Regional-scale 3D modelling in metamorphic belts: An implicit model-driven workflow applied in the Pennine Alps

Leveraging a high resolution geological and structural dataset acquired over decades of fieldwork, we build the 3D structural model of a portion of the highly deformed core of the Alpine orogen, in the Northern Aosta Valley. The model represents tectonic contacts separating the tectono-metamorphic units outcropping along the section between Mont Blanc and Monte Rosa, and it covers an area of ca. 1500 km2. The input source data include original 1:10,000 geological surveys synthetised in a 1:75,000 tectonic map, and a dense database of structural stations. After a first orientation statistics study of the structural field database, our workflow develops through structural interpretation in vertical cross-sections that allow including in the modelling process structural drivers such as crosscutting relationships, interference patterns, kinematic constraints and fold morphology from detailed field studies. Three-dimensional interpolation on a tetrahedral mesh using the implicit Discrete Smooth Interpolator method follows, using also foliation and fold axes data as interpolation constraints. After describing the workflow and the model, we discuss the difficulties of modelling in polydeformed metamorphic complexes. In particular, we address the issue of modelling shear zones, refolded, isoclinal and/or recumbent folds and dense networks of faults, that characterise the geology of the Northern Aosta Valley.