From finite strain data to strain history: a model for a sector of the Ligurian Alps, Italy

Bulk strain measurements were made in a Penninic sector of the Ligurian Alps. Previous detailed mapping, supported by petrographic and structural analyses, had shown that the oldest (D1), complex Alpine episode produced km-scale sheath-like folds, involving basement and cover, before the activation of a set of thrusts leading to nappe superposition. By combining all data, a kinematic model has been developed into which the subsequent deformation steps have been set. In particular, total strain constraints led to the suggestion of a combination of relatively low values of pure shear and simple shear for the genesis of the sheath-like folds. A computer simulation has proved that this suggestion is tenable. The model was then used to factor the bulk strain into increments—starting from the diagenetic compaction of the cover, up to the last ‘late D1’ phase—necessary to obtain results that compare well with the finite strain data. Some theories were also deduced on the possible attitude of the pre-Alpine schistosity in the basement rocks at the beginning of Late Variscan times.