Time Constraints on the Metamorphic and Structural Evolution of the Southern Sesia-Lanzo Zone, Western Italian Alps

Abstract

The Sesia-Lanzo Zone (SLZ) is important as one of the most extensive segments of continental crust metamorphosed under eclogite facies conditions (Compagnoni et al., 1977). Parts of the SLZ record a complex thermal and structural evolution including metamorphism under widely varying conditions over a long (probably >300Ma) timespan, whereas other elements of the SLZ seem to record only portions of this history (Lardeaux and SpaUa, 1991). Aiming primarily to understand the mechanisms by which deep crust is exhumed, this study had a number of objectives: I) Definition of a structural framework based on progressive deformation phases, tracking changes in the nature and site of the deformation flow through time. 2) Characterisation of metamorphism conditions under which diagnostic mineral fabrics were formed, thereby linking the strain history with the P-T evolution. 3) Isotopic dating of minerals which could be related to specific segments of the P-T-deformation path, to define the age of the high-pressure metamorphic peak and rates of subsequent exhumation which might be related to regional tectonics.