EROSION OF THE ALPS - USE OF RB-SR ISOTOP IC DATA FROM MOLASSIC SEDIMENTS TO IDENTIFY THE AGES OF THE METAMORPHISM RECORDED BY THE ERODED ROCKS

Rb-Sr isotopic data from Oligocene and Miocene peri-alpine molassic se diments allow us to identify the different periods for which the erode d rocks have or have not recorded an alpine metamorphism. The Chattian and the Burdigalian sediments result from the erosion of rocks for wh ich the latest metamorphic event was variscan, while the Stampian, Aqu itanian and ''Helvetian'' sediments show evidence for the erosion of r ocks which have recorded alpine metamorphic events. The application of this method to old detrital sediments could permit determination of t he ages of the tectonic events which occurred in the sediment source r egions.