Using 3D models to test geological hypotheses for sill complex geometries: Application to Jurassic dolerite intrusions, Tasmania

This study employs three-dimensional (3D) geological modelling to test competing hypotheses regarding the subsurface architecture of Jurassic dolerite sills in the Hobart region, Tasmania. Although this sill complex has been extensively studied, there is little subsurface data, making it an excellent case study for using 3D models to better understand its architecture. Four alternative models are built using the LoopStructural Python library, which incorporates rules from intrusion emplacement mechanisms into the modelling workflow. All four models are constrained using the same input dataset, comprising field measurements, most of which are located in the southwest part of the study area. The differences between the models are governed primarily by which pre-intrusion mechanical anisotropy facilitated emplacement of the dolerite. The models are visually and quantitatively compared with the published geological map of the area and with field observations. The results of this comparison suggest that northeast and northwest-trending outcrop patterns of the dolerite are likely related to the presence of transgressive sheets within sedimentary host rocks of the Permo-Triassic Parmeener Supergroup, and that the occurrence of dolerite sills at different stratigraphic and structural levels is likely due to a combination of primary intrusive steps and post-intrusion faults. • 3D modelling advances enable efficient testing of sill complex geometries. • Four 3D models of the Hobart region were built using LoopStructural. • Models suggest dolerite exploited NE and NW fractures, forming step-like sills. • Key areas for further geological investigation have been identified.