3D structural modelling in the North-Western Alps (Aosta Valley, Italy): a powerful tool for exploring the tectonic evolution of the Alps

Three-dimensional visualisation and conceptualisation are always, knowingly or unknowingly, part of the process of studying a geological phenomenon. As a standard it is accepted that, when 3D structures are too complex to deal with, a two-dimensional study is the preferred way of simplifying a problem into smaller ones (divide et impera). Since Argand, in the case of tectonic interpretation studies, vertical cross-sections are appreciated since, if serialised, they can stand in for a 3D conceptual model. However, this method has limitations when interpreting non-cylindrical structures, as visualisation is confined to 2D formats. Here we present the new 3D structural model of a portion of the North-Western Italian Alps, built in the context of the ReservAqua INTERREG project. Input data come from about 1300 km2 of 1:10,000 maps with rich structural data and thousands of samples and thin sections. Thanks to the very rugged topography, with 4000 meters of elevation difference between the highest peaks (e.g., Cervino-Matterhorn) and the lowest valleys, this is a truly 3D dataset. After an orientation statistics study, the geological interpretation is performed on densely serialised cross-sections, eventually used to guide 3D interpolation with implicit algorithms. In this contribution we focus on the structural principles that allow us building the array of cross-sections and the implications that these decisions have on the final 3D model. We also account for the beneficial effects that three-dimensional modelling has on the process of tectonic interpretation, and we discuss its applications in mountain ranges (hydrogeology, thermal springs, etc.).