the Latest Carboniferous. Alpine orogeny s tarted with a sinistral transpression which formed the N-S trending po sitive Pormenaz flower structure. This event was predated by affected Triassic rocks and postdated by the Oligocene overthrust of the Helvet ic Morcles nappe. In all post Mid Carboniferous rocks a pervasive foli ation was produced under low-grade metamorphic conditions (max. T belo w 290 degrees C) during nappe emplacement (transport towards NW; to W) . Normal faults provide evidence for a later extension. The Upper Carb oniferous sedimentary rocks of the Pormenaz - Coupeau basin underwent a foliation producing deformation during the Alpine orogeny only.