Propogation of Deformation Traced by 40 Ar/39 Ar Dating of White Mica in the Grand St. Bernard Nappe, Western Alps

Due to the dynamics of plate interactions, deformation and fabrics resulting from deformation are expected to form sequentially and diachronously across an orogen. However, it has been difficult to directly date deformation fabrics sufficiently accurately to detect the propagation of deformation. This project will utilize an area in the western Alps where temperature during deformation remained low so that the fabric-forming common white mica should have refrained radiogenic argon. The work will attempt to date deformation in four basement-cored nappes of the Grand Saint-Bernard Nappe complex. Results should distinguish between cooling ages and deformation ages, thus providing the basis for a very detailed tectonic interpretation of the progress of fabric development during orogenesis.