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42359-AC8
Development of Materials and CT-Scanning Techniques for the Visualization of Structures in Centrifuge Analogue Models of Basin Evolution
1. CENTRIFUGE MODELING
Centrifuge modeling undertaken in this project provided exciting results. Models were undertaken by three students to study the effects of pre-existing normal and transfer faults and differences in the rheological properties of layers on the progressive development of diapirs during rifting. Results of some models were input into gOcad for 3D visualization, and further 3D visualization based on CT scans is planned for the coming year. Although models were aimed at simulating salt and shale diapirs in sedimentary basins, results are also of interest in interpreting structures associated with granite emplacement in Archean granite-greenstone terrains. Models suggest that faulting or fracturing of overlying competent horizons is required to initiate diapirism. Diapirs were emplaced along normal faults especially at the junction with transfer faults which also controlled some vertical rise of less dense material. Centrifuge modeling of diapirs differs to sandbox modeling in enabling active folding processes due to differences in the rheology of host layers to be investigated. The location, style and geometry of complex folds developed during diapir emplacement in surrounding layers and the diapirs themselves were investigated. Folds were also sometimes developed beneath diapirs; such sub-salt structures may aid interpretation in areas such as the Gulf of Mexico where poor data quality beneath diapirs hinders structural interpretations.
Centrifuge modeling by a fourth student investigated the progressive development of structures during displacement between convergent and divergent lateral ramps during rifting. Longitudinal variations in structural style were observed. Early-formed tensional fractures developed along conjugate zones oblique to the extension direction; these zones subsequently developed as normal faults. Folds developed with axes orthogonal and parallel to the transport direction during collapse between convergent lateral ramps. Normal faults were consequently folded in the zone of converging ramps. Thrust faults were developed in the “toe” of models during collapse. Results have implications for interpretation of structures in deltas.
A malfunction of the CT scanner in April 2007 stopped all centrifuge modeling and an extension of the project was sought and granted. The existing scanner was not repaired due to excessive costs as installation of a new CT scanner (coincident with a move to new laboratory facilities) is planned for end 2007.
2. IMAGE ANALYSIS
A computer algorithm was completed to provide a semi-automatic method of selecting model layers from CT images and to input them into a 3D visualization and modeling software, gOcad. An MSc thesis on image analysis of models is in its final stages of writing (delays were incurred as the student spent a period employed on another subject).
3. SANDBOX MODELING OF STRUCTURES ASSOCIATED WITH BASEMENT DISCONTINUITIES AND LATERAL RAMPS
Further sandbox models to study the effects of basement structures on faulting and the formation of triangle zones also benefited from CT scanning techniques developed in this project.
