3D geomodelling in polydeformed metamorphic mountain belts: an implicit geomodel-driven workflow applied to large scale modelling of the Northern Aosta Valley (North-Western Alps, Italy)

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 the tectonic contacts separating the tectono-metamorphic units outcropping along the section between Mont Blanc and Monte Rosa. 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. The model area has an areal extension of ca. 1,500 km2 and a vertical elevation difference between the highest mountains (e.g., Cervino-Matterhorn) and the valley floors of ca. 4,000 meters, making up a truly three-dimensional dataset. After a first orientation statistics study of the structural field database, our workflow comprises a structural interpretation in vertical cross-sections for the creation of a conceptual model based on sound geological knowledge. Three-dimensional interpolation on a tetrahedral mesh using the implicit structural modelling approach follows, using notably foliation and fold axes data as interpolation constraints. After describing the orogenic tectonic setting and the geomodelling workflow, we present the new publicly available 3D structural model of the Northern Aosta Valley. Finally, we discuss the difficulties of modelling in polydeformed metamorphic units. In particular we address the issue of modelling shear zones, refolded, isoclinal and/or recumbent folds and dense networks of faults.