Stratigraphy,structure and metamorphism in the western Alps

The French Alps may be divided into a series of longitudinal structural zones. For the most part these zones represent thrust slices or nappes and they are often separated by sheets of salt and gypsum which have been squeezed out from the Triassic strata and act as lubricants. The Mesozoic strata in the several structural zones vary in both thickness and facies. These variations are described and their palaeogeographic significance discussed. From west to east an increase in the amount of deformation shows in the folding and faulting with a corresponding, though not strictly related, increment in the amount of recrystallisation and regional metamorphism. The Mesozoic rocks show a continuous series of changes so that across the region unmodified sediments are seen, altered first to slates, then phyllites, and finally to schists, with glaucophane, chloritoid and garnet.