Combining traditional and quantitative multiscale structural analysis to reconstruct the tectonometamorphic evolution of migmatitic basements: the case of the Valpelline Series, Dent-Blanche Tectonic System, Western Alps

Geological investigations across various scales. These techniques, such as 3D outcrop modeling through aerial photogrammetry and quantitative microstructural analysis, prove valuable in studies of crystalline basement rocks. This contribution merges traditional and quantitative multiscale structural analysis techniques applied to the migmatitic rocks of the Valpelline Series within the Dent-Blanche Tectonic System in the Western Alps. Conventional structural analysis is augmented by extracting structural data from 3D models of representative, smoothly exposed outcrops. Quantitative microstructural and mineral-chemical analyses are integrated to establish links between structural and metamorphic evolution. This approach enables the identification and correlation of foliations that evolved during three tectonometamorphic stages. The first stage (D1) involves solid-state deformation, characterized by an early foliation (S1) preserved within metabasite boudins enclosed within migmatite gneiss. The second stage (D2) corresponds to the dominant foliation in migmatite gneiss (S2), concurrent with regional-scale anatexis and the growth of garnet and cordierite. The third stage (D3) is associated with the late folding of S2 and the development of a sillimanite-rich axial plane foliation (S3), which wraps around garnet and cordierite.Finally, this work discusses the advantages and limitations of each innovative methodology while emphasizing the importance of using manually acquired field data as ground control (Caso et al., 2024).