Late orogenic evolution of the Variscan lithosphere: Nd isotopic constraints from the western Alps

Abstract : We performed geochemical analyses (major- and trace-elements, Nd isotopes) of Late Variscan igneous rocks from the western Alps in order to better constrain the lithospheric evolution at the end of the Variscan orogeny. In the western Alps, the shoshonitic suite from the Croix de Fer pass and the alkaline Combeynot granite were emplaced during the Late Carboniferous. They were followed during the Early Permian by the calc-alkaline diorite porphyries from the “Zone Houillère Briançonnaise”, dated by 40Ar–39Ar, and by the calc-alkaline rhyodacites from the Guil valley. These suites postdate the Variscan orogeny and originated in a regime of lithospheric extension and thinning affecting the entire domain of the European Variscan belt. They display subduction-related geochemical features with the exception of the Combeynot granite. The Croix de Fer suite, the diorite porphyries from the Zone Houillère Briançonnaise and the felsic lavas from the Guil valley show the lowest (–7 >