3D structural implicit modelling of folded metamorphic units at Lago di Cignana with uncertainty assessment

Abstract

We present a modelling workflow for the creation of a km-scale, three-dimensional representation of the tectonic architecture exposed in the Lago di Cignana region within the Italian Pennine Alps. The model portrays notable tectonic boundaries such as the Dent Blanche Basal Thrust, the Combin Fault and the Roisan-Cignana Shear Zone. Our approach employs the implicit Discrete Smooth Interpolator, which represents the tectonic sequence as a volumetric scalar field generalising a relative distance function. The interpolation process is constrained by geological and structural field data. To model folds that outcrop in the region, we perform three-dimensional interpolation of fold axes, and we enforce these interpolated directions on the fold geometries through tangent constraints complementing the regularisation term in the least-squares system. Furthermore, we address structural uncertainty on isoclinal recumbent folds exposed in the area by simulating a collection of virtual data at randomly located outcrops and stochastically simulating fold axes away from direct observations. These simulated fold axes are arranged in spherical orientation distributions consistent with field data and are used as additional constraints for implicit interpolation. The uncertainty analysis generates multiple scenarios for non-cylindrical folds in terms of axis orientations and interlimb angle.