title: 4D reconstruction of the Aar Massif: An evolutionary history from a passive margin to the Central Swiss Alpine valleys
Creators: name: Musso Piantelli, Ferdinando
Publisher: name: Universität Bern
Year: 2024
Subjects: subject: 000 Computer science, knowledge &amp; systems
subject: 550 Earth sciences &amp; geology

description: In this thesis, a methodology for the construction of an explicit large-scale 3D geological model of Alpine regions has been developed. The selected study area is the Aar Massif, the easternmost of the External Crystalline Massifs of the European Alps. This methodology allowed us to integrate a complete dataset into a large-scale 3D geological model of the main lithostratigraphic and tectonic boundaries of the massif. The development of a coherent structural interpretation of the area, coupled with the knowledge gained from the 3D structural modelling, has provided fundamental insights into its present-day 3D geometry. In addition, the application/integration of the 3D model with a wide range of complementary methods allowed us to design three scientific studies to unravel the evolution of the massif under different points of view. In fact, cross-section restoration, remote sensing techniques, drone mapping, 3D paleo-temperature distribution, and field-based rock hardness analyses were used to study the evolution of: (i) the crystalline units of the entire Aar Massif; (ii) the sedimentary cover of the massif; and (iii) the valley morphologies as a consequence of tectonic preconditioning. Three main outcomes summarise the obtained results: (1) The Aar Massif results from inversion of the former passive European margin, characterized by complex rifting structures that formed local half graben basins and a topographic high. Exhumation of the basement units occurred in a distinct in-sequence deformation style, where inherited along-strike variations in the thickness and density of the basement units induced a non-cylindrical exhumation resulting in the present dome-shape of the massif. (2) The variations in the thickness of sedimentary units, defined by the initial basement geometry of the passive margin, controlled the architecture of the developing nappes before the exhumation of the Aar Massif. The case of the Doldenhorn Nappe showed that large half grabens with thick sedimentary units developed a large amplitude nappe with a single detachment horizon. In contrast, the thinner sedimentary units developed a small amplitude nappe dissected by in-sequence set of detachment horizons. (3) The efficiency of erosional processes active in Alpine valleys is closely related to the inherited collisional tectonic architecture of the orogen. Indeed, variations in fault frequency and orientation, induced by the collisional dynamics, largely control the bedrock erosion processes, revealing an integral link between deep-seated collisional dynamics and long-term landscape erosion patterns.
This work highlights the importance of incorporating 3D considerations when investigating complex geological systems, such as a fold-and-thrust belt or an orogen. It is essential to broaden single cross-sectional interpretations into the third dimension and incorporate their immense along-strike 3D variability. This is the key to gaining a deep understanding of the evolution and dynamics of such systems.