DIFFICULTY IS IN THE DETAILS: A CANADIAN CASE STUDY IN COUPLING CLASSICAL METHODS, KINEMATIC THEORY, AND OPTIMIZATION TECHNIQUES TO CONSTRUCT REGIONAL 3D KINEMATIC MODELS IN EXHUMED FOLD AND THRUST BELTS

We present an integrated approach to modeling 3D structures in thin-skinned fold and thrust belts using high-resolution field mapping, multispectral satellite images, and high-resolution digital elevation data. Our approach employs a new, automated method for defining fault and bedding attitude measurements which inform retrodeformable cross sections and 3D structural models. We illustrate this approach in the Front Ranges of the Southern Canadian Rockies, which offer spectacular field exposures but have limited subsurface data. Here, the general structural framework consists of imbricated thrust faults with steepening of beds from the foreland to the hinterland. Difficulties in representing the three-dimensional geology arise from structural and stratigraphic complexities including tear faults, reef-to-basin transition in sedimentary facies, and out-of-sequence thrust sheets. The incorporation of these details into a 3D model is necessary for our understanding of the development of the foreland belt and the paleo-Pacific passive margin architecture.

Attitude data (e.g., strike and dip) is critical for our representation of these details. Classically, field observations and three-point problem (TPP) calculations have provided us with such data but are limited in scale and time efficacy. To counter these limitations, we incorporate segmented linear least squares into a numerical method to automate attitude calculations and splits a mapped geologic horizon (e.g., polylines) into quantitatively significant attitude segments. This data establishes quantitative fault-fold relationships that inform 3D extrapolation of fault geometries. In particular, we highlight how our detection of variation in the bedding geometry of the hanging wall of the Rundle and Sulphur Mountain Thrust sheets inform us of changes in detachment levels and transfer of slip.

Generally, we illustrate our workflow for 3D model development using retrodeformable cross-sections, regional strike and dip data, and geologic maps as constraints.In this approach, we highlight adaptations & limitations to our workflow for utilization in other fold and thrust belts.