Towards dynamic restoration of geologic profiles: Some lessons from analogue modelling

Restoration of geologic profiles aims to achieve geometric consistency and kinematic compatibility between deformed and restored sections. During restoration, major folds and faults can be fairly easily detected and accounted for. However, mass transfer and volume changes cannot be measured as easily and therefore cannot be accurately accounted for during the restoration. Accurate restoration requires not only correct geometric and kinematic restoration, but also consideration of strain balancing (e.g. penetrative strain) and material flow into and out of the restored profile. Two examples from analogue models are described here to illustrate; first, the significance of area change in restoration, and second, how to account for it. Since their initial dimensions and material properties are well documented, analogue modelling can be a useful tool for testing restoration of profiles in extensional and contractional provinces. Models simulating both extensional and contractional areas show that mass transfer is a significant component of deformation. Modelling of a ductile material simulating rock salt in extensional areas reveals that the three-dimensional flow plays a significant role in the deformation. Similarly, models of contractional areas illustrate that tectonic compaction can account for 15% of the shortening. Therefore, change in area due to threedimensional flow of ductile substrates and tectonic compaction should be accounted for during restoration of geologic profiles. As a first step towards dynamic restoration of geologic profiles, a preliminary approach to restore the 3-D flow of rocksalt by calculation of 3-D differential loading is presented here. Since passive margins are areas where non-evaporitic sediments can undergo both extension (at the trailing updip areas) and compression (in the leading downdip deformation front) during their gravitational gliding above a layer of rock salt or lubricant shale, the results of the current study can give insights to restoring deformation in passive margins.